Control method and system for AC / DC access flexible interconnection device

Abstract

The invention discloses a control method and system for an AC / DC access flexible interconnection device. The method comprises the following steps: judging an operation mode of a transformer area; calculating an interconnection voltage difference value and a phase angle difference value; if the voltage difference is smaller than the closed-loop voltage difference threshold value and the phase angle difference threshold value, the flexible interconnection device is switched into an interconnection operation mode; acquiring input and output voltage and current, direct current bus voltage and current and direct current leading-out bus voltage and current of the series-parallel module; converting the three-phase voltage and current measurement value into a voltage and current value under a dq coordinate system; outputting optimized voltage and current values by adopting a PSO (particle swarm optimization) algorithm; calculating a reference voltage current vector and action time, and generating switching signals of each phase; performing error calculation to obtain a voltage and current error signal value; issuing voltage and phase regulation and current regulation instructions, and dynamically regulating voltage and current signals. According to the method, the electric energy quality treatment requirements of the micro-grid in complex dynamic scenes such as high-power pulsating load and distributed power supply power fluctuation can be met.

Description

Technical Field

[0001] The present invention relates to power electronic control technology, and particularly to a control method and system for an AC-DC access flexible interconnection device. Background Art

[0002] With the proposal of the goals of "carbon peak" and "carbon neutrality", vigorously developing microgrid technology is an inevitable choice to address the energy crisis and optimize the energy structure, and also an inevitable requirement to provide safe, reliable, and high-quality power services. Since the microgrid system uses a variety of power conversion devices to achieve energy flow, the control of the microgrid has a certain degree of complexity.

[0003] Currently, the compensation of harmonics, reactive power, unbalanced current, unbalanced voltage, voltage sags and swells, power fluctuations, and load fluctuations are extremely challenging power quality problems in the microgrid. This is because the power quality of the microgrid is not only related to the operating characteristics of distributed power sources, energy storage devices, and various loads inside, but also has an interactive impact with the connected distribution network outside. Therefore, it is crucial to comprehensively manage the power quality problems of the microgrid, which is not only necessary to meet the power supply quality requirements of sensitive loads, but also an important guarantee for the safe and stable operation of the microgrid and better consumption of renewable energy.

[0004] The publication number is CN114142515A, and the name is a flexible interconnection coordination control method and device for a distribution network. The method includes the operation control of the AC port of the flexible interconnection device, the multi-source load control of the AC-DC power grid, and the coordination control of the AC-DC co-construction area; the operation control of the AC port of the flexible interconnection device includes the steady-state control of the AC port and the load transfer control for AC grid faults, and the load transfer control for AC grid faults is preferentially performed; the multi-source load control of the AC-DC power grid is to perform partitioned autonomous control on the AC source load and the DC source load when there is a new type of DC load connected to the DC side, and the new type of DC load includes photovoltaic, energy storage, or charging piles; the coordination control of the AC-DC co-construction area includes the DC voltage coordination control and the converter capacity coordination control.

[0005] The publication number is CN116613726A, and the name is a control method, system, and device for a flexible interconnection device integrated with energy storage, belonging to the field of flexible interconnection equipment for distribution networks. The method includes: 1) using droop control by converters at each port to access the AC bus to participate in voltage and frequency regulation; 2) the battery inside the flexible interconnection device is connected to the common DC bus through a bidirectional buck-boost converter to maintain power / voltage balance; 3) measuring and calculating the state of charge of the energy storage system inside the flexible interconnection device; 4) limiting the maximum power of the primary regulation power of each port converter through the state of charge of the energy storage; 5) switching the control parameters and operating modes of each port converter and the energy storage system through the state of charge of the energy storage.

[0006] Generally, traditional custom power devices (CPDs), such as static var compensators (SVG), active power filters (APF), dynamic voltage restorers (DVR), and unified power quality conditioners (UPQC), are used to mitigate the above-mentioned power quality problems. However, traditional CPDs have gradually been unable to meet the power quality management requirements of microgrids in complex dynamic scenarios such as high-power pulsating loads and distributed power source power fluctuations. As an important part of ensuring the safe and stable operation of microgrids, energy storage devices have opened up a new direction for the application of power quality regulators through combination with CPDs. Summary of the Invention

[0007] Object of the Invention: The object of the present invention is to provide a control method and system for an AC-DC access flexible interconnection device, which can meet the power quality management requirements of microgrids in complex dynamic scenarios such as high-power pulsating loads and distributed power source power fluctuations.

