Self-voltage-stabilizing system and method for active and passive integrated ground fault regulation and control device

Abstract

The invention discloses a self-voltage-stabilizing system and method for a power distribution network active and passive integrated ground fault regulation and control device, and the system comprises a fault judgment module, the active and passive integrated ground fault regulation and control device, an arc extinction reactive energy output module and a fault elimination module based on the active and passive integrated ground fault regulation and control device. The method comprises the following steps: measuring resistance to ground and capacitance to ground of a line during normal operation of a system, and judging whether a single-phase ground fault occurs or not; if the grounding fault does not occur, measuring the three-phase voltage and current of the load and performing split-phase injection of reactive compensation current; after the system has a single-phase earth fault, controlling the active and passive integrated earth fault regulation and control device to output active energy to be 0, and outputting reactive energy required by arc extinction according to reactive compensation current injected into the power distribution network at present; and reducing the injected arc extinction current after the time period t, and observing whether the neutral point voltage changes proportionally.

Description

Technical Field

[0001] The present invention relates to the technical field of distribution networks, and particularly to a self-voltage stabilizing system and method for an active and passive integrated grounding fault control device. Background Art

[0002] Among various faults in distribution networks, single-phase grounding faults account for the largest proportion, about 60% - 80%; with the large-scale access of new energy, the proportion of active components and harmonic components in the single-phase grounding fault current is continuously increasing, and the arc is difficult to extinguish by itself; if the single-phase grounding fault is not handled in time, it will cause personal electric shock, fire accidents and equipment insulation breakdown. Therefore, realizing the active control of single-phase faults is an important guarantee for the safe and reliable operation of distribution networks.

[0003] The development of arc suppression for faults has gone through 3 stages. Currently, the neutral point passive arc suppression method is widely used in distribution networks. Although this method has a simple topology and can compensate the single-phase grounding fault current to a certain extent, the arc suppression coil is bulky and is in an idle state for a long time, with low utilization rate; secondly, the arc suppression coil can only compensate the reactive component in the grounding current and cannot compensate the active and harmonic components.

[0004] With the development of power electronics technology, domestic and foreign scholars have conducted preliminary research on active arc suppression methods. Compared with passive arc suppression methods, active arc suppression methods can achieve full compensation of grounding fault current. The neutral point active arc suppression method uses an active inverter in cooperation with a fixed-step arc suppression coil, injects a compensation current at the system neutral point through the active inverter, and then controls the neutral point voltage of the system. However, this method has problems such as difficult power extraction from the DC side and low equipment utilization rate; the non-neutral point active arc suppression method directly connects the converter to the three-phase line, combines the reactive power compensation function and the arc suppression function, and improves the utilization rate and practicability of the device; when the power grid is operating normally, the device outputs reactive power compensation current; when a single-phase grounding fault occurs in the power grid, the device outputs arc suppression current to realize the control of single-phase grounding faults; however, the non-neutral point active arc suppression device needs to maintain the stability of the DC side capacitor voltage by adding an additional power supply device, which greatly increases the overall cost of the device.

[0005] Based on the problems existing in the existing arc suppression schemes, those skilled in the art then proposed an active and passive integrated grounding fault control device for distribution networks, such as Figure 1As shown in the figure, the active part is composed of cascaded H-bridges, and the passive part is composed of arc suppression coils. In the fault mode, the passive part undertakes the phase voltage to realize active fault regulation, and improves the overall economy of the device, providing strong support for the "reliability, safety, and economy" of the operation of the distribution network. However, when using the traditional active arc suppression method, the energy of the capacitor on the DC side of the converter is limited and it is difficult to continuously output the active energy required for arc suppression. Therefore, the DC side voltage continues to drop. As the DC side voltage of the converter continues to decrease, the grounding fault current increases continuously at this time, and the converter loses the arc suppression effect, seriously threatening the operation safety of the non-neutral point active arc suppression device and even the system. Summary of the Invention

[0006] In view of this, the present invention provides a self-voltage stabilizing system and method for an active and passive integrated grounding fault regulation device, which is used to at least solve the problem of how to achieve full compensation of single-phase grounding fault current and stable DC side capacitor voltage for the active and passive integrated grounding fault regulation device of the distribution network without relying on an external energy supply device.

[0007] In order to achieve the above object, the present invention adopts the following technical solutions:

[0008] A self-voltage stabilizing system for an active and passive integrated grounding fault regulation device of a distribution network, based on the active and passive integrated grounding fault regulation device, includes:

[0009] A fault judgment module, used to measure the line-to-ground resistance and capacitance during normal system operation, calculate the total arc suppression current to complete arc suppression, and judge whether a single-phase grounding fault occurs according to the change of the neutral point voltage;

[0010] An active and passive integrated grounding fault regulation device, used to measure the three-phase voltage and current of the load and inject reactive compensation current in a phase-by-phase manner;

[0011] An arc suppression reactive energy output module, used to control the active energy output of the active and passive integrated grounding fault regulation device to be 0 after a single-phase grounding fault occurs in the system, and output the reactive energy required for arc suppression according to the current reactive compensation current injected into the distribution network;

[0012] A fault elimination module, used to reduce the reactive compensation current and observe whether the neutral point voltage changes proportionally; if the neutral point voltage decreases proportionally, it means that the fault is eliminated and the distribution network resumes normal operation; if the neutral point voltage does not decrease proportionally, the faulty line is isolated.

