Control method and system for planned off-grid operation of power system

Abstract

The invention relates to a control method and system for planned off-grid operation of an electric power system, and belongs to the technical field of electric power systems. When a switching instruction for switching an operation mode of the electric power system from a grid-connected mode to an off-grid mode is received and an execution condition for executing pre-control operation is met, the pre-control operation is executed before a grid-connected circuit breaker is disconnected, and the pre-control operation is executed after the grid-connected circuit breaker is disconnected; the pre-control operation is to reduce the exchange power of the regional power grid to a preset power range; after the preset power range is reached, the operation mode of the power system is switched to off-grid operation; wherein the preset power range is + / -0.5%-2% Pn, cooperative assistance can be provided for planned off-grid switching, correctness and safety of off-grid switching are guaranteed, safety and stability of energy supply are improved, and in emergencies such as natural disasters and wars, the system can guarantee power supply of key areas.

Description

Technical Field

[0001] This invention relates to a control method and system for planned off-grid operation of a power system, belonging to the field of power system technology. Background Technology

[0002] The new power system emphasizes the interaction between power generation, grid, load, and storage, as well as multi-energy complementarity. This means that the system includes various energy forms, such as wind, solar, and hydropower. These energy sources have different characteristics and operating patterns, requiring the power system to have the ability to flexibly adjust and coordinate operations. With the large-scale integration of distributed energy resources, the security and stability of the power grid face new challenges.

[0003] Planned off-grid operation refers to an independent power supply mode that does not rely on the public power grid (generating power through renewable sources such as solar and wind power). It can serve as an emergency measure to ensure the safe operation of the power grid under specific circumstances. For example, when equipment needs maintenance or repair, to avoid affecting the normal operation of the entire power grid, the microgrid or local power grid containing the relevant equipment can be switched to planned off-grid operation mode. This allows for safe equipment maintenance and repair work without affecting the power supply to other areas. Similarly, during emergencies (such as natural disasters or wars), to ensure power supply to critical areas, the power grid in non-critical areas can be switched to planned off-grid operation mode. This concentrates limited power resources to critical areas, ensuring the normal operation of important facilities. Summary of the Invention

[0004] The purpose of this invention is to provide a control method and system for planned off-grid operation of a power system, in order to solve the problem that frequency and voltage changes caused by instantaneous power imbalance in the regional power grid after off-grid operation prevent the regional power grid from operating normally. This invention enables the regional power grid to reduce its switching power to near zero before disconnecting the grid-connected circuit breaker and then switching the operating mode.

[0005] To achieve the above objectives, this invention proposes a control method for planned off-grid operation of a power system, comprising the following steps: 1) When a switching instruction to switch the power system operation mode from grid-connected to off-grid is received, and the execution conditions for performing pre-control operations are met, the pre-control operations are performed before disconnecting the grid-connected circuit breaker. The pre-control operations are to reduce the regional power grid switching power to a preset power range. 2) After reaching the preset power range, the operation mode of the power system is switched to off-grid operation; The preset power range is ±0.5%~2%Pn, where Pn is the total rated power of the inverter.

[0006] Furthermore, the regional power grid switching power is reduced to a preset power range using the following methods: Within a preset time period, other targets' control over the regional power grid is blocked, and the output of new energy sources and the charging and discharging of storage are adjusted so that the active power exchange power is reduced to the preset power range. Adjust the reactive power compensation equipment of the power plant and the reactive power output of the new energy power plant to reduce the reactive power exchange power to the preset power range.

[0007] Furthermore, the power exchange capacity of the regional power grid is determined to have dropped to a preset power range by the following method: periodically judging whether the pre-control termination condition is met; if it is met, the power exchange capacity of the regional power grid is determined to have dropped to a preset power range.

[0008] Furthermore, a duration threshold for the pre-control operation is set; When the execution time of the pre-control operation reaches the duration threshold and the pre-control termination condition is not met, the adjustment of active power exchange and reactive power exchange ends.

[0009] Furthermore, it also includes: setting adjustment time thresholds for active power exchange and reactive power exchange; When the adjustment time of active power exchange and reactive power exchange reaches the adjustment time threshold and the pre-control termination condition is not met, the adjustment of active power exchange and reactive power exchange ends. Wherein, the duration threshold is less than the adjustment time threshold.

