CN115513969B - Low-capacitance cascaded H-bridge STATCOM and switch modulation and control method thereof - Google Patents
Low-capacitance cascaded H-bridge STATCOM and switch modulation and control method thereof Download PDFInfo
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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
- H02J3/1835—Arrangements for adjusting, eliminating or compensating reactive power in networks using shunt compensators with stepless control
- H02J3/1842—Arrangements for adjusting, eliminating or compensating reactive power in networks using shunt compensators with stepless control wherein at least one reactive element is actively controlled by a bridge converter, e.g. active filters
- H02J3/1857—Arrangements for adjusting, eliminating or compensating reactive power in networks using shunt compensators with stepless control wherein at least one reactive element is actively controlled by a bridge converter, e.g. active filters wherein such bridge converter is a multilevel converter
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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
- 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
- H02M1/00—Details of apparatus for conversion
- H02M1/0067—Converter structures employing plural converter units, other than for parallel operation of the units on a single load
- H02M1/007—Plural converter units in cascade
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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
- H02M1/00—Details of apparatus for conversion
- H02M1/12—Arrangements for reducing harmonics from ac input or output
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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
- H02M5/00—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases
- H02M5/02—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases without intermediate conversion into dc
- H02M5/04—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases without intermediate conversion into dc by static converters
- H02M5/22—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases without intermediate conversion into dc by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
- H02M5/275—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases without intermediate conversion into dc by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
- H02M5/293—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases without intermediate conversion into dc by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only
- H02M5/2932—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases without intermediate conversion into dc by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only with automatic control of output voltage, current or power
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- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
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Abstract
The invention discloses a low-capacitance value cascade H-bridge STATCOM and a switch modulation and control method thereof, wherein a small capacitor is adopted for a submodule capacitor of the low-capacitance value cascade H-bridge STATCOM, and a parallel voltage-sharing loop between adjacent H-bridge submodules is constructed by controlling parallel control switches to realize voltage balance of the submodule capacitor; the parallel voltage-sharing state only occurs when the adjacent submodules are simultaneously in the bypass state, and the normal operation of the cascade H bridge cannot be influenced. The low-capacitance cascaded H-bridge STATCOM direct-current side capacitor voltage ripple is large, the sub-module capacitor voltage balance control difficulty is greatly improved, the complexity of a control system is greatly simplified by adopting a hardware balance mode, and meanwhile, a large number of sub-module capacitor voltage sensors and corresponding controllers are removed. A control method of a low-tolerance value cascade H-bridge STATCOM based on hardware balance is designed based on the proposed hardware balance mode.
Description
Technical Field
The invention relates to the technical field of dynamic reactive power compensation of a power system, in particular to a low-capacitance value cascade H-bridge STATCOM and a switch modulation and control method thereof.
Background
The static reactive compensator provides or absorbs reactive power to the power grid by controlling the amplitude and the phase of the output voltage of the static reactive compensator, and is the most effective tool for improving the quality of electric energy. The cascaded H-bridge topological structure has the characteristics of high reliability, high voltage, large capacity, low current harmonic, easiness in expansion and the like, and is a mainstream trend of being applied to STATCOM (static synchronous compensator) devices.
The cascade H-bridge STATCOM improves the application voltage level through cascade H-bridge sub-modules, and because the capacitors of the DC side sub-modules are mutually independent, the situation of unbalanced capacitor voltage exists in practical application, and the problems of overvoltage and deterioration of output waveforms of a switching device are easily caused. Particularly in the application occasion of the low-capacitance cascaded H-bridge STATCOM, the sub-modules adopt small capacitors, so that the fluctuation amplitude of the capacitor voltage is increased, and the difficulty in balance control of the capacitor voltage is increased.
In the existing low-capacitance value cascade H-bridge STATCOM control, the balance control of sub-module capacitor voltage adopts an independent voltage control method. The independent voltage control method needs to sample the capacitor voltage of each submodule of the cascaded H bridge and modify the modulation wave of the submodule through an independent PI controller, and along with the increase of the number of the submodules of the cascaded H bridge, the calculation pressure of the controller and the load of a communication system are increased sharply. In addition, the tracking effect of the PI controller is limited under operating conditions of large capacitor voltage fluctuations. Therefore, a better sub-module capacitance-voltage balancing scheme needs to be researched for the low-capacitance cascaded H-bridge STATCOM.
