CN110212545B - Static var generator - Google Patents
Static var generator Download PDFInfo
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- CN110212545B CN110212545B CN201810166929.XA CN201810166929A CN110212545B CN 110212545 B CN110212545 B CN 110212545B CN 201810166929 A CN201810166929 A CN 201810166929A CN 110212545 B CN110212545 B CN 110212545B
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/01—Arrangements for reducing harmonics or ripples
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/18—Arrangements for adjusting, eliminating or compensating reactive power in networks
- H02J3/1821—Arrangements for adjusting, eliminating or compensating reactive power in networks using shunt compensators
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/26—Arrangements for eliminating or reducing asymmetry in polyphase networks
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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
- Y02E40/00—Technologies for an efficient electrical power generation, transmission or distribution
- Y02E40/30—Reactive power compensation
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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
- Y02E40/00—Technologies for an efficient electrical power generation, transmission or distribution
- Y02E40/40—Arrangements for reducing harmonics
-
- 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
- Y02E40/00—Technologies for an efficient electrical power generation, transmission or distribution
- Y02E40/50—Arrangements for eliminating or reducing asymmetry in polyphase networks
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- Power Engineering (AREA)
- Inverter Devices (AREA)
- Supply And Distribution Of Alternating Current (AREA)
Abstract
The invention provides a static var generator, comprising: the system comprises a main control board and at least one inverter module, wherein the at least one inverter module detects load current and output current of the static var generator; the main control board determines a direct current component of the load current and a direct current component of the output current according to the load current and the output current, and generates a driving pulse signal for controlling the at least one inverter module according to the direct current component of the load current, the direct current component of the output current and an alternating current component of the output current, so that the at least one inverter module outputs a current with a phase opposite to that of the load current. The static var generator can simultaneously compensate three-phase unbalance of reactive power and load current and low-order harmonic current, and can reduce fault maintenance time and improve the availability.
Description
Technical Field
The present invention relates generally to the field of wind power technology, and more particularly, to a static var generator.
Background
In the process of consumption of alternating current energy through an actual power load, because the power load is not a pure resistive load, reactive exchange between the load and a power grid end can be caused, and the effective capacity of the power grid is reduced; on the other hand, with the increase of nonlinear loads such as a load end fan and a water pump, the harmonic hazard of the power grid is increasingly severe. With the development of power electronic technology, Static Var Generators (SVG) are commonly used in low-voltage power distribution networks for reactive power compensation and harmonic compensation of the power grid. Conventional high power static var generators typically include discrete components of high power Insulated Gate Bipolar Transistors (IGBTs), capacitors, and busbars.
At present, when a certain power device in the static var generator breaks down, the whole static var generator is out of operation; moreover, the conventional static var generator is large in size, and during fault maintenance, maintenance can be performed only by dismantling a plurality of parts, connecting a busbar and a cable, so that time and labor are consumed, and great inconvenience is caused. In addition, the traditional large-capacity static var generator is basically one capacity and one specification, and the applicability is poor.
Disclosure of Invention
The invention aims to provide a static var generator which can simultaneously compensate three-phase unbalance of reactive power and load current and low-order harmonic current, reduce fault maintenance time and improve the availability.
The invention provides a static var generator, comprising: the system comprises a main control board and at least one inverter module, wherein the at least one inverter module detects load current and output current of the static var generator; the main control board determines a direct current component of the load current and a direct current component of the output current according to the load current and the output current, and generates a driving pulse signal for controlling the at least one inverter module according to the direct current component of the load current, the direct current component of the output current and an alternating current component of the output current, so that the at least one inverter module outputs a current with a phase opposite to that of the load current.
Optionally, the static var generator further comprises: the inverter module comprises a plurality of inverter modules connected in parallel, the alternating current side of each inverter module is connected in parallel to the alternating current bus, any one of the inverter modules detects the load current and the output current, and the sum of the output currents of the inverter modules is a current opposite to the phase of the load current.
Optionally, when the inverter module fails, the failed inverter module generates a fault signal, and the master control board deactivates the failed inverter module based on the fault signal.
Optionally, the main control board is configured to: performing a first proportional integration process based on the direct-current component of the load current and the direct-current component of the output current, and performing a repetitive control process based on a result of the first proportional integration process and the alternating-current component of the output current, thereby obtaining a modulation wave for generating a fundamental wave of a PWM waveform; performing a second proportional-integral process based on the direct-current component of the load current and the direct-current component of the output current, and performing a proportional-control process based on a result of the second proportional-integral process, thereby obtaining a modulation wave for generating a harmonic of a PWM waveform; generating a driving pulse signal for controlling the at least one inverter module based on a modulation wave for generating a fundamental wave of the PWM waveform and a modulation wave for generating a harmonic wave of the PWM waveform.
