Optimal coordinated control method for distribution network based on full-cycle grid-connected pre-synchronization under feeder fault

Abstract

The application discloses a power distribution network optimization coordination control method based on full-cycle grid-connection pre-synchronization under feeder fault, relates to the field of power distribution network coordination control, and comprises the following steps: monitoring the working states of all AC feeders in real time, and determining the operation state of the power distribution network system according to the working states; in the autonomous operation state, when the fault of the AC feeder corresponding to the AC port of any voltage source converter is cleared and the grid-connection signal is received, the grid-connection pre-synchronization starting instruction is simultaneously sent to the AC ports of all voltage source converters; based on the grid-connection pre-synchronization starting instruction, each voltage source converter executes the multi-port full-cycle grid-connection pre-synchronization control strategy, the voltage source converter receiving the grid-connection signal executes the grid-connection operation, and the voltage source converter not receiving the grid-connection signal keeps the off-grid operation state. The application can realize the smooth transition of the island to the network without disturbance after the feeder fault is cleared.

Description

Technical Field

[0001] This application relates to the field of distribution network coordination control, and in particular to a distribution network optimization coordination control method, equipment, medium and product based on full-cycle grid-connected pre-synchronization under feeder faults. Background Technology

[0002] Traditional distribution networks typically employ a closed-loop design and open-loop operation, with feeders connected via tie switches. However, traditional tie switches only have two states: on and off. This results in weak network structure, uneven local load distribution, and insufficient power supply capacity in traditional distribution networks. Flexible multi-state switches (FMSS), as power electronic devices connected between two or more feeders to adjust the flow of active power between them, not only possess the on and off states of conventional switches but also enable continuous and controllable power. They have promising applications in distribution network power flow optimization, power quality control, and rapid fault recovery.

[0003] When the feeders of the distribution network connected to the FMSS are operating normally, the FMSS can avoid power outages and loop-closing impacts caused by conventional switching operations, and can also alleviate voltage drops and three-phase imbalances, promoting balanced load distribution and improved power quality. However, when the feeders of the distribution network connected to the FMSS fail, the lack of grid support and the switching of the FMSS control strategy often lead to bus voltage fluctuations and reduced power quality. To address these issues, energy storage systems with energy storage capabilities are introduced into the FMSS, forming an energy storage-type flexible multi-state switch (E-FMSS).

[0004] Depending on the operating status of the distribution network feeders, E-FMSS has three operating states: flexible interconnection, load transfer, and autonomous operation. Among them, flexible interconnection and load transfer operate in the network interconnection state, while autonomous operation operates in the islanded state.

[0005] Existing control strategies for FMSS all provide some control over energy storage FMSS, but they operate under a single control objective. To improve system efficiency, one or more control objectives can be set under different operating conditions, allowing for optimized system operation under each condition. Simultaneously, the control strategy can be adjusted to ensure smooth switching. This involves the transition between the three operating states of E-FMSS.

[0006] When the AC feeder connected to the FMSS needs to be reconnected to the grid after a fault is cleared, grid pre-synchronization is required, similar to that of a microgrid, to reduce bus voltage fluctuations. While existing pre-synchronization schemes can achieve a smooth transition from off-grid to grid-connected microgrids, they still have two significant technical shortcomings: (1) All of them use the control strategy of FMSS itself to switch the feeder off the grid, but they do not cover FMSS with energy storage. In the process of FMSS feeder off the grid, energy storage can be used as an energy unit to quickly provide the missing power. Therefore, the control strategy of energy storage element in the process of FMSS feeder off the grid is one of the important research directions of FMSS. (2) All of these studies were conducted under microgrids, while there is currently not much research on grid-connected pre-synchronization of FMSS. Summary of the Invention

[0007] The purpose of this application is to provide a distribution network optimization and coordination control method, equipment, medium and product based on full-cycle grid pre-synchronization under feeder faults, which can realize a smooth and disturbance-free transition from islanded to grid connection after the feeder fault is cleared, thereby improving the power supply reliability and power quality of the distribution network.

[0008] To achieve the above objectives, this application provides the following solution: In a first aspect, this application provides a distribution network optimization and coordination control method based on full-cycle grid-connected pre-synchronization under feeder fault conditions, applicable to a distribution network system including an energy storage-type flexible multi-state switch; the energy storage-type flexible multi-state switch includes multiple back-to-back connected voltage source converters, the AC ports of each voltage source converter are respectively connected to different AC feeders, and the DC ports are commonly connected to a DC bus, and an energy storage system consisting of a battery and a bidirectional DC / DC converter is connected to the DC bus; the method includes: The operating status of each AC feeder is monitored in real time, and the operating status of the distribution network system is determined based on the operating status; the operating status includes flexible interconnection operation status, load transfer operation status, and autonomous operation status; In autonomous operation mode, when the fault of the AC feeder corresponding to the AC port of any voltage source converter is cleared and the grid connection signal is received, the grid connection pre-synchronization start command is sent to the AC ports of all voltage source converters at the same time. Based on the grid-connected pre-synchronization start command, each voltage source converter executes a multi-port full-cycle grid-connected pre-synchronization control strategy. Voltage source converters that receive a grid-connection signal perform grid-connection operations, while voltage source converters that do not receive a grid-connection signal maintain off-grid operation. Among them, the multi-port full-cycle grid-connected pre-synchronization control strategy is based on a control architecture consisting of a power calculation unit, a droop control unit, a voltage synthesis unit, and a voltage and current dual-loop control unit. The power calculation unit is used to calculate active power and reactive power based on the output voltage and output current of the voltage source converter. The droop control unit, connected to the power calculation unit, is used to generate a compensation amount based on the grid-side voltage and the voltage source converter port-side voltage, and to perform droop characteristic calculations based on active power and reactive power to generate frequency reference values ​​and voltage amplitude reference values. The droop control unit includes: a pre-synchronization control module, used to calculate the voltage amplitude difference, frequency difference, and phase difference between the grid-side voltage and the voltage source converter port-side voltage, and to generate a compensation amount; and a droop control module, connected to both the pre-synchronization control module and the power calculation unit, used to perform droop characteristic calculations based on the active power, the reactive power, and the compensation amount to generate frequency reference values ​​and voltage amplitude reference values. The voltage synthesis unit is connected to the droop control unit and is used to generate a three-phase voltage control signal based on the frequency reference value and the voltage amplitude reference value, and convert it into a dq axis reference voltage. The voltage and current dual-loop control unit is connected to the voltage synthesis unit and is used to generate a pulse width modulation signal to drive the voltage source converter based on the dq axis reference voltage through decoupling control of the voltage outer loop and the current inner loop.

