A method and device for shutting down a three-terminal hybrid DC transmission system without inter-station communication

Abstract

The present invention provides a method for shutting down a three-terminal hybrid direct current transmission system without inter-station communication, comprising the following steps: Step 1: Controlling the power of station 1 to reduce to a first power P1set of station 1; Step 2: Controlling the power of station 3 to reduce to the minimum power allowed by station 3 and then locking and isolating the station; Step 3: Controlling the power of station 1 to reduce to the minimum power allowed by station 1 and then locking and isolating the station; Step 4: Blocking and shutting down station 2. Through the above-described sequential steps, the present application achieves a smooth shutdown of converter stations at each end of the system without inter-station communication.

Description

Technical Field

[0001] The present invention belongs to the field of multi-terminal direct current (DC) power transmission, and in particular relates to a method and device for shutting down a three-terminal hybrid DC power transmission system without inter-station communication. Background Art

[0002] With the continuous advancement of power electronics technology, multi-terminal direct current (HVDC) transmission technology can achieve multi-source power supply and multi-point power reception, providing a more flexible transmission method. As a new generation of HVDC transmission technology, flexible HVDC technology does not suffer from commutation failure, can provide dynamic reactive power, and can improve voltage stability. It is one of the effective means to improve the safety and stability of multi-DC centralized feed-in power grids. Therefore, hybrid HVDC transmission technology, which uses conventional HVDC technology based on line commutated converters (LCCs) at the sending end and flexible HVDC based on multiple voltage source converters (VSCs) at the receiving end, has attracted increasing attention due to its advantages of no commutation failure, relatively low overall losses, and relatively low cost.

[0003] Because LCC converters' unidirectional power transmission is subject to minimum operating current limitations, hybrid LCC-VSC DC transmission systems lack the control flexibility of pure VSC systems. They require coordinated control via communication between multiple terminals to ensure that each terminal meets its power constraints. In the event of an inter-station communication failure, sequential control operations are required to shut down the system. During this process, voltage and current must be maintained within the designed range. Improper control can lead to system loss of control.

[0004] After an inter-station communication failure occurs, the system's operating mode can only be manually confirmed by the operator, so the operating steps should be as reliable and simple as possible. Summary of the Invention

[0005] The purpose of the present invention is to provide a method and device for shutting down a three-terminal hybrid DC transmission system without inter-station communication, which can realize the smooth shutdown of converter stations at each end of the system without inter-station communication through a certain sequence of operating steps.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is:

[0007] On the one hand, the present application proposes a method for shutting down a three-terminal hybrid DC transmission system without inter-station communication. The three-terminal hybrid DC transmission system includes an LCC converter station, denoted as station 1, and two VSC converter stations, denoted as stations 2 and 3, respectively. Station 1 is a power control station, station 2 is a voltage control station, and station 3 is a power control station. The shutdown method includes the following steps:

[0008] Step 1: Control the power of station 1 to reduce to the first power P1set of station 1, where P1set must satisfy P1set≤max(P2NORM, P3NORM) and P1set≥P1NROM-min(P2NORM, P3NORM), where P1NORM, P2NORM, and P3NORM are the rated capacities of stations 1, 2, and 3, respectively.

[0009] Step 2: After the power of control station 3 is reduced to the minimum power allowed by station 3, the station is locked and isolated;

[0010] Step 3: After the power of control station 1 drops to the minimum power allowed by station 1, the station is locked and isolated;

[0011] Step 4: Lock and shut down station 2.

[0012] Furthermore, the rated capacities of the three converter stations satisfy the following relationship: P1NORM≥P2NORM≥P3NORM.

[0013] Furthermore, in step 1, the real-time active power of the three converter stations is greater than or equal to the minimum power of the station, and the vector sum of the active power of the three stations is zero.

[0014] Furthermore, the stations 1 and 3 control active power, and the station 2 controls the DC voltage to maintain power balance of the three-terminal converter station.

