Network construction type STATCOM topological structure with super capacitor and control method thereof

Abstract

The invention relates to the technical field of power electronics, in particular to a network construction type STATCOM topological structure with a super-capacitor and a control method thereof, the topological structure is a star-shaped chain network construction type STATCOM system with a super-capacitor module power unit, the power unit comprises a super-capacitor module and an H-bridge module, and the super-capacitor module is connected with the H-bridge module in parallel; the super-capacitance module is formed by cascading three sub-modules, and each sub-module comprises a super-capacitor, a filter inductor and a DCDC circuit; the control method comprises the steps of voltage feed-forward unit phasor calculation, reactive voltage control and virtual internal potential angle calculation, virtual impedance amplitude limiting logic, bridge arm current reference instruction calculation and modulation wave instruction calculation. According to the invention, the applicability of the super capacitor module is enhanced, the design cost is saved, mutual interference between the frequency modulation characteristic and the inertia damping characteristic is avoided, the active power steady state control precision is improved, and the product safety is improved.

Description

Technical Field

[0001] This invention relates to the field of power electronics technology, and in particular to a STATCOM topology with supercapacitor and its control method. Background Technology

[0002] STATCOMs with supercapacitors possess inertia support capabilities, enabling rapid grid voltage recovery during short-circuit faults. They offer advantages such as high power density, fast charging and discharging speeds, and strong overload capacity, making them a crucial component in supporting the construction of new power systems and ensuring their operational reliability. Supercapacitors, with their low-voltage, high-current characteristics, are suitable for short-term, high-power output applications. However, due to considerations of product design costs and standardization, supercapacitor modules typically have lower voltage ratings, limiting their applicability and making them less compatible with high-voltage power modules. In grid-connected STATCOMs with energy storage components, the frequency regulation characteristics and inertia damping characteristics interact in the active frequency control loop of traditional virtual synchronous generators (VSGs), requiring the design of a reasonable, simple, effective, and easily implementable control strategy. During transient faults, the arm current reference command is large, necessitating the design of reasonable limiting logic to ensure device safety. To address these issues, this invention proposes a grid-connected STATCOM topology with supercapacitors and its control method. Summary of the Invention

[0003] This invention provides a supercapacitor-based STATCOM topology and its control method. The DC-DC circuit in the supercapacitor module adopts a cascaded control method, which enhances the applicability of the supercapacitor module and can be applied to the design of power unit modules with higher voltage levels, saving design costs. The active power frequency control method is improved to avoid mutual interference between frequency modulation characteristics and inertia damping characteristics. The steady-state control accuracy of active power is improved to avoid the influence of high-frequency noise caused by analog sampling and reduce steady-state error. The method is simple, effective, and highly implementable. By using virtual impedance limiting logic and dynamically updating the gain coefficient and time constant of the first-order inertial element, the transient overcurrent problem of the device is limited, thus improving the safety of the product.

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

[0005] A supercapacitor-equipped STATCOM topology is a star-chain STATCOM system. The power units in the star-chain STATCOM system include supercapacitor modules and H-bridge modules, which are connected in parallel.

[0006] The supercapacitor module consists of three cascaded sub-modules. Each sub-module includes a supercapacitor, a filter inductor, and a DC-DC circuit. The DC-DC circuit is composed of two sets of IGBT anti-parallel diodes in a half-bridge structure. One set of IGBT anti-parallel diodes is then connected in parallel with a series circuit of the filter inductor and the supercapacitor, and then connected in series with another set of IGBT anti-parallel diodes.

[0007] A control method for a STATCOM topology with overcapacity includes:

[0008] (1) 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] (2) Calculation of reactive voltage control and active frequency control of virtual synchronous machine VSG: The amplitude of virtual internal electromotive force is obtained through reactive voltage droop control loop. Limits are added to the integral and output of PI regulator respectively. At the same time, the integral term is cleared to zero during short circuit fault. The phase angle of virtual internal electromotive force is obtained through active frequency control loop.

[0010] (3) Calculation of bridge arm current reference command: Subtract the phasor of the grid voltage and the virtual internal electromotive force, and apply it to the first-order inertial element to obtain the bridge arm current reference command.

[0011] (4) Arm current reference command limiting logic: The virtual impedance limiting logic obtains the voltage deviation by the difference between the three-phase grid voltage and the virtual internal electromotive force, divides it by the maximum limit value of the arm current, and obtains the equivalent impedance of the STATCOM three-phase arm. By selecting the maximum value and dividing it by the rated equivalent impedance, the dynamic limiting coefficient of the equivalent impedance is obtained, thereby changing the time constant and gain coefficient of the first-order inertial element to ensure that the maximum arm current reference command is always less than the maximum withstand current.

