Patent Application
20190376489
The present disclosure relates generally to wind turbines and, more particularly, to a system and method for minimizing inrush of current during start-up of an electrical power system connected to a power grid.
Wind power is considered one of the cleanest, most environmentally friendly energy sources presently available, and wind turbines have gained increased attention in this regard. A modern wind turbine typically includes a tower, generator, gearbox, nacelle, and one or more rotor blades. The rotor blades capture kinetic energy of wind using known airfoil principles. For example, rotor blades typically have the cross-sectional profile of an airfoil such that, during operation, air flows over the blade producing a pressure difference between the sides. Consequently, a lift force, which is directed from a pressure side towards a suction side, acts on the blade. The lift force generates torque on the main rotor shaft, which is geared to a generator for producing electricity.
During operation, wind impacts the rotor blades and the blades transform wind energy into a mechanical rotational torque that drives a low-speed shaft. The low-speed shaft is configured to drive the gearbox that subsequently steps up the low rotational speed of the low-speed shaft to drive a high-speed shaft at an increased rotational speed. The high-speed shaft is generally coupled to the generator so as to rotatably drive a generator rotor. In many wind turbines, the generator may be electrically coupled to a bi-directional power converter that includes a rotor-side converter joined to a line-side converter via a regulated DC link. As such, the generator is configured to convert the rotational mechanical energy to a sinusoidal, three-phase alternating current (AC) electrical energy signal in a generator stator. The rotational energy is converted into electrical energy through electromagnetic fields coupling the rotor and the stator, which is supplied to a power grid via a grid breaker. Thus, the main transformer steps up the voltage amplitude of the electrical power such that the transformed electrical power may be further transmitted to the power grid.
Such wind turbine power systems are generally referred to as a doubly-fed induction generator (DFIG). DFIG operation is typically characterized in that the rotor circuit is supplied with current from a current-regulated power converter. As such, the wind turbine produces variable mechanical torque due to variable wind speeds and the power converter ensures this torque is converted into an electrical output at the same frequency of the grid.
In addition, wind turbines (and solar converters) also often have capacitance built into the AC interface. For example, such capacitance may be part of a filter to ensure power quality of the power system. During startup, a disconnect switch is closed in order to connect the system to the grid. When the switch is closed, however, there can be an inrush of current when the grid voltage is applied to the capacitance. The inrush of current can cause voltage drops and overshoots at the connection point and throughout the power distribution of the wind turbine, thereby causing stress to auxiliaries/accessories in the wind turbine.
Thus, the present disclosure is directed to a system and method for minimizing inrush of current during start-up of an electrical power system connected to a power grid to address the aforementioned issues.
Aspects and advantages of the invention will be set forth in part in the following description, or may be obvious from the description, or may be learned through practice of the invention.
In one aspect, the present disclosure is directed to a method for a method for minimizing inrush of current during start-up of an alternating current (AC) electrical power system connected to a power grid. The method includes determining a grid voltage of the power grid. The method also includes charging an AC capacitance of a grid filter of the electrical power system from an initial capacitance value to a predetermined percentage of the grid voltage. Further, the method includes connecting the electrical power system to the power grid when the AC capacitance in the grid filter reaches the predetermined percentage of the grid voltage. Moreover, the method includes initiating start-up of the electrical power system.
In one embodiment, the method may include charging the AC capacitance in the grid filter of the electrical power system with at least one additional electrical component coupled to the grid filter. In such embodiments, the additional electrical component(s) may include one or more resistors, a contactor, and/or any other suitable electrical components or combinations thereof that are capable of limiting electrical transients. In addition, the method may include bypassing the at least one additional electrical component after connecting the electrical power system to the power grid but before initiating start-up the electrical power system.
In another embodiment, the method may include charging the AC capacitance in the grid filter of the electrical power system via a power converter of the electrical power system operating in a first operating mode. As such, the power converter is configured to produce a voltage in sync with the grid voltage prior to connecting the electrical power system to the power grid.
