Control method and device considering access of hybrid power flow controller

Abstract

The invention provides a control method and device considering access of a hybrid power flow controller, and belongs to the field of power control. The hybrid power flow controller comprises a phase-shifting transformer and a cascaded H-bridge converter, and the method comprises the steps that when a fault isolation instruction is received, the gear of the phase-shifting transformer is adjusted to be zero; controlling the voltage input end of the cascaded H-bridge converter to input the characteristic voltage, and obtaining the output current of the cascaded H-bridge converter; wherein the characteristic voltage is a staged voltage; and determining a fault property discrimination result according to the characteristic voltage and the output current, and carrying out fault positioning according to the fault property discrimination result. According to the method, the flexible and controllable characteristics of the hybrid power flow controller are utilized, the staged characteristic voltage signals are actively injected into the fault line, fault judgment and fault distance measurement are achieved, and meanwhile the stability of electrical equipment and the overall stability are guaranteed.

Description

Technical Field

[0001] The present invention relates to the technical field of power grid control, and in particular to a control method and device taking into account access of a hybrid power flow controller. Background Art

[0002] The hybrid power flow controller based on cascade H-bridge is a power flow control device improved on the basis of dual-core phase-shifting transformer. Its promotion and application can meet the needs of power grid for power flow optimization, new energy transmission, regional flexible interconnection and other aspects. However, when the three-phase reclosing switch of the line overlaps with a permanent fault, the secondary short-circuit current brings further impact to the system, endangering the electrical equipment and overall stability in the power system. Therefore, it is necessary to take relevant measures to judge the nature of the fault of the hybrid power flow controller access line, realize the three-phase reclosing switch that is adaptive to various types of faults, and ensure the fault recovery capability of the line. At the same time, after the hybrid power flow controller is connected to the line, the traditional fault distance measurement method is not adaptable enough, and the measurement accuracy is greatly affected. Therefore, it is urgent to propose a new fault property identification and positioning scheme suitable for the hybrid power flow controller access line. Summary of the invention

[0003] The embodiments of the present invention provide a control method and device taking into account the access of a hybrid power flow controller, so as to solve the problem of identifying and locating the nature of a new fault of a line accessed by the hybrid power flow controller.

[0004] In a first aspect, an embodiment of the present invention provides a control method taking into account access to a hybrid power flow controller, the hybrid power flow controller comprising: a phase-shifting transformer and a cascaded H-bridge converter; the method comprising:

[0005] When receiving the fault isolation instruction, adjusting the gear position of the phase-shifting transformer to zero;

[0006] Controlling the voltage input terminal of the cascaded H-bridge converter to input a characteristic voltage, and obtaining the output current of the cascaded H-bridge converter; wherein the characteristic voltage is a step-type voltage;

[0007] A fault property identification result is determined according to the characteristic voltage and the output current, and the fault is located according to the fault property identification result.

[0008] In a possible implementation, the voltage value corresponding to each stage of the characteristic voltage is different and is less than the rated voltage of the cascaded H-bridge converter; and the voltage maintenance time corresponding to each stage is the same.

[0009] In a possible implementation, determining a fault property determination result according to the characteristic voltage and the output current includes:

[0010] In the first voltage input stage, the input voltage is controlled to be a first voltage value, and the output current of the cascaded H-bridge converter is integrated to obtain a first current integral value. When the first current integral value is greater than a first set current value, it is determined to be a permanent fault; otherwise, the second voltage input stage is entered;

[0011] In the second voltage input stage, the input voltage is controlled to be a second voltage value, and the output current of the cascaded H-bridge converter is integrated to obtain a second current integral value. When the second current integral value is greater than the second set current value, it is determined to be a permanent fault; otherwise, the third voltage input stage is entered;

[0012] In the third voltage input stage, the input voltage is controlled to be a third voltage value, and an output current of the cascaded H-bridge converter is integrated to obtain a third current integral value. When the third current integral value is greater than a third set current value, it is determined to be a permanent fault; otherwise, it is determined to be a transient fault;

[0013] Among them, the third voltage value is greater than the second voltage value; the second voltage value is greater than the first voltage value.

[0014] In a possible implementation manner, the first voltage value is 10% of the rated voltage of the cascaded H-bridge converter; and the second voltage value and the third voltage value are integer multiples of the first voltage value.

[0015] In a possible implementation, locating the fault according to the fault property determination result includes:

[0016] When it is determined to be a transient fault, a single-ended electrical quantity differential equation is written according to the voltage value and output current corresponding to the transient fault to calculate the fault distance.