Optionally, the main control board is configured to: determining a direct current component of a positive sequence reactive component of the load current, a direct current component of a negative sequence active component of the load current, a direct current component of a negative sequence reactive component of the load current and a direct current component of a zero sequence current of the load; determining a direct current component of each harmonic current of the load current; determining a direct current component of the positive sequence reactive component of the output current, a direct current component of the negative sequence active component of the output current, a direct current component of the negative sequence reactive component of the output current and a direct current component of the output zero sequence current; determining a direct current component of each harmonic current of the output current; obtaining a modulation wave for generating fundamental wave of PWM waveform according to the direct current component of the load current positive sequence reactive component, the direct current component of the load current negative sequence active component, the direct current component of the load current negative sequence reactive component and the load zero sequence current, the direct current component of the output current positive sequence reactive component, the direct current component of the output current negative sequence active component, the direct current component of the output current negative sequence reactive component, the direct current component of the output zero sequence current and the alternating current component of the output current; obtaining a modulation wave for generating a harmonic wave of a PWM waveform according to the direct current component of each harmonic current of the load current and the direct current component of each harmonic current of the output current; and adding the modulation wave for generating the fundamental wave of the PWM waveform and the modulation wave for generating the harmonic wave of the PWM waveform to obtain a total modulation wave for generating the PWM waveform so as to generate a driving pulse signal for controlling the at least one inverter module.
Optionally, the main control board is further configured to: carrying out rotation coordinate transformation on each phase of alternating current components of the load current by using a rotation coordinate transformation factor to obtain a load current positive sequence reactive component, a load current negative sequence active component and a load current negative sequence reactive component; determining a three-phase average value of the load current as the load zero sequence current; obtaining a direct current component of the load current positive sequence reactive component, a direct current component of the load current negative sequence active component and a direct current component of the load current negative sequence reactive component by performing moving average filtering on the load current positive sequence reactive component, the load current negative sequence active component and the load current negative sequence reactive component; and multiplying the load zero-sequence current by the rotating coordinate conversion factor, performing moving average filtering on the multiplied result, and multiplying the moving average filtering result by 2 to obtain the direct-current component of the load zero-sequence current.
Optionally, the main control board is further configured to: and multiplying each phase alternating current component of the load current by an odd rotation coordinate conversion factor respectively, performing moving average filtering on the multiplied result, and multiplying the result of the moving average filtering by 2 to obtain each harmonic current direct current component of the load current.
Optionally, the main control board is further configured to: carrying out rotation coordinate transformation on each phase of alternating current components of the output current by using a rotation coordinate transformation factor to obtain an output current positive sequence reactive component, an output current negative sequence active component and an output current negative sequence reactive component; determining a three-phase average value of the output current as the output zero sequence current; obtaining a direct current component of the output current positive sequence reactive component, a direct current component of the output current negative sequence active component and a direct current component of the output current negative sequence reactive component by performing moving average filtering on the output current positive sequence reactive component, the output current negative sequence active component and the output current negative sequence reactive component; and multiplying the output zero sequence current by the rotating coordinate conversion factor, performing a moving average filter on the multiplied result, and multiplying the moving average filter result by 2 to obtain the direct current component of the output zero sequence current.
Optionally, the main control board is further configured to: and multiplying each phase alternating current component of the output current by an odd rotation coordinate conversion factor respectively, performing moving average filtering on the multiplied result, and multiplying the moving average filtering result by 2 to obtain each harmonic current direct current component of the output current.
Optionally, the main control board is further configured to: carrying out priority selection and amplitude limiting processing on the direct current component of the positive sequence reactive component of the load current, the direct current component of the negative sequence active component of the load current, the direct current component of the negative sequence reactive component of the load current and the direct current component of the zero sequence current of the load current to obtain the given positive sequence reactive component of the load current, the given negative sequence active component of the load current, the given negative sequence reactive component of the load current and the given direct current component of the zero sequence current of the load current; subtracting the direct current component of the positive sequence reactive component of the output current, the direct current component of the negative sequence active component of the output current, the direct current component of the negative sequence reactive component of the output current and the direct current component of the output zero sequence current from the positive sequence reactive component of the load current, the negative sequence active component of the load current and the direct current component of the load zero sequence current respectively, executing third proportional integral processing on the subtraction result, and performing positive sequence inverse transformation, negative sequence inverse transformation and zero sequence inverse transformation on the third proportional integral processing result; adding the result obtained by positive sequence inverse transformation, the result obtained by negative sequence inverse transformation and the result obtained by zero sequence inverse transformation respectively to obtain the given instantaneous value of the three-phase fundamental current; instantaneous values of the three-phase fundamental wave currents are given and subtracted from respective alternating-current components of the output current, and repetitive control processing is performed on the result of the subtraction to obtain a modulation wave of the fundamental wave for generating a PWM waveform.
Optionally, the main control board is further configured to: carrying out harmonic selection and amplitude limiting processing on the direct current component of each subharmonic current of the load current to obtain each subharmonic current given value of the load current; subtracting the direct current components of the harmonic currents of the output current from the harmonic current of the load current, executing fourth proportional integral processing on the subtraction result, multiplying the result of the fourth proportional integral processing by the odd rotation coordinate conversion factors, and adding the multiplication results to obtain the alternating current component setting of the harmonic currents; and multiplying the given alternating current quantity of each subharmonic current by an impedance coefficient respectively, and adding the multiplication results respectively to obtain a modulation wave for generating the harmonic wave of the PWM waveform.