[0008] Technical Solution: A control method for an AC-DC access flexible interconnection device of the present invention includes:

[0009] Judge whether the operation mode of the substation area is split or interconnected;

[0010] If it is in split operation, calculate the interconnected voltage difference and interconnected phase angle difference on both sides of the interconnection switch. When the threshold conditions are met, switch to the interconnected mode;

[0011] In the interconnected mode, obtain the voltages, currents, and powers of the series and parallel modules and the DC bus of the flexible interconnection device;

[0012] Convert the three-phase voltages output from the power supply side and the series transformer into regulated voltage values in the rotating coordinate system, and obtain the compensation current values through calculation;

[0013] Use the PSO algorithm to optimize the regulated voltage values and compensation current values, generate the vectors and action times of the reference voltage and reference current, and output the switch signals;

[0014] According to the error values between the actual state information of the voltage and current in the line and the reference signals, issue voltage regulation, phase regulation, and current adjustment commands.

[0015] Further, when the operation mode of the substation area is split operation, it is also necessary to obtain the states of the outgoing line switches of the standby intervals on both sides of the substation area, the states of the incoming line switch and the outgoing line switch of the AC-DC access flexible interconnection device, and the state of the AC-DC access flexible interconnection device;

[0016] When the outgoing line switches of the standby intervals on both sides of the substation area are in the off state, the incoming line switch and the outgoing line switch of the AC-DC access flexible interconnection device are in the off state, and the AC-DC access flexible interconnection device is in the shutdown state, connect the AC-DC access flexible interconnection device to the outgoing line of the standby interval.

[0017] Furthermore, if it is in split operation, calculate the difference in interconnected voltage and the difference in interconnected phase angle on both sides of the interconnected switch. When the threshold conditions are met, switch to the interconnected mode, including:

[0018] When the operation mode of the transformer substation is split operation, calculate the difference in interconnected voltage and the difference in interconnected phase angle on both sides of the interconnected switch according to the voltage values and phase angle values on both sides of the interconnected switch;

[0019] If the difference in interconnected voltage is less than the closed-loop voltage difference threshold of the flexible interconnection device and the difference in interconnected phase angle is also less than the closed-loop phase angle difference threshold of the flexible interconnection device, then automatically switch the flexible interconnection device to the interconnected operation mode;

[0020] If the difference in interconnected voltage and the difference in interconnected phase angle on both sides of the interconnected switch do not meet the closed-loop voltage difference threshold and phase angle difference threshold of the flexible interconnection device, then send the target voltage value and target phase angle value to the power electronic device through the closed-loop total control device. The closed-loop total control device issues an interconnected control instruction, and the flexible interconnection device enters the interconnected state.

[0021] Furthermore, convert the three-phase voltages output by the power supply side and the series transformer into the regulated voltage value in the rotating coordinate system, and obtain the compensation current value through calculation, including:

[0022] Convert the three-phase voltages u a , u b , u c on the input side of the series transformer from the abc stationary coordinate system to the dq rotating coordinate system. The used expressions are as follows:

[0023]

[0024] where the θ value is obtained by the phase-locked loop PLL module;

[0025] Convert the three-phase voltages u ma , u mb , u mc on the output side of the series transformer from the abc stationary coordinate system to the dq rotating coordinate system. The used expressions are as follows:

[0026]

[0027] The difference between the input-side voltage and the output-side voltage is the regulated voltage value of the series transformer, as shown in the following formula:

[0028] ΔU d =U d -U md

[0029] ΔU q =U q -U mq

[0030] The lateral component ΔU of the regulated voltage value in the dq coordinate system d and the longitudinal component ΔU q are optimized by a PI regulator to obtain the lateral component U dout and the longitudinal component U qout of the output voltage value, as shown in the following formula:

[0031] err ud =ΔU dref -ΔU d +err′ ud

[0032] err uq =ΔU qref -ΔU q +err′ uq

[0033] U dout =K p err d +K i ∫err d dt

[0034] U qout =K p err q +K i ∫err q dt

[0035] where err′ ud is the lateral component of the voltage error signal value feedback by the feedback module, and err′ uq is the longitudinal component of the feedback voltage error signal value.

[0036] Furthermore, the PSO algorithm is used to optimize the regulated voltage value and the compensation current value, generate the vectors and action time of the reference voltage and reference current, and output the switching signal, including:

[0037] The output voltage values U dout , U qout in the dq rotating coordinate system are input into the optimization module, and the particle swarm optimization algorithm is used to output the optimized lateral component and longitudinal component U dref , U qref of the voltage reference value in the dq rotating coordinate system:

[0038] f = PSO(U dout , U qout ).

[0039] Furthermore, the PSO algorithm is used to optimize and adjust the voltage value and compensation current value, generate the vectors and action time of the reference voltage and reference current, and output the switching signal, including:

[0040] Reference voltage vector U ref which is synthesized from the voltage reference values U dref and U qref in the dq rotating coordinate system as follows:

[0041] U ref = U dref + jU qref

[0042] Project the reference voltage vector U ref onto the αβ coordinate system to obtain the rotation angle θ. The sector division in the SVPWM generation module is determined according to the value of θ:

[0043]

[0044] Calculate the action time of the two adjacent basic vectors and the zero vector according to the position of the reference voltage vector U ref in the αβ plane as follows:

[0045]

[0046] where k represents the current sector, T1 and T2 represent the action time, U α and U β represent the projection of the reference voltage vector U ref in the αβ plane, and U dc is the DC bus voltage;

[0047] Generate the switching signals for each phase according to the calculated action time T1 and T2, and allocate the on-off time of each switch to ensure that the total time in each cycle is equal to T s ;

[0048]

[0049] where T0 represents the action time of the zero vector, S a is the switching signal, which means on when S a = 1 and off when S a = 0.