[0013] Preferably, the arc suppression reactive energy output module includes: a reactive power acquisition unit, a power loop, a DC side capacitor voltage acquisition unit, a voltage stabilizing loop, a current loop, and a carrier phase-shifted modulation unit;

[0014] A reactive power acquisition unit, configured to calculate the reactive energy Q required for arc suppression in the Y-phase and Z-phase when a single-phase grounding fault occurs in the X-phase Y * and Q Z * , and obtain the actual value of the reactive energy, where X represents any one of the A-phase, B-phase, and C-phase, and Y and Z respectively represent the remaining two phases;

[0015] The power loop includes a Y-phase power loop and a Z-phase power loop. Subtract Q Y * and Q Z * from the actual reactive energy values of the Y-phase and Z-phase respectively to obtain the reactive energy differences on the Y-phase and Z-phase, and respectively pass the reactive energy differences on the Y-phase and Z-phase through the Y-phase power loop and the Z-phase power loop to obtain the arc suppression current reference values i zY and i zZ ;

[0016] A DC-side capacitor voltage acquisition unit, configured to obtain the actual value and the reference value of the DC-side capacitor voltage of the Y-phase and Z-phase when a single-phase grounding fault occurs in the X-phase;

[0017] The voltage stabilization loop includes a Y-phase voltage stabilization loop and a Z-phase voltage stabilization loop. Subtract the reference value and the actual value of the DC-side capacitor voltage of the Y-phase and Z-phase respectively to obtain the DC-side capacitor voltage differences on the Y-phase and Z-phase, and respectively pass the DC-side capacitor voltage differences on the Y-phase and Z-phase through the Y-phase voltage stabilization loop and the Z-phase voltage stabilization loop to obtain the voltage stabilization current reference values i dcY and i dcZ ;

[0018] The current loop includes a Y-phase current loop and a Z-phase current loop. Subtract the sum of i zY and i dcY from the actual output current i cY to obtain the Y-phase deviation amount. Subtract the sum of i zZ and i dcZ from the actual output current i cZ to obtain the Z-phase deviation amount. Take the Y-phase deviation amount and the Z-phase deviation amount as the inputs of the Y-phase current loop and the Z-phase current loop respectively. The outputs of the Y-phase current loop and the Z-phase current loop are respectively added with the Y-phase grid connection point voltage u sY and the Z-phase grid connection point voltage u sZ to generate a modulation signal;

[0019] The carrier phase-shifted modulation unit is configured to form a switching signal after subjecting the modulation signal to carrier phase-shifted PWM modulation.

[0020] Preferably, both the Y-phase power loop and the Z-phase power loop include an adder, a power loop PI controller, a phase-locked loop PLL, a cosine function, and a multiplier;

[0021] The adder is used to obtain the reactive power difference on the Y-phase or Z-phase;

[0022] The reactive power difference on the Y-phase or Z-phase is output to the multiplier after passing through the power loop PI controller;

[0023] The line voltages of the YX-phase or ZX-phase are sequentially processed by the phase-locked loop PLL and the cosine function and then output a control signal to the multiplier;

[0024] The multiplier multiplies the obtained signals and then outputs to obtain the reference value of the arc suppression current.

[0025] Preferably, both the Y-phase voltage stabilizing loop and the Z-phase voltage stabilizing loop include an adder, a voltage loop PI controller, a phase-locked loop PLL, a sine function, and a multiplier;

[0026] The adder is used to obtain the DC-side capacitor voltage difference on the Y-phase or Z-phase;

[0027] The DC-side capacitor voltage difference on the Y-phase or Z-phase is output to the multiplier after passing through the voltage loop PI controller;

[0028] The line voltages of the YX-phase or ZX-phase are sequentially processed by the phase-locked loop PLL and the sine function and then output a control signal to the multiplier;

[0029] The multiplier multiplies the obtained signals and then outputs to obtain the reference value of the voltage stabilizing current.

[0030] A self-voltage stabilizing method for an active and passive integrated grounding fault regulation device for a distribution network, based on the active and passive integrated grounding fault regulation device, includes the following steps:

[0031] S1. Measure the line-to-ground resistance and capacitance during normal system operation, and determine whether a single-phase grounding fault occurs; if no grounding fault occurs, measure the three-phase voltages and currents of the load and inject reactive compensation currents in a phase-by-phase manner; otherwise, enter S2;

[0032] S2. After a single-phase grounding fault occurs in the system, control the active and passive integrated grounding fault regulation device to output zero active power, and output the reactive power required for arc suppression according to the current reactive compensation current injected into the distribution network;

[0033] S3. After t time periods, reduce the injected arc suppression current and observe whether the neutral point voltage changes proportionally; if the neutral point voltage decreases proportionally, it means that the fault is eliminated and the distribution network resumes normal operation; if the neutral point voltage does not decrease proportionally, isolate the faulty line, where t is any preset time period.

