CN104811064B - Energy conversion system, photovoltaic energy conversion system and method - Google Patents
Energy conversion system, photovoltaic energy conversion system and method Download PDFInfo
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- CN104811064B CN104811064B CN201410038726.4A CN201410038726A CN104811064B CN 104811064 B CN104811064 B CN 104811064B CN 201410038726 A CN201410038726 A CN 201410038726A CN 104811064 B CN104811064 B CN 104811064B
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
- H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E10/00—Energy generation through renewable energy sources
- Y02E10/50—Photovoltaic [PV] energy
- Y02E10/56—Power conversion systems, e.g. maximum power point trackers
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Abstract
The invention relates to an energy conversion system, a photovoltaic energy conversion system and a method. The method disclosed therein comprises at least the following steps: generating at least one maximum phase angle limit signal and a minimum phase angle limit signal based at least on a current threshold associated with the converter device; generating a phase angle limit adjustment signal based on at least the DC voltage command signal and an actual voltage signal associated with the DC link; adjusting at least one of the maximum phase angle limit signal and the minimum phase angle limit signal using the phase angle limit adjustment signal; and limiting the phase angle command signal using at least one of the adjusted maximum phase angle limit signal and the adjusted minimum phase angle limit signal.
Description
Technical Field
The disclosed embodiments relate to systems and methods, and more particularly, to a system and method that may be used to coordinate control of output current and dc bus voltage.
Background
Energy conversion systems, including devices such as photovoltaic power generation devices, wind power generation devices, and the like, are being developed to replace conventional power generation devices, such as fossil fuel-based power generation devices, and the like. At least a part of the known energy conversion systems are arranged to make a grid-tie connection, which may convert energy obtained from e.g. renewable energy sources into energy meeting the requirements of the grid, e.g. having a certain voltage and frequency, etc., and feed the converted energy into the grid.
In order to enhance the control capability of the output current of the power conversion system designed based on the voltage source model, a phase current control algorithm or a control method has been proposed in the industry. When the phase current control algorithm or the phase current control method is actually executed, the voltage amplitude limiting signal is provided to limit the amplitude of the voltage command signal and/or the phase angle limiting signal is provided to limit the phase angle of the phase angle command signal at least based on the preset current threshold value, so that the current output by an inverter of the electric energy conversion system is indirectly controlled, and therefore, semiconductor devices in the inverter can be prevented from being damaged when low-voltage events and/or zero-voltage events occur.
In addition, during actual operation, it is desirable to control the voltage of the dc bus in the power conversion system to be maintained at a constant value or within an acceptable voltage range. However, the dc bus voltage control algorithm implemented in the conventional power conversion system still faces considerable challenges when encountering transient events or grid faults.
Therefore, there is a need to provide an improved system and method to solve the above technical problems or to meet the above technical needs.
Disclosure of Invention
In view of the above-mentioned technical problems or needs, an aspect of the present invention is to provide an energy conversion system. The energy conversion system comprises a direct current link, a converter device and a converter controller. The converter device is connected with the direct current link and is configured to convert direct current electric energy provided by the direct current link and provide alternating current electric energy. The converter controller is connected to the dc link and the converter device, and includes a hybrid dc voltage and output current control module for limiting an output current of the ac power provided by the converter device and regulating a dc voltage of the dc link when the power conversion system encounters at least one transient event. The hybrid direct-current voltage and output current control module comprises a phase angle regulator, a direct-current voltage regulator and a current limiter; the phase angle adjuster is used for generating a phase angle instruction. The DC voltage regulator is configured to generate a phase angle limit adjustment signal based on at least a DC voltage command signal and an actual DC voltage signal associated with the DC link. The current limiter is coupled to the phase angle regulator and the dc voltage regulator, the current limiter configured to generate at least one of a maximum phase angle limit signal and a minimum phase angle limit signal based on at least a current threshold associated with the converter device, the maximum phase angle limit signal and the minimum phase angle limit signal configured to limit the phase angle command signal. The current limiter is also for adjusting at least one of the maximum phase angle limit signal and the minimum phase angle limit signal using the phase angle limit adjustment signal.
Another aspect of the invention is to provide a method for detecting operation of an energy conversion system including a dc link, a converter device and a converter controller. The method at least comprises the following steps: generating at least one maximum phase angle limit signal and a minimum phase angle limit signal based at least on a current threshold associated with the converter device; generating a phase angle limit adjustment signal based on at least the DC voltage command signal and an actual voltage signal associated with the DC link; adjusting at least one of the maximum phase angle limit signal and the minimum phase angle limit signal using the phase angle limit adjustment signal; and limiting the phase angle command signal using at least one of the adjusted maximum phase angle limit signal and the adjusted minimum phase angle limit signal.
Another aspect of the present invention is to provide a photovoltaic energy conversion system connected to a power grid. The photovoltaic energy conversion system comprises a direct current link, a photovoltaic converter and a photovoltaic controller; the dc link is configured to receive dc electrical energy from a photovoltaic energy source. The photovoltaic converter is connected with the direct current link, the photovoltaic converter is configured to convert direct current electric energy provided by the direct current link and provide active power to the power grid, and the photovoltaic controller is connected with the direct current link and the photovoltaic converter. The photovoltaic controller is configured to: generating a phase angle command signal to directly control a phase angle of an output voltage of the photovoltaic converter; generating a maximum phase angle limit signal and a minimum phase angle limit signal for limiting an output current provided by the photovoltaic converter; and adjusting at least one of the maximum phase angle limit signal and the minimum phase angle limit signal based at least on a voltage difference between a dc voltage command signal and an actual voltage signal associated with the dc link to adjust a value of active power provided by the photovoltaic converter to allow a dc voltage of the dc link to be controlled.
According to the energy conversion system, the photovoltaic energy conversion system, the related method and the like, the direct-current voltage control algorithm and the phase current control algorithm are combined, so that the direct-current voltage of the direct-current link can be effectively controlled.
Drawings
The invention may be better understood by describing embodiments thereof in conjunction with the following drawings, in which:
FIG. 1 is a block schematic diagram of one embodiment of an energy conversion system provided with a hybrid DC voltage and output current control block;
FIG. 2 is a block schematic diagram of one embodiment of a photovoltaic energy conversion system provided with a hybrid DC voltage and output current control module;
FIG. 3 is a generalized block diagram of one embodiment of a hybrid DC voltage and output current control block;
FIG. 4 is a detailed block diagram of one embodiment of a hybrid DC voltage and output current control module;
FIG. 5 is a detailed block diagram of another embodiment of a hybrid DC voltage and output current control module;
FIG. 6 is a detailed block diagram of another embodiment of a hybrid DC voltage and output current control module;
FIG. 7 is a simplified circuit model schematic of an embodiment of a grid-side converter and a power grid;
FIG. 8 is a voltage vector diagram of one embodiment associated with implementing a hybrid DC voltage and output current control module;
FIG. 9 is a voltage vector diagram of another embodiment associated with implementing a hybrid DC voltage and output current control module;
FIG. 10 is a schematic diagram of various signal waveforms for one embodiment generated during implementation of the hybrid DC voltage and output current control module;
FIG. 11 is a detailed block diagram of another embodiment of a hybrid DC voltage and output current control module;
FIG. 12 is a voltage vector diagram illustrating another embodiment associated with implementing a hybrid DC voltage and output current control module; and
FIG. 13 is a flow diagram illustrating one embodiment of a method of controlling operation of an energy conversion system.
