Patent Application
20070273342
An electric power supply apparatus according to embodiments of the present invention will be described in detail below with reference to the accompanying drawings. The same or corresponding members or elements are denoted by the same reference numerals throughout views and will not be described repetitively.
The inverter 15 constitutes a voltage-controlled inverter apparatus for converting the DC electric power from the DC power supply 13 into AC electric power having a frequency and a voltage based on command values. The inverter 15 has a plurality of power switching elements that are selectively turned on and off by a pulse width modulation signal for converting DC electric power into AC electric power. The inverter apparatus (power converter) has various types of sensors and control units associated with the inverter 15. Such sensors and control units include a voltage detector 18 for detecting an output voltage from the inverter 15, a current detector 19 for detecting an output current from the inverter 15, a power detector 20 for detecting an output power from the inverter 15, a voltage command computing unit 21 for computing a voltage command value based on command values for a frequency and a voltage and feedback values detected by the above detectors 18, 19 and 20, a voltage control unit 22, and a pulse width modulator 23 for generating a pulse width modulation signal for performing on-off control of the power switching elements of the inverter 15.
The electric power supply apparatus 10 is of a unitized structure including the electric generator 11 and the power converter comprising the inverter apparatus for converting electric power generated by the electric generator 11 into AC electric power having a required frequency and a required voltage. For example, the electric generator 11 may be an electric generator having a capability for generating electric power of 100 kW, and the power converter may be a voltage-controlled inverter apparatus for converting the electric power generated by the electric generator into AC electric power having a frequency and a voltage of a commercial power supply system. The electric generator 11 and the power converter are unitized and housed in a single housing (package). The user may have a single electric power supply apparatus 10 for outputting a maximum of 100 kW of AC electric power having the same frequency and voltage as those of the commercial power supply system, to a load that can be connected to the commercial power supply system.
The users of the electric power supply apparatus have a diversity of electric power requirements. To meet such electric power requirements, it has been customary to connect a plurality of electric power supply apparatuses 10 in parallel and operate them in a parallel-run mode, as shown in
Each of the electric power supply apparatuses 10 includes a control unit 24 having output voltage vs. output current characteristics for determining an output voltage corresponding to the output current from the inverter apparatus and automatically controlling the electric power supply apparatus 10 to share the load while the electric power supply apparatuses 10 are operating in the parallel-run mode. The voltage command computing unit 21, the voltage control unit 22, the pulse width modulator 23, and the control unit 24 jointly make up a controller 25. The output voltage determined by the control unit 24 is applied to the voltage command computing unit 21. Since the electric power supply apparatuses 10 have respective output terminals connected in parallel, the control units 24 for commanding identical output voltages with respect to the identical output currents, which are provided in the respective electric power supply apparatuses 10, are effective to substantially equalize the load sharing rates of the electric power supply apparatuses 10. If the electric power supply apparatuses 10 are controlled to produce different output currents under the same output voltage, then the electric power supply apparatuses 10 can positively have different load sharing rates. Therefore, the load sharing rates of the electric power supply apparatuses 10 can automatically be substantially equalized or be positively differentiated without the need for dedicated hardware for sharing information of the electric power supply apparatuses 10.
When the control unit determines an output voltage command value for a voltage-controlled inverter apparatus, it is customary to determine an output voltage only in consideration of weather the output current or output power of the inverter apparatus falls in a rated capacity range thereof or not.
If the inverter apparatus having this type of control unit is combined with the electric generator to construct an electric power supply apparatus, then when the power generation capability of the electric generator is greater than the output capability of the inverter apparatus, no problem arises on condition that the electric generator is operated within the output capability of the inverter apparatus. However, when the power generation capability of the electric generator is smaller than the output capability of the inverter apparatus, the electric generator may be overloaded before the output capability (normally, the rated capacity range) of the inverter apparatus is reached, and a safety device is activated to shut down the entire electric power supply apparatus.
In order to solve the above problem, according to the electric power supply apparatus of the present invention, the control unit 24 of the controller 25 for the inverter apparatus (power converter) is given an output voltage vs. output current control characteristics shown in
The dropping characteristic (the output voltage vs. output current characteristics) can be realized by storing a table or function of output currents of the inverter apparatus and corresponding output voltages of the inverter apparatus in a memory of the control unit 24, detecting an output current of the inverter apparatus, and referring to the table or function with a CPU of the control unit 24 to determine an output voltage command value based on the detected output current.
