A green electricity direct connection and power grid weak grid-connected power supply switching control system and method

Abstract

The application discloses a power supply switching control system and method for green electricity direct connection and weak grid connection, and relates to the technical field of grid control. The system comprises a first incoming line unit, a second incoming line unit, a bus unit and an automatic switching control device. The first incoming line unit is connected with a load-side green electricity direct connection power generation system, is provided with a circuit breaker, a mutual inductor and a synchronization detection module, and collects voltage amplitude, frequency and phase information of the green electricity side incoming line. The second incoming line unit is connected with an external grid, is provided with corresponding devices and a synchronization detection module, and collects electrical parameters of the grid side incoming line. The bus unit is connected with a load-side power utilization system and is provided with a bus mutual inductor. The automatic switching control device is connected with each unit, independently controls the opening and closing states of the two-way incoming line circuit breakers according to preset switching strategies and real-time electrical parameters. The application can improve the smoothness and reliability of power supply switching in a weak grid connection environment, shorten the power supply interruption time, and ensure stable power supply on the load side.

Description

Technical Field

[0001] This application relates to the field of power grid control technology, and in particular to a power switching control system and method for direct green power connection and weak grid connection. Background Technology

[0002] With the deepening of the "dual carbon" goals, load-side green electricity direct connection technology has become an important way to realize the local consumption of clean energy, which can effectively reduce power transmission and distribution losses and lower end-user electricity costs. However, green electricity direct connection systems are mostly deployed in the end areas of the power grid, and the connection with the external power grid exhibits weak grid connection characteristics. The system inertia is low, the short-circuit ratio at the common coupling point is at a critical value and is subject to time-varying fluctuations. At the same time, the renewable energy generation is intermittent and volatile, requiring frequent switching of incoming power sources between green electricity direct connection and grid power supply.

[0003] The relevant dual-power switching device does not have independent synchronization detection units for the two incoming lines, making it impossible to accurately collect the voltage amplitude, frequency, and phase information of the two incoming lines. When the voltage and frequency fluctuate drastically in a weak grid environment, it is difficult to accurately determine the synchronization closing conditions, which can easily generate large inrush currents. Furthermore, it lacks independent and refined control over the circuit breakers of the two incoming lines, resulting in insufficient adaptability of the switching logic. This leads to low switching reliability, long power outage time, and an inability to fully guarantee the continuity of power supply to the load side and the safety of equipment operation. It is also difficult to adapt to the incoming line switching requirements of the load side green power direct connection weak grid scenario. Summary of the Invention

[0004] This application provides a power switching control system and method for direct green power connection and weak grid connection. It can solve the problems in related technologies, such as insufficient synchronization judgment accuracy, large switching inrush current, and low power supply reliability in weak grid connection scenarios, caused by the lack of independent synchronization detection and independent circuit breaker control mechanisms for the two incoming lines.

[0005] According to a first aspect of this application, a power switching control system for direct green electricity connection and weak grid connection is provided, comprising:

[0006] The first incoming line unit is connected to the load-side green electricity direct-connection generation system and includes a first incoming line circuit breaker, a first voltage transformer, a first current transformer, and a first synchronization detection module. The first synchronization detection module is used to collect the voltage amplitude, frequency, and phase information of the green electricity side incoming line. The second incoming line unit, connected to the external power grid, includes a second incoming line circuit breaker, a second voltage transformer, a second current transformer, and a second synchronization detection module. The second synchronization detection module is used to collect the voltage amplitude, frequency, and phase information of the incoming line on the power grid side. Busbar unit, connected to the load-side power system, includes busbar voltage transformer and busbar current transformer; An automatic switching control device is connected to the first incoming line unit, the second incoming line unit, and the busbar unit respectively. Based on a preset switching strategy and real-time collected electrical parameters, it independently controls the opening and closing status of the first and second incoming line circuit breakers.

[0007] According to a second aspect of this application, a power switching control method for direct green electricity connection and weak grid connection is provided, comprising: S1 collects system status information in real time, including voltage amplitude, frequency, phase angle of the first incoming line side, the second incoming line side and the bus side, as well as active power and reactive power data of each branch. S2, Power quality assessment and priority determination of two incoming power supplies: Based on the collected real-time data, calculate the voltage deviation, frequency deviation and harmonic distortion rate of the first and second incoming power supplies respectively, and determine the preferred power supply according to the preset priority rules. S3, Weak grid connection status identification: Based on the system impedance parameters obtained from the second incoming line side, the equivalent short-circuit ratio of the new energy power station is calculated in real time. When the short-circuit ratio is lower than the preset weak grid threshold, it is determined that the current operation is in a weak grid connection state and a weak grid flag is generated. S4, Receive a switching start signal and determine the switching direction. The switching start signal includes an externally input active switching command and a fault trigger signal generated by the monitoring module. The switching direction includes switching from direct connection to green electricity to grid power supply and switching from grid power supply to direct connection to green electricity supply. S5, execute the corresponding pre-synchronization control according to the switching direction; S6, execute switching timing control, and complete the switching operation of the incoming power supply according to the preset switching timing strategy; S7: After the switching is completed, the function is reset and the status is maintained. After the incoming line switching is completed, the converter operating mode is restored to the initial setting mode, the fault flag is cleared, and the system operating status is updated.

[0008] This application addresses the issue of insufficient synchronization judgment, large switching inrush current, and low power supply reliability in weak grid-connected scenarios due to the lack of independent synchronization detection and circuit breaker control mechanisms for the two incoming lines. By setting up a first incoming line unit on the green electricity side and a second incoming line unit on the grid side, each equipped with an independent synchronization detection module, and configuring an automatic switching control device that can independently control the opening and closing status of the circuit breakers on the two incoming lines, the application can accurately collect the voltage amplitude, frequency, and phase information of the two incoming lines and achieve fine-grained switching control. Therefore, it can solve the problems in related technologies where the lack of independent synchronization detection and circuit breaker control mechanisms for the two incoming lines leads to insufficient synchronization judgment accuracy, large switching inrush current, and low power supply reliability. This achieves the technical effects of improving the smoothness and reliability of power switching in weak grid-connected environments, shortening the power outage time, and ensuring stable power supply to the load side.