[0012] (5) H-bridge module modulation wave command calculation: The difference between the reference command of each phase arm current and the feedback of the arm current 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 superimposed with the grid voltage feedforward, the final modulation signal is generated.

[0013] (6) Calculation of modulation wave command for supercapacitor module: The output of AC side voltage control loop of DC-DC circuit in supercapacitor module and active current command of STATCOM are superimposed and subtracted from AC side current of DC-DC circuit in supercapacitor module. The current deviation is superimposed with the compensation amount of balance control output of supercapacitor sub-module through PI regulator to generate the final modulation signal of each sub-module of supercapacitor.

[0014] Furthermore, the voltage feedforward unit phasor calculation specifically includes: Phase A grid voltage. Divide by the rated phase voltage 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.

[0015] Furthermore, the virtual synchronous machine (VSG) reactive voltage control and active frequency control specifically include: 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; dividing it by the slope gives the voltage deviation between the two. 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 can be obtained. Among them, the limiting of the integral element in the PI controller is set independently, and the final output limiting of the PI controller is also set independently; the deviation of the virtual internal electromotive force. Compared with the virtual internal electromotive force reference value Adding them together, we obtain the final virtual internal electromotive force reference value. ,in, The typical value is 1.0; Through the delay process ,generate Among them, the delay phase The time constant in The virtual internal electromotive force reference value is 40ms during the transient fault period. equal This refers to the value before the short-circuit fault occurred; at the same time, the integral value in the PI controller is cleared to prevent the error from accumulating and saturating.

[0016] Through the three-phase power grid voltage , , and three-phase power grid current , , Calculate the active power of the power grid. Subtracting this from the target value of 0 yields the deviation in active power. The traditional virtual synchronizer VSG control outer loop adopts Due to the damping coefficient D, the primary frequency modulation and inertia damping are coupled. The VSG control algorithm was improved by using an integral element with virtual rotational inertia, the corresponding time constant of which is denoted as... Increased the active power deviation of the power grid. The feedforward element has a feedforward coefficient of 1. A first-order high-pass filter is used. The frequency deviation generated by the outer loop is controlled by a modified virtual synchronizer, replacing the damping coefficient D. After being added to 1.0, the frequency is limited by a limiter to obtain the per-unit frequency value. With the rated angular frequency By multiplying and further integrating, the phase angle of the STATCOM virtual internal potential can be obtained. The virtual internal electromotive force reference value As the d-axis component of the dq coordinate system, and 0 as the q-axis component of the dq coordinate system, the phase angle used for the coordinate transformation is the phase angle of the STATCOM virtual internal potential. After the inverse Park transformation, the phasor of the virtual internal electromotive force is obtained. , , .

[0017] Furthermore, the calculation of the bridge arm current reference command specifically includes: Phase A grid voltage. With virtual internal electromotive force phasor Subtracting the two yields the voltage deviation, which then acts on the first-order inertial element. The reference command for the A-phase bridge arm current is obtained. Then, through a second-order low-pass filter Then, the DC component of the A-phase bridge arm current reference command is obtained. ; Set the A-phase bridge arm current reference command Subtract DC component This yields the A-phase bridge arm current reference command that does not include a DC component. The calculation method for the reference current of phase B and phase C bridge arms is the same as that of phase A.

[0018] Furthermore, the virtual impedance limiting logic specifically includes: Phase A grid voltage With virtual internal electromotive force phasor The difference is obtained by using 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. That is, the peak value of the voltage deviation; the peak value of the voltage deviation Divide by the peak value of the phase voltage rating Then, its per-unit value is obtained, and then divided by the short-time overcurrent factor. The per-unit value of the equivalent impedance of phase A is obtained. The calculation method for the equivalent impedance of phases B and C is the same as that of phase A, denoted as... , ;

[0019] This is the per-unit value of the inductance in the STATCOM equivalent impedance, typically 0.1. This represents the per-unit value of the resistance in the STATCOM equivalent impedance, typically 0.05. and Taking the square root of the sum of squares gives the per-unit value of the equivalent impedance. Select the per-unit value of the three-phase equivalent impedance. , , The maximum value in the range, divided by the per-unit value of the equivalent impedance. Subtract 1.0, then add 1.0 after passing through the limiter to obtain the limiting factor of the equivalent impedance. The value range of the limiter is 0 to 100;

[0020] Peak value of phase voltage rating Divide by the peak value of the phase current rating The rated value of the equivalent impedance is obtained. ;

