Fault discrimination method, device and equipment suitable for access of optical storage power station to power distribution network

Abstract

The invention provides a fault discrimination method, device and equipment suitable for access of an optical storage power station to a power distribution network, and relates to the technical field of power distribution network fault discrimination. The method comprises the following steps: monitoring a reactive power value output by a grid-connected point of the optical storage power station and an active power direction of a distribution line between the optical storage power station and a power distribution network in real time, and recording as a first active power direction; when the reactive power value is equal to zero, judging and recording the operation state of the optical storage power station through the first active power direction; when the reactive power value is greater than zero, judging that a fault occurs, measuring the grid-connected point voltage of the optical storage power station, monitoring the active power direction of the distribution line between the optical storage power station and the power distribution network again, and recording the active power direction as a second active power direction; and determining a fault line position according to the recorded operation state of the optical storage power station, the grid-connected point voltage of the optical storage power station, the second active power direction and the over-current protection device state of each node of the distribution line. The fault location of the optical storage power station connected to the power distribution network can be correctly judged.

Description

Technical Field

[0001] This invention relates to the field of power distribution network fault identification technology, and in particular to a fault identification method, device and equipment suitable for photovoltaic and energy storage power stations connected to the power distribution network. Background Technology

[0002] Photovoltaic output is greatly affected by factors such as time and weather. As the proportion of photovoltaic power connected to the distribution network increases, the randomness, intermittency and volatility of photovoltaic output have led to two major problems: curtailment of photovoltaic power is likely to occur during the off-peak electricity demand period, while there is a power generation gap during the peak electricity demand period. This makes the risk of reverse overload and voltage over-limit of the distribution network more and more serious, affecting the safe and stable operation of the distribution network.

[0003] The key to solving the aforementioned problems in photovoltaic power generation lies in energy storage technology. Future development requires exploring different integrated development models that combine new energy storage technologies with the generation, grid, and user sides. Energy storage, characterized by its rechargeability and fast response, can smooth the output of photovoltaic power generation, enhance the absorption capacity of new energy sources, and improve the security and reliability of the distribution network. Therefore, photovoltaic systems are typically paired with energy storage of appropriate scale to form photovoltaic-storage power stations. When photovoltaic power generation is excessive, energy storage stores the excess energy in real time; during periods of insufficient power generation, the stored power is released through grid-coordinated dispatch.

[0004] Currently, photovoltaic (PV) power stations are deeply integrating forecasting algorithms and electricity market mechanisms to build a dynamically optimized operation system centered on price signals. By introducing a high-precision PV power generation forecasting system and intelligent dispatching algorithms, combined with day-ahead and intraday two-tier electricity market coordination, the system can accurately respond to price fluctuations across different time dimensions. Specifically, during periods of high PV power generation and low electricity prices, energy storage actively absorbs excess power based on PV output forecasts; during periods of peak load or low power generation and high electricity prices, it releases power through cross-period energy shifting strategies, effectively improving the utilization rate of renewable energy. This price-oriented intelligent operation mode not only improves the system's regulation accuracy to the minute level but also maximizes the value of energy storage through electricity market mechanisms, providing key technical support for building a new type of power system.

[0005] While economic efficiency is important, safety is also paramount. Speed, sensitivity, reliability, and selectivity are the core performance requirements of relay protection devices as the first line of defense in distribution network fault prevention. This is achieved through relay protection devices installed at various nodes of the distribution lines. By monitoring the characteristics of electrical parameters such as current and voltage in real time, these devices accurately identify abnormal conditions such as short circuits. Once a fault is detected, the protection device, based on preset timing logic and action settings, drives the corresponding circuit breaker to trip, quickly disconnecting the faulty section from the power grid and preventing the fault from spreading to the next level of the grid or adjacent feeders.

[0006] To further improve fault handling efficiency, modern distribution networks typically employ a multi-level protection coordination system. For example, instantaneous overcurrent protection enables the immediate clearing of near-end faults, time-limited overcurrent protection covers the entire length of the line and serves as backup for adjacent lines, and automatic reclosing functionality is combined to handle transient faults. In complex grid structures or distribution networks containing distributed generation, directional elements are also required to accurately determine the fault direction and prevent maloperation or failure of protection systems.

[0007] The short-circuit current characteristics of photovoltaic (PV) and energy storage (ESS) power stations are influenced by converter control strategies, exhibiting "limited amplitude and controlled phase." Furthermore, the charging and discharging modes of energy storage result in source-load duality in PV-ESS power stations, leading to more complex and diverse fault modes compared to traditional synchronous power sources and single photovoltaic power stations. Specifically, PV-ESS power stations are inverter-type power sources composed of numerous power electronic devices with limited overcurrent capacity; the short-circuit current amplitude they provide is typically only 1.2 times the rated current. Simultaneously, after a short-circuit fault, national standards require PV-ESS power stations to provide a certain amount of reactive power output to boost the grid connection voltage based on the voltage drop. Finally, unlike traditional renewable energy sources, PV-ESS power stations operate in both charging and discharging states, altering the current direction at the protection installation point. These factors make traditional direction discrimination elements less applicable in scenarios where PV-ESS power stations are connected to the distribution network, prone to misjudgments, leading to expanded fault ranges or failure to isolate the fault. Therefore, researching fault discrimination methods suitable for PV-ESS power stations connected to the distribution network is of great significance. Summary of the Invention

[0008] This invention provides a fault identification method, device, and equipment suitable for photovoltaic-storage power stations connected to the distribution network, in order to solve the problem of correctly determining the fault location of the photovoltaic-storage power station connected to the distribution network when the fault current exhibits nonlinear time-varying characteristics.

