A negative sequence voltage compensation control method for a network-constructed STATCOM

Abstract

The present application relates to the technical field of power electronics application, and particularly relates to a negative sequence voltage compensation control method of a grid-forming STATCOM, comprising bridge arm current reference instruction unit phasor calculation, reactive power voltage control, bridge arm positive sequence and negative sequence reactive current instruction calculation, bridge arm current reference instruction limiting logic, zero sequence voltage injection control and modulation wave instruction calculation; the present application realizes that the negative sequence current output by the grid-forming STATCOM in the asymmetric transient fault is always inductive, the negative sequence current instruction amplitude size can be adjusted according to the project demand proportional coefficient, and the cost is reduced; by dynamically solving the monomial quadratic equation of the reactive current limiting coefficient, the active current instruction is not limited, the balance control of the direct current voltage is preferentially ensured, the reactive current is reasonably limited, the total current reference instruction value is always in the range of the maximum design value of the short-time overcurrent, and the stability and safety of the device are improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of power electronic applications, and particularly relates to a negative sequence voltage compensation control method of a grid-connected STATCOM. BACKGROUND

[0002] The grid-connected STATCOM is a dynamic reactive power compensation device without energy storage devices. In the case of transient faults, the current instruction adopts a transient value calculation method, showing voltage source characteristics, and the response speed is greatly improved. The grid adaptability is strong, and even in the case of weak grid, it can still operate stably, ensuring the reliability of the power system operation.

[0003] Since the grid-connected STATCOM does not have batteries or super capacitors, it does not have inertia support capability. The capacitor on the DC side of the power unit only plays a role in supporting the voltage. Considering the design cost, the capacitor value is usually small. In the case of asymmetric transient faults, the active power loss of the three phases of the grid-connected STATCOM is inconsistent, and a reasonable control algorithm needs to be designed to ensure the balance of the DC voltage energy between the phases, especially in the case of transient multiple overloads. At the same time, the current reference instruction during the transient fault is large, and a reasonable limiting logic needs to be designed to ensure that the reactive current instruction is dynamically limited and the active current instruction is not limited, so as to ensure the balance of the DC voltage energy. In addition, the polarity of the negative sequence current output by the grid-connected STATCOM should always be inductive to avoid the non-fault phase grid voltage becoming high, causing other power equipment connected to the system to be disconnected from the grid. In order to solve the above problems, the present application proposes a new negative sequence voltage compensation control method. SUMMARY

[0004] The present application provides a negative sequence voltage compensation control method of a grid-connected STATCOM, which realizes that the negative sequence current output by the grid-connected STATCOM is always inductive in the case of asymmetric transient faults, and the magnitude of the negative sequence current instruction can be adjusted according to the proportion coefficient of the engineering project demand, thereby reducing the cost. By dynamically solving the quadratic equation of the reactive current limiting coefficient, the active current instruction is not limited, the balance control of the DC voltage is preferentially ensured, the reactive current is reasonably limited, the total current reference instruction value is always within the range of the maximum design value of the short-time overcurrent, and the stability and safety of the device are improved.

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

[0006] A negative sequence voltage compensation control method of a grid-connected STATCOM, comprising:

[0007] (1) Calculation of positive sequence voltage phasors: 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 and negative sequence voltage phasors;

[0008] (2) Calculation of unit phasor of voltage feedforward: A second-order generalized integrator is used for single-phase grid voltage to generate two-phase quadrature signals, thereby calculating the unit phasor of the three-phase grid feedforward voltage and filtering out high-order harmonics.

[0009] (3) 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, which is used for the optimal dynamic adjustment of the active energy deviation during zero-sequence voltage injection.

[0010] (4) Reactive voltage control: 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. At the same time, the integral term is cleared during short circuit faults.

[0011] (5) 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 current command is obtained by subtracting the positive sequence voltage of the grid.

[0012] (6) Calculation of negative sequence reactive current command of bridge arm: Set the target value of negative sequence voltage to 0, subtract it from the negative sequence voltage of the grid to obtain the negative sequence current command, and add the negative sequence current command adjustment coefficient;

[0013] (7) Bridge arm current reference command limiting logic: ensure that the maximum current reference command is always less than the maximum withstand current. The input signal of the current reference command 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.

[0014] (8) 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;

[0015] (9) Modulation wave command calculation: 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. After being fed forward with the zero-sequence voltage and the grid voltage, the final modulation signal is generated.