[0010] On the other hand, the present invention also proposes a control system for planned off-grid operation of a power system, including a switching service module and an auxiliary control service module; wherein, the switching service module is used to receive a switching instruction to switch the operation mode of the power system from grid-connected to off-grid, and to determine whether the auxiliary control service module meets the execution conditions for performing pre-control operations, and when the conditions are met, to send a start instruction to the auxiliary control service module to start the pre-control operations; In response to the start command, the auxiliary control service module performs the pre-control operation: reducing the regional power grid switching power to a preset power range so that after reaching the preset power range, the power system's operation mode is switched to off-grid operation; wherein, the preset power range is ±0.5%~2%Pn, where Pn is the total rated power of the inverter.

[0011] Furthermore, the auxiliary control service includes an active power control service unit and a reactive power control service unit; wherein, performing the pre-control operation includes: The active power control service unit is used to shield other targets from controlling the regional power grid within a preset time period, and to adjust the output of new energy sources and the charging and discharging of storage, so that the active power exchange power is reduced to the preset power range. The reactive power control service unit is used to adjust the reactive power compensation equipment of the power plant and the reactive power output of the new energy power plant so that the reactive power exchange power is reduced to the preset power range.

[0012] Furthermore, the switching server module is also used to periodically determine whether the pre-control termination condition is met; if it is met, then it is determined that both the active power exchange power and the reactive power exchange power are reduced to the preset power range.

[0013] Furthermore, the switching server module is also used to set a duration threshold for the pre-control operation; When the execution time of the pre-control operation in the auxiliary control service module reaches the duration threshold and the pre-control termination condition is not met, the control of active power exchange and reactive power exchange ends.

[0014] Furthermore, the auxiliary control service module is also used to set the adjustment time thresholds for active power exchange and reactive power exchange; When the adjustment time of active power exchange and reactive power exchange reaches the adjustment time threshold and the pre-control termination condition is not met, the control of active power exchange and reactive power exchange ends. Wherein, the duration threshold is less than the adjustment time threshold.

[0015] The beneficial effects of this invention are as follows: When a switching command to switch the power system's operation mode from grid-connected to off-grid is received, and the execution conditions for performing pre-control operations are met, a pre-control operation is performed before disconnecting the grid-connected circuit breaker. The pre-control operation involves reducing the regional power grid's switching power to a preset power range. After reaching the preset power range, the power system's operation mode is switched to off-grid operation. The preset power range is ±0.5%~2%Pn, where Pn is the total rated power of the inverter. This provides coordinated assistance for planned off-grid switching, ensuring the correctness and safety of off-grid switching, improving the safety and stability of energy supply, and enabling the system to guarantee power supply in critical areas during emergencies such as natural disasters and wars. Attached Figure Description

[0016] Figure 1 This is a flowchart of a control method for planned off-grid operation of a power system proposed in this invention; Figure 2 This is a schematic diagram of data interaction between modules in a practical application scenario of a control system for planned off-grid operation of a power system proposed in this invention. Detailed Implementation

[0017] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0018] The inventive concept of this invention is as follows: When a new power system is undergoing planned off-grid mode switching, in order to avoid the occurrence of frequency and voltage sudden changes caused by instantaneous power imbalance in the regional power grid after off-grid switching, which may lead to the inability of the regional power grid to operate normally after off-grid switching, this invention proposes a collaborative control interaction method that integrates operation mode switching service, active power control service, reactive power control service, and operation mode switching interface client.

[0019] Detailed implementation method 1: like Figure 1 The diagram shows a flowchart of a control method for planned off-grid operation of a power system proposed in this invention, including steps S11 and S12, specifically: Step S11: When a switching command to switch the power system's operation mode from grid-connected to off-grid is received, and the execution conditions for performing pre-control operations are met, a pre-control operation is performed before disconnecting the grid-connected circuit breaker. The pre-control operation involves reducing the regional grid's switching power to a preset power range. Here, the preset power range is ±0.5%~2%Pn, where Pn is the total rated power of the inverter. In practical applications, pre-processing is generally required, with the following exceptions: 1. If the capacity of the microgrid's internal power sources (such as energy storage or distributed power sources) is much greater than the load, and the load fluctuation is small, it can quickly self-balance after switching, simplifying or even eliminating the power pre-adjustment step. 2. If the microgrid is equipped with a high-speed energy storage converter (PCS), virtual synchronous machine, etc., it can instantly fill the power gap and dynamically adjust during the switching process, without the need for pre-balancing.