Detailed Description
One or more embodiments disclosed herein relate to an energy conversion system, or more particularly, to an energy generation system or a power conversion system, and more particularly, to a system and method for performing output current control and dc link voltage control in a coordinated manner. In some embodiments, at least a portion of the parameters related to the output current of the power conversion system can be dynamically adjusted according to the adjustment requirement of the dc voltage of the dc link, so as to achieve coordinated control. For example, in some embodiments, the phase angle limit signal for limiting the overcurrent problem in the output current of the converter may be dynamically adjusted according to a dc link voltage deviation signal indicating that the dc voltage of the actual dc link deviates from the normal or expected dc link voltage. In some embodiments, the phase angle limit signal may also be adjusted according to the reactive power that needs to be provided.
The system and the method disclosed by the invention can at least obtain the following technical advantages or technical effects: one of the technical advantages or effects is that the control of the dc link voltage can be made faster by integrating the dc link voltage control algorithm with the output current control algorithm; another technical advantage or effect is that over-current problems encountered by the converter and over-voltage problems encountered by the dc link can be avoided or mitigated such that the power conversion system can successfully ride through one or more transient events; yet another technical advantage or effect is that an electrical energy conversion system may be protected from unnecessary tripping (trip) by mitigating over-voltage or under-voltage problems of a dc link. It will be readily apparent to those skilled in the art that other technical advantages or effects may be produced by the specific embodiments of the present invention from the following detailed description when taken in conjunction with the accompanying drawings.
One or more specific embodiments of the present invention will be described below. It is first noted that in the detailed description of these embodiments, for the sake of brevity, this specification is not intended to describe in any detail all of the features of the actual embodiments. It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation-specific decisions are made to achieve the developers' specific goals, such as compliance with system-related and business-related constraints, which may vary from one implementation to another. Moreover, it should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation-specific decisions must be made to achieve the developers' specific goals, such as compliance with system-related and business-related constraints, which may vary from one implementation to another.
Unless otherwise defined, technical or scientific terms used herein in the specification and claims should have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. As used in this specification and the appended claims, the terms "first" or "second," and the like, do not denote any order, quantity, or importance, but rather are used to distinguish one element from another. The terms "a" or "an," and the like, do not denote a limitation of quantity, but rather denote the presence of at least one. "or" includes any or all of the enumerated items. The word "comprise" or "comprises", and the like, means that the element or item listed before "comprises" or "comprising" covers the element or item listed after "comprising" or "comprises" and its equivalent, and does not exclude other elements or items. The terms "connected" or "coupled" and the like are not restricted to physical or mechanical connections, but may include electrical connections, whether direct or indirect. Furthermore, a "circuit" or "circuitry" and a "controller" or the like may comprise a single component or a collection of multiple active or passive elements connected directly or indirectly, such as one or more integrated circuit chips, to provide the corresponding described functionality.
Referring first to fig. 1, a schematic block diagram of an embodiment of an energy conversion system 10 according to the present invention is shown. The energy conversion system 10 referred to herein may include photovoltaic energy conversion systems, wind energy conversion systems, fuel cell energy conversion systems, hydro or tidal energy conversion systems, combinations thereof, and the like. As shown in fig. 1, the energy conversion system 10 includes a converter device 14 electrically connected between an energy source 12 and a load 16, the converter device 14 may be configured to convert first electrical energy 18 (e.g., direct current electrical energy or alternating current electrical energy) obtained from the energy source 12 into second electrical energy 22 (e.g., direct current electrical energy or alternating current electrical energy), and to provide the second electrical energy 22 to the load 16. In one particular application, the load 16 may be a power grid, and the desired secondary power 22 may be three-phase ac power and have a particular voltage and/or frequency (e.g., 60 hz or 50 hz). In other embodiments, the load 16 may also include an electrical energy consuming device such as an electric motor (motor), or the like.
As shown in fig. 1, the converter device 14 is also communicatively coupled to a converter controller 30. Although the converter device 14 and the converter controller 30 are shown as separate components in the embodiment shown in fig. 1, in other embodiments, the converter device 14 and the converter controller 30 may be integrated together to form a single device. The converter controller 30 is configured to execute one or more control algorithms to adjust or tune various electrical characteristic parameters, etc. associated with the operation of the converter assembly 14. For example, to meet the needs of the power grid or to ensure safe and stable operation of the energy conversion system 10, the converter controller 30 may be configured to regulate and control parameters such as active power, reactive power, power factor, voltage, current, frequency, phase angle, etc. output by the converter device 14.
In accordance with a particular configuration provided by the present invention, the converter controller 30 may include a hybrid dc voltage and output current control module 28, and the hybrid dc voltage and output current control module 28 may be implemented by computer software, algorithms or program instructions and may be stored on a non-transitory computer-readable storage medium (non-transient computer-readable storage medium). The converter controller 30 may include one or more processors for executing the software algorithms or programs to perform the various functions described herein as being required. In alternative embodiments, the hybrid dc voltage and output current control module 28 may also be implemented by a hardware circuit, or may also be implemented in a form of hardware in combination with software. In particular, the hybrid dc voltage and output current control module 28, when executed, may perform a coordinated control to limit the output current of the converter device 14 and regulate the dc voltage of the dc link 15.
In particular embodiments, the hybrid dc voltage and output current control module 28 may be communicatively coupled to the output of the converter device 14, or more particularly, to a junction 24 defined between the converter device 14 and the load or grid 16, through which junction 24 one or more feedback signals, such as ac voltage and/or ac current signals, etc., may be obtained that represent the actual ac voltage and ac current at the output of the converter device 14. Upon encountering at least one transient event, such as a low voltage event or a zero voltage event, the converter device 14 may not be able to provide active power to the load 16, which may result in a rapid rise in current at the output of the converter device 14. At this point, the hybrid dc voltage and output current control module 28 is further configured to generate a control signal 32 based on at least the obtained one or more feedback signals 26 and one or more current thresholds 33, wherein the current thresholds 33 define a maximum value of the current flowing from the converter device 2. The converter device 14 operates in a specific manner based on the control signal 32 sent from the converter controller 30 to prevent the output current of the converter device 14 from exceeding the current threshold.
