Patent Application
20130214537
The present invention relates to a power generating apparatus of renewable energy type, which generates power by transmitting rotation energy of a rotating shaft to a generator via a hydraulic transmission and supplies the power to a grid, and an operation method of the power generating apparatus of renewable energy type. The power generating apparatus of renewable energy type generates power from a renewable energy such as wind, tidal current, ocean current and river current and, for instance, includes a wind turbine generator, a tidal generator, an ocean current generator, a river current generator or the like.
In recent years, from a perspective of preserving the environment, it is becoming popular to use a power generating apparatus of renewable energy type such as a wind turbine generator utilizing wind power and renewable energy type turbine generator such as a tidal current generator utilizing tidal. In the power generating apparatus of renewable energy type, a motion energy of the wind, the tidal current, the ocean current or the river current is converted into the rotation energy of the rotor (a rotating shaft) and the rotation energy of the rotor is converted into electric power by the generator.
In this type of the power generating apparatus of renewable energy type, the generator is normally connected to the grid. In the case of the wind turbine generator, the connection between the generator and grid is categorized according to a type of the generator and a connection to the grid, for instance, as shown in
In a type shown in
In view of this, wind turbine generators being capable of variable speed operation are proposed by adopting methods as show in
In the wind turbine generator of the type shown in
In the wind turbine generator of the type shown in
In recent years, power generating apparatuses of renewable energy type using a hydraulic transmission including a hydraulic pump and a hydraulic motor are attracting more attentions.
For instance, Patent Literature 1 discloses a wind turbine generator using a hydraulic transmission including a hydraulic pump rotated by a rotor and a hydraulic motor connected to a generator. In the hydraulic transmission of this wind turbine generator, the hydraulic pump and the hydraulic motor are connected via a high-pressure reservoir and a low-pressure reservoir. By this, the rotation energy of the rotor is transmitted to the generator via the hydraulic transmission. Further, the hydraulic pump is constituted of a plurality of sets of pistons and cylinders, and cams which periodically reciprocate the pistons in the cylinders.
Although not directly related to a variable-speed operation technology or a grid connection technology of the power generating apparatus of renewable energy type, there is an operation technology of a wind turbine generator when a grid voltage drops due to lightening strike and a failure of a transmission facility such as falling of a steel tower (See Patent Literatures 2 through 9).
Although not directly related to a variable-speed operation technology or a grid connection technology of the power generating apparatus of renewable energy type, there are know technology to suppress a generator swing when the grid voltage drops by means of a high initial response excitation system and a power system stabilizer (See Non-Patent Literature 1). The “swing” of the generator means an oscillation of an internal phase angle of the synchronous generator connected to the grid.
The high initial response excitation system is an excitation system which promptly detects voltage decline of the generator terminal, immediately increases field current, raises internal induced voltage of the generator to increase synchronizing power so as to suppress a first-wave swing of the generator when a major disturbance occurs at the grid such as a short-circuit fault and a grounding fault. Further, the power system stabilizer is a device which suppresses the generator swing promptly by controlling the exciter to increase a damping torque in order to improve steady-state stability which declines by using the high initial response excitation system.
As described above, in the existing power generating apparatuses of renewable energy type, the systems shown in
In the systems show in
In view of the above issues, it is an object of the present invention is to provide a power generating apparatus of renewable energy type which can achieve both the variable speed operation and the grid connection without a frequency converting circuit and which uses a hydraulic transmission, and an operation method of the power generating apparatus of renewable energy type.
The present invention provides a power generating apparatus of renewable energy type which generates power using renewable energy which may include, but is not limited to:
a blade;
a rotating shaft which is rotated by the renewable energy received via the blade;
a hydraulic transmission which includes a hydraulic pump driven by the rotating shaft and a hydraulic motor driven by pressurized oil supplied from the hydraulic pump;
a synchronous generator which is driven by the hydraulic motor to generate power and coupled to a grid without an intervening frequency-conversion circuit, the generated power being supplied to the grid;
a transmission controller which controls the hydraulic transmission in a normal operation mode to adjust displacement of each of the hydraulic pump and the hydraulic motor such that the rotating shaft rotates at a rotational speed that is variable with respect to flow speed of the renewable energy while keeping a rotational speed of the synchronous generator at a synchronous speed based on frequency of the grid during normal operation of the power generating apparatus.
The “renewable energy” indicates, for instance, wind in the case where the power generating apparatus of renewable energy is a wind turbine generator. In such case, the “flow speed of the renewable energy” is a wind speed.
In the power generating apparatus of renewable energy type, the synchronous generator which is connected to the grid without a frequency converting circuit is used as a generator. Thus, it is now possible to achieve both the variable speed operation and the grid connection in the normal operation by means of the transmission controller without relying on the frequency converting circuit. Specifically, the transmission controller adjusts displacement of each of the hydraulic pump and the hydraulic motor such that the rotating shaft rotates at a rotational speed that is variable with respect to flow speed of the renewable energy while keeping the rotational speed of the synchronous generator at the synchronous speed based on frequency of the grid so as to achieve both the variable speed operation and the grid connection.
In the above power generating apparatus of renewable energy type, the transmission controller may include, but is not limited to:
a target torque determination unit which, in the normal operation mode, determines a target torque of the hydraulic pump based on an optimal torque of the rotating shaft in accordance with the flow speed of the renewable energy;
a pump demand determination unit which, in the normal operation mode, determines a demand DP of the displacement of the hydraulic pump from the target torque of the hydraulic pump; and
a pump control unit which adjusts the displacement of the hydraulic pump at the demand DP.
By this, the target torque of the hydraulic pump is determined based on the optimal torque in accordance with the flow speed of the renewable energy, e.g. the wind speed, and the displacement of the hydraulic pump is adjusted at the demand DP of the displacement determined from the target torque. By this, the rotation speed of the rotating shaft can be variable with respect to the flow speed of the renewable energy. In other words, by means of the transmission controller, the variable speed operation of the power generating apparatus of renewable energy type can be achieved.
In the above power generating apparatus of renewable energy type, the transmission controller may include, but is not limited to:
a motor target power determination unit which determines a target output power POWERM of the hydraulic motor based on a target output power POWERP of the hydraulic pump;
a motor demand determination unit which, in the normal operation mode, determines a demand DM of the displacement of the hydraulic motor based on the determined target output power POWERM such that the synchronous generator rotates at the synchronous speed; and
a motor control unit which adjusts the displacement of the hydraulic motor at the demand DM.
By this, the displacement of the hydraulic motor is adjusted to the demand DM of the displacement of the hydraulic motor determined based on the determined target output power POWERM such that the synchronous generator rotates at the synchronous speed and thus, the rotation speed of the synchronous generator can be maintained at a synchronous speed. In other words, the synchronous generator can be connected to the grid by means of the transmission controller.
To do this, in the wind turbine generator 1, the transmission controller 40 controls the hydraulic transmission 10 to keep a rotational speed of the synchronous generator 20 at a synchronous speed based on frequency (e.g., 50 Hz or 60 Hz) of the grid 50. Specific control procedures of the transmission controller 40 are described later in detail.
The above power generating apparatus of renewable energy type may further include:
a terminal voltage detector which detects a terminal voltage of the synchronous generator;
an exciter which supplies a field current to a field winding of the synchronous generator; and
an exciter controller which controls the exciter based on a difference between the terminal voltage detected by the terminal voltage detector and a command value for the terminal voltage.