[0016] 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 of the A-phase grid voltage 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 phasor 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.

[0017] Furthermore, the calculation of the bridge arm current reference command unit phasor 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 calculation method for the phasor unit of the reference command for the current of the bridge arms in phases B and C is consistent with that of phase A.

[0018] Furthermore, the reactive power voltage control 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 amplitude limit of the integral term in the PI controller is set independently, and the final output amplitude limit of the PI controller is also set independently. The proportional coefficient of the regulator. The integral coefficient of the regulator. For the transfer function complex frequency operator; the deviation of the virtual internal electromotive force. Compared with the virtual internal electromotive force reference value Adding them together, we obtain the virtual internal electromotive force reference value. ; Through the delay process , the delayed virtual internal electromotive force reference value is generated , wherein the time constant in the delay link is 40 ms , during the transient fault, the virtual internal electromotive force reference value is equal to , i.e. the value before the short-circuit fault occurs; at the same time, the integral value in the PI regulator is cleaned up to avoid saturation caused by continuously accumulated errors.

[0019] Further, the bridge arm positive sequence reactive current instruction calculation specifically includes: 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; after the virtual internal electromotive force phasor is subtracted from the positive sequence voltage component , , , the voltage deviation is multiplied by the reciprocal of the virtual impedance to obtain the positive sequence current reference instruction value , , , wherein is the virtual inductance, and is the virtual resistance.

[0020] Further, the bridge arm negative sequence reactive current instruction calculation specifically includes: the negative sequence voltage component , , is subtracted from the target value 0, the negative sequence voltage deviation is multiplied by the reciprocal of the virtual impedance to obtain the bridge arm negative sequence reactive current reference instruction value , , ; after the virtual internal electromotive force reference value is multiplied by the peak value of the phase voltage rated value , the virtual internal electromotive force nominal value is obtained; after the positive sequence voltage component is squared and summed with , the amplitude of the positive sequence voltage is obtained; after the amplitude of the positive sequence voltage is multiplied by the peak value of the phase voltage rated value , the positive sequence voltage nominal value is obtained; then, after the positive sequence voltage deviation value is obtained by subtracting the nominal value of the virtual internal electromotive force reference value , the positive sequence voltage deviation value is obtained; after the negative sequence voltage component is squared and summed with , the amplitude of the positive sequence voltage is obtained, and the amplitude of the positive sequence voltage is multiplied by the peak value of the phase voltage rated value After multiplication, the negative sequence voltage is obtained , i.e. the deviation value of the negative sequence voltage ; Divided by , since the virtual impedance is the same, both are ; Therefore, the actual is the ratio of the positive sequence current and the negative sequence current Amplitude, that is ; Further, through the limiter, the result after limiting is recorded as the coefficient ; That is ; After the coefficient , multiply the coefficient again, recorded as ; Thus, the negative sequence current whose distribution proportion coefficient can be adjusted is obtained, that is , multiplied by the negative sequence current reference value , , , After multiplication, the negative sequence current reference instruction with the amplitude multiple of the positive sequence current is obtained, recorded as , that is , .

[0021] Further, the bridge arm current reference instruction limiting logic specifically includes: the bridge arm positive sequence reactive current reference instruction , , , , , After adding the bridge arm negative sequence reactive current reference instruction , , , the total three-phase bridge arm reactive current reference instruction is obtained ; After adding the three-phase bridge arm reactive current reference instruction value, divided by 3, the zero sequence component is obtained ; The bridge arm reactive current reference instruction value is respectively subtracted from the zero sequence component , to obtain , ; Further, after the second-order low-pass filter , the direct current component is obtained , , ; In order to isolate the direct current component in the current reference instruction value, , , Subtract the direct current component respectively to obtain the bridge arm unlimiter reactive current reference instruction , , ; wherein is the filter passband gain; is the transfer function cut-off frequency; is the filter damping coefficient;

[0022] bridge arm unclamped reactive current reference instruction 、 、 divide by the peak value of the bridge arm current rating , and then get its per-unit value, and do CLARK transformation on the current instruction after per-unit, convert the three-phase stationary coordinate system to the two-phase stationary coordinate system, and get the orthogonal AC signal and ; further convert the two-phase stationary coordinate system to the two-phase rotating orthogonal coordinate system, i.e. the dq coordinate system, and the angle used in the coordinate transformation is the A-phase positive sequence voltage angle, to get the orthogonal DC signal and ; through the calculation of square and square root, the amplitude of the signal ;