In further embodiments, the method may include charging a DC link of the power converter to a predetermined power level prior to charging the AC capacitance in the grid filter of the electrical power system via the power converter. Alternatively, the method may include supplying a DC link of the power converter with additional power prior to charging the capacitance in the grid filter of the electrical power system via the power converter. In several embodiments, the method may also include transitioning from the first operating mode of the power converter to a second operating mode after charging the AC capacitance of the grid filter of the electrical power system. In such embodiments, the first operating mode may correspond to an AC charging mode, whereas the second operating mode may correspond to a standard operating mode.
In additional embodiments, the predetermined percentage of the grid voltage may be up to about 100% of the grid voltage. Therefore, in certain embodiments, the predetermined percentage of the grid voltage may be less than 100% of the grid voltage.
In particular embodiments, the electrical power system may be a wind turbine power system or a solar power system.
In another aspect, the present disclosure is directed to a wind turbine power system. The wind turbine power system includes a generator having a rotor and a stator and a power converter having a line-side converter coupled to a rotor-side converter via a DC link. The rotor-side converter is coupled to the rotor. The wind turbine power system also includes a grid filter coupled between the line-side converter and a power grid. Further, the wind turbine power system includes a controller configured to perform one or more operations, including but not limited to charging the grid filter from an initial voltage value to a predetermined percentage of a grid voltage of the power grid, connecting the wind turbine power system to the power grid when the initial voltage value in the grid filter reaches the predetermined percentage of the grid voltage, and initiating start-up of the wind turbine power system after the initial voltage value in the grid filter reaches the predetermined percentage of the grid voltage. It should be understood that the method system may further include any of the additional steps and/or features as described herein. It should be understood that the system may further include any of the additional features as described herein.
In yet another aspect, the present disclosure is directed to an alternating current (AC) electrical power system. The electrical power system includes a generator having a rotor and a stator and a power converter having a line-side converter coupled to a rotor-side converter via a DC link. The rotor-side converter is coupled to the rotor. The electrical power system also includes a grid filter coupled between the line-side converter and a power grid. Further, the electrical power system includes a controller configured to control the electrical power system, including but not limited to determining a grid voltage of the power grid, charging an AC capacitance of the grid filter from an initial capacitance value to a predetermined percentage of the grid voltage, connecting the electrical power system to the power grid when the AC capacitance in the grid filter reaches the predetermined percentage of the grid voltage, and initiating start-up of the electrical power system.
It should be understood that the electrical power system may further include any of the additional features as described herein.
These and other features, aspects and advantages of the present invention will become better understood with reference to the following description and appended claims. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.
A full and enabling disclosure of the present invention, including the best mode thereof, directed to one of ordinary skill in the art, is set forth in the specification, which makes reference to the appended figures, in which:
Reference now will be made in detail to embodiments of the invention, one or more examples of which are illustrated in the drawings. Each example is provided by way of explanation of the invention, not limitation of the invention. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the scope or spirit of the invention. For instance, features illustrated or described as part of one embodiment can be used with another embodiment to yield a still further embodiment. Thus, it is intended that the present invention covers such modifications and variations as come within the scope of the appended claims and their equivalents.
In general, the present disclosure relates to pre-charging the capacitor of the grid filter in an electrical power system to the AC grid voltage to reduce electrical transients and/or inrush upon start-up of the system. Such pre-charging can be accomplished with resistors, a contactor, and/or via the power converter which produces a voltage in sync with the grid voltage prior to closing the connection to the power grid. In certain embodiments, the voltage on the capacitor can be less than 100% of the grid voltage to reduce the inrush of current. In addition, the voltage on the capacitor does not have to be perfectly aligned with the grid voltage to reduce the inrush. In further embodiments, for the power converter to effectively charge the capacitance, the DC link must be charged and/or supplied with enough power to apply an AC voltage for a sufficient time period to connect to the power grid.
Accordingly, the present disclosure provides numerous advantages over prior art systems and methods. For example, the systems and methods of the present disclosure is capable of reducing the stress on fuses, power supplies, UPSs, motors, and/or other components of the power system. Reduced stress can thereby increase component life. The systems and methods of the present disclosure can avoid catastrophic destruction due to voltage spikes occurring as a result of the inrush current.