Disclosure of Invention
In view of the above problems, an object of the present invention is to provide a low-capacitance cascaded H-bridge STATCOM and a switching modulation and control method thereof, which use a small capacitor, have low cost and good capacity of controlling voltage balance of the capacitor, and can significantly reduce the complexity of a control system, and meanwhile, the designed control method can effectively avoid the problem that a double-frequency ripple is introduced into the control system, and has good output waveform. The technical scheme is as follows:
a cascaded H-bridge STATCOM with a low capacitance value comprises an alternating current power supplyv g Filter inductorL、NA deformable H-bridge sub-module andN-1 parallel control switches;
the deformed H-bridge submodule comprises four full-control type switching devices arranged on four bridge armsS i1 ~S i4 And a DC capacitor connected with the four bridge armsC i The middle point of the bridge arm of the H bridge sub-module is in a disconnected form, and the adjacent second bridge armiIs first and secondiThe +1 deformed H bridge submodule is connected to the same parallel control switchS iPC The two poles of the power amplifier are cascaded;
when the adjacent deformed H bridge sub-modules are in an upper bypass state or a lower bypass state at the same time, a capacitor parallel voltage-sharing loop of the adjacent sub-modules is constructed by controlling the parallel control switch and modifying the modulation signals of the H bridge, so that the capacitor voltage balance is realized.
Further, the direct current capacitor is a thin film capacitor with a low capacitance value.
A switch modulation method of a low-capacitance value cascade H-bridge STATCOM based on hardware balance is provided, for the secondiA first and a secondi+1 deformed H-bridge sub-modules and parallel control switch between themS iPC Two upper switches of the deformed H bridge submoduleS i1 、S i3 Defining an upper bypass state when the two lower switches are closed simultaneously, and changing the shape of the H bridge submodule into two lower switchesS i2 、S i4 And defining a lower bypass state when closed;
if and only ifiIs first and secondiWhen +1 deformed H bridge submodules are simultaneously in an upper bypass state, the control switches are connected in parallelS iPC Turn off and simultaneously open the lower switchS i4 AndS i(+1)2 (ii) a Or when it comes toiIs first and secondi+1 deformed H bridge submodules are in a lower bypass state at the same time and are connected with control switches in parallelS iPC Opening the upper switch at the same time as the disconnectionS i3 AndS i(+1)1 (ii) a First, theiIs first and secondi+1 D.C. capacitor of H bridge submodule moduleC i AndC i+1 constructing a closed loop path for parallel voltage sharing; the parallel control switch modulation signal is expressed as:
in the formula, a switching signal with a PWM subscript is a switching control signal generated by carrier phase-shift sinusoidal pulse width modulation (CPS-SPWM);
the switch modulation signal of the deformed H-bridge submodule is a phase-shifted carrier signal superposed parallel control switch modulation signal, and is expressed as:
a control method of a low-capacity value cascade H-bridge STATCOM based on hardware balance comprises the following steps:
step 1: determining total capacitor voltage of low-capacitance value cascade H-bridge STATCOM direct-current sidev dc (t) Expression (c):
wherein the content of the first and second substances,V ic_ is shown asiThe capacitance voltage of each deformed H bridge submodule;V peak the peak value of the total voltage of the direct current side;kis an equivalent capacitanceC eq And submodule DC side capacitorC dc The ratio of (a) to (b);V ab outputting a voltage effective value for the cascade H bridge; omega is angular frequency;I g the current is the effective value of the power grid current;mis the peak value of the total voltage on the DC sideV peak The adjustment coefficient of (a);
squaring equation (3) yields:
and 2, step: determining a control process comprising voltage outer loop control, current inner loop control and modulation signal per unit; voltage outer loop control:
step a1: reference value according to the effective value of the networkV g_ref Rated of combined settingThe work power being obtained as a reference value of the effective value of the reference currentI g_ref And a reference value for the effective value of the output voltage of the cascaded H-bridgeV ab_ref ；
Step a2: taking into account a given adjustment factormSubstituting formula (6) to obtain a square reference value controlled by the capacitor voltage and a compensation value of the capacitor voltage;
step a3: multiplying the measured value of the capacitor voltage of the submodule of the first deformed H bridge by the number of cascaded H bridgesNAs the measured value of the total capacitance voltage on the direct current side;