[0023] three-phase bridge arm active current reference instruction 、 、 , respectively through the second-order generalized integrator and , both of which get the orthogonal two-way AC signal; further convert the two-phase stationary coordinate system to the two-phase rotating orthogonal coordinate system, i.e. the dq coordinate system, and the angles used in the coordinate transformation are the unit phasors of A, B and C three-phase voltage feedforward, to get the orthogonal DC signal 、 , 、 and 、 ; square and square root, get the peak value of the three-phase active current reference instruction 、 、 ;

[0024] by solving the quadratic equation of the reactive current limiting coefficient in real time, the reference instruction value is ensured to be within the maximum design value range of the short-time overcurrent, and the active current instruction is preferentially ensured not to be limited, for controlling the DC voltage balance, while the reactive current is limited, to get the final three-phase bridge arm current unified limiting coefficient take 、 、 the minimum value of the three.

[0025] Further, the zero sequence voltage injection control specifically includes: the average value of the sum of the DC voltage average values of the three-phase valve group is denoted as , by a sliding filter composed of a time delay sampling link and an integration link with a time constant T of 10 ms, for filtering out the double frequency component in the direct voltage, the filtered signal is recorded as , i.e. the average value of the three-phase direct voltage; the average value of the direct voltage of each valve group is filtered through a sliding filter with a time constant of 10 ms, and the difference between the average value of the direct voltage of each valve group and is obtained, i.e. the deviation of the active power of the three-phase valve group from the average value , , , ; after passing through three independent PI regulators, the respective outputs , , are obtained, which are then multiplied by the current reference phasor , , and superimposed together, i.e. the injected zero sequence voltage component , for regulating the balance of the active power among the three phases.

[0026] Further, the modulation wave instruction calculation specifically comprises: the average value of the direct voltage of the three-phase valve group reflects the overall level of the direct voltage, which is subtracted from the target value 1.0 and then 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 current reference instruction , , ; the bridge arm unclipped reactive current reference instruction , , is multiplied by the dynamic clipping coefficient to obtain the final reactive current reference instruction , , ; and the active current reference instruction , , is added to obtain the total current reference instruction , , ; and then the difference between the three-phase current feedback , , is obtained, i.e. 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 、 、 , wherein the fundamental current control voltage is , wherein Kp is a proportional gain, , wherein Ks is a resonance gain, , wherein B is a resonance bandwidth, , wherein s is a complex frequency variable, , wherein f is a resonance frequency; the feedforward unit phasor of the three-phase grid voltage 、 、 is multiplied by a proportional coefficient to obtain the unitized grid voltage feedforward phasor, wherein is 0.75-0.85; after the fundamental current control voltage is superimposed with the unitized three-phase grid voltage feedforward phasor and the zero-sequence voltage injection component , a final modulation wave signal is obtained 、 、 .

[0027] Compared with the prior art, the present application has the following beneficial effects:

[0028] 1) The present application proposes a negative sequence current instruction calculation method, which ensures that the polarity of the instruction value is always inductive, effectively ensuring that the grid voltage of the non-fault phase is reduced, especially in a weak grid, this phenomenon is particularly obvious, and capacitive negative sequence current can cause the grid voltage of the non-fault phase to rise, causing other connected devices to overvoltage and disconnect from the grid;

[0029] 2) The present application designs a negative sequence current instruction independent calculation method, the amplitude size of which can be adjusted through a proportional coefficient, and the negative sequence component injected into the grid can be reasonably increased or decreased according to the actual engineering requirements; since the device needs to inject additional zero-sequence current or zero-sequence voltage when outputting negative sequence current, to balance the functional quantity between the phases of the STATCOM in the angular type and star type structure; therefore, while meeting the design requirements of the engineering project, the product design cost can be reduced;

[0030] 3) The present application designs a current reference instruction limiting logic, which solves a quadratic equation of one variable in real time to ensure that the reference instruction value is within the maximum design value range of the short-time overcurrent, and preferentially ensures that the active current instruction is not limited, for controlling the DC voltage balance, while the reactive current is reasonably limited. This method is more reasonable, avoids directly limiting the total current instruction, affects the active control link, and improves the stability and safety of the product. BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1 is the star chain type STATCOM system connection topology diagram described in the present application;

[0032] Figure 2 is the schematic diagram of the positive and negative sequence component calculation structure of the grid voltage of the present application;