[0034] Preferably, the specific content of S2 includes:

[0035] When a single-phase grounding fault occurs in the X phase, calculate the reactive energy Q required for arc suppression in the Y phase and the Z phase Y * and Q Z * , and obtain the actual value of the reactive energy. Here, X represents any one of the A phase, B phase, and C phase, and Y and Z respectively represent the remaining two phases; at the same time, obtain the actual value and the reference value of the DC-side capacitor voltage in the Y phase and the Z phase;

[0036] Subtract Q Y * and Q Z * from the actual reactive energy values corresponding to the Y phase and the Z phase respectively to obtain the reactive energy differences on the Y phase and the Z phase, and respectively pass the reactive energy differences on the Y phase and the Z phase through the Y-phase power loop and the Z-phase power loop to obtain the reference arc suppression current values i zY and i zZ ;

[0037] Subtract the reference value and the actual value of the DC-side capacitor voltage in the Y phase and the Z phase to obtain the DC-side capacitor voltage differences on the Y phase and the Z phase respectively, and respectively pass the DC-side capacitor voltage differences on the Y phase and the Z phase through the Y-phase voltage stabilization loop and the Z-phase voltage stabilization loop to obtain the reference voltage stabilization current values i dcY and i dcZ ;

[0038] Subtract i zY 、i zZ as well as i dcY and i dcZ from the actual output current to obtain the deviation amount, which is used as the input of the Y-phase current loop and the Z-phase current loop. The outputs of the Y-phase current loop and the Z-phase current loop are respectively added with the voltage differences between the grid connection point and the power grid to generate the modulation signal;

[0039] The modulation signal is formed into a switching signal through carrier phase-shifted PWM modulation.

[0040] Preferably, the specific content of obtaining the reference arc suppression current value includes:

[0041] Obtain the reactive energy difference on the Y phase or the Z phase;

[0042] The reactive energy difference on the Y phase or the Z phase is output to the multiplier after passing through the power loop PI controller;

[0043] The line voltage of the YX phase or the ZX phase is output to the multiplier as a control signal after passing through the phase-locked loop PLL and the cos function processing in sequence;

[0044] The multiplier multiplies the obtained signals and outputs to obtain the reference arc suppression current value.

[0045] Preferably, the specific content of obtaining the regulated current reference value includes:

[0046] Obtain the DC-side capacitor voltage difference on the Y-phase or Z-phase;

[0047] The DC-side capacitor voltage difference on the Y-phase or Z-phase is output to the multiplier after passing through the voltage-loop PI controller;

[0048] The line voltage of the YX-phase or ZX-phase is output to the multiplier as a control signal after passing through the phase-locked loop PLL and the sin function processing in sequence;

[0049] The multiplier multiplies the obtained signals and outputs to obtain the regulated current reference value.

[0050] It can be seen from the above technical solutions that, compared with the prior art, the present invention discloses a self-regulation method for a distribution network active and passive integrated grounding fault control device, which has the following beneficial effects:

[0051] The present invention discloses a self-regulation system and method for a distribution network active and passive integrated grounding fault control device, which is applicable to the distribution network active and passive integrated grounding fault control device. After a single-phase grounding occurs in the system, at this time, the active energy output by the non-neutral-point active arc suppression device is controlled to be zero, and only the reactive energy required for arc suppression is output, effectively suppressing the single-phase grounding fault and maintaining the stability of the DC-side capacitor voltage of the arc suppression device at the same time; by adopting the proposed self-regulation arc suppression method, the present invention effectively avoids adding an additional energy supply device to the DC side of the active and passive integrated grounding fault control device, reduces the overall cost of the device, and ensures the safe operation of the active and passive integrated grounding fault control device. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0053] Figure 1 Structural diagram of the active and passive integrated grounding fault control device provided by the embodiment of the present invention;

[0054] Figure 2 Zero-sequence power flow diagram of the traditional two-phase arc suppression method provided by the embodiment of the present invention;

[0055] Figure 3 Phasor diagram of the traditional two-phase arc suppression method provided by the embodiment of the present invention;

[0056] Figure 4Zero-sequence power flow diagram of a self-voltage regulation method for an active and passive integrated grounding fault regulation device provided by an embodiment of the present invention;

[0057] Figure 5 Flowchart of a self-voltage regulation method for an active and passive integrated grounding fault regulation device provided by the present invention;

[0058] Figure 6 Structural schematic diagram of a self-voltage regulation system for an active and passive integrated grounding fault regulation device provided by the present invention;

[0059] Figure 7 Simulation waveform diagram obtained without using the self-voltage regulation method of the present invention for regulation; Figure 7 (a) Waveform diagrams of U dca 、U dcb 、U dcc ; Figure 7 (b) Waveform diagram of fault current I g during the simulation;