step a4: the active current amplitude reference value is output by making a difference value with a given reference value of a capacitor voltage control module through a ripple compensation and a frequency doubling filter module and a PI controller as the control of a voltage outer ringI d_ref ；
Controlling the current inner ring:
step b1: the voltage outer ring is controlled to output an active current amplitude reference valueI d_ref Sin output from phase locked loop PLLθMultiplying to obtain the reference value of the active currenti d_ref ；
Step b2: given reactive current amplitude reference valueI q_ref Cos with PLL outputθMultiplying the terms to obtain a reactive current reference valuei q_ref ；
Step b3: reference value of active currenti d_ref And a reactive current reference valuei q_ref Adding to obtain the output current reference value of the cascade H bridgei g_ref (ii) a Outputting current reference value of cascaded H bridgei g_ref And the measured current valuei g Differencing the output current by a PR controllerv PR ；
Per unit of the modulation signal:
step c1: controlling the current inner loop to output a signalv PR Adding a voltage feedforward termV ab_ref* sinθObtaining the modulation wave which is not unified by the cascaded H bridgev ref ；
Step c2: obtaining the capacitance voltage fluctuation according to the substituted parameter of formula (3)v dc (t) For modulated wavev ref Performing per-unit to obtain per-unit modulated signalv ref * 。
Compared with the prior art, the invention has the beneficial effects that:
according to the invention, the sub-module capacitor voltage balance is realized by adopting a hardware balance mode, a large number of sub-module voltage sensors and corresponding controllers are removed, the bandwidth requirement of a control system is greatly improved, and the control complexity of the sub-module capacitor voltage balance is also reduced; the proposed capacitor parallel voltage-sharing loop only occurs when the adjacent sub-modules are in a bypass state at the same time, and the normal operation of a main circuit cannot be influenced; in addition, the control system designed by the invention can effectively solve the problem that low-voltage subharmonics are introduced into the control system, and has a good control effect.
Drawings
Fig. 1 is a schematic circuit diagram of a low-capacitance cascaded H-bridge STATCOM based on hardware balance.
Fig. 2 (a) is a diagram showing the parallel control switch being kept in a conducting state under normal operation.
Fig. 2 (b) is a schematic diagram of the parallel control switch being turned off and the direct current capacitors of the adjacent sub-modules constructing a parallel voltage-sharing loop.
Fig. 3 is a schematic diagram of the parallel control switch modulation signal generation of the low-capacitance cascaded H-bridge STATCOM based on hardware balance.
Fig. 4 (a) is a diagram of an operation mode of the low-capacitance cascaded H-bridge STATCOM based on hardware balance, namely a capacitance mode.
Fig. 4 (b) is a diagram of an operation mode, i.e., an inductance mode, of the low-capacitance cascaded H-bridge STATCOM based on hardware balance.
FIG. 5 is a control block diagram of the low-tolerance cascaded H-bridge STATCOM based on hardware balance.
Fig. 6 is a voltage waveform diagram of the dc side capacitor of the low-capacitance cascaded H-bridge STATCOM based on hardware balancing according to the present invention.
Fig. 7 (a) shows the FFT analysis result of the output reactive current, i.e., the low harmonic analysis with the output reactive power of 100 VA.
Fig. 7 (b) shows the FFT analysis result of the output reactive current, i.e., the low harmonic analysis with output reactive power of 150 VA.
Detailed Description
The invention is described in further detail below with reference to the figures and specific embodiments.
As shown in FIG. 1, a low-capacitance cascaded H-bridge STATCOM based on hardware balance comprises an AC power supplyvg. Filter inductorL、NA plurality of deformed H-bridge sub-modules,N-1 parallel control switch. The deformed H-bridge submodule comprises: four full-control type switching devicesS i1 ~S i4 (i=1,2,···N) And the deformed H bridge sub-modules are in a mode of breaking the middle points of bridge arms of the traditional H bridge sub-modules, and the adjacent deformed H bridge sub-modules are cascaded by connecting two poles of the same parallel control switch.
The direct current capacitor with the low capacitance value is a film capacitor with a much smaller capacitance value than that of a traditional cascade H-bridge, the direct current side capacitor of the traditional cascade H-bridge STATCOM is in a millifarad level, and the direct current side capacitor can be reduced to a microfarad level. In practical application, a specific appropriate capacity value can be selected according to specific working condition analysis.