[0017] In a possible implementation, the single-ended electrical quantity differential equation includes:

[0018] When a single-phase grounding fault occurs, after the characteristic voltage is input, the fault phase voltage and phase current meet the following conditions:

[0019]

[0020] In the formula, u A 、i A are the voltage and current of the fault phase respectively; i 0 K is the zero-sequence current measured for the access line; r , K l are the zero-sequence current compensation coefficients of the access line resistance and inductance, K r =(r 1 -r 0 ) / 3r 1 , K l=(l 1 -l 0 ) / 3l 1 ; r 1 , l 1 and r 0 , l 0 are respectively the positive sequence and zero sequence resistance and inductance of the access line per unit length of the hybrid power flow controller based on the cascade H-bridge; L is the distance from the fault point to the line outlet of the hybrid power flow controller based on the cascade H-bridge;

[0021] When a phase-to-phase short circuit fault occurs, after the characteristic voltage is input, the fault phase voltage and phase current meet the following conditions:

[0022]

[0023] In the formula, u AB 、i AB are the fault phase line voltage and line current measured by the hybrid power flow controller connected to the line; R f is the transition resistance; L is the distance from the fault point to the line outlet of the hybrid power flow controller based on the cascaded H-bridge.

[0024] In a possible implementation manner, before determining the fault property determination result according to the characteristic voltage and the output current, the method further includes:

[0025] A permanent single-phase grounding fault is set at the end of the line, the transition resistance is set to a first resistance value, a second resistance value and a third resistance value respectively, and a corresponding injection voltage is respectively corresponding to the first voltage value, the second voltage value and the third voltage value;

[0026] The output current integral values ​​corresponding to the first voltage value, the second voltage value and the third voltage value are calculated respectively and determined as the current setting values ​​corresponding to each stage of the characteristic voltage; wherein the current setting values ​​include the first set current value, the second set current value and the third set current value.

[0027] In a possible implementation manner, the first resistance, the second resistance, and the third resistance are 20Ω, 100Ω, and 200Ω, respectively.

[0028] In a possible implementation, circuit breakers are connected to both sides of the hybrid power flow controller; after determining the fault property determination result according to the characteristic voltage and the output current, the method further includes:

[0029] When a permanent fault is determined, the three-phase reclosing switch is controlled to lock, and the fault line is measured and shut down for maintenance;

[0030] When it is determined to be a transient fault, the grounding switch is controlled to be disconnected, and the three-phase reclosing switch is controlled to control the circuit breakers on both sides to be closed in sequence, so that the hybrid power flow controller access line can resume operation.

[0031] In a second aspect, an embodiment of the present invention provides a control device taking into account access to a hybrid power flow controller, the hybrid power flow controller comprising: a phase-shifting transformer and a cascaded H-bridge converter; the device comprising:

[0032] A transformer control module, configured to adjust the gear position of the phase-shifting transformer to zero upon receiving a fault isolation instruction;

[0033] A converter control module, used for controlling the voltage input terminal of the cascaded H-bridge converter to input a characteristic voltage and obtaining the output current of the cascaded H-bridge converter; wherein the characteristic voltage is a step-type voltage;

[0034] The fault judgment module is used to determine a fault property judgment result according to the characteristic voltage and the output current, and to locate the fault according to the fault property judgment result.

[0035] The embodiment of the present invention provides a control method and device taking into account the access of a hybrid power flow controller. When a fault isolation instruction is received, the gear of the phase-shifting transformer is adjusted to zero to ensure that there is no voltage on the line when the grounding switch on the bus side is closed, thereby improving the safety of operation. The voltage input end of the cascaded H-bridge converter is controlled to input a characteristic voltage, and the output current of the cascaded H-bridge converter is obtained, and the nature of the line fault is judged by the characteristics of the output current. In addition, the characteristic voltage is set to a stage voltage to avoid excessive voltage input to ensure the stability of the electrical equipment and the overall stability. Afterwards, the fault nature judgment result is determined based on the characteristic voltage and the output current, and the fault is located based on the fault nature judgment result. The embodiment of the present application realizes the use of the flexible and controllable characteristics of the hybrid power flow controller to actively inject a staged characteristic voltage signal into the fault line, realize fault judgment and complete fault distance measurement, and at the same time, ensure the electrical equipment and the overall stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, 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.

[0037] Figure 1 is a schematic diagram of the topological structure of the hybrid power flow controller topological structure provided by an embodiment of the present invention;

[0038] Figure 2It is an equivalent model of the access line of the hybrid power flow controller provided in the embodiment of the present invention;

[0039] Figure 3 It is a schematic diagram of the characteristic voltage injection line direction provided by an embodiment of the present invention;

[0040] Figure 4 is a schematic diagram of a control system of a hybrid power flow controller provided by an embodiment of the present invention;

[0041] Figure 5 A flow chart for implementing a control method taking into account access to a hybrid power flow controller provided in an embodiment of the present invention;

[0042] Figure 6 It is a flow chart of the active injection three-phase adaptive reclosing scheme based on hybrid power flow controller;

[0043] Figure 7a and 7b This is a schematic diagram of the electrical circuit in case of failure;

[0044] Figure 8 A schematic diagram of the structure of a control device taking into account access to a hybrid power flow controller provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0045] In the following description, specific details such as specific system structures, technologies, etc. are provided for the purpose of illustration rather than limitation, so as to provide a thorough understanding of the embodiments of the present invention. However, it should be clear to those skilled in the art that the present invention may be implemented in other embodiments without these specific details. In other cases, detailed descriptions of well-known systems, devices, circuits, and methods are omitted to prevent unnecessary details from obstructing the description of the present invention.

