A control method of a star-type chain network configuration STATCOM

Abstract

The present application relates to the technical field of power electronics application, and particularly relates to a control method of a star chain type network STATCOM, which comprises positive sequence voltage unit phasor calculation, voltage feedforward unit phasor calculation, bridge arm current reference instruction unit phasor calculation, reactive voltage control, bridge arm reactive current reference instruction calculation without limiting amplitude, bridge arm reactive current reference instruction limiting amplitude logic, zero sequence voltage injection control and modulation wave instruction calculation; the bridge arm current reference instruction contains negative sequence components, negative sequence compensation of grid voltage is realized; the bridge arm current reference instruction limiting amplitude logic is designed, the safety of the device is effectively guaranteed; in the zero sequence voltage injection control link, the phase of the function amount deviation amount adopts the current reference instruction phasor signal, the dynamic adjustment efficiency is optimized; the balance control effect of the interphase DC voltage is enhanced, the overcurrent problem in the transient fault of the network STATCOM is solved, and the problem that the current instruction contains DC components is solved.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of power electronic applications, in particular to a control method of a star-type chain-type network-structured STATCOM. BACKGROUND

[0002] The star-type chain-type network-structured STATCOM is a new type of power electronic equipment without inertia, can provide fast dynamic reactive voltage support, can stably operate even in the case that the short-circuit capacity of the power grid is small, and does not have frequency coupling with the power grid. Especially during a short-circuit fault, the bridge arm current reference instruction is calculated by using instantaneous value, the response time is fast, and the star-type chain-type network-structured STATCOM is widely applied in the fields of wind power plants and photovoltaic grid connection, and has important significance for maintaining the stability of the power grid operation.

[0003] During a transient fault, the bridge arm current reference instruction of the star-type chain-type network-structured STATCOM changes fast and has a large amplitude, the device is prone to overcurrent, and the modulation wave appears overmodulation, and the energy balance effect among three-phase direct-current voltages is not ideal. In order to solve the problem, the application provides a new control method. SUMMARY

[0004] The application provides a control method of a star-type chain-type network-structured STATCOM, enhances the balance control effect of inter-phase direct-current voltages, solves the problems that the network-structured STATCOM is prone to overcurrent during a transient fault and the current instruction contains a direct-current component, and improves the stability of the device.

[0005] In order to achieve the above purpose, the application adopts the following technical scheme:

[0006] The application provides a control method of a star-type chain-type network-structured STATCOM, and the control method comprises the following contents.

[0007] (1) Positive sequence voltage unit phasor calculation: the positive and negative sequence component method based on a second-order generalized integrator is adopted to decompose the positive and negative sequence components of the grid voltage, so that the positive sequence phasor and the negative sequence phasor are obtained.

[0008] (2) Voltage feedforward unit phasor calculation: the second-order generalized integrator is adopted for single-phase grid voltage to generate two-phase quadrature signals, so that the phase information of each-phase grid voltage is calculated.

[0009] (3) Bridge arm current reference instruction unit phasor calculation: the second-order generalized integrator is adopted for the STATCOM bridge arm current reference instruction to generate two-phase quadrature signals, so that the phasor information of the bridge arm current is calculated.

[0010] (4) Reactive voltage control: the amplitude of the virtual internal electromotive force is obtained through a reactive voltage droop control link, and the integral and output of the PI regulator are respectively increased by limiting amplitude.

[0011] (5) Calculation of unlimited reactive current reference command for bridge arm: The virtual internal electromotive force is obtained by subtracting the instantaneous value of each phase voltage of the grid from the positive sequence phase of the grid voltage. The voltage difference generated is divided by the virtual impedance to obtain the unlimited reactive current reference command for the bridge arm.

[0012] (6) Reactive current reference command limiting of bridge arm: The maximum reference command is always less than the maximum withstand current through the bridge arm reactive current reference command limiting logic.

[0013] (7) Zero-sequence voltage injection control: 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, and generates an adjustment amount of functional quantity through a PI regulator;

[0014] (8) Modulation wave command calculation stage: The difference between the reference command of each phase arm current and the arm current is obtained by passing through a three-phase independent quasi-proportional resonant regulator to obtain the control voltage of the fundamental current of each phase. After being fed forward with the zero-sequence voltage and the grid voltage, the final modulation signal is generated.