[0021] Equivalent impedance rating Per-unit value of resistance in equivalent impedance Multiplying them gives the nominal value of the resistance in the equivalent impedance. The limiting factor of the equivalent impedance Multiplying them together gives the nominal value of the resistor after limiting. ; 1.0 divided by the nominal value of the resistor after limiting A first-order inertial element is obtained. Gain in The rated value of the equivalent impedance Per-unit value of inductance in equivalent impedance Multiply, then divide by the rated angular frequency The named value of the inductance in the equivalent impedance is obtained. The limiting factor of the equivalent impedance Multiplying them together gives the nominal value of the inductor after limiting. The inductor after limiting has a nominal value. The resistor value after division by the limiter is a nominal value. A first-order inertial element is obtained. The time constant in .

[0022] Furthermore, the H-bridge module modulation wave command calculation specifically includes: referencing the three-phase bridge arm currents that do not contain a DC component with the command. , , 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. , , Phasor and proportionality coefficient Multiplying these yields the per-unit grid voltage feedforward phasor, where... The value range is 0.75 to 0.85; by superimposing the fundamental current control voltage with the feedforward phasor of the per-unit three-phase grid voltage, the final modulation wave signal of the H-bridge module in the power unit is obtained. , , .

[0023] Furthermore, the calculation of the modulation wave command in the supercapacitor module specifically includes: The supercapacitor module employs three cascaded sub-modules, each sub-module comprising a supercapacitor, a filter inductor, and a DC-DC circuit. The DC-DC circuit consists of two sets of IGBT anti-parallel diodes, forming a half-bridge structure. The supercapacitors within the three sub-modules are denoted as... , , The voltage across the supercapacitor is denoted as , , The filter inductor is denoted as , , The voltage of the three sub-modules in the overcapacity module , , After adding them together, divide by 3 to obtain the average value of the submodule voltage, denoted as . Average voltage of submodule The voltage difference between the first submodule of the overcapacitance module and the voltage of the first submodule is used to obtain the voltage compensation amount after passing through a PI regulator. Average voltage of submodule The voltage difference between the second submodule of the overcapacitance module and the voltage of the second submodule is used to obtain the voltage compensation amount after passing through a PI regulator. Average voltage of submodule The voltage difference between the third submodule of the overcapacitance module and the voltage of the third submodule is used to obtain the voltage compensation amount after passing through a PI regulator. Port voltage feedback value after cascading DC-DC circuits Through bandpass filter Filter out the second harmonic component in the voltage, and then use the voltage feedback value. Subtracting the second harmonic component yields the filtered voltage feedback value. The target value of the port voltage after cascading the DC-DC circuit is denoted as . , and the filtered voltage feedback value Subtracting the two values ​​and passing them through a PI controller yields the active current compensation. With STATCOM overall active current command The values ​​are superimposed and then combined with the AC side current feedback value of the DC-DC circuit. Subtracting the two values ​​yields the deviation of the active current, which, after passing through a PI regulator, becomes the modulation signal for the overcapacitor module. ; Modulation signal of the overcapacitive module Voltage compensation amount of the first sub-module of the overcapacitance module By superimposing the signals, the final modulation signal of the first sub-module of the supercapacitive module is obtained. ; Modulation signal of the overcapacitive module Voltage compensation amount with the second sub-module of the overcapacitance module By superposition, the final modulation signal of the second submodule of the supercapacitive module is obtained. ; Modulation signal of the overcapacitive module Voltage compensation amount with the third sub-module of the overcapacitance module By superposition, the final modulation signal of the third submodule of the supercapacitive module is obtained. .

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

[0025] 1) This invention designs a control method for cascading DC-DC circuits, which enhances the applicability of supercapacitor modules and can be applied to the design of power unit modules with higher voltage levels, saving design costs;

[0026] 2) This invention designs an active power frequency control method that avoids mutual interference between frequency modulation characteristics and inertia damping characteristics. It improves the steady-state control accuracy of active power, avoids the influence of high-frequency noise caused by analog sampling, and reduces steady-state error. This method is simple, effective, and highly feasible.

[0027] 3) This invention designs a virtual impedance limiting logic, which limits the transient overcurrent of the device by dynamically updating the gain coefficient and time constant of the first-order inertial element, thus ensuring the safety of the product. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the star-shaped chain network STATCOM system structure described in this invention.

[0029] Figure 2 This is a schematic diagram of the structure of the supercapacitor described in this invention.

