A network configuration control method of a dual-star STATCOM

Abstract

The application relates to the technical field of power electronic applications, in particular to a network construction control method of a double-star STATCOM, which comprises a positive sequence voltage phasor calculation link, a current reference instruction unit phasor calculation link, a reactive voltage control link, a bridge arm positive sequence reactive current instruction calculation link, a bridge arm negative sequence current instruction calculation link, a bridge arm current reference instruction limiting logic link and a modulation wave instruction calculation link; wherein the modulation wave generation link comprises a first converter valve DC side overvoltage prevention control link, a second converter valve DC side overvoltage prevention control link, a DC circulating current control link and a DC voltage balance control link; after the generated control voltage is superimposed with zero sequence voltage and grid voltage feedforward, a final modulation signal is formed; the output satisfies the demand of a negative sequence current amplitude, single converter valve overload is avoided, compensation accuracy is ensured, and stronger asymmetric load adaptability is achieved.

Description

Technical Field

[0001] This invention relates to the field of power electronics application technology, and in particular to a grid control method for a dual-star STATCOM. Background Technology

[0002] Grid-type STATCOMs are key devices in power systems used to improve power quality. Their core functions include reactive power compensation, flicker suppression, negative sequence compensation, and harmonic compensation. Negative sequence compensation aims to offset negative sequence current / voltage components in the system. When operating under three-phase unbalanced loads (such as electric arc furnaces and rolling mills), the system generates negative sequence components, leading to problems such as motor overheating and protection malfunctions. Single-star STATCOMs are limited by a single neutral point and converter valve capacity. The current regulation of the three-phase converter valves is coupled, meaning that adjusting the current in one phase affects the other two. Furthermore, when severe load asymmetry occurs, such as a sudden change in load on one phase, a single-star STATCOM may not be able to fully compensate for negative sequence due to saturation of the bridge arm current or modulation waveform in one phase of the converter valve. Therefore, single-star STATCOMs have significant limitations in compensating for asymmetric amplitude. However, when a delta-type STATCOM outputs negative-sequence current, the phase-to-phase DC voltage balancing control generates a zero-sequence current inside the converter valve, and its amplitude increases with the magnitude of the negative-sequence current. This wastes a significant amount of IGBT power switching device capacity, resulting in low cost-effectiveness. To address these issues, this invention proposes a dual-star network STATCOM control method. Summary of the Invention

[0003] This invention provides a network control method for a dual-star STATCOM. Through the coordinated control of two converter valves, the current of each phase can vary independently over a wider range, outputting a negative sequence current amplitude that meets the requirements, and has a higher negative sequence current output capability. Through the DC circulating current control of the two converter valves, the pressure of negative sequence compensation is distributed to other arms of the converter valve, avoiding overload of a single converter valve, ensuring compensation accuracy, and having a stronger ability to adapt to asymmetrical loads.

[0004] To achieve the above objectives, the present invention employs the following technical solution:

[0005] A network control method for a binary star STATCOM includes the following:

[0006] (1) Positive sequence voltage phasor calculation process: The positive and negative sequence component method based on the second-order generalized integrator is used to decompose the grid voltage, thereby obtaining the positive sequence voltage phasor and the negative sequence voltage phasor;

[0007] (2) Calculation of unit phasor of bridge arm current reference command: A second-order generalized integrator is used for the STATCOM current reference command to generate two-phase quadrature signals, thereby calculating the unit phasor of the current reference command;

[0008] (3) Reactive voltage control loop: The amplitude of the virtual internal electromotive force is obtained through the reactive voltage droop control loop, which increases the limit on the integral and output of the PI regulator respectively;

[0009] (4) Calculation of positive sequence reactive current command of bridge arm: The virtual internal electromotive force adopts the positive sequence phase of the grid voltage, and the positive sequence voltage of the grid is subtracted to obtain the positive sequence reactive current command of the bridge arm.

[0010] (5) Calculation of negative sequence reactive current command for bridge arm: Set the target value of negative sequence voltage to 0, subtract it from the negative sequence voltage of the grid, and obtain the negative sequence reactive current command for bridge arm.

[0011] (6) Bridge arm current reference command limiting logic: The input signal of the limiting logic is the total current reference command, and only the reactive current is dynamically limited. The active current is used for DC voltage equalization control and is not limited.

[0012] (7) Modulation wave command calculation stage: The difference between the current reference command and the current feedback of each phase is passed through a three-phase independent quasi-proportional resonant regulator to obtain the control voltage of the fundamental current of each phase;

[0013] The modulation wave command calculation includes a voltage feedforward unit phasor calculation stage, a zero-sequence voltage injection control stage, a current loop control stage, a first converter valve DC side overvoltage protection control stage, a second converter valve DC side overvoltage protection control stage, a DC circulating current control stage, and a DC voltage equalization control stage. The generated control voltage is fed forward and superimposed with the zero-sequence voltage and the grid voltage to form the final modulation signal.

[0014] Furthermore, the voltage feedforward unit phasor calculation stage uses a second-order generalized integrator for the single-phase grid voltage to generate two-phase quadrature signals, thereby calculating the unit phasor of the three-phase grid voltage, specifically including: Phase A grid voltage. Divide by the peak value of the phase voltage rating Then, the per-unit value is obtained. Through a second-order generalized integrator and Obtain in-phase signal and orthogonal signals Taking the square root of the sum of squares yields the peak values ​​of the two orthogonal signals. ,Will and Divide by peak value respectively The voltage of phase A of the power grid can then be obtained. Feedforward unit phasor , and phasors with a phase lag of 90° ,Will With proportionality coefficient Multiply to obtain the per-unit grid voltage feedforward phasor. Among them, the proportionality coefficient The value is 0.75–0.85. The calculation method for the unit phasor of the voltage feedforward in phases B and C is consistent with that in phase A; where k is the damping ratio. Let be the center frequency, and s be the complex frequency variable.

[0015] Furthermore, the bridge arm current reference command unit phasor calculation step specifically includes: bridge arm current reference command. Through a second-order generalized integrator and Obtain in-phase signal and orthogonal signals Taking the square root of the sum of squares yields the peak values ​​of the two orthogonal signals. , Divide by peak value This allows us to obtain the unit phasor of the A-phase bridge arm current reference command. The unit phasor calculation method for the reference command of the bridge arm currents of phases B and C is consistent with that of phase A.

[0016] Furthermore, the reactive power voltage control loop specifically includes: a voltage reference value. The settings are configured via the HMI (Host Management Interface) and are related to the effective value of the mains voltage. Subtracting them gives the voltage difference between the two, which is then divided by the slope. The corresponding reactive power reference value is obtained. And thus related to reactive power feedback value Subtract, and pass through a PI regulator The deviation of the virtual internal electromotive force is obtained. In this context, the limiting of the integral element in the PI controller is set independently, as is the final output limiting of the PI controller, and the deviation of the virtual internal electromotive force is also set independently. Compared with the virtual internal electromotive force reference value Adding them together, we obtain the virtual internal electromotive force reference value. ; Through the delay phase Generate a delayed virtual internal electromotive force reference value. Among them, the delay phase The time constant in The virtual internal electromotive force reference value is 40ms during the transient fault period. equal This refers to the value before the short-circuit fault occurred; at the same time, the integral value in the PI controller is cleared to prevent the error from accumulating and saturating.