[0009] In a first aspect, embodiments of the present invention provide a fault detection method applicable to the connection of photovoltaic and energy storage power stations to the distribution network, including: Real-time monitoring of the reactive power output at the grid connection point of the photovoltaic-storage power station and the active power direction of the power distribution line between the photovoltaic-storage power station and the power distribution network is recorded as the first active power direction. When the reactive power value is equal to zero, the operating status of the photovoltaic-storage power station is determined and recorded by the direction of the first active power; the operating status of the photovoltaic-storage power station includes charging and discharging. When the reactive power value is greater than zero, a fault is determined to have occurred. The voltage at the grid connection point of the photovoltaic-storage power station is measured, and the active power direction of the distribution line between the photovoltaic-storage power station and the distribution network is monitored again and recorded as the second active power direction. The location of the faulty line is determined by the recorded operating status of the photovoltaic-storage power station, the voltage at the grid connection point of the photovoltaic-storage power station, the second active power direction, and the overcurrent protection device status of each node of the distribution line.

[0010] In one possible implementation, determining the location of the faulty line by recording the operating status of the photovoltaic-storage power station, the grid connection voltage of the photovoltaic-storage power station, the direction of the second active power, and the status of the overcurrent protection devices at each node of the distribution line includes: The grid connection voltage of the photovoltaic-storage power station is compared with the first threshold and the second threshold, respectively. When the grid connection point voltage of the photovoltaic-storage power station is less than the first threshold, the location of the faulty line is determined based on the second active power direction monitored by the photovoltaic-storage power station side component and the second active power direction monitored by the distribution network side component in the second active power direction. When the grid connection point voltage of the photovoltaic-storage power station is between the first threshold and the second threshold, determine whether the recorded operating state of the photovoltaic-storage power station is charging or discharging: When the recorded photovoltaic-storage power station is in the charging state, the location of the faulty line is determined by the status of the overcurrent protection devices at each node of the power distribution line. When the recorded photovoltaic-storage power station is in a discharge state, the location of the faulty line is determined based on the second active power direction monitored by the photovoltaic-storage power station side component and the second active power direction monitored by the distribution network side component.

[0011] In one possible implementation, when the grid connection point voltage of the photovoltaic-storage power station is between the first threshold and the second threshold, determining whether the recorded operating state of the photovoltaic-storage power station is charging or discharging includes: Retrieve the operating status of the photovoltaic-storage power station at the last moment of the recorded operating status when the reactive power value is equal to zero, and record it as the first operating status of the photovoltaic-storage power station. Calculate the duration for which the operating status of the first photovoltaic-storage power station remains consistent with the operating status recorded at the previous time point from the last time point. When the duration exceeds the duration threshold, the operating status of the first photovoltaic-storage power station is taken as the recorded operating status of the photovoltaic-storage power station. When the duration is less than or equal to the duration threshold, the opposite state of the first photovoltaic-storage power station operation state is taken as the recorded photovoltaic-storage power station operation state.

[0012] In one possible implementation, when the recorded photovoltaic-storage power station is in a charging state, the location of the faulty line is determined by the overcurrent protection device status of each node of the power distribution line, including: Determine whether the overcurrent protection device status at each node of the power distribution line indicates overcurrent. If the distribution network side of the aforementioned distribution line is N The overcurrent protection device status of each node indicates overcurrent, and the status of the overcurrent protection device on the distribution network side is monitored sequentially. N-1Does each node in the set time delay have an overcurrent protection device activated? If the distribution network side is in front N-1 The node in the node K If the overcurrent protection device of a node operates within a preset time delay, then the node is determined to be... K The node and the first K+1 The lines between these nodes are faulty lines; If the distribution network side is in front N-1 If no overcurrent protection device operates within the preset time delay for each of the nodes, then the distribution network side is determined to be the first node. N The node and the first N+1 The lines between these nodes are faulty lines.

[0013] In one possible implementation, after determining whether the overcurrent protection device status at each node of the power distribution line indicates an overcurrent, the method further includes: If the overcurrent protection device of the first node on the distribution network side of the power distribution line indicates overcurrent, then the line between the first node and the second node on the distribution network side is determined to be a faulty line.

[0014] In one possible implementation, the preset time ranges from 0.2 to 0.5 seconds.