In the interval 1 shown in
When the output current of the inverter apparatus increases beyond the output current A, in the interval 2, the output voltage vs. output current characteristics has the first dropping characteristic showing a drop of the output voltage while keeping the generated electric power constant, so that the electric generator 11 will not undergo a load greater than its limit capability. Specifically, the output power of the electric generator 11 is limited to a constant level. When the output current further increases beyond the output current B exceeding the conversion capability of the inverter apparatus, in the interval 3, the output voltage vs. output current characteristics has the third dropping characteristic showing a sharp drop (lowering) of the output voltage as the output current increases, so that the power converter will not undergo a load greater than its limit capability.
In each of the intervals 2 shown in
In the case where the electric generator 11 of each of the electric power supply apparatuses comprises a gas turbine generator, the power generation capability limit value of the gas turbine generator is strongly affected by the exhaust gas temperature (EGT) or the inlet air temperature, and is thus determined by these temperatures. A controller of the gas turbine generator determines a power generation capability limit value that can be outputted in a safe operation range of the gas turbine generator from the exhaust gas temperature or the inlet air temperature, and transmits the determined power generation capability limit value to the controller 25 for controlling the inverter apparatus. The control unit 24 of the controller 25 controls the inverter apparatus on the basis of the transmitted power generation capability limit value utilizing the dropping characteristic in the interval 2. Therefore, the electric power supply apparatus includes a device for detecting the power generation capability of the electric generator 11 and a device for setting the dropping characteristic in the interval 2 on the basis of the detected power generation capability.
As described above, the control based on the dropping characteristic is performed by referring to the output voltage vs. output current characteristics as the table or function based on the detected output current by the current detector 19 to output a voltage command value and to control the inverter apparatus based on the voltage command value. Therefore, the device for setting the dropping characteristic in the interval 2 based on the detected power generation capability is capable of setting the range of the interval 2 from the output current A at the power generation capability limit value of the electric generator 11 and the output current (rated current) B that can be outputted from the inverter apparatus, and is capable of setting the gradient of the output voltage vs. output current characteristics from the output power at the power generation capability limit value of the electric generator 11.
In each of the intervals 3 shown in
An electric power supply system according to a first embodiment of the present invention will be described below with reference to
The electric power supply apparatus 1 outputs a predetermined voltage (e.g., a rated voltage) V0 at the time of no load (output current is 0). The electric power supply apparatus 2 also outputs a predetermined voltage V0 at the time of no load. Actually, however, the electric power supply apparatus 2 produces an output voltage V0′ due to errors of sensors, filter circuits and the like, the output voltage V0′ being different from the predetermined voltage V0 by a slight quantity (e.g., about 0.5% of the rated voltage).
The electric power supply apparatus 1 has the mild dropping characteristic in the interval 1 up to the output current A at the power generation capability limit of the electric generator 11, the dropping characteristic for keeping the generated power of the electric generator 11 constant in the interval 2 from the output current A up to the output current B at the output capability limit of the inverter apparatus, and the sharp dropping characteristic in the interval 3 beyond the output current B. The electric power supply apparatus 2 has the mild dropping characteristic in the interval 1 up to the output current C at the power generation capability limit of the electric generator 11, the dropping characteristic for keeping the generated power of the electric generator 11 constant in the interval 2 from the output current C up to the output current B at the output capability limit of the inverter apparatus, and the sharp dropping characteristic in the interval 3 beyond the output current B. As described above, since the output power is controlled so as to be a predetermined value or less by the dropping characteristic in the interval 2, it is possible to keep the output power from the electric power supply apparatus within the range of the power generation capability of the electric generator 11.
