Fault ride-through and restart control strategy for hybrid power flow controller under power grid fault

Abstract

The invention provides a hybrid power flow controller fault ride-through and restart control strategy under a power grid fault, which comprises the following steps: S1, detecting a system state, and when the system state is abnormal, performing system fault judgment and selectively performing fault exit; s2, after the fault exits, performing intra-region and intra-region fault judgment by using various intra-region and intra-region fault criteria; s3, if it is judged that the fault is an external fault, a fault recovery criterion is used for judgment; s4, if a fault recovery criterion is met, executing automatic restart of the HPFC, and if the fault recovery criterion is met, executing automatic restart of the HPFC; and if the fault recovery criterion is not met, the operation of the HPFC is stopped. According to the method, various criteria and multi-aspect fault distinguishing are introduced, so that the processing of the HPFC under the fault condition is more flexible and reliable.

Description

Technical Field

[0001] The present invention relates to the technical field of flexible power transmission, and in particular to a hybrid power flow controller fault ride-through and restart control strategy. Background Art

[0002] As the most typical FACTS device, the unified power flow controller (UPFC) has good effects in power flow regulation and load balancing. However, since UPFC adopts high-power power electronic devices on a large scale, its topology is relatively complex, the construction cost is high and the floor space requirement is large.

[0003] Hybrid Power Flow Controller (HPFC) is an advanced device that combines traditional mechanical phase angle regulators and modern power electronics technology. It is used to more effectively control the power flow in the power system. Its core equipment includes series transformers, shunt transformers and power electronic converters. Due to the special topological structure and grid access method of power electronic converters, their ability to withstand fault voltage and current during grid faults is higher than that of traditional equipment. When an AC system fails, the system short-circuit current will flow through the series transformer windings and couple to the shunt transformer and power electronic converter. When the HPFC cannot effectively suppress the short-circuit current, the fault current will damage the internal components of the HPFC. For different fault situations, the fault ride-through requirements for the HPFC are also different and should be formulated according to the equipment tolerance and grid demand. For overcurrent or overvoltage caused by grid faults, if it does not exceed the tolerance of the HPFC, the HPFC should be kept in operation. During the grid fault, a certain control strategy can be adopted to suppress the grid fault current. When the overcurrent or overvoltage caused by a grid fault exceeds the tolerance of the HPFC, the HPFC should be able to exit in time, and after the fault is cleared and the grid-connected line returns to normal, the HPFC should be automatically switched on and adjusted according to the set power flow control strategy. Fault ride-through measures must be taken to protect the safety of the equipment. Therefore, it is necessary to study the control strategy and fault ride-through measures of the HPFC during the fault period.

[0004] The invention patent with the publication number CN106026137B discloses that when a fault is detected, the series side converter is exited; it is determined whether the fault is a recoverable line fault. If it is not a recoverable line fault, the unified power flow controller shutdown process is executed; if it is a recoverable line fault, the AC line is detected in real time to see whether it has resumed normal operation. After the AC line is detected to be restored to normal, the series side converter is unlocked, the series transformer secondary side bypass switch is disconnected, and the unified power flow controller resumes operation. This method can quickly isolate the fault point and the unified power flow controller device after a line fault occurs, and quickly re-enter the unified power flow controller after the line fault is cleared and the line resumes normal operation, thereby improving the reliability of the entire system, protecting the safety of the unified power flow controller device, and improving the utilization rate of the unified power flow controller. However, this invention only focuses on the locking and recovery of the series side converter, does not distinguish in detail between faults within and outside the area, and does not describe in detail the specific fault location determination method, so that the control strategy is not flexible and reliable enough. Summary of the invention

[0005] In view of the technical problem that the control strategies of the prior art are not flexible and accurate enough, the present invention proposes a hybrid power flow controller fault ride-through and restart control strategy under power grid faults. By introducing multiple criteria and multi-faceted fault differentiation, the handling of HPFC in fault conditions is improved to be more flexible and reliable.