[0009] Secondly, this application provides a computer device, including: a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the computer program to implement the above-mentioned distribution network optimization and coordination control method based on full-cycle grid-connected pre-synchronization under feeder faults.

[0010] Thirdly, this application provides a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the aforementioned distribution network optimization and coordination control method based on full-cycle grid-connected pre-synchronization under feeder fault conditions.

[0011] Fourthly, this application provides a computer program product, including a computer program that, when executed by a processor, implements the aforementioned distribution network optimization and coordination control method based on full-cycle grid-connected pre-synchronization under feeder fault conditions.

[0012] According to the specific embodiments provided in this application, this application has the following technical effects: This application identifies three operating states of the distribution network system in real time. During the autonomous islanding grid connection phase after feeder fault clearance, it performs full-cycle grid connection pre-synchronization on all ports and adopts port-specific differentiated grid connection logic. On the one hand, it fills the gaps in existing technologies, such as the lack of grid connection pre-synchronization strategies adapted to E-FMSS multi-feeder scenarios and the lack of optimization of islanding switching in conjunction with energy storage units. On the other hand, it effectively suppresses grid connection impact and large fluctuations in bus voltage, achieving a smooth transition from autonomous operation to grid-connected operation. At the same time, it can distinguish the grid connection needs of multiple feeders, and feeders that have not been repaired continue to maintain stable off-grid operation. Combined with the dynamic power support of the DC-side energy storage system, it balances feeder load and improves the power quality and power supply reliability of the distribution network under fault conditions. Attached Figure Description

[0013] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the 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.

[0014] Figure 1 A flowchart illustrating a distribution network optimization and coordination control method based on full-cycle grid-connected pre-synchronization under feeder fault conditions, provided as an embodiment of this application; Figure 2 A schematic diagram of the topology of a distribution network system that includes an energy storage-type flexible multi-state switch; Figure 3 A schematic diagram of the total load power during the grid connection pre-synchronization process; Figure 4 A schematic diagram showing the power of the AC power grid connected to the three ports of the FMSS. Figure 5 This is a schematic diagram of the battery power. Figure 6 This is a schematic diagram of the bus voltage during the entire grid connection pre-synchronization process; Figure 7 This is a schematic diagram of the voltage waveform at the grid connection point of VSC1 in FMSS. Figure 8 This is a schematic diagram of the voltage waveform at the grid connection point of VSC2 in FMSS. Figure 9 This is a schematic diagram of the voltage waveform at the grid connection point of VSC3 in FMSS. Figure 10 This is a schematic diagram of the current in AC distribution network 1; Figure 11 This is a schematic diagram of the current in AC distribution network 2; Figure 12 This is a schematic diagram of the current in AC distribution network 3; Figure 13 This is a schematic diagram of the state of charge of a storage battery; Figure 14 A schematic diagram of the phase angles of AC distribution network 1 and VSC1 in FMSS; Figure 15 A schematic diagram of the phase angles of AC distribution network 2 and VSC2 in FMSS; Figure 16 A schematic diagram of the phase angles of AC distribution network 3 and VSC3 in FMSS; Figure 17 The following diagrams illustrate the simulation waveforms under light load during autonomous operation: (a) AC load power connected to VSC1; (b) AC load power connected to VSC2; (c) AC load power connected to VSC3; (d) Total system power; (e) Output power of each of the three ports of FMSS (VSC1~VSC3); (f) AC grid 1 power connected to VSC1; (g) Battery power; (h) Battery SOC power; and (i) DC bus voltage. Figure 18 The following diagrams illustrate the simulated waveforms under autonomous operation: (a) AC load power connected to VSC1; (b) AC load power connected to VSC2; (c) AC load power connected to VSC3; (d) Total system power; (e) Output power of each of the three ports of FMSS (VSC1~VSC3); (f) AC grid output power connected to the three ports of FMSS; (g) Battery power; (h) Battery SOC power; and (i) DC bus voltage. Detailed Implementation

[0015] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0016] To make the above-mentioned objectives, features and advantages of this application more apparent and understandable, the application will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0017] In an exemplary embodiment, a distribution network optimization and coordination control method based on full-cycle grid-connected pre-synchronization is provided under feeder fault conditions. This method is applied to a distribution network system including an energy storage flexible multi-state switch. The energy storage flexible multi-state switch includes multiple back-to-back connected voltage source converters. The AC ports of each voltage source converter are respectively connected to different AC feeders, and the DC ports are commonly connected to a DC bus. An energy storage system consisting of a battery and a bidirectional DC / DC converter is connected to the DC bus.

[0018] An energy storage system consisting of batteries and a bidirectional DC / DC converter is connected to the DC bus of the FMSS, enabling the FMSS to not only have power flow regulation capabilities, but also energy storage and rapid power support capabilities, providing a physical basis for off-grid operation.

[0019] like Figure 2 As shown, the flexible multi-state switch is composed of back-to-back voltage source converters VSC1~VSC3. The AC ports of VSC1~VSC3 are connected to the feeder ends of three independent 10kV AC distribution networks (AC distribution network 1~AC distribution network 3) via transformers T1, T2, and T3, respectively. An energy storage system consisting of batteries and bidirectional DC / DC converters is connected to the DC ports of VSC1~VSC3. Considering the importance of the loads in the power system, this application sets three loads with different priority levels. Among them, feeder load 1 is a first-level load, and feeder load 2 and feeder load 3 have decreasing priority levels, being second-level and third-level loads, respectively.

[0020] like Figure 1 As shown, this application provides a distribution network optimization and coordination control method based on full-cycle grid-connected pre-synchronization under feeder faults, which includes the following steps S1 to S3.

[0021] S1: Monitor the working status of each AC feeder in real time, and determine the operating status of the distribution network system based on the working status; the operating status includes flexible interconnection operating status, load transfer operating status, and autonomous operating status.