[0015] On the other hand, the present application proposes a shutdown device for a three-terminal hybrid DC transmission system without inter-station communication, wherein the three-terminal hybrid DC transmission system includes an LCC converter station, denoted as station 1, and two VSC converter stations, denoted as stations 2 and 3, respectively, wherein station 1 is a power control station, station 2 is a voltage control station, and station 3 is a power control station, and the device includes: an LCC power reduction control unit, a VSC power station control unit, an LCC locking control unit, and a VSC voltage station control unit, which are connected in sequence;

[0016] The LCC power reduction control unit is used to control the power of station 1 to be reduced to the first power P1set of station 1, wherein P1set needs to satisfy P1set≤max(P2NORM, P3NORM) and P1set≥P1NROM-min(P2NORM, P3NORM), where P1NORM, P2NORM, and P3NORM are the rated capacities of station 1, station 2, and station 3 respectively;

[0017] The VSC power station control unit is used to control the power of station 3 to drop to the minimum power allowed by station 3 and then lock and isolate the station;

[0018] The LCC blocking control unit is used to control the power of station 1 to drop to the minimum power allowed by station 1 after station 3 is blocked and isolated, and then block and isolate the station;

[0019] The VSC voltage station control unit is used to perform a locking and shutdown operation on station 2 after both stations 1 and 2 have completed locking and isolation.

[0020] Furthermore, the rated capacities of the three converter stations satisfy the following relationship: P1NORM≥P2NORM≥P3NORM.

[0021] Furthermore, the LCC power reduction control unit ensures that the real-time active powers of the three converter stations are all greater than or equal to the minimum power of the station, and the vector sum of the active powers of the three stations is zero.

[0022] Furthermore, the stations 1 and 3 control active power, and the station 2 controls the DC voltage to maintain power balance of the three-terminal converter station.

[0023] The beneficial effect of the present application is that by adopting the cloud-stopping scheme of the present application, the power balance of the three-terminal converter station can be maintained throughout the entire process, the DC voltage can also be kept stable, and finally the shutdown operation of the three-terminal hybrid DC transmission system without inter-station communication can be successfully completed. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a flow chart of a method for shutting down a three-terminal hybrid direct current transmission system without inter-station communication according to an embodiment of the present application.

[0025] Figure 2 It is a typical system topology of a three-terminal hybrid DC transmission system.

[0026] Figure 3 This is a schematic diagram of a three-terminal hybrid DC transmission system without inter-station communication shutdown device in an embodiment of the present application. DETAILED DESCRIPTION

[0027] The technical solution of the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0028] like Figure 1 The flowchart of a method for shutting down a three-terminal hybrid DC transmission system without inter-station communication is shown in an embodiment of the present application. The three-terminal hybrid DC transmission system includes an LCC converter station, designated as Station 1, and two VSC converter stations, designated as Station 2 and Station 3. Station 1 is a power control station, Station 2 is a voltage control station, and Station 3 is a power control station. The shutdown method includes the following steps:

[0029] S100, control the power of station 1 to be reduced to the first power P1set of station 1, where P1set must satisfy P1set≤max(P2NORM, P3NORM) and P1set≥P1NROM-min(P2NORM, P3NORM), where P1NORM, P2NORM, and P3NORM are the rated capacities of station 1, station 2, and station 3, respectively;

[0030] S200, the power of control station 3 is reduced to the minimum power allowed by station 3 and then the station is locked and isolated;

[0031] S300, controlling the power of station 1 to drop to the minimum power allowed by station 1 and then locking and isolating the station;

[0032] S400: Lock and shut down station 2.

[0033] In the above embodiment, the stations 1 and 3 control the active power, and the station 2 controls the DC voltage to maintain the power balance of the three-terminal converter station.

[0034] In step S100, the real-time active power of the three converter stations is greater than or equal to the minimum power of the station, and the vector sum of the active power of the three stations is zero.