[0060] Figure 8 Simulation waveform diagram obtained by using the self-voltage regulation method provided by the present invention for regulation; Figure 8 (a) Waveform diagrams of grounding fault current I f and fault phase voltage U f ; Figure 8 (b) Waveform diagram of the capacitor voltage of the B-phase converter of the active and passive integrated grounding fault regulation device; Figure 8 (c) Waveform diagram of the capacitor voltage of the C-phase converter of the active and passive integrated grounding fault regulation device; Figure 8 (d) Waveform diagrams of output currents I ia 、I ib 、I ic ; Detailed implementation manners

[0061] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0062] The structure of the active and passive integrated grounding fault regulation device is as Figure 1 shown in the figure, where are the power supply voltages of the A, B, and C phases respectively; r A 、r B 、r CThey are the line-to-ground resistances of phases A, B, and C respectively; C 0A , C 0B , C 0C They are the line-to-ground capacitances of phases A, B, and C respectively; R f is the transition resistance of the grounding fault; is the neutral point voltage of the power grid. The zero-sequence power flow diagram of the traditional two-phase arc suppression method is as shown in Figure 2 . Assuming a single-phase grounding fault occurs in phase A and the phase A converter exits operation, write the KCL equation for point D and substitute the voltage and network parameters to obtain:

[0063]

[0064] Among them, Assume C 0A = C 0B = C 0C = C0, r A = r B = r C = r0. Substitute the above relationships into Equation (1) to obtain the injected arc suppression current as:

[0065]

[0066] The phase B and phase C converters jointly inject the total arc suppression current into the power grid. Among them, are the arc suppression currents of the phase B and phase C converters of MC respectively; α is the angle between the line-to-ground resistance and capacitance, which can be expressed as: α = arctan(1 / ωC0r0).

[0067] As shown in Figure 3 , the zero-sequence active power P zbc and reactive power Q zbc output by the phase B and phase C converters are:

[0068]

[0069] To sum up, when the traditional two-phase arc suppression method is adopted, it is necessary to output both active power and reactive power at the same time. Therefore, an additional energy supply device needs to be connected to the DC side of the active part to maintain the stability of the DC side capacitor voltage.

[0070] As shown in Figure 4 , in view of the above problems, the present invention proposes a self-voltage stabilizing system and method for an active and passive integrated grounding fault regulation device for a distribution network, which controls the active and passive integrated grounding fault regulation device to only output reactive power in the fault regulation mode, and realizes the full compensation of the single-phase grounding fault current and the stability of the DC side capacitor voltage without relying on an external energy supply device.

[0071] The present invention provides a self - voltage - stabilizing system for an active - passive integrated grounding - fault regulation device for a distribution network. Based on the active - passive integrated grounding - fault regulation device, it includes:

[0072] A fault judgment module, which is used to measure the line - to - ground resistance and line - to - ground capacitance during normal system operation, calculate the total arc - suppression current to complete arc - suppression, and judge whether a single - phase grounding fault occurs according to the change of the neutral - point voltage;

[0073] An active - passive integrated grounding - fault regulation device, which is used to measure the three - phase voltage and current of the load and inject reactive - power compensation current in a phase - by - phase manner;

[0074] An arc - suppression reactive - power output module, which is used to control the active - power output of the active - passive integrated grounding - fault regulation device to be 0 after a single - phase grounding fault occurs in the system, and output the reactive - power required for arc - suppression according to the current reactive - power compensation current injected into the distribution network;

[0075] A fault elimination module, which is used to reduce the reactive - power compensation current and observe whether the neutral - point voltage changes proportionally; if the neutral - point voltage decreases proportionally, it means that the fault is eliminated and the distribution network resumes normal operation; if the neutral - point voltage does not decrease proportionally, the faulty line is isolated.

[0076] It should be noted that:

[0077] In this embodiment, when the change of the neutral - point voltage exceeds 15% of the phase voltage, it is judged that a single - phase grounding fault occurs; this threshold is determined according to the actual situation.

[0078] The reactive - power compensation current is reduced by linearly reducing the arc - suppression current. The specific method is: reduce the arc - suppression current in multiple times. For example, the arc - suppression current is reduced by 1A for the first time, and still reduced by 1A for the second and third times, and observe the change amount of the neutral - point voltage. For example, if the neutral - point voltage decreases by 10V all three times, the fault is eliminated; otherwise, the fault still exists.

[0079] To further implement the above - mentioned technical solution, the arc - suppression reactive - power output module includes: a reactive - power acquisition unit, a power loop, a DC - side capacitor voltage acquisition unit, a voltage - stabilizing loop, a current loop, and a carrier - phase - shift modulation unit;

[0080] The reactive - power acquisition unit is used to calculate the reactive - power Q Y * and Q Z * required for arc - suppression of the Y - phase and Z - phase when a single - phase grounding fault occurs in the X - phase, and obtain the actual value of the reactive - power, where X represents any one of the A - phase, B - phase, and C - phase, and Y and Z respectively represent the remaining two phases;

[0081] The power loop includes a Y-phase power loop and a Z-phase power loop, and Q Y * and Q Z * are respectively subtracted from the actual reactive energy values of the Y-phase and Z-phase to obtain the reactive energy differences on the Y-phase and Z-phase, and the reactive energy differences on the Y-phase and Z-phase are respectively passed through the Y-phase power loop and the Z-phase power loop to obtain the arc suppression current reference values i zY and i zZ ;