In the embodiment shown in fig. 1, the hybrid dc voltage and output current control module 28 is also communicatively coupled to the dc link 15 to receive a feedback signal 17 representing the actual dc voltage of the dc link 15. The dc link 15 may encounter an over-voltage condition or an under-voltage condition when a transient event occurs, such as a low voltage event or a zero voltage event. The mixed dc voltage and output current control module 28 is further configured to adjust the control signal 32 based on at least the dc voltage feedback signal 17 and one or more voltage set point signals 35, wherein the voltage set point signals 35 may represent a desired dc voltage value or a dc voltage range value of the dc link 15. The converter device 14 operates according to the adjusted control signal 32 to allow the actual dc voltage of the dc link 35 to be adjusted according to the voltage setting signal 35.
Referring next to fig. 2, a block diagram of an embodiment of a photovoltaic energy conversion system 100 is shown. The photovoltaic energy conversion system 100 may be configured to implement the hybrid dc voltage and output current control module 28 shown in fig. 1. As shown in fig. 2, the photovoltaic energy conversion system 100 includes a photovoltaic converter module 104, the photovoltaic converter module 104 being used to convert dc electrical energy provided from a photovoltaic energy source 102 into ac electrical energy having a suitable voltage and frequency and to provide the ac electrical energy to a power grid 110. In one embodiment, the photovoltaic energy source 102 may include one or more photovoltaic arrays, each having a plurality of photovoltaic cells connected together in parallel and/or series, the photovoltaic arrays or photovoltaic cells of the photovoltaic energy source 102 converting photovoltaic radiant energy into direct current electrical energy according to the photovoltaic effect.
In one embodiment, the photovoltaic converter module 104 shown in fig. 2 is based on a two-stage architecture, which includes a photovoltaic-side converter 106 (i.e., a converter on the side near the photovoltaic energy source 102) and a grid-side converter 108 (i.e., a converter on the side near the grid 110). The photovoltaic side converter 106 may include a dc-dc converter, such as a boost dc-dc converter, which may boost the dc voltage converted and output by the photovoltaic energy source 12 and provide the boosted dc voltage to the dc link 128. The dc link (or dc bus, dc link) 128 may include one or more capacitors to maintain the dc voltage of the dc link 128 at a particular value or range of values, thereby controlling the flow of energy from the dc link 128 to the power grid 110. The grid-side converter 108 may include a dc-ac converter to convert the dc voltage at the dc link 128 into an ac voltage of suitable frequency, phase and/or amplitude for delivery by the ac power grid 18. In some embodiments, the photovoltaic energy conversion system 100 may further include a grid-side filter 134, the grid-side filter 134 being connected to any point of the line defined between the grid-side converter 108 and the grid 18, the grid-side filter 134 being used to remove undesired signals emitted by the grid-side converter 108, such as high frequency harmonic signals contained in the output ac power. It will be appreciated that although not shown, one or more other components, such as transformers, circuit breakers, etc., may be connected between the grid-side converter 108 and the grid 110 to perform the corresponding functions.
In one embodiment, the photovoltaic energy conversion system 100 shown in fig. 2 further includes a photovoltaic converter control device 112, the photovoltaic converter control device 112 configured to execute a control algorithm based on various system feedback signals and command signals to control the operation of the photovoltaic side converter 106 and the grid side converter 108. More specifically, in one embodiment, the photovoltaic converter control apparatus 112 includes a photovoltaic side controller 114 connected to the photovoltaic converter 106 and a grid side controller 116 connected to the grid side converter 108, the photovoltaic side controller 114 and the grid side controller 116 being configured to be responsible for controlling the operation of the photovoltaic converter 106 and the grid side converter 108, respectively.
For convenience in describing the present invention, in the embodiment shown in fig. 2, the photovoltaic-side controller 114 and the grid-side controller 116 are illustrated as separate modules in block diagram form, however, in some embodiments, the photovoltaic-side controller 114 and the grid-side controller 116 may be implemented by a single controller. The photovoltaic Controller 114 and the grid Controller 116 may include any suitable Programmable Circuit or device, including a Digital Signal Processor (DSP), a Field Programmable Gate Array (FPGA), a Programmable Logic Controller (PLC), an Application Specific Integrated Circuit (ASIC), and the like. In some embodiments, the photovoltaic side controller 114 and the photovoltaic side converter 106 may be assembled within a single housing, among other components. Similarly, the grid-side converter 108 and the grid-side controller 116 may be assembled within a single housing, among other components. Further, the photovoltaic side controller 114, the photovoltaic side converter 106, the grid side converter 108 and the grid side controller 116 may be assembled within a single housing, among other components.
In one embodiment, the photovoltaic-side controller 114 may be configured to provide the photovoltaic-side control signal 148 to the photovoltaic-side current transformer 106 based at least on a maximum power point reference signal 158 provided by the maximum power point tracking device 126. The maximum power point reference signal 158 is generated in a specific manner to ensure that the photovoltaic energy source 102 is always capable of providing maximum electrical power output under varying conditions, such as varying optical radiation intensity and temperature. The maximum power point reference signals 158 may include voltage, current, and/or power reference signals, and these reference signals may be updated by performing a particular maximum power point tracking algorithm, such as a perturbation observation method or a conductance delta method, for example. Also, a photovoltaic current feedback signal 122 obtained by one or more current sensors 120 and a photovoltaic voltage feedback signal 124 obtained by one or more voltage sensors 118 may be used when performing the maximum power point tracking algorithm.
Referring further to fig. 2, in one embodiment, the grid-side controller 116 may be configured to adjust or control various electrical characteristic parameters, including active power and reactive power, output by the grid-side converter 108 based on at least an active power command signal 144, a reactive power command signal 146, a voltage feedback signal 140 measured by one or more voltage sensors 136, and a current feedback signal 142 measured by one or more current sensors 138. The grid-side controller 116 may also be configured to regulate or control the dc voltage at the dc link 128 based on at least a dc bus voltage feedback signal 130 and a dc bus voltage command signal 132 measured by the voltage sensor 129.
Referring further to fig. 2, the network-side controller 116 may include a mixed dc voltage and output current control module 117, and the mixed dc voltage and output current control module 117 may be implemented in hardware, software, or a combination of hardware and software. In one embodiment, the hybrid dc voltage and output current control module 117 is configured to generate the grid-side control signal 150 based at least on the current feedback signal 142 and one or more current threshold signals or values 119 to avoid the output current of the grid-side converter 108 exceeding a maximum current threshold.
In some embodiments, the hybrid dc voltage and output current control module 117 is further configured to adjust the grid-side control signal 150 based on the dc voltage feedback signal 130 and the dc voltage command signal 132 such that the dc voltage of the dc link 128 is regulated to a particular value or range of values.
Fig. 3 is a generalized block diagram of one embodiment of a hybrid dc voltage and output current control block 200. In some embodiments, the hybrid dc voltage and output current control module 200 is designed based on a voltage source control architecture. By "voltage source control architecture" is meant that in one particular control system embodiment, the primary control variables include the magnitude and phase angle of the ac side voltage.
In the embodiment shown in fig. 3, the hybrid dc voltage and output current control module 200 includes a phase angle regulator 210, a voltage magnitude regulator 220, a current limiter 230, a dc voltage regulator 250, and a signal generation unit 240.