[0050] Furthermore, convert the three-phase voltages output from the power supply side and the series transformer into the regulated voltage values in the rotating coordinate system, and obtain the compensation current value through calculation, including:

[0051] The line current i is decomposed by FFT by the control module to obtain the harmonic current i har and unbalanced current iun and add i har to i un to obtain the current control target value i la :

[0052] i l = i har + i un

[0053] Convert the current control target value i la from the abc stationary coordinate system to the dq rotating coordinate system, and the calculation formula is as follows:

[0054]

[0055] Adopt the power detection method, using the active power P ref and reactive power Q ref in the line as reference values to obtain the transverse component I pref of the current reference value and the longitudinal component I qref in the dq rotating coordinate system.

[0056]

[0057] Similarly, optimize the compensation current value through a PI regulator to obtain the output values of i dout and i qout .

[0058] err id = i dref - i d + err′ id

[0059] err iq = i qref - i q + err′ iq

[0060]

[0061] where err′ id and err′ iq are the current error signal values fed back by the feedback module.

[0062] Furthermore, adopt the PSO algorithm to optimize and adjust the voltage value and compensation current value, generate the vectors and action times of the reference voltage and reference current, and output the switching signal, including:

[0063] The output current values i dout and i qoutThe input optimization module uses the particle swarm optimization algorithm and outputs the transverse component i of the current reference value in the optimized dq rotating coordinate system dref and the longitudinal component i qref :

[0064] f = PSO(i dout , i qout ).

[0065] Furthermore, the PSO algorithm is used to optimize and adjust the voltage value and the compensation current value, generate the vectors and action time of the reference voltage and the reference current, and output the switching signal, including:

[0066] The reference current vector i ref is synthesized from the voltage reference values i dref and i qref in the dq rotating coordinate system:

[0067] i ref = i dref + ji qref

[0068] Project the reference current vector i ref onto the αβ coordinate system to obtain the rotation angle θ. The sector division in the SVPWM generation module is determined according to the value of θ:

[0069]

[0070] According to the position of the reference current vector i ref in the αβ plane, calculate the action time of the two adjacent basic vectors and the zero vector, as follows:

[0071]

[0072] where k represents the current sector;

[0073] Generate the switching signals of each phase according to the calculated action times T1 and T2, and allocate the on-off times of each switch to ensure that the total time in each cycle is equal to T s :

[0074]

[0075] where T0 represents the action time of the zero vector.

[0076] Based on the same inventive concept, a control system of an AC-DC access flexible interconnection device of the present invention includes:

[0077] A judgment module for judging whether the operation mode of the power distribution area is split or interconnected;

[0078] If it is in split operation, the judgment module is further configured to calculate the difference in the interconnected voltage and the difference in the interconnected phase angle on both sides of the interconnected switch, and when the threshold condition is met, switch to the interconnected mode;

[0079] The judgment module is further configured to obtain the voltages, currents, and powers of the series and parallel modules of the flexible interconnection device and the DC bus in the interconnected mode;

[0080] The virtual synchronous control module is configured to convert the three-phase voltages output from the power supply side and the series transformer into regulated voltage values in the rotating coordinate system, and obtain the compensation current values through calculation;

[0081] The optimization module is configured to optimize the regulated voltage and the compensation current by using the PSO algorithm; generate the vectors and action times of the reference voltage and reference current, and output the switching signals;

[0082] The SVPWM generation module is configured to generate the vectors and action times of the reference voltage and reference current, and output the switching signals;

[0083] The feedback module is configured to perform error calculation between the actual state information of the voltage and current in the line and the reference signal to obtain the voltage error signal value and the current error signal value;

[0084] The control module is configured to issue voltage regulation, phase regulation, and current adjustment instructions according to the error values between the actual and reference signals.

[0085] The remarkable effects of the present invention are as follows:

[0086] According to the precise control of the output voltage and current, the stability and response characteristics of the system are enhanced, flexible interconnection between substations can be achieved, and the utilization rate of the distribution transformer capacity in the substation area can be improved. At the same time, the present invention can improve the power supply quality of the voltage and current in the substation area, and ensure the reliability and stability of user power consumption. Description of the Drawings

[0087] Figure 1 is a schematic flow chart of a control method for an AC-DC access flexible interconnection device disclosed in an embodiment of the present invention;

[0088] Figure 2 is a system topology diagram of a parallel module disclosed in an embodiment of the present invention;

[0089] Figure 3 is a system topology diagram of a series module disclosed in an embodiment of the present invention;

[0090] Figure 4 is a control schematic diagram of a control system of an AC-DC access flexible interconnection device for a parallel module disclosed in an embodiment of the present invention;

[0091] Figure 5It is the control schematic diagram of the control system of an AC / DC access flexible interconnection device disclosed in the embodiments of the present invention for series modules. Specific embodiments

[0092] The technical solutions of the present invention will be introduced in detail below in conjunction with the specific embodiments and the accompanying drawings of the specification.