[0009] It should be understood that the description in this section is not intended to identify key or essential features of the embodiments of this application, nor is it intended to limit the scope of this application. Other features of this application will become readily apparent from the following description. Attached Figure Description

[0010] To more clearly illustrate the embodiments of this application, the accompanying drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0011] Figure 1 A schematic diagram of the structure of a power switching control device for direct green electricity connection and weak grid connection provided in an embodiment of this application; Figure 2 This is a flowchart illustrating a power switching control method for direct green electricity connection and weak grid connection provided in an embodiment of this application. Detailed Implementation

[0012] The following description, in conjunction with the accompanying drawings, illustrates exemplary embodiments of this application, including various details to aid understanding. These should be considered merely exemplary. Therefore, those skilled in the art will recognize that various changes and modifications can be made to the embodiments described herein without departing from the scope and spirit of this application. Similarly, for clarity and brevity, descriptions of well-known functions and structures are omitted in the following description.

[0013] The following describes, with reference to the accompanying drawings, a power switching control system and method for direct green electricity connection and weak grid connection according to embodiments of this application.

[0014] Figure 1 This is a schematic diagram of the power switching control system for direct green electricity connection and weak grid connection provided in an embodiment of this application.

[0015] like Figure 1 As shown, the system includes: The first incoming line unit 1 is connected to the load-side green electricity direct-connection generation system 5, and includes a first incoming line circuit breaker, a first voltage transformer, a first current transformer, and a first synchronization detection module. The first synchronization detection module is used to collect the voltage amplitude, frequency, and phase information of the green electricity side incoming line. The second incoming line unit 2 is connected to the external power grid 6 and includes a second incoming line circuit breaker, a second voltage transformer, a second current transformer, and a second synchronization detection module. The second synchronization detection module is used to collect the voltage amplitude, frequency, and phase information of the incoming line on the power grid side. Bus unit 3 is connected to the load-side power system 7 and includes a bus voltage transformer and a bus current transformer; The automatic switching control device 4 is connected to the first incoming line unit 1, the second incoming line unit 2 and the bus unit 3 respectively. Based on the preset switching strategy and the electrical parameters collected in real time, it independently controls the opening and closing status of the first incoming line circuit breaker and the second incoming line circuit breaker.

[0016] In some embodiments, the system comprises a first incoming line unit 1, a second incoming line unit 2, a busbar unit 3, and an automatic switching control device 4.

[0017] The first incoming line unit 1 is connected to the load-side green electricity direct-connection generation system 5, forming the main power supply incoming line circuit. The first incoming line unit 1 is equipped with a first incoming line circuit breaker, a first voltage transformer, a first current transformer, and a first synchronization detection module. The first incoming line circuit breaker is connected in series in the green electricity side power supply line and can receive control commands to execute the connection and disconnection of the power supply circuit. The first voltage transformer and the first current transformer respectively isolate, transform, and acquire the voltage and current signals of the green electricity side incoming line, outputting standard-range electrical signals. The first synchronization detection module performs synchronous sampling and calculation processing on the incoming line electrical quantities, accurately acquiring the voltage amplitude, frequency, and phase information of the green electricity side incoming line, providing a data basis for subsequent power supply synchronization status determination.

[0018] The second incoming line unit 2 is connected to the external power grid 6, forming a backup power supply incoming line circuit. Together with the first incoming line unit 1, it forms a dual-incoming power supply system, with the two power supplies serving as backups for each other. The second incoming line unit 2 is equipped with a second incoming line circuit breaker, a second voltage transformer, a second current transformer, and a second synchronization detection module. The second incoming line circuit breaker is connected in series in the power grid-side supply line and can receive control commands to execute the on / off action of the power grid-side circuit. The second voltage transformer and the second current transformer respectively collect the voltage and current signals of the power grid-side incoming line. The second synchronization detection module independently completes the synchronous calculation of the electrical quantities of the power grid-side incoming line, extracts the voltage amplitude, frequency, and phase information of the power grid-side incoming line, and realizes the independent detection and parallel monitoring of the synchronization parameters of the two incoming power supplies.

[0019] Bus unit 3, as an intermediate node for power distribution, is connected to the load-side power system 7 and is used to distribute power to the terminal loads. Bus unit 3 is equipped with bus voltage transformers and bus current transformers to collect the voltage and current operating parameters on the bus side in real time, accurately reflect the actual power supply status on the load side, and provide a reference benchmark on the bus side for power switching control.

[0020] The automatic switching control device 4 establishes signal connections with the first incoming line unit 1, the second incoming line unit 2, and the bus unit 3 respectively, and acquires the electrical parameters uploaded by each unit in real time. The automatic switching control device 4 has a built-in preset switching strategy, which can independently generate and output opening and closing control commands based on the real-time acquired electrical parameters and switching trigger conditions, and manage the opening and closing status of the first incoming line circuit breaker and the second incoming line circuit breaker respectively, so as to complete the switching operation of the two incoming power supplies.

[0021] Because of the architecture of independently configured detection and switching devices for dual incoming lines, the operating parameters of the two power supplies can be independently acquired and monitored in parallel. The automatic switching control device 4 can independently control the opening and closing of the two incoming circuit breakers. Therefore, it can solve the problem of insufficient switching control accuracy caused by the lack of independent incoming line monitoring and control architecture for dual power supply switching on the load side in related technologies, and achieve the technical effect of providing hardware support for reliable power supply switching in weak grid connection scenarios and ensuring the continuity of power supply on the load side.

[0022] Compared with related technologies, in this embodiment, a first incoming line unit 1 is connected to the load-side green electricity direct-connection generation system 5, including a first incoming line circuit breaker, a first voltage transformer, a first current transformer, and a first synchronization detection module. The first synchronization detection module is used to collect the voltage amplitude, frequency, and phase information of the green electricity side incoming line. A second incoming line unit 2 is connected to the external power grid 6, including a second incoming line circuit breaker, a second voltage transformer, a second current transformer, and a second synchronization detection module. The second synchronization detection module is used to collect the voltage amplitude, frequency, and phase information of the power grid side incoming line. A bus unit 3 is connected to the load-side power consumption system 7, including a bus voltage transformer and a bus current transformer. An automatic switching control device 4 is connected to the first incoming line unit 1, the second incoming line unit 2, and the bus unit 3 respectively, and independently controls the opening and closing states of the first and second incoming line circuit breakers based on a preset switching strategy and real-time collected electrical parameters. It can solve the problems in related technologies where the lack of independent synchronization detection and independent circuit breaker control mechanism for two incoming lines leads to insufficient synchronization judgment accuracy, large switching inrush current, and low power supply reliability in weak grid connection scenarios. It achieves the technical effects of improving the smoothness and reliability of power switching in weak grid connection environments, shortening the power outage time, and ensuring stable power supply to the load side.