[0082] The DC-side capacitor voltage acquisition unit is used to acquire the actual DC-side capacitor voltage values and the DC-side capacitor voltage reference values of the Y-phase and Z-phase when a single-phase grounding fault occurs in the X-phase;

[0083] The voltage stabilization loop includes a Y-phase voltage stabilization loop and a Z-phase voltage stabilization loop. The DC-side capacitor voltage reference values and the actual DC-side capacitor voltage values of the Y-phase and Z-phase are subtracted from each other to obtain the DC-side capacitor voltage differences on the Y-phase and Z-phase respectively, and the DC-side capacitor voltage differences on the Y-phase and Z-phase are respectively passed through the Y-phase voltage stabilization loop and the Z-phase voltage stabilization loop to obtain the voltage stabilization current reference values i dcY and i dcZ ;

[0084] The current loop includes a Y-phase current loop and a Z-phase current loop. The sum of i zY and i dcY is subtracted from the actual output current i cY to obtain the Y-phase deviation amount. The sum of i zZ and i dcZ is subtracted from the actual output current i cZ to obtain the Z-phase deviation amount. The Y-phase deviation amount and the Z-phase deviation amount are respectively used as the inputs of the Y-phase current loop and the Z-phase current loop, and the outputs of the Y-phase current loop and the Z-phase current loop are respectively added with the Y-phase grid connection point voltage u sY and the Z-phase grid connection point voltage u sZ to generate a modulation signal;

[0085] The carrier phase-shifted modulation unit is used to form a switching signal after modulating the modulation signal through carrier phase-shifted PWM modulation.

[0086] To further implement the above technical solution, both the Y-phase power loop and the Z-phase power loop include an adder, a power loop PI controller, a phase-locked loop PLL, a cosine function, and a multiplier;

[0087] The adder is used to obtain the reactive energy difference on the Y-phase or Z-phase;

[0088] The reactive energy difference on the Y-phase or Z-phase is output to the multiplier after passing through the power loop PI controller;

[0089] The line voltage of the YX phase or ZX phase passes through a phase-locked loop (PLL) and a cosine function in sequence, and then outputs a control signal to a multiplier.

[0090] The multiplier multiplies the obtained signals and outputs to obtain the reference value of the arc suppression current.

[0091] To further implement the above technical solution, both the Y-phase voltage stabilizing loop and the Z-phase voltage stabilizing loop include an adder, a voltage loop PI controller, a phase-locked loop (PLL), a sine function, and a multiplier.

[0092] The adder is used to obtain the DC-side capacitor voltage difference on the Y phase or Z phase.

[0093] The DC-side capacitor voltage difference on the Y phase or Z phase is output to the multiplier after passing through the voltage loop PI controller.

[0094] The line voltage of the YX phase or ZX phase passes through a phase-locked loop (PLL) and a sine function in sequence, and then outputs a control signal to a multiplier.

[0095] The multiplier multiplies the obtained signals and outputs to obtain the reference value of the voltage stabilizing current.

[0096] A self-voltage stabilizing method for an active and passive integrated grounding fault control device for a distribution network, based on the active and passive integrated grounding fault control device, includes the following steps:

[0097] S1. During normal system operation, measure the line-to-ground resistance and capacitance, and determine whether a single-phase grounding fault occurs; if no grounding fault occurs, measure the three-phase voltage and current of the load and inject reactive compensation current in a phase-by-phase manner; otherwise, enter S2.

[0098] S2. After a single-phase grounding fault occurs in the system, control the active and passive integrated grounding fault control device to output 0 active power, and output the reactive power required for arc suppression according to the current injected reactive compensation current into the distribution network.

[0099] S3. After t time periods, reduce the injected arc suppression current and observe whether the neutral point voltage changes proportionally; if the neutral point voltage decreases proportionally, it means the fault is eliminated and the distribution network resumes normal operation; if the neutral point voltage does not decrease proportionally, isolate the faulty line, where t is any preset time period.

[0100] To further implement the above technical solution, the specific content of S2 includes:

[0101] When a single-phase grounding fault occurs in the X phase, calculate the reactive power Q required for arc suppression in the Y phase and Z phase Y * and Q Z *, and obtain the actual value of the reactive power. Here, X represents any one of phase A, phase B, and phase C, and Y and Z respectively represent the remaining two phases; meanwhile, obtain the actual value and the reference value of the DC-side capacitor voltage of phase Y and phase Z;

[0102] Subtract Q Y * from Q Z * respectively to obtain the reactive power differences on phase Y and phase Z by taking the differences with the actual values of the reactive power of phase Y and phase Z, and respectively pass the reactive power differences on phase Y and phase Z through the power loop of phase Y and the power loop of phase Z to obtain the reference value of the arc suppression current i zY and i zZ ;