[0022] S2: In autonomous operation mode, when the fault of the AC feeder corresponding to the AC port of any voltage source converter is cleared and the grid connection signal is received, the grid connection pre-synchronization start command is sent to the AC ports of all voltage source converters at the same time.

[0023] S3: Based on the grid-connected pre-synchronization start command, each voltage source converter executes the multi-port full-cycle grid-connected pre-synchronization control strategy. Voltage source converters that receive the grid-connection signal perform grid-connection operations, while voltage source converters that do not receive the grid-connection signal maintain off-grid operation.

[0024] Furthermore, step S1 specifically includes: if all AC feeders are working normally, the distribution network system is determined to be in a flexible interconnected operation state; if some AC feeders fail, the distribution network system is determined to be in a load transfer operation state; if all AC feeders fail, the distribution network system is determined to be in an autonomous operation state.

[0025] Depend on Figure 2 It can be seen that, depending on whether the AC feeder connected to each port of the FMSS is faulty, each port of the FMSS can operate in two states: one is that the AC feeder connected to the FMSS is working normally, and the other is that the AC feeder connected to the FMSS is faulty. Therefore, the following three operating states can be formed: If all three AC feeders connected to the FMSS ports are working normally, that is, all three AC distribution networks are connected to the FMSS, the distribution network system is operating in a flexible interconnection state at this time. If the AC feeder connected to 1-2 ports of the FMSS fails, meaning only 1-2 AC distribution networks are connected to the FMSS, the distribution network system will be operating in load transfer mode. If all three AC feeders connected to the FMSS ports fail, meaning all three AC distribution networks are disconnected from the FMSS, the distribution network system will operate in an autonomous mode.

[0026] Furthermore, under load transfer operation, multiple operating modes are defined based on the number of faulty AC feeder ports, battery charge status, and load type.

[0027] Specifically, under load transfer operation, the system capacity will vary depending on the number of AC feeder faults, as shown in the following formula: In the formula, For the system's maximum capacity, For the status of whether the AC feeder connected to the i-th FMSS is working properly, when When it is 1, it indicates that the AC feeder connected to the i-th FMSS is working normally. When the value is 0, it indicates that there is a fault in the AC feeder connected to the i-th FMSS; Let be the capacity of the i-th FMSS.

[0028] According to the above formula, loads of different capacities can be divided into three types: light load, medium load, and heavy load. Under light load, the FMSS can simultaneously meet the charging requirements of both the load and the battery's rated power. Under medium load, the FMSS can only meet the low-power charging requirements of both the load and the battery. Under heavy load, the FMSS cannot meet the load requirements, and the battery must discharge to provide energy.

[0029] The load transfer operation status is divided into working modes based on the load power (light load, medium load, and heavy load) as the main axis, the fault scenarios of the AC feeder connected to the FMSS (single-port fault and dual-port fault) as branches, and the state of charge of the battery as the backbone. The specific analysis is as follows: (1) Branch 1: FMSS single-port failure scenario.

[0030] 1) The system is running under light load, when SOC < SOC max If the feeder connected to the FMSS voltage regulator port fails, the system is defined to operate in mode 1, where SOC refers to the battery's state of charge. max This represents the battery's maximum state of charge. If a fault occurs in the feeder connected to the FMSS non-regulated port, the system is defined to operate in Mode 2. In this mode, due to the single-port feeder fault and relatively small load power, the goal is to improve system power supply reliability, achieve load balancing, and extend the power supply time of the faulty feeder. Therefore, the normal FMSS port with constant current charging and a large adjustable capacity is set as U. dc / Q control is used to stabilize the DC bus voltage. The other normally operating FMSS ports are controlled by PQ, and the faulty FMSS ports are controlled by multi-port full-cycle grid-connected pre-synchronization control to achieve the corresponding control objectives.

[0031] 2) The system operates under light load, when SOC ≥ SOC max If a fault occurs in the feeder connected to the FMSS regulated port, the system is defined to operate in mode 3; if a fault occurs in the feeder connected to the FMSS unregulated port, the system is defined to operate in mode 4. In this mode, since the battery's state of charge has reached its maximum, the system's power supply reliability is maximized. To achieve load balancing and extend the power supply time for faulty feeders, the battery is set to float charge, and the FMSS normal port with a larger adjustable capacity is U. dc / Q control is used to stabilize the DC bus voltage. The other normal FMSS ports are controlled by PQ, and the faulty FMSS ports are controlled by multi-port full-cycle grid-connected pre-synchronization control to achieve the corresponding control objectives.

[0032] 3) The system is running when SOC < SOC max If a fault occurs in the feeder connected to the FMSS regulated port, the system is defined to operate in mode 5; if a fault occurs in the feeder connected to the FMSS unregulated port, the system is defined to operate in mode 6. In this mode, due to a single-port feeder fault, the goal is to improve system power supply reliability, achieve load balancing, and extend the power supply time of the faulty feeder. Because the load power is large, it cannot meet the constant current charging requirements of the battery. Therefore, constant voltage control for the battery (charging with excess power within the system), PQ control for the normally operating FMSS port (outputting its maximum power), and multi-port full-cycle grid-connected pre-synchronization control for the faulty FMSS port are set to achieve the corresponding control objectives.

[0033] 4) The system is running when SOC ≥ SOC max If a fault occurs in the feeder connected to the FMSS regulated port, the system is defined to operate in mode 7; if a fault occurs in the feeder connected to the FMSS unregulated port, the system is defined to operate in mode 8. In this mode, since the battery's state of charge has reached its maximum, the system's power supply reliability is maximized. To achieve load balancing and extend the power supply time of the faulty feeder, the normal FMSS port with a larger adjustable capacity and battery float charging capability is set to U. dc / Q control: the FMSS port is PQ control during normal operation and multi-port full-cycle grid-connected pre-synchronization control during faulty FMSS port, in order to achieve the corresponding control objectives.