[0006] In order to achieve the above object, the technical solution of the present invention is achieved as follows:

[0007] A hybrid power flow controller fault ride-through and restart control strategy under power grid fault, characterized in that it includes the steps of:

[0008] S1: Detect system status. When the system status is abnormal, determine the system fault and selectively exit the fault;

[0009] S2: After the fault exits, multiple internal and external fault judgment criteria are used to judge the internal and external faults;

[0010] S3: If it is determined to be an out-of-zone fault, the fault recovery criterion is used for determination; if it is determined to be an in-zone fault, the HPFC is stopped;

[0011] S4: If the fault recovery criterion is met, the HPFC is automatically restarted; if the fault recovery criterion is not met, the HPFC is stopped.

[0012] The system state described in step S1 includes HPFC protection state, line voltage state, line current state and line protection state; the HPFC protection state includes series transformer winding overcurrent protection state, series transformer series winding port overvoltage protection state and HPFC other protection states.

[0013] The method for performing system fault determination and selective fault exit described in step S1 is: obtaining the overcurrent or overvoltage caused by the grid fault according to the line voltage state and the line current state; when the overcurrent or overvoltage caused by the grid fault does not exceed the tolerance of the HPFC, keeping the HPFC in operation; when the overcurrent or overvoltage caused by the grid fault exceeds the tolerance of the HPFC, executing the HPFC fault exit operation.

[0014] The HPFC fault exit operation is: switching off the cascaded H-bridge converter CHBC, bypassing the HPFC through the bypass switch BPS and disconnecting the main circuit breaker.

[0015] The various in-zone and out-of-zone fault criteria described in step S2 include main criteria and auxiliary criteria. The main criteria are overcurrent of the HPFC series transformer winding, overvoltage of the HPFC series transformer series winding port and line protection action. The auxiliary criteria are abnormal line voltage and inaction of other HPFC protections.

[0016] The method for distinguishing the faults inside and outside the area in step S2 is: using the fault criterion formula P flt To judge; to meet the fault judgment formula P inside and outside the area flt When it is judged as an out-of-zone fault; it does not meet the in-zone fault judgment formula P flt When the fault occurs, it is judged as an internal fault of HPFC.

[0017] The fault criterion formula P flt for:

[0018]

[0019]

[0020] Among them, P1 is the overcurrent criterion of the series transformer winding, I BI ,I BII and I BIII are the currents corresponding to the series transformer windings B1, B2 and B3, Δ I1 =Δ I2 The threshold value of the current corresponding to the series transformer windings B1 and B2, Δ I3 represents the threshold value of the current corresponding to the series transformer winding B3; P2 is the overvoltage criterion of the series transformer series winding port of HPFC, dU B is the voltage between the two terminals of the series winding of the series transformer, Δ u It represents the threshold value of the voltage at the two terminals of the series winding of the series transformer; P3 is the abnormal criterion of line voltage, U s1 It represents the positive sequence component of the voltage at the sending end S, U s2 Indicates the negative sequence component of the voltage at the sending end S, Us0 Indicates the zero-sequence voltage component at the sending end S, U L1 Represents the positive sequence component of the voltage at the receiving end L, U L2 Indicates the negative sequence component of the voltage at the receiving end L, U L0 Represents the zero-sequence component of the voltage at the receiving end L, Δ S1 , Δ S2 , Δ S0 They represent the threshold values ​​corresponding to the positive sequence component, negative sequence component, and zero sequence component of the voltage at the sending end S, respectively. L1 , Δ L2 , Δ L0 They represent the threshold values ​​corresponding to the positive sequence component, negative sequence component and zero sequence component of the voltage at the sending end L respectively; P4 is the line protection action criterion; It is the criterion for the non-action of other protections of HPFC.

[0021] The fault recovery criteria in step S3 include a line current limit satisfying criterion, a line voltage normal criterion, and a line circuit breaker closing criterion.

