A closed-loop control method, medium, and device for a closed-loop control device of a distribution network

Abstract

The present invention discloses a closed-loop control method, medium, and equipment for a closed-loop control device for a distribution network. The method starts the inverter. When the effective value of the difference between the collected voltage of the first substation and the voltage of the second substation is lower than the rated voltage of the secondary side of the series transformer, all circuit breakers on the series transformer series loop are closed. The inverter AC output is unlocked. If the current flows from the first substation to the second substation, the inverter controls the secondary current of the series transformer to gradually increase from its no-load excitation current, and the secondary current of the series transformer causes the current direction to flow from the first substation to the second substation. As the inverter controls the secondary current of the series transformer to increase to its rated value, or to the load current of the second substation, or the current increases to reduce the effective value of the difference between the voltage of the first substation and the voltage of the second substation to meet the closed-loop condition, the current is maintained unchanged. Advantages: The method of first excitation and then gradually increasing the current is controllable, avoiding impact current and the generation of circulating current.

Description

Technical Field

[0001] The present invention relates to a closed-loop control method, a medium and equipment for a closed-loop control device of a distribution network, and belongs to the technical field of power equipment of distribution networks. Background Art

[0002] Due to considerations such as short-circuit currents, domestic distribution networks generally utilize a closed-loop, open-loop power supply system. Under this system, each load is supplied by a single busbar. Load areas on different busbars are isolated by tie switches, forming load islands. Under normal circumstances, tie switches operate in an open-loop manner. During distribution network maintenance or system failures, load transfer can be achieved through loop closing, avoiding power outages and improving power supply reliability. However, since the grid's operational status after loop closing is not transparent to dispatchers, loop closing operations can cause significant current flow in the system, overloading some equipment and threatening its safe operation. It can also trigger relay protection to fail, leading to power outages. Failure to operate a protection relay can damage equipment or cause the activation of a higher-level protection level, expanding the outage.

[0003] The traditional method of using back-to-back AC / DC conversion can achieve interconnection between two substations, but the ratio of transmission capacity to equipment capacity of this equipment is 1:1, the equipment capacity is large, the cost is high, the floor space is large, and the power supply loss is also large.

[0004] In response to the above-mentioned problem of closed-loop control between two distribution substations, this application proposes a distribution network closed-loop control device and a closed-loop method thereof, which mainly solve the following problems: (1) having a high regulation ratio, realizing the control of large currents with small-capacity equipment, reducing equipment investment and footprint; (2) avoiding impact current when two substations are interconnected; (3) avoiding current circulation when two substations are interconnected. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to overcome the defects of the prior art and provide a closed-loop control method, medium and equipment for a closed-loop control device of a distribution network.

[0006] In order to solve the above technical problems, the present invention provides a closed-loop control method of a closed-loop control device for a distribution network, wherein the closed-loop control device for the distribution network comprises: a series transformer, a parallel transformer, an inverter and a rectifier;

[0007] The secondary side of the series transformer is connected in series between the first and second substations of the distribution network; the primary side of the shunt transformer is connected to the first substation of the distribution network; the secondary side of the shunt transformer is connected to the rectifier, the inverter and the primary side of the series transformer in sequence;

[0008] The secondary side and primary side of the series transformer are isolated; the distribution network loop to which the series transformer is connected in series also includes at least one series circuit breaker;

[0009] The steps include:

[0010] Starting the inverter, collecting the voltage of the first substation area and the voltage of the second substation area of the distribution network; when the effective value of the difference between the voltage of the first substation area and the voltage of the second substation area is lower than the rated voltage of the secondary side of the series transformer, closing all series circuit breakers on the series circuit of the series transformer;

[0011] Unlock the inverter AC output. If the first and second substations are interconnected through a series circuit breaker, the power flow will flow from the first substation to the second substation. The inverter controls the secondary current of the series transformer to gradually increase from its no-load excitation current, and the secondary current of the series transformer causes the power flow direction to flow from the first substation to the second substation.

[0012] As the inverter controls the secondary current of the series transformer to increase to its rated value, or increases to the load current of the second station area, or the current increases to reduce the effective value of the difference between the first station area voltage and the second station area voltage to meet the loop closing condition, the current is maintained unchanged.

[0013] Furthermore, the DC side of the inverter is powered by a rectifier, and the AC side input of the rectifier is powered by a parallel transformer connected to the distribution network where the distribution network closing control device is located.