The working principle and the switch modulation method of the low-capacitance value cascade H-bridge STATCOM based on hardware balance are as follows:
to a first orderiIs first and secondi+1 submodules as an example for the secondiA parallel control switchS iPC And (4) carrying out analysis. In the case of normal operation of the machine,S iPC the on state is maintained as shown in fig. 2 (a). It can be seen thatS iPC When the low-capacitance cascaded H-bridge STATCOM based on hardware balance is kept to be conducted, the low-capacitance cascaded H-bridge STATCOM is equivalent to a traditional cascaded H-bridge STATCOM, and a sub-module switching signal can be obtained by carrier phase-shifted sinusoidal pulse width modulation (CPS-SPWM). Switching the submodule two timesS i1 、S i3 When closed, the sub-module is defined as an upper bypass state (OU state), and two sub-modules are arranged below the sub-moduleSwitch with a switch bodyS i2 、S i4 And the lower bypass state is defined as the lower bypass state (OL state) when the valve is closed.
If and only ifiSubmodule and secondi+1 sub-modules are in the OU state at the same time,S iPC switch on while offS i4 AndS i(+1)2 . Or, when it comes toiSubmodule and secondi+1 sub-modules are in the OL state at the same time,S iPC switch on while offS i3 AndS i(+1)1 . First, theiSubmodule and secondi+1 dc capacitor of sub-moduleC i AndC i+1 and (3) constructing a closed loop path for parallel voltage sharing, as shown in fig. 2 (b). The above process can be represented by fig. 3, and the parallel control switch signal can be represented as:
the switching signal with PWM subscript in the formula is a switching control signal generated by carrier phase-shifted sinusoidal pulse width modulation (CPS-SPWM).
As can be seen from the above formula, the control signal of the parallel control switch is directly obtained by an XOR logic operation from the existing switch signal, and the control method is simple. However, the switching signals on adjacent bridge arms need to be modified, and parallel control switching signals are added, which are expressed as:
the invention relates to a control method of a low-capacity value cascade H-bridge STATCOM based on hardware balance, which is specifically realized in the following way:
under the ideal condition, the grid voltage and the grid current are sine waveforms, and the output voltage of the cascade H-bridgev ab Ignoring high frequency components may be equivalent to a pure sinusoidal waveform. Under the low-capacitance value cascade H-bridge STATCOM operation mode, the power grid voltage,The grid current may be expressed as:
wherein the content of the first and second substances,V g 、I g the effective values of the voltage and the current of the power grid are represented,V ab representing the effective value of the output voltage of the cascaded H bridge. Whether the cascaded H-bridge operates in the capacitive mode or the inductive mode depends on the phase of the compensating reactive current with the grid voltage, as can be seen in fig. 4 (a) and 4 (b).
Based on the premise, the total capacitor voltage of the DC side of the cascade H-bridge STATCOM with the low capacitance value can be obtained by derivationv dc (t) Expression:
wherein the content of the first and second substances,V ic_ is shown asiCapacitance voltage, coefficient of submoduleskDefined as the ratio of the equivalent capacitance to the sub-module dc side capacitance:
wherein the content of the first and second substances,V peak the peak value of the total voltage on the direct current side is expressed as:
mis the peak voltageV peak The maximum value or the minimum value of the fluctuation of the total capacitance voltage can be adjusted according to the size of the rated power.
Squaring equation (4) yields:
by combining the formula (4) and the formula (7), the control method of the low-capacitance cascaded H-bridge STATCOM based on hardware balance is designed:
fig. 5 is a control block diagram of the low-capacitance cascaded H-bridge STATCOM based on hardware balance, which is divided into three control parts, namely voltage outer loop control, current inner loop control and modulation signal per unit. Reference value of voltage outer ring control part according to effective value of power gridV g_ref The reference value of the reference current effective value can be obtained by combining the set rated reactive powerI g_ref And reference value of low-capacitance value cascade H-bridge output voltage effective valueV ab_ref Then considering the given adjustment coefficientmThe square reference value controlled by the capacitor voltage and the compensation value of the capacitor voltage can be obtained by substituting the formula (7); multiplying the measured value of the capacitor voltage of the first submodule by the number of cascaded H-bridgesNThe measured value of the total capacitor voltage at the direct current side is used as the measured value, the difference value is made by the ripple compensation and the given reference value of the capacitor voltage control module, and the measured value is used as the control of the voltage outer loop through a frequency doubling filter module and a PI controller. Voltage outer ring control output active current amplitude reference valueI d_ref Sin output from phase locked loop PLLθMultiplying to obtain the reference value of the active currenti d_ref Given reference value of reactive current amplitudeI q_ref Cos with PLL outputθMultiplying the terms to obtain a reactive current reference valuei q_ref ，i d_ref Andi q_ref adding to obtain the output current reference value of the cascade H bridgei g_ref The difference value between the current value and the measured current value is obtained through a PR controller and the addition of a voltage feedforward term to obtain the unimodulated modulation wave of the cascade H bridgev ref (ii) a The capacitance voltage fluctuation can be obtained by substituting the parameter according to the formula (4)v dc (t) For modulated wavev ref Is subjected to per unit to obtainv ref * 。
By adopting the control method, the control system of the cascade H-bridge STATCOM with the low capacitance value introduced by the double frequency of the capacitor voltage can be effectively avoided.