[0022] The method of using the fault recovery criterion for determination in step S3 is: if it is determined to be an out-of-zone fault, a time delay of T is performed, and within the delay time T, the fault recovery criterion formula P is used to determine the fault. nor Make a judgment, when the fault recovery criterion P is met nor When , it is judged that the line has resumed normal operation.

[0023] The fault recovery criterion P nor for:

[0024] P nor =(P6&P7)&P8

[0025]

[0026] Among them, P6 means that the line current meets the limit criterion, I L represents the line current, Δ I is the threshold value corresponding to the line current; P7 represents the normal line voltage criterion; P8 represents the line circuit breaker closing criterion.

[0027] Beneficial effects of the present invention:

[0028] The present invention uses multiple criteria to accurately determine the fault location, thereby more accurately controlling the exit and recovery of the HPFC;

[0029] The present invention implements exit and recovery strategies of HPFC under different fault conditions, including processing methods of in-zone faults and out-of-zone faults, as well as specific delay times and recovery conditions, which makes the processing of HPFC under fault conditions more flexible and reliable.

[0030] The present invention has more advantages in improving the safety of HPFC through detailed fault location identification and comprehensive fault exit and recovery strategies, and can more effectively protect the equipment from damage. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0032] Figure 1 It is a flow chart of the HPFC fault ride-through and restart control strategy.

[0033] Figure 2 It is a topology diagram of a thyristor controlled phase shifting transformer combined with a cascaded H-bridge converter.

[0034] Figure 3 It is a structural diagram of the power grid system of the present invention.

[0035] Figure 4 It is the operation timing diagram of the HPFC fault ride-through and restart control strategy.

[0036] Figure 5 It is the fault location determination logic diagram.

[0037] Figure 6 It is a fault recovery judgment logic diagram.

[0038] Figure 7 2 is a simulation circuit diagram of an embodiment.

[0039] Figure 8 is the active power flowing through the HPFC, bypass and line.

[0040] Fig. 9 is the current flowing through the HPFC.

[0041] Fig.10 is the current flowing through the cascaded H-bridge converter CHBC.

[0042] Fig.11 It is the average voltage of the internal capacitor of the cascaded H-bridge converter CHBC. DETAILED DESCRIPTION

[0043] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0044] Example 1

[0045] A hybrid power flow controller fault ride-through and restart control strategy under power grid fault is applicable to a controllable phase shifter combined with a cascaded H-bridge converter (CHBC), i.e., a new type of HPFC.

[0046] like Figure 2 As shown, the HPFC includes a three-phase series transformer (BT), a three-phase shunt transformer (ET) (with a tap switch on the secondary side), and a cascaded H-bridge converter CHBC; the primary side of the shunt transformer obtains voltage from the power grid to generate an adjustable voltage on the secondary side, and combines it with the output voltage of the cascaded H-bridge converter to generate a phase-shifted voltage with adjustable phase and amplitude, and the phase-shifted voltage is compensated to the primary side of the series transformer through circuit connection.

[0047] The parallel transformer adopts a Y / Y connection mode, the positive polarity end of the primary side is connected to the power grid through the series transformer, the negative polarity end is grounded, the positive polarity end of the secondary side is connected to the secondary side of the series transformer, and the negative polarity end is connected to the cascaded H-bridge converter CHBC, wherein the parallel transformer ratio is N E1 :N E2 =220:40.

[0048] The series transformer is a three-winding transformer, adopts a Y / D connection method, the primary side of the series transformer is connected in series to the power grid line through the sending end S and the receiving end L, and the secondary side of the series transformer is connected to the secondary side of the parallel transformer, wherein the transformation ratio of the secondary side winding of the series transformer is NB1:NB2=1:1, and the head end a of the series transformer series transformer a is connected to the tail end z of the series transformer series transformer c, the tail end x of the series transformer series transformer a is connected to the head end b of the series transformer series transformer b, and the tail end y of the series transformer series transformer b is connected to the head end c of the series transformer series transformer c; the head and tail ends of the three windings B3a, B3b and B3c are connected in series in sequence to form a D connection.