[0017] Furthermore, the calculation step for the positive sequence reactive current command of the bridge arm specifically includes: a virtual internal electromotive force reference value. With the positive sequence voltage unit phasor respectively , , After multiplication, the phasor of the virtual internal electromotive force is obtained. The virtual internal electromotive force phasor is related to the positive sequence voltage component. , , After subtracting, multiply the voltage deviation by the reciprocal of the virtual impedance. Obtain the reference command value of the positive sequence reactive current of the bridge arm. , , ,in, For virtual inductance, This is a virtual resistor.

[0018] Furthermore, the bridge arm negative sequence reactive current command calculation step specifically includes: negative sequence voltage component. , , The difference from the target value of 0 is calculated by multiplying the negative sequence voltage deviation by the reciprocal of the virtual impedance. Obtain the negative sequence current reference command value , , Virtual internal electromotive force reference value Peak value of phase voltage rating After multiplying, we obtain the named value of the virtual internal electromotive force. The positive sequence voltage component and Taking the square root of the sum of squares yields the magnitude of the positive-sequence voltage. Peak value of phase voltage rating After multiplication, the nominal value of the positive sequence voltage is obtained. Furthermore, the named value of the virtual internal electromotive force reference value. After subtraction, the deviation value of the positive sequence voltage is obtained. The negative sequence voltage component and Taking the square root of the sum of squares yields the magnitude of the positive-sequence voltage. Peak value of phase voltage rating After multiplication, the nominal value of the negative sequence voltage is obtained. That is, the deviation value of the negative sequence voltage. , Divide by Since the virtual impedances are the same, they are all... Therefore, it is actually a positive sequence current. With negative sequence current The proportion of amplitude, i.e. Then, using a limiter, the result after limiting is recorded as a coefficient. ,Right now ; in coefficient Then, again with the coefficient Multiplication, coefficient The value range is determined according to the project's requirements for negative sequence current, with a default value of 0.5; thus, an adjustable negative sequence current distribution ratio coefficient is obtained, i.e. , and sequence current reference command value , , After multiplication, we obtain the positive sequence current with the magnitude of the product. The bridge arm negative sequence current reference command, which is a multiple of the reference current, is denoted as... .

[0019] Furthermore, the bridge arm current reference command limiting logic specifically includes: positive sequence current command. , , With negative sequence current reference command , , After summing, the total current reference command is obtained. , , The zero-sequence component is obtained by summing the three-phase current reference command values ​​and dividing by 3. ;

[0020] The zero-sequence component is subtracted from the bridge arm current reference command value respectively. To avoid disturbing the system, a reference command for the reactive current of the bridge arm containing a DC component is obtained. , , Then, through a second-order low-pass filter Then, the DC component is extracted. , , In order to isolate the DC component in the reactive current reference command value of the bridge arm, , , Subtracting the DC component from each component yields the unlimited reactive current reference command for the bridge arm. , , ;in, This refers to the filter's passband gain. The transfer function cutoff frequency; This is the filter damping coefficient;

[0021] Unlimited reactive current reference command for bridge arm , , Divide by the peak value of the bridge arm current rating Then, its per-unit value is obtained, and a Clark transformation is performed on the current command after the per-unit value to transform the three-phase stationary coordinate system into a two-phase stationary coordinate system, thus obtaining an orthogonal AC signal. and This process transforms the two-phase stationary coordinate system into a two-phase rotating orthogonal coordinate system, namely the dq coordinate system. The angle used in the coordinate transformation is the positive sequence voltage angle of phase A, resulting in orthogonal DC signals. and The amplitude of the signal can be obtained by taking the square root of the sum of squares. ;

[0022] Bridge arm active current reference command Each is obtained through a second-order generalized integrator. and Afterwards, an in-phase signal was obtained. and orthogonal signals The two are orthogonal; therefore, the two-phase stationary coordinate system is transformed into a two-phase rotating orthogonal coordinate system, namely the dq coordinate system. The angle used in the coordinate transformation process is the unit phasor of the three-phase voltage feedforward, resulting in two orthogonal DC signals. , Taking the square root of the sum of squares yields the peak value of the active current reference command for phase A bridge arm. The peak value calculation process for the active current reference command of phase B and phase C bridge arms is consistent with that of phase A.

[0023] By solving the quadratic equation for the reactive current limiting coefficient in real time, the reference command value is ensured to be within the range of the maximum design value of short-time overcurrent. Priority is given to ensuring that the active current command is not limited for DC voltage balance control, while the reactive current is limited, resulting in the final unified limiting coefficient for the three-phase bridge arm current. Take the dynamic limiting factor of the three-phase bridge arm current , , The minimum of the three.

[0024] Furthermore, in the zero-sequence voltage injection control loop, the zero-sequence voltage injection uses the average value of each phase DC voltage and the deviation from the average value of the total DC voltage. This deviation is used by a PI regulator to generate an adjustment quantity of functional quantity. The phase of the adjustment quantity uses the phasor of the current reference command for each phase, specifically including: the instantaneous value of the three-phase DC voltage at the first converter valve. , , Passing sequentially through the delayed sampling stage And points process The sliding filter, with a mean time constant of 10ms, is used to filter out the second harmonic component in the DC voltage. The filtered signals are as follows: , , The average of the three is denoted as ;

[0025] Instantaneous value of three-phase DC voltage at the second converter valve , , Passing sequentially through the delayed sampling stage And points process The sliding filter, with a mean time constant of 10ms, is used to filter out the second harmonic component in the DC voltage. The filtered signals are as follows: , , The average of the three is denoted as ;

[0026] Average DC voltage of the first converter valve Average DC voltage of the second converter valve The average value is denoted as the overall DC voltage mean of the first and second converter valves. Average A-phase voltage of the first converter valve Average A-phase voltage of the second converter valve The average value, compared with the overall DC voltage average of the first and second converter valves. The difference is denoted as the total difference between the A-phase DC voltages of the first and second converter valves. ; via PI controller Then, the output result is denoted as ;in, This is the proportionality coefficient. The integral coefficient is used; the control methods for phases B and C of the converter valve are consistent with those for phase A, resulting in... , ; and the three-phase current reference command unit vector of the first converter valve , , Multiplying them separately and then adding them together gives the injected zero-sequence voltage component. It is used to regulate the balance of active quantities between the three phases of the converter valve.