By adjusting the field current to be supplied to the field winding of the synchronous generator from the exciter, the terminal voltage of the synchronous generator can be maintained in accordance with the command value for the terminal voltage of the synchronous generator. Further, such control to maintain the terminal voltage may be performed by means of an automatic voltage regulator (AVR).
In the above power generating apparatus of renewable energy type, the exciter controller may control the exciter such that the field current is increased immediately after the terminal voltage of the synchronous generator decreases due to the fault event at the grid or a transmission line from the synchronous generator to the grid.
When the fault even occurs at the transmission line or the grid, the terminal voltage of the generator declines abruptly, instantly lowering an electrical output power (active power) of the generator. Thus, the mechanical input power from the hydraulic motor becomes excessive with respect to the electrical output power of the generator, causing the rotator of the synchronous generator to accelerate. This may result in step-out of the synchronous generator. Thus, by increasing the field current immediately after the terminal voltage of the synchronous generator decreases due to the fault event at the transmission line or the grid, the induced voltage inside the generator increases, causing the electrical output power of the generator to increase. Therefore, the synchronizing power of the synchronous generator 20 increases, suppressing the first-wave swing of the synchronous generator after the occurrence of the fault event. As a result, the transient ability is improved. In this manner, the step-out of the synchronous generator is prevented.
Further, the above control of the exciter to enhancing the transient stability can be preferably performed by a superquick excitation system which is an excitation system of an extremely fast response speed, such as a thyristor excitation system.
In the case of increasing the field current immediately after the terminal voltage decreases due to the occurrence of the fault event, after increasing the field current by the exciter, the exciter controller may control the exciter such that the field current is increased when an internal phase angle of the synchronous generator increases and is decreased when the internal phase angle of the synchronous generator decreases.
By increasing the field current immediately after the decline of the terminal voltage due to the fault event, the first-wave swing of the synchronous generator is suppressed as described above, hence improving the transient stability. However, the improved responsiveness may impair the steady-state stability after the first-wave swing.
Therefore, the field current is increased when increasing the internal phase angle and the field current is reduced when reducing the field current so as to suppress the swing of the synchronous generator promptly and to improve the steady-state stability. The above control of the exciter to improve the steady-state stability is preferably achieved by means of the power system stabilizer (PSS).
Further, when the terminal voltage of the synchronous generator decreases due to the fault event at the transmission line or the grid, the transmission controller may control the hydraulic transmission in a fault event response mode to adjust the displacement of the hydraulic motor such that a difference between a load torque of the synchronous generator and a torque inputted to the synchronous generator by the hydraulic motor decreases when a terminal voltage of the synchronous generator decreases due to the fault event at the transmission line from the synchronous generator to the grid or at the grid.
When the fault event occurs, the terminal voltage of the generator and the electrical output power of the synchronous generator decline almost simultaneously with the occurrence of the fault event. Thus, an extremely prompt response to the fault event is needed to prevent the step-out of the synchronous generator. From this aspect, controlling the hydraulic motor in the normal operation mode is not enough to adjust the torque of the hydraulic motor in response to the sudden change of the torque of the generator. This causes an unbalance between the torque of the generator and the torque of the hydraulic motor, causing the internal phase angle of the internal synchronous to change significantly. Thus, in the fault event response mode, the displacement of the hydraulic motor is adjusted to reduce the difference between the torque of the generator and the torque of the hydraulic motor. This allows the torque of the hydraulic motor to follow the sudden change of the torque of the generator, thereby suppressing the change of the internal phase angle of the synchronous generator. As a result, the swing of the synchronous generator due to the fault event can be promptly suppressed.
In the case of adjusting the torque of the hydraulic motor in response to the change of the torque of the generator in the fault event response mode, the transmission controller may include:
a motor demand determination unit which, in the fault event response mode, determines a demand DM of the displacement of the hydraulic motor based on the power generated by the synchronous generator; and
a motor control unit which adjusts the displacement of the hydraulic motor at the demand DM.
In this manner, by adjusting the displacement of the hydraulic motor at the demand DM based on the power generated by the synchronous generator, it is possible to change the displacement of the hydraulic motor in response to the change of the power generated by the synchronous generator after the fault event, and to reduce the difference between the torque of the generator and the torque of the hydraulic motor. As a result, the swing of the synchronous generator due to the fault even can be promptly suppressed.
In the case of adjusting the displacement of the hydraulic motor at the demand DM determined based on the power generated by the synchronous generator in the fault event response mode, the above power generating apparatus of renewable energy type may further include a pitch driving mechanism which adjusts a pitch angle of the blade and the pitch driving mechanism may change the pitch angle of the blade toward a feathering position during the fault event at the grid or the transmission line.
During the fault event, the terminal voltage of the synchronous generator decreases compared to that in the normal operation and thus, the electrical output power of the synchronous generator (the power generated by the synchronous generator) is small compared to that in the normal operation. Therefore, by adjusting the displacement of the hydraulic motor at the demand DM determined based on the power generated by the synchronous generator, the output power of the hydraulic motor declines, causing the output power of the hydraulic pump to be excessive. By changing the pitch angle of the blade toward the feather position by means of the pitch driving mechanism, the output power of the hydraulic pump can be restricted in response to the decline of the output power of the hydraulic motor while suppressing the acceleration of the hydraulic pump.
In the case of changing the pitch angle of the blade toward the feathering position during the fault event, after recovery from the fault event begins, the pitch driving mechanism changes the pitch angle of the blade toward a fine position and the motor demand determination unit increases the demand DM of the displacement of the hydraulic motor to increase the power generated by the synchronous generator.
By this, after the recovery from the fault even starts, it is possible to generate more power by increasing the displacement of the hydraulic motor.
The fault event may be, for instance, a condition where a voltage of the grid drops to a voltage specified in grid code or lower.
In the above power generating apparatus of renewable energy type, the exciter controller may include a thyristor which excites a stator field of the exciter, and the exciter may be an AC exciter which is provided with the stator field excited by the thyristor and a rotor armature rotating with the shaft of the synchronous generator, the DC field current being supplied from the rotor armature to the field winding of the synchronous generator via a rotary rectifier.
In this manner, AC from the rotating armature of the AC exciter is rectified by the rotary rectifier and supplied to the field winding of the synchronous generator. By this, it is possible to achieve a brushless structure, hence eliminating the need for brush maintenance (periodic replacement of the brush). As the wind turbine generators are often installed in a remote area such as in mountains and offshore, the fact that there is no need for the brush maintenance (the periodic replacement of the brush) significantly contributes to reducing a running cost.
The above power generating apparatus of renewable energy type may further include an auxiliary exciter which includes a permanent magnetic generator attached to a common shaft with the synchronous generator, and the thyristor of the exciter controller may use the auxiliary exciter as power source and excite the stator field of the exciter.
In this manner, the PMG attached to a common shaft of the synchronous generator, is used as power source for the thyristor of the exciter controller so as to excite the synchronous generator without an external power source even before connecting to the power grid. This is extremely advantageous for the wind turbine generator, which normally has a difficulty in obtaining power from the external power source.
Further, the power generating apparatus may be a wind turbine generator which generates the power from wind as the renewable energy.