[0030] Figure 3 This is a schematic diagram of the voltage feedforward unit phasor calculation structure described in this invention;

[0031] Figure 4 This is a schematic diagram of the reactive voltage control and active frequency control structure of the virtual synchronous machine (VSG) described in this invention;

[0032] Figure 5 This is a schematic diagram of the bridge arm current reference command calculation structure described in this invention;

[0033] Figure 6 This is a schematic diagram of the virtual impedance limiting logic structure described in this invention;

[0034] Figure 7 This is a schematic diagram of the modulation wave command calculation structure of the H-bridge module described in this invention;

[0035] Figure 8 This is a schematic diagram of the supercapacitive module modulation wave command calculation structure described in this invention. Detailed Implementation

[0036] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings:

[0037] See Figure 1 This is a schematic diagram of the system described in this invention. This invention provides a supercapacitive STATCOM topology, which is a star-chain STATCOM system, see [link / details]. Figure 2The power unit in the star-chain network STATCOM system includes a supercapacitor module and an H-bridge module, with the supercapacitor module connected in parallel with the H-bridge module; the supercapacitor module is a supercapacitor module.

[0038] The supercapacitor module consists of three cascaded sub-modules. Each sub-module includes a supercapacitor, a filter inductor, and a DC-DC circuit. The DC-DC circuit is composed of two sets of IGBT anti-parallel diodes in a half-bridge structure. One set of IGBT anti-parallel diodes is then connected in parallel to a series circuit of the filter inductor and the supercapacitor, and then connected in series to another set of IGBT anti-parallel diodes. In addition, a series circuit of a switch and a resistor is connected in parallel to each supercapacitor for energy dissipation.

[0039] A control method for a STATCOM topology with supercapacitor includes: voltage feedforward unit phasor calculation, reactive voltage control and virtual internal potential angle calculation, virtual impedance limiting logic, arm current reference command calculation, and modulation wave command calculation.

[0040] (1) 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 unit phasor of three-phase grid voltage and filtering out high-order harmonics;

[0041] See Figure 3 Phase A grid voltage Divide by the rated phase voltage 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.

[0042] The meanings of some variables in this control method are as follows:

[0043] : The transfer function of the second-order generalized integrator SOGI;

[0044] : The transfer function of the second-order generalized integrator SOGI.

[0045] (2) Virtual Synchronous Machine (VSG) reactive voltage control and active frequency control: The deviation of the virtual internal electromotive force is obtained through the reactive voltage droop control loop, which increases the limit on the integral and output of the PI regulator respectively. At the same time, the integral term is cleared during short circuit faults.

[0046] See Figure 4 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; dividing it by the slope gives the voltage deviation between the two. 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 can be obtained. Among them, the limiting of the integral element in the PI controller is set independently, and the final output limiting of the PI controller is also set independently; the deviation of the virtual internal electromotive force. Compared with the virtual internal electromotive force reference value Adding them together, we obtain the final virtual internal electromotive force reference value. ,in, The typical value is 1.0; Through the delay phase ,generate Among them, the delay phase The time constant in The virtual internal electromotive force reference value is 40ms during the transient fault period. equal This refers to the value before the short-circuit fault occurred; at the same time, the integral value in the PI controller is cleared to prevent the error from accumulating and saturating.

[0047] Through the three-phase power grid voltage , , and three-phase power grid current , , The active power of the power grid can be calculated. Subtracting this from the target value of 0 yields the deviation in active power. Traditional Virtual Synchronizer (VSG) control outer loop adopts Due to the damping coefficient D, the primary frequency modulation and inertia damping are coupled. The VSG control algorithm was improved by using an integral element with virtual rotational inertia, the corresponding time constant of which is denoted as... Increased the active power deviation of the power grid. The feedforward element has a feedforward coefficient of 1. To avoid mutual interference between frequency modulation characteristics and inertia damping characteristics, a first-order high-pass filter is used. Replacing the damping coefficient D improves the system's transient stability and simultaneously enhances the steady-state control accuracy of active power, avoiding the influence of high-frequency noise caused by analog sampling and reducing steady-state error. This method is compatible with... The process is simple, effective, and highly implementable; the frequency deviation generated by the outer loop is controlled by the improved virtual synchronizer. After being added to 1.0, the frequency is limited by a limiter to obtain the per-unit frequency value. With the rated angular frequency By multiplying and further integrating, the phase angle of the STATCOM virtual internal potential can be obtained. The virtual internal electromotive force reference value As the d-axis component of the dq coordinate system, and 0 as the q-axis component of the dq coordinate system, the phase angle used for the coordinate transformation is the phase angle of the STATCOM virtual internal potential. After the inverse Park transformation, the phasor of the virtual internal electromotive force is obtained. , , ;

[0048] The inverse Park transform formula used in this section is:

[0049] ;

[0050] The meanings of the variables in this section are as follows:

[0051] Before transformation Axial components;

[0052] : Indicates the state before transformation Axial components;

[0053] The A-axis components in the transformed three-phase stationary coordinate system:

[0054] B-axis component in the transformed three-phase stationary coordinate system:

[0055] C-axis components in the transformed three-phase stationary coordinate system:

[0056] : Phase angle of the coordinate transformation signal.

