A parallel and off-grid fault detection method

Abstract

The application discloses a kind of parallel and off-grid fault detection methods, comprising the following steps: S1, monitoring grid data, photovoltaic side data, battery side data and load data;S2, based on grid data, photovoltaic side data and battery side data whether grid, photovoltaic side and battery side occur fault;S3, if grid and photovoltaic side are normal, based on load power and photovoltaic side capacity load is switched to photovoltaic side or grid to carry out power supply;If grid is normal, photovoltaic side occurs fault, load is switched to grid to carry out power supply;If grid and photovoltaic side occur fault, battery side is normal, load is switched to battery side to carry out power supply;If grid, photovoltaic side and battery side all occur fault, based on repair completion time load is switched to grid, photovoltaic side or battery side.The beneficial effects of the present application: whether grid, photovoltaic side and battery side can be judged to occur fault, so as to timely alarm and maintenance, simultaneously, according to the fault of grid, photovoltaic side and battery side, parallel and off-grid switching can be carried out, to meet the power supply demand of load.

Description

Technical Field

[0001] This invention relates to the field of fault detection technology, and specifically to a method for detecting faults in parallel and offline networks. Background Technology

[0002] Photovoltaic power generation is a technology that directly converts solar energy into electrical energy using solar cells. When sunlight shines on a solar cell, the energy of the photons is absorbed by the semiconductor material, giving electrons in the semiconductor enough energy to generate electron-hole pairs. Under the influence of the electric field inside the cell, electrons and holes move towards the two poles of the cell, creating a potential difference. If an external circuit is connected, current will flow, realizing the direct conversion of light energy into electrical energy. This electrical energy is then stored in energy storage devices such as batteries.

[0003] In existing technologies, when the power grid, photovoltaic side, and battery side are all operating normally, the power grid is usually preferred to supply power to the load side. This increases the power supply burden on the power grid and is not conducive to the utilization of renewable resources. At the same time, fault detection on the photovoltaic side and battery side is usually done manually, which is time-consuming and labor-intensive, and is not conducive to switching between grid connection and off-grid. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this application proposes a grid-connected / off-grid fault detection method that can determine whether faults have occurred on the power grid, photovoltaic side, and battery side, so as to provide timely alarms and maintenance. At the same time, it can switch between grid-connected and off-grid based on faults on the power grid, photovoltaic side, and battery side to meet the power supply needs of the load.

[0005] The following is the technical solution of the present invention: a method for detecting grid connection and disconnection faults, comprising the following steps:

[0006] S1. Monitor grid data, photovoltaic data, battery data, and load data;

[0007] S2. Determine whether a fault has occurred on the power grid, photovoltaic side, and battery side based on power grid data, photovoltaic side data, and battery side data.

[0008] S3. If both the power grid and the photovoltaic side are normal, the load will be switched to the photovoltaic side or the power grid for power supply based on the load power and the capacity of the photovoltaic side.

[0009] If the power grid is normal, and a fault occurs on the photovoltaic side, the load will be switched to the power grid for power supply.

[0010] If a fault occurs on the power grid or the photovoltaic side, but the battery side is normal, the load will be switched to the battery side for power supply.

[0011] If a fault occurs on the grid, photovoltaic side, and battery side, the load will be switched to the grid, photovoltaic side, or battery side based on the repair completion time.

[0012] As a preferred embodiment of the present invention, the conditions for determining a grid fault based on grid data are: the grid voltage amplitude is lower than 70% of the rated voltage, or the grid frequency deviation exceeds ±0.5Hz and lasts for more than 0.15 seconds.

[0013] As a preferred embodiment of the present invention, the conditions for determining a fault on the photovoltaic side based on photovoltaic data are: the current of a certain component is lower than 75% of the standard value, or the voltage is higher than 115% of the rated open circuit voltage, or the actual output power is lower than 80% of the expected power, or the temperature of a certain component is higher than the component's maximum operating temperature by 10°C.

[0014] As a preferred embodiment of the present invention, the conditions for determining a battery-side fault based on battery data are: the voltage of a single battery cell is greater than or less than 8% of the rated battery voltage, or the temperature exceeds 60°C.