[0046] The present application scheme improves the fault recovery capability of the hybrid power flow controller access line on the basis of making full use of the power flow regulation capability of the hybrid power flow controller, and provides further guarantee for the reliability of the operation of the hybrid power flow controller after it is connected to the power grid.

[0047] To facilitate understanding of the present invention, the application scenarios of the hybrid power flow controller and the control method taking into account the access of the hybrid power flow controller are briefly introduced below.

[0048] Figure 1 A schematic diagram of the topological structure of the hybrid power flow controller topological structure provided in an embodiment of the present invention. Figure 1 As shown, the hybrid power flow controller topology includes: a phase shifting transformer (PST) and a cascaded H-bridge (CHB) converter;

[0049] Among them, PST is a dual-core phase-shifting transformer. The dual-core phase-shifting transformer includes the function of realizing the same input voltage and output voltage amplitude and phase change, and changing the voltage phase shift phase and leading or lagging through the switching of gears and converters; realizing the same input current and output current amplitude and phase change, and changing the current phase shift phase and leading or lagging through gear switching.

[0050] The cascaded H-bridge converter includes injecting an AC voltage with adjustable amplitude into the secondary side of the excitation transformer to achieve the expansion of the voltage phase modulation range and the flexible and controllable adjustment of the phase shift; it is used to ensure that the current on the secondary side of the excitation transformer does not change. Since the cascaded H-bridge converter used is a voltage source converter, it is only equivalent to injecting an AC voltage on the secondary side of the excitation transformer, and has no effect on the relationship between the input current and the output current.

[0051] Taking a certain phase as an example, the primary side of the excitation transformer is derived from the midpoint of the primary side of the series transformer to obtain the excitation voltage, and the secondary side of the excitation transformer is connected to the on-load tap changer to adjust the excitation transformer ratio. The cascaded H-bridge converter is connected in series to the secondary side of the excitation transformer, and the output AC voltage is superimposed on the secondary side voltage to achieve fine-tuning of the ratio. The two ends of the secondary side of the series transformer are respectively connected to the secondary sides of the other two-phase excitation transformers. A voltage with a continuously adjustable amplitude is induced on the secondary side of the series transformer. This voltage is coupled to the primary side and superimposed on the input voltage to change the phase of the output voltage.

[0052] like Figure 2 As shown in FIG. 1 , the equivalent model of the hybrid power flow controller access line includes an ideal phase-shifting transformer, equivalent impedance and CHB superimposed voltage.

[0053] Among them, the ideal phase-shifting transformer includes the phase adjustment of the input side and output side voltage and current by the phase-shifting transformer; the relationship expression between the phase shifting phase of the input side and output side voltage and current of the double-core symmetrical phase-shifting transformer and the transformation ratio of the series transformer and the excitation transformer is obtained.

[0054] The equivalent impedance includes the leakage impedance of the primary and secondary windings of the series transformer and the excitation transformer; the relationship expression between the equivalent impedance and the leakage impedance of the primary and secondary windings of the series transformer and the excitation transformer is obtained.

[0055] CHB superimposed voltage, including the impact of the access of the power electronic converter on the amplitude and phase of the output voltage; obtain the relationship expression between the CHB superimposed voltage and the output voltage of the cascaded H-bridge converter. CHB superimposed voltage The output voltage of the power electronic converter Series transformer ratio n BT and excitation transformer ratio n ET The relationship expression is:

[0056]

[0057] For the hybrid power flow controller, after a fault occurs, the circuit breakers QF1 and QF2 are disconnected, the gear position of the excitation transformer is adjusted to zero, and the coupling relationship between the series transformer and the excitation transformer is released, so that the output voltage of the cascaded H-bridge converter can only be injected into the fault line through the series transformer. Since the output voltage of the cascaded H-bridge converter is sensed to the primary side of the excitation transformer, this induced voltage is superimposed on the secondary side voltage of the series transformer and injected into the fault line, which changes the amplitude and phase of the injected characteristic voltage and affects the control system design during fault distance measurement. Therefore, it is necessary to adjust the gear position of the phase-shifting transformer to zero before changing the control method of the hybrid power flow controller based on the cascade H-bridge, so that the output voltage of the cascaded H-bridge converter can only be injected into the fault line through the series transformer, so as to better realize the control of the amplitude and phase of the output voltage of the cascaded H-bridge converter. The direction of the characteristic voltage injection line is as follows: Figure 3 shown.