[0034] 5) System under heavy load operation, when SOC ≥ SOC max If a fault occurs in the feeder connected to the FMSS regulated port, the system is defined to operate in mode 9; if a fault occurs in the feeder connected to the FMSS unregulated port, the system is defined to operate in mode 10. In this case, due to a single-port feeder fault, the goal is to extend the power supply time to the faulty feeder load. Because the load power is large, constant voltage control (discharging) of the battery is set, PQ control (outputting their respective maximum power) is used for the normally operating FMSS port, and multi-port full-cycle grid-connected pre-synchronization control is used for the faulty FMSS port to achieve the corresponding control objectives.

[0035] (2) Branch 2: FMSS dual-port fault scenario.

[0036] 1) The system is running under light load, when SOC < SOC max If the faulty feeder port includes an FMSS regulated port, the system is defined to operate in mode 11; if all faulty feeder ports are FMSS unregulated ports, the system is defined to operate in mode 12. In this case, due to the dual-port feeder fault and relatively small load power, the goal is to improve system power supply reliability and extend the power supply time of the faulty feeder load. Therefore, the battery is set to constant current charging, and the FMSS normal port is set to U. dc / Q control uses stable DC bus voltage and faulty FMSS port as multi-port full-cycle grid-connected pre-synchronization control to achieve the corresponding control objectives.

[0037] 2) The system operates under light load, when SOC ≥ SOC maxIf the faulty feeder port includes an FMSS regulated port, the system is defined to operate in mode 13; if all faulty feeder ports are FMSS unregulated ports, the system is defined to operate in mode 14. In this mode, since the battery's state of charge has reached its maximum, the system's power supply reliability is maximized. To extend the power supply time of the faulty feeder, battery float charging is configured, the normal FMSS port uses Udc / Q control, and the faulty FMSS port uses multi-port full-cycle grid-connected pre-synchronization control to achieve the corresponding control objectives.

[0038] 3) The system is running when SOC < SOC max If the faulty feeder port includes an FMSS regulated port, the system is defined to operate in mode 15; if all faulty feeder ports are FMSS unregulated ports, the system is defined to operate in mode 16. In this case, due to the dual-port feeder fault, the goal is to improve system power supply reliability and extend the power supply time of the faulty feeder load. Because the load power is large, the constant current charging requirement of the battery cannot be met. Therefore, constant voltage control of the battery (charging with excess power within the system), PQ control (outputting maximum power) for the normally operating FMSS port, and multi-port full-cycle grid-connected pre-synchronization control for the faulty FMSS port are set to achieve the corresponding control objectives.

[0039] 4) The system is running when SOC ≥ SOC max If the faulty feeder port includes an FMSS regulated port, the system is defined to operate in mode 17; if all faulty feeder ports are FMSS unregulated ports, the system is defined to operate in mode 18. In this mode, since the battery's state of charge has reached its maximum, the system's power supply reliability is maximized. Therefore, with the sole objective of extending the power supply time of the faulty feeder, the equipment control layer sets the battery to float charge, the normal operating FMSS port to Udc / Q control, and the faulty FMSS port to multi-port full-cycle grid-connected pre-synchronization control, in order to achieve the corresponding control objectives.

[0040] 5) System under heavy load operation, when SOC ≥ SOC max If the faulty feeder port includes an FMSS regulated port, the system is defined to operate in mode 19; if all faulty feeder ports are FMSS unregulated ports, the system is defined to operate in mode 20. In this case, due to the dual-port feeder fault, the goal is only to extend the power supply time of the faulty feeder load. Because the load power is large, constant voltage control (discharging) of the battery is set, PQ control (maximum output power) is set for the normally operating FMSS port, and multi-port full-cycle grid-connected pre-synchronization control is set for the faulty FMSS port to achieve the corresponding control objectives.

[0041] Furthermore, step S3 specifically includes: When the fault in the AC feeder connected to one of the FMSS ports is cleared, the FMSS receives the grid connection signal and initiates FMSS grid connection pre-synchronization control. This synchronizes the voltage amplitude, frequency, and phase of that port with the corresponding grid during autonomous operation before grid connection is performed. For grid connection of an AC feeder to a single FMSS port, the ideal goal is for the voltage amplitude (ΔU), frequency (Δf), and phase (Δθ) of the FMSS and the grid to be completely identical. The conditions for determining single-port grid connection and synchronization closing of the FMSS can be expressed as: In the formula, , and These are the threshold values ​​for judging the voltage phase difference, frequency difference, and voltage amplitude difference on both sides of the PCC switch.

[0042] According to the synchronization standard IEEE 1547-2003, systems with a rated capacity of less than 500kVA must meet the following requirements when connected to the power grid: phase difference less than 20°, frequency difference less than 0.3Hz, and voltage difference less than 10% of the rated voltage. However, due to the fast response and low inertia characteristics of the power electronic inverters used in FMSS, the current should be kept as small as possible to reduce the impact at the closing moment. Therefore, in accordance with the above standards, this application... , and The values ​​are 5°, 0.1Hz and 5V respectively.

[0043] Since the grid-connected pre-synchronization control strategy of the three port converters of FMSS is the same, this embodiment will use VSC1 as an example for explanation.

[0044] Before grid connection, VSC1 needs to detect the voltage of FMSS and AC distribution network 1, and pre-synchronize the voltage amplitude, frequency, and phase of both. VSC1 can only be connected to the grid after meeting the grid connection standards. In this application, the multi-port full-cycle grid connection pre-synchronization control strategy is based on a control architecture consisting of a power calculation unit, a droop control unit, a voltage synthesis unit, and a voltage and current dual-loop control unit. Each unit is described in detail below.

[0045] (1) Power calculation unit.

[0046] The power calculation unit is used to calculate the power based on the output voltage of the voltage source converter. and output current Calculate the active power P and reactive power Q. The specific calculation formula is as follows: In the formula, , , , They are respectively , The d-axis and q-axis currents and voltages obtained after dq transformation.

[0047] (2) It has a droop control unit with grid-connected pre-synchronization.

[0048] The droop control unit is connected to the power calculation unit and is used to generate compensation based on the grid-side voltage and the voltage source converter port-side voltage, and to perform droop characteristic calculations in combination with active power and reactive power to generate frequency reference values ​​and voltage amplitude reference values.

[0049] The droop control unit is the core component of the multi-port full-cycle grid-connected pre-synchronization control strategy, which includes a pre-synchronization control module and a droop control module.