[0057] (3) Calculation of bridge arm current reference command: Subtract the phasor of the grid voltage and the virtual internal electromotive force, and apply it to the first-order inertial element to obtain the bridge arm current reference command.

[0058] See Figure 5 Phase A grid voltage With virtual internal electromotive force phasor Subtracting the two yields the voltage deviation, which then acts on the first-order inertial element. The reference command for the A-phase bridge arm current is obtained. Then, through a second-order low-pass filter Then, the DC component of the A-phase bridge arm current reference command is obtained. ; Set the A-phase bridge arm current reference command Subtract DC component This yields the A-phase bridge arm current reference command that does not include a DC component. The calculation method for the reference current of phase B and phase C bridge arms is the same as that of phase A.

[0059] The transfer function of the second-order low-pass filter (LPF) used is as follows:

[0060] ;

[0061] The meanings of the variables in this section are as follows:

[0062] : Complex frequency operator of transfer function;

[0063] Filter passband gain;

[0064] : Transfer function cutoff frequency;

[0065] : Filter damping coefficient;

[0066] The transfer function of the first-order inertial element used is: ;

[0067] The meanings of the variables in this section are as follows:

[0068] Gain coefficient;

[0069] Time constant.

[0070] (4) Virtual impedance limiting logic: The voltage deviation is obtained by the difference between the three-phase grid voltage and the virtual internal electromotive force. The equivalent impedance of the three-phase bridge arm is obtained by dividing it by the maximum limit value of the bridge arm current. The dynamic limiting coefficient of the equivalent impedance is obtained by selecting the maximum value and dividing it by the rated equivalent impedance. Then, the time constant and gain coefficient of the first-order inertial element are changed to ensure that the maximum bridge arm current reference command is always less than the maximum withstand current.

[0071] See Figure 6 Phase A grid voltage With virtual internal electromotive force phasor The difference is obtained by using 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. That is, the peak value of the voltage deviation; the peak value of the voltage deviation Divide by the peak value of the phase voltage rating Then, its per-unit value is obtained, and then divided by the short-time overcurrent factor. The per-unit value of the equivalent impedance of phase A is obtained. The calculation method for the equivalent impedance of phases B and C is the same as that of phase A, denoted as... , ;

[0072] This is the per-unit value of the inductance in the STATCOM equivalent impedance, typically 0.1. This represents the per-unit value of the resistance in the STATCOM equivalent impedance, typically 0.05. and Taking the square root of the sum of squares gives the per-unit value of the equivalent impedance. Select the per-unit value of the three-phase equivalent impedance. , , The maximum value in the range, divided by the per-unit value of the equivalent impedance. Subtract 1.0, then add 1.0 after passing through the limiter to obtain the limiting factor of the equivalent impedance. The value range of the limiter is 0 to 100;

[0073] Peak value of phase voltage rating Divide by the peak value of the phase current rating The rated value of the equivalent impedance is obtained. ;

[0074] Equivalent impedance rating Per-unit value of resistance in equivalent impedance Multiplying them gives the nominal value of the resistance in the equivalent impedance. The limiting factor of the equivalent impedance Multiplying them together gives the nominal value of the resistor after limiting. ; 1.0 divided by the nominal value of the resistor after limiting A first-order inertial element is obtained. Gain in The rated value of the equivalent impedance Per-unit value of inductance in equivalent impedance Multiply, then divide by the rated angular frequency The named value of the inductance in the equivalent impedance is obtained. The limiting factor of the equivalent impedance Multiplying them together gives the nominal value of the inductor after limiting. The inductor after limiting has a nominal value. The resistor value after division by the limiter is a nominal value. A first-order inertial element is obtained. The time constant in .

[0075] (5) H-bridge module modulation wave command calculation: The difference between the three-phase bridge arm current reference command without DC component and the three-phase bridge arm current feedback is obtained by passing through the three-phase independent quasi-proportional resonant regulator to obtain the control voltage of the fundamental current of each phase. This voltage is then superimposed with the per-unit grid voltage feedforward phasor to generate the final modulation signal.