The present invention provides an operation method of a power generating apparatus of renewable energy type which may include: a rotating shaft rotated by renewable energy received via a blade; a hydraulic transmission which includes a hydraulic pump driven by the rotating shaft and a hydraulic motor driven by pressurized oil supplied from the hydraulic pump; and a synchronous generator which is driven by the hydraulic motor to generate power and coupled to a grid without an intervening frequency-conversion circuit, the generated power being supplied to the grid, and the operation method may include, but is not limited to, the steps of:
controlling the hydraulic transmission in a normal operation mode to adjust displacement of each of the hydraulic pump and the hydraulic motor such that the rotating shaft rotates at a rotational speed that is variable with respect to flow speed of the renewable energy while keeping a rotational speed of the synchronous generator at a synchronous speed based on frequency of the grid during normal operation of the power generating apparatus.
According to the operation method of the power generating apparatus of renewable energy type, the displacement of each of the hydraulic pump and the hydraulic motor is adjusted such that the rotating shaft rotates at a rotational speed that is variable with respect to flow speed of the renewable energy while keeping a rotational speed of the synchronous generator at a synchronous speed based on frequency of the grid during normal operation of the power generating apparatus. As a result, it is possible to achieve both the variable speed operation and the grid connection.
The above operation method of a power generating apparatus of renewable energy type may further include the step of:
increasing a field current to be supplied to a field winding of the synchronous generator immediately after a terminal voltage of the synchronous generator decreases due to a fault event at the grid or a transmission line from the synchronous generator to the grid.
When the fault even occurs at the transmission line or the grid, the terminal voltage of the generator declines abruptly, instantly lowering an electrical output power (active power) of the generator. Thus, the mechanical input power from the hydraulic motor becomes excessive with respect to the electrical output power of the generator, causing the rotator of the synchronous generator to accelerate. This may result in step-out of the synchronous generator. Thus, by increasing the field current immediately after the terminal voltage of the synchronous generator decreases due to the fault event at the transmission line or the grid, the induced voltage inside the generator increases, causing the electrical output power of the generator to increase. Therefore, the synchronizing power of the synchronous generator 20 increases, suppressing the first-wave swing of the synchronous generator after the occurrence of the fault event. As a result, the transient ability is improved. In this manner, the step-out of the synchronous generator is prevented.
The above operation method of a power generating apparatus of renewable energy type may further include the step of:
controlling the hydraulic transmission in a fault event response mode to adjust the displacement of the hydraulic motor such that a difference between a load torque of the synchronous generator and a torque inputted to the synchronous generator by the hydraulic motor decreases when a terminal voltage of the synchronous generator decreases due to the fault event at a transmission line from the synchronous generator to the grid or the grid.
When the fault event occurs, the terminal voltage of the generator and the electrical output power of the synchronous generator decline almost simultaneously with the occurrence of the fault event. Thus, an extremely prompt response to the fault event is needed to prevent the step-out of the synchronous generator. From this aspect, controlling the hydraulic motor in the normal operation mode is not enough to adjust the torque of the hydraulic motor in response to the sudden change of the torque of the generator. This causes an unbalance between the torque of the generator and the torque of the hydraulic motor, causing the internal phase angle of the internal synchronous to change significantly. Thus, in the fault event response mode, the displacement of the hydraulic motor is adjusted so as to reduce the difference between the torque of the generator and the torque of the hydraulic motor. This allows the torque of the hydraulic motor to follow the sudden change of the torque of the generator, thereby suppressing the change of the internal phase angle of the synchronous generator. As a result, the swing of the synchronous generator due to the fault event can be promptly suppressed.
According to the present invention, the displacement of each of the hydraulic pump and the hydraulic motor is adjusted such that the rotating shaft rotates at a rotational speed that is variable with respect to flow speed of the renewable energy while keeping a rotational speed of the synchronous generator at a synchronous speed based on frequency of the grid. As a result, it is possible to achieve both the variable speed operation and the grid connection without using the frequency converting circuit.
Embodiments of the present invention will now be described in detail with reference to the accompanying drawings. It is intended, however, that unless particularly specified, dimensions, materials, shape, its relative positions and the like shall be interpreted as illustrative only and not limitative of the scope of the present invention.
While the present invention is described below with reference to exemplary embodiments, it is obvious to those skilled in the art that various changes may be made without departing from the scope of the invention.
In the following embodiments, a wind turbine generator is described as an example of the power generating apparatus of renewable energy type. However, the present invention is not limited to this example and can be applied to various types of power generating apparatuses of renewable energy type such as a tidal generator, an ocean current generator and a river current generator.
(Structure of Wind Turbine Generator)
As illustrated in
The hydraulic transmission 10 and the synchronous generator 20 may be housed in a nacelle 22 or a tower 24 supporting the nacelle 22.
The rotor 2 is configured such that a rotating shaft 8 is connected to a hub 6 having blades 4. Specifically, three blades 4 extend radially from the hub 6 and each of the blades 4 is mounted on the hub 6 connected to the rotating shaft 8. This allows the power of the wind acting on the blades 4 to rotate the entire rotor 2, and the rotation of the rotor 2 is inputted to the hydraulic transmission 10 via the rotating shaft 8. An actuator (pitch driving mechanism) 5 for adjusting the pitch angle of the blade 4 is attached to the blade 4, as shown in
As illustrated in
The high pressure oil line 16 connects an outlet of the hydraulic pump 12 to an inlet of the hydraulic motor 14. The low pressure oil line 18 connects an inlet of the hydraulic pump 12 to an outlet of the hydraulic motor 14. The operating oil (low pressure oil) discharged from the hydraulic pump 12 flows into the hydraulic motor 14 via the high pressure oil line 16. The operating oil having worked in the hydraulic motor 14 flows into the hydraulic pump 12 via the low pressure oil line 18 and then the pressure thereof is raised by the hydraulic pump 12 and finally the operating oil flows into the hydraulic motor 14 so as to drive the hydraulic motor 14.
As described below, in an embodiment, the hydraulic pump 12 and the hydraulic motor 14 may have specific structures shown in
As shown in
In an operation of the hydraulic pump 12, the ring cam 84 rotates with the rotating shaft 8 and the pistons 82 is cyclically moved upward and downward in accordance with the cam profile to repeat a pump cycle of the pistons 82 starting from the bottom dead center and reaching the top dead center and an intake cycle of the pistons starting from the top dead center and reaching the bottom dead center. Thus, each working chamber 83 has a volume defined by the piston 82 and an interior surface of the cylinder 80 that varies cyclically.
The hydraulic pump 12 can select the operation mode of each working chamber 83 from an active state and an idling state by opening and closing of the high pressure valve 86 and the low pressure valve 88. When the active state is selected for a working chamber 83, the high pressure valve 86 is closed and the low pressure valve 88 is opened during the intake cycle so that the operating oil flows into that working chamber 83, whereas the high pressure valve 86 is opened and the low pressure valve 88 is closed during the pump cycle so that the pressurized oil is displaced to the high pressure oil line 16 from that working chamber 83. In contrast to this, when the idling state is selected for a working chamber 83, the high pressure valve 86 is kept closed and the low pressure valve 88 is kept open during both the intake and pump cycles so that the operating oil flows back and forth between the working chamber 83 and the low pressure oil line 18, i.e. there is no displacement of the pressurized oil to the high pressure oil line 16. Accordingly, the net displacement of the hydraulic pump 12 can be adjusted by varying a ratio of the number of the working chambers 83 in the active state with respect to the total number of the working chambers 83. The control of the net displacement of the hydraulic pump 12 is performed by the transmission controller 40 described later in detail.
As illustrated in
In an operation of the hydraulic motor 14, the pistons 92 are periodically moved upward and downward to repeat a motor cycle of the pistons 92 starting from the top dead center and reaching the bottom dead center and a discharge cycle of the pistons starting from the bottom dead center and reaching the top dead center. In the operation of the hydraulic motor 14, the volume of each working chamber 93 defined by the piston 92 and an interior surface of the cylinder 90 varies cyclically.