[0103] Subtract the reference value of the DC-side capacitor voltage of phase Y and phase Z from the actual value of the DC-side capacitor voltage of phase Y and phase Z respectively to obtain the DC-side capacitor voltage differences on phase Y and phase Z, and respectively pass the DC-side capacitor voltage differences on phase Y and phase Z through the voltage stabilization loop of phase Y and the voltage stabilization loop of phase Z to obtain the reference value of the voltage stabilization current i dcY and i dcZ ;

[0104] Respectively subtract i zY , i zZ and i dcY from i dcZ and the actual output current to obtain the deviation, which is used as the input of the current loop of phase Y and the current loop of phase Z. The outputs of the current loop of phase Y and the current loop of phase Z are respectively added with the voltage difference between the grid connection point and the power grid to generate the modulation signal;

[0105] The modulation signal is processed by carrier phase-shifted PWM modulation to form the switching signal.

[0106] To further implement the above technical solution, the specific content of obtaining the reference value of the arc suppression current includes:

[0107] Obtain the reactive power difference on phase Y or phase Z;

[0108] The reactive power difference on phase Y or phase Z is output to the multiplier after passing through the power loop PI controller;

[0109] The line voltage of phase YX or phase ZX is output to the multiplier as the control signal after passing through the phase-locked loop PLL and the cosine function processing in sequence;

[0110] The multiplier multiplies the obtained signals and outputs to obtain the reference value of the arc suppression current.

[0111] To further implement the above technical solution, the specific content of obtaining the reference value of the voltage stabilization current includes:

[0112] Obtain the DC-side capacitor voltage difference on phase Y or phase Z;

[0113] The voltage difference of the DC-side capacitors on the Y-phase or Z-phase is output to the multiplier after passing through the voltage-loop PI controller;

[0114] The line voltages of the YX-phase or ZX-phase are sequentially output to the multiplier as control signals after passing through the phase-locked loop PLL and the sin function processing;

[0115] The multiplier multiplies the obtained signals and outputs to obtain the regulated current reference value.

[0116] The zero-sequence active power P z ' bc and the zero-sequence reactive power Q z ' bc of the non-fault phase converters are:

[0117]

[0118] Therefore, when the active and passive integrated grounding fault control device adopts the self-regulated voltage control method, the B-phase and C-phase converters compensate the zero-sequence reactive power, and the grid side compensates the zero-sequence active power.

[0119] According to equations (2) and (4), by controlling the active and reactive powers of the control device to make the device only absorb reactive power and the grid side only output active power, it is possible to maintain the stability of the DC-side voltage and effectively control the single-phase grounding fault.

[0120] In this embodiment, taking the single-phase grounding fault of the C-phase as an example, the system principle is as Figure 6 shown. In the figure, Q a * and Q b * represent the reactive power reference values of the A-phase and B-phase, Q a and Q b represent the actual reactive power values of the A-phase and B-phase, i za and i zb represent the current reference values corresponding to the power loops of the A-phase and B-phase, i dca and i dcb represent the current reference values corresponding to the voltage-regulated loops of the A-phase and B-phase, E ac and E bc represent the line voltages of the AC-phase and BC-phase, N represents the number of cascades, U dca.ref and U dcb.ref represent the reference values of the DC-side capacitor voltages, ∑U dcai and ∑U dcbi represent the actual values of the DC-side capacitor voltages.

[0121] When a single-phase grounding fault occurs in the C-phase, calculate the reactive powers Q a * 、Qb * , after taking the difference between it and the actual value, the arc suppression current reference value \(i\) is obtained through the power loop PI za 、\(i\) zb . In the voltage stabilization loop part, after taking the difference between the reference value and the actual value of the DC-side voltage, the voltage stabilization current reference value \(i\) is obtained through the voltage loop PI dca 、\(i\) dcb . In the current loop part, the difference between the current reference value obtained from the power loop and the voltage stabilization loop and the actual output current is calculated to obtain a deviation, which is used as the input of the current loop PI. The output of the current loop PI is added to the voltage difference between the grid connection point and the power grid to generate a modulation signal, which is formed into a switching signal after carrier phase-shifted PWM modulation and output to the converter in the active and passive integrated grounding fault control device

[0122] Figure 7 is the simulation waveform diagram obtained by controlling without using the self-voltage stabilization method of the present invention. The simulation sets that the power grid operates normally from 0.8 s to 0.9 s; a single-phase grounding fault occurs in phase A at 0.9 s, and the non-neutral point active arc suppression device outputs the arc suppression current. In the figure, \(U\) dca 、\(U\) dcb 、\(U\) dcc are the DC-side capacitor voltages, and \(I\) g is the fault current. As can be seen from Figure 7 (a), the arc suppression current is injected into phase B, the non-fault phase, at 0.913 s. Since the energy of the DC-side capacitor of the arc suppression device is limited and it is difficult to continuously output the active power required for arc suppression, the DC-side voltage drops continuously. As can be seen from Figure 7 (b), during the period from 0.913 s to 1.105 s, the arc suppression device can effectively suppress the arc. As the DC-side voltage continues to decrease, the grounding fault current increases continuously at this time, and the arc suppression device loses the arc suppression effect