[0035] In an optional embodiment, the rated capacities of the three converter stations satisfy the following relationship: P1NORM≥P2NORM≥P3NORM.

[0036] The following combination Figure 2 A typical three-terminal hybrid DC transmission system is shown, and a specific embodiment is described. In this embodiment, the three-terminal hybrid DC transmission system includes three converter stations, S1, S2, and S3. S1 is an LCC converter station, and S2 and S3 are VSC converter stations. The rated capacities of S1, S2, and S3 are P1NORM = 8000MW, P2NORM = 5000MW, and P3NORM = 3000MW, respectively. S1 and S3 control DC power, and S2 controls DC voltage. Power flowing from the converter station to the DC side is defined as positive, and power flowing from the DC side to the converter station is defined as negative. When the system is operating at full power, P1 = 8000MW (positive direction), P2 = 5000MW (negative direction), and P3 = 3000MW (negative direction). The minimum power of S1, S2, and S3 is P1min = 800MW, P2min = 500MW, and P3min = 300MW, respectively.

[0037] When an inter-station communication failure occurs, you can perform a shutdown operation by following the steps below:

[0038] Step 1: Control the power of S1 to reduce to the first power P1set of station 1. P1set≤max(P2NORM, P3NORM) and P1set≥P1NROM-min(P2NORM, P3NORM) must be satisfied. Calculation shows that max(P2NORM, P3NORM)=5000MW and min(P2NORM, P3NORM)=3000MW, so 3000MW≤P1set≤5000MW. In this embodiment, P1set=4000MW is selected. After execution, the powers of the three stations are: P1=4000MW, positive direction, P2=1000MW, negative direction, and P3=3000MW, negative direction.

[0039] Step 2: After the power of S3 is reduced to the minimum power, the station is locked and isolated. The power of the three stations becomes: P1 = 4000MW, direction is positive, P2 = 4000MW, direction is negative;

[0040] Step 3: After the power of S1 is reduced to the minimum power, the station is locked and isolated;

[0041] Step 4: Lock and shut down S2.

[0042] During the entire process, the power balance of the three-terminal converter station can be maintained, and the DC voltage can be kept stable, ultimately successfully completing the shutdown process of the three-terminal hybrid DC transmission system without inter-station communication.

[0043] The embodiment of the present application provides a three-terminal hybrid DC transmission system without inter-station communication shutdown device. Figure 3 As shown, the shutdown device 1000 includes: an LCC power reduction control unit 1001, a VSC power station control unit 1002, an LCC locking control unit 1003 and a VSC voltage station control unit 1004 connected in sequence;

[0044] The LCC power reduction control unit 1001 is used to control the power of station 1 to be reduced to the first power P1set of station 1, where P1set needs to satisfy P1set≤max(P2NORM, P3NORM) and P1set≥P1NROM-min(P2NORM, P3NORM), where P1NORM, P2NORM, and P3NORM are the rated capacities of station 1, station 2, and station 3 respectively;

[0045] The VSC power station control unit 1002 is configured to control the power of station 3 to decrease to the minimum power allowed by station 3 and then lock and isolate the station;

[0046] The LCC blocking control unit 1003 is configured to control the power of station 1 to drop to the minimum power allowed by station 1 after blocking and isolating station 3, and then block and isolate the station;

[0047] The VSC voltage station control unit 1004 is used to perform a locking and shutting down operation on station 2 after both stations 1 and 2 have completed locking and isolation.

[0048] Among them, the rated capacities of the three converter stations satisfy the following relationship: P1NORM≥P2NORM≥P3NORM.

[0049] In the LCC power reduction control unit 1001, the real-time powers of the three converter stations are all greater than or equal to the minimum power of the station, and the power vector sum of the three stations is zero.

[0050] The stations 1 and 3 control the active power, and the station 2 controls the DC voltage to maintain the power balance of the three-terminal converter station.