When the two electric power supply apparatuses operated in a parallel-run mode produce an output voltage V3 in the interval 1, the electric power supply apparatus 1 shares an output current E and the electric power supply apparatus 2 shares an output current D. If any output voltage difference between the electric power supply apparatus 1 and the electric power supply apparatus 2 is caused by a voltage difference due to errors of sensors, filter circuits and the like, then the output current E and the output current D are approximately close to each other, and hence the electric power supply apparatus 1 and the electric power supply apparatus 2 can have substantially identical load sharing rates. When the output current of the electric power supply apparatus 1 reaches the power generation capability limit (the output current A) of the electric generator 11, the output voltage vs. output current characteristics enters the dropping characteristic in the interval 2, and the output power is controlled so as to be limited to the power generation capability limit to prevent the electric power supply apparatus 1 from being overloaded. Thus, the electric power supply apparatus 2 is controlled to increase its load sharing rate. When the output current of the electric power supply apparatus 2 reaches the power generation capability limit (the output current C) of the electric generator 11, the output voltage vs. output current characteristics enters the dropping characteristic in the interval 2, and the output power is controlled so as to be limited to the power generation capability limit to prevent the electric power supply apparatus 2 from being overloaded. When a load current exceeding the output capability (the rated current) B of the inverter apparatus is required, the output voltage vs. output current characteristics enters the dropping characteristic in the interval 3, and the output voltage is sharply dropped to prevent the inverter apparatus from being overloaded. If there is another electric power supply apparatus operated in the parallel-run mode, then such electric power supply apparatus supplies electric power to the load.
In the above first embodiment, while the electric generator 11 has excess power generation capability, the load sharing rates of the electric power supply apparatuses are kept to be substantially equalized. When the power generation capability of the electric generator 11 reaches its limit, the output power is limited to prevent the electric generator from being overloaded, and the load sharing rate of another electric power supply apparatus is increased. However, if the load sharing rates of the plural electric power supply apparatuses are to be positively changed, e.g., if one of two electric power supply apparatuses preferentially supplies electric power to the load, then the output voltage vs. output current characteristics of the electric power supply apparatuses are differentiated from each other in advance for causing the electric power supply apparatus with the higher output voltage to preferentially supply electric power to the load. Further, when the power generation capability limit of the electric generator 11 is reached, the output voltage is dropped to make the electric power constant, i.e., to prevent the electric power from exceeding the electric power limit. Thus, the electric power supply apparatus is not shut down, and the other electric power supply apparatus is controlled to supply electric power to the load.
An electric power supply system according to a second embodiment of the present invention will be described below with reference to
In the interval 1 up to the output current A at which the output current is determined by the power generation capability limit of the electric generator 11, the output voltages (command values) of the electric power supply apparatus 1 and the electric power supply apparatus 2 are made constant as V0 (actual output voltages are different due to errors of their components including sensors, filter circuits, etc.), thereby substantially equaling the load sharing rates of the electric power supply apparatuses 1, 2 operated in the parallel-run mode. Although the output voltages (command values) are constant in the interval 1, because a voltage drop is produced by the filter 16 composed of the coil L and the capacitor C which are connected between the output terminal of the inverter 15 and the output terminal of the entire electric power supply apparatus, the voltage at the output terminal decreases as the output current increases, thereby substantially equalizing the load sharing rates.
In the interval 1 up to the output current A at which the output current is determined by the power generation capability limit of the electric generator 11, the output voltages (command values) of the electric power supply apparatus 1 and the electric power supply apparatus 2 may be differentiated from each other. When the electric power supply apparatus 1 and the electric power supply apparatus 2 produce output voltages (command values) V0, V1, the electric power supply apparatus having the higher output voltage (command value) may preferentially supply electric power to the load.
When the load current increases until the output power exceeds the power generation capability limit (the output current A) of the electric generator 11, the generated electric power is controlled to be constant to prevent the electric generator 11 from being overloaded in the interval up to the output capability limit (the output current B) of the inverter apparatus, thereby lowering the output voltage to cause other electric power supply apparatus to supply electric power to the load. When the load current further increases until the output current exceeds the output capability limit (the output current B) of the inverter apparatus, the output voltage is sharply dropped (in the interval 3) to prevent the inverter apparatus from being overloaded and to cause other electric power supply apparatus to supply electric power to the load. This operation is the same as that of the electric power supply system according to the first embodiment.