[0093] Embodiment 1

[0094] As Figure 1 、 Figure 4 and Figure 5 shown, a control method for an AC / DC access flexible interconnection device of the present invention includes the following steps:

[0095] S1. Determine whether the operation mode of the substation area is split or interconnected.

[0096] S2. If it is in split operation, calculate the interconnection voltage difference and the interconnection phase angle difference on both sides of the interconnection switch. When the threshold conditions are met, switch to the interconnected mode. The specific steps are as follows:

[0097] S2.1. When the operation mode of the substation area is split operation, calculate the interconnection voltage difference and the phase angle difference according to the voltage values and phase angle values on both sides of the interconnection switch.

[0098] In this step, when the operation mode of the substation area is split operation, it is also necessary to obtain the states of the outgoing line switches of the spare intervals on both sides of the substation area, the states of the incoming line switch and the outgoing line switch of the AC / DC access flexible interconnection device, and the state of the AC / DC access flexible interconnection device.

[0099] When the outgoing line switches of the spare intervals on both sides of the substation area are in the off state, the incoming line switch and the outgoing line switch of the AC / DC access flexible interconnection device are in the off state, and the AC / DC access flexible interconnection device is in the shutdown state, connect the AC / DC access flexible interconnection device to the outgoing line of the spare interval.

[0100] S2.2. If the interconnection voltage difference is less than the closed-loop voltage difference threshold of the flexible interconnection device and the interconnection phase angle difference is also less than the closed-loop phase angle difference threshold of the flexible interconnection device, automatically switch the flexible interconnection device to the interconnected operation mode.

[0101] S2.3. If the interconnection voltage difference and the interconnection phase angle difference on the left and right sides of the interconnection switch QF3 do not meet the closed-loop voltage difference threshold and the phase angle difference threshold of the flexible interconnection device, send the target voltage value and the target phase angle value to the power electronic device through the closed-loop total control device, and the closed-loop total control device sends an interconnection control instruction, and the flexible interconnection device enters the interconnected state.

[0102] If the voltage difference and phase angle difference between the left and right sides of the interconnection switch QF3 meet the closed-loop voltage difference threshold and phase angle difference threshold of the flexible interconnection device, the interconnection control instruction is sent through the closed-loop total control device, and the device enters the interconnection state.

[0103] In this embodiment, the closed-loop voltage difference threshold ΔU of the flexible interconnection device is ≤ 2V, and the phase angle difference threshold Δψ is ≤ 1°.

[0104] S3. In the interconnection mode, obtain the voltages, currents, and powers of the series, parallel modules, and DC bus of the flexible interconnection device. Specifically as follows:

[0105] When the operation mode of the power distribution area is interconnection operation, obtain the input and output voltages and currents of the series module and parallel module in the flexible interconnection device, the DC bus voltage and current, and the DC lead-out bus voltage and current, and calculate the powers of the series module, parallel module, DC bus, and DC lead-out bus.

[0106] In this embodiment, as Figure 2 and Figure 3 shown, when the flexible interconnection device is in the interconnection state, obtain the input voltage u i of the parallel module, the input current i1, the DC bus voltage U dc1 on the parallel module side, the DC bus current i dc1 , the DC bus voltage U dc2 on the series module side, the DC bus current i dc2 , the voltage U dc3 on the DC lead-out bus side, the current i dc3 , the output voltage u r of the series module, and the output current is i2. The voltage on the power supply side is u, the voltage on the output side of the series transformer is u m , and the line current is i.

[0107] S4. Convert the three-phase voltages of the power supply side and the output of the series transformer into the regulated voltage values in the rotating coordinate system, and obtain the compensation current value through calculation. The specific steps are as follows:

[0108] S4.1. Convert the measured values of the three-phase voltages of the power supply side and the output of the series transformer in the flexible interconnection device from the abc stationary coordinate system to the dq rotating coordinate system to generate the voltages in the dq coordinate system; subtract the voltages of the power supply side and the output of the series transformer in the dq coordinate system to obtain the regulated voltage value.

[0109] In this embodiment, both the series and parallel modules adopt the three-phase converter structure with three-phase three-arm bridges. Take S 1n (n = a, b, c) as the switching function of the parallel three-phase converter, and S 2n (n = a, b, c) as the switching function of the series three-phase converter.