[0027] Furthermore, the current loop control circuit specifically includes: the overall average DC voltage of the first converter valve and the second converter valve. This reflects the overall level of the DC voltage of the first and second converter valves, and is subtracted from the target value of 1.0 before being passed through the PI regulator. The output of the regulator is the amplitude of the active quantity deviation, and the positive sequence voltage unit phasor. , , After multiplication, the three-phase active current reference command is obtained. , , Unlimited reactive current reference command for bridge arm , , With dynamic limiting coefficient After multiplication, the final bridge arm reactive current reference command is obtained. , , With reference command for active current of bridge arm , , Adding them together, we obtain the total bridge arm current reference command. , , This leads to three-phase current feedback. , , The difference is calculated, and the resulting current deviation is the sum of the three independent proportional resonant regulators. The input signal is the closed-loop output of each of the three-phase current loops. , , That is, the fundamental current controls the voltage; where, For proportional gain, This is the proportionality coefficient. For resonant gain, For the resonant bandwidth, For complex frequency variables, It is the resonant frequency.

[0028] Furthermore, the DC-side overvoltage protection control circuit of the first converter valve, the DC-side overvoltage protection control circuit of the second converter valve, the DC circulating current control circuit, and the DC voltage equalization control circuit specifically include:

[0029] The overvoltage protection control circuit on the DC side of the first converter valve: the average value of the A-phase DC voltage after filtering at the first converter valve. The average value of the DC voltage after filtering in phase B Average value of C-phase DC voltage after filtering Select the maximum value from the middle The difference between the voltage and the overvoltage threshold of 1.1 pu is calculated and then passed through a PI regulator. The output of the regulator is the active quantity adjustment. ,when When the voltage is less than 1.1 pu, the output of the PI regulator is 0, which is the lower limit of the amplitude limit; the overvoltage protection control method on the DC side of the second converter valve is the same as that of the first converter valve.

[0030] DC circulating current control circuit: Phase A current of the first converter valve Phase A current of the second converter valve Half of the vector sum is the DC circulating current between the two converter valves. The total difference between the A-phase DC voltage of the first converter valve and the second converter valve By subtracting the values, the deviation of the A-phase DC circulating current of the first and second converter valves is obtained. Through the proportional resonant regulator Then, the DC circulating current control voltage is obtained. The superposition is applied to the modulation wave; the control methods for phases B and C are consistent with those for phase A.

[0031] DC voltage equalization control stage: Average DC voltage of phase A at the first converter valve Average DC voltage of phase A of the second converter valve Difference, by proportion Multiply the coefficients and add them to the unit phasor of the positive sequence voltage of phase A. After multiplication, the AC component is obtained. This is superimposed on the modulation wave; the overall average DC voltage of the first converter valve. Average DC voltage of the second converter valve Difference, through proportion Multiply the coefficients and add them to the unit phasor of the positive sequence voltage of phase A. After multiplication, the AC component is obtained. It is superimposed on the modulated wave;

[0032] Ultimately, the A-phase modulation wave of the first converter valve includes functional quantity regulation. DC circulating current control voltage , exchange quantity , exchange quantity feedforward unit phasor of grid voltage Closed-loop output of the current loop Zero-sequence voltage component ;

[0033] The A-phase modulation wave of the second converter valve includes functional quantity adjustment. feedforward unit phasor of grid voltage Closed-loop output of the current loop Zero-sequence voltage component ;

[0034] The calculation method for the B and C phase modulation waves of the first and second converter valves is consistent with that of phase A.

[0035] Compared with the prior art, the beneficial effects of the present invention are:

[0036] 1) This invention designs a DC circulating current control method and a DC voltage equalization control method for a dual-star STATCOM. Under asymmetrical operating conditions, the pressure of negative sequence compensation is distributed to the bridge arms of other converter valves through the coordinated control of two converter valves, avoiding the saturation or overload of the modulation wave of a single converter valve, thereby ensuring the compensation accuracy and improving the adaptability of asymmetrical loads.

[0037] 2) This invention designs an overvoltage protection control method for the DC side of the converter valve of a dual-star STATCOM. Under severe asymmetrical operating conditions, by increasing the DC circulating current component, the voltage stress of the power unit is reduced, thereby allowing the current of each phase to change independently over a wider range, and outputting a negative sequence current amplitude that meets the requirements, thus having a higher negative sequence current output capability.

[0038] 3) This invention designs a zero-sequence voltage injection method for a dual-star STATCOM, which improves the equalization control effect of the DC voltage between phases of the converter valve under transient unbalanced conditions. Attached Figure Description

[0039] Figure 1 This is a connection topology diagram of the star-chain network type STATCOM system described in this invention;

[0040] Figure 2 This is a block diagram for calculating the positive and negative sequence components of the power grid voltage as described in this invention;

[0041] Figure 3 This is a block diagram for calculating the positive sequence voltage unit phasor as described in this invention;

[0042] Figure 4 This is a block diagram for calculating the voltage feedforward unit phasor as described in this invention;

[0043] Figure 5 This is a block diagram of the current reference command unit phasor calculation described in this invention;

[0044] Figure 6 This is a block diagram of the reactive voltage control and bridge arm positive and negative sequence reactive current reference command calculation described in this invention;

[0045] Figure 7 This is a block diagram of the bridge arm current reference command limiting logic described in this invention;

[0046] Figure 8 This is a block diagram of the zero-sequence voltage injection control method described in this invention;

[0047] Figure 9This is a block diagram of the current loop control circuit described in this invention;

[0048] Figure 10 This is a block diagram of the modulation wave command calculation method described in this invention. Detailed Implementation

[0049] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings:

[0050] See Figure 1 This is a connection topology diagram of the star-chain network-type STATCOM system described in this invention. The present invention provides a network control method for a dual-star STATCOM system, comprising the following:

[0051] (1) Calculation of positive sequence voltage phasors: see Figure 2-3 The positive and negative sequence component method based on the second-order generalized integrator is used to decompose the grid voltage, thereby obtaining the positive sequence voltage phasor and the negative sequence voltage phasor.

[0052] (2) Voltage feedforward unit phasor calculation stage: A second-order generalized integrator is used for single-phase grid voltage to generate two-phase quadrature signals, thereby calculating the unit phasor of three-phase grid voltage and filtering out high-order harmonics;

[0053] (3) Bridge arm current reference command unit phasor calculation stage: A second-order generalized integrator is used for the STATCOM current reference command to generate two-phase quadrature signals, thereby calculating the unit phasor of the current reference command, which is used for the optimal dynamic adjustment of the active energy deviation during zero-sequence voltage injection.

[0054] (4) Reactive voltage control loop: The amplitude of the virtual internal electromotive force is obtained through the reactive voltage droop control loop. Limits are added to the integral and output of the PI regulator to avoid excessive saturation of the integral term during fault ride-through. At the same time, the integral term is cleared to zero during short-circuit faults to reduce the long recovery time of the current command after the fault is cleared.

[0055] (5) Calculation of negative sequence reactive current command for bridge arm: Set the target value of negative sequence voltage to 0, subtract it from the negative sequence voltage of the grid, and obtain the negative sequence reactive current command for bridge arm.