Referring now to the drawings,
Referring now to
As such, a rotating magnetic field may be induced by the generator rotor 122 and a voltage may be induced within a generator stator 120 that is magnetically coupled to the generator rotor 122. In such embodiments, the generator 118 is configured to convert the rotational mechanical energy to a sinusoidal, three-phase alternating current (AC) electrical energy signal in the generator stator 120. The associated electrical power can be transmitted to a main transformer 234 via a stator bus 208, a stator synchronizing switch 206, a system bus 216, a main transformer circuit breaker 214, and a generator-side bus 236. The main transformer 234 steps up the voltage amplitude of the electrical power such that the transformed electrical power may be further transmitted to a power grid 243 via a grid circuit breaker 238, a breaker-side bus 240, and a grid bus 242.
In addition, the electrical power system 200 may include a wind turbine controller 202 configured to control any of the components of the wind turbine 100 and/or implement the method steps as described herein. For example, as shown particularly in
As used herein, the term “processor” refers not only to integrated circuits referred to in the art as being included in a computer, but also refers to a controller, a microcontroller, a microcomputer, a programmable logic controller (PLC), an application specific integrated circuit, and other programmable circuits. The processor 204 is also configured to compute advanced control algorithms and communicate to a variety of Ethernet or serial-based protocols (Modbus, OPC, CAN, etc.). Additionally, the memory device(s) 207 may generally comprise memory element(s) including, but not limited to, computer readable medium (e.g., random access memory (RAM)), computer readable non-volatile medium (e.g., a flash memory), a floppy disk, a compact disc-read only memory (CD-ROM), a magneto-optical disk (MOD), a digital versatile disc (DVD) and/or other suitable memory elements. Such memory device(s) 207 may generally be configured to store suitable computer-readable instructions that, when implemented by the processor(s) 204, configure the controller 202 to perform the various functions as described herein.
Referring back to
The power conversion assembly 210 may include a rotor filter 218 that is electrically coupled to the generator rotor 122 via the rotor bus 212. In addition, the rotor filter 218 may include a rotor-side reactor. A rotor filter bus 219 electrically couples the rotor filter 218 to a rotor-side power converter 220. Further, the rotor-side power converter 220 may be electrically coupled to a line-side power converter 222 via a single direct current (DC) link 244. Alternatively, the rotor-side power converter 220 and the line-side power converter 222 may be electrically coupled via individual and separate DC links. In addition, as shown, the DC link 244 may include a positive rail 246, a negative rail 248, and at least one capacitor 250 coupled therebetween.
In addition, a line-side power converter bus 223 may electrically couple the line-side power converter 222 to a line filter 224. Also, a line bus 225 may electrically couple the line filter 224 to a line contactor 226. In addition, the line filter 224 may include a line-side reactor. Moreover, the line contactor 226 may be electrically coupled to a conversion circuit breaker 228 via a conversion circuit breaker bus 230. In addition, the conversion circuit breaker 228 may be electrically coupled to the main transformer circuit breaker 214 via system bus 216 and a connection bus 232. The main transformer circuit breaker 214 may be electrically coupled to an electric power main transformer 234 via a generator-side bus 236. The main transformer 234 may be electrically coupled to a grid circuit breaker 238 via a breaker-side bus 240. The grid circuit breaker 238 may be connected to the electric power transmission and distribution grid via a grid bus 242.
Referring particularly to
The line side converter 222 converts the DC power on the DC link 244 into AC output power suitable for the electrical grid bus 242. In particular, switching elements 247 (e.g. IGBTs) used in bridge circuits of the line side power converter 222 can be modulated to convert the DC power on the DC link 244 into AC power on the line side bus 225. The AC power from the power conversion assembly 210 can be combined with the power from the stator 120 to provide multi-phase power (e.g. three-phase power) having a frequency maintained substantially at the frequency of the electrical grid bus 242 (e.g. 50 Hz/60 Hz).