[0023] As a specific embodiment of this application, based on the basic solution, the automatic switching control device 4 is further defined as follows: The data acquisition and monitoring module is used to acquire the first incoming line voltage / current, the second incoming line voltage / current, and the bus voltage / current data in real time, and to continuously monitor the power quality and operating status of the two incoming power supplies. The weak grid connection status identification module is used to calculate the system short-circuit ratio in real time based on the electrical parameters of the second incoming line side. When the short-circuit ratio is lower than a preset threshold, it is determined to be a weak grid connection status. The synchronous pre-synchronization adjustment module is used to perform synchronous pre-synchronization control under weak grid connection conditions, adjusting the voltage amplitude, frequency and phase angle of the target incoming line side to be consistent with the bus side; The adaptive switching module for grid-connected / grid-following mode is used to control the green electricity direct-connection side converter to switch between grid-connected mode and grid-following mode based on the weak grid connection status identification result and switching direction. The switching strategy execution module is used to output opening and closing control commands to the first incoming circuit breaker and / or the second incoming circuit breaker according to the switching request, the weak grid connection status identification result and the synchronous pre-synchronization completion signal, and in accordance with the preset switching priority and logical timing.

[0024] Specifically, based on the above system architecture, the automatic switching control device 4 adopts a modular functional design, which integrates a data acquisition and monitoring module, a weak grid connection status identification module, a synchronous pre-synchronization adjustment module, a grid connection / follow-the-grid mode adaptive switching module, and a switching strategy execution module. Each module works together to achieve precise switching control of incoming power supply in weak grid connection scenarios.

[0025] The data acquisition and monitoring module is responsible for the real-time acquisition of electrical quantities and monitoring of the operating status of the entire system. This module is equipped with a high-precision synchronous sampling circuit to synchronously acquire full electrical data of the first incoming line voltage and current, the second incoming line voltage and current, and the bus voltage and current at a set sampling frequency. Based on this, it continuously calculates power quality indicators such as voltage deviation, frequency deviation, and harmonic distortion rate of the two incoming power supplies, tracks the operating conditions of the two power supplies in real time, and promptly identifies fault states such as voltage exceeding limits and frequency anomalies on the power supply side, providing underlying data support for subsequent status identification and switching control.

[0026] The weak grid connection status identification module is used to assess the system strength level of the grid side in real time. Based on electrical parameters collected from the second incoming line side, this module calculates the equivalent short-circuit ratio of the renewable energy power station through small disturbance injection or system impedance identification algorithms. The short-circuit ratio is a core quantitative indicator characterizing the grid's voltage support capability; a lower value indicates smaller grid inertia and weaker grid connection strength. The module has a preset weak grid judgment threshold. When the calculated short-circuit ratio is lower than this threshold, the current system is determined to be in a weak grid connection operation state, and a corresponding weak grid flag is generated, providing a basis for the adaptive adjustment of subsequent control strategies. In practical applications, the weak grid threshold can be set to 3.0; when the short-circuit ratio is less than 3.0, the dedicated weak grid control logic is triggered.

[0027] The pre-synchronization adjustment module undertakes the pre-synchronization control function before circuit breaker closing in weak grid environments. When the system is in a weak grid connection state and there is a power switching requirement, this module starts the closed-loop pre-synchronization control logic. For the target incoming power supply to be connected, it continuously adjusts the voltage amplitude, frequency and phase angle, so that the electrical parameters of the target power supply gradually track the corresponding parameters on the bus side until the deviation between the two is reduced to the preset allowable range. This ensures that the two power supplies are in a synchronous state at the moment the circuit breaker closes, suppressing the closing inrush current from the source and reducing the power supply disturbance to the load side during the switching process.

[0028] The grid-connected / grid-following mode adaptive switching module is responsible for the intelligent adaptation of the operating mode of the green energy side converter. This module combines the weak grid connection status identification results with the current switching direction to automatically adjust the control mode of the green energy direct-connected side converter. Under conditions of high grid strength, the converter operates in grid-following mode, achieving grid-connected operation by following the grid voltage phase through a phase-locked loop. Under weak grid connection conditions, the converter switches to grid-connected mode, actively constructing a stable voltage and frequency reference, improving the system's operational stability in weak grid environments, and providing a reliable control basis for the pre-synchronization adjustment process.

[0029] The switching strategy execution module is the output unit for executing switching actions. This module receives external switching requests, weak grid connection status identification results, and synchronization pre-synchronization completion signals. According to preset power priority rules and switching logic timing, it generates corresponding opening and closing control commands and outputs them to the first and second incoming circuit breakers. The module can choose to control one circuit breaker individually or control the two circuit breakers to operate in a coordinated manner according to the actual operating conditions, ensuring that the switching process is strictly executed in accordance with the preset logic.

[0030] The automatic switching control device 4 integrates a full-process functional module of status monitoring, weak grid identification, pre-synchronization adjustment, mode adaptation and strategy execution. It can achieve precise switching control in a hierarchical manner for weak grid scenarios. Therefore, it can solve the problem of large switching impact and insufficient reliability caused by the lack of systematic management logic for dual power supply switching in weak grid environments in related technologies, and achieve the technical effect of improving the smoothness of power switching and ensuring the continuity of power supply in weak grid scenarios.

[0031] As a specific implementation of this application, based on the basic scheme, the first incoming line unit 1 is further defined to include an energy storage coordination interface. The energy storage coordination interface is used to connect to the supporting energy storage system. When the incoming line is switched under weak grid connection, the bus voltage and frequency fluctuations are smoothed by the rapid charging and discharging response of the energy storage system.

[0032] Specifically, the first incoming line unit 1 is also equipped with an energy storage coordination interface, which is used to connect to the supporting energy storage system, provide power support capability in weak grid connection switching scenarios, and ensure the operational stability of the power supply bus.

[0033] The energy storage coordination interface is integrated into the circuit and control link of the first incoming line unit 1. It also has an electrical power access port and a control signal interaction port, which can establish a stable connection with external energy storage devices, incorporate the energy storage system into the unified management and control system of the green electricity side incoming line, and realize the coordinated linkage of energy storage operation status and switching control logic.