In one embodiment, the phase angle adjuster 210 receives an active power command signal 212 and an active power feedback signal 214 and generates a phase angle command signal 216 based on at least the active power command signal 212 and the active power feedback signal 214. The active power command signal 212 represents the active power desired to be output by the grid-side converter 108, which may be given by the grid operator, and the active power feedback signal 214 represents the actual active power output by the grid-side converter 108. The active power feedback signal 214 may be obtained by multiplying the net side current feedback signal 142 and the net side voltage feedback signal 152 as shown in fig. 2. The phase angle command signal 216 generated by the phase angle adjuster 210 may have some variations in particular embodiments. For example, in one embodiment, the phase angle command signal 216 represents a phase shift or difference between the ac side voltage of the grid side converter 108 and the grid voltage or a voltage taken at a point proximate to the grid 18. In another embodiment, the phase angle command signal 216 may also represent the desired phase of the ac voltage of the grid-side converter 108. The phase of the ac voltage of the grid-side converter 108 can be obtained by adding the phase of the grid-side voltage to the phase difference. The ac-side voltage of the grid-side converter 108 as described herein may be the ac voltage at the output of the grid-side converter 108. In an alternative embodiment, the ac-side voltage of the grid-side converter 108 may also be an internal voltage taking into account the internal impedance of the grid-side converter 108. Further, in some embodiments, the ac-side voltage of the grid-side converter 108 may also be a voltage measured from the output of the grid-side converter 108 along any point on the transmission line.
In one embodiment, the voltage magnitude regulator 250 receives the reactive power command signal 222 and the reactive power feedback signal 224 and generates the voltage magnitude command signal 226 based on the received signals. The reactive power command signal 222 represents the reactive power desired to be output by the grid-side converter 108, which may be given by the grid operator, while the reactive power feedback signal 224 represents the measured actual delivered reactive power output by the grid-side converter 108. The reactive power feedback signal 224 may be obtained by multiplying the net side current feedback signal 142 and the net side voltage feedback signal 140. The voltage magnitude command signal 226 represents the magnitude of the ac voltage that is expected to be available at the grid side converter 108, wherein the ac voltage of the grid side converter 108 may be the ac voltage at the output of the grid side converter 108. Alternatively, the ac voltage of the grid-side converter 108 may also be an internal ac voltage taking into account the grid-side converter internal or virtual impedance.
In one embodiment, the current limiter 230 may specifically include a phase current limiter configured to provide a phase angle limit signal to the phase angle command signal 216 generated by the phase angle adjuster 210. In one embodiment, the phase current limiter 230 is further configured to provide a voltage magnitude limiting signal to the voltage magnitude command signal 226 generated by the voltage magnitude regulator 220. The phase angle limit signal and the voltage magnitude limit signal are generated based on a variety of signals or values, such as a current feedback signal 262, a voltage feedback signal 264, a current threshold 266, and an impedance value 268.
In the embodiment shown in fig. 3, the dc voltage regulator 250 is configured to generate a phase angle limit adjustment signal 256 based on at least a dc voltage command signal 252 and a dc voltage feedback signal 254. The phase angle limit adjustment signal 256 reflects the degree to which the actual dc voltage of the dc link 128 deviates from the dc voltage command signal 252. In one embodiment, the phase angle limit adjustment signal 256 is used by the current limiter 230 to adjust the phase angle limit signal. The inventor of the present invention has found through research that, when the dc voltage of the dc link 128 deviates, the active power output from the grid-side converter 120 may be increased or decreased by adjusting the phase angle limit signal according to the phase angle limit adjustment signal 256, and the control of the dc voltage of the dc link 128 may be achieved by increasing or decreasing the output active power. More specifically, when an over-voltage condition occurs in the dc link 128, adjusting the phase angle limit signal using the phase angle limit adjustment signal 256 in a particular manner may result in an increase in the active power output by the grid-side converter 108, thereby further causing the dc voltage of the dc link 128 to drop after one or more control cycles, which may eliminate or mitigate the over-voltage condition of the dc link 128. Similarly, when an under-voltage condition occurs in the dc link 128, adjusting the phase angle limit signal using the phase angle limit adjustment signal 256 in a particular manner may result in a reduction in the active power output by the grid-side converter 108, thereby further causing the dc voltage of the dc link 128 to rise after one or more control cycles, which may eliminate or mitigate the under-voltage condition of the dc link 128.
Referring further to fig. 3, the adjusted phase angle command signal 232 and the adjusted voltage magnitude command signal 234 generated by the current limiter 230 are used by a signal generation unit 240 to generate a grid-side control signal 242, and the grid-side control signal 242 is applied to the grid-side converter 108 to control its operation in a particular manner. Upon encountering a transient event, the current drawn by the grid-side converter 108 may be controlled indirectly by adjusting the ac voltage associated with the grid-side converter. Therefore, by implementing the hybrid dc voltage and output current control module 200 disclosed herein, the power conversion system 100 can be enabled to successfully ride through a transient event, such as a grid transient event, to avoid the semiconductor devices in the grid-side converter 144 from being damaged due to an over-current problem caused by the transient event. In addition, by implementing the hybrid dc voltage and output current control module 200, the dc voltage of the dc link 128 can be effectively controlled.
Fig. 4 is a detailed block diagram of one embodiment of a hybrid dc voltage and output current control module 410. As shown in fig. 4, the hybrid dc voltage and output current control module 410 includes a first summing element 412, a second summing element 422, a dynamic current threshold calculation unit 428, a voltage difference calculation unit 438, a phase angle limit signal calculation unit 444, a voltage magnitude limit signal calculation unit 452, a third summing element 462, a voltage regulator 472, a phase angle limit signal adjustment unit 476, and a voltage command signal limitation unit 484.
In one embodiment, the first summing element 412 is configured to subtract a maximum current threshold signal 414 from a current feedback signal negative sequence component 416 and generate a maximum current threshold signal positive sequence component 418, wherein the maximum current threshold signal 414 is predetermined based on a variety of factors, such as the ability of the grid-side converter 108 to handle current. The current feedback signal negative sequence component 416 may be decomposed from the current feedback signal 142 (shown in fig. 2) in a known manner.
In one embodiment, the second summing element 422 is coupled to the first summing element 412 to receive the maximum current threshold signal positive sequence component 418. The second summing element 422 is further configured to subtract the maximum current threshold signal positive sequence component 418 and the current feedback signal positive sequence component 424 to obtain a current offset signal 426. The current feedback signal positive sequence component 424 may also be decomposed from the current feedback signal 142 (shown in fig. 2) in a known manner.
In one embodiment, the dynamic current threshold calculation unit 428 may include a proportional-integral regulator or any other suitable regulator for generating a dynamic maximum current threshold signal 436 based on the current deviation signal 426. In some embodiments, the dynamic current threshold calculation unit 428 may be provided with an upper value 432 and a lower value 434 for clipping the dynamic maximum current threshold signal 436. In other embodiments, a separate clipping element may also be used to clip the dynamic maximum current threshold signal 436.