[0015] Furthermore, the voltage feedforward unit phasor calculation specifically includes: 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. unit feedforward phasor and unit phasor 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.

[0016] Furthermore, the calculation of the bridge arm current reference command unit phasor specifically includes: the total 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 The unit phasor of the A-phase bridge arm current reference instruction is obtained The unit phasor calculation method of the B-phase and C-phase bridge arm current reference instructions is consistent with that of the A-phase.

[0017] Further, the reactive voltage control specifically comprises: subtracting the voltage reference value from the effective value of the grid voltage , and dividing the voltage deviation by the slope to obtain the corresponding reactive reference value ; then, the reactive feedback value is subtracted, and the PI regulator is used to obtain the deviation of the virtual internal electromotive force ; wherein, the amplitude limit of the integral element in the PI regulator is independently set and is not cleared in the transient fault; in addition, the amplitude limit of the final output of the PI regulator is also independently set; the deviation of the virtual internal electromotive force is added to the virtual internal electromotive force reference value to obtain the final virtual internal electromotive force reference value .

[0018] Further, the bridge arm non-amplitude-limited reactive current reference instruction calculation specifically comprises: multiplying the virtual internal electromotive force reference value by the positive sequence voltage unit phasor , , to obtain the phasor of the virtual internal electromotive force; the grid voltage , , is filtered by a second-order band-pass filter to obtain the 50Hz power frequency signal after filtering; after the voltage deviation is subtracted from the phasor of the virtual internal electromotive force, the voltage deviation is multiplied by the inverse of the virtual impedance to obtain the bridge arm reactive current reference instruction value , , , wherein, is the virtual inductance, is the virtual resistance; after the three-phase bridge arm reactive current reference instruction values are added and divided by 3, the zero sequence component is obtained; the bridge arm reactive current reference instruction values are respectively subtracted by the zero sequence component to obtain , , ; further, a second-order high-pass filter is used to isolate the direct current component in the bridge arm current reference instruction value to obtain the bridge arm non-amplitude-limited reactive current reference instruction , , , wherein, for filter passband gain, for filter damping coefficient, for transfer function cut-off frequency.

[0019] Further, the bridge arm reactive current reference instruction limiting specifically comprises: three-phase bridge arm non-limited reactive current reference instruction 、 、 Each is passed through a second-order generalized integrator and After, two orthogonal signals are obtained, square and then take the square root to obtain the peak 、 、 ; By comparison, the maximum value among the three is selected, recorded as , divided by the peak value of the bridge arm current rating After, the per unit value is obtained; is the maximum overload factor of the device, divided by the per unit value , through the rate limiting module, and then compared with 1.0, the minimum value of the two comparisons is recorded as the dynamic limiting coefficient ; Wherein, the rate limiting module has an upward rate of 5-50 / s and an infinite downward rate; The three-phase bridge arm non-limited reactive current reference instruction 、 、 is multiplied by the dynamic limiting coefficient , and the final bridge arm reactive current reference instruction 、 、 is obtained.

[0020] Further, the zero sequence voltage injection control specifically comprises: the average value of the sum of the average values of the direct voltages of the three-phase valve groups is recorded as , which is filtered through a sliding filter composed of a delay sampling link and an integral link , and the time constant T is 10ms, which is used to filter out the second harmonic component in the direct voltage, and the filtered signal is recorded as , that is, the average value of the three-phase direct voltage; The average value of the direct voltage of each phase valve group is filtered through a sliding filter with a time constant of 10ms, and the difference between is obtained, that is, the deviation 、 、 of the three-phase valve group active power from the average value ; After passing through three independent PI regulators, the respective outputs 、 、 are obtained, and then compared with the bridge arm current reference instruction 、 、 are multiplied and superimposed together, which is the injected zero sequence voltage component , for regulating the balance of active power among three phases.