[0020] The process of reducing the regional power grid's switching power to a preset power range includes shielding the regional power grid from other targets' control within a preset time period, adjusting the output of new energy sources and the charging and discharging of storage to reduce the active power switching power to the preset power range, and adjusting the reactive power compensation equipment of power plants and the reactive power output of new energy power plants to reduce the reactive power switching power to the preset power range.

[0021] Step S12: After reaching the preset power range, switch the operation mode of the power system to off-grid operation.

[0022] Through the above steps S11-S12, the regional power grid switching power is reduced to a preset power range before the grid-connected circuit breaker is disconnected, thereby enabling the power system to stably switch from grid-connected operation to off-grid operation.

[0023] Method Detailed Implementation 2: Following the specific embodiments of the present invention described above, the method for determining that the regional power grid exchange power has dropped to a preset power range in step S11 is as follows: periodically judging whether the pre-control termination condition is met; if it is met, then determining that the regional power grid exchange power has dropped to a preset power range.

[0024] In addition, to ensure the execution and termination of the pre-control operation, a duration threshold for the pre-control operation is set; when the execution time of the pre-control operation reaches the duration threshold and the pre-control termination condition is not met, the adjustment of active power exchange and reactive power exchange is terminated.

[0025] Alternatively, adjustment time thresholds for active power exchange and reactive power exchange can be set; when the adjustment time for active power exchange and reactive power exchange reaches the adjustment time threshold and the pre-control termination condition is not met, the adjustment of active power exchange and reactive power exchange is terminated; here, the duration threshold is less than the adjustment time threshold.

[0026] System Specific Implementation Method 1: like Figure 2 The diagram shown illustrates the data interaction between modules in a practical application scenario of a control system for planned off-grid operation of a power system proposed in this invention. The system includes an operation mode switching service A, an operation mode auxiliary control service B (which includes active power control service AGC and reactive power control service AVC), and an operation mode switching interface client C.

[0027] In response to the operator triggering an identifier for generating an operation mode switching request on the operation mode switching interface client C, the operation mode switching interface client C sends a switching request message 1 for switching between grid-connected and off-grid operation modes to the operation mode switching service A.

[0028] After receiving the switching request message 1, the operation mode switching service A determines whether the switching conditions are met. If the switching conditions are not met, it returns a rejection control message 2 to the operation mode switching interface client B. Here, it determines whether the total output of distributed power sources (such as photovoltaic and wind power) and energy storage systems within the regional power grid system meets the switching conditions. The switching conditions refer to all critical equipment (energy storage, inverters, protection devices, etc.) being in a ready state with no fault alarms; and, under grid-connected conditions, the power, voltage, and frequency fluctuations of the tie lines must be within allowable ranges, with no risk of exceeding limits. This can also be understood as determining whether the total output of distributed power sources (such as photovoltaic and wind power) and energy storage systems within the regional power grid system can match the real-time demand of all loads within the isolated grid.

[0029] If the conditions are met, the operation mode switching service A continues to determine whether pre-control is needed. When pre-control is needed, a pre-control start message 3 is sent to the operation mode auxiliary control service B (here, the operation mode auxiliary control service B includes active power control service and reactive power control service). In practical application scenarios, pre-processing is generally required, with the following exceptions: 1. If the capacity of the power sources (such as energy storage, distributed power sources) within the microgrid is much larger than the load, and the load fluctuation is small, it can quickly self-balance after switching, simplifying or even eliminating the power pre-regulation step. 2. If the microgrid is equipped with high-speed energy storage converters (PCS), virtual synchronous machines, etc., it can instantly fill the power gap and can dynamically adjust during the switching process without the need for pre-balancing.

[0030] In response to the pre-control start message 3, the active power control service in Operation Mode Auxiliary Control Service B temporarily blocks the control of other targets and reduces the exchange power to near the zero threshold (the zero threshold is the preset power range) by adjusting the output of new energy sources and the charging and discharging of energy storage. Here, the other targets include, but are not limited to, conventional / economic dispatch, voltage / reactive power / power quality regulation, and power market / dispatch response; the zero threshold range is typically ±0.5%~2%Pn (where Pn is the total rated power of the inverter). Next, in response to the pre-control start message 3, the reactive power control service in Operation Mode Auxiliary Control Service B reduces the reactive power exchange power to the zero threshold by adjusting the reactive power compensation equipment of the power plant and the reactive power output of the new energy plant. This effectively avoids the occurrence of frequency and voltage surges caused by instantaneous power imbalances in the off-grid regional power grid (the regional power grid refers to the local regional power grid that is to be switched from grid-connected operation to off-grid operation, the object being separated), which could prevent the off-grid regional power grid from operating normally.