Optionally, each of the at least one inverter module comprises: the inverter control board detects the load current, the output current and the fault signal and sends the load current, the output current and the fault signal to a main control board.
The static var generator can simultaneously compensate reactive power, three-phase unbalance of load current and low-order harmonic current, specifically, first proportional integral processing is executed on a direct current component of the load current and a direct current component of output current of the static var generator, and repeated control processing is executed based on a result of the first proportional integral processing and an alternating current component of the output current, so that fundamental wave control is carried out; harmonic control is also performed by performing a second proportional-integral process on the direct-current component of the load current and the direct-current component of the output current, and performing a proportional control process based on the result of the second proportional-integral process. In addition, the static var generator can also reduce the fault maintenance time, improve the availability ratio and is particularly suitable for a three-phase four-wire system.
Drawings
The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings, in which:
fig. 1 shows a schematic diagram of a static var generator according to an embodiment of the invention;
fig. 2 shows a schematic diagram of an inverter module according to an embodiment of the invention;
FIG. 3 illustrates a schematic diagram of a master control board determining reactive and unbalanced DC components of a load current according to an embodiment of the present invention;
FIG. 4 illustrates a schematic diagram of a master control board determining a harmonic DC component of a load current according to an embodiment of the present invention;
fig. 5 shows a schematic diagram of the main control board determining reactive and unbalanced dc components of the output current of the static var generator according to an embodiment of the invention;
fig. 6 shows a schematic diagram of the main control board determining the harmonic dc component of the output current of the static var generator according to an embodiment of the invention;
FIG. 7 is a schematic diagram illustrating a master control board determining a fundamental modulated wave according to an embodiment of the present invention;
fig. 8 shows a schematic diagram of a master control board determining a harmonic modulated wave according to an embodiment of the invention;
fig. 9 shows a waveform diagram of measured output current when compensating a single-phase unbalanced load of a static var generator according to an embodiment of the present invention.
Detailed Description
Various example embodiments will now be described more fully with reference to the accompanying drawings, in which some example embodiments are shown.
A static var generator according to an embodiment of the present invention is described below with reference to fig. 1 to 9.
Fig. 1 shows a schematic diagram of a static var generator according to an embodiment of the invention.
Referring to fig. 1, a static var generator according to an embodiment of the present invention includes: a main control board 100 and at least one inverter module 200.
Here, at least one inverter module 200 detects the load current and the output current of the static var generator.
The main control board 100 determines a direct current component of the load current and a direct current component of the output current according to the load current and the output current of the static var generator, and generates a driving pulse signal for controlling at least one inverter module 200 according to the direct current component of the load current, the direct current component of the output current and an alternating current component of the output current, so that the at least one inverter module 200 outputs a current having a phase opposite to that of the load current.
Preferably, at least one inverter module 200 is connected to the main control board 100 through a fiber optic network. The inverter module 200 transmits the load current and the output current of the static var generator to the main control board 100.
Here, the at least one inverter module 200 includes a plurality of inverter modules 200 connected in parallel.
In one example, a maximum of 8 inverter modules 200 are supported to be connected in parallel due to a limitation of an operation speed of the microprocessor. Specifically, 8 optical fiber interfaces on the main control board 100 are respectively connected to the optical fiber interfaces of each inverter module 200 to perform parallel control, and the 8 optical fiber interfaces can synchronize the driving pulse signals for controlling the inverter modules 200 through corresponding control on the main control board 100, so as to reduce the circulating current between the inverter modules 200.
Further, when any one inverter module 200 fails, the failed inverter module 200 generates a fault signal, the main control board 100 deactivates the failed inverter module 200 (i.e., removes the failed inverter module) based on the fault signal, and other inverter modules that do not fail can continue to operate normally, thereby implementing redundancy control, effectively improving the redundancy of the system, and reducing the loss caused by the fault.
When a plurality of inverter modules 200 are applied in parallel, the compensated reactive, unbalanced and harmonic currents can be freely distributed. As an example, assuming that the number of inverter modules is 3, the first inverter module may only compensate for reactive power, the second inverter module may only compensate for imbalance, the third inverter module may only compensate for harmonics, or other free combinations, which significantly increases the flexibility of the system; when an inverter module is switched in (activated) or switched out (deactivated), the current allocated by the inverter module that is switched out can be allocated to other inverter modules that are normally used within the current range allowed by the inverter module.
Preferably, the inverter module 200 is a three-phase two-level inverter module, and the weight of the inverter module 200 is less than 30 kg. The size and the weight of the inverter module 200 are small, the wiring is simple and flexible, when fault maintenance is carried out, only the inverter module with the fault needs to be replaced, the installation and the maintenance operation are convenient, the maintenance time is obviously reduced, and the availability of the static var generator is increased.
In addition, the static var generator further comprises an alternating current busbar 300.
Here, the ac side of each inverter module 200 is connected in parallel to the ac busbar 300, respectively.
Specifically, any one of the inverter modules 200 detects a load current and an output current of the static var generator, and the sum of the output currents of the inverter modules 200 is a current in phase opposite to the load current.