[0076] See Figure 7 The three-phase bridge arm current reference command does not include a DC component. , , 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. , , Phasor and proportionality coefficient Multiplying these yields the per-unit grid voltage feedforward phasor, where... The value range is 0.75 to 0.85; by superimposing the fundamental current control voltage with the feedforward phasor of the per-unit three-phase grid voltage, the final modulation wave signal of the H-bridge module in the power unit is obtained. , , ;

[0077] The meanings of some variables in the H-bridge module modulation wave command calculation method are as follows:

[0078] : Quasi-PR regulator transfer function.

[0079] (6) Calculation of modulation wave command for overcapacitor module: The output of the AC side voltage control loop of the DC-DC circuit and the active current command of the STATCOM are superimposed, and then subtracted from the AC side current of the DC-DC circuit. The current deviation obtained is passed through the PI regulator and then superimposed with the compensation amount of the balance control output of the overcapacitor submodule to generate the final modulation signal of each submodule of the overcapacitor;

[0080] See Figure 2 The supercapacitor module employs three cascaded sub-modules. Each sub-module primarily consists of a supercapacitor, a filter inductor, and a DC-DC converter circuit. The DC-DC converter circuit comprises two sets of IGBTs connected in anti-parallel diodes, forming a half-bridge structure. The supercapacitors within the three sub-modules are denoted as follows: , , The voltage across the supercapacitor is denoted as , , The filter inductor is denoted as , , ;

[0081] See Figure 8 The voltage of the three sub-modules of the supercapacitor , , After adding them together, divide by 3 to obtain the average value of the submodule voltage, denoted as . Average voltage of submodule The voltage difference between the first submodule of the overcapacitance module and the voltage of the first submodule is used to obtain the voltage compensation amount after passing through a PI regulator. Average voltage of submodule The voltage difference between the second submodule of the overcapacitance module and the voltage of the second submodule is used to obtain the voltage compensation amount after passing through a PI regulator. Average voltage of submodule The voltage difference between the third submodule of the overcapacitance module and the voltage of the third submodule is used to obtain the voltage compensation amount after passing through a PI regulator. Port voltage feedback value after cascading DC-DC circuits Through bandpass filter Filter out the second harmonic component in the voltage, and then use the voltage feedback value. Subtracting the second harmonic component yields the filtered voltage feedback value. ,in, The damping coefficient is... For complex frequency variables, The resonant frequency is denoted as ; the target value of the port voltage after cascading the DC-DC circuit is denoted as . , and the filtered voltage feedback value Subtracting the two values ​​and passing them through a PI controller yields the active current compensation. With STATCOM overall active current command The values ​​are superimposed and then combined with the AC side current feedback value of the DC-DC circuit. Subtracting the two values ​​yields the deviation of the active current, which, after passing through a PI regulator, becomes the modulation signal for the overcapacitor module. ; Modulation signal of the overcapacitive module Voltage compensation amount of the first sub-module of the overcapacitance module By superimposing the signals, the final modulation signal of the first sub-module of the supercapacitive module is obtained. ; Modulation signal of the overcapacitive module Voltage compensation amount with the second sub-module of the overcapacitance module By superposition, the final modulation signal of the second submodule of the supercapacitive module is obtained. ; Modulation signal of the overcapacitive module Voltage compensation amount with the third sub-module of the overcapacitance module By superposition, the final modulation signal of the third submodule of the supercapacitive module is obtained. .

[0082] The above embodiments are implemented based on the technical solution of the present invention, providing detailed implementation methods and specific operation processes. However, the scope of protection of the present invention is not limited to the above embodiments. Unless otherwise specified, the methods used in the above embodiments are conventional methods.

Claims

1. A STATCOM topology with overcapacity, which is a star-chain STATCOM system, characterized in that, The power unit in the star-chain network STATCOM system includes an overcapacitor module and an H-bridge module, which are connected in parallel. The supercapacitor module consists of three cascaded sub-modules. Each sub-module includes a supercapacitor, a filter inductor, and a DC-DC circuit. The DC-DC circuit is composed of two sets of IGBT anti-parallel diodes in a half-bridge structure. One set of IGBT anti-parallel diodes is then connected in parallel with a series circuit of the filter inductor and the supercapacitor, and then connected in series with another set of IGBT anti-parallel diodes.