[0014] Furthermore, a bypass switch is connected in parallel to the secondary side of the series transformer.

[0015] Furthermore, a thyristor bypass switch is connected in parallel to the secondary side or the primary side of the series transformer.

[0016] Furthermore, when the effective value of the difference between the first substation voltage and the second substation voltage meets the loop closing condition, the bypass switch is closed and the inverter stops outputting.

[0017] Furthermore, during the process of increasing the secondary current of the series transformer, the power flow of the first substation or the second substation is monitored. If the power flow output direction of any substation is from the load to the power supply, the current increase is stopped.

[0018] Furthermore, if the effective value of the difference between the first section voltage and the second section voltage does not meet the loop closing condition when the increase of the secondary side current of the series transformer stops, the inverter gradually stops outputting.

[0019] Furthermore, after the inverter controls the secondary current of the series transformer to decrease to 0, a series circuit breaker in a distribution network loop to which at least one series transformer is connected in series is disconnected.

[0020] A computer-readable storage medium storing one or more programs, the one or more programs comprising instructions that, when executed by a computing device, cause the computing device to perform any of the methods described.

[0021] A computing device comprising:

[0022] One or more processors, a memory, and one or more programs, wherein the one or more programs are stored in the memory and configured to be executed by the one or more processors, and the one or more programs include instructions for executing any of the methods described.

[0023] The beneficial effects achieved by the present invention are:

[0024] (1) This application takes advantage of the fact that the voltage difference between two distribution areas in the distribution network is often very small, and takes advantage of the fact that the series transformer can only withstand the voltage difference between the two areas, so as to achieve the purpose of controlling a larger power flow with a lower capacity device, and has the advantages of a high regulation ratio, low equipment cost, and a small footprint.

[0025] (2) By adopting the closed-loop control method disclosed in the present application, all switches are first closed to connect the series transformer between the two substations, and then the current is gradually increased. This can achieve a slow increase in the current between the two substations, fully avoiding the generation of impact current, until the voltage difference is small enough to meet the interconnection conditions, or does not meet the closed-loop conditions and exits operation.

[0026] (3) After the interconnection conditions are met, the bypass switch can be closed for direct connection, or the grid can be allowed to operate in this state for a long time, providing a flexible scheduling method for grid operation. Since the current between substations increases slowly, the current at the power source can be monitored to avoid the generation of circulating current. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a typical application topology of the closed-loop control device of the present invention in a 10kV distribution network;

[0028] Figure 2 The invention provides a closed-loop control method for a closed-loop control device of a distribution network.

[0029] Figure 1 and Figure 2 1. Series transformer; 1-1. Secondary side of series transformer; 1-2. Primary side of series transformer; 2. Inverter; 3. Rectifier; 4. Parallel transformer; 5-1. First series circuit breaker; 5-2. Second series circuit breaker; 6. Thyristor bypass switch; 7. Bypass switch. DETAILED DESCRIPTION

[0030] The present invention will be further described below in conjunction with the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention.

[0031] In a specific embodiment 1, Figure 1 As shown, the distribution network closed-loop control device includes a series transformer 1 with a secondary side 1-1 connected in series between the first and second substations of the 10kV distribution network. The secondary side of the series transformer is 1200V, and the rated voltage of the primary side 1-2 of the series transformer is 380V. It is connected to the inverter 2. The series transformer 1 adopts a star-delta connection method, and the secondary side 1-1 and the primary side 1-2 of the series transformer are isolated.

[0032] The series transformer 1 connected in series to the distribution network loop also includes at least one series circuit breaker, which is set as two here. The first series circuit breaker 5-1 is connected in series on the first substation side, and the second series circuit breaker 5-2 is connected in series on the second substation side.

[0033] The inverter 2 has a power of 1 MVA, an AC side rated voltage of 380 V, a DC side voltage of 750 V, and is powered by a rectifier 3 .

[0034] Rectifier 3 has a capacity of 1 MVA and a rated AC voltage of 380 V. Its input AC voltage is supplied by a shunt transformer 4 connected to the first substation of the distribution network where the closed-loop control device resides. This shunt transformer is a 10 kV / 380 V step-down transformer connected in a star-delta configuration. The control objective of rectifier 3 is to maintain a stable DC voltage of approximately 750 V.