In some alternative embodiments, rather than filtering the negative sequence component of the current feedback signal from the total current feedback signal as shown in fig. 4, the dynamic power threshold calculation unit 428 may also directly vary the maximum current threshold signal 414 based on the negative sequence current signal 142.
In one embodiment, the voltage difference calculation unit 438 is configured to calculate a voltage difference signal 442 based on the dynamic maximum current threshold signal 436 and an impedance signal 437. In other embodiments, the voltage difference signal 442 may be calculated directly by using the preset maximum current threshold 414 and the impedance signal 437 instead of using the dynamic maximum current threshold signal 436. In one embodiment, as shown in fig. 7, when the voltage to be controlled is the converter internal voltage 716 (see fig. 7), the impedance signal 437 is the sum of the internal impedance 712 and the grid impedance 714. In other embodiments, the impedance signal 437 is the grid impedance 714 when the voltage to be controlled is the converter terminal voltage 718 (see fig. 7). In a particular embodiment, the voltage difference calculation unit 438 may be configured to calculate the voltage difference signal 442 using the following equation (1):
dV=Imax_d*[(Xbrg+Xvir)*j](l)，
where dV is the voltage difference signal 442, Imax_dIs a dynamic maximum current threshold signal 436, XbrgIs the grid impedance 714, XvirIs the internal impedance 712.
With continued reference to fig. 4, the voltage difference signal 442 is used by the phase angle limit signal calculation unit 444 to calculate the phase angle limit signals 446, 448 and/or by the voltage amplitude limit signal calculation unit 452 to calculate the voltage amplitude limit signals 454, 456. In a particular embodiment, the phase angle limit signal calculation unit 444 is configured to calculate the phase angle limit signals 446, 448 using the following equations (2) and (3):
θmin=-θmax(3),
wherein, thetamaxLimit the signal 446, theta for the maximum phase angleminThe signal 448 is limited for a minimum phase angle, dV represents the voltage difference signal generated by the virtual impedance 712 and the grid impedance 714 (shown in FIG. 7), and Vg_potcIs the voltage measured at the point of common connection adjacent to grid 110.
In one embodiment, the voltage magnitude limit signal calculation unit 452 is configured to calculate the voltage magnitude limit signal 454, 456 using the following equations (4), (5), and (6):
wherein, Vmag_maxLimiting the signal 454, V for maximum voltage amplitudemag_minLimit signal 456, θ for minimum voltage amplituderealFor actual phase angle signals, Vmag_diffIs the magnitude of the voltage difference across the virtual impedance 712 and the grid impedance 714.
The maximum and minimum phase angle limit signals 446, 448 generated by the phase angle limit signal calculation unit 444 are provided to the phase angle limit signal adjustment unit 476. The phase angle limit signal adjustment unit 476 is configured to adjust at least one of the maximum and minimum phase angle limit signals 446 based at least on the phase angle adjustment signal 474. In one embodiment, the phase angle adjustment signal 474 is generated by a voltage regulator 472 (e.g., a proportional-integral regulator) based on a dc voltage difference signal 468, where the dc voltage difference signal 468 is obtained by a third summing element 462 subtracting the dc voltage command signal 464 from a dc voltage feedback signal 466.
In one specific embodiment, the phase angle adjustment signal 474 has a negative value when the dc voltage command signal 464 is less than the dc voltage feedback signal 466, i.e., when the dc link 128 encounters an over-voltage condition. In this case, the phase angle limit signal adjustment unit 476 may generate the adjusted maximum and minimum phase angle command signals 478, 482 using the following equations (7) and (8):
θmax_new=θmax(7),
θmin_new=-θdc(8),
wherein, thetamax_newLimiting the signal 478, θ for the adjusted maximum phase anglemin_newLimiting the signal 482, θ for the adjusted minimum phase angledcIs the phase angle adjustment signal 474.
As shown in FIG. 8, the adjusted maximum phase angle limit signal θmax_newWith maximum phase angle limit signal theta before adjustmentmaxEqual and the phase angle value is positive, as shown by the angle formed by the two lines 802 and 804 in fig. 8. And the adjusted minimum phase angle limit signal thetamin_newIs larger than the minimum phase angle limit signal before adjustment and has a positive phase angle value, as shown by the angle formed by the two lines 802 and 806 in fig. 8. It will be appreciated that setting the minimum phase angle limit signal 482 to a positive value may cause the grid-side converter 108 to provide more active power output in the next control cycle or cycles. As the grid-side converter 108 provides more active power output, the dc voltage at the dc link 128 will gradually drop, and the overvoltage condition at the dc link 128 will gradually be relieved until eliminated.
In another specific embodiment, the phase angle adjustment signal 474 has a positive value when the dc voltage command signal 464 is greater than the dc voltage feedback signal 466, i.e., when the dc link 128 encounters an under-voltage condition. In this case, the phase angle limit signal adjustment unit 476 may generate the adjusted maximum and minimum phase angle command signals 478, 482 using the following equations (9) and (10):
θmax_new=-θdc(9),
θmin_new=θmin(10),
wherein, thetamax_newLimiting the signal 478, θ for the adjusted maximum phase anglemin_newLimiting the signal 482, θ for the adjusted minimum phase angledcIs the phase angle adjustment signal 474.
As shown in fig. 9, the adjusted maximum phase angle limit signal θmax_newNegative values, e.g. two lines in FIG. 9802, and 814. And the adjusted minimum phase angle limit signal thetamin_newEqual to the minimum phase angle limit signal before adjustment, as shown by the angle formed by the two lines 802 and 812 in fig. 9. It will be appreciated that setting the maximum phase angle limit signal 482 to a negative value may cause the grid-side converter 108 to provide less active power output in the next control cycle or cycles. Since the grid-side converter 108 provides less active power output, the dc voltage at the dc link 128 will gradually rise, and thus the undervoltage condition at the dc link 128 will gradually be alleviated until eliminated.
With continued reference to fig. 4, the adjusted maximum and minimum phase angle limit signals 478, 482 and maximum and minimum voltage amplitude limit signals 454, 456 are provided to the voltage command signal limit unit 484. In one embodiment, the voltage command signal limiting unit 484 is configured to limit the phase angle command signal 486 based on the adjusted maximum and minimum phase angle limit signals 478, 482 and provide a limited phase angle command signal 492.
The voltage command signal limiting unit 484 is further configured to limit the voltage magnitude command signal 488 in accordance with the maximum and minimum voltage magnitude limit signals 454, 456 and provide a limited voltage magnitude command signal 494. In some embodiments, the limited phase angle command signal 492 and the limited voltage magnitude command signal 494 may be used by the signal generation unit 240 shown in fig. 3 to generate the grid-side control signal 242 (e.g., a PWM control signal) to control the operation of the grid-side converter 108.