According to the topological design and the control method thereof, matlab/Simulink is utilized to carry out simulation experiments, the feasibility of the invention is verified, and the simulation parameters are shown in Table 1:
TABLE 1 simulation parameters
Fig. 6 shows a low-capacitance value cascade H-bridge STATCOM direct-current side capacitor voltage waveform based on hardware balance, a power sudden change is set at 0.1s, output reactive power is suddenly changed from set rated reactive power 100VA to 150VA, and it can be seen that capacitor voltages of three sub-modules are in a balanced state, and a balance effect is good.
Fig. 7 (a) and 7 (b) show the FFT analysis result of the output current of the low-capacitance cascaded H-bridge STATCOM based on hardware balance of the present invention, wherein fig. 7 (a) is the low harmonic analysis with the output reactive power of 100 VA; fig. 7 (b) is a low harmonic analysis of the output reactive power of 150VA, and it can be seen that the output reactive current has low harmonic content, and the effectiveness of the control system is verified.
Claims (4)
1. A cascaded H-bridge STATCOM with a low capacitance value is characterized in that the topology of the cascaded H-bridge STATCOM comprises an alternating current power supplyv g Filter inductorL、NA deformable H-bridge sub-module andN-1 parallel control switches;
the deformed H-bridge submodule comprises four fully-controlled switching devices arranged on four bridge armsS i1 ~S i4 And a DC capacitor connected with the four bridge armsC i ，i=1,2,···N(ii) a The middle point of the bridge arm of the deformed H-bridge submodule is in a disconnected form, and the adjacent second bridge armiIs first and secondiThe +1 deformed H bridge submodule is connected to the same parallel control switchS iPC The two poles of the power amplifier are cascaded;
when the adjacent deformed H bridge sub-modules are in an upper bypass state or a lower bypass state at the same time, a parallel connection voltage-sharing loop of the capacitors of the adjacent sub-modules is constructed by controlling a parallel connection control switch and modifying a switch modulation signal of the H bridge, so that the voltage balance of the capacitors of the sub-modules is realized;
for the firstiIs first and secondi+1 deformed H-bridge sub-modules and parallel control switch between themS iPC Two upper switches of the deformed H bridge sub-moduleS i1 、S i3 Defining an upper bypass state when the two lower switches are closed simultaneously, and changing the shape of the H bridge submodule into two lower switchesS i2 、S i4 And defining a lower bypass state when closed;
if and only ifiIs first and secondiWhen +1 deformed H bridge submodules are simultaneously in an upper bypass state, the control switches are connected in parallelS iPC Turn off and simultaneously open the lower switchS i4 AndS i(+1)2 (ii) a Or when it comes toiIs first and secondiThe +1 deformed H bridge submodules are simultaneously in a lower bypass state and are connected with the control switch in parallelS iPC Turn off while opening the upper switchS i3 AndS i(+1)1 (ii) a First, theiA first and a secondi+1 D.C. capacitors of deformed H-bridge sub-modulesC i AndC i+1 and constructing a closed loop path to carry out parallel voltage sharing.