[0035] The series transformer secondary side 1-1 or primary side 1-2 is connected in parallel with a thyristor bypass switch 6, which is used to quickly bypass the series transformer 1 in the event of a fault. The thyristor bypass switch 6 has a fast response time and can quickly bypass the series transformer 1 when a fault on one side of the power grid is detected, reducing the risk of the series transformer 1 being subjected to excessive voltage.

[0036] The secondary side 1 - 1 of the series transformer is connected in parallel with a bypass switch 7 for completely bypassing the series transformer 1 so that the two power grids are directly interconnected.

[0037] The distribution network closed loop control device adopts the following method for closed loop control: Figure 2 The control method shown:

[0038] (1) Inverter 2 is turned on to collect the voltages of the first and second substations of the distribution network. When the effective value of the voltage difference between the first and second substations is lower than the rated voltage of the secondary side 1-1 of the series transformer, all circuit breakers 5-1 and 5-2 on the series circuit of the series transformer 1 are closed one by one. At this time, the current of the secondary side 1-1 of the series transformer is the no-load excitation current, which is about 0A.

[0039] (2) Unlock the AC output of inverter 2, and inverter 2 controls the current of the secondary side 1-1 of the series transformer to gradually increase from about 0A. If the power flow flows from the first area to the second area after the first area is interconnected with the second area through the circuit breaker, the current of the secondary side 1-2 of the series transformer causes the power flow direction to flow from the first area to the second area; because the current increases gradually under controllable conditions, the inrush current can be fully avoided.

[0040] Assuming that the first substation and the second substation are interconnected through a circuit breaker, the flow direction after interconnection can be verified by calculation. The calculation method is an existing mature technology and will not be repeated here.

[0041] Inverter 2 is connected to the primary side of transformer 1-2. Inverter control of transformer current is a mature technology that can be achieved by using classic control methods such as dq decoupling control, which will not be described here.

[0042] (3) As the inverter 3 controls the current of the secondary side 1-1 of the series transformer to increase to its rated value, or increase to the load current of the second station area, or the voltage difference between the first station area and the second station area decreases to meet the loop closing condition, the current is maintained unchanged.

[0043] (4) When the voltage difference between the first and second substations meets the loop closing condition, the bypass switch 7 is closed, the inverter 2 stops outputting, and the current on the secondary side 1-1 of the series transformer is 0 A. At this point, the two power grids are fully interconnected.

[0044] Furthermore, during the current increase process of the secondary side 1-1 of the series transformer, the power flow of the first or second substation is monitored. If the power flow output direction of either substation is from the load to the power source, the current increase is stopped. The purpose of this process is to prevent power circulation.

[0045] If the voltage difference between substations 1 and 2 does not meet the loop closing condition when the current increase stops, inverter 2 controls the current in the secondary side of series transformer 1-1 to decrease to zero and disconnects at least one series circuit breaker 5-1 or 5-2 in the distribution network loop connected in series with series transformer 1. This process is equivalent to abandoning loop closing and returning to the initial state when loop closing by circuit breaker is not required and long-term interconnection of converters is not required.

[0046] The present invention proposes a closed-loop control method for a distribution network closed-loop control device. While its topology is similar to that of traditional DVRs and UPFCs, the present application applies this topology to distribution network power flow control scenarios, addressing the high cost and large footprint of distribution network power flow control equipment. This application addresses the fact that the voltage difference between two distribution substations in a distribution network is often very small, leveraging the advantage of a series transformer that can only withstand the voltage difference between the two substations. This allows for the use of lower-capacity equipment to control larger power flows, resulting in a high regulation ratio, low equipment cost, and a small footprint. Furthermore, by first closing all switches to connect the series transformer between the two substations and then gradually increasing the current, a slow increase in power flow between the two substations can be achieved, effectively avoiding the generation of inrush currents until the voltage difference is sufficiently small to meet interconnection conditions. Once the interconnection conditions are met, the bypass switch can be closed for direct connection, or the grid can operate in this state for a long time, providing a flexible scheduling method for grid operation. Because the power flow between substations increases slowly, the power flow at the power source can be monitored to avoid the generation of circulating currents.