[0058] like Figure 4 As shown in the figure, it is the control system diagram of the hybrid power flow controller. ref is the reference power flowing through the line. V ch is the selected characteristic voltage amplitude. D is the selected phase-shifting transformer gear. D is the transmission power of the line in D gear. V dcref is the reference value of the DC voltage of the cascaded H-bridge converter. V dcave is the average value of the capacitor voltage of all submodules. V dcavej V is the average value of the capacitor voltage of all submodules in phase j (j=a, b, c). dcij is the capacitor voltage of the i-th submodule of phase j. (i is a positive integer, and 1≤i≤m) m is the number of submodules per phase of the cascaded H-bridge converter. d 、i q It is the current on the d and q axes after the cascaded H-bridge converter current is decoupled. and is the voltage phasor of the primary and secondary sides of the excitation transformer. is the output voltage phasor of the cascaded H-bridge converter. S is the reference phase of the j-phase output AC voltage. a For amplitude control switching, S p Toggle switch for phase control.

[0059] In steady-state operation, the amplitude and phase control switch is in the "0" position, and in transient state, the amplitude and phase control switch is in the "1" position. In steady-state operation, the cascaded H-bridge converter adopts two-layer voltage regulation control. The single-phase DC voltage control aims to make the average voltage V dcavej (j=a,b,c) tracks the global average DC voltage Vdcave The control idea is to superimpose a compensation voltage command that is inversely proportional to the reference voltage command on the converter reference voltage command.

[0060] The purpose of unit DC voltage control is to make the DC side capacitor voltage of each H-bridge submodule equal to the average DC voltage of the converter. The control idea is to superimpose a compensation voltage instruction with the same phase or opposite phase as the reactive current on the AC side reference voltage instruction of a single H-bridge submodule.

[0061] The overall control strategy of the hybrid power flow controller in steady state is to use the power flow reference power. First, the phase-shifting transformer is controlled to adjust the power flow alone, and the line power flow data of each gear adjustment is recorded. Since the gear is fixed, the adjusted power flow is a fixed value, and the power interval corresponding to each gear is set according to the obtained line power flow data. When the target power flow is in a certain interval, the phase-shifting transformer is adjusted significantly to approach the target power flow through the selection of the power interval, and the remaining power difference ΔP is adjusted by the cascaded H-bridge converter. The power loss of the device components is compensated by the power exchange between the cascaded H-bridge device and the external system to make the overall voltage V dcave Stablize.

[0062] During fault distance measurement, the cascaded H-bridge DC voltage control strategy remains unchanged, while the overall control of the hybrid power flow controller is changed from power difference control in steady state to control using the calculated characteristic voltage amplitude voltage. In order to minimize the errors caused by various aspects to fault distance measurement and facilitate the acquisition of characteristic signals, the output voltage of the cascaded H-bridge converter needs to have a suitable frequency and amplitude. Taking into account the influence of line distributed capacitance and the tolerance of power electronics, the frequency of the injected characteristic voltage is selected to be 50Hz. According to the relationship expression between the CHB superimposed voltage and the output voltage of the power electronic converter, the frequency of the cascaded H-bridge converter output voltage is 50Hz. Taking into account the fault distance measurement requirements and the current tolerance limit of the power electronic device, the injected characteristic voltage is selected. The amplitude is 10% of the rated voltage. (ie 0.1pu) 0.1pu is divided into 1 / T se Transformed into the output voltage amplitude of the cascaded H-bridge converter, T se The expression is as follows:

[0063]

[0064] When a permanent fault occurs, the hybrid power flow controller forms a loop with the fault point through the fault line, generating a characteristic current on the fault line; while for a transient fault, after deionization, the fault is eliminated and the line is open, so there is no characteristic current. Therefore, the nature of the fault can be determined by judging whether the hybrid power flow controller connected to the line generates a characteristic current.

[0065] The above is an introduction to the application background of the control method for hybrid power flow controller access provided by the embodiment of the present application. To make the purpose, technical solution and advantages of the present invention clearer, the following will be described through specific embodiments in conjunction with the accompanying drawings.

[0066] Figure 5 The implementation flow chart of the control method taking into account the access of the hybrid power flow controller provided in the embodiment of the present invention is described in detail as follows:

[0067] Step S501, when receiving a fault isolation instruction, adjusting the gear position of the phase-shifting transformer to zero.

[0068] Among them, the gear position of the phase-shifting transformer is adjusted to zero, so that the output voltage of the cascaded H-bridge is 0, ensuring that the bus side grounding switch QE (such as Figure 3 There is no voltage on the line when the switch is closed, which improves the safety of operation.

[0069] Step S502, controlling the voltage input terminal of the cascaded H-bridge converter to input a characteristic voltage, and obtaining the output current of the cascaded H-bridge converter; wherein the characteristic voltage is a step-type voltage.

[0070] Step S503, determining a fault property determination result according to the characteristic voltage and the output current, and locating the fault according to the fault property determination result.

[0071] Among them, after the fault is located according to the fault nature judgment result, for a recoverable fault, the circuit breaker QF1, QF2 and the grounding switch QE (such as Figure 3 (as shown) action to restore the operation of the hybrid power flow controller access line.