[0110] The parallel module can be represented by the following mathematical model:

[0111]

[0112] The series module can be represented by the following mathematical model:

[0113]

[0114] Therefore, the DC side can be represented by the following mathematical model:

[0115]

[0116] Therefore

[0117]

[0118] In this embodiment, the measured values of the three-phase voltages on the power supply side and the output side of the series transformer in the flexible interconnection device are converted from the abc stationary coordinate system to the dq rotating coordinate system to generate the voltages in the dq coordinate system; the voltages on the power supply side and the output side of the series transformer in the dq coordinate system are subtracted to obtain the regulated voltage value, including:

[0119] The three-phase voltages u a 、u b 、u c of the input side of the series transformer are converted from the abc stationary coordinate system to the dq rotating coordinate system, and the used expressions are as follows:

[0120]

[0121] Among them, the θ value is obtained by the phase-locked loop PLL module.

[0122] The three-phase voltages u ma 、u mb 、u mc of the output side of the series transformer are converted from the abc stationary coordinate system to the dq rotating coordinate system, and the used expressions are as follows:

[0123]

[0124] The difference between the input side voltage and the output side voltage is the regulated voltage value of the series transformer, as shown in the following formula:

[0125] ΔU d =U d -U md

[0126] ΔU q =U q -U mq

[0127] Adjust the lateral component ΔU of the regulated voltage value in the dq coordinate system d , and the longitudinal component ΔU q After optimizing with a PI regulator, the lateral component U of the output voltage value is obtained dout , and the longitudinal component U qout , as shown in the following formula:

[0128] err ud =ΔU dref -ΔU d +err′ ud

[0129] err uq =ΔU qref -ΔU q +err′ uq

[0130] U dout =K p err d +K i ∫err d dt

[0131] U qout =K p err q +K i ∫err q dt

[0132] Among them, err′ ud is the lateral component of the voltage error signal value fed back by the feedback module, and err′ uq is the longitudinal component of the feedback voltage error signal value.

[0133] S4.2. Convert the compensation current value obtained by FFT decomposition of the line current measurement value in the flexible interconnection device from the abc stationary coordinate system to the dq rotating coordinate system to generate the compensation current value in the dq coordinate system.

[0134] In this embodiment, converting the compensation current value obtained by FFT decomposition of the line current measurement value in the flexible interconnection device from the abc stationary coordinate system to the dq rotating coordinate system to generate the compensation current value in the dq coordinate system includes:

[0135] The line current i is subjected to FFT decomposition by the control module to obtain the harmonic current i har and the unbalanced current i un , and add i har and i un to obtain the current governance target value i la :

[0136] i l =ihar +i un

[0137] Convert the current control target value i la from the abc stationary coordinate system to the dq rotating coordinate system, and the calculation formula is as follows:

[0138]

[0139] Adopt the power detection method, and use the active power P ref and reactive power Q ref in the line as reference values to obtain the transverse component I pref of the current reference value in the dq rotating coordinate system, and the longitudinal component I qref .

[0140]

[0141] Similarly, optimize the compensation current value through a PI regulator to obtain the output values of i dout and i qout .

[0142] err id = i dref - i d + err′ id

[0143] err iq = i qref - i q + err′ iq

[0144] i dout = K p err id + K i ∫err id dt

[0145] i qout = K p err iq + K i ∫err iq dt

[0146] Among them, err′ id and err′ iq are the current error signal values fed back by the feedback module.

[0147] S5. Optimize and adjust the voltage value and compensation current value by using the PSO algorithm to generate the vectors and action time of the reference voltage and reference current, and output the switching signal. The specific steps are as follows:

[0148] S5.1. Apply the PSO particle swarm optimization algorithm to the regulated voltage value and compensation current value in the dq coordinate system, and output the optimized regulated voltage value and compensation current value.

[0149] In this embodiment, applying the PSO particle swarm optimization algorithm to the regulated voltage value in the dq coordinate system and outputting the optimized regulated voltage value includes:

[0150] Input the output voltage values U dout , U qout in the dq rotating coordinate system into the optimization module, and use the particle swarm optimization algorithm to output the lateral component and longitudinal component U dref , U qref of the voltage reference value in the optimized dq rotating coordinate system:

[0151] f = PSO(U dout , U qout ).

[0152] In this embodiment, applying the PSO particle swarm optimization algorithm to the compensation current value in the dq coordinate system and outputting the optimized compensation current value includes:

[0153] Input the output current values i dout , i qout in the dq rotating coordinate system into the optimization module, and use the particle swarm optimization algorithm to output the lateral component i dref and longitudinal component i qref of the current reference value in the optimized dq rotating coordinate system:

[0154] f = PSO(i dout , i qout ).

[0155] S5.2. Calculate the reference voltage vector according to the optimized regulated voltage value, and further calculate the action time of the reference voltage vector; calculate the reference current vector according to the optimized compensation current value, and further calculate the action time of the reference current vector, and then generate the switching signals of each phase according to the calculated action time.