[0056] (6) Bridge arm current reference command limiting logic: The input signal of the limiting logic is the total current reference command, and only the reactive current is dynamically limited. The active current is used for DC voltage equalization control and is not limited.

[0057] Furthermore, a negative-sequence current command adjustment factor has been added to reduce product design costs. To avoid disturbances caused by zero-sequence current in the current loop, it needs to be directly subtracted from the current reference command. The DC component in the current reference command is isolated using a second-order low-pass filter.

[0058] (7) Bridge Arm Current Reference Command Limiting Logic: During a power outage, the voltage difference between the grid voltage and the virtual internal electromotive force is large after the grid voltage drops, resulting in a large current reference command acting on the virtual impedance, exceeding the current carrying capacity of the device. By using the current reference command limiting logic, the maximum reference command is always less than the maximum carrying current, ensuring the safety of the device. The input signal of the limiting logic is the total current reference command, and only the reactive current is dynamically limited, while the active current used for DC voltage balancing control is not limited. This method is more reasonable and improves the stability of the device.

[0059] (8) Zero-sequence voltage injection control loop: Zero-sequence voltage injection uses the average value of each phase DC voltage and the deviation of the total DC voltage from the average value. The PI regulator generates an adjustment amount of functional quantity. The phase of the adjustment amount adopts the phasor of the current reference command of each phase, and the regulation efficiency is the highest.

[0060] (9) Modulation wave command calculation stage: The difference between the current reference command and the current feedback of each phase is passed through a three-phase independent quasi-proportional resonant regulator to obtain the control voltage of the fundamental current of each phase;

[0061] The modulation wave command calculation includes a voltage feedforward unit phasor calculation stage, a zero-sequence voltage injection control stage, a current loop control stage, a first converter valve DC side overvoltage protection control stage, a second converter valve DC side overvoltage protection control stage, a DC circulating current control stage, and a DC voltage equalization control stage. The generated control voltage is fed forward and superimposed with the zero-sequence voltage and the grid voltage to form the final modulation signal.

[0062] See Figure 4 This is a block diagram for calculating the unit phasor of the voltage feedforward. The voltage feedforward unit phasor calculation stage uses a second-order generalized integrator for the single-phase grid voltage to generate two-phase quadrature signals, thereby calculating the unit phasor of the three-phase grid voltage. The specific implementation process is as follows:

[0063] Phase A grid voltage Divide by the peak value of the phase voltage rating Then, the per-unit value is obtained. Through a second-order generalized integrator and Obtain two orthogonal signals and The square root of the sum of squares gives the peak value. ,Will and Divide by peak value respectively The voltage of phase A of the power grid can then be obtained. feedforward phasor , and phasors with a phase lag of 90° The calculation method for the unit phasor of the voltage feedforward in phases B and C is consistent with that in phase A; where k is the damping ratio. Let be the center frequency, and s be the complex frequency variable.

[0064] The meanings of some variables in this control method are as follows:

[0065] The transfer function of the second-order generalized integrator SOGI;

[0066] : The transfer function of the second-order generalized integrator SOGI.

[0067] See Figure 5 This is a block diagram for calculating the unit phasor of the current reference command described in this invention. The specific implementation process is as follows:

[0068] Bridge arm current reference command Through a second-order generalized integrator and Obtain in-phase signal and orthogonal signals Taking the square root of the sum of squares yields the peak values ​​of the two orthogonal signals. , Divide by peak value This allows us to obtain the unit phasor of the A-phase bridge arm current reference command. The unit phasor calculation method for the reference command of the bridge arm currents of phases B and C is consistent with that of phase A.

[0069] See Figure 6 This is a block diagram of the reactive power control loop, and the specific implementation process is as follows:

[0070] Voltage reference value The settings are configured via the HMI (Host Management Interface) and are related to the effective value of the mains voltage. Subtracting them gives the voltage difference between the two, which is then divided by the slope. The corresponding reactive power reference value is obtained. And thus related to reactive power feedback value Subtract, and pass through a PI regulator The deviation of the virtual internal electromotive force is obtained. In this context, the limiting of the integral element in the PI controller is set independently, as is the final output limiting of the PI controller, and the deviation of the virtual internal electromotive force is also set independently. Compared with the virtual internal electromotive force reference value Adding them together, we obtain the virtual internal electromotive force reference value. ; Through the delay phase Generate a delayed virtual internal electromotive force reference value. Among them, the delay phase The time constant in The virtual internal electromotive force reference value is 40ms; during the transient fault, the reference value is... equal This refers to the value before the short-circuit fault occurred; at the same time, the integral value in the PI controller is cleared to prevent the error from accumulating and saturating.

[0071] Virtual internal electromotive force reference value respectively with Figure 2 The positive sequence voltage unit phasor obtained in , , After multiplication, the phasor of the virtual internal electromotive force is obtained. The virtual internal electromotive force phasor is... Figure 2 Middle sequence voltage component , , After subtracting, multiply the voltage deviation by the reciprocal of the virtual impedance. Obtain the reference command value of the positive sequence reactive current of the bridge arm. , , ,in, For virtual inductance, This is a virtual resistor.

[0072] Negative sequence voltage components , , The difference from the target value of 0 is calculated by multiplying the negative sequence voltage deviation by the reciprocal of the virtual impedance. Obtain the negative sequence current reference command value , , Virtual internal electromotive force reference value Peak value of phase voltage rating After multiplying, we obtain the named value of the virtual internal electromotive force. The positive sequence voltage component and Taking the square root of the sum of squares yields the magnitude of the positive-sequence voltage. Peak value of phase voltage rating After multiplication, the nominal value of the positive sequence voltage is obtained. Furthermore, the named value of the virtual internal electromotive force reference value. After subtraction, the deviation value of the positive sequence voltage is obtained. The negative sequence voltage component and Taking the square root of the sum of squares yields the magnitude of the positive-sequence voltage. Peak value of phase voltage rating After multiplication, the nominal value of the negative sequence voltage is obtained. That is, the deviation value of the negative sequence voltage. , Divide by Since the virtual impedances are the same, they are all... Therefore, it is actually a positive sequence current. With negative sequence current The proportion of amplitude, i.e. Then, using a limiter, the result after limiting is recorded as a coefficient. ,Right now ; in coefficient Then, again with the coefficient Multiplication, coefficient The value range is determined according to the project's requirements for negative sequence current, with a default value of 0.5; thus, an adjustable negative sequence current distribution ratio coefficient is obtained, i.e. , and sequence current reference command value , , After multiplication, we obtain the positive sequence current with the magnitude of the product. The bridge arm negative sequence current reference command, which is a multiple of the reference current, is denoted as... That is , , .