Referring next to fig. 10, a schematic diagram of various signal waveforms generated by the hybrid dc voltage and output current control module 410 of fig. 4 according to one embodiment is shown. Therein, graph 610 shows three-phase grid voltages 612, 614, 616 measured at a point of common connection adjacent to grid 110. Graph 620 shows a maximum phase angle limit signal 622, a minimum phase angle limit signal 624 and an actual phase angle 626 of the grid side converter output. Graph 630 shows the feedback dc voltage 632 at the dc link 128. As shown on these graphs, the first time point t0 represents that the grid has encountered a grid fault, e.g., a line fault, and the grid fault persists until the second time point t 1. Before the first point in time t0, the three-phase grid voltages 612, 614, 616 have substantially equal magnitudes and phase angles 120 degrees apart from each other, and the maximum phase angle limit signal 622 and the minimum phase angle limit signal 624 have opposite polarities, while the actual phase angle signal 622 falls between them and has a positive value to allow the grid-side converter to provide an active power output. After the grid fault at the first time point t0, the dc voltage of the dc link 128 gradually increases from approximately 600 volts to approximately 700 volts, i.e., the dc link 128 encounters an overvoltage condition. To address the overvoltage condition, the hybrid dc voltage and output current control module 410 is executed to adjust or increase the value of the minimum phase angle command signal 624 to have a positive value, thereby causing the grid-side converter 108 to provide more active power output. Thus, the dc voltage 632 of the dc link 128 gradually decreases from approximately 700 volts to approximately 600 volts. After the second time t1, the maximum and minimum phase angle limit signals 622, 624 are restored to normal values and have opposite polarities because the grid fault has disappeared. The three-phase grid voltages 612, 614, 616 are also substantially normal, with substantially equal magnitudes and phase angles 120 degrees apart.
Fig. 5 is a detailed block diagram of another embodiment of the hybrid dc voltage and output current control module 420. Similar to the mixed dc voltage and output current control module 410 shown in fig. 4, in some embodiments, the mixed dc voltage and output current control module 420 may also be implemented in hardware, software, or a combination of hardware and software, and may be executed by the converter controller 30 shown in fig. 1 or the grid-side controller 116 shown in fig. 2. One difference is that the voltage magnitude limit signal calculation unit 452 in the mixed dc voltage and output current control module 420 is configured to generate maximum and minimum voltage magnitude limit signals 454, 456 based on at least a voltage feedback signal 458. More specifically, in some embodiments, the power conversion systems 10, 100 shown in fig. 1 and 2 may be designed to provide zero reactive power output to the grid 110. To meet this reactive power requirement, in one embodiment, the voltage magnitude limit signal calculation unit 452 may be configured to generate the maximum and minimum voltage magnitude limit signals 454, 456 using equation (11) and equation (12) as follows:
Vmag_max_new=Vg_potc(11),
Vmag_min_new=Vg_potc(12),
wherein, Vmag_max_newLimiting the signal 454, V for the adjusted maximum voltage amplitudemag_min_newLimit signal 456, V for the adjusted minimum voltage amplitudeg_potcIs the voltage measured at the point of common connection adjacent to grid 110.
As can be seen from equations (11) and (12), the adjusted maximum and minimum voltage amplitude limit signals 454, 456 are set to have equal values. When the dc link 128 encounters an overvoltage condition, as shown in fig. 8, the vector end of the converter voltage 716 is forced to move along a circular segment 808, where one end of the circular segment 808 is the end point of the voltage vector 806 having the smallest phase angle and the other end is the end point of the voltage vector 804 having the largest phase angle. Similarly, when the dc link 128 encounters an undervoltage condition, as shown in fig. 9, the vector ends of the converter voltage 716 are forced to move along a circular segment 816, wherein one end of the circular segment 816 is the end point of the voltage vector 812 with the smallest phase angle and the other end is the end point of the voltage vector 814 with the largest phase angle.
With continued reference to FIG. 5, the maximum and minimum voltage magnitude limit signals 454, 456 are used by the voltage command signal limit unit 484 to limit the voltage magnitude command signal 488 and generate a limited voltage magnitude command signal 494. Likewise, the limited phase angle command signal 492 and the limited voltage magnitude command signal 494 may be used by the signal generating unit 240 shown in fig. 3 to generate the grid-side control signal 242 (e.g., a PWM control signal) to control the operation of the grid-side converter 108.
Fig. 6 is a detailed block diagram of another embodiment hybrid dc voltage and output current control module 430. As with the mixed dc voltage and output current control module 410 shown in fig. 4, in some embodiments, the mixed dc voltage and output current control module 430 may also be implemented in hardware, software, or a combination of hardware and software, and may be executed by the converter controller 30 shown in fig. 1 or the grid-side controller 116 shown in fig. 2. One difference is that the mixed dc voltage and output current control module 430 further comprises a voltage limiting unit 469, the voltage limiting unit 469 being connected between the third summing element 462 and the voltage regulator 472. The voltage limiting unit 469 is configured to compare the dc voltage deviation signal 468 provided by the third summing element 462 with a voltage threshold 467, where the voltage threshold 467 is a value indicative of the range of acceptable normal fluctuation of the dc voltage feedback signal 466 relative to the dc voltage command signal 464. More specifically, when the dc voltage offset signal 468 is less than the voltage threshold 467, the voltage limiting element 469 stops providing signals to the voltage regulator 472. The result in this situation is that the dc voltage regulation function is temporarily disabled in the hybrid dc voltage and output current control module 430. Once the voltage limiting unit 469 determines that the dc voltage deviation signal 468 is greater than the voltage threshold 467, the dc voltage regulation function is not restored, i.e., the voltage limiting unit 469 provides the dc voltage deviation signal 471 to the voltage regulator 472 and the voltage regulator 472 generates a phase angle adjustment signal 474 for adjusting the phase angle limit signals 446, 448.
Fig. 11 is a detailed block diagram of another embodiment hybrid dc voltage and output current control module 440. Similar to the hybrid dc voltage and output current control module 410 shown in fig. 4, in some embodiments, the hybrid dc voltage and output current control module 440 may also be implemented in hardware, software, or a combination of hardware and software, and may be executed by the converter controller 30 shown in fig. 1 or the grid-side controller 116 shown in fig. 2. One difference is that the hybrid dc voltage and output current control module 440 shown in fig. 11 further includes a q-axis current calculation unit 415 and a d-axis current calculation unit 419. The q-axis current calculation unit 415 is configured to receive a voltage magnitude command signal 413 and to generate a q-axis current command signal 417 based on the voltage magnitude command signal 413, wherein the voltage magnitude command signal 413 represents the reactive power that needs to be provided from the grid-side converter 108 to the grid 110. More specifically, in one embodiment, the q-axis current calculation unit 415 may calculate the q-axis current command signal 417 using the following equation (13):
Q=Vmag_potc*Iq(13),
where Q is the reactive power output desired to be provided, which may be set by a particular standard (e.g., e.on), Vmag_potcIs the magnitude of the voltage measured at the point of common connection adjacent to the grid 110, IqIs a q-axis current command value.