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

[0034] Figure 4 is the schematic diagram of the voltage feedforward unit phasor calculation structure of the present application;

[0035] Figure 5 is the schematic diagram of the bridge arm current reference instruction unit phasor calculation structure of the present application;

[0036] Figure 6 is the schematic diagram of the reactive voltage control and bridge arm positive and negative sequence reactive current reference instruction calculation structure of the present application;

[0037] Figure 7 is the schematic diagram of the bridge arm reactive current reference instruction limiting logic structure of the present application;

[0038] Figure 8 is the schematic diagram of the zero sequence voltage injection control method structure of the present application;

[0039] Figure 9 is the schematic diagram of the modulation wave instruction calculation link structure of the present application. DETAILED DESCRIPTION

[0040] The specific embodiments of the present application will be further described below in combination with the drawings:

[0041] See Figure 1 , the star chain type STATCOM system connection topology diagram of the present application. The negative sequence voltage compensation control method of the grid type STATCOM of the present application includes positive sequence voltage phasor calculation, voltage feedforward unit phasor calculation, current reference instruction unit phasor calculation, reactive voltage control, positive sequence current instruction calculation, negative sequence current instruction calculation, current reference instruction limiting logic, zero sequence voltage injection control and modulation wave instruction calculation.

[0042] (1) Positive sequence voltage phasor calculation: see Figures 2-3 , the positive and negative sequence component method based on the second-order generalized integrator is adopted to decompose the grid voltage, so as to obtain the positive sequence voltage and negative sequence voltage phasor.

[0043] (2) Voltage feedforward unit phasor calculation: the second-order generalized integrator is adopted for single-phase grid voltage to generate two-phase orthogonal signals, so as to calculate the unit phasor of three-phase grid voltage and filter out high-order harmonics;

[0044] See Figure 4 , the A-phase grid voltage Divide by the peak value of the phase voltage rating Then, the per-unit value of the A-phase grid voltage 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 phasor Phasors with a phase lag of 90° The calculation method for the voltage feedforward phasors of phases B and C is consistent with that of phase A; where k is the damping ratio. The center frequency is s, and the complex frequency variable is s.

[0045] The meanings of some variables in this control method are as follows:

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

[0047] : The transfer function of the second-order generalized integrator SOGI.

[0048] (3) 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, which is used for the optimal dynamic adjustment of the active energy deviation during zero-sequence voltage injection.

[0049] See Figure 5 The calculation of the bridge arm current reference command unit phasor 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 The phasor of the A-phase bridge arm current reference command can then be obtained. The calculation method for the phasor unit of the reference command for the current of the bridge arms in phases B and C is consistent with that of phase A.

[0050] (4) Reactive voltage control: 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. At the same time, the integral term is cleared during short circuit faults.

[0051] See Figure 6 , voltage reference value Set by HMI host computer interface, and the effective value of grid voltage Subtract, get the voltage deviation of the two; divided by the slope , get the corresponding reactive power reference value , and then subtract the reactive power feedback value , and through the PI regulator , the deviation of the virtual internal electromotive force can be obtained ; wherein the amplitude of the integral element in the PI regulator is independently set, and 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 . Through the delay element , generate , wherein the time constant in the delay element is 40ms, during transient fault, the virtual internal electromotive force reference value is equal to , that is, the value before the short-circuit fault occurs; at the same time, the integral value in the PI regulator is cleaned up to avoid saturation due to continuous error accumulation.

[0052] (5) Bridge arm positive sequence reactive current command calculation: the grid voltage positive sequence phase is used for the virtual internal electromotive force, and the bridge arm positive sequence reactive current command is obtained by subtracting the grid positive sequence voltage;

[0053] See Figure 7 , the virtual internal electromotive force reference value is multiplied by the positive sequence voltage unit phasor Figure 2 , , , obtained in Figure 2 , respectively, to obtain the phasor of the virtual internal electromotive force; after subtracting the positive sequence voltage component , , in , the voltage deviation is multiplied by the reciprocal of the virtual impedance , , to obtain the positive sequence current reference command value

[0054] (6) Bridge arm negative sequence reactive current command calculation: set the target value of negative sequence voltage to 0, subtract the grid negative sequence voltage to obtain the bridge arm negative sequence reactive current command, and increase the negative sequence current command adjustment coefficient;