[0049] The cascaded H-bridge converter CHBC is composed of multiple groups of H-bridge commutation units connected in series, wherein each H-bridge commutation unit includes four IG series transformer switch tubes (first to fourth switch tubes) equipped with reverse parallel freewheeling diodes and a DC capacitor. The first IG series transformer switch tube and the second IG series transformer switch tube constitute the left bridge arm, and the third IG series transformer switch tube and the fourth IG series transformer switch tube constitute the right bridge arm. The forward conduction direction of the four IG series transformer switch tubes is consistent, and the forward conduction direction of the freewheeling diode is opposite to that of the switch tube. The two bridge arms and the DC capacitor are connected in parallel to form an H-bridge commutation module, and a line is led out from the common point of the IG series transformer switch tubes of each bridge arm and connected to an external circuit. The IG series transformer switch tube IG series transformer gate is connected to an external PWM control circuit, and the carrier phase-shift PWM technology is used to control the output voltage amplitude and phase of the cascaded H-bridge module.

[0050] Preferably, the cascaded H-bridge converter CHBC includes three working states, namely, a compensation state, a cut-out state and a locking state.

[0051] according to Figure 2 From the circuit structure of the cascaded H-bridge converter module inside the CHBC circuit, it can be seen that the working state of the CHBC can be controlled by controlling the four IG series transformer switches. The switching states corresponding to the three working states are shown in the following table.

[0052]

[0053] In the compensation state, the cascaded H-bridge converter CHBC operates normally and is used to fine-tune the compensation voltage injected into the line by the phase-shifting transformer; in the cut-out state, all IG series transformers inside the cascaded H-bridge converter CHBC are turned on, the internal capacitors are short-circuited, and the cascaded H-bridge converter CHBC is cut out for operation; in the locked state, all IG series transformers inside the cascaded H-bridge converter CHBC are turned off, and the freewheeling diodes charge the capacitors.

[0054] like Figure 3As shown, when the HPFC access system detects a fault in the line through the voltage and current transformers on both sides of the HPFC, the fault exit strategy is immediately executed. Since the response speed of the power electronic switch is much faster than that of the circuit breaker, the controller of the cascaded H-bridge converter CHBC can quickly switch the working state of the cascaded H-bridge converter CHBC to the cut-out state, thereby realizing the rapid isolation of the cascaded H-bridge converter CHBC. Further, the HPFC bypass switch BPS is closed to isolate the fault current path from the HPFC, and then the main circuit breakers 1 and 2 on both sides of the HPFC are disconnected, and the HPFC temporarily exits, and then waits for the line protection to trip the line circuit breakers (1, 2). At the same time, according to the fault judgment criteria inside and outside the zone, the fault location is judged to decide whether to restart the HPFC. If it is an internal fault in the zone, that is, an internal fault of the HPFC, it will not be restarted, and the HPFC will permanently exit or wait for the fault to recover; if it is an external fault, that is, a fault occurs in the line where the HPFC is located, then after the line state is restored, the automatic restart strategy is executed to realize the restart of the HPFC.

[0055] A hybrid power flow controller fault ride-through and restart control strategy under power grid faults, such as Figure 1 As shown, the steps include:

[0056] S1: Detect system status. When the system status is abnormal, make a system fault determination and selectively exit the fault.

[0057] The HPFC protection states, line voltage states, line current states and line protection states are detected respectively; the HPFC protection states include the series transformer winding overcurrent protection state (such as current flowing through windings B1a, B2a and B3a of phase A), the series transformer series winding port overvoltage protection state (such as the voltage between SA and LA of phase A) and other HPFC protections.

