Power distribution network instantaneous fault recovery control method based on cooperation of energy storage and circuit breaker

Abstract

The invention discloses a power distribution network instantaneous fault recovery control method based on cooperation of energy storage and a circuit breaker. Firstly, a reclosing starting threshold value is set based on a power distribution network voltage after a fault is cleared; then, for a continuous arcing fault, after a circuit breaker trips, an energy storage converter is switched to arcing suppression control with the aim of reducing the voltage of an energy storage grid-connected point; and finally, after the fault arc is extinguished, acquiring the voltage at the downstream outlet of the circuit breaker, and if the voltage at the downstream outlet of the circuit breaker is greater than or equal to the reclosing starting threshold value within the fault detection time, indicating that the fault is eliminated, and reclosing after the first time delay; and if the voltage at the downstream outlet of the circuit breaker in the fault detection time is smaller than the reclosing starting threshold value, it is indicated that the fault is not cleared, and reclosing is carried out after second time delay. According to the method, the circuit breaker is combined with the energy storage power station, the energy storage power station adopts arcing suppression control and supplies power to the downstream load after the fault occurs, the downstream load does not need to operate off the grid, and the power supply reliability of the power grid is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of distribution network fault recovery, and in particular relates to a distribution network instantaneous fault recovery control method based on the collaboration of energy storage and circuit breaker. Background Art

[0002] As the penetration rate of distributed renewable energy continues to climb in distribution networks, energy storage is being deployed within them to address the power fluctuations caused by the high proportion of distributed renewable energy and the weak voltage support issues associated with the electrification of the main grid. However, the integration of a high proportion of distributed renewable energy and energy storage into the distribution network will radically alter the fault characteristics of the distribution network, degrading or even rendering ineffective traditional distribution network fault recovery strategies. Following a transient fault in the distribution network, existing fault recovery strategies that extend the dead time of reclosing require that all distributed renewable energy and energy storage be disconnected from the grid. This can lead to dramatic changes in distribution network power flow before and after the fault, misoperation of protection systems, and secondary impacts on the system.

[0003] With the continuous expansion of distribution networks and the significant increase in cable usage, extinguishing arcs during single-phase ground faults has become increasingly difficult. In such cases, the arc often exhibits alternating extinction and reignition, forming intermittent restrike arcs. Intermittent restrike arcs, also known as intermittent restrike arcs, are difficult to effectively capture due to their complex intermittent reignition characteristics and high randomness. This makes traditional relay protection devices face significant challenges in identifying faults, especially as zero-sequence current protection may fail to operate, making it impossible to quickly remove the faulted phase, thereby causing the distribution network to operate in a faulty state for extended periods. Arc extinction control can help extinguish fault arcs more quickly and shorten reclosing time, making it extremely important for ensuring the safe and stable operation of distribution networks.

[0004] In the prior art, the research on the improvement of reclosing for renewable energy distribution networks is mainly divided into three categories: increasing delay setting, adding no-voltage detection and adaptive reclosing. Among them, the increasing delay setting method coordinates with new energy island protection and fault ride-through to fixedly increase the reclosing delay (usually 3s or more) to avoid the impact of new energy access. However, this method is too time-consuming, and even transient faults will cause all renewable energy to be disconnected from the grid, which is not conducive to rapid system recovery. The adding no-voltage detection method identifies the disconnection status of renewable energy by detecting voltage, but it cannot distinguish it from the zero-voltage situation of a three-phase metallic fault, and still cannot solve the impact problem of reclosing on the fault. Adaptive reclosing refers to first judging the fault status after the circuit breaker trips. If it is determined to be a transient fault and has been cleared, the reclosing is accelerated, otherwise it is locked to prevent reclosing on a permanent fault.

[0005] Existing adaptive reclosing methods are mainly divided into two types: active injection and passive detection. Active injection-based adaptive reclosing uses grid-connected inverters or external equipment to inject high-frequency signals, characteristic voltages, etc. into the downstream system after tripping to determine whether the fault has been cleared. This method requires additional equipment, and the safety of the injected signal for converters and sensitive loads remains to be studied. Passive detection-based adaptive reclosing determines the fault status by detecting information such as the free oscillation frequency, non-fault phase induced current, and phase voltage in the line after tripping. However, these methods are designed for transmission lines with single-phase reclosing and large oscillation time constants, and are not suitable for distribution feeder oscillation components with short duration or three-phase tripping. It can be seen that existing adaptive reclosing methods have problems such as high cost, low safety, and poor applicability. Summary of the Invention

[0006] In view of the deficiencies in the prior art, the technical problem to be solved by the present invention is to provide a distribution network instantaneous fault recovery control method based on the collaboration of energy storage and circuit breakers.