[0021] Further, the modulation wave instruction calculation part specifically comprises: three-phase valve group filtered direct current voltage average value reflects the overall level of the direct current voltage, and the PI regulator is used after the target value 1.0 is subtracted , and the output of the regulator is the amplitude of the active power deviation, which is multiplied with the positive sequence voltage unit phasor 、 、 to obtain the three-phase active current reference instruction 、 、 wherein, is the proportional coefficient of the regulator, is the integral coefficient of the regulator, is a complex frequency variable; the bridge arm reactive current reference instruction 、 、 is the sum of the bridge arm active current reference instruction 、 、 , which is the total bridge arm current reference instruction 、 、 ; and then, the three-phase current feedback 、 、 is subtracted to obtain the input signal of the three independent proportional resonant regulators , and the output is the respective closed-loop output of the three-phase current loop 、 、 , which is the fundamental current control voltage, wherein, is the proportional gain, is the resonant gain, is the resonant bandwidth, is a complex frequency variable, is the resonant frequency;

[0022] the feedforward unit phasor of the three-phase power grid voltage 、 、 is multiplied with the proportional coefficient to obtain the per-unit grid voltage feedforward phasor, wherein, is 0.75-0.85;

[0023] The fundamental current control voltage is fed forward with the phasor of the three-phase grid voltage after normalization, and a zero sequence voltage injection component After superposition, the final modulation wave signal is obtained 、 、 .

[0024] Compared with the prior art, the beneficial effects of the present application are:

[0025] 1) By injecting a zero sequence voltage component, a bridge arm reactive current reference instruction limiting logic, and a high-pass filter link, the balance control effect of the inter-phase DC voltage is enhanced, the overcurrent problem in the transient fault of the grid-connected STATCOM is solved, and the current instruction contains a DC component, thereby improving the stability of the device;

[0026] 2) The bridge arm current reference instruction contains a negative sequence current instruction, which can realize negative sequence compensation of the grid voltage. For the DC component in the bridge arm current reference instruction, a second-order high-pass filter is used to isolate the DC component. A bridge arm current reference instruction limiting logic is designed to ensure that the maximum reference instruction is always less than the maximum bearing current, thereby ensuring the safety of the device. In the zero sequence voltage injection control link, the phase of the function quantity deviation is adopted to use the bridge arm current reference instruction unit phasor signal to optimize the dynamic adjustment efficiency;

[0027] 3) By calculating the virtual impedance, when a transient fault occurs, the bridge arm current reference instruction will automatically contain a negative sequence current instruction, thereby realizing negative sequence component compensation of the grid voltage;

[0028] 4) The present application designs a three-phase independent quasi-proportional resonant regulator to realize fast control of the three-phase bridge arm current loop. The method is simple and easy to implement, the program code design amount is small, and the tedious positive and negative sequence current separation control is avoided;

[0029] 5) The present application designs a bridge arm current reference instruction limiting logic to ensure that the bridge arm current reference value is always less than the maximum reference instruction value of the device, thereby ensuring the safety of the device;

[0030] 6) The present application designs a zero sequence voltage injection method, which is simple, highly implementable, and has high function quantity balance adjustment efficiency; BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1 is a star-type chain grid-connected STATCOM system connection topology structure of the present application;

[0032] Figure 2 is a grid voltage positive sequence unit phasor calculation structure schematic diagram of the present application;

[0033] Figure 3 is a voltage feedforward unit phasor calculation structure schematic diagram of the present application;

[0034] Figure 4 This is a schematic diagram of the bridge arm current reference command unit phasor calculation structure described in this invention;

[0035] Figure 5 This is a schematic diagram of the reactive voltage control loop structure described in this invention;

[0036] Figure 6 This is a schematic diagram of the structure of the bridge arm unlimited reactive current reference command calculation link described in this invention;

[0037] Figure 7 This is a schematic diagram of the bridge arm reactive current reference command limiting logic structure described in this invention;

[0038] Figure 8 This is a schematic diagram of the zero-sequence voltage injection control method described in this invention;

[0039] Figure 9 This is a schematic diagram of the modulation wave command calculation structure. Detailed Implementation

[0040] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings:

[0041] See Figure 1 This is a connection topology diagram of a star-chain network-type STATCOM system according to the present invention. The present invention provides a control method for a star-chain network-type STATCOM, comprising the following:

[0042] (1) Calculation of positive sequence voltage unit phasor: see Figure 2 The positive and negative sequence components of the grid voltage are decomposed using the positive and negative sequence component method based on the second-order generalized integrator, thereby obtaining the positive sequence phasor and the negative sequence phasor.