Here, when the static var generator needs to have an extended capacity, the ac sides of the plurality of inverter modules 200 need only be connected directly in parallel to the ac busbar.
It should be understood that, since the dc side of the static var generator does not need to be connected to a load, a dc bus bar (not shown) does not need to be connected out and suspended.
The inverter module of the embodiment of the present invention is described in detail below with reference to fig. 2.
Fig. 2 shows a schematic view of an inverter module according to an embodiment of the invention.
Referring to fig. 2, an inverter module 200 according to an embodiment of the present invention includes: an inverter control board 201 and a plurality of groups of power devices 202.
Here, a plurality of groups of power devices 202 are connected to the ac busbar 300.
Preferably, the plurality of sets of power devices 202 includes four sets of power devices. Here, the plurality of groups of power devices 202 form a two-level four-leg inverter topology, which can be used to compensate for unbalanced current and harmonics in a three-phase four-wire system.
Preferably, each group of power devices 202 includes a driving board 203 and an IGBT cell 204.
The inverter control board 201 detects a load current, an output current of the static var generator, and a fault signal of the static var generator, and transmits the load current, the output current, and the fault signal to the main control board 100 through optical fiber communication. Meanwhile, the inversion control board 201 receives the driving digital pulse signal transmitted by the main control board 100 through optical fiber communication, thereby completing the inversion control of the inverter module.
In addition, the inverter module 200 further includes a heat pipe radiator (not shown), a thin film support capacitor 205, an IGBT high frequency absorption capacitor (not shown), and a 24V controlled heat dissipation fan (not shown).
The following describes in detail the process of reactive, current imbalance and harmonic compensation of the static var generator according to the embodiment of the present invention with reference to fig. 3 to 9.
Specifically, the main control board 100 is configured to: performing a first proportional integration process based on the direct-current component of the load current and the direct-current component of the output current, and performing a Repetitive Control (RC) process based on a result of the first proportional integration process and the alternating-current component of the output current, thereby obtaining a modulation wave for generating a fundamental wave of a PWM waveform; performing a second proportional-integral process based on the direct-current component of the load current and the direct-current component of the output current, and performing a proportional-control process based on a result of the second proportional-integral process, thereby obtaining a modulation wave for generating a harmonic of a PWM waveform; generating a driving pulse signal for controlling the at least one inverter module based on a modulation wave for generating a fundamental wave of the PWM waveform and a modulation wave for generating a harmonic wave of the PWM waveform.
Fig. 3 shows a schematic diagram of a main control board determining reactive and unbalanced dc components of a load current according to an embodiment of the invention.
Referring to fig. 3, the main control board 100 is configured to: and determining a direct current component L _ ILqP of the positive sequence reactive component of the load current, a direct current component L _ ILdN of the negative sequence active component of the load current, a direct current component L _ ILqN of the negative sequence reactive component of the load current and direct current components L _ IL0X and L _ IL0Y of the zero sequence current iL0 of the load current.
Specifically, the main control board 100 is configured to: performing rotation coordinate transformation on the alternating-current components iLa, iLb and iLc of the load current by using a rotation coordinate transformation factor to obtain a load current positive sequence reactive component iLqp, a load current negative sequence active component iLdn and a load current negative sequence reactive component iLqn; determining the three-phase average value of the load current as the load zero sequence current iL 0; obtaining a direct current component L _ iLqp of the load current positive sequence reactive component, a direct current component L _ iLdn of the load current negative sequence active component and a direct current component L _ iLqn of the load current negative sequence reactive component by performing Moving Averaging Filtering (MAF) on the load current positive sequence reactive component iLqp, the load current negative sequence active component iLdn and the load current negative sequence reactive component iLqn; multiplying the load zero-sequence current iL0 by a rotating coordinate transformation factor, performing moving average filtering on the multiplication result, and multiplying the moving average filtering result by 2 to obtain direct-current components L _ IL0X and L _ IL0Y of the load zero-sequence current iL 0.
The rotating coordinate transformation factor is the sine value sin (wt) of the phase of the grid voltage and the cosine value cos (wt) of the phase of the grid voltage, which are obtained by the grid voltage Ua, Ub, Uc detected by any one of the inverter modules 200 through the phase-locked loop PLL.
Fig. 4 shows a schematic diagram of a main control board determining a harmonic dc component of a load current according to an embodiment of the invention.
Referring to fig. 4, the main control board 100 is configured to: determining direct current components L _ ILakX, L _ ILakY, L _ ILbkX, L _ ILbkY, L _ ILckX and L _ ILckY of each harmonic current of the load current.
Specifically, the main control board 100 is configured to: and multiplying the alternating current components iLa, iLb and iLc of the load current by the odd-order rotation coordinate conversion factor respectively, performing moving average filtering on the multiplied result, and multiplying the moving average filtering result by 2 to obtain direct current components L _ ILakX, L _ ILakY, L _ ILbkX, L _ ILbkY, L _ ILckX and L _ ILckY of the harmonic current of each order of the load current.