[0058] Perform system fault determination and selectively perform fault exit: obtain the overcurrent or overvoltage caused by the grid fault according to the line voltage state and the line current state. When the overcurrent or overvoltage on the line caused by the grid fault does not exceed 1.2 times the HPFC voltage and current rating, keep the HPFC in operation. When the overvoltage or overcurrent caused by the grid fault exceeds 1.2 times the HPFC voltage and current rating, execute the HPFC fault exit strategy, and quickly cut the cascaded H-bridge converter CHBC out of operation by controlling the IGBT inside the cascaded H-bridge converter CHBC to control the disconnection of the series transformer. Furthermore, in order to avoid the fault current flowing through the series transformer and the IGBT inside the cascaded H-bridge converter CHBC for a long time, after the cascaded H-bridge converter CHBC is cut out, send the bypass switch BPS closing command in time to bypass the HPFC, and disconnect the main circuit breakers 1 and 2 on both sides of the HPFC, so as to achieve fault exit.

[0059] S2: After the fault is exited, multiple internal and external fault judgment criteria are used to judge the internal and external faults.

[0060] like Figure 5 As shown in the fault location judgment logic diagram, the main judgment criteria are the HPFC series transformer winding overcurrent, the HPFC series transformer series winding port overvoltage and line protection action, and the line voltage abnormality and HPFC other protection failure are used as auxiliary judgment criteria to judge the faults inside and outside the area.

[0061] In order to improve the accuracy of out-of-zone fault judgment, the line voltage state is introduced as an auxiliary criterion. When an AC system fault occurs, the voltage of the HPFC access line will be abnormal. Its abnormal characteristics are manifested in different sequence components of the voltage, such as low positive sequence voltage, large zero sequence voltage or large negative sequence voltage. Here, taking one phase as an example, the in-zone and out-of-zone fault judgment criterion P flt as follows:

[0062]

[0063]

[0064] Among them, P1 is the overcurrent criterion of the HPFC series transformer winding, I BI ,I BII and I BIII are the currents corresponding to the series transformer windings B1, B2 and B3, Δ I1 =Δ I2 Indicates the threshold value of the current corresponding to the series transformer windings B1 and B2, Δ I3 represents the threshold value of the current corresponding to the series transformer winding B3; P2 is the overvoltage criterion of the series transformer series winding port of HPFC, dU B The voltage between the two terminals of the series winding of the series transformer (phase A is the voltage between SA and LA), Δ u It represents the threshold value of the voltage at two terminals of the series winding of the series transformer;

[0065] P3 is the line voltage abnormality criterion, U s1 It represents the positive sequence component of the voltage at the sending end S, U s2 Indicates the negative sequence component of the voltage at the sending end S, U s0 Indicates the zero-sequence voltage component at the sending end S, U L1 Represents the positive sequence component of the voltage at the receiving end L, U L2 Indicates the negative sequence component of the voltage at the receiving end L, U L0 Represents the zero-sequence component of the voltage at the receiving end L, Δ S1 , Δ S2 , Δ S0 They represent the threshold values ​​corresponding to the positive sequence component, negative sequence component, and zero sequence component of the voltage at the sending end S, respectively. L1 , ΔL2 , Δ L0 They represent the threshold values ​​corresponding to the positive sequence component, negative sequence component and zero sequence component of the voltage at the sending end L respectively; P4 is the line protection action criterion; It is the criterion for the non-action of other protections of HPFC.

[0066] When the fault criterion P is satisfied flt When the fault is outside the zone, it is judged as an out-of-zone fault, and the HPFC automatic restart is allowed to be executed; if the above judgment logic is not satisfied, it is judged as an HPFC internal fault, and the HPFC automatic restart is not allowed to be executed.

[0067] S3: If it is determined to be an out-of-zone fault, the fault recovery criterion is used for determination; if it is determined to be an in-zone fault, the HPFC is stopped.