With continued reference to fig. 11, the d-axis current calculation unit 419 is connected to the q-axis current calculation unit 415 and the dynamic current threshold calculation unit 428. The d-axis current calculation unit 419 is configured to generate a d-axis current command signal 421 using the q-axis current command signal 417 provided by the q-axis current calculation unit 415 and a dynamic maximum current threshold signal 436 provided by the dynamic current threshold calculation unit 428. More specifically, the d-axis current calculation unit 419 generates the d-axis current command signal 421 using the following equation (14):
Id 2+Iq 2=Imax_d 2(14),
wherein, IdIs a d-axis current command signal, IqFor q-axis current command signal, Imax_dIs a dynamic maximum current threshold signal.
With continued reference to fig. 11, the voltage difference calculation unit 423 is configured to calculate a d-axis voltage difference signal 425 and a q-axis voltage difference signal 427 according to at least a d-axis current command signal 421 provided by the d-axis current calculation unit 419 and a q-axis current command signal 417 provided by the q-axis current calculation unit 415. More specifically, the voltage difference calculation unit 423 is configured to calculate the d-axis and q-axis voltage difference signals using the following equations (15) and (16):
dVd=Iq*[(Xbrg+Xvir)*j](15),
dV=Id*[(Xbrg+Xvir)*j](16),
wherein, dVdIs d-axis voltage difference signal 425, dVqIs a q-axis voltage difference signal 4427, IdIs a d-axis current command signal, IqFor q-axis current command signals, XbrgIs the grid impedance 714, XvirIs the transformer internal impedance 712.
In one embodiment, the phase angle limit signal calculation unit 444 is configured to generate a maximum phase angle limit signal 446 and a minimum phase angle limit signal 448 based at least on the d-axis voltage difference signal 425 and the q-axis voltage difference signal 427. In a more specific embodiment, the phase angle limit signal calculation unit 444 is configured to calculate the maximum and minimum phase angle limit signals 446, 448 using the following equations (17) and (18):
wherein, dVdIs the d-axis voltage difference signal 425 (shown in FIG. 12), dVqIs the q-axis voltage difference signal 427,
is the voltage measured at the point of common connection adjacent to grid 110.
In one embodiment, the voltage amplitude limit signal calculation unit 452 is configured to generate a maximum voltage amplitude limit signal 454 and a minimum voltage amplitude limit signal 456 based on at least the d-axis voltage offset signal 425, the q-axis voltage offset signal 427, and the feedback voltage signal 458. In a particular embodiment, the voltage magnitude limiting signal calculation unit 452 is configured to calculate the voltage magnitude limiting signal 454, 456 using equation (19), equation (20), and equation (21) as follows:
Vmag_max=Vg_ootc*cosθreal+Vmag_diff (20),
wherein, Vmag_maxLimiting the signal 454, V for maximum voltage amplitudemag_minLimit signal 456, θ for minimum voltage amplituderealFor actual phase angle signals, Vmag_diffIs the magnitude of the voltage difference across the virtual impedance 712 and the grid impedance 714.
With continued reference to fig. 11, the maximum phase angle limit signal 446 and the minimum phase angle limit signal 448 are adjusted by the phase angle limit signal adjustment unit 476 in accordance with the phase angle adjustment signal 474. For example, when the dc link 128 encounters an overvoltage condition, the phase angle limit signal adjustment unit 476 may adjust the maximum and minimum phase angle limit signals 446, 448 using equations (7) and (8) as described above in connection with fig. 4. Similarly, when the dc link 128 encounters an under-voltage condition, the phase angle limit signal adjustment unit 476 may adjust the maximum and minimum phase angle limit signals 446, 448 using equation (9) and equation (10) as described above in connection with fig. 4. The phase angle limit signal adjustment unit 476 provides an adjusted maximum phase angle limit signal 478 and an adjusted minimum phase angle limit signal 482 to a voltage command signal limit unit 484 and is used by the voltage command signal limit unit 484 to limit a phase angle command signal 486. Likewise, the limited phase angle command signal 492 and the limited voltage magnitude command signal 494 may be used by the signal generating unit 240 shown in fig. 3 to generate the grid-side control signal 242 (e.g., a PWM control signal) to control the operation of the grid-side converter 108.
FIG. 13 is a flow diagram illustrating one embodiment of a method 1300 of controlling operation of an energy conversion system. The method 1300 may be programmed as program instructions or computer software and stored on a storage medium readable by a computer or processor. When the program instructions are executed by a computer or processor, the steps shown in the flow chart can be realized. It is understood that the computer-readable medium may include volatile and nonvolatile, removable and non-removable media implemented in any method or technology. More specifically, the computer-readable medium includes, but is not limited to, RAM, ROM, EEPROM, flash memory or other technology memory, CD ROM, DVD, or other form of optical storage, magnetic cassettes, magnetic tape, magnetic disk, or other form of magnetic storage devices, and any other form of storage medium which can be used to store the desired information and which can be accessed by the instruction execution system.
In one embodiment, the method 1300 may be performed beginning with step 1302, where in performing step 1302, a current threshold associated with a converter device in a power conversion system (e.g., the power conversion systems 10, 100 of fig. 1 and 2) is obtained. In one embodiment, the current threshold value is predefined and represents the maximum permissible current value flowing out of the converter device.
In step 1304, the method 1300 generates a maximum phase angle limit signal and a minimum phase angle limit signal based on the current threshold. As described above, the maximum and minimum phase angle limit signals may be calculated using formula (1), formula (2), and formula (3). In some embodiments, the current threshold may have a fixed value. In other embodiments, the current threshold may also have a varying value. For example, the current threshold may have a dynamic current threshold that may be dynamically adjusted based on the current feedback signal, e.g., directly adjusted based on the negative sequence component signal. In other embodiments, the negative sequence component of the current feedback signal may be removed, and the positive sequence component of the current feedback signal may be used to generate the dynamic current threshold signal.
In some embodiments, the method 1300 may also generate a maximum voltage magnitude limit signal and a minimum voltage magnitude limit signal based on the current threshold in step 1304.
In some embodiments, the maximum and minimum phase angle limit signals and the maximum and minimum voltage magnitude limit signals may be generated based on the reactive power output that needs to be provided. For example, the maximum and minimum voltage magnitude limit signals may be set to have a value equal to the grid voltage when it is not necessary to provide reactive power to the grid.
In step 1306, the method 1300 generates a phase angle limit adjustment signal based on at least the DC voltage command signal and the actual feedback DC voltage signal. The phase angle limit adjustment signal has different values according to the voltage condition of the dc link 128. For example, in one embodiment, the phase angle limit adjustment signal may have a negative value when the dc link 128 encounters an over-voltage condition and a positive value when the dc link 128 encounters an under-voltage condition. It is noted that in some embodiments, step 1306 described herein may be performed before step 1304 or may be performed in synchronization with step 1304.