[0034] When performing incoming line switching operations under weak grid connection conditions, the overall system inertia level is low, and pre-synchronization adjustment and circuit breaker opening and closing actions may cause instantaneous fluctuations in bus voltage and frequency. The energy storage coordination interface can synchronously receive switching control commands and send fast charge and discharge adjustment signals to the supporting energy storage system. Utilizing the millisecond-level power response speed of the energy storage system, it can smooth bus frequency fluctuations through rapid active power throughput and maintain stable bus voltage amplitude through dynamic reactive power compensation. This effectively reduces electrical disturbances during the switching transient process, provides a stable bus reference benchmark for synchronous pre-synchronization adjustment, and ensures the accuracy of closing synchronization determination.

[0035] The first incoming line unit 1 is equipped with an energy storage coordination interface, which can link the energy storage system to provide rapid power compensation during weak grid connection switching. Therefore, it can solve the problem of severe bus fluctuations during the switching process caused by insufficient system inertia in weak grid environment in related technologies, and achieve the technical effect of smoothing transient voltage frequency disturbances during switching and improving power supply reliability during switching.

[0036] As a specific implementation of this application, based on the basic scheme, the automatic switching control device 4 is further defined to include a black start control module. When the green power direct connection side is completely de-energized and the grid side is in an abnormal state, the black start control module is used to perform the following steps: disconnect all incoming circuit breakers, start the black start mode of the energy storage system, establish a bus voltage reference by the energy storage system, and gradually connect after the green power direct connection power generation system is restored.

[0037] Specifically, the automatic switching control device 4 also includes a black start control module, which is used to deal with extreme power loss conditions when both incoming power supplies are abnormal at the same time, and to provide the load side with the ability to restore power supply independently.

[0038] When the green power direct connection side is completely de-energized and the grid side is in an abnormal state, and the conventional dual power supply switching logic cannot be executed normally, the black start control module initiates a dedicated recovery process. The module first outputs trip control commands to all incoming circuit breakers, disconnecting the first and second incoming circuit breakers to achieve complete electrical isolation between the busbar and the two faulty incoming lines. This prevents the faulty side from interfering with the busbar recovery process and also prevents backfeeding to the faulty lines after power is restored, ensuring electrical safety during the recovery process.

[0039] After completing electrical isolation, the black-start control module sends a start command to the supporting energy storage system, triggering the energy storage system to enter black-start operation mode. The energy storage system establishes a stable bus voltage reference through autonomous grid construction, outputting voltage amplitude and operating frequency that meet the rated standards, providing initial power supply support for important loads on the bus side, and ensuring the basic operational needs of core loads.

[0040] Subsequently, the black start control module continuously monitors the operating status and output level of the green power generation system. When the green power generation system recovers to meet the grid connection conditions, it controls the green power generation system to gradually connect to the bus according to the preset step-by-step connection logic, gradually improving the overall power supply capacity of the system and completing the power supply restoration under the power failure condition.

[0041] Because the automatic switching control device 4 is equipped with a black start control module, it can autonomously restore the bus power supply and gradually connect to the green power source in extreme scenarios where both incoming lines lose power at the same time. Therefore, it can solve the problem of complete power loss on the load side and inability to autonomously restore power supply when both power sources are abnormal at the same time in related technologies, improve the power supply recovery capability under extreme conditions, and enhance the system's power supply resilience.

[0042] As a specific implementation of this application, the system is further defined to include a human-computer interaction and remote communication module on the basis of the basic solution. This module is used to display the operating status, power quality indicators, switching records and fault alarm information of the two incoming power supplies in real time, and supports data interaction with the upper-level energy management system or intelligent operation and maintenance platform through wired or wireless networks.

[0043] Specifically, the system also includes a human-computer interaction and remote communication module, which serves as the system's local operation and maintenance interface and external data interaction hub, enabling visualized display of operating status and cross-level scheduling and collaboration.

[0044] The human-machine interaction and remote communication module features local status display and operation and maintenance interaction functions. It can display the real-time operating status of the two incoming power supplies, including the opening and closing status of the incoming circuit breakers, the current power supply circuit affiliation, and the real-time values ​​of electrical quantities in each branch. The module simultaneously displays the power quality indicators of the two incoming power supplies, intuitively presenting parameters such as voltage deviation, frequency deviation, and harmonic distortion rate, facilitating maintenance personnel's understanding of power supply quality. The module stores and displays the system's historical switching records, fully recording the triggering reason, switching direction, action sequence, and execution result of each switch, providing data support for operation analysis and fault tracing. When the system detects abnormal power supply or abnormal switching actions, the module can promptly output fault alarm information, prompting maintenance personnel to take appropriate action.

[0045] In terms of remote communication capabilities, the module supports connection to external systems via wired or wireless networks, and can establish a two-way data interaction link with the superior energy management system or intelligent operation and maintenance platform. The module can upload real-time system operation data, power quality statistics, and fault alarm information to the upper-level platform, supporting centralized monitoring and unified operation and maintenance management of multiple sites; at the same time, it can receive dispatch instructions and operating parameter configuration information issued by the superior platform, realizing remote control and remote operation and maintenance, and improving the system's intensive management and control level.

[0046] By configuring human-computer interaction and remote communication modules, local visual control of system operation status and remote data interaction with the upper-level scheduling system can be realized. Therefore, it can solve the problem of the single operation and maintenance management method of dual power switching system in related technologies and the difficulty in integrating it into the regional energy scheduling system, thereby achieving the technical effect of improving operation and maintenance management efficiency and supporting the large-scale deployment and application of the system.

[0047] Figure 2 This is a flowchart illustrating a power switching control method for direct green electricity connection and weak grid connection provided in an embodiment of this application.

[0048] like Figure 2 As shown, the method includes the following steps: S1 collects system status information in real time, including voltage amplitude, frequency, phase angle of the first incoming line side, the second incoming line side and the bus side, as well as active power and reactive power data of each branch. S2, Power quality assessment and priority determination of two incoming power supplies: Based on the collected real-time data, calculate the voltage deviation, frequency deviation and harmonic distortion rate of the first and second incoming power supplies respectively, and determine the preferred power supply according to the preset priority rules. S3, Weak grid connection status identification: Based on the system impedance parameters obtained from the second incoming line side, the equivalent short-circuit ratio of the new energy power station is calculated in real time. When the short-circuit ratio is lower than the preset weak grid threshold, it is determined that the current operation is in a weak grid connection state and a weak grid flag is generated. S4, Receive a switching start signal and determine the switching direction. The switching start signal includes an externally input active switching command and a fault trigger signal generated by the monitoring module. The switching direction includes switching from direct connection to green electricity to grid power supply and switching from grid power supply to direct connection to green electricity supply. S5, execute the corresponding pre-synchronization control according to the switching direction; S6, execute switching timing control, and complete the switching operation of the incoming power supply according to the preset switching timing strategy; S7: After the switching is completed, the function is reset and the status is maintained. After the incoming line switching is completed, the converter operating mode is restored to the initial setting mode, the fault flag is cleared, and the system operating status is updated.