[0043] (2) Voltage feedforward unit phasor calculation: A second-order generalized integrator is used for single-phase grid voltage to generate two-phase quadrature signals, thereby calculating the phase information of each phase grid voltage and filtering out high-order harmonics;

[0044] See Figure 3 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 unit phasor of the A-phase grid voltage The feedforward unit phasor of the A-phase grid voltage The unit phasor with a phase lag of 90° The feedforward unit phasor calculation method of the B-phase and C-phase voltages is consistent with that of the A-phase; wherein k is a damping ratio, is a center frequency, and s is a complex frequency variable;

[0045] In the partial control method, the meanings of partial variables are as follows:

[0046] : transfer function of a second-order generalized integrator SOGI;

[0047] : transfer function of a second-order generalized integrator SOGI;

[0048] (3) Bridge arm current reference instruction unit phasor calculation: a second-order generalized integrator is used for the STATCOM bridge arm current reference instruction, two-phase orthogonal signals can be generated, and thus phasor information of the bridge arm current is calculated, which is used for optimal dynamic adjustment of the active component deviation amount in zero sequence voltage injection;

[0049] See Figure 4 , the total bridge arm current reference instruction is obtained through a second-order generalized integrator and , in-phase signal and quadrature signal are obtained, the peak value of the two-phase orthogonal signals is obtained after squaring and square root operation ; Divide by the peak value , and the unit phasor of the A-phase bridge arm current reference instruction is obtained ; the unit phasor calculation method of the B-phase and C-phase bridge arm current reference instructions is consistent with that of the A-phase.

[0050] (4) Reactive voltage control: the amplitude of the virtual internal electromotive force is obtained through a reactive voltage droop control link, and the integral and output of a PI regulator are respectively increased in amplitude to avoid that, in the fault ride-through process, the integral item is too large due to saturation, and the current instruction recovery time is relatively long after the fault is cleared.

[0051] See Figure 5 , the voltage reference value is set through an HMI host computer interface, and the voltage deviation between the voltage reference value and the effective value of the grid voltage is obtained. Divide the voltage deviation by the slope , and the corresponding reactive reference value is obtained, and then the reactive reference value is subtracted from the reactive feedback value , and the PI regulator The deviation of the virtual internal electromotive force The limit of the integral part of the PI regulator is set independently and is not cleared in transient faults. In addition, the limit of the final output of the PI regulator is also set independently. The deviation of the virtual internal electromotive force is added to the virtual internal electromotive force reference value to obtain the final virtual internal electromotive force reference value ;

[0052] In the reactive voltage control method, part of the variables have the following meanings:

[0053] : Transfer function of the reactive voltage control PI regulator;

[0054] : Proportional coefficient of the regulator;

[0055] : Integral coefficient of the regulator;

[0056] : Complex frequency operator of the transfer function.

[0057] (5) Bridge arm unclamped reactive current reference instruction calculation: the virtual internal electromotive force is subtracted from the grid voltage positive sequence phase, and the resulting voltage difference is divided by the virtual impedance to obtain the bridge arm current reference instruction; when a transient fault occurs, the bridge arm current reference instruction will contain a negative sequence current instruction due to the presence of negative sequence components in the grid voltage, thereby achieving negative sequence compensation of the grid voltage; in order to avoid the disturbance of zero sequence current in the current loop, the bridge arm current reference instruction needs to be directly subtracted; for the direct current component in the bridge arm current reference instruction, a second-order high-pass filter is used to filter out the direct current component and isolate the direct current component;

[0058] See Figure 6 , which is a block diagram of the bridge arm reactive current reference instruction calculation link. The specific implementation process is as follows:

[0059] The virtual internal electromotive force reference value is multiplied by the positive sequence voltage unit phasor , , respectively to obtain the virtual internal electromotive force phasor; the grid voltage , , is filtered through a second-order band-pass filter to obtain a 50Hz power frequency signal after filtering; after subtracting the virtual internal electromotive force phasor, the voltage deviation is multiplied by the inverse of the virtual impedance to obtain the bridge arm reactive current reference instruction value , , wherein, is a virtual inductance, is a virtual resistance; the sum of the three-phase bridge arm reactive current reference command values divided by 3 is the zero sequence component ; the zero sequence component is subtracted from the bridge arm reactive current reference command values respectively , to obtain , , ; the DC component in the bridge arm reactive current reference command value is isolated by a second-order high-pass filter , to obtain the bridge arm reactive current reference command without limiting amplitude , , .