[0031] Simultaneously, after sending the switching request message 1, the client C of the operation mode switching interface begins to receive control message process records from the active power control service and reactive power control service in the operation mode auxiliary control service B, and displays them in the control execution information display area so that operators can view the control process of the active power control service and reactive power control service in real time. This completes the triggering and initiation of the pre-control operation.

[0032] During the pre-control execution of the auxiliary control service in the operating mode, when an emergency termination of the switching operation is required, the operator sends a termination switching request message 4 to the operating mode switching service A through the switching service interface client C. This causes the operating mode switching service A to send a termination switching request message 4 to the operating mode auxiliary control service B, and the auxiliary control service B delays the termination of its auxiliary service. Emergency termination of the switching operation is required in the following situations: during the pre-synchronization phase or at the moment of switching, the electrical parameters of the grid connection point exceed the allowable range; the energy storage converter or main power supply that plays a role in grid construction fails or alarms; the system enters a "blind operation" or "out-of-control" state, making it impossible to guarantee the accuracy and safety of the switching process. In particular, if active / reactive power control is immediately terminated during the switching process, it may cause a sudden change in power, leading to severe voltage / frequency fluctuations, and even causing equipment tripping or damage. Therefore, delaying the termination of the auxiliary service by the auxiliary control service B allows the system to gradually and smoothly exit the power control state, reducing the impact.

[0033] During the pre-control execution of the operation mode auxiliary control service, after the operation mode switching service A sends the pre-control start message 3, it periodically checks whether the pre-control termination condition is met. If the termination condition is met, it sends the termination pre-control message 5 to the operation mode auxiliary control service B, and the switching service continues to perform mode switching sequence control. Here, the control termination condition includes, but is not limited to, the switching power reaching near the zero threshold; voltage, frequency, and phase angle meeting synchronization conditions; system stability; no equipment faults / protection alarms; and normal communication and control links. The continued mode switching sequence control by the switching service refers to the switching server performing the operation mode switch (i.e., from grid-connected to off-grid) after the termination condition is met. In practical application scenarios, after the pre-control ends, the mode switching sequence control specifically includes: 1. Switching action (opening / closing the grid-connected switch); 2. PCS / inverter control mode switching (PQ ↔ V / F / VSG); 3. Energy storage and distributed power control strategy adjustment; 4. Load classification management and switching; 5. Protection and alarm system switching; 6. Communication and scheduling status reporting.

[0034] During the pre-control execution of the operation mode auxiliary control service, the timeout handling process I in operation mode switching service A is as follows: operation mode switching service A collects and judges the pre-control execution duration in operation mode auxiliary control service B, and if the pre-control execution duration exceeds the "maximum allowed duration of pre-control" (i.e., timeout time t1) and the pre-control termination condition is still not met, operation mode switching service A sends termination request message 6 to operation mode auxiliary control service B, and operation mode auxiliary control service B terminates the auxiliary service.

[0035] Timeout handling process II in the operating mode switching service A: The operating mode switching service A sends an end message to the switching service interface client C. The switching service interface client C prompts on the user page that the switching condition is not met and no longer receives control messages such as active power control service and reactive power control service, and the switching service ends this switching. Here, it should be noted that the two timeout handling processes must be coordinated and executed sequentially. These two processes are complementary and sequential safety measures, ensuring that the system can safely and completely exit the switching attempt and return to stability from the two dimensions of the control background and the human-machine interface / message link under timeout faults.

[0036] Meanwhile, in the operating mode auxiliary control service B, timeout handling process I: The active power control service and reactive power control service judge the pre-control execution duration. If the pre-control end request has not been received after exceeding the longest allowable time limit for grid connection to off-grid (i.e., the timeout time t2, where t1 < t2), the auxiliary service ends.

[0037] The beneficial effects of the present invention are as follows: It can provide collaborative assistance for planned off-grid switching, ensuring the correctness and safety of off-grid switching, improving the security and stability of energy supply. In emergencies such as natural disasters and wars, the system can ensure the power supply in key areas.

[0038] In summary, the present invention discloses a control method and system for planned off-grid operation of a power system. When the new power system performs a planned off-grid operation mode switching, in order to avoid frequency and voltage mutations caused by instant power imbalance in the regional power grid after off-grid, which may lead to abnormal operation of the regional power grid after off-grid, the regional power grid exchange power needs to be reduced to near zero before actually disconnecting the grid-connected circuit breaker and then perform the operation mode switching. To achieve the above functions, the present invention proposes a collaborative control interaction method integrating an operating mode switching service, an active power control service, a reactive power control service, and an operating mode switching interface client.