[0049] In some embodiments, step S1 involves real-time acquisition of system status information. High-precision synchronous sampling technology is employed to acquire the three-phase voltage amplitude, frequency, and phase angle at a sampling frequency of 20kHz for the first incoming line side, the second incoming line side, and the bus side. Simultaneously, active and reactive power data for each branch are acquired, providing complete electrical quantity data support for subsequent power quality assessment, grid connection status identification, and switching control.

[0050] Step S2 involves power quality assessment and priority determination for the two incoming power supplies. Based on real-time collected electrical data, the voltage deviation, frequency deviation, and harmonic distortion rate are calculated for the first and second incoming power supplies, respectively. The voltage deviation assessment index is within ±7% of the rated voltage, the frequency deviation assessment index is within ±0.5Hz, and the harmonic distortion rate assessment index is no more than 5%. The system sorts the two power supplies according to preset priority rules, defaulting to the principle of prioritizing green electricity consumption. When the output of the green electricity side meets the load demand and the power quality meets the standards, the green electricity direct connection side is determined as the current preferred power supply.

[0051] Step S3 is for weak grid connection status identification. Based on the system impedance parameters obtained from the second incoming line side, the equivalent short-circuit ratio of the renewable energy power station is calculated in real time through small disturbance injection and impedance identification. The short-circuit ratio is a core indicator characterizing grid strength; the lower the value, the smaller the grid inertia and the weaker the voltage support capability. When the calculated short-circuit ratio is lower than the preset weak grid threshold, the current system is determined to be in a weak grid connection operation state, and a corresponding weak grid flag is generated. In actual operation, the weak grid threshold can be set to 3.0, that is, when the short-circuit ratio is less than 3.0, the weak grid-specific control logic is triggered.

[0052] Step S4 involves receiving the switching initiation signal and determining the switching direction. The system continuously monitors for the switching initiation signal, which can originate from external active switching commands issued by maintenance personnel, as well as fault trigger signals generated by the monitoring module based on abnormal power supply conditions. Fault trigger conditions include the current power supply voltage being lower than 0.8 times the rated voltage for more than 2 seconds, a frequency deviation exceeding ±1.5Hz, and a harmonic distortion rate exceeding 8%. The system determines the switching direction based on the current power supply circuit and the target power supply circuit, specifically including two categories: switching from direct connection to green electricity to grid power supply and switching from grid power to direct connection to green electricity.

[0053] Step S5 involves executing corresponding pre-synchronization control based on the switching direction. According to the determined switching direction, the system invokes the corresponding pre-synchronization control logic to perform closed-loop adjustment of the voltage, frequency, and phase of the target incoming power supply. This gradually brings the electrical parameters of the target power supply closer to the corresponding parameters on the bus side, creating suitable synchronization conditions for circuit breaker closing and reducing the electrical impact at the moment of closing from the source.

[0054] Step S6 involves executing the switching sequence control. The system controls the opening and closing actions of the two incoming circuit breakers in an orderly manner according to the preset switching sequence strategy, completing the switching operation of the incoming power supply. The switching process strictly follows the preset action sequence and electrical interlocking logic to ensure the continuity of power supply to the busbar and load side, keeping the power interruption time within the preset allowable range.

[0055] Step S7 is for function reset and status maintenance after the switch is completed. After the incoming power supply switch is completed and the system is running stably, the operating mode of the green power side converter is restored to the initial setting mode before the switch, the fault flag bit associated with this switch is cleared, the current operating status data and power supply circuit identifier of the system are updated, and then the system re-enters the real-time monitoring cycle to continuously track the operating status of the two power supplies.

[0056] By adopting a step-by-step control process of status acquisition, quality assessment, weak grid identification, pre-synchronization control and timing execution, the switching control logic can be adaptively adjusted for weak grid connection scenarios. Therefore, it can solve the problems of large power switching impact and insufficient switching reliability in weak grid connection environments in related technologies, and achieve the technical effect of fast and smooth power switching in weak grid scenarios and ensuring the continuity of power supply to the load side.

[0057] As a specific implementation of this application, based on the basic scheme, the following green electricity pre-synchronization control sub-step is further defined in S5: when the switching direction is from the power grid to direct green electricity supply, the following green electricity pre-synchronization control sub-step is executed: S5a1, confirms the current weak grid connection status based on the weak grid connection status flag bit; S5a2 switches the working mode of the green power direct-connected converter from grid-connected to grid-connected mode. In grid-type control mode, S5a3 adjusts the voltage amplitude, frequency, and phase of the green power side converter output to track the electrical parameters on the bus side until the synchronous closing conditions are met. |U1-U s |≤ε u ,|f1-f s |≤ε_f,|θ1-θ s |≤ε_θ; Where U1, f1, and θ1 are the voltage amplitude, frequency, and phase angle of the green electricity side incoming line, respectively. s f s θ s These represent the voltage amplitude, frequency, and phase angle on the bus side, respectively, ε u ε_f and ε_θ are the preset voltage difference threshold, frequency difference threshold, and phase difference threshold, respectively; S5a4: After the synchronous closing conditions are met, a closing command is output to the first incoming circuit breaker.

[0058] Specifically, when the switching direction is from the power grid to direct green electricity supply, the system executes a pre-synchronization control process specific to the green electricity side, which includes the following sub-steps.

[0059] S5a1 is the weak grid connection status confirmation step. The system reads the current weak grid connection status flag to confirm that the system is in a weak grid connection operation state. In a weak grid connection environment, the grid voltage support capacity is insufficient, and conventional grid connection control logic is difficult to achieve accurate synchronization. Therefore, it is necessary to complete the weak grid status determination first in order to start the pre-synchronization control strategy adapted to the weak grid scenario.

[0060] S5a2 describes the converter operating mode switching procedure. After confirming the weak grid connection status, the system sends a mode switching command to the converter on the green power direct connection side, switching the converter's operating mode from grid-following to grid-connecting. In grid-following mode, the converter relies on a phase-locked loop to track the grid phase for grid-connected operation, which is prone to phase loss and stability degradation in weak grid environments. In grid-connecting mode, the converter can simulate the operating characteristics of a synchronous generator, autonomously construct a stable voltage and frequency reference, and has active voltage support capability, providing a more controllable regulation object for subsequent pre-synchronization regulation.