[0015] In one possible implementation, determining the location of the faulty line based on the second active power direction monitored by the photovoltaic-storage power station-side components and the second active power direction monitored by the distribution network-side components in the second active power direction includes: If the second active power direction detected by the photovoltaic power station side component and the second active power direction detected by the distribution network side component of the same line in the second active power direction are both positive, then the line is determined to be a faulty line.

[0016] In one possible implementation, the first threshold is: ; in, U 1 is the first threshold. U 2 is the second threshold. The line impedance angle. I This is the maximum overcurrent of the inverter. K This is the dynamic reactive power proportional coefficient.

[0017] Secondly, embodiments of the present invention provide a fault detection device suitable for photovoltaic-storage power stations connected to a distribution network, comprising: The real-time monitoring module is used to monitor the reactive power output of the photovoltaic-storage power station at the grid connection point and the active power direction of the power distribution line between the photovoltaic-storage power station and the power distribution network in real time, which is denoted as the first active power direction. The photovoltaic-storage power station operation status recording module is used to determine and record the operation status of the photovoltaic-storage power station by the first active power direction when the reactive power value is equal to zero; the operation status of the photovoltaic-storage power station includes charging and discharging. The fault line location module is used to determine the occurrence of a fault when the reactive power value is greater than zero, measure the voltage at the grid connection point of the photovoltaic-storage power station, and monitor the active power direction of the distribution line between the photovoltaic-storage power station and the distribution network again, which is recorded as the second active power direction. The location of the fault line is determined by the recorded operating status of the photovoltaic-storage power station, the voltage at the grid connection point of the photovoltaic-storage power station, the second active power direction, and the overcurrent protection device status of each node of the distribution line.

[0018] Thirdly, embodiments of the present invention provide an electronic device, including a memory and a processor, wherein the memory stores a computer program, and the processor executes the computer program to implement the method described in the first aspect or any possible implementation thereof.

[0019] In this embodiment of the invention, by real-time monitoring of the reactive power output at the grid connection point of the photovoltaic-storage power station, the operating status of the photovoltaic-storage power station and the fault and normal operation status of the distribution network can be quickly and accurately determined. By recording the operating status of the photovoltaic-storage power station and combining it with the grid connection point voltage of the photovoltaic-storage power station, the active power direction of the distribution line between the photovoltaic-storage power station and the distribution network when the fault occurs, and the overcurrent protection device status of each node of the distribution line, the location of the faulty line can be accurately determined, which helps the distribution network to quickly disconnect the short-circuit fault and effectively avoids the directional misjudgment that may occur in the charging state of the power station under traditional protection. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the grid connection structure of a photovoltaic-storage power station provided in an embodiment of the present invention; Figure 2 This is a flowchart illustrating the implementation of a fault detection method for photovoltaic and energy storage power stations connected to a power distribution network, as provided in this embodiment of the invention. Figure 3 This is a topology diagram of a photovoltaic-storage power station connected to a power distribution network provided in an embodiment of the present invention; Figure 4 This is a flowchart illustrating the implementation of the fault identification method based on topology provided in this embodiment of the invention. Figure 5 This is a schematic diagram of the structure of a fault detection device for photovoltaic and energy storage power stations connected to the power distribution network provided in an embodiment of the present invention; Figure 6 This is a schematic diagram of an electronic device provided in an embodiment of the present invention. Detailed Implementation

[0021] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0022] To allow for flexible energy storage configuration and simplify operational strategies, energy storage systems and photovoltaic systems are typically coupled on the AC side. For example... Figure 1 As shown, the photovoltaic-storage power station adopts a two-stage structure. The photovoltaic front-end uses a Boost converter to complete the DC voltage boost and maximum power point tracking (MPPT) functions. The energy storage front-end uses a bidirectional Buck-Boost converter to realize charging and discharging and maintain the stability of the DC bus voltage. The photovoltaic-storage power station's back-end consists of power conversion systems (PCS) that convert DC power into AC power, and finally feed the power into the distribution network through a filter circuit.

[0023] The subsequent PCS uses constant power control, employing a dual closed-loop control strategy consisting of a power outer loop and a current inner loop. The power outer loop tracks power commands in real time and outputs a current reference value for the current inner loop. The current inner loop then tracks and adjusts the output commands from the outer loop.

[0024] like Figure 1 As shown, the three-phase voltage on the AC side ( u sabc ), AC three-phase current ( i abc Transformed to via Park transform dq In a rotating coordinate system, the phase-locked loop (PLL) simultaneously tracks the phase and frequency of the grid voltage in real time, ensuring that the AC output of the PCS is synchronized with the grid. The instantaneous power output from the AC side of the photovoltaic system and energy storage system in a photovoltaic-storage power station is: (1) In the formula, P This refers to the active power output from the AC side of the photovoltaic system and energy storage system. Q This refers to the reactive power output from the AC side of the photovoltaic system and energy storage system. For grid connection point d Axis positive sequence voltage, For grid connection point q Positive sequence voltage, For grid connection point d negative sequence voltage of shaft, Grid connection point q Negative sequence voltage; For grid connection point d Positive sequence current of shaft, For grid connection point q Positive sequence current of the shaft. For grid connection point d negative sequence current of shaft, For grid connection point q Negative sequence current.