[0072] In a possible implementation, circuit breakers are connected to both sides of the hybrid power flow controller respectively; after determining the fault property judgment result according to the characteristic voltage and the output current, the method further includes:

[0073] When a permanent fault is determined, the three-phase reclosing switch is controlled to lock, and the fault line is measured and shut down for maintenance;

[0074] When it is determined to be a transient fault, the grounding switch is controlled to be disconnected, and the three-phase reclosing switch is controlled to control the circuit breakers on both sides to be closed in sequence, so that the hybrid power flow controller access line can resume operation.

[0075] When it is determined to be a permanent fault, the three-phase reclosing switch is controlled to be locked to prevent the three-phase reclosing switch from affecting the safety of line operation. When it is determined to be a transient fault, it is a recoverable fault. By controlling the grounding switch to disconnect, the three-phase reclosing switch is controlled, and the circuit breakers on both sides are controlled to close in sequence, the hybrid power flow controller is restarted.

[0076] In this embodiment, when a fault isolation instruction is received, the gear position of the phase-shifting transformer is adjusted to zero to ensure that there is no voltage on the line when the grounding switch on the bus side is closed, thereby improving the safety of operation. The voltage input terminal of the cascaded H-bridge converter is controlled to input a characteristic voltage, and the output current of the cascaded H-bridge converter is obtained, and the nature of the line fault is judged by the characteristics of the output current. In addition, the characteristic voltage is set to a stage voltage to avoid excessive voltage input to ensure the stability of the electrical equipment and the overall stability. Afterwards, the fault nature judgment result is determined based on the characteristic voltage and the output current, and the fault is located based on the fault nature judgment result. The embodiment of the present application realizes the use of the flexible and controllable characteristics of the hybrid power flow controller to actively inject a staged characteristic voltage signal into the fault line, realize fault judgment and complete fault ranging, and at the same time, ensure the electrical equipment and the overall stability.

[0077] like Figure 6 The figure shows a schematic diagram of an active injection three-phase adaptive reclosing scheme based on a hybrid power flow controller. The scheme is divided into four stages:

[0078] (1) In the first stage, i.e., the fault isolation stage, when a fault occurs in the line to which the hybrid power flow controller is connected, the circuit breakers QF1 and QF2 at both ends of the line are tripped, the faulty line is isolated, and the fault point is isolated (i.e., Figure 6 (as shown in action ①);

[0079] (2) In the second stage, i.e., the injection preparation stage, the gear of the phase shifting transformer (PST) is adjusted to zero and switched to the additional control mode. In the additional control, the characteristic voltage amplitude command Uch is selected to be kept at 0, so that the output voltage of the cascaded H-bridge is 0, ensuring that there is no voltage on the line when the bus side grounding switch QE is closed, thereby improving the safety of operation (i.e., Figure 6 (as shown in action ② in the figure);

[0080] (3) In the third stage, i.e., the fault nature determination stage, the grounding switch QE on the bus side of the hybrid power flow controller is closed, and a characteristic voltage with selected amplitude and frequency is injected into the fault line using CHB, and the line fault type (i.e., Figure 6 (as shown in action ③);

[0081] (4) The fourth stage is the fault repair / recovery stage: If a permanent fault occurs on the line, the three-phase reclosing switch is locked, and the fault line distance measurement and shutdown maintenance are performed; if a transient fault occurs on the line, the grounding switch QE is disconnected, the three-phase reclosing switch is performed, and the circuit breakers QF1 and QF2 on both sides are closed in sequence, and the hybrid power flow controller is connected to the line to resume operation.

[0082] In a possible implementation, the voltage value corresponding to each stage of the characteristic voltage is different and is less than the rated voltage of the cascaded H-bridge converter; and the voltage maintenance time corresponding to each stage is the same.

[0083] In this embodiment, the characteristic voltage is set to be less than the rated voltage of the cascaded H-bridge converter to ensure that the line can operate safely during the fault type determination process. The voltage values ​​corresponding to each stage of the characteristic voltage are different. When the current corresponding to the previous voltage value is not obvious and the fault cannot be identified, the voltage value is increased to achieve the purpose of fault identification while ensuring the stability of line operation.

[0084] In a possible implementation, determining a fault property determination result according to the characteristic voltage and the output current includes:

[0085] In the first voltage input stage, the input voltage is controlled to be a first voltage value, and the output current of the cascaded H-bridge converter is integrated to obtain a first current integral value. When the first current integral value is greater than a first set current value, it is determined to be a permanent fault; otherwise, the second voltage input stage is entered;

[0086] In the second voltage input stage, the input voltage is controlled to be a second voltage value, and the output current of the cascaded H-bridge converter is integrated to obtain a second current integral value. When the second current integral value is greater than the second set current value, it is determined to be a permanent fault; otherwise, the third voltage input stage is entered;

[0087] In the third voltage input stage, the input voltage is controlled to be a third voltage value, and an output current of the cascaded H-bridge converter is integrated to obtain a third current integral value. When the third current integral value is greater than a third set current value, it is determined to be a permanent fault; otherwise, it is determined to be a transient fault;

[0088] Among them, the third voltage value is greater than the second voltage value; the second voltage value is greater than the first voltage value.