[0061] S5a3 represents the closed-loop adjustment step for synchronization parameters. In network-type control mode, the system employs a proportional-integral-preset controller to perform closed-loop adjustment of the voltage amplitude, frequency, and phase output from the green power side converter, ensuring that the electrical parameters on the green power side continuously track the corresponding parameters on the bus side until the synchronization closing conditions are met. The synchronization closing conditions are quantified and determined using three sets of deviation thresholds, with the specific expression as follows: |U1-U s |≤ε u ,|f1-f s |≤ε_f,|θ1-θ s |≤ε_θ; Where U1, f1, and θ1 are the voltage amplitude, frequency, and phase angle of the green electricity side incoming line, respectively. s f s θ s These represent the voltage amplitude, frequency, and phase angle on the bus side, respectively, ε u ε_f and ε_θ are the preset voltage difference threshold, frequency difference threshold, and phase difference threshold, respectively. In practical applications, the voltage difference threshold can be set to 5% of the rated voltage, the frequency difference threshold can be set to 0.2Hz, and the phase difference threshold can be set to 5°. When all three sets of deviations simultaneously meet the threshold requirements and remain continuously and stably for at least three cycles, the synchronous closing condition is determined to be met.

[0062] S5a4 is the closing command output step. After confirming that the synchronization closing conditions are met, the system outputs a closing control command to the first incoming circuit breaker, controlling the green power side incoming circuit breaker to perform the closing action, completing the grid connection of the green power side power supply.

[0063] In weak grid scenarios where power is switched from the main grid to green electricity supply, the green electricity side converter is first switched to a grid-type mode to obtain active control capability. Then, the green electricity side parameters are synchronized with the bus side through closed-loop regulation before the switch is closed. Therefore, the problems of poor synchronization accuracy and large closing inrush current on the green electricity side in weak grid connection environments can be solved, thereby achieving the technical effect of improving the smoothness of green electricity access in weak grid scenarios and reducing electrical disturbances during the switching process.

[0064] As a specific implementation of this application, based on the basic scheme, the following grid pre-synchronization control sub-step is further defined in S5: when the switching direction is from direct connection to green electricity to grid power supply, the following sub-step is executed: S5b1: Confirm the current weak grid connection status based on the weak grid connection status flag bit; S5b2: In a weak grid connection state, auxiliary power compensation and voltage support are provided to the grid-side incoming line through an energy storage system or auxiliary regulation device; S5b3: Adjust the electrical parameters on the second incoming line side to track the electrical parameters on the bus side until the synchronous closing conditions are met; S5b4: After the synchronous closing conditions are met, a closing command is output to the second incoming circuit breaker.

[0065] Specifically, when the switching direction is from direct connection to green electricity to grid power supply, the system executes a grid-side exclusive pre-synchronization control process, which ensures the synchronization accuracy of closing in a weak grid environment through a combination of auxiliary support and parameter adjustment. This process includes the following sub-steps.

[0066] S5b1 is the weak grid connection status confirmation step. The system reads the current weak grid connection status flag to confirm that the system is in a weak grid connection operation state. Under weak grid connection conditions, the external power grid has low system inertia and weak voltage and frequency disturbance immunity. Directly carrying out synchronous regulation is prone to problems such as large parameter fluctuations and slow convergence speed. Therefore, it is necessary to complete the weak grid status determination first in order to start the corresponding auxiliary support control logic.

[0067] S5b2 is the grid-side auxiliary support step. After confirming a weak grid connection state, the system calls upon the energy storage system or its supporting auxiliary regulating device to provide auxiliary power compensation and voltage support for the grid-side incoming line. The energy storage system can smooth out frequency fluctuations on the grid side through millisecond-level active power throughput and maintain the stability of the grid-side voltage amplitude through dynamic reactive power output. The auxiliary regulating device can further optimize the power quality on the incoming line side, keeping the electrical parameters of the grid-side incoming line within a stable range, providing a controllable regulation basis for subsequent synchronous regulation.

[0068] S5b3 is the closed-loop adjustment step for synchronization parameters. Based on auxiliary support, the system performs closed-loop adjustment of the electrical parameters on the second incoming line side, ensuring that the voltage amplitude, frequency, and phase of the grid-side incoming line continuously track the corresponding electrical parameters on the bus side, gradually reducing the deviation between the two until the preset synchronization closing conditions are met. During the adjustment process, the values ​​of voltage difference, frequency difference, and phase difference are continuously verified to ensure that the deviation gradually converges to the allowable range.

[0069] S5b4 is the closing command output step. After confirming that the synchronization closing conditions are met, the system outputs a closing control command to the second incoming circuit breaker, controlling the grid-side incoming circuit breaker to perform the closing action and complete the grid connection of the power supply.

[0070] In weak grid scenarios where power is switched from green electricity to grid power, power compensation and voltage support are first provided to the grid side through energy storage or auxiliary devices, and then synchronization parameter adjustment and closing operation are carried out. Therefore, it can solve the problem of large fluctuations in grid side incoming line parameters and insufficient synchronization adjustment accuracy leading to excessive closing inrush current in related technologies under weak grid connection environment, and achieve the technical effect of improving the smoothness of grid access in weak grid scenarios and ensuring the stability of power supply during the switching process.

[0071] As a specific implementation of this application, based on the basic scheme, the switching timing strategy in S6 is further defined as a first-merge-then-separate strategy: Once the synchronization conditions are met, a closing command is first sent to the target incoming circuit breaker. After the target incoming circuit breaker is successfully closed and the bus voltage is stable, a tripping command is then sent to the original power supply incoming circuit breaker.

[0072] Specifically, step S6 adopts a switching sequence strategy of first connecting and then disconnecting, which is suitable for the working condition where two power supplies are electrically allowed to operate in parallel for a short period of time, and can effectively ensure the continuity of power supply to the load side during the switching process.

[0073] When the synchronization conditions are met, and it is confirmed that the voltage amplitude, frequency, and phase deviation of the target incoming power supply and the bus-side power supply are all within the preset allowable range, thus establishing the basis for parallel operation, the system first issues a closing command to the target incoming circuit breaker to control the target-side incoming circuit to connect to the bus. The system monitors the closing feedback signal of the circuit breaker and the operating status of the bus voltage in real time. After the target incoming circuit breaker is closed and the bus voltage remains stable, the system then issues a tripping command to the original power supply incoming circuit breaker to disconnect the original power supply circuit, completing the switching operation of the two incoming power supplies.