In step 1308, the method 1300 adjusts at least one of the maximum phase angle limit signal and the minimum phase angle limit signal using the phase angle limit adjustment signal. More specifically, the maximum and minimum phase angle limit signals may be adjusted using equations (7) and (8) as described above. In other embodiments, the maximum and minimum phase angle limit signals may be adjusted using equations (9) and (10) as described above in connection with fig. 4.
In step 1312, the method 1300 limits the phase angle command signal using at least one of the adjusted maximum phase angle limit signal and the minimum phase angle limit signal. In one embodiment, the phase angle command signal may be generated by the phase angle adjuster 210 described above in connection with fig. 3.
In step 1314, the method 1300 also limits the voltage magnitude command signal using at least one voltage magnitude limit signal. In one embodiment, the voltage magnitude regulator 220 described above in connection with FIG. 3 may be used to generate the voltage magnitude signal.
It is to be appreciated that the method 1300 described herein may also include other steps. For example, the method 1300 may also use the limited phase angle command signal and the limited voltage magnitude command signal to generate a grid-side control signal (e.g., a PWM control signal).
While the invention has been described in conjunction with specific embodiments thereof, it will be understood by those skilled in the art that many modifications and variations may be made to the invention. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit and scope of the invention.
Claims (8)
1. An energy conversion system, characterized by: the energy conversion system includes:
a direct current link;
a converter device connected to the dc link, the converter device configured to convert dc power provided by the dc link and provide ac power; and
a converter controller; the converter controller is connected to the dc link and the converter device, the converter controller including a hybrid dc voltage and output current control module for limiting an output current of the ac power provided by the converter device and regulating a dc voltage of the dc link when the energy conversion system encounters at least one transient event, wherein the hybrid dc voltage and output current control module includes:
a phase angle adjuster for generating a phase angle command signal;
a DC voltage regulator for generating a phase angle limit adjustment signal based on at least a DC voltage command signal and an actual DC voltage signal associated with the DC link; and
a current limiter; the current limiter is connected to the phase angle regulator and the dc voltage regulator, the current limiter being configured to generate at least one of a maximum phase angle limit signal and a minimum phase angle limit signal based on at least a current threshold value associated with the converter device, wherein the maximum phase angle limit signal and the minimum phase angle limit signal are used to limit the phase angle command signal, the current limiter being further configured to adjust at least one of the maximum phase angle limit signal and the minimum phase angle limit signal using the phase angle limit adjustment signal, wherein the current threshold value is dynamically adjusted according to a negative sequence current component of the output current, the current limiter comprising a dynamic current threshold value calculation unit that subtracts a positive sequence component of the output current from a positive sequence component of a maximum current threshold signal derived from a difference of the current threshold value and the negative sequence current component of the output current, the resulting dynamic maximum current threshold signal,
wherein the current limiter is configured to generate at least one of a maximum phase angle limit signal and a minimum phase angle limit signal based at least on the dynamic maximum current threshold signal.
2. The energy conversion system of claim 1, wherein: the current limiter is configured to increase the minimum phase angle limit signal using the phase angle limit adjustment signal when the actual dc voltage signal is determined to be greater than the dc voltage command signal.
3. The energy conversion system of claim 1, wherein: the current limiter is configured to reduce the maximum phase angle limit signal using the phase angle limit adjustment signal when the actual dc voltage signal is determined to be less than the dc voltage command signal.
4. The energy conversion system of claim 1, wherein: the hybrid direct current voltage and output current control module includes a voltage amplitude regulator for generating a voltage amplitude command signal; the current limiter is configured to generate at least one of a maximum voltage magnitude limit signal and a minimum voltage magnitude limit signal based at least on the current threshold, wherein the maximum voltage magnitude limit signal and the minimum voltage magnitude limit signal are used to limit the voltage magnitude command signal.
5. The energy conversion system of claim 4, wherein: the current limiter is configured to set the maximum voltage magnitude limit signal and the minimum voltage magnitude limit signal to be equal to a voltage value associated with the load to allow the converter device to provide substantially zero reactive power to the load.
6. A method for controlling operation of an energy conversion system comprising a dc link, a converter device and a converter controller, the method comprising: the method at least comprises the following steps:
generating at least one of a maximum phase angle limit signal and a minimum phase angle limit signal based at least on a current threshold associated with the converter device, wherein the current threshold is dynamically adjusted according to a negative sequence current component of an output current of the converter device;
generating a phase angle limit adjustment signal based on at least the DC voltage command signal and an actual DC voltage signal associated with the DC link;
adjusting at least one of the maximum phase angle limit signal and the minimum phase angle limit signal using the phase angle limit adjustment signal; and
limiting a phase angle command signal using at least one of the adjusted maximum and minimum phase angle limit signals, subtracting a positive sequence component of the output current from a maximum current threshold signal positive sequence component derived from a difference between the current threshold and a negative sequence current component of the output current to produce a dynamic maximum current threshold signal, and generating at least one of a maximum and minimum phase angle limit signal based at least on the dynamic maximum current threshold signal.
7. The method of claim 6, wherein: wherein, the method also comprises the following steps:
increasing the minimum phase angle limit signal using the phase angle limit adjustment signal when the actual DC voltage signal is determined to be greater than the DC voltage command signal; and
when the actual DC voltage signal is determined to be less than the DC voltage command signal, the maximum phase angle limit signal is decreased using the phase angle limit adjustment signal.
8. A photovoltaic energy conversion system, this photovoltaic energy conversion system is connected with the electric wire netting, its characterized in that: the photovoltaic energy conversion system includes:
a DC link configured to receive DC electrical energy from a photovoltaic energy source;
a photovoltaic converter connected to the DC link, the photovoltaic converter configured to convert DC electrical energy provided by the DC link and provide active power to the grid; and
a photovoltaic controller; the photovoltaic controller is connected with the direct current link and the photovoltaic converter, and is configured to:
generating a phase angle command signal to control a phase angle of an output voltage of the photovoltaic converter;
dynamically adjusting a current threshold according to a negative sequence current component of the output current of the photovoltaic converter;
generating a maximum phase angle limit signal and a minimum phase angle limit signal for limiting the output current provided by the photovoltaic converter in accordance with the dynamically adjusted current threshold; and
adjusting at least one of the maximum phase angle limit signal and the minimum phase angle limit signal based on at least a voltage difference between a dc voltage command signal and an actual dc voltage signal associated with the dc link to adjust a value of active power provided by the photovoltaic converter such that the dc voltage of the dc link is controlled, subtracting a positive sequence component of an output current from a positive sequence component of a maximum current threshold signal obtained by a difference between the current threshold and a negative sequence current component of the output current to generate a dynamic maximum current threshold signal, and generating at least one of the maximum phase angle limit signal and the minimum phase angle limit signal based on at least the dynamic maximum current threshold signal.
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| CN102904272A (en) * | 2011-07-29 | 2013-01-30 | 通用电气公司 | Energy conversion system with improved transient event ride through and method |
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