[0068] When a grid fault causes the HPFC to temporarily fail and exit, before the HPFC is put back into operation, it is necessary to determine whether the grid has resumed normal operation, re-check the status of the circuit breaker (1, 2), the line voltage status and the line current status, and use the line voltage being normal, the line current meeting the limit value (minimum current for normal operation) and the circuit breaker being closed as the judgment criteria, such as Figure 5 As shown, the fault recovery judgment is performed. Here, one phase is taken as an example. The fault recovery judgment criterion P nor as follows:

[0069] P nor =(P6&P7)&P8

[0070]

[0071] Among them, P6 means that the line current meets the limit criterion, I L represents the line current, Δ I is the threshold value corresponding to the line current; P7 represents the normal line voltage judgment criterion; P8 represents the line circuit breaker closing judgment criterion. At this time, the bypass switch BPS is closed and the line circuit breaker is also closed, because when judging the fault recovery, the line needs to be energized to obtain the line voltage and line current information in the judgment criterion.

[0072] If it is determined to be an out-of-zone fault, a time delay of T is performed (the delay is greater than the line circuit breaker reclosing time, and a certain margin is left, which can be 2 to 5 seconds based on engineering experience). Within the delay time T, the fault recovery criterion formula P is used. nor Make a judgment, when the fault recovery criterion P is met nor When the line is judged to have resumed normal operation, the HPFC automatic restart is allowed;

[0073] When the fault recovery criterion P is met nor When , it is judged that the line has resumed normal operation.

[0074] S4: If the fault recovery criterion is met, the HPFC is automatically restarted; if the fault recovery criterion is not met, the HPFC is stopped.

[0075] Execute automatic restart of HPFC: After the line resumes normal operation, close main circuit breaker 1 and main circuit breaker 2 (at this time, the cascaded H-bridge converter CHBC is still in the cut-out operation state), exit the bypass switch BPS, wait for the system to stabilize and start adjusting the line power flow (coarse adjustment of the parallel transformer). After it stabilizes again, put the cascaded H-bridge converter CHBC into operation (the working state is switched to the compensation state) to fine-tune the line power flow and complete the restart process of HPFC.

[0076] Example 2

[0077] A hybrid power flow controller fault ride-through and restart control strategy under power grid fault, assuming that the HPFC is installed in the 220kV line for power flow regulation. Figure 7 This is a simulation circuit diagram of an embodiment. When the cascaded H-bridge converter CHBC is not put into operation (the CHBC circuit is in a cut-out operation state), the phase shift angle range is ±10.53°, and the carrier frequency is 1kHz. Figure 8 is the active power curve flowing through HPFC and bypass, Figure 8 is the current curve flowing through the HPFC, Fig. 9 is the current curve flowing through the cascaded H-bridge converter CHBC, Fig.10 It is the output voltage curve of the cascaded H-bridge converter CHBC. The power control target is set to 118MW, the HPFC is put into operation at 1.3s, the HPFC gear is in gear 2 at 2.5s, the line power is adjusted by the cascaded H-bridge converter CHBC at 4s, and a phase A grounding fault occurs in the line where the HPFC is located at 10s. The fault lasts for 0.2s, the signal delay of the cascaded H-bridge converter CHBC is 10ms, the bypass switch action delay is 35ms, the line circuit breaker delay is 80ms, and the reclosing delay is 0.3s.

[0078] Figure 8 The changes in line power, bypass power and HPFC power during the entire HPFC fault ride-through process are demonstrated. After the fault occurs, the fault exit strategy is executed, the bypass operates to isolate the HPFC, the line circuit breaker trips to isolate the fault, and the power of each power drops to 0. After the fault is cleared and the line status is restored, the restart strategy is executed, the bypass exits, the bypass power drops, the HPFC is put back into operation, and the HPFC power increases.

[0079] Fig. 9 The change of current flowing through HPFC during the entire HPFC fault ride-through process is shown. After the fault occurs, the HPFC current increases suddenly. After the fault exit strategy is executed, the bypass action isolates the HPFC, and the current on the HPFC decreases rapidly, protecting the HPFC equipment.