Here, the odd-rotation coordinate conversion factor is an odd-times sine value sin (kgt) of the phase and an odd-times cosine value cos (kgt) (k ═ 3, 5, 7, 11, 13) of the phase.
Fig. 5 shows a schematic diagram of the main control board determining the reactive and unbalanced dc components of the output current of the static var generator according to an embodiment of the invention.
Referring to fig. 5, the main control board 100 is configured to: determining a direct current component L _ IFqP of an output current positive sequence reactive component, a direct current component L _ IFdN of an output current negative sequence active component, a direct current component L _ IFqN of an output current negative sequence reactive component and direct current components L _ IF0X and L _ IF0Y of an output zero sequence current iF0 of the static var generator.
Specifically, the main control board 100 is configured to: performing rotation coordinate transformation on the alternating-current components iFa, iFb and iFc of the output current by using a rotation coordinate transformation factor to obtain an output current positive sequence reactive component iFqp, an output current negative sequence active component iFdn and an output current negative sequence reactive component iFqn; determining the three-phase average value of the output current as the output zero sequence current iF 0; obtaining a direct current component L _ IFqP of the positive sequence reactive component of the output current, a direct current component L _ IFdN of the negative sequence reactive component of the output current and a direct current component L _ IFqN of the negative sequence reactive component of the output current by performing sliding average filtering on the positive sequence reactive component iFqp of the output current, the negative sequence active component iFdn of the output current and the negative sequence reactive component iFqn of the output current; multiplying the output zero sequence current iF0 by the rotating coordinate conversion factor, performing a moving average filter on the multiplication result, and multiplying the moving average filter result by 2 to obtain direct current components L _ IF0X and L _ IF0Y of the output zero sequence current iF 0.
Fig. 6 shows a schematic diagram of the main control board determining the harmonic dc component of the output current of the static var generator according to an embodiment of the invention.
Referring to fig. 6, the main control board 100 is configured to: determining direct current components L _ IFakX, L _ IFakY, L _ IFbkX, L _ IFbkY, L _ IFckX and L _ IFckY of each harmonic current of the output current of the static var generator.
Specifically, the main control board 100 is configured to: the respective ac components iFa, iFb, and iFc of the output current are multiplied by odd-order rotation coordinate conversion factors, respectively, the multiplication results are subjected to moving average filtering, and the moving average filtering results are multiplied by 2, thereby obtaining dc components L _ IFakX, L _ IFakY, L _ IFbkX, L _ IFbkY, L _ IFckX, and L _ IFckY of the respective harmonic currents of the output current.
Fig. 7 shows a schematic diagram of the determination of the fundamental modulated wave by the main control board according to the embodiment of the invention, and fig. 7 also shows a reactive and unbalanced current loop control schematic block diagram.
Referring to fig. 7, the main control board 100 is configured to: the modulation wave PWM _ ifout, PWM _ IFbout, PWM _ IFcout for generating fundamental wave of PWM waveform is obtained from the direct current component L _ ILqP of the load current positive sequence reactive component, the direct current component L _ ILdN of the load current negative sequence active component, the direct current component L _ iL0X, L _ iL0Y of the load current negative sequence active component, the direct current component L _ IFqP of the output current positive sequence reactive component of the static var generator, the direct current component L _ IFdN of the output current negative sequence active component of the static var generator, the direct current component L _ IFdN of the output current negative sequence reactive component of the static var generator, the direct current component L _ iF0X of the output current iF0 of the static var generator, and the alternating current component of the output current of the static var generator.
Specifically, the main control board 100 is configured to: carrying out priority selection and amplitude limiting treatment on a direct current component L _ ILqP of a load current positive sequence reactive component, a direct current component L _ ILdN of a load current negative sequence active component, a direct current component L _ ILqN of a load current negative sequence reactive component and direct current components L _ IL0X and L _ IL0Y of a load zero sequence current iL0 (the priority selection can select reactive priority, unbalanced priority or simultaneous compensation, and an amplitude limiting link is used for limiting the effective value of the total compensation current not to exceed the maximum current allowed by a module), so as to obtain a positive sequence reactive component given Iqref of the load current, a negative sequence active component given IdNRef of the load current, a negative sequence reactive component given IqNRef of the load current and direct current components given I0XRef and I0YRef of the load zero sequence current; subtracting the positive sequence reactive component of the load current given IqRef, the negative sequence active component of the load current given IdNRef, the negative sequence reactive component of the load current given IqNRef and the direct current component of the load zero sequence current given I0XRef and I0YRef from the direct current component L _ IFqP of the positive sequence reactive component of the output current, the direct current component L _ IFdN of the negative sequence active component of the output current, the direct current component L _ IFqN of the negative sequence reactive component of the output current and the direct current component L _ IF0X and L _ IF0Y of the positive sequence reactive component of the output zero sequence current iF0 respectively, performing third Proportional Integral (PI) processing on the subtraction result, and performing positive sequence transformation, negative sequence inverse transformation and zero sequence inverse transformation on the result of the third proportional integral processing; adding the result obtained by positive sequence inverse transformation, the result obtained by negative sequence inverse transformation and the result obtained by zero sequence inverse transformation respectively to obtain the instantaneous values of the three-phase fundamental current, namely iaRef, ibRef and icRef; instantaneous values of the three-phase fundamental wave currents, i ref, are subtracted from the respective ac components iFa, iFb, i fc of the output current, and repetitive control processing is performed on the subtraction result to obtain modulated waves PWM _ IFaout, PWM _ IFbout, PWM _ IFcout of the fundamental wave for generating the PWM waveform.