The hydraulic motor 14 can select the operation mode of each working chamber 93 from an active state and an idling state by opening and closing of the high pressure valve 96 and the low pressure valve 98. When the active state is selected for a working chamber 93, the high pressure valve 96 is opened and the low pressure valve 98 is closed during the motor cycle so that the operating oil flows into the working chamber 93 from the high pressure oil line 16, whereas the high pressure valve 96 is closed and the low pressure valve 98 is opened during the discharge cycle so that the pressurized oil is displaced to the low pressure oil line 18 from that working chamber 93. In contrast to this, when the idling state is selected for a working chamber 93, the high pressure valve 96 is kept closed and the low pressure valve 98 is kept open during both the motor and pump cycles so that the operating oil flows back and forth between the working chamber 93 and the low pressure oil line 18, i.e. there is no feeding of the pressurized oil form the high pressure oil line 16 to the working chamber 93. Like the hydraulic pump 12, the hydraulic motor 14 can adjust its net displacement by varying a ratio of the number of the working chambers 93 in the active state with respect to the total number of the working chambers 93. The control of the net displacement of the hydraulic motor 14 is performed by the transmission controller 40 described later in detail.
The pressure in the accumulator 64 can be measured using a pressure sensor 68.
A bypass line 60 is arranged between the high pressure oil line 16 and the low pressure oil line 18 to bypass the hydraulic motor 14 and a relief valve 62 is arranged in the bypass line 60 to maintain hydraulic pressure of the high pressure oil line 16 not more than a prescribed pressure. By this, the relief valve 62 automatically opens when the pressure in the high pressure oil line 16 reaches the prescribed pressure of the relief valve 62, to allow the high pressure oil to escape to the low pressure oil line 18 via the bypass line 60.
Further, the hydraulic transmission 10 has an oil tank 70, a supplementary line 72, a boost pump 74, an oil filter 76, a return line 78 and a low pressure relief valve 79.
The oil tank 70 stores supplementary operating oil. The supplementary line 72 connects the oil tank 70 to the low pressure oil line 18. The boost pump 74 is arranged in the supplementary line 72 so as to replenish the low pressure oil line 18 with the supplementary operating oil from the oil tank 70.
The return line 78 is installed between the oil tank 70 and the low pressure oil line 18. The low pressure relief valve 79 is arranged in the return line 78 and the pressure in the low pressure oil line 18 is maintained at the prescribed pressure or below. By this, even with the boost pump 74 supplying the supplementary operating oil to the low pressure oil line 18, the low pressure relief valve 79 can automatically open to release the operating oil to the oil tank 70 via the return line 78 once the pressure in the low pressure oil line 18 reaches the prescribed pressure of the low pressure relief valve 79.
As illustrated in
The synchronous generator 20 is coupled to the output shaft 15 of the hydraulic motor 14. The synchronous generator 20 is connected to the grid without a frequency converting circuit such as frequency converting circuits 530 and 550 of
Further, the synchronous generator 20 includes a field winding 21 which rotates with the hydraulic motor 14 and the output shaft 15, and a stationary armature (not shown) to which the booster transformer 51 is connected. To the filed winding 21, DC field current is supplied from an exciter 100.
An exciter controller 110 is provided to control a magnitude of the field current supplied to the field winding 21. A terminal voltage detector 59 (a potential transformer) is provided to detect the terminal voltage of the synchronous generator 20. Based on the detected terminal voltage of the synchronous generator 20, the exciter controller 110 may control the exciter 100 so that the terminal voltage becomes a set value (a command value).
As a specific structure of the exciter 100, the exciter 100 may be an AC exciter as illustrated in
In such case, the exciter 100 is an AC exciter directly connected to the output shaft 15 of the hydraulic motor 14 and AC outputted from the rotating armature of the exciter 100 is converted into DC by a rectifier (a rotary rectifier) 103 and then supplied to the field winding 21 of the synchronous generator 20 as the field current. The field winding 21, the armature of the exciter 100 and the rectifier 103 rotate with the output shaft 15 of the hydraulic motor 14. In this manner, AC from the rotating armature of the AC exciter 100 is rectified by the rectifier (the rotary rectifier) 103 and supplied to the field winding 21 which is a rotator. By this, it is no longer necessary to provide a brush, thereby eliminating the need for brush maintenance (periodic replacement of the brush). As the wind turbine generators are often installed in a remote area such as in mountains and offshore, the fact that there is no need for the brush maintenance (the periodic replacement of the brush) significantly contributes to reducing a running cost.
In the example shown in
In such case, the exciter controller 110 may be formed by a voltage setter 112, a comparison circuit 113, an automatic voltage regulator (AVR) 114 and a thyristor 116, as shown in
In this manner, the PMG 106 which is directly connected to the output shaft 15 of the hydraulic motor 14 and attached to a common shaft of the synchronous generator 20, is used as power source of the thyristor 116 so as to excite the synchronous generator without an external power source even before connecting to the power grid 50. This is extremely advantageous for the wind turbine generator, which normally has a difficulty in obtaining power from the external power source.
From a perspective of improving the steady-state stability of the synchronous generator 20, the exciter controller 110 may be provided with a power system stabilizer (PSS) as shown in
(Operation Control of Wind Turbing Generator in Normal Operation Mode)
In the normal operation when there is no fault event such as short-circuit, disconnection or grounding (the transmission wire touching the ground) at the grid 50 or the transmission line 54, the wind turbine generator 1 of the above structure controls the hydraulic transmission 10 in a normal operation mode described below.
As shown in
In the normal operation mode, the transmission controller 40 controls the hydraulic transmission 10 such that the rotating shaft 8 rotates at a rotational speed that is variable with respect to the wind speed while keeping a rotational speed of the synchronous generator 20 at a synchronous speed based on frequency of the grid 50. By this, the synchronous generator 20 can be coupled to the grid 50 without an intervening frequency-conversion circuit and the power generation efficiency of the wind turbine generator 1 can be enhanced by rotating the rotor 2 at the rotation speed in accordance with the wind speed.
Hereinafter, operations of each unit of the transmission controller 40 in the normal operation mode are explained. The functions of the transmission controller 40 are broadly divided into controlling of the hydraulic pump 12 and controlling of the hydraulic motor 14. The controlling of the hydraulic pump 12 to adjust displacement thereof is described first and next, the controlling of the hydraulic motor 14 to adjust displacement thereof is described.
An example of the Wr-Ti function stored in the memory unit 49 is now explained.
The Wr-Ti function stored in the memory unit 49 may be a function 310 which is defined by the maximum Cp curve 300 between an operating point a and an operating point b and defined by a straight line between the operating point b and an operating point c as indicated by a heavy line in
By using the function 310, in a wind speed area between the cut-in wind speed V0 and the wind speed V3, the rotations peed Wr of the hydraulic pump 12 (the rotor rotation speed) can be adjusted in accordance with the wind speed in the area between the initial rotation speed W0 and the rated rotation speed Wrated, the wind turbine generator can operated in a condition where the power coefficient Cp is maximum. Specifically, in the variable speed range between the initial rotation speed W0 and the rated rotation speed Wrated, the wind turbine generator can operate at maximum efficiency. Further, in the wind speed area between the wind speed V3 and the rated wind speed V4, the rotation speed Wr of the hydraulic pump 12 is kept at the rated rotation speed Wrated. In a high wind speed area between the rated wind speed V4 and the cut-out wind speed, the pitch angle of the blade 4 is regulated by an actuator (a pitch driving mechanism) to maintain the rated power.