[0073] Positive sequence reactive current command of bridge arm , , With bridge arm negative sequence reactive current reference command , , After summing, the total bridge arm reactive current reference command is obtained. , , The zero-sequence component is obtained by summing the reference command values ​​of the reactive current of the three-phase bridge arms and dividing by 3. The current reference command value is subtracted by the zero-sequence component. To avoid disturbing the system, a reference command for the reactive current of the bridge arm containing a DC component is obtained. , , Then, through a second-order low-pass filter Then, the DC component was obtained. , , In order to isolate the DC component in the current reference command value, , , Subtracting the DC component from each component yields the unlimited reactive current reference command for the bridge arm. , , ;

[0074] The meanings of some variables in the reactive voltage control method are as follows:

[0075] : Transfer function of reactive voltage control PI regulator;

[0076] : Regulator proportional coefficient;

[0077] : Integral coefficient of the regulator;

[0078] The meanings of some variables in the virtual impedance calculation are as follows:

[0079] Virtual resistance;

[0080] Virtual inductance;

[0081] The transfer function of the second-order low-pass filter (LPF) used is as follows:

[0082] (3)

[0083] The meanings of the variables in this section are as follows:

[0084] Filter passband gain;

[0085] : Transfer function cutoff frequency;

[0086] : Filter damping coefficient.

[0087] See Figure 7 This is the logic block diagram for limiting the bridge arm current reference command. The specific implementation process is as follows:

[0088] Unlimited reactive current reference command for bridge arm , , Divide by the peak value of the bridge arm current rating Then, its per-unit value is obtained, and a Clark transformation is performed on the current command after the per-unit value to transform the three-phase stationary coordinate system into a two-phase stationary coordinate system, thus obtaining an orthogonal AC signal. and This process transforms the two-phase stationary coordinate system into a two-phase rotating orthogonal coordinate system, namely the dq coordinate system. The angle used in the coordinate transformation is the positive sequence voltage angle of phase A, resulting in orthogonal DC signals. and The amplitude of the signal can be obtained by taking the square root of the sum of squares. ;

[0089] Bridge arm active current reference command Each is obtained through a second-order generalized integrator. and Afterwards, an in-phase signal was obtained. and orthogonal signals The two are orthogonal. Then, the two-phase stationary coordinate system is transformed into a two-phase rotating orthogonal coordinate system, i.e., the dq coordinate system. The angle used in the coordinate transformation is the unit phasor of the three-phase voltage feedforward, resulting in two orthogonal DC signals. , Taking the square root of the sum of squares yields the peak value of the active current reference command for phase A bridge arm. The peak value calculation process for the active current reference command of phase B and phase C bridge arms is consistent with that of phase A.

[0090] The current command limiting logic ensures that the reference command value is within the range of the maximum design value of short-time overcurrent by solving the quadratic equation of reactive current limiting coefficient in real time. It also prioritizes ensuring that the active current command is not limited, which is used to control DC voltage balance, while the reactive current is reasonably limited. This method is more reasonable and avoids directly limiting only the total current command, which would affect the active power control link.

[0091] The following uses phase A current limiting as an example to illustrate the calculation process of the formula:

[0092] Hypothetical variables Let be the reactive current dynamic limiting coefficient to be solved, and let be the total transient short-time current overload factor. By projecting the positive and negative sequence current reference commands and the active current onto the dq coordinate system, the following equation can be obtained:

[0093]

[0094] After the formula is expanded,

[0095]

[0096] It can be seen that the position variable in the formula is only a variable. It is about variables. The quadratic equation of .

[0097] because , Therefore, the above formula can be simplified to:

[0098]

[0099] The standard form of a quadratic equation in one variable is:

[0100] ,

[0101] According to the quadratic formula: , thus obtaining variables The root is:

[0102]

[0103] B and C phase current dynamic limiting coefficients , The calculation process is the same as that for phase A current, and the final three-phase current unified limiting coefficient is... Pick , , The minimum of the three.

[0104] The meanings of the variables in this section are as follows:

[0105] Transient short-time current overload factor;

[0106] The formula for the Park transform used in this section is as follows:

[0107]

[0108] The meanings of the variables in this section are as follows:

[0109] Before transformation Axial components;

[0110] Before transformation Axial components;

[0111] : The transformed D-axis component;

[0112] : Transformed Q-axis component;

[0113] : Phase angle of the coordinate transformation signal.

[0114] See Figure 8 This is a block diagram of a zero-sequence voltage injection control method. In the zero-sequence voltage injection control loop, the zero-sequence voltage injection uses the average value of each phase DC voltage and the deviation from the average value of the total DC voltage. A PI regulator generates an adjustment quantity with functional properties. The phase of the adjustment quantity uses the phasor of the current reference command for each phase. The specific implementation process is as follows:

[0115] Instantaneous value of three-phase DC voltage at the first converter valve , , Passing sequentially through the delayed sampling stage And points process The sliding filter consists of a time constant. The 10ms interval is used to filter out the second harmonic component in the DC voltage. The filtered signals are as follows: , , The average of the three is denoted as .

[0116] Instantaneous value of three-phase DC voltage at the second converter valve , , Passing sequentially through the delayed sampling stage And points process The sliding filter consists of a time constant. The 10ms interval is used to filter out the second harmonic component in the DC voltage. The filtered signals are as follows: , , The average of the three is denoted as .

[0117] Average DC voltage of the first converter valve Average DC voltage of the second converter valve The average value is denoted as the overall DC voltage mean of the first and second converter valves. The average A-phase voltage of the first converter valve Average A-phase voltage of the second converter valve The average value, compared with the overall DC voltage average of the first and second converter valves. The difference is denoted as the total difference between the A-phase DC voltages of the first and second converter valves. via PI regulator Then, the output result is denoted as The control methods for phases B and C of the converter valve are the same as those for phase A, which can be obtained. , The current reference command unit vector of the first converter valve. , , Multiplying them separately and then adding them together gives the injected zero-sequence voltage component. It is used to regulate the balance of active quantities between the three phases of the converter valve.

[0118] The meanings of some variables in the zero-sequence voltage control method are as follows:

[0119] : Average DC voltage of phase A of the first converter valve;

[0120] : Average DC voltage of phase B of the first converter valve;

[0121] : Average DC voltage of phase C of the first converter valve;

[0122] : The average value of the DC voltage of phase A of the first converter valve after filtering;

[0123] : The average value of the B-phase DC voltage of the first converter valve after filtering;

[0124] : The average value of the C-phase DC voltage of the first converter valve after filtering;

[0125] : Average DC voltage of phase A of the second converter valve;

[0126] : Average DC voltage of phase B of the second converter valve;

[0127] : Average DC voltage of phase C of the second converter valve;

[0128] The average value of the DC voltage of phase A of the second converter valve after filtering;

[0129] The average value of the B-phase DC voltage of the second converter valve after filtering;

[0130] : The average value of the C-phase DC voltage of the second converter valve after filtering;

[0131] The average DC voltage of phase A of the first and second converter valves;

[0132] : The average DC voltage of phase B of the first and second converter valves;

[0133] : The average DC voltage of phase C of the first and second converter valves;

[0134] The average DC voltage of the first converter valve;

[0135] The average DC voltage of the second converter valve;

[0136] The average DC voltage of the first and second converter valves;

[0137] Average A-phase voltage of the first converter valve Average A-phase voltage of the second converter valve The average value, compared with the overall DC voltage average of the first and second converter valves. The difference;

[0138] Average B-phase voltage of the first converter valve Average voltage of phase B of the second converter valve The average value, compared with the overall DC voltage average of the first and second converter valves. The difference;

[0139] Average C-phase voltage of the first converter valve Average C-phase voltage of the second converter valve The average value, compared with the overall DC voltage average of the first and second converter valves. The difference;

[0140] : The reference value for the A-phase current command of the first converter valve;

[0141] : Reference value of B-phase current command for the first converter valve;

[0142] : The reference value for the C-phase current command of the first converter valve;

[0143] The PI regulator transfer function of the average DC voltage of phase A of the first and second converter valves and the overall average DC voltage of the first and second converter valves.