[0050] 1) Pre-synchronization control module.

[0051] The pre-synchronization control module is used to calculate the voltage amplitude difference, frequency difference, and phase difference between the grid-side voltage and the voltage source converter port-side voltage, and generate compensation quantities.

[0052] As analyzed above, pre-synchronization control includes frequency, phase, and voltage pre-synchronization. FMSS can only be connected to the grid after the frequency, phase, and voltage all meet the grid connection standards. Therefore, the pre-synchronization control unit can be divided into four parts: a measurement submodule, a frequency and phase pre-synchronization submodule, a voltage pre-synchronization submodule, and a synchronization standard monitoring submodule. To accelerate the grid connection pre-synchronization speed, a linear active disturbance rejection controller (LADRC) is set in the pre-synchronization control module.

[0053] When the grid-connected pre-synchronization module is working, it first needs to monitor the voltage, angular frequency, and phase variables of the power grid and the FMSS port in real time. The differences between the angular frequency and angle variables and their respective reference values ​​are then adjusted using a PI controller and superimposed on the reactive droop component in the droop control to complete the angle synthesis. Combined with the active droop component in the droop control, the d-axis reference voltage in VSC1 can be generated. The control voltage and the q-axis reference voltage of VSC1 Part of the voltage. Based on this, the above... The partial voltage and the voltage deviation adjusted by LADRC are superimposed to obtain the result. The final control voltage.

[0054] through , After adjustment, the frequency, phase, and voltage of the FMSS can be changed. Once the deviations of these three variables from the grid voltage meet the grid connection requirements, a grid connection signal can be issued after a delay.

[0055] 2) Droop control module.

[0056] The droop control module is connected to the pre-synchronization control module and the power calculation unit, respectively, and is used to perform droop characteristic calculations based on the active power, the reactive power and the compensation amount to generate frequency reference values ​​and voltage amplitude reference values.

[0057] The droop control module, based on the power calculation unit, obtains the inverter output voltage deviation signal through the droop characteristic. ), frequency deviation signal ( Then, it is compared with the rated frequency signal. Rated voltage signal By superimposing these signals, the final frequency control signal can be obtained. and voltage control signal The corresponding drooping characteristic can be expressed as: In the formula, , ,and , The droop coefficient is... It is the maximum frequency that the system is allowed to output. To maximize the reactive power output of VSC1, It is the minimum voltage amplitude that the system is allowed to output. This is the maximum output power allowed when the system voltage drops. This is the baseline value for reactive power. This is the baseline value for active power.

[0058] exist Based on this, when the AC feeder undergoes grid connection / off-grid switching, the grid connection pre-synchronization angular frequency ω can be obtained. vf and the phase angle frequency ω of the network-locked loop mv By superimposing the two, the output frequency of VSC1 can be obtained. and angle .

[0059] (3) Voltage synthesis unit.

[0060] The voltage synthesis unit is connected to the droop control unit and is used to generate a three-phase voltage control signal based on the frequency reference value and the voltage amplitude reference value, and convert it into a dq axis reference voltage.

[0061] This section is passed Three-phase voltage control signals can be obtained. , and The control signal of VSC1 is then obtained. , The calculation formula is as follows: (4) Voltage and current dual-loop control unit.

[0062] The voltage and current dual-loop control unit is connected to the voltage synthesis unit and is used to generate a pulse width modulation signal to drive the voltage source converter based on the dq axis reference voltage through decoupling control of the voltage outer loop and the current inner loop.

[0063] When controlling the current along the d and q axes, it is often subject to current cross-coupling term ω. m1 L g i q and ω m1 L g i d The impact of voltage cross-coupling is significant. To eliminate current coupling, current decoupling control needs to be introduced into the current loop. Similarly, when controlling the voltage along the d and q axes, it is also affected by voltage cross-coupling terms, so voltage decoupling control also needs to be introduced into the voltage loop. Based on the above analysis, the voltage and current dual-loop controllers respectively incorporate voltage decoupling and current decoupling into the traditional voltage and current PI regulators.

[0064] The outer voltage loop uses a PI regulator to achieve voltage tracking control; the inner current loop uses a P regulator to improve the regulation speed. To achieve voltage and current decoupling, voltage decoupling and current decoupling terms are introduced after the outer voltage loop and the inner current loop, respectively.

[0065] The multi-port full-synchronization grid-connection pre-synchronization control strategy can reduce the time of asynchronous grid connection for multiple ports. This strategy allows the other ports to simultaneously initiate grid-connection pre-synchronization control when one FMSS port starts its control. However, grid connection is determined based on the presence of a grid connection signal and synchronization standard monitoring. FMSS ports that do not require grid connection only need to track the amplitude, frequency, and phase of the grid to be connected to to the maximum extent possible, thus reducing the system's grid connection pre-synchronization time when the connected grid recovers. In autonomous operation, once any FMSS port receives a grid connection signal, the grid connection pre-synchronization control strategy for all three ports will be initiated simultaneously. When the port requiring grid connection meets the connection conditions, it can be connected and designated as a voltage-stabilized port. The remaining ports continue to undergo multi-port full-cycle grid connection pre-synchronization control and wait for the grid connection signal. Once the remaining ports receive the grid connection signal, since the frequencies and amplitudes of the three AC grids are not significantly different, grid connection can be achieved quickly. Based on the port capacity, a voltage-stabilized port is selected, and the control strategy for each FMSS port is adjusted until all three ports are fully connected.

[0066] Furthermore, under autonomous operation, a load switching control strategy is adopted based on the battery state of charge. The load switching control strategy is as follows: when the battery state of charge is lower than the first threshold, the third-level load is cut off; when the battery state of charge is lower than the second threshold, the second-level load is cut off; when the battery state of charge is lower than the third threshold, the first-level load is cut off.

[0067] In autonomous operation mode, due to the lack of power support from the power grid, a load switching control strategy can be adopted based on the battery's state of charge. This results in the following two operating modes: Mode 21: When the battery state of charge is greater than SOC min (Battery minimum state of charge) The battery has sufficient energy and can function normally as a voltage regulator port. At this time, the goal is to extend the power supply time for the faulty feeder load, supplying power to all AC feeder loads of the FMSS. The battery uses constant voltage control, and each port of the FMSS is a multi-port, full-cycle grid-connected pre-synchronization control system.