The obtained optimal torque Ti of the hydraulic pump 12 is then modified by the torque target determination unit 42 to determine the torque target Td of the hydraulic pump 12.
The target torque determination unit 42 adjusts the optimal torque Ti by multiplying by a scale factor M to give an adjusted optimal torque MTi. The scale factor M can be any number between zero and one, and would typically be between 0.9 and 1. The multiplication of the scale factor M causes a slight reduction of the actual torque of the hydraulic pump 12 compared to the optimal torque Ti, thus allowing the rotor 2 to accelerate more rapidly during gusts. Accordingly, it is possible to capture more power than if the pump torque were not scaled from the optimal torque Ti. The scale factor M will cause the rotor 2 to decelerate more slowly, thus operating off its optimum operating point during lulls, however the additional power available due to tracking gusts is more significant than power loss due to sub-optimal operation during lulls.
The torque target Td obtained by the target torque determination unit 42 may be the difference between the adjusted optimal torque MTi and the output power of a torque feedback controller 201. The torque feedback controller 201 calculates an estimated aerodynamic torque, Taero, which is the sum of the current torque target and an acceleration torque which is derived from the angular acceleration ar of the rotor 2 multiplied by the moment of rotational inertia of the rotor 2, J. The output of the torque feedback controller 201 is the difference Texcess between the estimated aerodynamic torque and the adjusted optimal torque, which is then multiplied by a feedback gain, G to obtain a feedback torque Tfeedback. The feedback gain G can be any number greater than or equal to zero, with a value of zero acting to disable the torque feedback controller 201.
The torque feedback controller 201 will respond to the acceleration and deceleration of the rotor 2 by subtracting torque from the adjusted optimal torque MTi to slightly reduce the torque target Td in the case of acceleration, and adding torque to the adjusted optimal torque to slightly increase the torque target Td in the case of deceleration. This enables the rotor 2 to accelerate and decelerate faster in response to changes in input wind energy than adjusted optimal torque control alone, hence allowing for greater total energy capture from wind.
The torque target Td obtained by the torque target determination unit 42 is sent to the pump demand determination unit 43 and used for the calculation of the demand DP of the displacement of the hydraulic pump 12. The pump demand determination unit 43 calculates the demand DP of the displacement of the hydraulic pump 12 by dividing the target torque Td by the measured oil pressure P, in the high pressure oil line 16. The demand DP may be modified by a pressure limiter 202, which could be a PID type controller, the output of which is the demand DP of the displacement. The pressure limiter 202 acts to keep the pressure of the hydraulic pump 12 within the acceptable range, i.e. below a maximum level for safe operation of the wind turbine generator, by modifying the pump demanded rate of fluid quanta transfer. The pressure limit may be disabled in some operating modes where it is desirable to dissipate energy through the relief valve 62, for instance to prevent the wind turbine generator from operating above its rated speed during extreme gusts, or may be varied in use. The pump demand determination unit 43 may correct the demand DP of the displacement of the hydraulic pump 12 based on the oil temperature in the high pressure oil line 16.
Further, the pump demand determination unit 43 may use an adjuster 203 to correct the torque target Td of the hydraulic pump 12 in response to a power demand signal from an external command center such as a farm controller of the wind farm and dispatching center. By this, it is possible to produce power which meets the demand from the external command center.
The demand DP of the displacement of the hydraulic pump 12 having been calculated in the above manner, is then sent to the pump control unit 44 and the displacement of the hydraulic pump 12 is adjusted to the demand DP by the pump control unit 44. For instance, the pump control unit 44 controls opening and closing of the high pressure valve 86 and the low pressure valve 88 to change a ratio of the working chambers 83 in the active state to the total number of the working chambers, thereby adjusting the displacement of the hydraulic pump 12 to the demand DP of the displacement.
As shown in the drawing, the pump target power determination unit 45 calculates a base value of the target output power of the hydraulic pump 12, POWER0 by multiplying the target torque Td of the hydraulic pump 12 obtained by the target torque determination unit 42 by the rotation speed Wr of the rotating shaft 8 obtained by the rotation speed sensor 32. In the pump target power determination unit 45, corrected output power POWERC is calculated by an adjuster 212 in response to a power demand signal Sd from the external command center 210 such as a farm controller of the wind farm and dispatching center. Then, the corrected output power POWERC is added to the base value POWERC of the target output power which are obtained advance so as to calculate the target output power POWERP of the hydraulic pump 12.
The motor target output determination unit 46 calculates the target output power POWERM of the hydraulic motor 14 by processing the target output power POWERP of the hydraulic pump 12 using a first order low pass filter, whose transfer function is H(s)=1/(Ts+1).
Then, the motor demand determination unit 47 calculates the nominal demand Dn of the hydraulic motor 14 by dividing the target output power POWERM of the hydraulic motor 14 by the measured oil pressure Ps measured by the oil pressure sensor 31 and the measured rotation speed Wm of the hydraulic motor 14 measured by the rotation speed sensor 36.
The nominal demand Dn of the hydraulic motor 14 calculated in the above manner, is obtained by dividing energy from the hydraulic pump 12 to the hydraulic motor 14 per unit time by the rotation speed Wm of the pressure Ps of the high pressure oil line 16 and the rotation speed Wm of the hydraulic motor 14. Thus, when the rotation speed Wm of the hydraulic motor 14 is too low, the nominal demand Dn is high, thereby raising the rotation speed Wm of the hydraulic motor 14. In contrast, when the rotation speed Wm of the hydraulic motor 14 is too high, the nominal demand Dn is small, thereby lowering the rotation speed Wm of the hydraulic motor 14. Therefore, it is possible to maintain the rotation speed Wm of the hydraulic motor 14 at a constant rate, i.e. at the synchronous speed of the synchronous generator 20).
In the motor demand determination unit 47, a corrected demand Db is calculated from the target output power POWERM and then added to the nominal demand Dn to obtain a demand DM of displacement of the hydraulic motor 14. The corrected demand Db may be, for instance, calculated by a pressure feedback controller 220 by multiplying the difference between the target pressure Pd of the high pressure oil line 16 and the measured oil pressure Ps measured by the pressure sensor 31 by a variable gain Kp.
The target pressure Pd of the high pressure oil line 16 may be calculated by inputting the current target output power POWERM of the hydraulic motor to a function 230 indicating a relationship between a target motor output power set in advance and the target pressure of the high pressure oil line 16. The function 230 is at least partially defined by a curve in which the target pressure of the high pressure oil line 16 monotonically increases in accordance with increase of the motor target output power. Thus, the target pressure Pd of the high pressure line is set lower in the case where the target motor output power is small (i.e. the discharge rate of the hydraulic pump is low) than the case where the target output power of the hydraulic motor is high (i.e. the discharge rate of the hydraulic pump 12 is high). By this, it is possible to reduce the amount of internal leakage of the operation oil with respect to the discharge rate of the hydraulic pump 12 when the target motor output power is small, thereby suppressing the internal leakage of the operation oil affecting the control of the hydraulic transmission 10.