[0007] The present invention solves the technical problem by adopting the following technical solutions:

[0008] A method for controlling the recovery of a distribution network from a transient fault based on the coordination of energy storage and circuit breakers, comprising the following steps:

[0009] Step 1: Set the reclosing start threshold;

[0010] U set =ε·U(1)

[0011] Where U set represents the reclosing start threshold, U represents the distribution network voltage after the fault is cleared, and ε represents the error coefficient;

[0012] Step 2: For continuous arcing faults, after the circuit breaker trips, the energy storage converter is switched to arc suppression control with the goal of reducing the voltage at the energy storage grid connection point. The voltage at the energy storage grid connection point is calculated using the following formula:

[0013]

[0014] The output current of the energy storage power station arc suppression control is:

[0015]

[0016] Where, is the voltage at the energy storage grid connection point, are the output voltage and current of the energy storage station, |·| represents the amplitude, R T 、X T is the equivalent resistance and equivalent reactance of the distribution transformer, is the voltage control target of the energy storage grid connection point, Id , I q To suppress arcing in energy storage power stations and control the active and reactive output currents;

[0017] Step 3: After the fault arc is extinguished, the voltage at the downstream outlet of the circuit breaker is collected. If the voltage at the downstream outlet of the circuit breaker is greater than or equal to the reclosing start threshold within the fault detection time, it indicates that the fault has been cleared, and reclosing will be performed after the first delay; if the voltage at the downstream outlet of the circuit breaker is less than the reclosing start threshold within the fault detection time, it indicates that the fault has not been cleared, and reclosing will be performed after the second delay.

[0018] Furthermore, the fault detection time satisfies the following formula:

[0019] t d =min{t f -t trip +t u ,1.1-t trip ,t min} (6)

[0020] Where, t d is the fault detection time, t f is the failure time, t trip is the circuit breaker tripping time, t u is the detection voltage rise time, t min It is the time it takes for the circuit breaker to reset after tripping.

[0021] Furthermore, when the energy storage converter is in grid-type control, the distribution network voltage after the fault is cleared is equal to the rated voltage of the distribution network system; when the energy storage converter is in low voltage ride-through control, the distribution network voltage after the fault is cleared is calculated by the following formula:

[0022]

[0023] Where P represents the active power of the energy storage station when no fault occurs, P L Indicates the active power of the load when no fault occurs, U N Indicates the rated voltage of the distribution network system, K P Indicates the ratio of active power of energy storage power station to load.

[0024] Furthermore, the voltage control target of the energy storage grid connection point is 10% of the rated voltage of the distribution network system.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] 1. A circuit breaker and energy storage power station are combined. After the circuit breaker trips, the energy storage converter switches to arc suppression control to help extinguish the fault arc, eliminating the need for external equipment. After a fault occurs, the energy storage power station supplies power to downstream loads, eliminating the need for downstream power outages. This avoids load-side power outages, improves grid power reliability, and effectively prevents drastic changes in grid currents caused by large-scale disconnections of a high proportion of renewable energy sources.

[0027] 2. The reclosing initiation threshold is set based on the distribution network voltage after the fault is cleared. Using this threshold as a criterion allows for rapid determination of fault clearance, shortening the reclosing time compared to traditional delay strategies (2.5 to 3 seconds), improving power restoration speed and system reliability. By setting different reclosing delays for different fault clearance scenarios, the reclosing delay can be adaptively shortened based on fault detection results and protection action strategies, facilitating rapid power restoration. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is the overall flow chart;

[0029] Figure 2 This is the distribution network simulation system diagram;

[0030] Figure 3 : is a three-phase voltage waveform diagram at the downstream outlet of the circuit breaker in the embodiment;

[0031] Figure 4 Schematic diagram of voltage amplitude at the downstream outlet of the circuit breaker in the embodiment; DETAILED DESCRIPTION

[0032] Specific embodiments are given below in conjunction with the accompanying drawings. The specific embodiments are only used to introduce the technical solutions of the present invention in detail and are not intended to limit the scope of protection of the present application.

[0033] The present invention provides a distribution network transient fault recovery control method based on the collaboration of energy storage and circuit breakers. First, the reclosing start threshold is set based on the distribution network voltage after the fault is cleared. After a distribution network fault occurs, the energy storage power station serves as the main power source to supply energy to the downstream load and activates the back electromotive force to help extinguish the fault arc. The fault clearance status is determined based on the voltage at the downstream outlet of the circuit breaker. Different delays are preset for different situations to adaptively reclose the circuit breaker to restore power to the distribution network. This solves the problem that blind switching of the distribution network reclosing may cause the system to suffer secondary shocks. Specifically, the following steps are included:

[0034] Step 1: Set the reclosing start threshold based on the distribution network voltage after the fault is cleared;

[0035] U set =ε·U(1)