[0156] In this embodiment, calculating the reference voltage vector according to the optimized regulated voltage value and further calculating the action time of the reference voltage vector includes:

[0157] The reference voltage vector U ref is synthesized from the voltage reference values U dref and U qref in the dq rotating coordinate system:

[0158] U ref = U dref + jU qref

[0159] Project the reference voltage vector U ref onto the αβ coordinate system to obtain the rotation angle θ. The sector division in SVPWM is determined according to the value of θ:

[0160]

[0161] According to the reference voltage vector U ref in the αβ plane, calculate the action times of the two adjacent basic vectors and the zero vector as follows:

[0162]

[0163] where k represents the current sector; T1 and T2 represent the action times, U α , U β represent the projection of the reference voltage vector U ref in the αβ plane, and U dc is the DC bus voltage.

[0164] Generate the switching signals for each phase according to the calculated action times T1 and T2, and allocate the on-off times of each switch to ensure that the total time in each cycle is equal to T s ;

[0165]

[0166] where T0 represents the action time of the zero vector, S a is the switching signal, which means on when S a = 1 and off when S a = 0.

[0167] In this embodiment, calculate the reference current vector according to the optimized compensation current value, and further calculate the action time of the reference current vector, including:

[0168] The reference current vector i ref is synthesized from the voltage reference values i dref and i qref in the dq rotating coordinate system:

[0169] i ref = i dref + ji qref

[0170] Project the reference current vector i ref onto the αβ coordinate system to obtain the rotation angle θ. The sector division in SVPWM is determined according to the value of θ:

[0171]

[0172] According to the reference current vector i ref Based on its position in the αβ plane, calculate the action times of the two adjacent basic vectors and the zero vector as follows:

[0173]

[0174] where k represents the current sector;

[0175] Generate the switching signals for each phase according to the calculated action times T1 and T2, and allocate the on - off times of each switch to ensure that the total time in each period is equal to T s :

[0176]

[0177] where T0 represents the action time of the zero vector.

[0178] S6. Based on the error values between the actual state information of voltage and current in the line and the reference signal, issue voltage regulation, phase regulation, and current adjustment commands. The specific steps are as follows:

[0179] S6.1. According to the voltage U d , U q and the actual state information of current i d , i q , calculate the error with the reference signal to obtain the voltage error signal values err′ ud , err′ uq and the current error signal values err′ id , err′ iq .

[0180] err′ ud =U d -U dref

[0181] err′ uq =U q -U qref

[0182] err′ id =i d -i dref

[0183] err′ iq =i q -i qref

[0184] S6.2. Issue voltage regulation, phase regulation, and current adjustment commands, and dynamically adjust the voltage and current signals according to the voltage error signal values and current error signal values.

[0185] Embodiment 2

[0186] As Figure 4 and 5 shown, a control system of an AC / DC access flexible interconnection device according to the present invention includes:

[0187] A judgment module, configured to judge whether the operation mode of the substation area is split or interconnected;

[0188] If it is in split operation, the judgment module is further configured to calculate the interconnection voltage difference and the interconnection phase angle difference on both sides of the interconnection switch, and when the threshold condition is met, switch to the interconnected mode;

[0189] In the interconnected mode, obtain the voltages, currents, and powers of the series and parallel modules and the DC bus of the flexible interconnection device;

[0190] A virtual synchronous control module (VSCM), configured to convert the three-phase voltages output from the power supply side and the series transformer into regulated voltage values in the rotating coordinate system, and obtain the compensation current values through calculation;

[0191] An optimization module, configured to optimize the regulated voltage and the compensation current by using the PSO algorithm; generate the vectors and action times of the reference voltage and the reference current, and output switch signals.

[0192] An SVPWM generation module, configured to generate the vectors and action times of the reference voltage and the reference current, and output switch signals.

[0193] A feedback module, configured to perform error calculation on the actual state information of the voltage and current in the line with the reference signal to obtain the voltage error signal value and the current error signal value, and feedback them to the control module, so that the controller adjusts the output according to the error signal;

[0194] A control module, configured to issue voltage regulation, phase regulation, and current adjustment instructions according to the error value between the actual and reference signals, and ensure that the control substation area operates to the control target.

[0195] Among them, the virtual synchronous control module (VSCM) is configured to simulate the dynamic behavior of a synchronous generator, generate voltage and current instructions in the dq coordinate system according to the received three-phase voltage and current measurement values, realize the dynamic control of the system, ensure the precise control of the output voltage and current, and enhance the stability and response characteristics of the system.

[0196] In an optional embodiment, the control method of the AC / DC access flexible interconnection device includes: a) determining whether the operation mode of the transformer substation area is split or interconnected; b) if it is in split operation, calculating the interconnected voltage difference and interconnected phase angle difference on both sides of the interconnection switch, and switching to the interconnected mode when the threshold conditions are met; c) in the interconnected mode, obtaining the voltages, currents, and powers of the series and parallel modules of the flexible interconnection device and the DC bus; d) converting the three-phase voltages output by the power supply side and the series transformer into the regulated voltage values in the rotating coordinate system, and obtaining the compensation current values through calculation; e) optimizing the regulated voltage values and compensation current values by using the PSO algorithm, generating the vectors and action times of the reference voltage and reference current, and outputting the switch signals; f) issuing the voltage regulation, phase regulation, and current adjustment commands according to the error values between the actual state information of the voltage and current in the line and the reference signals.