[0015] As a preferred embodiment of the present invention, in S3, if both the power grid and the photovoltaic side are normal, the load is switched to the photovoltaic side or the power grid for power supply based on the load power and the photovoltaic side capacity, including the following steps:

[0016] S301. Calculate the load power;

[0017] S302. Calculate the duration for which the photovoltaic side supplies power to the load;

[0018] S303. If the power supply duration is greater than n hours, switch the load to the photovoltaic side for power supply and proceed with S301; otherwise, switch the load to the grid for power supply.

[0019] As a preferred embodiment of the present invention, in S3, if the power grid is normal and a fault occurs on the photovoltaic side, the load is switched to the power grid for power supply, including: installing a dynamic voltage restorer at the grid-connected switch to suppress voltage fluctuations, using phase-locked loop technology to achieve precise synchronization between the output voltage and the grid voltage, and switching the control mode to PQ control mode.

[0020] As a preferred embodiment of the present invention, in S3, if a fault occurs on the power grid and the photovoltaic side, but the battery side is normal, the load is switched to the battery side for power supply, including: switching the energy storage converter to VF control mode, setting the inverter output voltage amplitude to 220V and the frequency to 50Hz, switching the battery side from charging or standby state to discharging state, and using the intelligent load controller to perform hierarchical management and power supply on the load according to the load side power and the remaining power on the battery side.

[0021] As a preferred embodiment of the present invention, the intelligent load controller performs hierarchical management and power supply to the load based on the load-side power and the remaining battery power, including the following steps:

[0022] S311. Classify the load devices and calculate the load power of the first-level load devices;

[0023] S312. Calculate the estimated power required to support the operation of a Level 1 load device for several hours.

[0024] S313. If the estimated power is greater than or equal to the remaining power on the battery side, cut off the power supply to non-primary load devices; otherwise, supply power to all load devices and proceed to S311.

[0025] In a preferred embodiment of the present invention, in S311, the primary load device includes communication equipment, medical equipment, and lighting equipment.

[0026] In a preferred embodiment of the present invention, in S3, if a fault occurs on the power grid, the photovoltaic side, and the battery side, the load is switched to the power grid, the photovoltaic side, or the battery side based on the emergency repair completion time. The expression for the emergency repair completion time is as follows:

[0027]

[0028] In the above formula, t is the repair completion time, t0 is the repair start time, W is the fault workload, and η i Let represent the repair efficiency of the i-th repairman, and n represent the number of repairmen.

[0029] The beneficial effects of this invention are:

[0030] 1. It can determine whether faults have occurred on the power grid, photovoltaic side, and battery side based on power grid data, photovoltaic side data, and battery side data, so as to provide timely alarms and maintenance;

[0031] 2. It can switch between grid connection and off-grid operation based on faults in the power grid, photovoltaic side, and battery side to meet the power supply needs of the load;

[0032] 3. It can classify loads and prioritize the power supply needs of primary load devices. Attached Figure Description

[0033] Figure 1 This is a schematic diagram of the present invention;

[0034] Figure 2 This is a schematic diagram of the photovoltaic side and grid power supply of the present invention;

[0035] Figure 3 This is a schematic diagram of the battery-side power supply of the present invention. Detailed Implementation

[0036] To make the technical problems solved by the present invention, the technical solutions adopted, and the technical effects achieved clearer, the technical solutions of the embodiments of the present invention will be further described in detail below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0037] Example

[0038] like Figures 1 to 3 As shown, a method for detecting grid connection / offline faults includes the following steps:

[0039] S1. Monitor grid data, photovoltaic data, battery data, and load data;

[0040] S2. Determine whether a fault has occurred on the power grid, photovoltaic side, and battery side based on power grid data, photovoltaic side data, and battery side data.

[0041] S3. If both the power grid and the photovoltaic side are normal, the load will be switched to the photovoltaic side or the power grid for power supply based on the load power and the capacity of the photovoltaic side.

[0042] If the power grid is normal, and a fault occurs on the photovoltaic side, the load will be switched to the power grid for power supply.

[0043] If a fault occurs on the power grid or the photovoltaic side, but the battery side is normal, the load will be switched to the battery side for power supply.

[0044] If a fault occurs on the grid, photovoltaic side, and battery side, the load will be switched to the grid, photovoltaic side, or battery side based on the repair completion time.