2. The control method for a STATCOM topology with supercapacitor as described in claim 1, characterized in that, include: (1) 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. (2) Calculation of reactive voltage control and active frequency control of virtual synchronous machine VSG: The amplitude of virtual internal electromotive force is obtained through reactive voltage droop control loop. Limits are added to the integral and output of PI regulator respectively. At the same time, the integral term is cleared to zero during short circuit fault. The phase angle of virtual internal electromotive force is obtained through active frequency control loop. (3) Calculation of bridge arm current reference command: Subtract the phasor of the grid voltage and the virtual internal electromotive force, and apply it to the first-order inertial element to obtain the bridge arm current reference command. (4) Arm current reference command limiting logic: The virtual impedance limiting logic obtains the voltage deviation by the difference between the three-phase grid voltage and the virtual internal electromotive force, divides it by the maximum limit value of the arm current, and obtains the equivalent impedance of the STATCOM three-phase arm. By selecting the maximum value and dividing it by the rated equivalent impedance, the dynamic limiting coefficient of the equivalent impedance is obtained, thereby changing the time constant and gain coefficient of the first-order inertial element to ensure that the maximum arm current reference command is always less than the maximum withstand current. (5) H-bridge module modulation wave command calculation: The difference between the reference command of each phase arm current and the feedback of the arm current 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 superimposed with the grid voltage feedforward, the final modulation signal is generated. (6) Calculation of modulation wave command for supercapacitor module: The output of AC side voltage control loop of DC-DC circuit in supercapacitor module and active current command of STATCOM are superimposed and subtracted from AC side current of DC-DC circuit in supercapacitor module. The current deviation is superimposed with the compensation amount of balance control output of supercapacitor sub-module through PI regulator to generate the final modulation signal of each sub-module of supercapacitor.

3. The control method for a STATCOM topology with supercapacitor according to claim 2, characterized in that, The voltage feedforward unit phasor calculation specifically includes: Phase A grid voltage. Divide by the rated phase voltage 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.

4. The control method for a STATCOM topology with supercapacitor according to claim 2, characterized in that, The virtual synchronous machine (VSG) reactive voltage control and active frequency control specifically include: 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; dividing it by the slope gives the voltage deviation between the two. 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 can be obtained. Among them, the limiting of the integral element in the PI controller is set independently, and the final output limiting of the PI controller is also set independently; the deviation of the virtual internal electromotive force. Compared with the virtual internal electromotive force reference value Adding them together, we obtain the final virtual internal electromotive force reference value. ,in, The typical value is 1.0; Through the delay phase ,generate Among them, the delay phase The time constant in The virtual internal electromotive force reference value is 40ms during the transient fault period. equal This refers to the value before the short-circuit fault occurred; at the same time, the integral value in the PI controller is cleared to prevent the error from accumulating and saturating. Through the three-phase power grid voltage , , and three-phase power grid current , , Calculate the active power of the power grid. Subtracting this from the target value of 0 yields the deviation in active power. The traditional virtual synchronizer VSG control outer loop adopts Due to the damping coefficient D, the primary frequency modulation and inertia damping are coupled. The VSG control algorithm was improved by using an integral element with virtual rotational inertia, the corresponding time constant of which is denoted as... Increased the active power deviation of the power grid. The feedforward element has a feedforward coefficient of 1. A first-order high-pass filter is used. The frequency deviation generated by the outer loop is controlled by a modified virtual synchronizer, replacing the damping coefficient D. After being added to 1.0, the frequency is limited by a limiter to obtain the per-unit frequency value. With the rated angular frequency By multiplying and further integrating, the phase angle of the STATCOM virtual internal potential can be obtained. The virtual internal electromotive force reference value As the d-axis component of the dq coordinate system, and 0 as the q-axis component of the dq coordinate system, the phase angle used for the coordinate transformation is the phase angle of the STATCOM virtual internal potential. After the inverse Park transformation, the phasor of the virtual internal electromotive force is obtained. , , .

5. A control method for a STATCOM topology with supercapacitor network according to claim 4, characterized in that, The calculation of the bridge arm current reference command specifically includes: Phase A grid voltage. With virtual internal electromotive force phasor Subtracting the two yields the voltage deviation, which then acts on the first-order inertial element. The reference command for the A-phase bridge arm current is obtained. Then, through a second-order low-pass filter Then, the DC component of the A-phase bridge arm current reference command is obtained. ; Set the A-phase bridge arm current reference command Subtract DC component This yields the A-phase bridge arm current reference command that does not include a DC component. The calculation method for the reference current of phase B and phase C bridge arms is the same as that of phase A.

6. The control method for a STATCOM topology with supercapacitor according to claim 5, characterized in that, The virtual impedance limiting logic specifically includes: Phase A grid voltage. With virtual internal electromotive force phasor The difference is obtained by using 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. That is, the peak value of the voltage deviation; the peak value of the voltage deviation Divide by the peak value of the phase voltage rating Then, its per-unit value is obtained, and then divided by the short-time overcurrent factor. The per-unit value of the equivalent impedance of phase A is obtained. The calculation method for the equivalent impedance of phases B and C is the same as that of phase A, denoted as... , ; This is the per-unit value of the inductance in the STATCOM equivalent impedance, typically 0.