[0025] The grid voltage vector orientation control strategy will d - q Rotating coordinate system d The axis is aligned with the positive sequence component of the grid connection point voltage; at this time, the positive sequence voltage at the grid connection point... q The axis component is 0, thus achieving decoupled control of the voltage vector. Therefore, the positive-sequence component of the grid-connected point voltage can be expressed as: (2) in, The grid voltage vector at the point of connection of the photovoltaic-storage power station. This represents the positive sequence component amplitude of the grid voltage at the point of connection of the photovoltaic-storage power station.

[0026] In unbalanced operation or short-circuit faults in the distribution network, the emergence of negative-sequence current can adversely affect the stability of the photovoltaic-storage system, especially the stability of the PI regulator. To effectively suppress the generation of negative-sequence current components in the photovoltaic-storage system, a negative-sequence suppression circuit is usually added to the control strategy to make the negative-sequence current zero. Therefore, the output current of the photovoltaic system and the energy storage system in the photovoltaic-storage system... d , q The axis components contain only positive-sequence components, represented as: (3) Because the power flow direction differs between charging and discharging states in energy storage systems, to distinguish their operating states, positive values ​​represent discharging (power flows from the energy storage system to the distribution network) and negative values ​​represent charging (power flows from the distribution network to the energy storage system). Therefore, when the energy storage system is charging, the current in the energy storage system... d The axial components are: (4) When a fault occurs in the distribution network, the voltage at the grid connection point drops sharply. National standards require photovoltaic (PV) and energy storage systems to have low-voltage ride-through capability during this voltage drop. The PCS control objective switches from "active power priority" to "reactive power priority," supplying a certain amount of reactive power to the distribution network to support the voltage and a certain amount of active power to reduce grid fluctuations. At this time, the inner current loop reference value is directly given by segmenting the voltage drop depth. The inner current loop reference value is: (5) In the formula, and These are the actual and rated voltage values ​​at the grid connection point of the photovoltaic-storage power station, respectively. K The dynamic reactive power ratio should preferably be no less than 1.0. The maximum overcurrent of the inverter shall not be lower than the rated current on the AC side. 1.1 times.

[0027] Because photovoltaic and energy storage systems contain a large number of power electronic devices with weak current-carrying capacity, the total current output of the power converter (PCS) needs to be limited to prevent damage due to overload. Simultaneously, the PCS prioritizes reactive current output as its primary control objective, and the active current is also limited by the power converter capacity. d , q The shaft current limiting formula is as follows: (6) These complex internal control strategies ultimately manifest as a simple yet crucial output characteristic of a photovoltaic-storage power station: the phase of the current output from the AC side of the station is controlled. This is precisely the fundamental reason why, in fault diagnosis methods applicable to photovoltaic-storage power stations connected to the distribution network, the directional components on the photovoltaic-storage power station side can determine the power direction by measuring the phase and amplitude of the power frequency voltage and current.

[0028] Figure 2 The implementation flowchart of the fault identification method for photovoltaic and energy storage power stations connected to the distribution network provided in this embodiment of the invention is described in detail below: In step 201, the reactive power output of the photovoltaic-storage power station grid connection point and the active power direction of the power distribution line between the photovoltaic-storage power station and the power distribution network are monitored in real time and recorded as the first active power direction.

[0029] In step 202, when the reactive power value is equal to zero, the operating status of the photovoltaic-storage power station is determined by the first active power direction and recorded; the operating status of the photovoltaic-storage power station includes charging and discharging.

[0030] In this embodiment, when the direction of active power measured by the directional element on the side of the photovoltaic-storage power station is positive, the active power flows from the photovoltaic-storage power station to the distribution network, and the photovoltaic-storage power station is in a discharging state; when the direction of active power measured by the directional element on the side of the photovoltaic-storage power station is negative, the active power flows from the distribution network to the photovoltaic-storage power station, and the photovoltaic-storage power station is in a charging state.

[0031] In step 203, when the reactive power value is greater than zero, a fault is determined to have occurred. The voltage at the grid connection point of the photovoltaic-storage power station is measured, and the active power direction of the distribution line between the photovoltaic-storage power station and the distribution network is monitored again and recorded as the second active power direction. The location of the faulty line is determined by the recorded operating status of the photovoltaic-storage power station, the grid connection point voltage of the photovoltaic-storage power station, the second active power direction, and the overcurrent protection device status of each node of the distribution line.

[0032] In this embodiment, the method for determining the location of a faulty line by recording the operating status of the photovoltaic-storage power station, the grid connection voltage of the photovoltaic-storage power station, the direction of the second active power, and the status of the overcurrent protection devices at each node of the distribution line includes: The grid connection voltage of the photovoltaic-storage power station is compared with the first threshold and the second threshold, respectively.