[0080] Fig.10 , Fig.11 The changes in CHBC current and internal capacitor voltage during the entire HPFC fault ride-through process. After the fault occurs, CHBC switches to the cut-out operation state according to the fault exit strategy. At this time, the capacitor voltage drops rapidly, and the CHBC current decreases rapidly after the bypass action, protecting the safety of the CHBC internal switch elements and capacitor elements.

[0081] like Figure 4 As shown, the specific process is as follows:

[0082] S1: Detect system status. When the system status is abnormal, make a system fault determination and selectively exit the fault.

[0083] At 1.3s, the HPFC is put into normal system operation and performs power flow control, and monitors the HPFC protection status, line voltage status, line current status, and line protection status in real time.

[0084] At 10s, a single-phase grounding fault occurs in the line. After the fault exit command is issued, the cascaded H-bridge converter CHBC is switched out after a delay of 10ms, and the bypass switch BPS is closed after a delay of 35ms, and the bypass exits the HPFC.

[0085] S2: After the fault is exited, multiple internal and external fault judgment criteria are used to judge the internal and external faults.

[0086] During the period from when the HPFC bypass is removed to when the line circuit breaker is tripped, Figure 5 The fault location determination logic shown is used to determine the fault location.

[0087] S3: If it is determined to be an out-of-zone fault, the fault recovery criterion is used for determination; if it is determined to be an in-zone fault, the HPFC is stopped.

[0088] If it is determined to be an in-zone fault, that is, a HPFC fault, the HPFC will be permanently shut down, and the HPFC operation will be manually restored later based on the fault handling situation;

[0089] If it is judged as an out-of-zone fault, the HPFC is temporarily bypassed and the HPFC gear is adjusted to gear 0, allowing the HPFC to automatically restart. Figure 6 The fault recovery judgment logic shown detects whether the circuit has resumed normal operation.

[0090] S4: If the fault recovery criterion is met, the HPFC is automatically restarted; if the fault recovery criterion is not met, the HPFC is stopped.

[0091] When the fault recovery judgment logic is met, it is judged that the line has resumed normal operation, the HPFC has the restart conditions, and the HPFC is automatically restarted. The line circuit breaker is disconnected 80ms after the fault, and the line circuit breaker is reclosed 0.3s later; at this time, the bypass switch and the two line circuit breakers of the line are closed, and the line operates normally. After a delay of 1.5s, the main circuit breaker is closed, the bypass switch BPS is exited, and the HPFC is re-entered to perform power flow control.

[0092] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A hybrid power flow controller fault ride-through and restart control strategy under power grid fault, characterized in that: Includes steps: S1: Detect system status. When the system status is abnormal, determine the system fault and selectively exit the fault; S2: After the fault exits, multiple internal and external fault judgment criteria are used to judge the internal and external faults; S3: If it is determined to be an out-of-zone fault, the fault recovery criteria are used for judgment; if it is determined to be an in-zone fault, the HPFC is stopped: S4: If the fault recovery criterion is met, the HPFC is automatically restarted; if the fault recovery criterion is not met, the HPFC is stopped.

2. The hybrid power flow controller fault ride-through and restart control strategy under power grid fault according to claim 1, characterized in that: The system state described in step S1 includes HPFC protection state, line voltage state, line current state and line protection state; the HPFC protection state includes series transformer winding overcurrent protection state, series transformer series winding port overvoltage protection state and HPFC other protection states.

3. The hybrid power flow controller fault ride-through and restart control strategy under power grid fault according to claim 2, characterized in that: The method for performing system fault determination and selective fault exit described in step S1 is: obtaining the overcurrent or overvoltage caused by the grid fault according to the line voltage state and the line current state; when the overcurrent or overvoltage caused by the grid fault does not exceed the tolerance of the HPFC, keeping the HPFC in operation; when the overcurrent or overvoltage caused by the grid fault exceeds the tolerance of the HPFC, executing the HPFC fault exit operation.