[0045] In step S1, grid data, photovoltaic (PV) side data, and battery side data are monitored. Specifically, monitoring equipment, such as smart meters, voltage transformers, and current transformers, is installed on the grid to monitor grid data, including grid voltage, grid frequency, and grid phase. On the PV side, bypass diodes and blocking diodes are equipped on the PV modules to monitor PV data such as PV current and PV voltage. Battery data, such as battery voltage, battery temperature, and battery current, are monitored in real time through the BMS. Load data includes the number of load devices and the rated power of each load device.

[0046] In step S2, it is determined whether a fault has occurred on the power grid, photovoltaic side, and battery side based on the power grid data, photovoltaic side data, and battery side data.

[0047] The power grid is judged to have a fault based on power grid data. If the power grid voltage amplitude is lower than 70% of the rated voltage, or the power grid frequency deviation exceeds ±0.5Hz and lasts for more than 0.15 seconds, then the power grid is judged to have a fault.

[0048] Based on photovoltaic data, it is determined whether a fault has occurred on the photovoltaic side. When a photovoltaic module has a short circuit fault, the bypass diode will conduct, and the current will bypass the faulty module. When the photovoltaic current of a module is measured to be lower than 75% of the standard value, or the photovoltaic voltage is higher than 115% of the rated open circuit voltage, the module may have a fault, such as an internal short circuit or open circuit. If the actual output power of the photovoltaic side is lower than 80% of the theoretical expected power, there is an abnormal power output. If the temperature of a module is higher than the maximum operating temperature of the module by 10°C, there is an abnormal overheating of the module.

[0049] The system determines whether a battery-side fault has occurred based on battery data. If a single battery cell exhibits overvoltage, undervoltage, or overtemperature, the battery is considered faulty. A battery-side fault occurs when the voltage of a single battery cell is greater than or less than 8% of the rated battery voltage, or when the temperature exceeds 60°C.

[0050] In step S3, if both the power grid and the photovoltaic side are normal, the load is switched to the photovoltaic side or the power grid for power supply based on the load power and the photovoltaic side capacity; if the power grid is normal but the photovoltaic side fails, the load is switched to the power grid for power supply; if both the power grid and the photovoltaic side fail but the battery side is normal, the load is switched to the battery side for power supply; if the power grid, the photovoltaic side, and the battery side all fail, the load is switched to the power grid, the photovoltaic side, or the battery side based on the repair completion time.

[0051] If the power grid, photovoltaic side, and battery side are all functioning normally, the load will be switched to the photovoltaic side or the power grid for power supply based on the load power and photovoltaic side capacity.

[0052] Calculate the load power P total The expression is as follows:

[0053] P total =P1+P2+...+P n

[0054] In the above formula, P total For load power, P n Let be the power of the nth load device.

[0055] Estimate the duration t during which the photovoltaic side can independently provide power to the load. a The expression is as follows:

[0056]

[0057] In the above formula, t a To estimate the power supply duration, W1 represents the photovoltaic capacity, and P... total This represents the load power.

[0058] Prioritize using photovoltaic power to supply power to the load. When t≤1.2, switch the load to grid power.

[0059] If both the power grid and the photovoltaic (PV) side are functioning normally, the load will be switched to either the PV side or the power grid for power supply based on the load power and PV capacity, including the following steps:

[0060] S301. Calculate the load power;

[0061] S302. Calculate the duration for which the photovoltaic side supplies power to the load;

[0062] S303. If the power supply duration is greater than 1.2 hours, switch the load to the photovoltaic side for power supply and proceed with S301; otherwise, switch the load to the grid for power supply.

[0063] If the grid is normal and a fault occurs on the photovoltaic side, the load will be switched to the grid for power supply. When a fault is detected on the photovoltaic side, the photovoltaic inverter will first stop working, and then the grid connection switch will be closed to switch the load to grid power supply. The grid voltage and output voltage are sampled, and a dual closed-loop synchronization control strategy (phase and frequency) is used to adjust the phase and frequency of the output voltage, enabling rapid synchronization between the output voltage and the grid voltage. This strategy effectively reduces current and voltage surges during grid connection, ensuring the smoothness of the connection process. Phase-locked loop (PLL) technology is used to achieve precise synchronization between the output voltage and the grid voltage. The PLL automatically tracks the frequency and phase changes of the grid voltage and adjusts the phase and frequency of the local voltage to match the grid, ensuring that the phase and frequency differences between the two are within allowable limits at the moment of grid connection, achieving seamless grid connection.