[0055] See Figure 6 , negative sequence voltage component , , , difference from the target value 0, multiply the negative sequence voltage deviation by the inverse of the virtual impedance , obtain the negative sequence current reference value , , ; virtual internal electromotive force reference value , the peak value of the phase voltage rating , after multiplication, the nominal value of the virtual internal electromotive force is obtained ; square root of the sum of the positive sequence voltage component and , get the amplitude of the positive sequence voltage , after multiplication with the peak value of the phase voltage rating , the positive sequence voltage nominal value is obtained ; and then subtract the nominal value of the virtual internal electromotive force reference value , get the deviation value of the positive sequence voltage ; square root of the sum of the negative sequence voltage component and , get the amplitude of the positive sequence voltage , after multiplication with the peak value of the phase voltage rating , the negative sequence voltage nominal value is obtained , that is, the deviation value of the negative sequence voltage ; divided by , since the virtual impedance is the same, both are ; Therefore, the actual is the ratio of the amplitude of the positive sequence current and the negative sequence current , that is ; Further through the limiter, the result after limiting is recorded as the coefficient ; that is ; After the coefficient , multiply it again by the coefficient , record as , the value range of the coefficient is determined according to the demand of the project for the negative sequence current, and the default value is 0.5; Thus, the negative sequence current with adjustable distribution ratio coefficient is obtained, that is , after multiplication with the sequence current reference value , , , the negative sequence current reference instruction with the amplitude multiple of the positive sequence current is obtained, recorded as , that is , , .

[0056] (7) Bridge arm current reference command limiting logic: ensure that the maximum current reference command is always less than the maximum bearing current, the input signal of the current reference command limiting logic is the total current reference command, and only the reactive current is dynamically limited, the active current is used for DC voltage balance control and is not limited;

[0057] bridge arm positive sequence reactive current command , , and the bridge arm negative sequence reactive current reference command , , , the total current reference command , , is obtained after the addition; the three-phase current reference command value is added and then divided by 3, that is, the zero sequence component ; the current reference command value is respectively subtracted from the zero sequence component , to obtain , , ; and then through a second-order low-pass filter , the DC component , , is obtained; in order to isolate the DC component in the current reference command value, , , respectively subtract the DC component to obtain the bridge arm un-limited reactive current reference command , , ;

[0058] Among them, part of the variable meanings in the reactive voltage control method are as follows:

[0059] : Transfer function of reactive voltage control PI regulator;

[0060] : Regulator proportional coefficient;

[0061] : Regulator integral coefficient;

[0062] : Transfer function complex frequency operator;

[0063] Among them, part of the variable meanings in the virtual impedance calculation are as follows:

[0064] : Virtual resistance;

[0065] : virtual inductance;

[0066] Where the second-order low-pass filter (LPF) transfer function used is:

[0067]

[0068] The variable meanings in this section are as follows:

[0069] : transfer function complex frequency operator;

[0070] : filter passband gain;

[0071] : transfer function shear frequency;

[0072] : filter damping coefficient;

[0073] See Figure 7 , bridge arm unclipped reactive current reference instruction , , , i.e. divide by the peak value of the bridge arm current rating , to obtain its per-unit value; after per-unitization, the current instruction is subjected to CLARK transformation, converting the three-phase stationary coordinate system to the two-phase stationary coordinate system, to obtain orthogonal AC signals and , and then the two-phase stationary coordinate system is transformed to the two-phase rotating orthogonal coordinate system, i.e., the dq coordinate system, and the angle used in the coordinate transformation process is the A-phase positive sequence voltage angle, to obtain orthogonal DC signals and ; through square root calculation after squaring, the amplitude of the signal can be obtained;

[0074] Three-phase active current reference instruction , , , after passing through the second-order generalized integrator and , both obtain orthogonal two-way AC signals; then the two-phase stationary coordinate system is transformed to the two-phase rotating orthogonal coordinate system, i.e., the dq coordinate system, and the angles used in the coordinate transformation process are the unit phasors of A, B, and C three-phase voltage feedforward, respectively, to obtain orthogonal DC signals , , , and , ; square root after squaring, to obtain the peak value of the three-phase active current reference instruction 、 、 ;

[0075] The current command limiting logic ensures that the reference command value is within the maximum design value of the short-time overcurrent, and the active current command is preferentially ensured not to be limited, for controlling the DC voltage balance, and the reactive current is reasonably limited. The method is more reasonable, avoiding directly limiting the total current command, which affects the active control link;

[0076] Taking the A-phase current limiting as an example, the calculation process of the formula is specifically explained:

[0077] Variable is the dynamic limiting coefficient of the reactive current to be solved, and the total transient short-time current overload multiple is The positive and negative sequence current reference commands and the active current are projected and calculated in the dq coordinate system, and the following equation can be obtained:

[0078]

[0079] After expanding the formula,

[0080]

[0081] As can be seen, the position variable in the formula is only variable , which is a quadratic equation about variable .