[0033] For example, the first threshold is: ; in, U 1 is the first threshold. U 2 is the second threshold, taken as 0.85 pu. The line impedance angle. I This is the maximum overcurrent of the inverter. K This is the dynamic reactive power proportional coefficient.

[0034] When the voltage at the grid connection point of the photovoltaic-storage power station is less than the first threshold, the location of the faulty line is determined based on the second active power direction monitored by the photovoltaic-storage power station side components and the second active power direction monitored by the distribution network side components.

[0035] For example, if the second active power direction detected by the photovoltaic power station side component and the second active power direction detected by the distribution network side component of the same line in the second active power direction are both positive, then the line is determined to be a faulty line.

[0036] When the voltage at the grid connection point of the photovoltaic-storage power station is between the first and second thresholds, the recorded operating status of the photovoltaic-storage power station is determined as either charging or discharging.

[0037] For example, the operating state of the photovoltaic-storage power station at the last moment recorded when the reactive power value is equal to zero is retrieved and recorded as the first operating state of the photovoltaic-storage power station; the duration for which the operating state of the first photovoltaic-storage power station remains consistent with the operating state of the photovoltaic-storage power station recorded at the previous moment is calculated; when the duration is greater than the duration threshold, the operating state of the first photovoltaic-storage power station is recorded as the operating state of the photovoltaic-storage power station; when the duration is less than or equal to the duration threshold, the opposite state of the operating state of the first photovoltaic-storage power station is recorded as the operating state of the photovoltaic-storage power station.

[0038] When the recorded operating status of the photovoltaic-storage power station is charging, the location of the faulty line is determined by the status of the overcurrent protection devices at each node of the power distribution line.

[0039] For example, determine whether the overcurrent protection device status at each node of the power distribution line indicates an overcurrent.

[0040] If the distribution network side of the distribution line N The overcurrent protection device status of each node indicates overcurrent, and the status of the overcurrent protection device on the distribution network side is monitored sequentially. N-1 Does each node have an overcurrent protection device activated within a preset time delay?

[0041] If the distribution network side is in front N-1 The node in the node KIf the overcurrent protection device of a node operates within a preset time delay, then the node is determined to be... K The node and the first K+1 The lines between these nodes are faulty lines.

[0042] If the distribution network side is in front N-1 If no overcurrent protection device operates within the preset time delay for each of the nodes, then the distribution network side is determined to be the first node. N The node and the first N+1 The lines between these nodes are faulty lines.

[0043] The preset time ranges from 0.2 to 0.5 seconds.

[0044] If the overcurrent protection device at the first node on the distribution network side of the power distribution line indicates an overcurrent condition, then the line between the first and second nodes on the distribution network side is determined to be a faulty line.

[0045] When the recorded operating status of the photovoltaic-storage power station is discharge, the location of the faulty line is determined based on the second active power direction monitored by the photovoltaic-storage power station side component and the second active power direction monitored by the distribution network side component.

[0046] For example, if the second active power direction detected by the photovoltaic power station side component and the second active power direction detected by the distribution network side component of the same line in the second active power direction are both positive, then the line is determined to be a faulty line.

[0047] The following specific embodiments illustrate the fault identification method for photovoltaic and energy storage power stations connected to the power distribution network provided by the present invention: Photovoltaic-storage system access to distribution network topology such as Figure 3 As shown, the photovoltaic-storage power station is connected to bus C. Points A and B are the first and second nodes on the distribution lines between the distribution networks. Directional elements are installed at the protection points at both ends of each line segment. Protection directional elements R1 and R3 are grid-side directional elements, while protection directional elements R2 and R4 are photovoltaic-storage system-side directional elements.

[0048] For phase-to-phase short-circuit faults in dual-power lines, directional instantaneous overcurrent protection and overcurrent protection can be configured. When a fault occurs at point k, the directional protection elements R1, R3, and R4 should be treated as a positive-direction fault, and R2 should be treated as a negative-direction fault. When the power direction is consistent with the protection direction and the current value exceeds the setting value of the relay protection device, the protection device will operate after a set delay, tripping the circuit breaker and disconnecting the faulty line from the power system.

[0049] like Figure 4 As shown, based on Figure 3The illustrated photovoltaic-storage system access topology to the distribution network, and the fault detection method for photovoltaic-storage power station access to the distribution network, include: S1. Monitoring and Recording: During normal operation of the distribution network, the voltage and current sensors in the relay protection device collect the three-phase voltage U at the grid connection point of the photovoltaic-storage power station at a sampling frequency of 1.2kHz to 4kHz. PCC Based on the three-phase current, the relay protection device determines the active power value and reactive power direction by calculating the phase difference between the three-phase voltage and the three-phase current. Assuming the photovoltaic power station is charging, the direction of active power measured by the directional element on the photovoltaic power station side is negative (i.e., reversed), that is, active power flows from the distribution network to the photovoltaic power station, and reactive power is 0. The relay protection device determines that the photovoltaic power station is operating in the charging state through formulas (1), (2), and (4) and records it (at this time, it is the first active power direction).