1. This represents the per-unit value of the resistance in the STATCOM equivalent impedance, typically 0.

05. and Taking the square root of the sum of squares gives the per-unit value of the equivalent impedance. Select the per-unit value of the three-phase equivalent impedance. , , The maximum value in the range, divided by the per-unit value of the equivalent impedance. Subtract 1.0, then add 1.0 after passing through the limiter to obtain the limiting factor of the equivalent impedance. The value range of the limiter is 0 to 100; Peak value of phase voltage rating Divide by the peak value of the phase current rating The rated value of the equivalent impedance is obtained. ; Equivalent impedance rating Per-unit value of resistance in equivalent impedance Multiplying them gives the nominal value of the resistance in the equivalent impedance. The limiting factor of the equivalent impedance Multiplying them together gives the nominal value of the resistor after limiting. ; 1.0 divided by the nominal value of the resistor after limiting A first-order inertial element is obtained. Gain in The rated value of the equivalent impedance Per-unit value of inductance in equivalent impedance Multiply, then divide by the rated angular frequency The named value of the inductance in the equivalent impedance is obtained. The limiting factor of the equivalent impedance Multiplying them together gives the nominal value of the inductor after limiting. The inductor after limiting has a nominal value. The resistor value after being divided by the limiter is a nominal value. A first-order inertial element is obtained. The time constant in .

7. A control method for a STATCOM topology with supercapacitor network according to claim 6, characterized in that, The H-bridge module modulation command calculation specifically includes: using the three-phase bridge arm current reference command that does not contain a DC component. , , 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. , , Phasor and proportionality coefficient Multiplying these yields the per-unit grid voltage feedforward phasor, where... The value range is 0.75 to 0.85; by superimposing the fundamental current control voltage with the feedforward phasor of the per-unit three-phase grid voltage, the final modulation wave signal of the H-bridge module in the power unit is obtained. , , .

8. A STATCOM topology with supercapacitor and its control method according to claim 7, characterized in that, The supercapacitive module modulation wave command calculation specifically includes: The supercapacitive module employs three cascaded sub-modules. Each sub-module includes a supercapacitor, a filter inductor, and a DC-DC circuit. The DC-DC circuit consists of two sets of IGBT anti-parallel diodes, forming a half-bridge structure. The supercapacitors within the three sub-modules are denoted as... , , The voltage across the supercapacitor is denoted as , , The filter inductor is denoted as , , The voltage of the three sub-modules in the overcapacity module , , After adding them together, divide by 3 to obtain the average value of the submodule voltage, denoted as . Average voltage of submodule The voltage difference between the first submodule of the overcapacitance module and the voltage of the first submodule is used to obtain the voltage compensation amount after passing through a PI regulator. Average voltage of submodule The voltage difference between the second submodule of the overcapacitance module and the voltage of the second submodule is used to obtain the voltage compensation amount after passing through a PI regulator. Average voltage of submodule The voltage difference between the third submodule of the overcapacitance module and the voltage of the third submodule is used to obtain the voltage compensation amount after passing through a PI regulator. Port voltage feedback value after cascading DC-DC circuits Through bandpass filter Filter out the second harmonic component in the voltage, and then use the voltage feedback value. Subtracting the second harmonic component yields the filtered voltage feedback value. The target value of the port voltage after cascading the DC-DC circuit is denoted as . , and the filtered voltage feedback value Subtracting the two values ​​and passing them through a PI controller yields the active current compensation. With STATCOM overall active current command The values ​​are superimposed and then combined with the AC side current feedback value of the DC-DC circuit. Subtracting the two values ​​yields the deviation of the active current, which, after passing through a PI regulator, becomes the modulation signal for the overcapacitor module. ; Modulation signal of the overcapacitive module Voltage compensation amount of the first sub-module of the overcapacitance module By superimposing the signals, the final modulation signal of the first sub-module of the supercapacitive module is obtained. ; Modulation signal of the overcapacitive module Voltage compensation amount with the second sub-module of the overcapacitance module By superposition, the final modulation signal of the second submodule of the supercapacitive module is obtained. ; Modulation signal of the overcapacitive module Voltage compensation amount with the third sub-module of the overcapacitance module By superposition, the final modulation signal of the third submodule of the supercapacitive module is obtained. .

Images