It should be understood that the rotor-side power converter 220 and the line-side power converter 222 may have any configuration using any switching devices that facilitate operation of electrical power system 200 as described herein. For example,
Further, the power conversion assembly 210 may be coupled in electronic data communication with the turbine controller 202 and/or a separate or integral converter controller 262 to control the operation of the rotor-side power converter 220 and the line-side power converter 222. For example, during operation, the controller 202 may be configured to receive one or more voltage and/or electric current measurement signals from the first set of voltage and electric current sensors 252. Thus, the controller 202 may be configured to monitor and control at least some of the operational variables associated with the wind turbine 100 via the sensors 252. In the illustrated embodiment, each of the sensors 252 may be electrically coupled to each one of the three phases of the power grid bus 242. Alternatively, the sensors 252 may be electrically coupled to any portion of electrical power system 200 that facilitates operation of electrical power system 200 as described herein. In addition to the sensors described above, the sensors may also include a second set of voltage and electric current sensors 254, a third set of voltage and electric current sensors 256, a fourth set of voltage and electric current sensors 258 (all shown in
It should also be understood that any number or type of voltage and/or electric current sensors 252, 254, 256, 258 may be employed within the wind turbine 100 and at any location. For example, the sensors may be current transformers, shunt sensors, rogowski coils, Hall Effect current sensors, Micro Inertial Measurement Units (MIMUs), or similar, and/or any other suitable voltage or electric current sensors now known or later developed in the art.
Thus, the converter controller 262 is configured to receive one or more voltage and/or electric current feedback signals from the sensors 252, 254, 256, 258. More specifically, in certain embodiments, the current or voltage feedback signals may include at least one of line feedback signals, line-side converter feedback signals, rotor-side converter feedback signals, or stator feedback signals. For example, as shown in the illustrated embodiment, the converter controller 262 receives voltage and electric current measurement signals from the second set of voltage and electric current sensors 254 coupled in electronic data communication with stator bus 208. The converter controller 262 may also receive the third and fourth set of voltage and electric current measurement signals from the third and fourth set of voltage and electric current sensors 256, 258. In addition, the converter controller 262 may be configured with any of the features described herein in regards to the main controller 202. As such, the converter controller 262 is configured to implement the various method steps as described herein and may be configured similar to the turbine controller 202.
For conventional systems, during start-up of the power system, the grid filter is not connected to the grid (i.e. the line contactor is open). Therefore, once the DC link is charged, the line contactor is closed and the grid filter begins producing reactive power. Thus, a voltage spike can occur and travel through to the auxiliary power system, which generally includes an auxiliary transformer (not shown). As such, conventional systems can experience inrush of current upon start-up of the system. Accordingly, the present disclosure is directed to an improved system and method for minimizing inrush of current during start-up of an electrical power system connected to a power grid.
Referring now to
Referring particularly to
As shown at 302, the method 300 includes determining a grid voltage of the power grid 243. As shown at 304, the method 300 includes charging an AC capacitance of the grid filter 224 (also referred to herein as the line filter 224) from an initial capacitance value to a predetermined percentage of the grid voltage. In one embodiment, the predetermined percentage of the grid voltage may be 100% of the grid voltage. In alternative embodiments, the predetermined percentage of the grid voltage may include less than 100% of the grid voltage.
In particular embodiments, the method 300 may include charging the AC capacitance in the grid filter 224 with the additional electrical component(s) 268. In such embodiments, the method 300 may further include bypassing the additional electrical component(s) 268 after connecting the power system 200 to the power grid 243 but before initiating start-up. In alternative embodiment, the method 300 may include charging the AC capacitance in the grid filter 224 via the power converter 210, e.g. via the line side converter 222, operating in a first operating mode. In such embodiments, the line side converter 222 is configured to produce a voltage in sync with the grid voltage prior to connecting the power system 200 to the power grid 243.
In further embodiments, the method 300 may include charging the DC link 244 of the power converter 210 to a predetermined power level prior to charging the AC capacitance in the grid filter 224 via the line side converter 222. Alternatively, the method 300 may include supplying the DC link 244 with additional power prior to charging the capacitance in the grid filter 224. In several embodiments, the method 300 may also include transitioning from the first operating mode of the power converter 210 to a second operating mode after charging the AC capacitance of the grid filter 224 of the electrical power system 200. In such embodiments, the first operating mode may correspond to an AC charging mode, whereas the second operating mode may correspond to a standard operating mode. In such embodiments, the transitioning step may include detecting the contactor closure (e.g. from a change in shunt current) and subsequently stopping gating in the open-loop AC voltage mode and re-starting in standard operating mode and/or switching from one regulator topology to another.
Referring still to
This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they include structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.