In this embodiment, the repetitive control can suppress harmonics generated by the actual output current and eliminate steady-state errors of the current, and can correct the current output according to the historical deviation. In the embodiment, a method of advancing by 4 beats is adopted, the deviation is corrected by advancing by 4 beats according to the deviation of the current in the previous power grid period, the influence of a dead zone in IGBT driving pulse and power grid voltage harmonic on output current harmonic is effectively reduced, and the steady-state error of current tracking is greatly eliminated.
Here, the main control board 100 is configured to: subtracting the direct current component L _ IFqP of the positive sequence reactive component given IqRef of the load current and the positive sequence reactive component of the output current, executing third proportional integral processing on a subtraction result, and performing positive sequence inverse transformation on the result of the third proportional integral processing to obtain ipref a, ipref b and ipref c; subtracting the given IdNRef of the negative sequence active component of the load current from the direct current component L _ IFdN of the negative sequence active component of the output current, and performing third proportional integral processing on the subtraction result to obtain a first result; subtracting the given IqNRef of the negative sequence reactive component of the load current from the direct current component L _ IFqN of the negative sequence reactive component of the output current, performing third proportional integral processing on the subtraction result to obtain a second result, and performing negative sequence inverse transformation on the first result and the second result to obtain inRefa, inRefb and inRefc; subtracting the direct-current components I0XRef and I0YRef of the load zero-sequence current from the direct-current components L _ IF0X and L _ IF0Y of the output zero-sequence current iF0 respectively, performing third proportional integral processing on the two subtracted results, and performing zero-sequence inverse transformation on the third proportional integral processing result to obtain I0 Ref; then adding a result ipref a obtained by positive sequence inverse transformation, a result inRefa obtained by negative sequence inverse transformation and a result i0Ref obtained by zero sequence inverse transformation to obtain an instantaneous value given iaRef of the three-phase fundamental current, adding a result ipref b obtained by positive sequence inverse transformation, a result inRefb obtained by negative sequence inverse transformation and a result i0Ref obtained by zero sequence inverse transformation to obtain an instantaneous value given ibRef of the three-phase fundamental current, and adding a result ipref obtained by positive sequence inverse transformation, a result inRefc obtained by negative sequence inverse transformation and a result i0Ref obtained by zero sequence inverse transformation to obtain an instantaneous value given icRef of the three-phase fundamental current.
Fig. 8 shows a schematic diagram of the main control board determining the harmonic modulation wave according to the embodiment of the present invention, and also shows a harmonic current loop control principle block diagram.
Referring to fig. 8, the main control board 100 is configured to: and obtaining modulation waves Pwm _ IHaout, Pwm _ IHbout and Pwm _ IHcout for generating the harmonic waves of the PWM waveform according to the direct current components L _ ILakX, L _ ILakY, L _ ILbkX, L _ ILbkY, L _ ILckX and L _ ILckY of the subharmonic currents of the load current and the direct current components L _ IFakX, L _ IFakY, L _ IFbkX, L _ IFbkY, L _ IFckX and L _ IFckY of the subharmonic currents of the output current of the static var generator.
Specifically, the main control board 100 is configured to: carrying out harmonic selection and amplitude limiting treatment on direct-current components L _ ILakX, L _ ILakY, L _ ILbkX, L _ ILbkY, L _ ILckX and L _ ILckY of each subharmonic current of the load current to obtain each subharmonic current given IakXRef, IakYRef, IbkXRef, IbkYRef, IckXRef and IckYRef of the load current; subtracting the respective harmonic currents given by the load current iakXRef, iakYeref, IbkXRef, IbkYeref, IkXRef and IkYeref from the direct current components L _ IFakX, L _ IFakY, L _ IFbkX, L _ IFbkY, L _ IFckX and L _ IFckY (k is 3, 5, 7, 11 and 13) of the respective harmonic currents of the output current, performing fourth proportional integration on the subtraction result, multiplying the fourth proportional integration result by the odd-rotation coordinate conversion factors sin (kgt) and cos (kgt), and adding the multiplication results to obtain the alternating current quantities given by the respective harmonic currents iha Ref, ihbRef and ihcRef; and multiplying the given ihaRef, ihbRef and ihcRef of the alternating current quantity of each harmonic current by an impedance coefficient Ck respectively, and adding the multiplication results respectively to obtain modulation waves Pwm _ IHaout, Pwm _ IHbout and Pwm _ IHcout for generating the harmonic waves of the PWM waveform.
Here, each harmonic corresponds to a different impedance coefficient Ck.