In the above embodiment, the controller of the electric generator 11 determines an output power value at the power generation capability limit of the electric generator 11. However, the controller 25 of the power converter (inverter apparatus) may receive information of the exhaust gas temperature or the inlet air temperature, calculate a generated electric power limit value based on the received information, and use the calculated value for control. Although the gas turbine generator has been described in the above embodiments, a distributed electric generator such as a gas engine, a fuel cell, a water turbine or a solar cell may determine a power generation capability limit value depending on the operating environment, transmit the determined power generation capability limit value to the controller of the power converter, and set the dropping characteristic in the interval 2. Accordingly, the present invention is also applicable to an electric power supply apparatus including such a distributed electric generator.
The inverter 45 constitutes a voltage-controlled inverter apparatus for converting the DC electric power from the DC power supply 43 into AC electric power having a frequency and a voltage based on command values. The inverter 45 has a plurality of power switching elements that are selectively turned on and off by a pulse width modulation signal for converting DC electric power into AC electric power. The inverter apparatus (power converter) has various types of sensors and control units associated with the inverter 45. Such sensors and control units include a voltage detector 48a for detecting an output voltage from the inverter 45, a voltage detector 48b for detecting a voltage of a power line 59 to which a load is connected, a current detector 49 for detecting an output current from the inverter 45, a power detector 50 for detecting an output power from the inverter 45, a voltage command computing unit 51 for computing a voltage command value based on the output current or the like of the inverter 45, a voltage control unit 52 for controlling the output voltage of the inverter 45, a phase control unit 53 for controlling the output phase of the inverter 45, and a pulse width modulator 54 for generating a pulse width modulation signal for performing on-off control of the power switching elements of the inverter 45.
The electric power supply apparatus 40 is of a unitized structure including the electric generator 41 and the inverter apparatus (power converter) which converts the electric power generated by the electric generator 41 into AC electric power having a required frequency and a required voltage. For example, the electric generator 41 may be an electric generator having a capability for generating electric power of 100 kW, and the inverter apparatus may be a voltage-controlled inverter apparatus for converting the electric power generated by the electric generator 41 into AC electric power having a frequency and a voltage of a commercial power supply system. The electric generator 41 and the voltage-controlled inverter apparatus are unitized and housed in a single housing (package). The user may have a single electric power supply apparatus 40 for outputting a maximum of 100 kW of AC electric power having the same frequency and voltage as those of the commercial power supply system, to a load that can be connected to the commercial power supply system.
The users of electric power supply apparatus have a diversity of electric power requirements. To meet such electric power requirements, it has been customary to connect a plurality of electric power supply apparatuses 40 in parallel and operate them in a parallel-run mode, as shown in
When the unitized electric power supply apparatuses 40 are connected in parallel for operation in the parallel-run mode, the outputs from the inverter apparatuses of the electric power supply apparatuses 40 need to be synchronized with each other. For such synchronized operation, each of the electric power supply apparatuses 40 has the voltage detector 48b for detecting the voltage of the power line 59 and the phase control unit 53. By the phase control unit 53, the phase of the waveform (sine wave) of the output voltage of the inverter apparatus is brought in agreement with the phase of the waveform of the voltage of the power line 59, i.e., the synchronization is performed. In this manner, all the inverter apparatuses can be operated to produce their outputs in the voltage-controlled mode without the need for a synchronization signal for synchronizing the phase of the output voltages of the inverter apparatuses. Therefore, it is not necessary to connect the inverter apparatuses by a special signal line for synchronizing the output voltages of the inverter apparatuses, but the electric power supply apparatuses 40 can be operated in the parallel-run mode for coping with load variations simply by connecting the output terminals of the inverter apparatuses to the power line 59.
As shown in
Since the three-phase voltages of the power line 59 are transformed into dq coordinate components that rotate at the angular frequency in the inverter apparatus as shown in
Three-phase voltages Vu, Vv, Vw of the power line 59 and a d-axis component Vd and a q-axis component Vq which are produced by the dq transformation are related to each other at the phase θ according to the following equation (1):
A PI control process is performed to eliminate the d-axis component Vd′ (phase difference information) obtained by the dq transformation, thereby obtaining a correction variable Δf for the internal phase. The correction variable Δf is added to the output reference frequency (e.g., 50 or 60 Hz) of the inverter apparatus for thereby correcting the internal phase θ′. If the d-axis component Vd′ is eliminated by this correction, then it means that the internal phase θ′ of the inverter apparatus is in agreement with the phase θ of the voltage of the power line 59. It is therefore possible to perform the PI phase control for bringing the internal phase θ of the inverter apparatus into agreement with the phase θ of the voltage of the power line 59.