[0068] Mode 22: When the battery state of charge is less than SOC min If the battery power is insufficient, the goal is to extend the power supply time of the critical fault feeder loads. Following the FMSS load switching control strategy, three loads (L3 to L1) are sequentially reduced in load. The battery and FMSS control strategies are the same as in mode 21.

[0069] As analyzed above, during autonomous operation of the system, load shedding control strategies are crucial for extending the power supply time of critically faulted feeder loads. Once the fault is cleared and the FMSS can be connected to the grid, a reasonable load switching control strategy becomes the primary method for improving system operating efficiency. This application proposes a multi-port load switching control strategy for the FMSS, based on traditional microgrid load switching control strategies and considering system reliability.

[0070] System reliability U RI Represented as: In the formula, ω i To reduce the severity of the three loads respectively, with ω1~ω3 being 0.5, 0.3, and 0.2 respectively, P lossi For load L i The active power that is automatically cut off during the entire operating cycle, S i For load L i User electricity consumption intention curve throughout the entire operating cycle.

[0071] The load switching control strategy is discussed in two parts: grid connection and autonomous operation, as detailed below: (1) When the system is running autonomously, a step-by-step load reduction control strategy based on the state of charge of the battery is adopted. That is, when the SOC is 0.4, 0.3 and 0.2, the third-level, second-level and first-level loads are reduced respectively, thereby extending the power supply time of the first-level load to the maximum extent.

[0072] (2) When the system receives a grid connection signal, it can operate in flexible interconnection or load transfer mode. At this time, the timing of load activation at each level can be determined based on the system load power. This situation can be further subdivided into the following three types: 1) If the system operates under light or medium load after all loads are connected, the normal operation of all loads can be guaranteed. Then, the power supply to all loads will be restored, and the charging power of the system voltage regulator port and the battery will be determined according to the light or medium load condition of the system.

[0073] 2) If the system operates under heavy load after all loads are connected, the total power of the primary and secondary loads should be calculated to improve system reliability. If connecting the primary and secondary loads ensures light or medium load operation, power supply to the primary and secondary loads should be restored, and the battery charging power should be determined based on the current light or medium load condition. Otherwise, the power of the primary load should be calculated. If connecting only the primary load allows the system to operate under light load, power supply to the primary load should be restored, and the battery should be charged at a constant current. Otherwise, the system will operate under medium load, and the battery will be charged using the system's internal excess power.

[0074] By employing the above control strategies, after the FMSS is connected to the grid, it can quickly switch to loads at all levels, thereby maximizing the reliability of the system.

[0075] The following is a simulation analysis of the distribution network optimization and coordination control method based on full-cycle grid-connected pre-synchronization under the above-mentioned feeder fault.

[0076] (1) Simulation parameters.

[0077] To verify the effectiveness of the coordination and control strategy proposed in this project, in accordance with Figure 2 The topology shown is used to build a distribution network simulation model based on energy storage and FMSS. The DC bus voltage is 750V; the capacity of T1, T2 and T3 is 125kVA and the power factor is 0.8; the transformer ratio is 10 kV / 0.4 kV; the battery capacity is 654Ah and the terminal voltage is 400V.

[0078] (2) Multi-port simulation results.

[0079] The switching process from autonomous operation to flexible interconnection or load transfer operation includes autonomous operation, the full synchronization pre-synchronization process of the FMSS before the feeder disconnection / connection to the grid, and the operation state after the feeder is connected to the grid. Assume the initial state of charge of the battery is approximately 0.8. From 0 to 0.5 seconds, the system operates in autonomous operation. At 0.5 seconds, FMSS VSC1 receives the signal that the feeder fault has been cleared and grid connection is possible; at 1 second, FMSS VSC2 receives the signal; and at 1.5 seconds, FMSS VSC3 receives the signal. The simulation time is 2 seconds. The simulation results are as follows: Figures 3-16 As shown.

[0080] Depend on Figures 3-16 It can be seen that during the period from 0 to 0.5s, the total load power of FMSS is 60kW, the battery outputs 60kW of power, the system power is balanced, the SOC continues to decrease, and the initial load side voltage and phase are ahead of the corresponding grid side voltage and phase.

[0081] At 0.5s, FMSS VSC1 receives the feeder grid connection signal. FMSS VSC1, VSC2 and VSC3 simultaneously start the grid connection pre-synchronization control strategy, so the load-side voltage phase of VSC1, VSC2 and VSC3 gradually approaches the grid-side voltage phase.

[0082] At approximately 0.7 seconds, FMSS's VSC1 meets the feeder grid connection conditions. After a 100ms delay, the switch at VSC1's PCC closes, the voltage regulator port switches to VSC1, and power is supplied to extend the power supply time for faulty feeder loads 2 and 3. The battery is charged at a constant current. The SOC rises to improve system reliability. During the off-grid / on-grid switching, there is no significant voltage or current surge at the AC bus PCC.

[0083] At 1 second, VSC2 of FMSS receives the signal that the feeder fault has been cleared and it can be connected to the grid. Since the voltage and phase of the load side of VSC2 are basically close to those of the grid side, the grid connection requirements are quickly met, and the switch at the PCC of VSC2 is closed after a 100ms delay. After the feeder is connected to the grid, AC distribution network 1 and AC distribution network 2 output the same power, thus achieving load balancing.

[0084] At 1.5s, FMSS's VSC3 received a signal that the feeder fault had been cleared and it could be connected to the grid. Similar to 1s, since the voltage and phase of the load side of VSC3 were already close to the voltage and phase of the AC distribution network 3 side, VSC3 quickly completed the grid connection.

[0085] By comparing the asynchronous grid connection processes of VSC1 to VSC3, it can be found that the pre-synchronization process of full synchronization accumulates an advance grid connection time of about 0.23s and reduces DC bus voltage fluctuation by about 6V, thereby effectively realizing the system's mode switching from autonomous operation to grid-connected operation.

[0086] (3) Simulation results under light load conditions.