Furthermore, the main control board 100 is further configured to: and adding the modulation waves Pwm _ IFaout, Pwm _ IFbout and Pwm _ IFcout used for generating the fundamental wave of the PWM waveform and the modulation waves Pwm _ IHaout, Pwm _ IHbout and Pwm _ IHcout used for generating the harmonic wave of the PWM waveform to obtain a total modulation wave used for generating the PWM waveform so as to generate a driving pulse signal used for controlling the at least one inverter module.
Fig. 9 shows a waveform diagram of measured output current when compensating a single-phase unbalanced load of a static var generator according to an embodiment of the present invention.
Referring to fig. 9, A, B, C, N respectively represent each phase current output by the static var generator, and as can be seen from fig. 9, only a single-phase 180A unbalanced current is output between the a phase and the N phase to compensate for the unbalanced current of the load, thereby ensuring the balance of the grid current and effectively verifying the superiority of the three-phase four-leg topology structure of the present invention.
Because the internal control of the reactive, unbalanced and harmonic currents is controlled by the PI regulator, the PI regulator can only track the direct current without static error, and therefore the reactive, unbalanced and harmonic components of the load current need to be converted into direct current to be controlled. The embodiment of the invention adopts a Moving Average Filter (MAF) method to detect reactive power, unbalanced and harmonic current, the moving average filter is realized by continuously taking N sampling values as a circular queue, the length of the queue is fixed to be N, new data is sampled to be put into the tail of the queue each time, data at the head of the original queue is thrown away (first-in first-out principle), and the data output by the filter each time is always the arithmetic average value of the N data in the current queue. The method only needs to calculate the current sampling point each time, and the calculation amount is small. And only single-phase current is converted during harmonic control, and the method is more suitable for controlling the single-phase harmonic current by the three-phase four-wire static var generator, so that the method is simpler and more flexible in harmonic selection and amplitude limiting functions.
Further, the static var generator of the embodiment of the present invention is capable of simultaneously performing compensation of reactive power, three-phase imbalance of load current, and low-order harmonic current, specifically performing fundamental wave control by performing first proportional integration processing on a direct-current component of the load current and a direct-current component of output current of the static var generator, and performing repetitive control processing based on a result of the first proportional integration processing and an alternating-current component of the output current; harmonic control is also performed by performing a second proportional-integral process on the direct-current component of the load current and the direct-current component of the output current, and performing a proportional control process based on the result of the second proportional-integral process. In addition, the static var generator can also reduce the fault maintenance time, improve the availability ratio and is particularly suitable for a three-phase four-wire system.
While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims.
Claims (11)
1. A static var generator, comprising: a main control board and at least one inverter module,
wherein the at least one inverter module detects a load current and an output current of the static var generator;
the main control board determines a direct current component of the load current and a direct current component of the output current according to the load current and the output current, and generates a driving pulse signal for controlling the at least one inverter module according to the direct current component of the load current, the direct current component of the output current and an alternating current component of the output current so as to enable the at least one inverter module to output a current with a phase opposite to that of the load current;
the master control board is configured to:
performing a first proportional integration process based on the direct-current component of the load current and the direct-current component of the output current, and performing a repetitive control process based on a result of the first proportional integration process and the alternating-current component of the output current, thereby obtaining a modulation wave for generating a fundamental wave of a PWM waveform;
performing a second proportional-integral process based on the direct-current component of the load current and the direct-current component of the output current, and performing a proportional-control process based on a result of the second proportional-integral process, thereby obtaining a modulation wave for generating a harmonic of a PWM waveform;
generating a driving pulse signal for controlling the at least one inverter module based on a modulation wave for generating a fundamental wave of the PWM waveform and a modulation wave for generating a harmonic wave of the PWM waveform.
2. The static var generator according to claim 1, further comprising: an alternating current bus bar is arranged on the bus bar,
wherein the at least one inverter module comprises a plurality of inverter modules connected in parallel,
the alternating current side of each inverter module is respectively connected to the alternating current busbar in parallel,
wherein any one of the plurality of inverter modules detects the load current and the output current, and a sum of the output currents of the plurality of inverter modules is a current in phase opposite to the load current.
3. The static var generator according to claim 2, wherein when an inverter module fails, the failed inverter module generates a fault signal, the master control board deactivating the failed inverter module based on the fault signal.
4. The static var generator according to claim 1, wherein the master control board is configured to:
determining a direct current component of a positive sequence reactive component of the load current, a direct current component of a negative sequence active component of the load current, a direct current component of a negative sequence reactive component of the load current and a direct current component of a zero sequence current of the load;
determining a direct current component of each harmonic current of the load current;
determining a direct current component of the positive sequence reactive component of the output current, a direct current component of the negative sequence active component of the output current, a direct current component of the negative sequence reactive component of the output current and a direct current component of the output zero sequence current;
determining a direct current component of each harmonic current of the output current;
obtaining a modulation wave for generating fundamental wave of PWM waveform according to the direct current component of the load current positive sequence reactive component, the direct current component of the load current negative sequence active component, the direct current component of the load current negative sequence reactive component and the load zero sequence current, the direct current component of the output current positive sequence reactive component, the direct current component of the output current negative sequence active component, the direct current component of the output current negative sequence reactive component, the direct current component of the output zero sequence current and the alternating current component of the output current;
obtaining a modulation wave for generating a harmonic wave of a PWM waveform according to the direct current component of each harmonic current of the load current and the direct current component of each harmonic current of the output current;
and adding the modulation wave for generating the fundamental wave of the PWM waveform and the modulation wave for generating the harmonic wave of the PWM waveform to obtain a total modulation wave for generating the PWM waveform so as to generate a driving pulse signal for controlling the at least one inverter module.