The variable gain Kp is determined using the function 232 in accordance with the current pressure of the high pressure oil line 16, Ps (the pressure detected by the pressure sensor), the maximum pressure Pmax and the minimum pressure Pmin of the high pressure oil line 16 in an allowable range. For instance, when the current pressure Ps is outside the allowable range (i.s. Ps<Pmin or Ps>Pmax), the variable gain Kp is set at the maximum gain Kmax, and when the current pressure Ps is within the allowable range (i.e. Pmin less than or equal Ps less than or equal Pmax), the variable gain Kp may be increased toward the maximum gain Kmax as the current pressure Ps becomes closer to the minimum pressure Pmin or the maximum pressure Pmax. By this, when the pressure Ps is deviating from the allowable range, or when the pressure Ps is no longer in the allowable range, by increasing the variable gain Kp (or setting the variable gain at the maximum gain Kmax) by which the difference between the pressure Ps and the target pressure Pd is multiplied, the pressure Ps of the high pressure oil line is promptly adjusted to be within the allowable range and also closer to the target pressure Pd.
In the normal operation mode, the terminal voltage of the synchronous generator 20 is maintained by the exciter controller 100 controlling the exciter. For instance, as shown in
The set value (command value) of the generator inputted from the voltage setter 112 is, for instance, a voltage which conforms to the grid 50.
As described above, the transmission controller 40 controls the hydraulic transmission 10 in the normal operation mode such that the rotating shaft 8 rotates at a rotational speed that is variable with respect to the wind speed while keeping the rotation speed of the synchronous generator 20 at the synchronous speed based on the frequency of the grid 50.
Specifically, the transmission controller 40 calculates the optimal torque Ti of the rotating shaft by means of the optimal torque determination unit 41, and then based on the optimal torque Ti, determines the target torque Td of the hydraulic pump 12 by means of the target torque determination unit 42. Further, the transmission controller 40 calculates the demand DP of the displacement of the hydraulic pump 12 from the target torque Td by means of the pump demand determination unit 43, and then adjust the displacement of the hydraulic pump 12 to the demand DP of the displacement by means of the pump control unit 44. In this manner, the rotor 2 rotates at the rotation speed in accordance to the wind speed (i.e. the variable speed operation), thereby improving the power generation efficiency.
Furthermore, the hydraulic transmission controller 40 calculates the target output power POWERM of the hydraulic motor 14 by means of the motor target power determination unit 46 based on the target output power POWERP of the hydraulic pump 12. The hydraulic transmission controller 40 calculates, by means of the motor demand determination unit 47, the demand DM of the displacement of the hydraulic motor 14 such that the synchronous generator 20 rotates at the synchronous speed which corresponds to the frequency of the grid 50 and then, by means of the motor control unit 48, adjust the displacement of the hydraulic motor 14 to the demand DM. of the displacement By this, the synchronous generator 20 is maintained at the synchronous rotation speed and the synchronous generator can be connected to the grid 50 without a intervening frequency circuit.
(Operation Control of Wind Turbine in Fault Event Response Mode)
When there is a fault event such as such as short-circuit, disconnection or grounding (the transmission wire touching the ground) at the grid 50 or the transmission line 54, the power that can be sent to the grid 50 side is limited, instantly lowering an electrical output power (active power) of the synchronous generator 20. As a result, a mechanical input from the hydraulic motor 14 becomes excessive with respect to the electrical output power of the synchronous generator, causing the internal phase angle of the synchronous generator 20 to decrease abruptly. This may result in step-out of the synchronous generator 20.
The above phenomenon occurs in a short period of time (e.g. a few milliseconds to tends of seconds) immediately after the occurrence of the fault event. Thus, unlike the conventional wind turbine generator equipped with the frequency converting circuit 530, 550 functioning as a buffer (see
It is difficult to respond to the fault even sufficiently by the normal operation mode described above, in which control parameters are determined from an upstream side to a downstream side in the energy transmission path (the rotor 2>the hydraulic pump 12>the hydraulic motor 14>the synchronous generator 20). In the normal operation mode, the displacement of the hydraulic motor 14 is reduced with the synchronous generator 20 in response to increase of the current rotation speed of the hydraulic motor 14 as well as the synchronous generator 20. However, this is not enough to effectively prevent the step-out of the synchronous generator 20.
In the present embodiment, when the fault even occurs at the grid 50 and the transmission line 54, the wind turbine generator 1 operates in a fault event response mode which is different from the above normal operation mode.
In the fault event response mode, different from the normal operation in which the control parameters are calculated upstream to downstream in the energy transmission path, the control parameters are calculated downstream to upstream in the energy transmission path. Specifically, in the fault even response mode, the field current to be supplied to the field winding of the synchronous generator 20 is controlled immediately after the occurrence of the fault event and also the demand DM of the displacement of the hydraulic motor 14 is adjusted immediately such in response to the change in the electrical output power (electricity) of the synchronous generator 20 and, if necessary, the pitch and the hydraulic pump 12 are controlled as well.
In response to a sudden drop of the terminal voltage of the synchronous generator 20 and the electricity from the synchronous generator 20, a Low Voltage Detect signal is outputted. The operation of the wind turbine generator 1 may be switched from the normal operation mode to the fault event response mode in response to the Low Voltage Detect signal.
A specific example of the control by the exciter controller 110 and the transmission controller 40 when the short-circuit (disconnection and grounding) occurs between the circuit breakers 58 and 58 of the circuit 56B is explained below.
When the short-circuit occurs between the circuit breakers 58 and 58 of the circuit 56B, almost at the same time with the occurrence of the short-circuit fault, the terminal voltage of the synchronous generator 20 drops abruptly and the active power Pe outputted from the synchronous generator 20 drops suddenly as well (See
Before the occurrence of the short-circuit fault, the synchronous generator 20 operates at a point 1 on a Pe-A curve of the state 1 and the internal phase angle A is A0. The point 1 is an intersection of the mechanical input Pm from the hydraulic motor 14 (approximately the same as the target output power POWERM of
However, once the short-circuit fault occurs, the Pe-A curve shifts instantaneously from the state 1 to the state 2. Immediately after the occurrence of the short-circuit fault, the internal phase angle A remains at A0 by inertia of the rotator of the synchronous generator 20. Thus, upon the occurrence of the short-circuit fault, the operation point of the synchronous generator 20 shifts instantaneously from the operating point 1 to an operating point m. Meanwhile, the mechanical input Pm form the hydraulic motor 14 becomes excessive with respect to the electrical output power Pe of the synchronous generator 20, causing the rotator of the synchronous generator 20 to accelerate and the operating point of the synchronous generator 20 shifts from the operating point m to an operating point n. Thus, the internal phase angle A raises from A0 toward A1.
Once the internal phase angle A reaches A1, the circuit breakers 58 and 58 are opened to remove the short-circuit fault. By this, the Pe-A of the synchronous generator rises from the state 2 to the state 3. Meanwhile, shortly after removing the short-circuit fault, the internal phase angle A still remains at A1 due to the inertia of the rotator of the synchronous generator 20. Therefore, by removing the short-circuit fault, the operating point of the synchronous generator 20 instantaneously shifts from the operating point n to an operating point o. This causes the electrical output power Pe of the synchronous generator to exceed the mechanical input Pm from the hydraulic motor 14 and thus, the rotator of the synchronous generator 20 starts decelerating. Therefore, after the internal phase angle A reaches A2, the internal phase angle A decreases and thereafter the internal phase angle repeats gain and decline and oscillates. However, the damping force of the synchronous generator 20 eventually damps the internal phase angle and makes the internal phase angle stable. The operating point p which is a turning point of the internal phase angle A, is an operating point at which an acceleration energy shown as an area S1 formed between the input Pm from the hydraulic motor 14 and the Pe-A curve of the state 2, coincides with a deceleration energy shown as an area S2 formed between the Pe-A curve of the state 3 and output power Pm of the hydraulic motor.