[0036] Where U set represents the reclosing start threshold, U represents the distribution network voltage after the fault is cleared; ε represents the error coefficient, which ranges from 0 to 1;

[0037] After the fault is cleared, the energy storage station serves as the primary power source for the downstream loads. Based on the power relationship between the energy storage station and the loads, the energy storage converter control is divided into two situations:

[0038] 1) Energy storage converter grid control

[0039] After the fault is cleared, if the output power of the energy storage station is sufficient to meet the downstream load demand, the energy storage converter is in grid-type control, and the energy storage converter shows the characteristics of "voltage source" to the outside, with the ability to actively support the grid voltage and frequency; when the fault is cleared, the energy storage station under grid-type control will raise the downstream voltage to close to the rated voltage of the distribution network system, then U≈U N ;

[0040] 2) Energy storage converter low voltage ride-through control

[0041] After the fault is cleared, if the output power of the energy storage power station cannot meet the downstream load demand, the energy storage converter will be in low voltage ride-through control. The distribution network voltage after the fault is cleared is calculated using the following formula:

[0042]

[0043] Where P represents the active power of the energy storage station when no fault occurs, P L Indicates the active power of the load when no fault occurs, U N Indicates the rated voltage of the distribution network system, K P Indicates the ratio of active power of energy storage power station to load;

[0044] Step 2: For continuous arcing faults, the bidirectional power controllable characteristics of the energy storage converter are utilized. After the circuit breaker trips, the energy storage converter is switched to arc suppression control with the goal of reducing the voltage at the energy storage grid connection point, thereby promoting the extinction of the fault arc. The voltage at the energy storage grid connection point is calculated using the following formula:

[0045]

[0046] The output current of the energy storage power station arc suppression control is:

[0047]

[0048] Considering the distribution transformer R T <<X T , the above formula can be simplified to:

[0049]

[0050] Where, is the voltage at the energy storage grid connection point, are the output voltage and current of the energy storage station, |·| represents the amplitude, R T 、X T is the equivalent resistance and equivalent reactance of the distribution transformer; The voltage control target of the energy storage grid connection point is set to 10% U in this embodiment to reduce the voltage of the energy storage grid connection point to 0 and to consider that there may be distributed renewable energy sources that are not disconnected from the grid in the downstream system after the circuit breaker trips. N ;I d , I q To suppress arcing in energy storage power stations and control the active and reactive output currents;

[0051] Step 3: After the fault arc is extinguished, the voltage at the downstream outlet of the circuit breaker is collected, and the fault detection time is set by formula (6). If the voltage at the downstream outlet of the circuit breaker is greater than or equal to the reclosing start threshold within the fault detection time, it indicates that the fault has been cleared, and then reclosing is performed after the first delay; if the voltage at the downstream outlet of the circuit breaker is less than the reclosing start threshold within the fault detection time, it indicates that the fault has not been cleared, and then reclosing is performed after the second delay;

[0052] t d =min{t f -t trip +t u ,1.1-t trip ,t min} (6)

[0053] Where, t d is the fault detection time, t f is the failure time; t trip is the tripping time of the circuit breaker, which is related to the protection action; t u To detect the voltage rise time, usually within 50ms; t min It is the time it takes for the circuit breaker to reset after tripping.

[0054] Preferably, the first delay is 0.15s and the second delay is 2s.

[0055] Example

[0056] First, build in PSCAD / EMTDC Figure 2The simulation system shown includes two 200kW distributed energy storage power stations connected to a 10kV substation. A 256kW load is connected to the distribution network. The substation outlet circuit breaker is equipped with three-stage current protection. The energy storage power stations all have fault ride-through capabilities in accordance with national standards. The reclosing voltage measurement point is at the downstream outlet of the circuit breaker. The voltage signal sampling frequency is 10kHz. The reclosing time / lockout command is adjusted based on the voltage calculation at the downstream outlet of the circuit breaker after the circuit breaker trips. Different types of transient faults (lasting 70ms) and permanent faults are set on feeder F1, and the circuit breaker trips 30ms after the fault occurs. The fault types are two-phase phase-to-phase fault (AB), two-phase ground fault (ABG), and three-phase fault (ABC).

[0057] Before the fault occurs, the power of the energy storage power station and the load is collected, and the distribution network voltage after the fault is cleared is calculated as:

[0058]

[0059] The accuracy of voltage transformers in distribution networks is usually ±3%. If the error coefficient ε is set to 0.95, the reclosing start threshold is:

[0060] U set =0.95·U=0.76U N

[0061] When a fault occurs and the circuit breaker trips, the energy storage converter is switched to arc suppression control with the goal of reducing the voltage at the energy storage grid connection point to promote the extinguishing of the fault arc. After the fault arc is extinguished, the three-phase voltage at the downstream outlet of the circuit breaker is collected. Figure 3 , the corresponding per-unit values ​​can be found in Figure 4 .