[0087] Initially, the battery's state of charge was 50%, and the L1 power P L1 For 10kW, L2 power P L2 For 30kW, L3 power P L3 It is 30kW. Figure 17 This is a simulation waveform under light load in autonomous operation. From top to bottom, the waveform represents the load power, the power P at each port of the VSC, and so on. VSC AC power grid 1 output power P g1 Battery power P B SOC and DC bus voltage U dc .

[0088] Depend on Figure 17 As shown in (a)-(i), in the initial state, all three AC power grid feeders are faulty. Therefore, the battery acts as a voltage regulator port, generating 70kW of power to extend the power supply time of the faulty feeder load. The SOC continues to decrease, and the system operates in mode 20.

[0089] At approximately 0.3 seconds, the SOC reaches 0.4, meeting the load cut-off condition requirements. Therefore, according to the load importance, AC feeder 3 load L3 is cut off first, leaving a total system load of 40kW. The battery output power decreases to 40kW, and the system switches to mode 21 operation.

[0090] At approximately 0.8 seconds, the State of Charge (SOC) reaches 0.3, the load L2 on AC feeder 2 is disconnected, and the total system power drops to 10kW. As the load power decreases, the battery output power decreases to 10kW, and the system continues to operate in mode 21. At this time, the battery only supplies power to L1.

[0091] At 1.3s, FMSS's VSC1 receives a fault clearing signal, indicating that power supply can be restored. Therefore, FMSS's VSC1, VSC2, and VSC3 initiate the fully synchronous pre-synchronous grid connection control strategy.

[0092] At approximately 1.4 seconds, the load-side voltage of VSC1 meets the requirements for frequency, phase, and amplitude. After a 100ms delay, grid connection is completed, and VSC1 switches to a stable port.

[0093] At approximately 1.7 seconds, the bus voltage stabilized at around 750V. Since the system load was light, power supply to L2 and L3 was restored, and the battery switched to a constant current charging control strategy to improve system reliability. AC grid 1 generated 83kW of power, of which 13kW was for constant current battery charging and 70kW was for supplying power to L1, L2, and L3, extending the power supply time to the faulty feeder loads L2 and L3.

[0094] At 2.5s, FMSS's VSC2 received the fault clearing signal, allowing for the restoration of power supply to the grid. FMSS's VSC2 continued its grid pre-synchronization process. Since the VSC2 pre-synchronization signal had already been initiated at 1.3s, VSC2 quickly completed grid connection upon receiving the grid connection signal. Furthermore, VSC2's switching control strategy is PQ control, ensuring that AC distribution network 1 and AC distribution network 2 have the same output power. Figure 17 As shown in (g) in the figure, load balancing is thus achieved.

[0095] (4) Simulation results under medium load conditions.

[0096] Initially, the battery's state of charge was 50%, and the L1 power P L1 For 15kW, L2 power P L2 For 40kW, L3 power P L3 It has a power of 40kW. Figure 18 Download the simulation waveform in the autonomous operation state.

[0097] Depend on Figure 18 As shown in (a)-(i), in the initial state, all three AC power grid feeders are faulty. Therefore, the battery acts as a voltage regulator port, generating 95kW of power to extend the power supply time of the faulty feeder load, and the SOC continues to decrease.

[0098] At approximately 0.2 seconds, the SOC reaches 0.4. According to the load switching control strategy, the load L3 of AC feeder 3 is switched off, and the total system load remains at 55kW, with the battery output power decreasing to 55kW.

[0099] At approximately 0.5 seconds, FMSS's VSC2 receives a signal indicating fault clearance and grid reconnection is possible. The system then initiates a full-cycle grid reconnection pre-synchronization control strategy. At approximately 0.6 seconds, VSC2 completes grid reconnection pre-synchronization and connects to AC distribution network 2. AC distribution network 2 outputs 68kW of power, and the battery switches to constant current charging. The system then switches to voltage regulation via VSC2. At approximately 0.8 seconds, the bus voltage recovers to around 750V. Following the load switching control strategy, feeder load 3 is immediately connected. Due to the connection of load 3, the system operates again under medium load conditions. VSC2 outputs its maximum power of 100kW, and the battery charges using the system's internal excess power (-5kW) to improve system reliability.

[0100] At approximately 1.5 seconds, FMSS's VSC2 receives a fault-cleared signal indicating it can reconnect to the grid. Since VSC1 has already undergone pre-synchronization, it immediately synchronizes with AC distribution network 1 shortly after receiving the grid connection signal. Because the adjustable margin of VSC1 is greater than that of VSC2, VSC1 switches to a voltage regulator port and VSC2 switches to PQ control strategy the instant AC distribution network 2 connects. This allows AC distribution network 1 and AC distribution network 2 to output the same power. Furthermore, the connection of AC distribution network 2 increases the system capacity, allowing the system to operate under light load, and the battery charges at its rated power.

[0101] Approximately 2.1 seconds later, VSC3 of the FMSS receives a signal indicating that the fault has been cleared and grid connection is possible. Since VSC1 has already undergone grid connection pre-synchronization, it immediately completes synchronization with AC distribution network 3 shortly after receiving the grid connection signal. Because the adjustable margin of VSC3 is smaller than that of VSC1, the voltage regulator port remains unchanged. However, the output power of AC distribution networks 1 and 2 decreases with the connection of AC distribution network 3, ultimately resulting in the same output power for all three AC grids, and the system operates in a flexible interconnection state.

[0102] In an exemplary embodiment, a computer device is provided, including a memory and a processor. The memory stores a computer program, and the processor executes the computer program to implement the steps in the above-described method embodiments. The computer device can be a server or a terminal. The computer device includes a processor, a memory, an input / output interface (I / O), and a communication interface. The processor, memory, and I / O interface are connected via a system bus, and the communication interface is connected to the system bus via the I / O interface. The processor of the computer device provides computing and control capabilities. The memory of the computer device includes a non-volatile storage medium and internal memory. The non-volatile storage medium stores an operating system, a computer program, and a database. The internal memory provides an environment for the operation of the operating system and computer program in the non-volatile storage medium. The database of the computer device stores data to be processed. The I / O interface of the computer device is used for exchanging information between the processor and external devices. The communication interface of the computer device is used for communicating with an external terminal via a network connection. When the computer program is executed by the processor, it implements the steps in the above-described method embodiments.