In the embodiment, immediately after the occurrence of the fault event, the exciter controller 110 controls the exciter 100 to increase the field current supplied to the field winding 21 of the synchronous generator 20. This indicates upward shift of the Pe-A curve of the state 2 or the state 3 in
The control of the exciter 100 to improve the transient stability, may be preferably performed by a superquick excitation of thyristor type by means of the thyristor 116 and the AVR 114 as shown in
The technology to improve the transient stability of the synchronous generator by the superquick excitation control was established in power generating facilities using steam turbines and gas turbines. However, it was not known to apply that to the power generating apparatus of renewable energy type. This is because, in the conventional power generating apparatus of renewable energy type, the generator is connected to the grid via the frequency converting circuit which functions as a buffer and the transient stability of the generator was not much of an issue.
By magnetizing the synchronous generator 20 immediately after the decline of the terminal voltage of the generator due to the occurrence of the fault event, as described above, the first-wave swing of the synchronous generator 20 is suppressed, thereby improving the transient stability. However, the excellent responsiveness may lead to declining of the steady state stability after the first-wave swing.
In view of this, the exciter controller 110 controls the exciter 100 so that, when the internal phase angle A of the synchronous generator 20 increases, the field current of the field winding 21 rises, whereas when the internal phase angle A of the synchronous generator 20 decreases, the field current of the field winding 21 is reduced. In such case, it is possible to increase the exciter current when the internal phase angle A of the synchronous generator 20 increases, and to decrease the exciter current when the internal phase angle A of the synchronous generator 20 decreases, based on the electrical output power Pe of the synchronous generator 20 detected by a electrical power sensor 119 by means of the PSS 118 shown in
In power generating facilities using steam turbines, a governor control unit controls the turbine output to maintain a constant rotation speed of the generator. However, the governor control unit increases or reduces the flow of steam entering the steam turbine by opening and closing a steam regulating valve or an intercept valve in the steam turbine so as to adjust the turbine output. Thus, it takes at least a few seconds to start the operation. Therefore, in the power generating facilities using steam turbines and gas turbines, the fault even is handled solely by the superquick excitation control and the PSS.
In contrast, in the wind turbine generator 1 of the present embodiment, the output power of the hydraulic motor 14 can be controlled within few seconds from the occurrence of the fault event. Particularly, in the case of the hydraulic motor illustrated in
In view of this, in the fault event response mode, the transmission controller 40 may regulate the output power of the hydraulic motor 14 by adjusting the displacement of the hydraulic motor to reduce the difference between the torque inputted from the hydraulic motor 14 to the synchronous generator 20 and the load torque of the synchronous generator 20. Specifically, by moving up and down the mechanical output power Pm of the hydraulic motor 14 to the synchronous generator 20 in
Specifically, in the fault even response mode, the motor demand determination unit 47 calculates the demand DM of the displacement of the hydraulic motor 14 based on the electric power generated by the synchronous generator 20 and the motor control unit 48 adjusts the displacement of the hydraulic motor 14 to the demand DM of the displacement.
In this manner, by adjusting the displacement of the hydraulic motor 14 to the demand DM of the displacement calculated based on the electric power generated by the synchronous generator 20, it is possible to change the displacement of the hydraulic motor 14 in response to the change of the electric power generated by the synchronous generator 20 after the occurrence of the fault event. Therefore, the torque of the hydraulic motor 14 can be adjusted in response to a drastic change of the load torque of the synchronous generator, thereby promptly suppressing the swing of the synchronous generator 20 due to the fault event.
When the fault event occurs, the terminal voltage of the synchronous generator is low in comparison to the normal operation and thus, the electric power that can be outputted from the synchronous generator 20 to the grid 50 is low in comparison to the normal operation. This causes the output power of the hydraulic motor 14 to decline and the output power of the hydraulic pump 12 to increase excessively, when the displacement of the hydraulic motor 14 is adjusted to the demand DM of the displacement calculated based on the electricity of the synchronous generator.
Therefore, surplus of the high pressure oil discharged from the hydraulic pump 12 may be accumulated in the accumulator 64. Specifically, with the solenoid valve between the accumulator 64 and the high pressure oil line 16, immediately after the occurrence of the fault event, the solenoid valve 66 is opened to allow the accumulator 64 to communicate with the high pressure oil line 16 so as to accumulate the surplus of the high pressure oil in the accumulator 64. In contrast, in the case where the accumulator 64 is directly connected to the high pressure line 16 without the solenoid valve 66, immediately after the occurrence of the fault event, the surplus of the high pressure oil is accumulated in the accumulator 64 spontaneously and thus, a special process is not needed.
Once the accumulator 64 is filled with the high pressure oil, the pressure Ps of the high pressure oil line 16 increase to the set pressure of the relief valve 62 and thereafter, the relief valve 62 opens to release the surplus high pressure oil to the low-pressure oil line 18 via the bypass line 60.
Further, to balance the output power of the hydraulic pump 12 and the output power of the hydraulic motor 14 in the fault event response mode, the actuator 5 may change the pitch angle of the blade 4 toward a feathering position. By this, while preventing the hydraulic pump 12 from accelerating excessively (the rotation speed of the hydraulic pump 12 becomes excessively high), the output power of the hydraulic pump 12 can be restricted to some extent in response to the decline of the output power of the hydraulic motor 14.
Furthermore, when the output power of the hydraulic pump 12 and the output power of the hydraulic motor 14 are still not balanced after restricting the output power of the hydraulic pump 12, the surplus of the high pressure oil may be accumulated in the accumulator and the surplus of the high pressure oil may be released to the low pressure oil line 18 via the bypass line 60.
After recovering from the short-circuit fault of the circuit 2 by opening the circuit breaker 58, the actuator (the pitch driving mechanism) 5 may return the pitch angle of the blade 4 toward a fine position and the motor demand determination unit 47 may increase the demand DM of the displacement of the hydraulic motor 14 to increase the electric power generated by the synchronous generator 20.
By this, after recovering from the fault event, it is possible to enhance power generation by increasing the displacement of the hydraulic motor 14.
As described above, in the fault event response mode, the field current to be supplied to the field winding 21 of the synchronous generator 20 immediately after the fault event is controlled and also the demand DM of the displacement of the hydraulic motor 14 is adjusted in response to the change of the power generated in the synchronous generator 20 and further, if necessary, the pitch and the hydraulic pump 12 are controlled.
Specifically, immediately after the terminal voltage of the synchronous generator decreases due to the fault event, the exciter 110 controls the exciter 100 to increase the magnitude of the field current supplied to the field winding 21. By this, the synchronizing power of the synchronous generator 20 increases, suppressing the first-wave swing of the synchronous generator 20 after the occurrence of the fault event. As a result, the transient ability is improved.
Further, after increasing the field current supplied to the filed winding 21 by the exciter 100, the exciter controller 110 may control the exciter 100 such that the field current increases when the internal phase angle A of the synchronous generator 20 increases and such that the field current decreases when the internal phase angle A of the synchronous generator 20 decreases. By this, the steady-state stability is improved and it is now possible to promptly suppress the swing of the synchronous generator 20.