[0050] Assuming the photovoltaic-storage power station is discharging, the direction of active power measured by the directional element on the photovoltaic-storage power station side is positive (i.e., positive direction), that is, active power flows from the photovoltaic-storage power station to the distribution network, and reactive power is 0. The relay protection device determines that the photovoltaic-storage system is operating in the discharge state through formulas (1) and (2) and records it (at this time, it is the first active power direction).

[0051] A method for determining the operating status of a photovoltaic-storage power station is proposed, which monitors and records the direction of active power at the grid connection point of the station in real time using directional elements in the relay protection device. When the active power is greater than 0 (forward), it is determined to be in a discharging state; when it is less than 0 (reverse), it is determined to be in a charging state. This state quantity is stored as the operating status of the photovoltaic-storage power station before the fault, providing a comparative basis for subsequent fault direction determination.

[0052] S2. Triggering of Fault Direction Judgment: When a short-circuit fault occurs at point k, the voltage at the grid connection point of the photovoltaic-storage power station drops. The photovoltaic-storage power station outputs reactive current to support the grid voltage according to the grid connection standard, i.e., formula (6). The output reactive power and reactive current are shown in formula (3). This switch in control strategy causes the reactive power of the system measured by the directional element to change from a state close to zero during normal operation to a state significantly greater than zero. The relay protection device determines that a short-circuit fault has occurred on the line and caused the voltage drop by monitoring this sudden increase in reactive power caused by the internal control strategy in real time.

[0053] When a short-circuit fault occurs in the distribution network, the voltage at the grid connection point of the photovoltaic-storage power station decreases. According to regulations, the photovoltaic-storage power station has dynamic reactive power support capability, injecting reactive current into the grid. This method uses the judgment of reactive power values ​​to construct a fault detection initiation criterion. When the reactive power is detected to change from zero to greater than zero, a fault is determined to have occurred in the distribution network, and the fault direction determination procedure is initiated. This criterion transforms the requirements of power grid regulations into reliable fault detection characteristics.

[0054] S3. Fault Direction Identification and Location: When a short-circuit fault is severe, the voltage drop is significant. For example, if the voltage drops below 0.6 pu (first threshold), the short-circuit current flows towards the fault point. At this time, the active power direction measured by the directional element on the photovoltaic-storage power station side is positive (forward), indicating that the fault point is located in the positive direction at the relay protection device installation location (both the second active power direction and the second active power direction monitored by the distribution network side directional element are positive). The distribution network side directional element also measures that the active power flows from the distribution network side to the fault point, indicating a positive direction fault. Furthermore, the overcurrent protection device detects that the current exceeds the set value, and the relay protection device automatically controls the circuit breaker to trip, thus isolating the fault.

[0055] When the short-circuit fault is minor, the voltage drop is shallow, such as within the range of 0.6 pu to 0.85 pu (between the first and second thresholds). When the recorded operating state of the photovoltaic-storage power station is power generation, part of the short-circuit current flows to the fault point, and part flows to the photovoltaic-storage power station. At this time, the active power measured by the directional elements on the photovoltaic-storage power station side is negative. After a delay, the relay protection devices on the upstream line do not trip. This method locates the fault to section BC. A "trip permission" signal is sent to the relay protection devices on both sides, and the relay protection devices automatically control the circuit breaker to trip, thus isolating the fault. When the short-circuit fault is minor, the voltage drop is shallow, such as within the range of 0.6 pu to 0.85 pu (between the first and second thresholds). When the recorded operating state of the photovoltaic-storage power station is discharge, the short-circuit current flows towards the fault point. At this time, the active power direction measured by the directional element on the photovoltaic-storage power station side is positive (the second active power direction monitored by both the second active power direction and the distribution network side directional element are positive), indicating that the fault point is located in the positive direction of the relay protection device installation location. The distribution network side directional element also measures that the active power flows from the distribution network side to the fault point, indicating a positive direction fault. Furthermore, the overcurrent protection device detects that the current exceeds the set value, and the relay protection device automatically controls the circuit breaker to trip, clearing the fault.

[0056] After the fault diagnosis program is started, the direction of active power is immediately measured and compared with the time sequence of the operating status stored before the fault. When the direction of active power reverses (the second active power direction detected by the distribution network side directional element reverses), it indicates that the fault point is located upstream of the photovoltaic-storage power station, thereby triggering the protection action and realizing accurate diagnosis of serious faults.

[0057] To address the situation where the active power direction does not reverse when a minor short-circuit fault occurs upstream during the charging of a photovoltaic-storage power station, this invention employs a delay logic coordinated with the upstream protection system. The directional components on the photovoltaic-storage power station side will only activate if all upstream protection systems fail to operate. This mechanism effectively prevents protection failures caused by minor upstream faults at the photovoltaic-storage power station and achieves good coordination with existing distribution network relay protection devices.