[0062] Table 1 shows the fault detection time and reclosing delay for different types of transient faults. The fault detection time is calculated from the moment the circuit breaker trips to zero. After the transient fault is cleared, the fault detection time is 70ms + t u , t u Within 50ms; for AB and ABG permanent faults, the corresponding fault detection time is 120ms. If the voltage at the downstream outlet of the circuit breaker is less than the reclosing start threshold within the fault detection time, it is considered a permanent fault and is locked.

[0063] Table 1 Performance of this application under different types of faults

[0064] Fault type Test results Fault detection time / ms Reclosing command AB transient fault Troubleshooting 88.6 Reclosing after 0.239s AB permanent fault Fault not cleared 120 Locking after 2.12s ABG transient fault Troubleshooting 75.5 Reclosing after 0.226s ABG permanent failure Fault not cleared 120 Locking after 2.12s ABC transient fault Troubleshooting 78.8 Reclosing after 0.229s ABC permanent failure Fault not cleared 120 Locking after 2.12s

[0065] As can be seen from Table 1, after the circuit breaker trips, the present application can effectively distinguish between transient and permanent faults. Under transient faults, compared with the current engineering method that requires a delay of 2.5 to 3 seconds, the present application can effectively shorten the reclosing delay to within 2.5 seconds, which can greatly shorten the reclosing time. Especially for three-phase short-circuit faults, the present application can complete the judgment in 78.8ms after the fault is cleared, and the reclosing delay can be shortened to 229ms. By considering the protection action situation and incorporating the reclosing delay setting, the present application realizes real-time adaptive adjustment of the reclosing delay according to different fault conditions, which can flexibly shorten the reclosing delay and improve the distribution network fault recovery efficiency. In addition, after the fault occurs, the energy storage power station adopts arc suppression control to assist in extinguishing the fault arc, and uses the energy storage power station as the main power source to supply power to the downstream load. After the fault occurs, the downstream does not need to be disconnected from the grid, avoiding power outages on the load side and improving the reliability of the distribution network system power supply.

[0066] Any matters not described in the present invention are applicable to the prior art.

Claims

1. A distribution network transient fault recovery control method based on the collaboration of energy storage and circuit breakers, characterized in that: The following steps are involved: Step 1: Set the reclosing start threshold; IN set =ε·U(1) Where U set represents the reclosing start threshold, U represents the distribution network voltage after the fault is cleared, and ε represents the error coefficient; Step 2: For continuous arcing faults, after the circuit breaker trips, the energy storage converter is switched to arc suppression control with the goal of reducing the voltage at the energy storage grid connection point. The voltage at the energy storage grid connection point is calculated using the following formula: The output current of the energy storage power station arc suppression control is: Where, is the voltage at the energy storage grid connection point, are the output voltage and current of the energy storage station, |·| represents the amplitude, R T 、X T is the equivalent resistance and equivalent reactance of the distribution transformer, is the voltage control target of the energy storage grid connection point, I d , I q To suppress arcing in energy storage power stations and control the active and reactive output currents; Step 3: After the fault arc is extinguished, the voltage at the downstream outlet of the circuit breaker is collected. If the voltage at the downstream outlet of the circuit breaker is greater than or equal to the reclosing start threshold within the fault detection time, it indicates that the fault has been cleared, and reclosing is performed after the first delay; If the voltage at the downstream outlet of the circuit breaker is less than the reclosing start threshold within the fault detection time, indicating that the fault has not been cleared, reclosing will occur after the second delay.

2. The distribution network transient fault recovery control method based on energy storage and circuit breaker collaboration according to claim 1 is characterized in that: The fault detection time satisfies the following formula: t d =min{t f -t trip +t u ,1.1-t trip ,t min } (6) Where, t d is the fault detection time, t f is the failure time, t trip is the circuit breaker tripping time, t u is the detection voltage rise time, t min It is the time it takes for the circuit breaker to reset after tripping.

3. The distribution network transient fault recovery control method based on energy storage and circuit breaker collaboration according to claim 1 or 2, characterized in that: When the energy storage converter is in grid-type control, the distribution network voltage after the fault is cleared is equal to the rated voltage of the distribution network system; when the energy storage converter is in low voltage ride-through control, the distribution network voltage after the fault is cleared is calculated by the following formula: Where P represents the active power of the energy storage station when no fault occurs, P L Indicates the active power of the load when no fault occurs, U N Indicates the rated voltage of the distribution network system, K P Indicates the ratio of active power of energy storage power station to load.

4. The distribution network transient fault recovery control method based on energy storage and circuit breaker collaboration according to claim 1 is characterized in that: The voltage control target of the energy storage grid connection point is 10% of the rated voltage of the distribution network system.

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