[0060] wherein, the meanings of some variables in the virtual impedance calculation are as follows:

[0061] : virtual resistance;

[0062] : virtual inductance;

[0063] wherein, the transfer function of the high-pass filter (HPF) used is:

[0064]

[0065] The meanings of the variables in this part are as follows:

[0066] : complex frequency variable;

[0067] : filter passband gain;

[0068] : transfer function cut-off frequency;

[0069] : filter damping coefficient.

[0070] (6) Bridge arm reactive current reference command limiting: during the fault suspension period, the voltage difference between the grid voltage and the virtual internal electromotive force is large, which will generate a large bridge arm reactive current reference command acting on the virtual impedance, exceeding the current bearing capacity of the device; through the bridge arm reactive current reference command limiting logic, it is ensured that the maximum reference command is always less than the maximum bearing current, guaranteeing the safety of the device;

[0071] see Figure 7 , the three-phase bridge arm reactive current reference command without limiting amplitude , , each pass through a second-order generalized integrator and After obtaining two orthogonal signals, the square root of their sum is taken to obtain the peak value. , , The maximum value among the three is selected by comparison and denoted as . Divide by the peak value of the bridge arm current rating The per-unit value is then obtained. ; The maximum overload factor of the device, divided by the per-unit value. Then, the rate limiting module is used, and the result is compared with 1.0. The minimum value between the two is recorded as the dynamic limiting coefficient. The rate limiting module has an ascent rate of 20 and a descent rate of infinity; the three-phase bridge arm unlimited reactive current reference command. , , With dynamic limiting coefficient After multiplication, the final bridge arm reactive current reference command is obtained. , , ;

[0072] The formula for the Park transform used in this section is as follows:

[0073]

[0074] The meanings of the variables in this section are as follows:

[0075] Before transformation Axial components;

[0076] Before transformation Axial components;

[0077] : The transformed D-axis component;

[0078] : Transformed Q-axis component;

[0079] : Phase angle of the coordinate transformation signal.

[0080] (7) Zero-sequence voltage injection control: 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 uses the phasor of the bridge arm current reference command of each phase, which has the highest regulation efficiency.

[0081] See Figure 8 The average of the sum of the DC voltages of the three-phase valve group is denoted as Through the delayed sampling process and integral link The sliding filter composed of the time constant T is 10 ms, which is used to filter out the double frequency component in the DC voltage, and the filtered signal is denoted as , that is, the average value of the three-phase DC voltage. The average value of the DC voltage of each phase valve group is filtered through a sliding filter with a time constant of 10 ms, and the difference between is obtained, that is, the deviation of the three-phase valve group active power from the average value , , , After passing through three independent PI regulators, the respective outputs , , are obtained, which are then multiplied by the bridge arm current reference phasor , , and superimposed together, that is, the injected zero sequence voltage component , which is used to adjust the balance of the three-phase active power;

[0082] Among them, the meanings of some variables in the zero sequence voltage control method are as follows:

[0083] : PI regulator transfer function of A-phase DC voltage average value and three-phase DC voltage average value;

[0084] : PI regulator transfer function of B-phase DC voltage average value and three-phase DC voltage average value;

[0085] : PI regulator transfer function of C-phase DC voltage average value and three-phase DC voltage average value.

[0086] (8) Modulation wave instruction calculation link: the difference between the bridge arm current reference instruction and the bridge arm current is passed through three-phase independent quasi-proportional resonant regulators to obtain the control voltage of the fundamental current of each phase, which is superimposed with the zero sequence voltage and grid voltage feedforward to generate the final modulation signal;