[0144] : The PI regulator transfer function of the average B-phase DC voltage of the first and second converter valves and the overall average DC voltage of the first and second converter valves;

[0145] The PI regulator transfer function of the average C-phase DC voltage of the first and second converter valves and the overall average DC voltage of the first and second converter valves.

[0146] Zero-sequence voltage injection component.

[0147] See Figure 9 Here is a block diagram of the current loop control method, and the specific implementation process is as follows:

[0148] Average DC voltage of the first and second converter valves This reflects the overall level of the DC voltage of the first and second converter valves, and is subtracted from the target value of 1.0 before being passed through the PI regulator. The output of the regulator is the amplitude of the active quantity deviation, and the positive sequence voltage unit phasor. , , After multiplication, the reference command for the active current of the three-phase bridge arm is obtained. , , Unlimited reactive current reference command for bridge arm , , With dynamic limiting coefficient After multiplication, the final reactive current reference command is obtained. , , With active current reference command , , Add them together to obtain the total current reference command. , , This leads to three-phase current feedback. , , The difference is calculated, and the resulting current deviation is the sum of the three independent proportional resonant regulators. The input signal is the closed-loop output of each of the three-phase current loops. , , That is, the fundamental current controls the voltage; where, For proportional gain, For resonant gain, For the resonant bandwidth, For complex frequency variables, It is the resonant frequency.

[0149] The meanings of the variables in this section are as follows:

[0150] : The transfer function of the PI regulator for the average value of the three-phase DC voltage;

[0151] : Quasi-PR regulator transfer function;

[0152] See Figure 10 This is a block diagram of the modulation wave command calculation method. The specific implementation process is as follows:

[0153] The modulation wave command calculation stage, in addition to the voltage feedforward unit phasor calculation stage, zero-sequence voltage injection control stage, and current loop control stage, also includes the overvoltage protection control stage of the first converter valve DC side, the overvoltage protection control stage of the second converter valve DC side, the DC circulating current control stage, and the DC voltage equalization control stage.

[0154] The overvoltage protection control method for the DC side of the first converter valve is implemented as follows:

[0155] The average value of the A-phase DC voltage after filtering at the first converter valve The average value of the DC voltage after filtering in phase B Average value of C-phase DC voltage after filtering Select the maximum value from the middle The difference between the voltage and the overvoltage threshold of 1.1 pu is calculated and then passed through a PI regulator. The output of the regulator is the active quantity adjustment. .when When the voltage is less than 1.1 pu, the output of the PI regulator is 0, which is the lower limit of the amplitude limit. Since the average DC voltage is not high at this time, no adjustment is needed.

[0156] The overvoltage protection control method on the DC side of the second converter valve is the same as that of the first converter valve.

[0157] The meanings of the variables in this section are as follows:

[0158] PI controller transfer function;

[0159] The control method for the DC link control loop, and its specific implementation process are as follows:

[0160] Phase A current of the first converter valve Phase A current of the second converter valve Half of the vector sum is the DC circulating current between the two converter valves. The total difference between the A-phase DC voltage of the first converter valve and the second converter valve By subtracting the values, the deviation of the A-phase DC circulating current of the first and second converter valves is obtained. Through the proportional resonant regulator Then, the DC circulating current control voltage is obtained. The B and C phases are superimposed on the modulation wave, and their control methods are consistent with those of the A phase.

[0161] The meanings of the variables in this section are as follows:

[0162] : Quasi-PR regulator transfer function;

[0163] The DC voltage equalization control method is implemented as follows:

[0164] Average DC voltage of phase A of the first converter valve Average DC voltage of phase A of the second converter valve Difference, using the proportionality coefficient Multiply and add to the unit phasor of the positive sequence voltage of phase A. After multiplication, the AC component is obtained. It is superimposed on the modulated wave;

[0165] Average DC voltage of the first converter valve Average DC voltage of the second converter valve Difference, using the proportionality coefficient Multiply and add to the unit phasor of the positive sequence voltage of phase A. After multiplication, the AC component is obtained. It is superimposed on the modulated wave;

[0166] Ultimately, the A-phase modulation wave of the first converter valve includes functional quantity regulation. DC circulating current control voltage , exchange quantity , exchange quantity feedforward unit phasor of grid voltage after per unit Closed-loop output of the current loop Zero-sequence voltage component .

[0167] The A-phase modulation wave of the second converter valve includes functional quantity adjustment. feedforward unit phasor of grid voltage Closed-loop output of the current loop Zero-sequence voltage component .

[0168] The calculation method for the B and C phase modulation waves of the first and second converter valves is consistent with that of phase A.

[0169] The method of the present invention is based on Figure 1-10 The connection topology and control block diagram.

[0170] The above embodiments are implemented based on the technical solution of the present invention, providing detailed implementation methods and specific operation processes. However, the scope of protection of the present invention is not limited to the above embodiments. Unless otherwise specified, the methods used in the above embodiments are conventional methods.

Claims

1. A network control method for a dual-star STATCOM, characterized in that, Includes the following: (1) Positive sequence voltage phasor calculation process: The positive and negative sequence component method based on the second-order generalized integrator is used to decompose the grid voltage to obtain the positive sequence voltage component and the negative sequence voltage component. (2) Calculation of unit phasor of bridge arm current reference command: A second-order generalized integrator is used for the STATCOM current reference command to generate two-phase quadrature signals, thereby calculating the unit phasor of the current reference command. The unit phasor of the current reference command participates in the calculation of the zero-sequence voltage component to obtain the zero-sequence voltage component. (3) Reactive voltage control loop: The amplitude of the virtual internal electromotive force is obtained through the reactive voltage droop control loop, which increases the limit on the integral and output of the PI regulator respectively; (4) Calculation of reference command for positive sequence reactive current of bridge arm: After subtracting the positive sequence voltage component in the three-phase stationary coordinate system from the virtual internal electromotive force phasor, the voltage deviation is multiplied by the reciprocal of the virtual impedance to obtain the reference command value for positive sequence reactive current of bridge arm. (5) Calculation of negative sequence reactive current reference command for bridge arm: The negative sequence voltage component in the three-phase stationary coordinate system is subtracted from the target value of 0. The negative sequence voltage deviation is multiplied by the reciprocal of the virtual impedance to obtain the negative sequence current reference command value. (6) Bridge arm current reference command limiting logic: The positive sequence reactive current reference command and the negative sequence reactive current reference command are added together to obtain the total current reference command. The input signal of the limiting logic is the total current reference command, and only the reactive current is dynamically limited. The active current is used for DC voltage equalization control and is not limited. (7) Modulation wave command calculation stage: The difference between the current reference command and the current feedback of each phase is passed through a three-phase independent quasi-proportional resonant regulator to obtain the control voltage of the fundamental current of each phase; The modulation signal calculation includes a voltage feedforward unit phasor calculation stage, a zero-sequence voltage injection control stage, a current loop control stage, a DC-side overvoltage protection control stage for converter valve #1, a DC-side overvoltage protection control stage for converter valve #2, a DC circulating current control stage, and a DC voltage equalization control stage. The generated control voltage is superimposed with the zero-sequence voltage component and the grid voltage feedforward unit phasor to form the final modulation signal.