[0064] After grid synchronization is completed, the control mode is switched to PQ control mode, and the output power is set according to demand and actual conditions. PQ control mode can precisely control the active and reactive power output of the inverter, ensuring it delivers power to the grid according to set values, thus effectively supporting the grid and regulating power. Since photovoltaic side faults may cause system voltage fluctuations, devices such as dynamic voltage restorers (DVRs) are installed at the grid connection switch to suppress voltage fluctuations and ensure normal load operation. DVRs can quickly inject or absorb reactive power within milliseconds, limiting voltage fluctuations to within ±5%, ensuring system voltage stability.

[0065] If a fault occurs on the power grid or the photovoltaic side, but the battery side is normal, the load will be switched to the battery side for power supply.

[0066] Upon detecting a grid fault, the energy storage converter switches to VF control mode to provide a stable voltage and frequency reference. Under VF control, the inverter operates in a dual closed-loop voltage and current mode, with the output of the outer voltage regulator serving as the reference for the inner current regulator, thereby outputting a stable voltage and frequency. The inverter output voltage amplitude is set to 220V and the frequency to 50Hz.

[0067] When the battery is switched from charging or standby to discharging, the battery management system (BMS) adjusts the battery's discharge current according to load demand to maintain the system's power balance.

[0068] By installing intelligent load controllers, non-critical loads can be managed in a tiered manner based on the load-side power and the remaining battery power. For example, non-critical loads such as air conditioners and electric water heaters can be classified as lower priority. When the power generation is insufficient, the power supply to these loads will be cut off first to ensure the continuous power supply to primary load devices, including communication equipment, medical equipment, and lighting equipment.

[0069] When a grid fault is detected, the smart circuit breaker installed at the grid connection switch operates rapidly within milliseconds to tens of milliseconds to isolate the microgrid from the faulty grid and prevent the fault from spreading further.

[0070] When switching back to grid-connected mode from off-grid mode after a grid fault is recovered, phase-locked loop (PLL) technology is needed to achieve grid synchronization, ensuring that the voltage phase and frequency of the local grid connection point are consistent with the main grid, thus ensuring a smooth grid connection.

[0071] The intelligent load controller manages and supplies power to loads in a tiered manner based on the load-side power and the remaining battery capacity, including the following steps:

[0072] S311. Classify the load devices and calculate the load power of the first-level load devices;

[0073] S312. Calculate the estimated power required to support the operation of a Level 1 load device for several hours.

[0074] S313. If the estimated power is greater than or equal to the remaining power on the battery side, cut off the power supply to non-primary load devices; otherwise, supply power to all load devices and proceed to S311.

[0075] If faults occur on the grid, the photovoltaic (PV) side, and the battery side, the load will be switched to the grid, the PV side, or the battery side based on the repair completion time. Compared to faulty PV and battery sides, grid personnel are generally more efficient at repairs, and there are more personnel available for repairs. The expression for the repair completion time t is as follows:

[0076]

[0077] In the above formula, t is the repair completion time, t0 is the repair start time, W is the fault workload, and η i Let represent the repair efficiency of the i-th repairman, and n represent the number of repairmen.

[0078] When the number of faults is fixed, the grid workers are usually more efficient at repairing, and there are more repair workers available. Therefore, the grid repair time is shorter than that of the photovoltaic and battery sides.

[0079] When the load is switched to the grid, secondary failures and repair difficulties caused by weather and time-related factors can be avoided. Furthermore, after a failure on the photovoltaic side or the battery side, troubleshooting and repairing the fault requires professional technology and equipment, which is costly. In addition, the grid has abundant dispatchable power resources with a capacity far exceeding that of the typical photovoltaic and battery sides. For high-power loads or loads with large fluctuations in electricity demand, the grid can easily meet their power requirements.

[0080] This invention can determine whether faults have occurred on the power grid, photovoltaic side, and battery side based on power grid data, photovoltaic side data, and battery side data, so as to provide timely alarms and maintenance; it can perform grid-connected and off-grid switching based on faults on the power grid, photovoltaic side, and battery side to meet the power supply needs of the load; and it can classify the load and prioritize meeting the power supply needs of primary load devices.

[0081] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including both the preferred embodiments and all changes and modifications falling within the scope of the invention.