[0082] Since , , the above formula can be simplified as:

[0083]

[0084] The standard form of the quadratic equation is:

[0085] ,

[0086] According to the root formula: , the root of variable is:

[0087]

[0088] B, C-phase current dynamic limiting coefficient 、 The calculation engineering is consistent with the A-phase current, and is not repeated. The final three-phase bridge arm current unified limiting coefficient is obtained. 、 , the minimum of the three;

[0089] The variable meanings of this part are as follows:

[0090] : Transient short-time current overload factor;

[0091] The formula of the Park transformation used in this part is as follows:

[0092]

[0093] The variable meanings of this part are as follows:

[0094] : Pre-transformation axis component;

[0095] : Pre-transformation axis component;

[0096] : Post-transformation D-axis component;

[0097] : Post-transformation Q-axis component;

[0098] : Phase angle of coordinate transformation signal.

[0099] (8) Zero sequence voltage injection control: the zero sequence voltage injection adopts the average value of the DC voltage of each phase and the deviation amount from the average value of the total DC voltage to produce a functional quantity adjustment amount through a PI regulator;

[0100] See Figure 8 , the average value of the sum of the average values of the DC voltages of the three-phase valve groups is denoted as , which is filtered through a sliding filter composed of a time delay sampling link and an integral link with an average time constant of 10 ms to filter out the second harmonic component in the DC voltage, and the filtered signal is denoted as , i.e., 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 after the difference is made, which is the deviation amount , , of the functional quantity of the three-phase valve group from the average value ; after passing through three independent PI regulators, the respective outputs , , are obtained, and then the current reference phasor , is obtained. Multiplication and superposition together, namely the injected zero sequence voltage component , for regulating the balance of active power among three phases;

[0101] Wherein, the partial variable meaning in zero sequence voltage control method is as follows:

[0102] : PI regulator transfer function of A-phase DC voltage average value and three-phase DC voltage average value;

[0103] : PI regulator transfer function of B-phase DC voltage average value and three-phase DC voltage average value;

[0104] : PI regulator transfer function of C-phase DC voltage average value and three-phase DC voltage average value.

[0105] (9) Modulation wave instruction calculation: the difference between each phase current reference instruction and current feedback is obtained through three-phase independent quasi-proportional resonant regulator, and the control voltage of each phase fundamental current is obtained, and the final modulation signal is generated after superposition of zero sequence voltage and grid voltage feedforward;

[0106] See Figure 9 , three-phase valve group DC voltage average value Reflects the overall level of DC voltage, and the target value 1.0 is subtracted through the PI regulator , the output of the regulator is the amplitude of the active power deviation, and the positive sequence voltage unit phasor 、 、 Multiplication, three-phase active current reference instruction is obtained 、 、 ; The bridge arm non-amplitude limiting reactive current reference instruction 、 、 Is multiplied by the dynamic limiting coefficient , the final reactive current reference instruction 、 、 Is obtained; and the active current reference instruction 、 、 , 、 、 ; And then subtract three-phase current feedback 、 、 , the current deviation obtained is three independent proportional resonant regulators input signal, whose output is the respective closed-loop output of the three-phase current loop 、 、 , i.e. the fundamental current control voltage, wherein is a proportional gain, is a resonance gain, is a resonance bandwidth, is a complex frequency variable, is a resonance frequency; a feedforward unit phasor of the three-phase grid voltage 、 、 is multiplied by a proportional factor to obtain a normalized grid voltage feedforward phasor, wherein is 0.75; after superimposing the fundamental current control voltage with the normalized feedforward phasor of the three-phase grid voltage and the zero-sequence voltage injection component a final modulation wave signal 、 、 is obtained;

[0107] In the modulation wave instruction calculation method, the meanings of some variables are as follows:

[0108] : PI regulator transfer function of the three-phase DC voltage average value;

[0109] : quasi-PR regulator transfer function.