Claims

1. A control method for a flexible interconnection device with AC / DC access, characterized in that, Including: Judging whether the operation mode of the transformer substation area is split or interconnected; If it is in split operation, calculate the interconnected voltage difference and interconnected phase angle difference on both sides of the interconnection switch. When the threshold conditions are met, switch to the interconnected mode; In the interconnected mode, obtain the voltages, currents, and powers of the series and parallel modules of the flexible interconnection device and the DC bus; Convert the three-phase voltages output by the power supply side and the series transformer into the regulated voltage values in the rotating coordinate system, and obtain the compensation current values through calculation; Use the PSO algorithm to optimize the regulated voltage values and compensation current values, generate the vectors and action times of the reference voltage and reference current, and output the switch signals; According to the error values between the actual state information of the voltage and current in the line and the reference signals, issue voltage regulation, phase regulation, and current adjustment instructions.

2. The control method of the AC / DC access flexible interconnection device according to claim 1, characterized in that: When the operation mode of the transformer substation area is split operation, it is also necessary to obtain the states of the outgoing line switches of the standby intervals on both sides of the transformer substation area, the states of the incoming line switches and outgoing line switches of the AC / DC access flexible interconnection device, and the state of the AC / DC access flexible interconnection device; When the outgoing line switches of the standby intervals on both sides of the transformer substation area are in the open state, the incoming line switches and outgoing line switches of the AC / DC access flexible interconnection device are in the open state, and the AC / DC access flexible interconnection device is in the shutdown state, connect the AC / DC access flexible interconnection device to the outgoing line of the standby interval.

3. The control method of the AC / DC access flexible interconnection device according to claim 1, wherein If it is in split operation, calculate the interconnected voltage difference and interconnected phase angle difference on both sides of the interconnection switch. When the threshold conditions are met, switch to the interconnected mode, including: When the operation mode of the transformer substation area is split operation, calculate the interconnected voltage difference and interconnected phase angle difference on both sides of the interconnection switch according to the voltage values and phase angle values on both sides of the interconnection switch; If the interconnected voltage difference is less than the closed-loop voltage difference threshold of the flexible interconnection device and the interconnected phase angle difference is also less than the closed-loop phase angle difference threshold of the flexible interconnection device, automatically switch the flexible interconnection device to the interconnected operation mode; If the interconnected voltage difference and interconnected phase angle difference on both sides of the interconnection switch do not meet the closed-loop voltage difference threshold and phase angle difference threshold of the flexible interconnection device, send the target voltage value and target phase angle value to the power electronic device through the closed-loop total control device, the closed-loop total control device issues the interconnection control instruction, and the flexible interconnection device enters the interconnected state.

4. The control method of the AC / DC access flexible interconnection device according to claim 1, wherein Convert the three-phase voltages output by the power supply side and the series transformer into the regulated voltage values in the rotating coordinate system, and obtain the compensation current values through calculation, including: Transform the three-phase voltages u a 、u b 、u c at the input side of the series transformer from the abc stationary coordinate system to the dq rotating coordinate system. The expressions used are as follows: Among them, the θ value is obtained by the phase-locked loop PLL module; Convert the three-phase voltages u ma 、u mb 、u mc at the output side of the series transformer from the abc stationary coordinate system to the dq rotating coordinate system, and the used expressions are as follows: The difference between the input-side voltage and the output-side voltage is the regulated voltage value of the series transformer, as shown in the following formula: ΔU d = U d - U md ΔU q = U q - U mq Adjust the horizontal component ΔU of the voltage value in the dq coordinate system d and the vertical component ΔU q After optimizing with a PI regulator, the horizontal component U of the output voltage value is obtained dout and the vertical component U qout as shown in the following formula: err ud = ΔU dref -ΔU d + err′ ud err uq = ΔU qref -ΔU q + err′ uq U dout = K p err d + K i ∫ err d dt U qout = K p err q + K i ∫ err q dt Among them, err′ ud is the horizontal component of the voltage error signal value fed back by the feedback module, and err′ uq is the vertical component of the feedback voltage error signal value.

5. The control method of the AC / DC access flexible interconnection device according to claim 4, characterized in that Use the PSO algorithm to optimize the regulated voltage values and compensation current values, generate the vectors and action times of the reference voltage and reference current, and output the switch signals, including: The output voltage value U in the dq rotating coordinate system dout , U qout is input into the optimization module, which adopts the particle swarm optimization algorithm and outputs the transverse and longitudinal components U of the optimized voltage reference value in the dq rotating coordinate system dref , U qref : f = PSO(U dout , U qout ).