[0058] It should be understood that the sequence number of each step in the above embodiments does not imply 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 embodiments of the present invention.

[0059] The following are device embodiments of the present invention. For details not described in detail, please refer to the corresponding method embodiments described above.

[0060] Figure 5 A schematic diagram of a fault detection device for photovoltaic-storage power stations connected to a distribution network, provided in an embodiment of the present invention, is shown. For ease of explanation, only the parts relevant to the embodiment of the present invention are shown, and are described in detail below: like Figure 5 As shown, the fault detection device 5 suitable for photovoltaic and energy storage power stations connected to the distribution network includes: The real-time monitoring module 501 is used to monitor the reactive power output at the grid connection point of the photovoltaic-storage power station and the active power direction of the power distribution line between the photovoltaic-storage power station and the power distribution network in real time, which is denoted as the first active power direction.

[0061] The photovoltaic-storage power station operation status recording module 502 is used to determine and record the operation status of the photovoltaic-storage power station by the first active power direction when the reactive power value is equal to zero; the operation status of the photovoltaic-storage power station includes charging and discharging.

[0062] The fault line location module 503 is used to determine the occurrence of a fault when the reactive power value is greater than zero, measure the voltage at the grid connection point of the photovoltaic-storage power station, and monitor the active power direction of the distribution line between the photovoltaic-storage power station and the distribution network again, which is recorded as the second active power direction. The location of the fault line is determined by recording the operating status of the photovoltaic-storage power station, the grid connection point voltage of the photovoltaic-storage power station, the second active power direction, and the overcurrent protection device status of each node of the distribution line.

[0063] Figure 6 This is a schematic diagram of an electronic device provided in an embodiment of the present invention. For example... Figure 6 As shown, the electronic device 6 of this embodiment includes a processor 60 and a memory 61. The memory 61 stores a computer program 62. When the processor 60 executes the computer program 62, it implements the steps in the various method embodiments described above. Alternatively, when the processor 60 executes the computer program 62, it implements the functions of each module / unit in the various device embodiments described above.

[0064] For example, computer program 62 may be divided into one or more modules / units, which are stored in memory 61 and executed by processor 60 to complete the present invention. The one or more modules / units may be a series of computer program instruction segments capable of performing a specific function, which describe the execution process of computer program 62 in electronic device 6.

[0065] Electronic device 6 may include, but is not limited to, processor 60 and memory 61. Those skilled in the art will understand that... Figure 6 This is merely an example of electronic device 6 and does not constitute a limitation on electronic device 6. It may include more or fewer components than shown, or combine certain components, or different components. For example, electronic device 6 may also include input / output devices, network access devices, buses, etc.

[0066] For the sake of simplicity and clarity, only the above-described functional modules / units are used as examples. In practical applications, the functions described above can be assigned to different functional modules / units as needed. These modules / units can be implemented in hardware, software, or a combination of both.

[0067] In the above embodiments, the descriptions of each embodiment have their own emphasis. Parts not detailed or described in a particular embodiment can be referred to in the relevant descriptions of other embodiments. Unless otherwise specified or in conflict with logic, the terminology and / or descriptions between different embodiments are consistent and can be referenced interchangeably. Technical features in different embodiments can be combined to form new embodiments based on their inherent logical relationships.

[0068] The above-described embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention, and should all be included within the protection scope of the present invention.

Claims

1. A fault diagnosis method applicable to photovoltaic-storage power stations connected to a distribution network, characterized in that, include: Real-time monitoring of the reactive power output at the grid connection point of the photovoltaic-storage power station and the active power direction of the power distribution line between the photovoltaic-storage power station and the power distribution network is recorded as the first active power direction. When the reactive power value is equal to zero, the operating status of the photovoltaic-storage power station is determined and recorded by the direction of the first active power; the operating status of the photovoltaic-storage power station includes charging and discharging. When the reactive power value is greater than zero, a fault is determined to have occurred. The voltage at the grid connection point of the photovoltaic-storage power station is measured, and the active power direction of the distribution line between the photovoltaic-storage power station and the distribution network is monitored again and recorded as the second active power direction. The location of the faulty line is determined by the recorded operating status of the photovoltaic-storage power station, the voltage at the grid connection point of the photovoltaic-storage power station, the second active power direction, and the overcurrent protection device status of each node of the distribution line.

2. The fault diagnosis method applicable to photovoltaic-storage power stations connected to the distribution network according to claim 1, characterized in that, The method of determining the location of the faulty line by recording the operating status of the photovoltaic-storage power station, the grid connection voltage of the photovoltaic-storage power station, the direction of the second active power, and the status of the overcurrent protection devices at each node of the distribution line includes: The grid connection voltage of the photovoltaic-storage power station is compared with the first threshold and the second threshold, respectively. When the grid connection point voltage of the photovoltaic-storage power station is less than the first threshold, the location of the faulty line is determined based on the second active power direction monitored by the photovoltaic-storage power station side component and the second active power direction monitored by the distribution network side component in the second active power direction. When the grid connection point voltage of the photovoltaic-storage power station is between the first threshold and the second threshold, determine whether the recorded operating state of the photovoltaic-storage power station is charging or discharging: When the recorded photovoltaic-storage power station is in the charging state, the location of the faulty line is determined by the status of the overcurrent protection devices at each node of the power distribution line. When the recorded photovoltaic-storage power station is in a discharge state, the location of the faulty line is determined based on the second active power direction monitored by the photovoltaic-storage power station side component and the second active power direction monitored by the distribution network side component.