[0123] Figure 8 is the simulation waveform diagram obtained by controlling using the self-voltage stabilization method provided by the present invention. It is assumed that a single-phase grounding fault occurs in phase A of the distribution network at 0.3 s. During the period from 0.2 s to 0.3 s, the device operates in the reactive power compensation mode; during the period from 0.3 s to 0.5 s, the MTC operates in the fault control mode, and the simulation waveform is as shown in Figure 8 . The grounding fault current \(I\) f and the fault phase voltage \(U\) f waveforms are as shown in Figure 8 (a). After the device switches to the fault control mode, the fault current \(I\) f is suppressed to zero within 100 ms. At the same time, the fault phase voltage \(U\) f is also suppressed to zero. The capacitor voltages of the converters in phases B and C of the device are as shown in Figure 8(As shown in (b) to (c)), after switching to the fault regulation mode, the capacitor voltages of each sub-module are all stabilized at around 2 kV, thus ensuring that the device can accurately output the arc suppression current. Output currents I ia , I ib , Iic are as Figure 8 (d) shown. In the reactive power compensation mode, the MC accurately injects the reactive power compensation current; in the fault regulation mode, the calculated arc suppression currents injected into phases B and C are 73.7131∠-30.82° and 75.14∠-149.57° respectively, and the MC accurately injects the arc suppression current, thus realizing the single-phase grounding fault regulation.

[0124] The above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them; although the present application has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application, and should all be included in the protection scope of the present application.

Claims

1. A self-stabilizing voltage system for an active and passive integrated ground fault control device for a distribution network, based on an active and passive integrated ground fault control device, characterized in that: include: The fault judgment module is used to measure the line-to-ground resistance and ground capacitance during normal system operation, calculate the total arc extinguishing current to complete arc extinguishing, and judge whether a single-phase grounding fault occurs according to the change of the neutral point voltage; Active and passive integrated ground fault control device, used to measure the three-phase voltage and current of the load and inject reactive compensation current in phases; The arc extinguishing reactive energy output module is used to control the active passive integrated ground fault control device to output the reactive energy to 0 after a single-phase ground fault occurs in the system, and output the reactive energy required for arc extinguishing according to the reactive compensation current currently injected into the distribution network; Fault elimination module, used to reduce reactive compensation current and observe whether the neutral point voltage changes proportionally; If the neutral point voltage decreases proportionally, it means that the fault is eliminated and the distribution network resumes normal operation; if the neutral point voltage decreases disproportionately, the faulty line is isolated.

2. The self-stabilizing voltage system of the active and passive integrated ground fault control device for distribution network according to claim 1 is characterized in that: The arc extinguishing reactive energy output module includes: a reactive power acquisition unit, a power loop, a DC side capacitor voltage acquisition unit, a voltage stabilization loop, a current loop and a carrier phase shift modulation unit; Reactive power acquisition unit, used to calculate the reactive energy Q required for arc extinguishing of phases Y and Z when a single-phase grounding fault occurs on phase X Y * and Q Z * , and obtain the actual value of the reactive energy, where X represents any one of phases A, B and C, and Y and Z represent the remaining two phases respectively; The power loop includes the Y-phase power loop and the Z-phase power loop. Y * and Q Z * The reactive energy difference between the Y phase and the Z phase is obtained by subtracting the actual value of the reactive energy of the Y phase and the Z phase, and the reactive energy difference between the Y phase and the Z phase is passed through the Y phase power loop and the Z phase power loop to obtain the arc extinguishing current reference value i zY and i zZ ; A DC side capacitor voltage acquisition unit is used to acquire the actual value of the DC side capacitor voltage of the Y phase and the Z phase and the DC side capacitor voltage reference value when a single-phase grounding fault occurs in the X phase; The voltage stabilizing ring includes a Y-phase voltage stabilizing ring and a Z-phase voltage stabilizing ring. The DC side capacitor voltage reference value of the Y-phase and Z-phase and the actual value of the DC side capacitor voltage are subtracted to obtain the DC side capacitor voltage difference on the Y-phase and Z-phase, and the DC side capacitor voltage difference on the Y-phase and Z-phase is passed through the Y-phase voltage stabilizing ring and the Z-phase voltage stabilizing ring to obtain the voltage stabilizing current reference value i dcY and i dcZ ; The current loop includes the Y-phase current loop and the Z-phase current loop. zY and i dcY The sum of the actual output current i cY Calculate the difference to get the Y phase deviation, and then zZ and i dcZ The sum of the actual output current i cZ The difference is calculated to obtain the Z phase deviation, and the Y phase deviation and Z phase deviation are used as the input of the Y phase current loop and the Z phase current loop respectively. The outputs of the Y phase current loop and the Z phase current loop are added with the Y phase grid voltage u sY and Z phase grid voltage u sZ Then generate a modulation signal; The carrier phase shift modulation unit is used to form a switching signal after the modulation signal is subjected to carrier phase shift PWM modulation.