2. The network control method for a binary star STATCOM according to claim 1, characterized in that, The voltage feedforward unit phasor calculation stage uses a second-order generalized integrator for single-phase grid voltage to generate two-phase quadrature signals, thereby calculating the unit phasor of the three-phase grid voltage, specifically including: Phase A grid voltage. Divide by the peak value of the phase voltage rating Then, the per-unit value is obtained. Through a second-order generalized integrator and Obtain in-phase signal and orthogonal signals Taking the square root of the sum of squares yields the peak values ​​of the two orthogonal signals. ,Will and Divide by peak value respectively The voltage of phase A of the power grid can then be obtained. Feedforward unit phasor , and phasors with a phase lag of 90° ,Will With proportionality coefficient Multiply to obtain the per-unit grid voltage feedforward unit phasor. Among them, the proportionality coefficient The value is 0.75–0.

85. The calculation method for the unit phasor of the voltage feedforward in phases B and C is consistent with that in phase A; where k is the damping ratio. Let be the center frequency, and s be the complex frequency variable.

3. The network control method for a binary star STATCOM according to claim 2, characterized in that, The bridge arm current reference command unit phasor calculation process specifically includes: bridge arm current reference command. Through a second-order generalized integrator and Obtain in-phase signal and orthogonal signals Taking the square root of the sum of squares yields the peak values ​​of the two orthogonal signals. , Divide by peak value This allows us to obtain the unit phasor of the A-phase bridge arm current reference command. The unit phasor calculation method for the reference command of the bridge arm currents of phases B and C is consistent with that of phase A.

4. The network control method for a binary star STATCOM according to claim 3, characterized in that, The reactive power control mechanism specifically includes: voltage reference value. The settings are configured via the HMI (Host Management Interface) and are related to the effective value of the mains voltage. Subtracting them gives the voltage difference between the two, which is then divided by the slope. The corresponding reactive power reference value is obtained. And thus related to reactive power feedback value Subtract, and pass through a PI regulator The deviation of the virtual internal electromotive force is obtained. In this context, the limiting of the integral element in the PI controller is set independently, as is the final output limiting of the PI controller, and the deviation of the virtual internal electromotive force is also set independently. Compared with the virtual internal electromotive force reference value Adding them together, we obtain the virtual internal electromotive force reference value. ; Through the delay phase Generate a delayed virtual internal electromotive force reference value. Among them, the delay phase The time constant in The virtual internal electromotive force reference value after transient fault judgment is 40ms. equal This refers to the value before the short-circuit fault occurred; at the same time, the integral value in the PI controller is cleared to prevent the error from accumulating and saturating.

5. The network control method for a binary star STATCOM according to claim 4, characterized in that, The calculation step for the positive-sequence reactive current reference command of the bridge arm specifically includes: the virtual internal electromotive force reference value after transient fault judgment. With the positive sequence voltage unit phasor respectively , , After multiplication, the phasor of the virtual internal electromotive force is obtained. The virtual internal electromotive force phasor is then compared with the positive sequence voltage component in the three-phase stationary coordinate system. , , After subtracting, multiply the voltage deviation by the reciprocal of the virtual impedance. Obtain the reference command value of the positive sequence reactive current of the bridge arm. , , ,in, For virtual inductance, This is a virtual resistor.

6. The network control method for a binary star STATCOM according to claim 5, characterized in that, The calculation step for the negative sequence reactive current reference command of the bridge arm specifically includes: the negative sequence voltage component in the three-phase stationary coordinate system. , , The difference from the target value of 0 is calculated by multiplying the negative sequence voltage deviation by the reciprocal of the virtual impedance. Obtain the negative sequence current reference command value , , Virtual internal electromotive force reference value Peak value of phase voltage rating After multiplication, we obtain the named value of the virtual internal electromotive force. The positive sequence voltage components in the two-phase stationary coordinate system and Taking the square root of the sum of squares yields the magnitude of the positive-sequence voltage. Peak value of phase voltage rating After multiplication, the nominal value of the positive sequence voltage is obtained. Furthermore, the named value of the virtual internal electromotive force reference value. After subtraction, the deviation value of the positive sequence voltage is obtained. The negative sequence voltage component in the two-phase stationary coordinate system and Taking the square root of the sum of squares yields the magnitude of the negative-sequence voltage. Peak value of phase voltage rating After multiplication, the nominal value of the negative sequence voltage is obtained. That is, the deviation value of the negative sequence voltage. , Divide by Since the virtual impedances are the same, they are all... Therefore, it is actually a positive sequence current. With negative sequence current The proportion of amplitude, i.e. Then, using a limiter, the result after limiting is recorded as a coefficient. ,Right now ; in coefficient Then, again with the coefficient Multiplication, coefficient The value range is determined according to the project's requirements for negative sequence current; thus, an adjustable negative sequence current with a proportional distribution coefficient is obtained, i.e. , and the negative sequence current reference command value , , After multiplication, we obtain the positive sequence current with the magnitude of the product. The bridge arm negative sequence current reference command, which is a multiple of the reference current, is denoted as... That is , , .