[0089] In a possible implementation, the first voltage value is 10% of the rated voltage of the cascaded H-bridge converter; and the second voltage value and the third voltage value are integer multiples of the first voltage value.

[0090] In this embodiment, the first voltage value is determined to be 10% of the rated voltage of the cascaded H-bridge converter to prevent the first voltage value from being too large and affecting the circuit operation stability. In addition, the second voltage value and the third voltage value are integer multiples of the first voltage value to ensure the accuracy and consistency of fault judgment.

[0091] In the above embodiments, the first voltage input stage, the second voltage input stage and the third voltage input stage are introduced as fault judgment conditions based on the first set current value, the second set current value and the third set current value respectively, wherein the corresponding first set current value, the second set current value and the third set current value will be different according to different circuit impedance values. Therefore, before judging the nature of the fault, the first set current value, the second set current value and the third set current value need to be calibrated.

[0092] In a possible implementation, before determining the fault property determination result according to the characteristic voltage and the output current, the method further includes:

[0093] A permanent single-phase grounding fault is set at the end of the line, the transition resistance is set to a first resistance value, a second resistance value and a third resistance value respectively, and the injection voltage corresponds to the first voltage value, the second voltage value and the third voltage value respectively;

[0094] The output current integral values ​​corresponding to the first voltage value, the second voltage value and the third voltage value are calculated respectively and determined as the current setting values ​​corresponding to each stage of the characteristic voltage; wherein the current setting values ​​include the first set current value, the second set current value and the third set current value.

[0095] In a possible implementation manner, the first resistance value, the second resistance value, and the third resistance value are 20Ω, 100Ω, and 200Ω, respectively.

[0096] In a specific embodiment, considering the scenario of a permanent high-resistance grounding fault at the end of the line, if the characteristic voltage with an amplitude of 0.1pu is injected, the characteristic current is weak and may not reach the current value measurable by the CT. This paper designs and adopts a staged characteristic voltage injection method. That is, if the characteristic current generated after the injection of the characteristic voltage in stage I is not obvious, the characteristic voltages of stages II and III are injected in sequence, and the voltage amplitudes are 0.2pu and 0.3pu respectively, and the injection time of each stage is 20ms. The hybrid power flow controller based on active characteristic voltage injection is connected to the three-phase adaptive reclosing scheme of the line. The fault nature judgment criteria are as follows:

[0097] (1) Setting the integral value of characteristic current at each stage: A permanent single-phase grounding fault is set at the end of the line, and the transition resistance is set to 20Ω, 100Ω, and 200Ω respectively. The characteristic voltages of stage I, stage II, and stage III are injected accordingly, and then the integral value of the characteristic current corresponding to each stage is calculated, which is the setting value corresponding to each stage (respectively denoted as S setⅠ , S setⅡ , S setⅢ );

[0098] (2) Stage I judgment: After injecting the stage I characteristic voltage, if the start-up conditions are met, calculate the stage I characteristic current integral value S Ⅰ , if S is satisfied Ⅰ >S setⅠ , it is judged as a permanent fault; on the contrary, the integral value of the characteristic current in this stage is small, that is, the characteristic voltage injected in this stage is small, and the characteristic voltage of stage II needs to be injected;

[0099] (3) Stage II judgment: After injecting the stage II characteristic voltage, if the start-up conditions are met, calculate the stage II characteristic current integral value S Ⅱ , if S is satisfied Ⅱ >S setⅡ , it is judged as a permanent fault; otherwise, that is, the characteristic voltage injected in this stage is small, it is necessary to continue to inject the characteristic voltage of stage III;

[0100] (4) Stage III judgment: After injecting the stage III characteristic voltage, if the start-up conditions are met, calculate the stage III characteristic current integral value S Ⅲ , if S Ⅲ >S setⅢ , it is judged as a permanent fault; otherwise, it is judged as a transient fault. After judging it as a permanent fault, the fault location is performed according to the judgment result of the fault nature.

[0101] The above is an introduction to the fault type identification process based on the segmented characteristic voltage. In the specific implementation process, the fault location method is different according to the fault nature identification result.

[0102] In a possible implementation, locating the fault according to the fault property determination result includes:

[0103] When it is determined to be a transient fault, a single-ended electrical quantity differential equation is written according to the voltage value and output current corresponding to the transient fault to calculate the fault distance.