[0082] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A method for detecting grid connection and disconnection faults, characterized in that, Includes the following steps: S1. Monitor grid data, photovoltaic data, battery data, and load data; S2. Determine whether a fault has occurred on the power grid, photovoltaic side, and battery side based on power grid data, photovoltaic side data, and battery side data. S3. If both the power grid and the photovoltaic side are normal, the load will be switched to the photovoltaic side or the power grid for power supply based on the load power and the capacity of the photovoltaic side. If the power grid is normal, and a fault occurs on the photovoltaic side, the load will be switched to the power grid for power supply. If a fault occurs on the power grid or the photovoltaic side, but the battery side is normal, the load will be switched to the battery side for power supply. If a fault occurs on the grid, photovoltaic side, and battery side, the load will be switched to the grid, photovoltaic side, or battery side based on the repair completion time.

2. The method for detecting grid connection / disconnection faults according to claim 1, characterized in that, The conditions for determining a grid fault based on grid data are: the grid voltage amplitude is lower than 70% of the rated voltage, or the grid frequency deviation exceeds ±0.5Hz and lasts for more than 0.15 seconds.

3. The method for detecting grid connection / disconnection faults according to claim 1, characterized in that, The conditions for determining a photovoltaic-side fault based on photovoltaic data are: the current of a certain component is lower than 75% of the standard value, or the voltage is higher than 115% of the rated open-circuit voltage, or the actual output power is lower than 80% of the expected power, or the temperature of a certain component is higher than the component's maximum operating temperature by 10°C.

4. The method for detecting grid connection / disconnection faults according to claim 1, characterized in that, The conditions for determining a battery-side fault based on battery data are: the voltage of a single battery cell is greater than or less than 8% of the rated battery voltage, or the temperature exceeds 60°C.

5. The method for detecting grid connection / disconnection faults according to claim 1, characterized in that, In S3, if both the power grid and the photovoltaic side are normal, the load is switched to the photovoltaic side or the power grid for power supply based on the load power and the photovoltaic side capacity, including the following steps: S301. Calculate the load power; S302. Calculate the duration for which the photovoltaic side supplies power to the load; S303. If the power supply duration is greater than n hours, switch the load to the photovoltaic side for power supply and proceed with S301; otherwise, switch the load to the grid for power supply.

6. The method for detecting grid connection / disconnection faults according to claim 1, characterized in that, In S3, if the grid is normal but a fault occurs on the photovoltaic side, the load will be switched to the grid for power supply. This includes: installing a dynamic voltage restorer at the grid-connected switch to suppress voltage fluctuations, using phase-locked loop technology to achieve precise synchronization between the output voltage and the grid voltage, and switching the control mode to PQ control mode.

7. The method for detecting grid connection / disconnection faults according to claim 1, characterized in that, In S3, if a fault occurs on the grid and photovoltaic side, but the battery side is normal, the load will be switched to the battery side for power supply. This includes: switching the energy storage converter to VF control mode, setting the inverter output voltage amplitude to 220V and the frequency to 50Hz, switching the battery side from charging or standby state to discharging state, and using the intelligent load controller to manage and supply power to the load in a hierarchical manner based on the load side power and the remaining battery power.

8. The method for detecting grid connection / disconnection faults according to claim 7, characterized in that, The intelligent load controller manages and supplies power to loads in a tiered manner based on the load-side power and the remaining battery capacity, including the following steps: S311. Classify the load devices and calculate the load power of the first-level load devices; S312. Calculate the estimated power required to support the operation of a Level 1 load device for several hours. S313. If the estimated power is greater than or equal to the remaining power on the battery side, cut off the power supply to non-primary load devices; otherwise, supply power to all load devices and proceed to S311.

9. The method for detecting grid connection / disconnection faults according to claim 8, characterized in that, In S311, primary load devices include communication equipment, medical equipment, and lighting equipment.

10. The method for detecting grid connection / disconnection faults according to claim 1, characterized in that, In S3, if faults occur on the grid, photovoltaic side, and battery side, the load will be switched to the grid, photovoltaic side, or battery side based on the repair completion time. The expression for the repair completion time is as follows: In the above formula, t is the repair completion time, t0 is the repair start time, W is the fault workload, and η i Let represent the repair efficiency of the i-th repairman, and n represent the number of repairmen.

Images