7. The network control method for a binary star STATCOM according to claim 6, characterized in that, The bridge arm current reference command limiting logic specifically includes: positive sequence current command. , , With negative sequence current reference command , , After summing, the total current reference command is obtained. , , The zero-sequence component is obtained by summing the three-phase current reference command values ​​and dividing by 3. ; The total current reference command is reduced by the zero-sequence component. To avoid disturbing the system, a reference command for the reactive current of the bridge arm containing a DC component is obtained. , , Then, through a second-order low-pass filter Then, the DC component is extracted. , , In order to isolate the DC component in the reactive current reference command value of the bridge arm, , , Subtracting the DC component from each component yields the unlimited reactive current reference command for the bridge arm. , , ;in, This refers to the filter's passband gain. The transfer function cutoff frequency; This is the filter damping coefficient; Unlimited reactive current reference command for bridge arm , , Divide by the peak value of the bridge arm current rating Then, its per-unit value is obtained, and a Clark transformation is performed on the current command after the per-unit value to transform the three-phase stationary coordinate system into a two-phase stationary coordinate system, thus obtaining an orthogonal AC signal. and This process transforms the two-phase stationary coordinate system into a two-phase rotating orthogonal coordinate system, namely the dq coordinate system. The angle used in the coordinate transformation is the positive sequence voltage angle of phase A, resulting in orthogonal DC signals. and The amplitude of the signal can be obtained by taking the square root of the sum of squares. ; Bridge arm active current reference command Each is obtained through a second-order generalized integrator. and Afterwards, an in-phase signal was obtained. and orthogonal signals The two are orthogonal; therefore, the two-phase stationary coordinate system is transformed into a two-phase rotating orthogonal coordinate system, namely the dq coordinate system. The angle used in the coordinate transformation process is the unit phasor of the three-phase voltage feedforward, resulting in two orthogonal DC signals. , Taking the square root of the sum of squares yields the peak value of the active current reference command for phase A bridge arm. The peak value calculation process for the active current reference command of phase B and phase C bridge arms is consistent with that of phase A. By solving the quadratic equation for the reactive current limiting coefficient in real time, the reference command value is ensured to be within the range of the maximum design value of short-time overcurrent. Priority is given to ensuring that the active current command is not limited for DC voltage balance control, while the reactive current is limited, resulting in the final unified limiting coefficient for the three-phase bridge arm current. Take the dynamic limiting factor of the three-phase bridge arm current , , The minimum of the three.

8. The network control method for a binary star STATCOM according to claim 7, characterized in that, The zero-sequence voltage injection control loop uses the average value of each phase DC voltage and the deviation from the average value of the total DC voltage. A PI regulator generates an adjustment quantity for this adjustment quantity, with the phase of the adjustment quantity using the phasor of the current reference command for each phase. Specifically, this includes the instantaneous value of the three-phase DC voltage at converter valve #1. , , Passing sequentially through the delayed sampling stage And points process The sliding filter consists of a time constant. The 10ms interval is used to filter out the second harmonic component in the DC voltage. The average values ​​of the three-phase DC voltages after filtering are as follows: , , The average of the three is denoted as ; Instantaneous value of three-phase DC voltage of converter valve #2 , , Passing sequentially through the delayed sampling stage And points process The sliding filter consists of a time constant. The 10ms interval is used to filter out the second harmonic component in the DC voltage. The average values ​​of the three-phase DC voltages after filtering are as follows: , , The average of the three is denoted as ; Average DC voltage of converter valve #1 The average DC voltage of converter valve #2 The average value is denoted as the overall DC voltage mean of converter valves 1# and 2#. The average value of the A-phase DC voltage of converter valve #1 after filtering The average value of the A-phase DC voltage after filtering with converter valve #2 The average value, compared with the overall DC voltage average of converter valves #1 and #2 The difference is denoted as the total difference in the A-phase DC voltage between converter valves 1# and 2#. ; via PI controller Then, the output result is denoted as ;in, This is the proportionality coefficient. The integral coefficient is used; the control methods for phases B and C of the converter valve are consistent with those for phase A, resulting in... , ; and the three-phase current reference command unit vector of converter valve #1 , , Multiplying them separately and then adding them together gives the injected zero-sequence voltage component. It is used to regulate the balance of active quantities between the three phases of the converter valve.

9. The network control method for a binary star STATCOM according to claim 8, characterized in that, The current loop control circuit specifically includes: the average DC voltage of converter valves 1# and 2#. This reflects the overall level of the DC voltage of converter valves #1 and #2, and is subtracted from the target value of 1.0 before being passed through the PI regulator. The output of the regulator is the amplitude of the active quantity deviation, and the positive sequence voltage unit phasor. , , After multiplication, the three-phase active current reference command is obtained. , , Unlimited reactive current reference command for bridge arm , , With dynamic limiting coefficient After multiplication, the final bridge arm reactive current reference command is obtained. , , With reference command for active current of bridge arm , , Adding them together, we obtain the total bridge arm current reference command. , , This leads to three-phase current feedback. , , The difference is calculated, and the resulting current deviation is the sum of the three independent proportional resonant regulators. The input signal is the closed-loop output of each of the three-phase current loops. , , That is, the fundamental current controls the voltage; where, For proportional gain, This is the proportionality coefficient. For resonant gain, For the resonant bandwidth, For complex frequency variables, It is the resonant frequency.

10. A network control method for a binary star STATCOM according to claim 9, characterized in that, The overvoltage protection control circuit for the DC side of converter valve #1, the overvoltage protection control circuit for the DC side of converter valve #2, the DC circulating current control circuit, and the DC voltage equalization control circuit specifically include: Overvoltage protection control circuit for the DC side of converter valve #1: The average value of the A-phase DC voltage after filtering of converter valve #1 The average value of the DC voltage after filtering in phase B Average value of C-phase DC voltage after filtering Select the maximum value from the middle The difference between the voltage and the overvoltage threshold of 1.1 pu is calculated and then passed through a PI regulator. The output of the regulator is the active quantity adjustment. ,when When the voltage is less than 1.1 pu, the output of the PI regulator is 0, which is the lower limit of the voltage limit; the overvoltage protection control method on the DC side of converter valve #2 is the same as that for converter valve #1. DC circulating current control circuit: Phase A current of converter valve #1 Phase A current of converter valve #2 Half of the vector sum is the DC circulating current between the two converter valves. The total difference between the DC voltage of phase A of converter valves 1# and 2# By subtracting the values, the deviation of the A-phase DC circulating current of converter valves 1# and 2# is obtained. Through the proportional resonant regulator Then, the DC circulating current control voltage is obtained. The superposition is applied to the modulation wave; the control methods for phases B and C are consistent with those for phase A. DC voltage equalization control stage: Average value of the A-phase DC voltage after filtering at converter valve #1 The average value of the A-phase DC voltage after filtering with converter valve #2 Difference, by proportion Multiply the coefficients and add them to the unit phasor of the positive sequence voltage of phase A. After multiplication, the AC component is obtained. This is superimposed on the modulation wave; the overall average DC voltage of converter valve #1 The average DC voltage of converter valve #2 Difference, through proportion Multiply the coefficients and add them to the unit phasor of the positive sequence voltage of phase A. After multiplication, the AC component is obtained. It is superimposed on the modulated wave; Ultimately, the A-phase modulation wave of converter valve #1 includes functional quantity regulation. DC circulating current control voltage , exchange quantity , exchange quantity Unit phasor of grid voltage feedforward after per unit Closed-loop output of the current loop Zero-sequence voltage component ; The A-phase modulation wave of converter valve #2 includes functional quantity adjustment. feedforward unit phasor of grid voltage Closed-loop output of the current loop Zero-sequence voltage component ; The calculation method for the modulation waves of phases B and C of converter valves 1# and 2# is consistent with that of phase A.

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