[0074] Under this timing, the two power supplies operate in parallel for a short period of time, which can achieve uninterrupted power supply transition on the load side and avoid power interruption or large voltage drop at the moment of switching. It is suitable for important load scenarios with high power supply reliability requirements.

[0075] By adopting a switching sequence strategy of "connecting first and then disconnecting," the target power supply is put into operation first and the original power supply is taken out, provided that the synchronization conditions are met. Therefore, the problem of power interruption and impact on the normal operation of sensitive loads during power switching in related technologies can be solved, achieving the technical effect of uninterrupted smooth switching and improving the continuity and reliability of power supply on the load side.

[0076] As a specific implementation of this application, based on the basic scheme, it further includes an abnormal state pre-judgment sub-step before S4: If the detected value of the voltage amplitude on the bus side is lower than the preset low voltage protection threshold and the duration exceeds the first preset time, it is determined to be a bus side fault. The automatic switching control device will block the switching operation and only output a closing command to the standby incoming circuit breaker.

[0077] Specifically, before receiving the switching start signal in step S4, the system sets up an abnormal state pre-judgment sub-step to identify serious fault conditions on the bus side in advance, trigger emergency protection logic, and ensure power supply restoration efficiency in fault scenarios.

[0078] The system monitors the voltage amplitude on the bus side in real time. When the bus side voltage amplitude is detected to be lower than the preset low-voltage protection threshold, and the duration of this low-voltage state exceeds a first preset time, a bus side fault is determined to have occurred. In practical applications, the low-voltage protection threshold can be set to 0.7 times the rated voltage, and the first preset time can be set to 0.5 seconds. This judgment logic can accurately distinguish between instantaneous voltage fluctuations and continuous bus faults, avoiding false triggering of emergency logic.

[0079] Upon determining a busbar-side fault, the automatic switching control device immediately blocks the normal switching operation procedure, ceasing the pre-synchronization adjustment and timing control steps in the normal switching process to avoid delays in power restoration due to excessive time consumption in the normal procedure. The device directly outputs a closing command to the backup incoming circuit breaker, quickly restoring power supply to the busbar side through the backup power supply, minimizing the duration of the power outage and reducing the impact of the fault on the load side.

[0080] Before the switching starts, a pre-judgment logic for abnormal conditions on the bus side is added. When a severe low voltage fault is detected, the normal switching is blocked and the backup incoming line is directly closed. Therefore, it can solve the problems of slow response and expanded fault impact of the normal switching process when there is a severe fault on the bus side in related technologies, and achieve the technical effect of speeding up the power supply recovery speed under fault and improving the system's fault protection capability.

[0081] As a specific implementation of this application, based on the basic scheme, the method for switching between the network configuration mode and the follow-up network mode is further defined as follows: In the grid-type mode, a dual closed-loop control strategy of voltage outer loop plus current inner loop is adopted, while in the grid-type mode, a phase-locked loop synchronous plus PQ decoupling control strategy is adopted. During mode switching, an inner current loop compensator is used to filter and buffer the current command values ​​before and after switching in order to suppress sudden current changes and resonance at the moment of switching.

[0082] Specifically, in the grid-connected mode, a dual closed-loop control strategy of voltage outer loop and current inner loop is adopted. The voltage outer loop uses the amplitude and frequency of the output voltage as the control target, generates the inner loop current reference command, and is responsible for establishing and maintaining a stable voltage and frequency reference. The current inner loop receives the current command output by the voltage outer loop, quickly adjusts the converter output current, realizes accurate current tracking and current limiting protection, and enables the converter to have active voltage support capability, adapting to weak grid-connected operation environment. In the grid-following mode, a phase-locked loop synchronous plus PQ decoupling control strategy is adopted. The phase-locked loop tracks the phase and frequency of the grid voltage in real time, realizing the synchronous operation of the converter and the grid. The PQ decoupling control independently adjusts the active power and reactive power respectively, outputting the corresponding power according to the dispatch command, so that the converter follows the grid characteristics and adapts to strong grid scenarios.

[0083] During mode transition, a current inner-loop compensator is used to filter and buffer the current command values ​​before and after the switch. The current command generation logic differs between the two control modes; a direct switch would cause a step jump in the current command, leading to sudden changes in output current and system resonance. The current inner-loop compensator uses a smoothing filtering algorithm to perform a gradual transition on the command values, progressively adjusting the amplitude and phase of the current command, buffering the command jump amplitude, and simultaneously introducing damping control to suppress system resonance. This effectively reduces the current surge during the switch and ensures a smooth transition between the two operating modes.

[0084] The grid-connected and grid-following modes adopt corresponding control strategies, and the current command is filtered and buffered through the current inner loop compensator during mode switching. Therefore, it can solve the problem of sudden current change and easy resonance impact during converter mode switching in related technologies, and achieve the technical effect of smooth mode switching and improving the system operation stability in weak grid scenarios.

[0085] It should be noted that, in this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Unless otherwise specified, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes the element.

[0086] The above are merely specific embodiments of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to these embodiments, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A power switching control system for direct green electricity connection and weak grid connection, characterized in that, include: The first incoming line unit is connected to the load-side green electricity direct-connection generation system and includes a first incoming line circuit breaker, a first voltage transformer, a first current transformer, and a first synchronization detection module. The first synchronization detection module is used to collect the voltage amplitude, frequency, and phase information of the green electricity side incoming line. The second incoming line unit, connected to the external power grid, includes a second incoming line circuit breaker, a second voltage transformer, a second current transformer, and a second synchronization detection module. The second synchronization detection module is used to collect the voltage amplitude, frequency, and phase information of the incoming line on the power grid side. Busbar unit, connected to the load-side power system, includes busbar voltage transformer and busbar current transformer; An automatic switching control device is connected to the first incoming line unit, the second incoming line unit, and the busbar unit respectively. Based on a preset switching strategy and real-time collected electrical parameters, it independently controls the opening and closing status of the first and second incoming line circuit breakers.