Further, in the fault event response mode, when the terminal voltage of the synchronous generator 20 decreases due to the fault event, the transmission controller 40 adjusts the displacement of the hydraulic motor 14 so as to reduce the difference between the torque inputted to the synchronous generator 20 from the hydraulic motor 14 and the load torque of the synchronous generator 20. For instance, the transmission controller 40, in the fault event response mode, may calculate the demand DM of the displacement of the hydraulic motor 14 based on the power generated by the synchronous generator 20 by means of the motor demand determination unit 47, and adjust the displacement of the hydraulic motor 14 to the demand DM of the displacement by means of the motor control unit 48.
By this, it is possible to adjust the torque of the hydraulic motor in response to the abrupt change of the generator torque and thus, the swing of the synchronous generator 20 due to the fault even can be promptly suppressed.
A few specific examples of using the control in the fault event response mode are described now.
In the example of
In this example, when the terminal voltage Vt is 90% or below of the rated terminal voltage, the Low Voltage Detect signal is outputted.
In response to a sudden drop of the terminal voltage Vt, a difference between the output value of the comparison circuit 113 and the measured value measured by the terminal voltage detector 59, i.e. the command value of the terminal voltage becomes abruptly high. Thus, the exciter 100 being controlled by the exciter controller 110 (specifically, AVR 114 and the thyristor 116) increases the field current (exciter current) to be supplied to the field winding 21 of the synchronous generator 20. By this, the sudden increase of the internal phase angle A of the synchronous generator 20 is suppressed and the transient stability of the synchronous generator 20 is enhanced, Further, although not shown in the drawing, after the exciter 100 increases the field current under the control of the AVR 114 and the thyristor 116, the field current is adjusted by the PSS 118 and the steady-state stability is enhanced.
After the occurrence of the fault event at T0, the displacement DM of the hydraulic motor 14 is adjusted to decrease based on the power Pe generated by the synchronous generator 20. However, the electrical power Pe of the synchronous generator 20 has already increased by increasing the field current supplied to the field winding 21 and thus, it is not necessary to significantly reduce the displacement DM of the hydraulic motor 14. By this, the mechanical input power Pm from the hydraulic motor 14 declines, the difference between the mechanical input Pm and the electrical output power Pe (generated power) of the synchronous generator 20 becomes small and the increase of the internal phase due to the fault event is suppressed. As a result, the swing of the synchronous generator due to the fault event can be promptly suppressed. Further, when the fault event occurs at the time T0, the actuator (the pitch driving mechanism) 5 begins pitch control of the blade 4 and the pitch angle transits toward the feathering position. However, the pitch control by the actuator 5 can change the pitch angle only at a speed of, for instance, approximately 3 deg/s to 6 deg/s. This tends to causes a delay in responding to the fault event, in comparison to other controls in the exciter controller 110 and the hydraulic motor 14. By changing the pitch angle of the blade 4 toward the feathering position, it is possible to limit the output power of the hydraulic pump 12 to some extent in accordance with the decrease output power of the hydraulic motor 14 while preventing the excessive acceleration of the hydraulic pump 12.
Further, even after restricting the output power of the hydraulic pump 12, the output power of the hydraulic pump still remains excessive with respect to the output power of the hydraulic motor 14. This causes the pressure Ps of the high pressure oil line 16 to rise and the surplus of the high pressure oil is accumulated in the accumulator 64, As a result, the amount of the high pressure oil accumulated in the accumulator 64 increases abruptly from the time t0.
Next, at a time t1, the fault event is resolved and the terminal voltage Vt begins to recover and at a time t2, the terminal voltage Vt reaches 90% of the rated terminal voltage Vrated. Finally, at a time t3, the terminal voltage Vt reaches 94% of the rated terminal voltage Vrated. For instance, the time t1 is 0.14 second past the time t0 and the time t3 is 0.5 second past the time t0.
In response to the recovery of the terminal voltage Vt due to the recovery from the fault event, the output value of the comparison circuit 113, i.e. the difference between the command value of the terminal voltage and the measured terminal voltage detected by the terminal voltage detector 59 becomes small. Thus, the exciter 100, under the control of the exciter controller 110 (i.e. AVR 114 and the thyristor 116) reduces the field current (exciter current) to be supplied to the field winding 21 of the synchronous generator 20.
Further, when the fault even is resolved, the terminal voltage Vt reaches 90% of the rated terminal voltage Vrated (at t2), outputting of the low voltage detect signal stops and the operation of the wind turbine generator 1 is switched from the fault event response mode to the normal operation mode.
Thus, the displacement DM of the hydraulic motor 14 begins increasing at the time t2 where the terminal voltage Vt reaches 90% of the rated terminal voltage after the recovery from the fault event. This allows for an increased amount of power generated by the wind turbine generator 1 after the recovery from the fault event.
Further, past the time t2, the pitch angle of the blade 4 is gradually moved toward the fine position by the actuator (the pitch driving mechanism) 5. In response to this, the displacement DP of the hydraulic pump increases gradually. Meanwhile, by changing the pitch angle of the blade 4 and the displacement DP of the hydraulic pump 12 slower than the speed of increasing the displacement DM of the hydraulic motor 14, the high pressure oil accumulated in the accumulator 4 is released and the pressure Ps of the high pressure line 16 decreases.
The example shown in
In the example of
As shown in
In response to a sudden drop of the terminal voltage Vt, the output value of the comparison circuit 113, the command value of the terminal voltage, i.e, the difference between the output value of the comparison circuit 113 and the measured value measured by the terminal voltage detector 59 becomes abruptly big. Thus, the exciter 100 being controlled by the exciter controller 110 (specifically, AVR 114 and the thyristor 116) increases the field current (exciter current) to be supplied to the field winding 21 of the synchronous generator 20. Different from the example of
After the occurrence of the fault event at t0, the displacement DM of the hydraulic motor 14 is adjusted based on the power Pe generated by the synchronous generator 20 and then decreases. Meanwhile, the electrical output power Pe of the synchronous generator 20 is approximately zero even after increasing the field current to be supplied to the field winding 21 and thus, the displacement DM of the hydraulic motor 14 decreases to approximately zero in the attempt to balance the mechanical output power Pm from the hydraulic motor 14 and the electrical output power Pe of the synchronous generator 20. By this, the difference between the mechanical input power Pm and the electrical output power of the synchronous generator 20 (electricity) of the synchronous generator 20 is reduced, thereby preventing the internal phase angle A caused by the fault event from increasing. As a result, the generator swing of the synchronous generator 20 due to the fault event can be suppressed.
In the example of
In contrast, in the example of
In this manner, depending on a type of the fault event, the swing of the synchronous generator may be controlled in different manners.
While the present invention is described below with reference to exemplary embodiments, it is obvious to those skilled in the art that various changes may be made without departing from the scope of the invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 1020263.8 | Nov 2010 | GB | national |
| 1020264.6 | Nov 2010 | GB | national |
| PCT/JP10/06977 | Nov 2010 | JP | national |
| PCT/JP10/06978 | Nov 2010 | JP | national |
| PCT/JP10/06979 | Nov 2010 | JP | national |
| PCT/JP10/06981 | Nov 2010 | JP | national |
| PCT/JP10/06982 | Nov 2010 | JP | national |
| PCT/JP11/00917 | Feb 2011 | JP | national |
| PCT/JP11/00920 | Feb 2011 | JP | national |
| PCT/JP11/03000 | May 2011 | JP | national |
| PCT/JP11/03002 | May 2011 | JP | national |
| PCT/JP11/03005 | May 2011 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP11/06694 | 11/30/2011 | WO | 00 | 3/15/2013 |