[0047] Those skilled in the art will appreciate that the embodiments of the present application may be provided as methods, systems, or computer program products. Therefore, the present application may take the form of an entirely hardware embodiment, an entirely software embodiment, or an embodiment combining software and hardware. Furthermore, the present application may take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to magnetic disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0048] The present application is described with reference to the flowcharts and / or block diagrams of the methods, devices (systems), and computer program products according to the embodiments of the present application. It should be understood that each process and / or block in the flowchart and / or block diagram, as well as the combination of processes and / or blocks in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 a process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0049] These computer program instructions may also be stored in a computer readable memory that can direct a computer or other programmable data processing device to work in a specific manner, so that the instructions stored in the computer readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 a process or multiple processes and / or boxes Figure 1 The function specified in one or more boxes.

[0050] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operational steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing the instructions executed on the computer or other programmable device for implementing the process. Figure 1 a process or multiple processes and / or boxes Figure 1 A step that specifies a function in one or more boxes.

[0051] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A closed-loop control method for a closed-loop control device of a distribution network, characterized in that: The distribution network closed-loop control device comprises: a series transformer, a parallel transformer, an inverter and a rectifier; The secondary side of the series transformer is connected in series between the first and second substations of the distribution network; the primary side of the shunt transformer is connected to the first substation of the distribution network; the secondary side of the shunt transformer is connected to the rectifier, the inverter and the primary side of the series transformer in sequence; The secondary side and primary side of the series transformer are isolated; the distribution network loop to which the series transformer is connected in series also includes at least one series circuit breaker; The steps include: Starting the inverter, collecting the voltage of the first substation area and the voltage of the second substation area of the distribution network; when the effective value of the difference between the voltage of the first substation area and the voltage of the second substation area is lower than the rated voltage of the secondary side of the series transformer, closing all series circuit breakers on the series circuit of the series transformer; Unlock the inverter AC output. If the first and second substations are interconnected through a series circuit breaker, the power flow will flow from the first substation to the second substation. The inverter controls the secondary current of the series transformer to gradually increase from its no-load excitation current, and the secondary current of the series transformer causes the power flow direction to flow from the first substation to the second substation. As the inverter controls the secondary current of the series transformer to increase to its rated value, or increases to the load current of the second station area, or the current increases to reduce the effective value of the difference between the first station area voltage and the second station area voltage to meet the loop closing condition, the current is maintained unchanged.

2. The closed-loop control method of the closed-loop control device of the distribution network according to claim 1, characterized in that: The DC side of the inverter is powered by a rectifier, and the AC side input of the rectifier is powered by a parallel transformer connected to the distribution network where the distribution network closing control device is located.

3. The closed-loop control method of the closed-loop control device of the distribution network according to claim 1, characterized in that: The secondary side of the series transformer is connected in parallel with a bypass switch.

4. The closed-loop control method of the closed-loop control device of the distribution network according to claim 1, characterized in that: The secondary side or primary side of the series transformer is connected in parallel with a thyristor bypass switch.

5. The closed-loop control method of the closed-loop control device of the distribution network according to claim 3, characterized in that: When the effective value of the difference between the first substation voltage and the second substation voltage meets the loop closing condition, the bypass switch is closed and the inverter stops outputting.

6. The closed-loop control method of the closed-loop control device of the distribution network according to claim 1, characterized in that: During the process of increasing the secondary current of the series transformer, the power flow of the first or second substation is monitored. If the power flow output direction of any substation is from the load to the power supply, the current increase is stopped.

7. The closed-loop control method of the closed-loop control device of the distribution network according to claim 1, characterized in that: If the effective value of the difference between the first section voltage and the second section voltage does not meet the loop closing condition when the increase of the secondary side current of the series transformer stops, the inverter gradually stops outputting.

8. The closed-loop control method of the closed-loop control device of the distribution network according to claim 1, characterized in that: After the inverter controls the secondary current of the series transformer to be reduced to 0, a series circuit breaker in a distribution network loop to which at least one series transformer is connected in series is disconnected.

9. A computer-readable storage medium storing one or more programs, characterized in that: The one or more programs include instructions that, when executed by a computing device, cause the computing device to perform any one of the methods according to claims 1 to 8.

10. A computing device, characterized in that include, One or more processors, a memory, and one or more programs, wherein the one or more programs are stored in the memory and configured to be executed by the one or more processors, the one or more programs comprising instructions for executing any one of the methods according to claims 1 to 8.

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