[0104] In one possible implementation, the single-ended electrical quantity differential equation includes:

[0105] When a single-phase grounding fault occurs, after the characteristic voltage is input, the fault phase voltage and phase current meet the following conditions:

[0106]

[0107] In the formula, u A 、i A are the voltage and current of the fault phase respectively; i 0 K is the zero-sequence current measured for the access line; r , K l are the zero-sequence current compensation coefficients of the access line resistance and inductance, K r =(r1 -r 0 ) / 3r 1 , K l =(l 1 -l 0 ) / 3l 1 ; r 1 , l 1 and r 0 , l 0 are respectively the positive sequence and zero sequence resistance and inductance of the access line per unit length of the hybrid power flow controller based on the cascade H-bridge; L is the distance from the fault point to the line outlet of the hybrid power flow controller based on the cascade H-bridge;

[0108] When a phase-to-phase short circuit fault occurs, after the characteristic voltage is input, the fault phase voltage and phase current meet the following conditions:

[0109]

[0110] In the formula, u AB 、i AB are the fault phase line voltage and line current measured by the hybrid power flow controller connected to the line; R f is the transition resistance; L is the distance from the fault point to the line outlet of the hybrid power flow controller based on the cascaded H-bridge.

[0111] like Figure 7a and 7b The figure shows the electrical circuit when a fault occurs. Figure 7a It is the electrical circuit when a single-phase grounding fault occurs; Figure 7b This is the electrical circuit when a phase-to-phase short circuit occurs. Refer to the above two electrical quantity differential equations, which only contain the fault distance L and the transition resistance R f These two unknowns, therefore, by using the measured voltage and current at two different times to form an equation group and solve them simultaneously, the fault distance L and transition resistance R can be obtained. f .

[0112] It should be understood that the order of execution of the steps in the above embodiment does not necessarily mean the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiment of the present invention.

[0113] The following is an embodiment of the device of the present invention. For details not described in detail therein, reference may be made to the corresponding method embodiment described above.

[0114] Figure 8 A schematic diagram of the structure of a control device provided by an embodiment of the present invention taking into account access to a hybrid power flow controller is shown. For ease of description, only the parts related to the embodiment of the present invention are shown, which are described in detail as follows:

[0115] like Figure 8 As shown, the control device 8 taking into account the access of the hybrid power flow controller includes:

[0116] The transformer control module 801 is used to adjust the gear position of the phase-shifting transformer to zero when receiving a fault isolation instruction;

[0117] The converter control module 802 is used to control the voltage input terminal of the cascaded H-bridge converter to input a characteristic voltage and obtain the output current of the cascaded H-bridge converter; wherein the characteristic voltage is a step-type voltage;

[0118] The fault judgment module 803 is used to determine the fault property judgment result according to the characteristic voltage and the output current, and to locate the fault according to the fault property judgment result.

[0119] In this embodiment, when a fault isolation instruction is received, the gear position of the phase-shifting transformer is adjusted to zero to ensure that there is no voltage on the line when the grounding switch on the bus side is closed, thereby improving the safety of operation. The voltage input terminal of the cascaded H-bridge converter is controlled to input a characteristic voltage, and the output current of the cascaded H-bridge converter is obtained, and the nature of the line fault is judged by the characteristics of the output current. In addition, the characteristic voltage is set to a stage voltage to avoid excessive voltage input to ensure the stability of the electrical equipment and the overall stability. Afterwards, the fault nature judgment result is determined based on the characteristic voltage and the output current, and the fault is located based on the fault nature judgment result. The embodiment of the present application realizes the use of the flexible and controllable characteristics of the hybrid power flow controller to actively inject a staged characteristic voltage signal into the fault line, realize fault judgment and complete fault ranging, and at the same time, ensure the electrical equipment and the overall stability.

[0120] In the above embodiments, the description of each embodiment has its own emphasis. For parts that are not described or recorded in detail in a certain embodiment, reference can be made to the relevant descriptions of other embodiments.

[0121] Those of ordinary skill in the art will appreciate that the templates, units, and algorithm steps of each example described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are performed in hardware or software depends on the specific application and design constraints of the technical solution. Professional and technical personnel can use different methods to implement the described functions for each specific application, but such implementation should not be considered to be beyond the scope of the present invention.

[0122] If the module / unit is implemented in the form of a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the present invention implements all or part of the processes in the above-mentioned embodiment method, and can also be completed by instructing the relevant hardware through a computer program. The computer program can be stored in a computer-readable storage medium. When the computer program is executed by the processor, it can implement the steps of the above-mentioned control method embodiments taking into account the access of the hybrid power flow controller. Among them, the computer program includes computer program code, and the computer program code can be in source code form, object code form, executable file or some intermediate form. The computer-readable medium may include: any entity or device that can carry the computer program code, recording medium, U disk, mobile hard disk, disk, optical disk, computer memory, read-only memory, random access memory, electrical carrier signal, telecommunication signal and software distribution medium.

[0123] The embodiments described above are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. Such modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention, and should all be included in the protection scope of the present invention.

Claims

1. A control method taking into account the access of a hybrid power flow controller, the hybrid power flow controller comprising: Phase-shifting transformer and cascaded H-bridge converter; characterized in that the method comprises: When receiving the fault isolation instruction, adjusting the gear position of the phase-shifting transformer to zero; Controlling the voltage input terminal of the cascaded H-bridge converter to input a characteristic voltage, and obtaining the output current of the cascaded H-bridge converter; wherein the characteristic voltage is a step-type voltage; A fault property identification result is determined according to the characteristic voltage and the output current, and the fault is located according to the fault property identification result.