As shown in
The phase θ′ outputted from the integrator 66 is converted into a sine wave by a θ/sin θ converter 67. The sine wave outputted from the θ/sin θ converter 67 is combined with a voltage signal from the voltage control unit 52 by a combiner 68. The combiner 68 supplies a sine-wave output voltage command value to the pulse width modulator 54, which controls the inverter apparatus to produce an output voltage waveform.
While a first one of the electric power supply apparatuses is activated and outputs electric power, if the output frequency thereof reaches an upper limit value of the limiter 64 or a lower limit value thereof as divergent in the control process), then the internal phase θ′ of a second one of the electric power supply apparatuses cannot be corrected due to the effect of the limiter 64, and the voltages cannot be synchronized in phase.
After the first inverter apparatus is activated, when the second and other inverter apparatuses are to start operating in the parallel-run mode, the internal phase of the inverter apparatus and the phase of the detected voltage of the power line 59 are brought into synchronism with each other according to the above phase synchronizing process. After the internal phase of the inverter apparatus and the phase of the detected voltage of the power line 59 are synchronized with each other, the inverter apparatus starts operating in the parallel-run mode. For example, the parallel operation is not performed, until the difference between the internal phase of the inverter apparatus and the phase of the detected voltage of the power line 59 becomes ±5° or less, for example. When the phase difference reaches ±5° or less, it is judged that the synchronization is established, and a switch K1 (see
After the inverter apparatuses are activated in the manner described above, if one of the inverter apparatuses is to be shut down while the inverter apparatuses are being operated in the parallel-run mode, since no interlinked control process is performed between the inverter apparatuses, only the output of electric power from the inverter apparatus to be shut down should be stopped. The inverter apparatuses other than the inverter apparatus which is shut down can continuously be operated while keeping synchronization.
With the above arrangement, it is possible to synchronize the output voltages of the inverter apparatuses in phase with each other without the need for sharing information between the inverter apparatuses that operate in the parallel-run mode. If the above synchronization control process is performed using a microcomputer, for example, it may be carried out according to a timing sequence shown in
For synchronizing the internal phase of the second inverter apparatus or other inverter apparatuses with the phase of the voltage of the power line which has been established by the already activated inverter apparatus, the time T2 of 1/360 of one cycle at the reference frequency as an initial value is set in the timer 2. Then, the three-phase voltages shown at (a) in
According to the present invention, as described above, when the plural inverter apparatuses are connected in parallel, the output voltages of the inverter apparatuses can be synchronized in phase with each other by simply connecting the inverter apparatuses without the need for any special signal lines for synchronizing the output voltages of the parallel-connected inverter apparatuses in phase with each other. Specifically, the phases of the output voltages of the inverter apparatuses can be synchronized only by connecting the output terminals of the inverter apparatuses in parallel. Therefore, the number of signal lines or wires used can be reduced, and the electric power supply system is prevented from being shut down due to a synchronizing line disconnection or a master unit failure. Since the inverter apparatuses that are operated in the voltage-controlled mode can be synchronized with each other by using the voltage of the power line, a plurality of inverter apparatuses of different kinds and types can easily be operated synchronously in the parallel-run mode. Furthermore, the inverter apparatuses can be synchronized in phase with each other even if the frequency of the voltage of the power line is the same as the limit value of the limiter.
Since the dq transformer 61 and the phase adjuster 62 can easily be composed of a microprocessor, the electric power supply system can be constructed using the existing hardware including microprocessors, voltage detectors, etc. Thus, the electric power supply system can be constructed at low cost as it requires no new hardware.
In the above embodiments, a plurality of unitized electric power supply apparatuses, each of which comprises a distributed power generator and an inverter apparatus, are operated in the parallel-run mode. However, the present invention is also applicable to a system including a common DC power supply and a plurality of inverter apparatuses connected thereto and operable in the parallel-run mode.
Although certain preferred embodiments of the present invention have been shown and described in detail, it should be understood that various changes and modifications may be made therein without departing from the scope of the appended claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2006-145536 | May 2006 | JP | national |
| 2006-194605 | Jul 2006 | JP | national |