[0087] See Figure 9 , the filtered DC voltage average value of the three-phase valve group reflects the overall level of the DC voltage, which is subtracted from the target value 1.0 and passed through a PI regulator , the output of the regulator is the amplitude of the active power deviation, which is multiplied by the positive sequence voltage unit phasor , , to obtain the three-phase active bridge arm current reference instruction , , wherein, is the regulator proportional coefficient, is the regulator proportional coefficient, is the transfer function complex frequency operator; the bridge arm reactive current reference instruction , , and the active current reference instruction , , , that is, the total bridge arm current reference instruction in , , ; and then subtracted from the three-phase current feedback , , , the current deviation obtained is the input signal of the three independent proportional resonant regulators , and the output is the respective closed-loop output of the three-phase current loop , , , that is, the fundamental current control voltage, wherein, is the proportional gain, is the resonant gain, is the resonant bandwidth, is the complex frequency variable, is the resonant frequency; the feedforward unit phasor of the three-phase power grid voltage , , is multiplied by the proportional coefficient to obtain the per-unit grid voltage feedforward phasor. Wherein, the value is 0.75; after superimposing the fundamental current control voltage and the per-unit three-phase grid voltage feedforward phasor, and the zero-sequence voltage injection component , the final modulation wave signal , , is obtained.

[0088] In the modulation wave instruction calculation method, part of the variable meanings are as follows:

[0089] : PI regulator transfer function of the three-phase DC voltage average value;

[0090] : quasi-PR regulator transfer function.

[0091] The above embodiments are implemented on the premise of the technical solution of the present application, and give detailed implementation modes and specific operation processes, but the protection scope of the present application is not limited to the above embodiments. The methods used in the above embodiments are all conventional methods unless otherwise specified.

Claims

1. A control method of a star-type chain-link network configuration STATCOM, characterized by, The application comprises the following contents: (1) positive sequence voltage unit phasor calculation: the positive and negative sequence component method based on the second-order generalized integrator is adopted to decompose the positive and negative sequence components of the grid voltage, so as to obtain the positive sequence phasor and the negative sequence phasor; (2) voltage feedforward unit phasor calculation: the second-order generalized integrator is adopted for the single-phase grid voltage to generate two-phase orthogonal signals, so as to calculate the phase information of each-phase grid voltage; (3) bridge arm current reference instruction unit phasor calculation: the second-order generalized integrator is adopted for the STATCOM bridge arm current reference instruction to generate two-phase orthogonal signals, so as to calculate the phasor information of the bridge arm current; (4) reactive voltage control: the amplitude of the virtual internal electromotive force is obtained through the reactive voltage droop control link, and the integral and output of the PI regulator are respectively increased in amplitude; (5) bridge arm unamplified reactive current reference instruction calculation: the virtual internal electromotive force is obtained by subtracting the instantaneous value of each phase voltage of the grid from the positive sequence phase of the grid voltage and dividing the voltage difference by the virtual impedance; (6) bridge arm reactive current reference instruction amplitude limiting: through the bridge arm reactive current reference instruction amplitude limiting logic, it is ensured that the maximum reference instruction is always less than the maximum bearing current; that is, after the three-phase bridge arm unamplified reactive current reference instructions pass through the second-order generalized integrator, two orthogonal signals are obtained, and after squaring and taking the square root, the peak value is obtained; by comparing and selecting the maximum value, the peak value of the rated value of the bridge arm current is divided to obtain the per-unit value; after the maximum overload multiple of the device is divided by the per-unit value, it is compared with 1.0 through the rate limiting module, and the minimum value of the two comparisons is recorded as the dynamic amplitude limiting coefficient; after the three-phase bridge arm unamplified reactive current reference instructions are multiplied by the dynamic amplitude limiting coefficient, the final bridge arm reactive current reference instruction is obtained; (7) zero sequence voltage injection control: the zero sequence voltage injection adopts the average value of each-phase DC voltage and the average value deviation of the total DC voltage, and the PI regulator produces a function quantity adjustment amount; (8) modulation wave instruction calculation link: after the difference between each-phase bridge arm current reference instruction and bridge arm current is passed through three-phase independent quasi-proportional resonant regulators, the control voltage of each-phase fundamental current is obtained, and after the zero sequence voltage and the grid voltage feedforward are superimposed, the final modulation signal is generated.

2. The control method of a star chain network configuration type STATCOM according to claim 1, characterized by, The voltage feedforward unit phasor calculation specifically includes: 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. unit feedforward phasor and unit phasor 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.

3. The control method of a star chain network configuration type STATCOM according to claim 2, characterized by, The bridge arm current reference instruction unit phasor calculation specifically comprises: total bridge arm current reference instruction , through a second-order generalized integrator and obtaining in-phase signals and quadrature signals , square sum and then square root, obtaining the peak value of two-way quadrature signals ; divided by the peak value , the unit phasor of the A-phase bridge arm current reference instruction is obtained ; the unit phasor calculation method of the B-phase and C-phase bridge arm current reference instructions is consistent with that of the A-phase.