Claims

1. A control method for planned off-grid operation of a power system, characterized in that, Includes the following steps: 1) When a switching instruction to switch the power system operation mode from grid-connected to off-grid is received, and the execution conditions for performing pre-control operations are met, the pre-control operations are performed before disconnecting the grid-connected circuit breaker. The pre-control operations are to reduce the regional power grid switching power to a preset power range. 2) After reaching the preset power range, the operation mode of the power system is switched to off-grid operation; The preset power range is ±0.5%~2%Pn, where Pn is the total rated power of the inverter.

2. The control method for planned off-grid operation of a power system according to claim 1, characterized in that, The regional power grid switching power can be reduced to a preset range using the following method: Within a preset time period, other targets' control over the regional power grid is blocked, and the output of new energy sources and the charging and discharging of storage are adjusted so that the active power exchange power is reduced to the preset power range. Adjust the reactive power compensation equipment of the power plant and the reactive power output of the new energy power plant to reduce the reactive power exchange power to the preset power range.

3. The control method for planned off-grid operation of a power system according to claim 1, characterized in that, The power exchange capacity of the regional power grid is determined to have dropped to a preset power range by the following method: periodically judging whether the pre-control termination condition is met; if it is met, the power exchange capacity of the regional power grid is determined to have dropped to a preset power range.

4. The control method for planned off-grid operation of a power system according to claim 3, characterized in that, Set a duration threshold for the pre-control operation; When the execution time of the pre-control operation reaches the duration threshold and the pre-control termination condition is not met, the adjustment of active power exchange and reactive power exchange ends.

5. The control method for planned off-grid operation of a power system according to claim 4, characterized in that, Also includes: Set the adjustment time thresholds for active power exchange and reactive power exchange; When the adjustment time of active power exchange and reactive power exchange reaches the adjustment time threshold and the pre-control termination condition is not met, the adjustment of active power exchange and reactive power exchange ends. Wherein, the duration threshold is less than the adjustment time threshold.

6. A control system for planned off-grid operation of a power system, characterized in that, It includes a switching service module and an auxiliary control service module; wherein, the switching service module is used to receive a switching instruction to switch the operation mode of the power system from grid-connected to off-grid, and to determine whether the auxiliary control service module meets the execution conditions for performing pre-control operations, and when the conditions are met, to send a start instruction to the auxiliary control service module to start the pre-control operations; In response to the start command, the auxiliary control service module performs the pre-control operation: reducing the regional power grid switching power to a preset power range so that after reaching the preset power range, the power system's operation mode is switched to off-grid operation; wherein, the preset power range is ±0.5%~2%Pn, where Pn is the total rated power of the inverter.

7. The control system for planned off-grid operation of a power system according to claim 6, characterized in that, The auxiliary control service includes an active power control service unit and a reactive power control service unit; wherein, performing the pre-control operation includes: The active power control service unit is used to shield other targets from controlling the regional power grid within a preset time period, and to adjust the output of new energy sources and the charging and discharging of storage, so that the active power exchange power is reduced to the preset power range. The reactive power control service unit is used to adjust the reactive power compensation equipment of the power plant and the reactive power output of the new energy power plant so that the reactive power exchange power is reduced to the preset power range.

8. The control system for planned off-grid operation of a power system according to claim 7, characterized in that, The switching server module is also used to periodically determine whether the pre-control termination condition is met; if it is met, it determines that both the active power exchange power and the reactive power exchange power are reduced to the preset power range.

9. The control system for planned off-grid operation of a power system according to claim 8, characterized in that, The switching server module is also used to set a duration threshold for the pre-control operation; When the execution time of the pre-control operation in the auxiliary control service module reaches the duration threshold and the pre-control termination condition is not met, the control of active power exchange and reactive power exchange ends.

10. The control system for planned off-grid operation of a power system according to claim 9, characterized in that, The auxiliary control service module is also used to set the adjustment time thresholds for active power exchange and reactive power exchange. When the adjustment time of active power exchange and reactive power exchange reaches the adjustment time threshold and the pre-control termination condition is not met, the control of active power exchange and reactive power exchange ends. Wherein, the duration threshold is less than the adjustment time threshold.

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