[0051] The above embodiments are only for illustrating the technical idea of ​​the present invention and cannot be used to limit the protection scope of the present invention. Any changes made on the basis of the technical solution in accordance with the technical idea proposed by the present invention shall fall within the protection scope of the present invention.

Claims

1. A method for shutting down a three-terminal hybrid DC transmission system without inter-station communication, wherein the three-terminal hybrid DC transmission system includes an LCC converter station, denoted as station 1, and two VSC converter stations, denoted as stations 2 and 3, respectively. Station 1 is a power control station, station 2 is a voltage control station, and station 3 is a power control station. The method is characterized in that: The following steps are included: Step 1: Control the power of station 1 to reduce to the first power P1set of station 1, where P1set must satisfy P1set≤max(P2NORM, P3NORM) and P1set≥P1NROM-min(P2NORM, P3NORM), where P1NORM, P2NORM, and P3NORM are the rated capacities of stations 1, 2, and 3, respectively. Step 2: After the power of control station 3 is reduced to the minimum power allowed by station 3, the station is locked and isolated; Step 3: After the power of control station 1 drops to the minimum power allowed by station 1, the station is locked and isolated; Step 4: Lock and shut down station 2.

2. The method for shutting down a three-terminal hybrid HVDC power transmission system without inter-station communication according to claim 1, wherein: The rated capacities of the three converter stations satisfy the following relationship: P1NORM ≥ P2NORM ≥ P3NORM.

3. The method for shutting down a three-terminal hybrid HVDC power transmission system without inter-station communication according to claim 1, wherein: In step 1, the real-time active power of the three converter stations is greater than or equal to the minimum power of the station, and the vector sum of the active power of the three stations is zero.

4. The method for shutting down a three-terminal hybrid HVDC power transmission system without inter-station communication according to claim 1, wherein: The stations 1 and 3 control the active power, and the station 2 controls the DC voltage to maintain the power balance of the three-terminal converter station.

5. A shutdown device for a three-terminal hybrid DC transmission system without inter-station communication, the three-terminal hybrid DC transmission system comprising an LCC converter station, designated as station 1, and two VSC converter stations, designated as stations 2 and 3, wherein station 1 is a power control station, station 2 is a voltage control station, and station 3 is a power control station, characterized in that: The device comprises: an LCC power reduction control unit, a VSC power station control unit, an LCC locking control unit and a VSC voltage station control unit connected in sequence; The LCC power reduction control unit is used to control the power of station 1 to be reduced to the first power P1set of station 1, wherein P1set needs to satisfy P1set≤max(P2NORM, P3NORM) and P1set≥P1NROM-min(P2NORM, P3NORM), where P1NORM, P2NORM, and P3NORM are the rated capacities of station 1, station 2, and station 3 respectively; The VSC power station control unit is used to control the power of station 3 to drop to the minimum power allowed by station 3 and then lock and isolate the station; The LCC blocking control unit is used to control the power of station 1 to drop to the minimum power allowed by station 1 after station 3 is blocked and isolated, and then block and isolate the station; The VSC voltage station control unit is used to perform a locking and shutdown operation on station 2 after both stations 1 and 2 have completed locking and isolation.

6. The shutdown device for a three-terminal hybrid DC power transmission system without inter-station communication according to claim 5, characterized in that: The rated capacities of the three converter stations satisfy the following relationship: P1NORM ≥ P2NORM ≥ P3NORM.

7. The shutdown device for a three-terminal hybrid DC power transmission system without inter-station communication according to claim 5, characterized in that: The LCC power reduction control unit ensures that the real-time active power of the three converter stations is greater than or equal to the minimum power of the station, and the vector sum of the active power of the three stations is zero.

8. The shutdown device for a three-terminal hybrid DC power transmission system without inter-station communication according to claim 5, characterized in that: The stations 1 and 3 control the active power, and the station 2 controls the DC voltage to maintain the power balance of the three-terminal converter station.

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