[0103] In one exemplary embodiment, a computer-readable storage medium is provided storing a computer program that, when executed by a processor, implements the steps in the above-described method embodiments.

[0104] In one exemplary embodiment, a computer program product is provided, including a computer program that, when executed by a processor, implements the steps in the above-described method embodiments.

[0105] It should be noted that the user information (including but not limited to user device information, user personal information, etc.) and data (including but not limited to data used for analysis, data stored, data displayed, etc.) involved in this application are all information and data authorized by the user or fully authorized by all parties, and the collection, use and processing of the relevant data must comply with relevant regulations.

[0106] Those skilled in the art will understand that all or part of the processes in the above embodiments can be implemented by a computer program instructing related hardware. The computer program can be stored in a non-volatile computer-readable storage medium. When executed, the computer program can include the processes of the embodiments described above. Any references to memory, databases, or other media used in the embodiments provided in this application can include at least one of non-volatile and volatile memory. Non-volatile memory can include read-only memory (ROM), magnetic tape, floppy disk, flash memory, optical memory, high-density embedded non-volatile memory, resistive random access memory (ReRAM), magnetic random access memory (MRAM), ferroelectric random access memory (FRAM), phase change memory (PCM), graphene memory, etc. Volatile memory can include random access memory (RAM) or external cache memory, etc. By way of illustration and not limitation, RAM can take many forms, such as Static Random Access Memory (SRAM) or Dynamic Random Access Memory (DRAM).

[0107] The databases involved in the embodiments provided in this application may include at least one type of relational database and non-relational database. Non-relational databases may include, but are not limited to, blockchain-based distributed databases. The processors involved in the embodiments provided in this application may be general-purpose processors, central processing units, graphics processing units, digital signal processors, programmable logic devices, quantum computing-based data processing logic devices, etc., and are not limited to these.

[0108] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0109] This document uses specific examples to illustrate the principles and implementation methods of this application. The descriptions of the above embodiments are only for the purpose of helping to understand the methods and core ideas of this application. Furthermore, those skilled in the art will recognize that, based on the ideas of this application, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of this application.

Claims

1. A distribution network optimization and coordination control method based on full-cycle grid-connected pre-synchronization under feeder faults, characterized in that, The method is applied to a distribution network system including an energy storage-type flexible multi-state switch; the energy storage-type flexible multi-state switch includes multiple back-to-back connected voltage source converters, the AC ports of each voltage source converter are respectively connected to different AC feeders, and the DC ports are commonly connected to a DC bus, and an energy storage system consisting of a battery and a bidirectional DC / DC converter is connected to the DC bus. The system monitors the operating status of each AC feeder in real time and determines the operating status of the distribution network system based on the operating status. The operating status includes flexible interconnection operation status, load transfer operation status, and autonomous operation status. Specifically, if all AC feeders are operating normally, the distribution network system is determined to be in flexible interconnection operation status; if some AC feeders fail, the distribution network system is determined to be in load transfer operation status; if all AC feeders fail, the distribution network system is determined to be in autonomous operation status. In autonomous operation mode, when the fault of the AC feeder corresponding to the AC port of any voltage source converter is cleared and the grid connection signal is received, the grid connection pre-synchronization start command is sent to the AC ports of all voltage source converters at the same time. Based on the grid-connected pre-synchronization start command, each voltage source converter executes a multi-port full-cycle grid-connected pre-synchronization control strategy. Voltage source converters that receive a grid-connection signal perform grid-connection operations, while voltage source converters that do not receive a grid-connection signal maintain off-grid operation. Among them, the multi-port full-cycle grid-connected pre-synchronization control strategy is based on a control architecture consisting of a power calculation unit, a droop control unit, a voltage synthesis unit, and a voltage and current dual-loop control unit. The power calculation unit is used to calculate active power and reactive power based on the output voltage and output current of the voltage source converter. The droop control unit, connected to the power calculation unit, is used to generate a compensation amount based on the grid-side voltage and the voltage source converter port-side voltage, and to perform droop characteristic calculations based on active power and reactive power to generate frequency reference values ​​and voltage amplitude reference values. The droop control unit includes: a pre-synchronization control module, used to calculate the voltage amplitude difference, frequency difference, and phase difference between the grid-side voltage and the voltage source converter port-side voltage, and to generate a compensation amount; and a droop control module, connected to both the pre-synchronization control module and the power calculation unit, used to perform droop characteristic calculations based on the active power, the reactive power, and the compensation amount to generate frequency reference values ​​and voltage amplitude reference values; the pre-synchronization control module includes a linear active disturbance rejection controller, which adjusts the voltage amplitude difference. The voltage synthesis unit is connected to the droop control unit and is used to generate a three-phase voltage control signal based on the frequency reference value and the voltage amplitude reference value, and convert it into a dq axis reference voltage. The voltage and current dual-loop control unit is connected to the voltage synthesis unit and is used to generate a pulse width modulation signal to drive the voltage source converter based on the dq axis reference voltage through decoupling control of the voltage outer loop and the current inner loop. It also includes: in autonomous operation mode, adopting a load switching control strategy based on the battery state of charge; the load switching control strategy is as follows: when the battery state of charge is lower than the first threshold, disconnect the third-level load; when the battery state of charge is lower than the second threshold, disconnect the second-level load; when the battery state of charge is lower than the third threshold, disconnect the first-level load.

2. The distribution network optimization and coordination control method based on full-cycle grid-connected pre-synchronization under feeder faults according to claim 1, characterized in that, In load transfer operation, multiple working modes are defined based on the number of AC feeder fault ports, battery charge status, and load type.

3. A computer device, comprising: A memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that the processor executes the computer program to implement the distribution network optimization and coordination control method based on full-cycle grid-connected pre-synchronization under feeder faults as described in any one of claims 1-2.

4. A computer-readable storage medium having a computer program stored thereon, characterized in that, When executed by a processor, the computer program implements the distribution network optimization and coordination control method based on full-cycle grid-connected pre-synchronization under feeder faults as described in any one of claims 1-2.

5. A computer program product, comprising a computer program, characterized in that, When executed by a processor, the computer program implements the distribution network optimization and coordination control method based on full-cycle grid-connected pre-synchronization under feeder faults as described in any one of claims 1-2.

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