2. The cascaded H-bridge STATCOM of claim 1, wherein said dc capacitors are thin film capacitors of low capacitance.
3. The switch modulation method of the low-capacitance cascaded H-bridge STATCOM of claim 1, wherein for the secondiIs first and secondi+1 deformed H-bridge sub-modules and parallel control switch between themS iPC Two upper switches of the deformed H bridge submoduleS i1 、S i3 Defining an upper bypass state when the two lower switches are closed simultaneously, and changing the shape of the H bridge submodule into two lower switchesS i2 、S i4 And defining a lower bypass state when closed;
if and only ifiIs first and secondi+1 deformed H bridge sub-modules simultaneously on the upper sideWhen in road state, the switch is controlled in parallelS iPC Turn off and turn on the lower switch simultaneouslyS i4 AndS i(+1)2 (ii) a Or when it comes toiIs first and secondi+1 deformed H bridge submodules are in a lower bypass state at the same time and are connected with control switches in parallelS iPC Opening the upper switch at the same time as the disconnectionS i3 AndS i(+1)1 (ii) a First, theiIs first and secondi+1 D.C. capacitor of H bridge submodule moduleC i AndC i+1 constructing a closed loop path for parallel voltage sharing; the parallel control switch modulation signal is expressed as:
in the formula, a switching signal with a PWM subscript is a switching control signal generated by carrier phase-shifting sine pulse width modulation;
the switch modulation signal of the deformed H bridge submodule is a phase-shifted carrier signal superposed with a parallel control switch modulation signal and is expressed as follows:
4. the method for controlling the low-tolerance cascaded H-bridge STATCOM of claim 1, comprising the steps of:
step 1: determining total capacitor voltage of low-capacitance value cascade H-bridge STATCOM direct-current sidev dc (t) The expression of (c):
wherein, the first and the second end of the pipe are connected with each other,V ic_ is shown asiThe capacitance voltage of each deformed H bridge submodule;V peak the peak value of the total voltage of the direct current side;kis an equivalent capacitanceC eq And submodule DC side capacitorC dc The ratio of (A) to (B);V ab outputting a voltage effective value for the cascaded H bridge;ωis the angular frequency;I g the effective value of the current of the power grid is;mis the peak value of the total voltage on the DC sideV peak The adjustment coefficient of (a);
squaring equation (3) yields:
step 2: determining a control process comprising voltage outer loop control, current inner loop control and modulation signal per unit;
voltage outer loop control:
step a1: reference value according to the effective value of the networkV g_ref Obtaining a reference value of the reference current effective value by combining the set rated reactive powerI g_ref And a reference value for the effective value of the output voltage of the cascaded H-bridgeV ab_ref ；
Step a2: taking into account a given adjustment factormSubstituting formula (6) to obtain a square reference value controlled by the capacitor voltage and a compensation value of the capacitor voltage;
step a3: multiplying the measured value of the capacitor voltage of the submodule of the first deformed H bridge by the number of cascaded H bridgesNAs the measured value of the total capacitance voltage on the direct current side;
step a4: the active current amplitude reference value is output through the control of taking the difference value of the ripple compensation and the given reference value of the capacitor voltage control module and taking a frequency doubling filter module and a PI controller as a voltage outer ringI d_ref ；
Current inner loop control:
step b1: the voltage outer ring is controlled to output an active current amplitude reference valueI d_ref Sin output from phase locked loop PLLθMultiplying to obtain the reference value of the active currenti d_ref ；
Step b2: given reactive current amplitude reference valueI q_ref Cos with PLL outputθMultiplying the terms to obtain a reactive current reference valuei q_ref ；
And b3: reference value of active currenti d_ref And a reactive current reference valuei q_ref Adding to obtain the output current reference value of the cascade H bridgei g_ref (ii) a Outputting current reference value to cascaded H bridgei g_ref And the measured current valuei g Differencing the output current by a PR controllerv PR ；
Per unit of the modulation signal:
step c1: controlling the current inner loop to output a signalv PR Adding a voltage feedforward termV ab_ref* sinθObtaining the modulation wave which is not unified by the cascaded H bridgev ref ；
Step c2: obtaining the capacitance voltage fluctuation according to the substitution parameter of formula (3)v dc (t) For modulated wavev ref Performing per-unit to obtain a per-unit modulated signalv ref * 。
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| CN1933274B (en) * | 2006-09-30 | 2011-04-13 | 中国科学院电工研究所 | H bridge cascade active electric filter DC side capacitance-voltage equalizing controlling method |
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| CN101950969A (en) * | 2010-08-19 | 2011-01-19 | 中国科学院电工研究所 | H-bridge cascade type active power filter |
| CN102842858B (en) * | 2012-08-02 | 2015-09-09 | 广东电网公司东莞供电局 | Movable high-voltage high-capacity chain type STATCOM system container structure |
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