3. The fault diagnosis method applicable to photovoltaic-storage power stations connected to the distribution network according to claim 2, characterized in that, When the grid connection point voltage of the photovoltaic-storage power station is between the first threshold and the second threshold, determining whether the recorded operating state of the photovoltaic-storage power station is charging or discharging includes: Retrieve the operating status of the photovoltaic-storage power station at the last moment of the recorded operating status when the reactive power value is equal to zero, and record it as the first operating status of the photovoltaic-storage power station. Calculate the duration for which the operating status of the first photovoltaic-storage power station remains consistent with the operating status recorded at the previous time point from the last time point. When the duration exceeds the duration threshold, the operating status of the first photovoltaic-storage power station is taken as the recorded operating status of the photovoltaic-storage power station. When the duration is less than or equal to the duration threshold, the opposite state of the first photovoltaic-storage power station operation state is taken as the recorded photovoltaic-storage power station operation state.

4. The fault diagnosis method applicable to photovoltaic-storage power stations connected to the distribution network according to claim 2, characterized in that, When the recorded photovoltaic-storage power station is in charging mode, the location of the faulty line is determined by the status of the overcurrent protection devices at each node of the power distribution line, including: Determine whether the overcurrent protection device status at each node of the power distribution line indicates overcurrent. If the distribution network side of the aforementioned distribution line N The overcurrent protection device status of each node indicates overcurrent, and the status of the overcurrent protection device on the distribution network side is monitored sequentially. N-1 Does each node in the set time delay have an overcurrent protection device activated? If the distribution network side is in front N-1 The node in the node K If the overcurrent protection device of a node operates within a preset time delay, then the node is determined to be... K The node and the first K+1 The lines between these nodes are faulty lines; If the distribution network side is in front N-1 If no overcurrent protection device operates within the preset time delay for any of the nodes, then the distribution network side is determined to be the first node. N The node and the first N+1 The lines between these nodes are faulty lines.

5. The fault diagnosis method applicable to photovoltaic-storage power stations connected to the distribution network according to claim 4, characterized in that, After determining whether the overcurrent protection device status at each node of the power distribution line indicates an overcurrent, the process also includes: If the overcurrent protection device of the first node on the distribution network side of the power distribution line indicates overcurrent, then the line between the first node and the second node on the distribution network side is determined to be a faulty line.

6. The fault diagnosis method applicable to photovoltaic-storage power stations connected to the distribution network according to claim 4, characterized in that, The preset time ranges from 0.2 to 0.5 seconds.

7. The fault diagnosis method applicable to photovoltaic-storage power stations connected to the distribution network according to claim 2, characterized in that, The method of determining the location of the faulty line based on the second active power direction monitored by the photovoltaic power station side component and the second active power direction monitored by the distribution network side component includes: If the second active power direction detected by the photovoltaic power station side component and the second active power direction detected by the distribution network side component of the same line in the second active power direction are both positive, then the line is determined to be a faulty line.

8. The fault diagnosis method applicable to photovoltaic-storage power stations connected to the distribution network according to claim 2, characterized in that, The first threshold is: ； in, U 1 is the first threshold. U 2 is the second threshold. The line impedance angle. I This is the maximum overcurrent of the inverter. K This is the dynamic reactive power proportional coefficient.

9. A fault detection device suitable for photovoltaic-storage power stations connected to a distribution network, characterized in that, include: The real-time monitoring module is used to monitor the reactive power output of the photovoltaic-storage power station at the grid connection point and the active power direction of the power distribution line between the photovoltaic-storage power station and the power distribution network in real time, which is denoted as the first active power direction. The photovoltaic-storage power station operation status recording module is used to determine and record the operation status of the photovoltaic-storage power station by the first active power direction when the reactive power value is equal to zero; the operation status of the photovoltaic-storage power station includes charging and discharging. The fault line location module is used to determine the occurrence of a fault when the reactive power value is greater than zero, measure the voltage at the grid connection point of the photovoltaic-storage power station, and monitor the active power direction of the distribution line between the photovoltaic-storage power station and the distribution network again, which is recorded as the second active power direction. The location of the fault line is determined by the recorded operating status of the photovoltaic-storage power station, the voltage at the grid connection point of the photovoltaic-storage power station, the second active power direction, and the overcurrent protection device status of each node of the distribution line.

10. An electronic device, characterized in that, It includes a memory and a processor, the memory storing a computer program, and the processor executing the computer program to implement the method as described in any one of claims 1 to 8.

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