5. The static var generator according to claim 4, wherein the master control board is further configured to:
carrying out rotation coordinate transformation on each phase of alternating current components of the load current by using a rotation coordinate transformation factor to obtain a load current positive sequence reactive component, a load current negative sequence active component and a load current negative sequence reactive component;
determining a three-phase average value of the load current as the load zero sequence current;
obtaining a direct current component of the load current positive sequence reactive component, a direct current component of the load current negative sequence active component and a direct current component of the load current negative sequence reactive component by performing moving average filtering on the load current positive sequence reactive component, the load current negative sequence active component and the load current negative sequence reactive component;
and multiplying the load zero-sequence current by the rotating coordinate conversion factor, performing moving average filtering on the multiplied result, and multiplying the moving average filtering result by 2 to obtain the direct-current component of the load zero-sequence current.
6. The static var generator according to claim 4, wherein the master control board is further configured to:
and multiplying each phase alternating current component of the load current by an odd rotation coordinate conversion factor respectively, performing moving average filtering on the multiplied result, and multiplying the result of the moving average filtering by 2 to obtain each harmonic current direct current component of the load current.
7. The static var generator according to claim 4, wherein the master control board is further configured to:
carrying out rotation coordinate transformation on each phase of alternating current components of the output current by using a rotation coordinate transformation factor to obtain an output current positive sequence reactive component, an output current negative sequence active component and an output current negative sequence reactive component;
determining a three-phase average value of the output current as the output zero sequence current;
obtaining a direct current component of the output current positive sequence reactive component, a direct current component of the output current negative sequence active component and a direct current component of the output current negative sequence reactive component by performing moving average filtering on the output current positive sequence reactive component, the output current negative sequence active component and the output current negative sequence reactive component;
and multiplying the output zero sequence current by the rotating coordinate conversion factor, performing a moving average filter on the multiplied result, and multiplying the moving average filter result by 2 to obtain the direct current component of the output zero sequence current.
8. The static var generator according to claim 4, wherein the master control board is further configured to:
and multiplying each phase alternating current component of the output current by an odd rotation coordinate conversion factor respectively, performing moving average filtering on the multiplied result, and multiplying the moving average filtering result by 2 to obtain each harmonic current direct current component of the output current.
9. The static var generator according to claim 4, wherein the master control board is further configured to:
carrying out priority selection and amplitude limiting processing on the direct current component of the positive sequence reactive component of the load current, the direct current component of the negative sequence active component of the load current, the direct current component of the negative sequence reactive component of the load current and the direct current component of the zero sequence current of the load current to obtain the positive sequence reactive component given of the load current, the negative sequence active component given of the load current, the negative sequence reactive component given of the load current and the direct current component given of the zero sequence current of the load;
subtracting the direct current component of the positive sequence reactive component of the output current, the direct current component of the negative sequence active component of the output current, the direct current component of the negative sequence reactive component of the output current and the direct current component of the output zero sequence current from the positive sequence reactive component of the load current, the negative sequence active component of the load current and the direct current component of the load zero sequence current respectively, executing third proportional integral processing on the subtraction result, and performing positive sequence inverse transformation, negative sequence inverse transformation and zero sequence inverse transformation on the third proportional integral processing result;
adding the result obtained by positive sequence inverse transformation, the result obtained by negative sequence inverse transformation and the result obtained by zero sequence inverse transformation respectively to obtain the given instantaneous value of the three-phase fundamental current;
instantaneous values of the three-phase fundamental wave currents are given and subtracted from respective alternating-current components of the output current, and repetitive control processing is performed on the result of the subtraction to obtain a modulation wave of the fundamental wave for generating a PWM waveform.
10. The static var generator according to claim 4, wherein the master control board is further configured to:
carrying out harmonic selection and amplitude limiting processing on the direct current component of each subharmonic current of the load current to obtain each subharmonic current given value of the load current;
subtracting the direct current components of the harmonic currents of the output current from the harmonic current of the load current, executing fourth proportional integral processing on the subtraction result, multiplying the result of the fourth proportional integral processing by the odd rotation coordinate conversion factors, and adding the multiplication results to obtain the alternating current component setting of the harmonic currents;
and multiplying the given alternating current of each subharmonic current by an impedance coefficient Ck respectively, and adding the multiplication results respectively to obtain a modulation wave for generating the harmonic wave of the PWM waveform.
11. The static var generator according to claim 2, wherein each of the at least one inverter module comprises: an inversion control board and a plurality of groups of power devices,
wherein the plurality of groups of power devices are connected to the AC busbar,
the inverter control board detects the load current, the output current and the fault signal and sends the load current, the output current and the fault signal to the main control board.
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