[0110] The above embodiments are implemented on the premise of the technical solution of the present application, and detailed implementation manners and specific operation processes are given, 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 negative sequence voltage compensation control method for a network configuration type STATCOM, characterized by, Comprise: (1) Positive sequence voltage phasor calculation: using the positive and negative sequence component method based on second-order generalized integrator, the grid voltage is decomposed, so as to obtain the positive sequence voltage and negative sequence voltage phasor; (2) Voltage feedforward unit phasor calculation: using second-order generalized integrator for single-phase grid voltage, two-phase orthogonal signals are generated, so as to calculate the unit phasor of three-phase grid feedforward voltage, and high-order harmonics can be filtered out; (3) Bridge arm current reference instruction unit phasor calculation: using second-order generalized integrator for STATCOM current reference instruction, two-phase orthogonal signals are generated, so as to calculate the unit phasor of current reference instruction, which is used for optimal dynamic adjustment of active power deviation when zero sequence voltage injection; (4) Reactive voltage control: the amplitude of virtual internal electromotive force is obtained through the reactive voltage droop control link, the integral and output of PI regulator are increased in amplitude, and the integral term is cleared during short-circuit fault; (5) Bridge arm positive sequence reactive current instruction calculation: the virtual internal electromotive force uses the positive sequence phase of grid voltage, and the positive sequence current instruction is obtained by subtracting the grid positive sequence voltage; (6) Bridge arm negative sequence reactive current instruction calculation: the target value of negative sequence voltage is set to 0, and the negative sequence current instruction is obtained by subtracting the grid negative sequence voltage, and a negative sequence current instruction adjustment coefficient is added; (7) Bridge arm current reference instruction amplitude limiting logic: ensure that the maximum current reference instruction is always less than the maximum bearing current, the input signal of current reference instruction amplitude limiting logic is the total current reference instruction, and only the reactive current is dynamically limited, the active current is used for DC voltage balancing control and is not limited by amplitude limiting; The bridge arm current reference instruction limiting logic specifically comprises: a bridge arm positive sequence reactive current reference instruction , , and a bridge arm negative sequence reactive current reference instruction , , are added to obtain a total three-phase bridge arm reactive current reference instruction , , ; after the three-phase bridge arm reactive current reference instruction values are added and then divided by 3, a zero sequence component is obtained; the bridge arm reactive current reference instruction values are respectively subtracted by the zero sequence component to obtain , , ; then, after passing through a second-order low-pass filter , a direct current component , , is obtained; in order to isolate the direct current component in the current reference instruction value, , , are respectively subtracted by the direct current component to obtain bridge arm unclamped reactive current reference instructions , , ; wherein, is a filter passband gain; is a transfer function cut-off frequency; is a filter damping coefficient. Bridge arm unclamped reactive current reference instruction , , Divided by the peak value of the bridge arm current rating , and the unit value is obtained, and the current instruction after the unit is subjected to CLARK transformation to convert the three-phase stationary coordinate system to the two-phase stationary coordinate system to obtain orthogonal alternating signals and ; further, the two-phase stationary coordinate system is transformed to the two-phase rotating orthogonal coordinate system, i.e., the dq coordinate system, and the angle adopted in the coordinate transformation process is the A-phase positive sequence voltage angle, to obtain orthogonal direct current signals and ; through square and square root calculation, the amplitude of the signal can be obtained; Three-phase bridge arm active current reference instruction 、 、 , respectively through the second-order generalized integrator and , both get two-way alternating current signal; then two-phase static coordinate system is transformed to two-phase rotating orthogonal coordinate system, namely dq coordinate system, the angle used in the coordinate transformation process is the unit phasor of A, B, C three-phase voltage feedforward, get orthogonal DC signal 、 , 、 and 、 ; square root after square sum, get the peak value of three-phase active current reference instruction 、 、 ; By solving the one-dimensional quadratic equation of the reactive current limiting coefficient in real time, the reference instruction value is ensured to be within the maximum design value of the short-time overcurrent, and the active current instruction is preferentially ensured not to be limited, for controlling the DC voltage balance, while the reactive current is limited, and the final three-phase bridge arm current unified limiting coefficient is obtained Take , , The minimum value among the three (8) Zero sequence voltage injection control: the zero sequence voltage injection uses the average of each phase DC voltage and the average deviation of total DC voltage, and the PI regulator produces active power adjustment; (9) Modulation wave instruction calculation: the difference between each phase current reference instruction and current feedback is obtained through three-phase independent quasi-proportional resonant regulator, and the control voltage of each phase fundamental current is obtained, and the final modulation signal is generated after superimposing the zero sequence voltage and grid voltage feedforward.