4. The control method of a star chain network configuration type STATCOM according to claim 3, characterized by, The reactive voltage control specifically comprises a voltage reference value The setting is performed through an HMI host computer interface, and the effective value of the grid voltage Subtraction is performed to obtain the voltage deviation of the two; the voltage deviation is divided by the slope to obtain the corresponding reactive reference value , and then the reactive feedback value is subtracted, and the PI regulator is passed through to obtain the deviation of the virtual internal electromotive force ; wherein the amplitude of the integral element in the PI regulator is independently set and is not cleaned up in the transient fault; in addition, the amplitude of the final output of the PI regulator is also independently set; the deviation of the virtual internal electromotive force is added to the virtual internal electromotive force reference value to obtain the final virtual internal electromotive force reference value .

5. The control method of a star chain network configuration type STATCOM according to claim 4, characterized by, The bridge arm unclamped reactive current reference instruction calculation specifically comprises a virtual internal electromotive force reference value , , , , , , , , , , , , , , , , , , , , , , , , , 6. The control method of a star chain network configuration type STATCOM according to claim 5, characterized by, The bridge arm reactive current reference instruction limiting specifically comprises: three-phase bridge arm non-limiting reactive current reference instruction 、 、 Each is passed through a second-order generalized integrator and After, two orthogonal signals are obtained, square and then square root, to obtain the peak 、 、 ; By comparison, the maximum value among the three is selected, recorded as , divided by the peak value of the bridge arm current rating After, the per unit value is obtained; Divided by the per unit value , through the rate limiting module, then compared with 1.0, the minimum value of the two comparisons is recorded as the dynamic limiting coefficient ; Wherein, the rising rate of the rate limiting module is 5-50 / s, and the falling rate is infinite; Three-phase bridge arm non-limiting reactive current reference instruction 、 、 After being multiplied by the dynamic limiting coefficient , the final bridge arm reactive current reference instruction 、 、 is obtained.

7. The control method of a star chain network configuration type STATCOM according to claim 6, characterized by, The zero-sequence voltage injection control specifically includes: the average of the sum of the average DC voltages of the three-phase valve group is denoted as... Through the delayed sampling process And points process The sliding filter, with a time constant T of 10ms, is used to filter out the second harmonic component in the DC voltage. The filtered signal is denoted as... That is, the average value of the three-phase DC voltage; the average DC voltage of each phase valve group is passed through a sliding filter with a time constant of 10ms and compared with... After subtraction, the active and average values ​​of the three-phase valve group are obtained. deviation , , After passing through three independent PI controllers, their respective outputs are obtained. , , This is then compared with the bridge arm current reference command phasor. , , Multiplying and superimposing these components yields the injected zero-sequence voltage component. It is used to regulate the balance of active energy among the three phases.

8. The control method of a star chain network configuration type STATCOM according to claim 7, characterized by, The modulated wave instruction calculation link specifically comprises: three-phase valve group filtered direct current voltage average value The total level of the direct current voltage is reacted, and after being subtracted from the target value 1.0, the PI regulator is used The output of the regulator is multiplied by the positive sequence voltage unit phasor 、 、 to obtain the three-phase active current reference instruction 、 、 wherein, is the proportional coefficient of the regulator, is the integral coefficient of the regulator, is a complex frequency variable; the bridge arm reactive current reference instruction 、 、 is the sum of the bridge arm active current reference instruction 、 、 , that is, the total bridge arm current reference instruction 、 、 ; further, the three-phase current feedback 、 、 is subtracted to obtain the input signal of the three independent proportional resonant regulators , and the output is the respective closed-loop output of the three-phase current loop 、 、 , that is, the fundamental current control voltage, wherein, is the proportional gain, is the resonant gain, is the resonant bandwidth, is a complex frequency variable, is the resonant frequency; Feedforward unit phasor of three-phase grid voltage , , and the proportional coefficient are multiplied to obtain the unitized grid voltage feedforward phasor, wherein 0.75-0.85; The fundamental current control voltage is fed forward with the scaled three-phase grid voltage phasor and the zero-sequence voltage injection component After superposition, the final modulated wave signal is obtained 、 、 .

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