6. According to the control method of the AC / DC access flexible interconnection device described in claim 5, characterized in that Use the PSO algorithm to optimize the regulated voltage values and compensation current values, generate the vectors and action times of the reference voltage and reference current, and output the switch signals, including: Reference voltage vector U ref The voltage reference values U dref and U qref in the dq rotating coordinate system are synthesized to obtain: U ref = U dref + jU qref Project the reference voltage vector U ref onto the αβ coordinate system to obtain the rotation angle θ. The sector division in the SVPWM generation module is determined according to the value of θ: According to the reference voltage vector U ref Based on its position in the αβ plane, calculate the action times of the two adjacent basic vectors and the zero vector as follows: where k represents the current sector, T1 and T2 represent the action time, and U α , U β represent the projections of the reference voltage vector U ref in the αβ plane, and U dc is the DC bus voltage; Generate the switching signals for each phase according to the calculated action times T1 and T2, and allocate the on and off times of each switch to ensure that the total time in each period is equal to T s ; Among them, T0 represents the action time of the zero vector, S a is the switching signal. When S a = 1, it means conduction. When S a = 0, it means cut-off.

7. The control method of the AC / DC access flexible interconnection device according to claim 1, wherein Convert the three-phase voltages output by the power supply side and the series transformer into the regulated voltage values in the rotating coordinate system, and obtain the compensation current values through calculation, including: The line current i is decomposed by FFT by the control module to obtain the harmonic current i in the line har and the unbalanced current i un , and add i har and i un to get the current governance target value i la : i l = i har + i un Convert the current control target value i la from the abc stationary coordinate system to the dq rotating coordinate system, and the calculation formula is as follows: Using the power detection method, with the active power P in the line ref and the reactive power Q ref as the reference values, the transverse component I pref of the current reference value in the dq rotating coordinate system and the longitudinal component I qref are obtained; Similarly, the compensation current value is optimized by a PI regulator to obtain the output values of i dout and i qout . err id = i dref - i d + err' id err iq = i qref - i q + err' iq i dout = K p err id + K i ∫ err id dt i qout = K p err iq + K i ∫ err iq dt where err′ id and err′ iq are the current error signal values fed back by the feedback module.

8. The control method of the AC / DC access flexible interconnection device according to claim 7, characterized in that Optimize and adjust the voltage value and compensation current value using the PSO algorithm to generate the vectors and action time of the reference voltage and reference current, and output the switching signal, including: The output current value \(i\) in the dq rotating coordinate system dout and \(i\) qout are input into an optimization module, which adopts the particle swarm optimization algorithm and outputs the lateral component \(i\) dref and the longitudinal component \(i\) qref of the optimized current reference value in the dq rotating coordinate system: f = PSO(i dout , i qout ).

9. The control method of the AC / DC access flexible interconnection device according to claim 8, wherein Optimize and adjust the voltage value and compensation current value using the PSO algorithm to generate the vectors and action time of the reference voltage and reference current, and output the switching signal, including: Reference current vector i ref The voltage reference values i in the dq rotating coordinate system dref and i qref are synthesized to obtain: i ref = i dref + j iqref Project the reference current vector i ref onto the αβ coordinate system to obtain the rotation angle θ. The sector division in the SVPWM generation module is determined according to the value of θ: According to the position of the reference current vector \(i\) ref in the \(\alpha\beta\) plane, calculate the action times of the two adjacent basic vectors and the zero vector as follows: where k represents the current sector; Generate the switching signals for each phase based on the calculated action times T1 and T2, and allocate the on and off times of each switch to ensure that the total time in each period is equal to T s : where T0 represents the action time of the zero vector.

10. A control system for a flexible interconnection device with AC / DC access, characterized in that, Including: A judgment module for judging whether the operation mode of the transformer substation area is split or interconnected; If it is in split operation, the judgment module is also used to calculate the interconnected voltage difference and interconnected phase angle difference on both sides of the interconnected switch, and when the threshold condition is met, it switches to the interconnected mode; The judgment module is also used to obtain the voltages, currents, and powers of the series and parallel modules of the flexible interconnection device and the DC bus under the interconnected mode; A virtual synchronous control module for converting the three-phase voltages output by the power supply side and the series transformer into the regulated voltage value in the rotating coordinate system and obtaining the compensation current value through calculation; An optimization module for optimizing and adjusting the voltage and compensation current using the PSO algorithm; generating the vectors and action time of the reference voltage and reference current, and outputting the switching signal; An SVPWM generation module for generating the vectors and action time of the reference voltage and reference current, and outputting the switching signal; A feedback module for calculating the error between the actual state information of the voltage and current in the line and the reference signal to obtain the voltage error signal value and current error signal value; A control module for issuing voltage regulation, phase regulation, and current adjustment instructions according to the error value between the actual and reference signals.

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