2. The power switching control system for direct green power connection and weak grid connection according to claim 1, characterized in that, The automatic switching control device includes: The data acquisition and monitoring module is used to acquire the first incoming line voltage / current, the second incoming line voltage / current, and the bus voltage / current data in real time, and to continuously monitor the power quality and operating status of the two incoming power supplies. The weak grid connection status identification module is used to calculate the system short-circuit ratio in real time based on the electrical parameters of the second incoming line side. When the short-circuit ratio is lower than the preset threshold, it is determined to be a weak grid connection status. The synchronous pre-synchronization adjustment module is used to perform synchronous pre-synchronization control under weak grid connection conditions, adjusting the voltage amplitude, frequency and phase angle of the target incoming line side to be consistent with the bus side; The adaptive switching module for grid-connected / grid-following mode is used to control the green electricity direct-connection side converter to switch between grid-connected mode and grid-following mode based on the weak grid connection status identification result and switching direction. The switching strategy execution module is used to output opening and closing control commands to the first incoming circuit breaker and / or the second incoming circuit breaker according to the switching request, the weak grid connection status identification result and the synchronous pre-synchronization completion signal, and in accordance with the preset switching priority and logical timing.

3. The power switching control system for direct green power connection and weak grid connection according to claim 1, characterized in that, The first incoming line unit also includes an energy storage coordination interface, which is used to connect to a supporting energy storage system. When performing incoming line switching under weak grid connection conditions, the rapid charging and discharging response of the energy storage system can be used to smooth out bus voltage and frequency fluctuations.

4. The power switching control system for direct green power connection and weak grid connection according to claim 1, characterized in that, The automatic switching control device also includes a black start control module. When the green power direct connection side is completely de-energized and the grid side is in an abnormal state, the black start control module is used to perform the following steps: disconnect all incoming circuit breakers, start the black start mode of the energy storage system, establish a bus voltage reference by the energy storage system, and gradually connect after the green power direct connection generation system is restored.

5. The power switching control system for direct green power connection and weak grid connection according to claim 1, characterized in that, The system also includes a human-machine interaction and remote communication module, which is used to display the operating status, power quality indicators, switching records and fault alarm information of the two incoming power supplies in real time, and supports data interaction with the superior energy management system or intelligent operation and maintenance platform through wired or wireless networks.

6. A power supply switching control method for direct green electricity connection and weak grid connection, characterized in that, The method is applied to the power switching control system for direct green electricity connection and weak grid connection as described in any one of claims 1-5, including: S1 collects system status information in real time, including voltage amplitude, frequency, phase angle of the first incoming line side, the second incoming line side and the bus side, as well as active power and reactive power data of each branch. S2, Power quality assessment and priority determination of two incoming power supplies: Based on the collected real-time data, calculate the voltage deviation, frequency deviation and harmonic distortion rate of the first and second incoming power supplies respectively, and determine the preferred power supply according to the preset priority rules. S3, Weak grid connection status identification: Based on the system impedance parameters obtained from the second incoming line side, the equivalent short-circuit ratio of the new energy power station is calculated in real time. When the short-circuit ratio is lower than the preset weak grid threshold, it is determined that the current operation is in a weak grid connection state and a weak grid flag is generated. S4, Receive a switching start signal and determine the switching direction. The switching start signal includes an externally input active switching command and a fault trigger signal generated by the monitoring module. The switching direction includes switching from direct connection to green electricity to grid power supply and switching from grid power supply to direct connection to green electricity supply. S5, execute the corresponding pre-synchronization control according to the switching direction; S6, execute switching timing control, and complete the switching operation of the incoming power supply according to the preset switching timing strategy; S7: After the switching is completed, the function is reset and the status is maintained. After the incoming line switching is completed, the converter operating mode is restored to the initial setting mode, the fault flag is cleared, and the system operating status is updated.

7. The power switching control method for direct green power connection and weak grid connection according to claim 6, characterized in that, In step S5, when the switching direction is from the power grid to direct green electricity supply, the following green electricity pre-synchronization control sub-steps are executed: S5a1, confirms the current weak grid connection status based on the weak grid connection status flag bit; S5a2 switches the operating mode of the green power direct-connection side converter from grid-connected to grid-connected mode. In grid-type control mode, S5a3 adjusts the voltage amplitude, frequency, and phase of the green power side converter output to track the electrical parameters on the bus side until the synchronous closing conditions are met. |U1-U s |≤e u ,|f1-f s |≤ε_f,|θ1-θ s |≤ε_θ; Where U1, f1, and θ1 are the voltage amplitude, frequency, and phase angle of the green electricity side incoming line, respectively. s f s θ s These represent the voltage amplitude, frequency, and phase angle on the bus side, respectively, ε u ε_f and ε_θ are the preset voltage difference threshold, frequency difference threshold, and phase difference threshold, respectively; S5a4: After the synchronous closing conditions are met, a closing command is output to the first incoming circuit breaker.

8. The power switching control method for direct green power connection and weak grid connection according to claim 6, characterized in that, In step S5, when the switching direction is from direct connection to green electricity to grid power supply, the following grid pre-synchronization control sub-step is executed: S5b1: Confirm the current weak grid connection status based on the weak grid connection status flag; S5b2: In a weak grid connection state, auxiliary power compensation and voltage support are provided to the grid-side incoming line through an energy storage system or auxiliary regulation device; S5b3: Adjust the electrical parameters on the second incoming line side to track the electrical parameters on the bus side until the synchronous closing conditions are met; S5b4: After the synchronous closing conditions are met, a closing command is output to the second incoming circuit breaker.

9. The power switching control method for direct green power connection and weak grid connection according to claim 6, characterized in that, In step S6, the switching timing strategy is a merge-then-divide strategy: Once the synchronization conditions are met, a closing command is first sent to the target incoming circuit breaker. After the target incoming circuit breaker is successfully closed and the bus voltage is stable, a tripping command is then sent to the original power supply incoming circuit breaker.

10. The power switching control method for direct green power connection and weak grid connection according to claim 6, characterized in that, The step S4 is preceded by an abnormal state pre-judgment sub-step: If the detected value of the voltage amplitude on the bus side is lower than the preset low voltage protection threshold and the duration exceeds the first preset time, it is determined to be a bus side fault. The automatic switching control device will block the switching operation and only output a closing command to the standby incoming circuit breaker.

11. The power switching control method for direct green power connection and weak grid connection according to claim 6, characterized in that, The methods for switching between network topology mode and follow-network mode include: In the grid-type mode, a dual closed-loop control strategy of voltage outer loop plus current inner loop is adopted, while in the grid-type mode, a phase-locked loop synchronous plus PQ decoupling control strategy is adopted. During mode switching, an inner current loop compensator is used to filter and buffer the current command values ​​before and after switching in order to suppress sudden current changes and resonance at the moment of switching.

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