4. The hybrid power flow controller fault ride-through and restart control strategy under power grid fault according to claim 3, characterized in that: The HPFC fault exit operation is: switching off the cascaded H-bridge converter CHBC, bypassing the HPFC through the bypass switch BPS and disconnecting the main circuit breaker.

5. The hybrid power flow controller fault ride-through and restart control strategy under power grid fault according to any one of claims 2 to 4, characterized in that: The various in-zone and out-of-zone fault criteria described in step S2 include main criteria and auxiliary criteria. The main criteria are overcurrent of the HPFC series transformer winding, overvoltage of the HPFC series transformer series winding port and line protection action. The auxiliary criteria are abnormal line voltage and inaction of other HPFC protections.

6. The hybrid power flow controller fault ride-through and restart control strategy under power grid fault according to claim 5, characterized in that: The method for distinguishing the faults inside and outside the area in step S2 is: using the fault criterion formula P flt To judge; to meet the fault judgment formula P inside and outside the area flt When it is judged as an out-of-zone fault; it does not meet the in-zone fault judgment formula P flt When the fault occurs, it is judged as an internal fault of HPFC.

7. The hybrid power flow controller fault ride-through and restart control strategy under power grid fault according to claim 6, characterized in that: The fault criterion formula P flt for: Among them, P1 is the overcurrent criterion of the series transformer winding, I BI ,I BII and I BIII are the currents corresponding to the series transformer windings B1, B2 and B3, Δ I1 =Δ I2 The threshold value of the current corresponding to the series transformer windings B1 and B2, Δ I3 represents the threshold value of the current corresponding to the series transformer winding B3; P2 is the overvoltage criterion of the series transformer series winding port of HPFC, dU B is the voltage between the two terminals of the series winding of the series transformer, Δ u It represents the threshold value of the voltage at the two terminals of the series winding of the series transformer; P3 is the abnormal criterion of line voltage, U s1 It represents the positive sequence component of the voltage at the sending end S, U s2 Indicates the negative sequence component of the voltage at the sending end S, U s0 Indicates the zero-sequence voltage component at the sending end S, U L1 Represents the positive sequence component of the voltage at the receiving end L, U L2 Indicates the negative sequence component of the voltage at the receiving end L, U L0 Represents the zero-sequence component of the voltage at the receiving end L, Δ S1 , Δ S2 , Δ S0 They represent the threshold values ​​corresponding to the positive sequence component, negative sequence component, and zero sequence component of the voltage at the sending end S, respectively. L1 , Δ L2 , Δ L0 They represent the threshold values ​​corresponding to the positive sequence component, negative sequence component and zero sequence component of the voltage at the sending end L respectively; P4 is the line protection action criterion; It is the criterion for the non-action of other protections of HPFC.

8. The hybrid power flow controller fault ride-through and restart control strategy under power grid fault according to claim 7, characterized in that: The fault recovery criteria in step S3 include a line current limit satisfying criterion, a line voltage normal criterion, and a line circuit breaker closing criterion.

9. The hybrid power flow controller fault ride-through and restart control strategy under power grid fault according to claim 8, characterized in that: The method of using the fault recovery criterion for determination in step S3 is: if it is determined to be an out-of-zone fault, a time delay of T is performed, and within the delay time T, the fault recovery criterion formula P is used to determine the fault. nor Make a judgment, when the fault recovery criterion P is met nor When , it is judged that the line has resumed normal operation.

10. The hybrid power flow controller fault ride-through and restart control strategy under power grid fault according to claim 9, characterized in that: The fault recovery criterion P nor for: Among them, P6 means that the line current meets the limit criterion, I L represents the line current, Δ I is the threshold value corresponding to the line current; P7 represents the normal line voltage criterion; P8 represents the line circuit breaker closing criterion.

Images