2. The control method according to claim 1, characterized in that: The voltage values ​​corresponding to each stage of the characteristic voltage are different and are less than the rated voltage of the cascaded H-bridge converter; and the voltage maintenance time corresponding to each stage is the same.

3. The control method according to claim 2, wherein: Determining a fault property determination result according to the characteristic voltage and the output current includes: In the first voltage input stage, the input voltage is controlled to be a first voltage value, an output current of the cascaded H-bridge converter is integrated to obtain a first current integral value, and when the first current integral value is greater than a first set current value, a permanent fault is determined; Otherwise, enter the second voltage input stage; In the second voltage input stage, the input voltage is controlled to be a second voltage value, an output current of the cascaded H-bridge converter is integrated to obtain a second current integral value, and when the second current integral value is greater than a second set current value, a permanent fault is determined; Otherwise, enter the third voltage input stage; In the third voltage input stage, the input voltage is controlled to be a third voltage value, and an output current of the cascaded H-bridge converter is integrated to obtain a third current integral value. When the third current integral value is greater than a third set current value, it is determined to be a permanent fault; otherwise, it is determined to be a transient fault; Among them, the third voltage value is greater than the second voltage value; the second voltage value is greater than the first voltage value.

4. The control method according to claim 3 taking into account the access of the hybrid power flow controller, characterized in that: The first voltage value is 10% of the rated voltage of the cascaded H-bridge converter; the second voltage value and the third voltage value are integer multiples of the first voltage value.

5. The control method taking into account the access of the hybrid power flow controller as claimed in claim 3, characterized in that: The performing of fault location according to the fault property determination result includes: When it is determined to be a transient fault, a single-ended electrical quantity differential equation is written according to the voltage value and output current corresponding to the transient fault to calculate the fault distance.

6. The control method according to claim 5, characterized in that: The single-ended electrical quantity differential equation includes: When a single-phase grounding fault occurs, after the characteristic voltage is input, the fault phase voltage and phase current meet the following conditions: In the formula, u A 、i A are the voltage and current of the fault phase respectively; i0 is the zero-sequence current measured by the access line; K r , K l are the zero-sequence current compensation coefficients of the access line resistance and inductance, K r =(r1-r0) / 3r1, K l =(l1-l0) / 3l1; r1, l1 and r0, l0 are respectively the positive sequence and zero sequence resistance and inductance values ​​per unit length of the access line of the hybrid power flow controller based on the cascade H bridge; L is the distance from the fault point to the outlet of the line of the hybrid power flow controller based on the cascade H bridge; When a phase-to-phase short circuit fault occurs, after the characteristic voltage is input, the fault phase voltage and phase current meet the following conditions: In the formula, u AB 、i AB are the fault phase line voltage and line current measured by the hybrid power flow controller connected to the line; R f is the transition resistance; L is the distance from the fault point to the line outlet of the hybrid power flow controller based on the cascaded H-bridge.

7. The control method according to claim 3, characterized in that: Before determining the fault property determination result according to the characteristic voltage and the output current, the method further includes: A permanent single-phase grounding fault is set at the end of the line, the transition resistance is set to a first resistance value, a second resistance value and a third resistance value respectively, and a corresponding injection voltage is respectively corresponding to the first voltage value, the second voltage value and the third voltage value; The output current integral values ​​corresponding to the first voltage value, the second voltage value and the third voltage value are calculated respectively and determined as the current setting values ​​corresponding to each stage of the characteristic voltage; wherein the current setting values ​​include the first set current value, the second set current value and the third set current value.

8. The control method according to claim 7, characterized in that: The first resistance, the second resistance and the third resistance are 20Ω, 100Ω and 200Ω respectively.

9. The control method taking into account the access of the hybrid power flow controller according to claim 1, characterized in that: The hybrid power flow controller is connected to circuit breakers on both sides respectively; after determining the fault nature judgment result according to the characteristic voltage and the output current, it also includes: When a permanent fault is determined, the three-phase reclosing switch is controlled to lock, and the fault line is measured and shut down for maintenance; When it is determined to be a transient fault, the grounding switch is controlled to be disconnected, and the three-phase reclosing switch is controlled to control the circuit breakers on both sides to be closed in sequence, so that the hybrid power flow controller access line can resume operation.

10. A control device taking into account the access of a hybrid power flow controller, the hybrid power flow controller comprising: Phase-shifting transformer and cascaded H-bridge converter; characterized in that the device comprises: A transformer control module, configured to adjust the gear position of the phase-shifting transformer to zero upon receiving a fault isolation instruction; A converter control module, used for controlling the voltage input terminal of the cascaded H-bridge converter to input a characteristic voltage and obtaining the output current of the cascaded H-bridge converter; wherein the characteristic voltage is a step-type voltage; The fault judgment module is used to determine a fault property judgment result according to the characteristic voltage and the output current, and to locate the fault according to the fault property judgment result.

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