3. The self-stabilizing voltage system of the active and passive integrated ground fault control device for distribution network according to claim 2, characterized in that: Both the Y-phase power loop and the Z-phase power loop include an adder, a power loop PI controller, a phase-locked loop PLL, a cosine function and a multiplier; The adder is used to obtain the reactive energy difference on the Y phase or the Z phase; The reactive energy difference on the Y phase or Z phase is output to the multiplier after passing through the power loop PI controller; The line voltage of the YX phase or ZX phase is processed by the phase-locked loop PLL and the cosine function in turn, and then outputs the control signal to the multiplier; The multiplier multiplies the obtained signals and outputs an arc-extinguishing current reference value.

4. The self-stabilizing voltage system of the active and passive integrated ground fault control device for distribution network according to claim 2, characterized in that: Both the Y-phase voltage stabilizing loop and the Z-phase voltage stabilizing loop include an adder, a voltage loop PI controller, a phase-locked loop PLL, a sin function and a multiplier; The adder is used to obtain the DC side capacitor voltage difference on the Y phase or the Z phase; The DC side capacitor voltage difference on the Y phase or Z phase is output to the multiplier after passing through the voltage loop PI controller; The line voltage of the YX phase or ZX phase is processed by the phase-locked loop PLL and the sin function in turn, and then the control signal is output to the multiplier; The multiplier multiplies the obtained signals and outputs a regulated current reference value.

5. A self-stabilizing voltage method for an active and passive integrated ground fault control device for a distribution network, based on the active and passive integrated ground fault control device, characterized in that: The following steps are involved: S1. Measure the line-to-ground resistance and capacitance during normal system operation and determine whether a single-phase grounding fault occurs; If no ground fault occurs, the three-phase voltage and current of the load are measured and reactive compensation current is injected in phases; otherwise, S2 is entered; S2. After a single-phase grounding fault occurs in the system, the active and passive integrated grounding fault control device is controlled to output a functional energy of 0, and the reactive energy required for arc extinguishing is output according to the reactive compensation current currently injected into the distribution network; After the S3.t period, reduce the injected arc-extinguishing current and observe whether the neutral point voltage changes proportionally; If the neutral point voltage decreases proportionally, it means that the fault is eliminated and the distribution network resumes normal operation; If the neutral point voltage decreases disproportionately, the fault line is isolated, and t is a preset arbitrary period of time.

6. The self-voltage stabilization method for the active and passive integrated ground fault control device for distribution network according to claim 5, characterized in that: The specific contents of S2 include: When a single-phase grounding fault occurs on phase X, calculate the reactive energy Q required for arc extinguishing on phases Y and Z. Y * and Q Z * , and obtain the actual value of the reactive energy, where X represents any one of phases A, B and C, and Y and Z represent the remaining two phases respectively; at the same time, obtain the actual value of the DC side capacitor voltage of phase Y and phase Z and the reference value of the DC side capacitor voltage; Q Y * and Q Z * The reactive energy difference between the Y phase and the Z phase is obtained by subtracting the actual value of the reactive energy of the Y phase and the Z phase, and the reactive energy difference between the Y phase and the Z phase is passed through the Y phase power loop and the Z phase power loop to obtain the arc extinguishing current reference value i zY and i zZ ; The DC side capacitor voltage difference on the Y phase and the Z phase is obtained by subtracting the DC side capacitor voltage reference value and the actual DC side capacitor voltage value on the Y phase and the Z phase, and the DC side capacitor voltage difference on the Y phase and the Z phase is respectively passed through the Y phase voltage stabilizing ring and the Z phase voltage stabilizing ring to obtain the voltage stabilizing current reference value i dcY and i dcZ ; I zY 、i zZ and dcY and i dcZ The difference between the actual output current and the deviation is used as the input of the Y-phase current loop and the Z-phase current loop. The outputs of the Y-phase current loop and the Z-phase current loop are respectively added with the voltage difference between the grid connection point and the grid to generate a modulation signal. The modulation signal is modulated by carrier phase-shift PWM to form a switching signal.

7. The self-voltage stabilization method for the active and passive integrated ground fault control device for distribution network according to claim 6, characterized in that: The specific contents of obtaining the arc extinguishing current reference value include: Get the reactive energy difference on the Y phase or Z phase; The reactive energy difference on the Y phase or Z phase is output to the multiplier after passing through the power loop PI controller; The line voltage of the YX phase or ZX phase is processed by the phase-locked loop PLL and the cosine function in turn, and then outputs the control signal to the multiplier; The multiplier multiplies the obtained signals and outputs an arc-extinguishing current reference value.

8. The self-voltage stabilization method for the active and passive integrated ground fault control device for distribution network according to claim 6, characterized in that: The specific contents of obtaining the reference value of the voltage stabilization current include: Obtain the DC link capacitor voltage difference on the Y phase or the Z phase; The DC side capacitor voltage difference on the Y phase or Z phase is output to the multiplier after passing through the voltage loop PI controller; The line voltage of the YX phase or ZX phase is processed by the phase-locked loop PLL and the sin function in turn, and then the control signal is output to the multiplier; The multiplier multiplies the obtained signals and outputs a regulated current reference value.

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