2. The negative sequence voltage compensation control method of a network-constructed STATCOM according to claim 1, characterized by, The specific calculation of the voltage feedforward unit phasor includes: the grid voltage of phase A divided by the peak value of the rated phase voltage to obtain the per-unit value of the grid voltage of phase A ; through a second-order generalized integrator and to obtain the in-phase signal and the quadrature signal , take the square root after the sum of squares to obtain the peak value of the two quadrature signals ; divide and by the peak value respectively, and then the feedforward phasor of the grid voltage of phase A and the phasor with a 90° phase lag can be obtained; the calculation methods of the voltage feedforward unit phasors of phases B and C are the same as that of phase A; where, k is the damping ratio, is the center frequency, and s is the complex frequency variable.

3. The negative sequence voltage compensation control method of a network configuration type STATCOM according to claim 2, characterized by, The bridge arm current reference instruction unit phasor calculation specifically comprises: bridge arm current reference instruction , through a second-order generalized integrator and obtaining in-phase signal and quadrature signal , square and then take the square root to obtain the peak value of the two-way quadrature signal ; Divide the peak value , that is, the unit phasor of the A-phase bridge arm current reference instruction ; the B-phase and C-phase bridge arm current reference instruction unit phasor calculation method is consistent with that of the A-phase.

4. The negative sequence voltage compensation control method of a network- forming 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 is subtracted to obtain the voltage deviation of the two, which is divided by the slope to obtain the corresponding reactive reference value , which is further subtracted from the reactive feedback value , and is adjusted through a PI regulator 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 the amplitude limit of the final output of the PI regulator is also independently set, wherein, is the proportional coefficient of the regulator, is the integral coefficient of the regulator, is a transfer function complex frequency operator; the deviation of the virtual internal electromotive force is added to the virtual internal electromotive force reference value to obtain the virtual internal electromotive force reference value ; The delayed virtual internal electromotive force reference value is generated through a time delay element , wherein the time constant in the time delay element is 40 ms, and during the transient fault, the virtual internal electromotive force reference value is equal to , i.e. the value before the short-circuit fault occurs; at the same time, the integral value in the PI regulator is cleaned up to avoid saturation due to continuous accumulation of errors.

5. The negative sequence voltage compensation control method of a network-form STATCOM according to claim 4, characterized by, The calculation of the positive sequence reactive current command of the bridge arm specifically includes: 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 and the positive sequence voltage component are then multiplied. , , After subtracting, multiply the voltage deviation by the reciprocal of the virtual impedance. Obtain the positive sequence current reference command value , , ,in, For virtual inductance, This is a virtual resistor.

6. The negative sequence voltage compensation control method of a network-form STATCOM according to claim 5, characterized by, The calculation of the negative sequence reactive current command for the bridge arm 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 reference command value of the negative sequence reactive current of the bridge arm. , , 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 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. ; and thus 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, denoted as Thus, the negative sequence current that can be adjusted by the distribution ratio 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 negative sequence current reference command of the multiple is denoted as That is , , .

7. The negative sequence voltage compensation control method of a network-form 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 functional quantities and average values ​​of the three-phase valve group are obtained. deviation , , After passing through three independent PI controllers, their respective outputs are obtained. , , Furthermore, it is related to the current reference command phasor. , , Multiplying them and adding them together gives the injected zero-sequence voltage component. It is used to regulate the balance of active energy among the three phases.

8. The negative sequence voltage compensation control method of a network-form STATCOM according to claim 7, characterized by, The modulation wave command calculation specifically includes: the average DC voltage of the three-phase valve group. This reflects the overall level of DC voltage, and the result is subtracted from the target value of 1.0 and then passed through a 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 reactive current reference command is obtained. , , ; and active current reference command , , Add them together to obtain the total current reference command. , , ; and then with 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, The resonant frequency; the feedforward unit phasor of the three-phase grid voltage. , , With proportionality coefficient Multiplying these yields the per-unit grid voltage feedforward phasor, where... The value is 0.75–0.85; the feedforward phasor of the fundamental current control voltage and the per-unit three-phase grid voltage, as well as the zero-sequence voltage injection component, are used. After superposition, the final modulated wave signal is obtained. , , .

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