LCC-HVDC system adaptive line fault recovery method using DC source injection

Abstract

The invention relates to an LCC-HVDC system self-adaptive line fault recovery method using direct current source injection, which comprises the following steps: firstly, after a direct current line protection device detects a line fault, a control system executes a phase shift instruction and line deionization, and after a line deionization stage is completed, a direct current voltage source is injected to the valve side of a smoothing reactor at a rectification side; the resistance value of the line side of the rectification side smoothing reactor is calculated by measuring the direct current component of the voltage and current of the line side of the rectification side smoothing reactor. And the type of the fault and whether the system executes a restart command can be judged according to the resistance value. According to the method, only rectification side data is utilized, opposite side converter station data is not needed, the action speed is high, the requirement for the device sampling rate is low, hardware implementation is easy, and the good anti-transition resistance capability is achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of relay protection in power systems, and particularly to an adaptive line restoration method for an LCC-HVDC system using DC source injection. Background Art

[0002] With the large-scale development of wind energy and photovoltaic power generation in desert areas and deep-sea offshore wind farms in China, driven by the spatial distribution of energy production and consumption, the demand for centralized energy aggregation and long-distance transmission is increasing day by day. LCC is the most commonly used long-distance high-voltage DC transmission technology globally. It has several advantages, including low investment cost, minimum transmission loss, high power capacity, and strong fault handling capabilities, making it a key solution for modern power systems.

[0003] Currently, many protection methods for identifying DC line faults have been proposed, with good accuracy and high reliability. However, in practical engineering applications, it is difficult to distinguish the fault types of DC lines after the relay determines that the fault is a DC line fault. Therefore, once the fault is identified as a DC line fault, it is directly regarded as a transient fault, and the DC line fault recovery sequence (DFRS) is executed to achieve a rapid system restart. This recovery process usually includes three stages: the phase-shifting stage, the deionization stage, and the restart stage. In practical engineering applications, the blindness of DFRS may lead to unnecessary system locking and have a negative impact on system stability. Therefore, an adaptive line restoration method for the LCC-HVDC system is urgently needed. Summary of the Invention

[0004] Based on this, in view of the above technical problems, the present invention proposes an adaptive line restoration method for an LCC-HVDC system using DC source injection, which has a simple and reliable principle and strong resistance to transition resistance. The present invention uses the injection method and the method of measuring the resistance value on the rectifier side to determine the nature of the fault, has a low requirement for the sampling rate of the device, does not require data from the opposite converter station, has a fast action speed, and has strong resistance to transition resistance.

[0005] An adaptive line fault restoration method for an LCC-HVDC system using DC source injection, the method comprising:

[0006] After the DC line protection device detects a line fault, it sends the fault information to the control system, and the control system executes a phase-shifting instruction and line deionization;

[0007] After the line deionization is completed, a DC voltage source is injected on the valve side of the smoothing reactor on the rectifier side;

[0008] Calculate the resistance value here by measuring the DC components of the voltage and current on the line side of the smoothing reactor on the rectifier side;

[0009] Compare the magnitude of the resistance value with the threshold value to determine the type of fault and whether the system executes the restart command.

[0010] Furthermore, the amplitude of the injected DC voltage source is selected as 0.1 p.u.

[0011] Furthermore, the calculation of the resistance value by measuring the DC components of the voltage and current on the line side of the smoothing reactor on the rectifier side

[0012] R m =U m(DC) / I m(DC)

[0013] In the formula, m is the measurement point on the line side of the smoothing reactor of the rectifier station; U m(DC) is the DC component of the voltage on the line side of the smoothing reactor on the rectifier side; I m(DC) is the DC component of the current on the line side of the smoothing reactor on the rectifier side; R m is the calculated resistance value on the line side of the smoothing reactor on the rectifier side.

[0014] Furthermore, the comparison of the magnitude of the resistance value with the threshold value can determine the type of fault and whether the system executes the restart command, including:

[0015] Judge whether the calculated R m on the line side of the smoothing reactor on the rectifier side is greater than the threshold value; if so, determine that the line fault is a transient fault, and the system executes the restart instruction; if not, continue to inject the DC voltage source signal, and continuously compare the measured and calculated R m with the threshold value. If the value of R m is continuously less than the threshold value within a period of time, determine that the line fault is a permanent fault, and the system executes the blocking instruction. Brief Description of the Drawings

[0016] Figure 1 is a flowchart of the adaptive line restoration method for the LCC-HVDC system using DC source injection in an embodiment;

[0017] Figure 2 is a schematic diagram of the system for implementing the adaptive line restoration method for the ±500 kV HVDC transmission line;

[0018] Figure 3 is a flowchart for comparing and determining the resistance value calculated on the line side of the smoothing reactor on the rectifier side;

[0019] Figure 4It is a schematic diagram of the system simulation result when a permanent fault occurs in the DC transmission line with high-resistance grounding.

[0020] In the figure: 1. Converter transformer; 2. Converter; 3. DC filter bank configured at both ends of the DC transmission line; 4. Grounding electrode lead and grounding electrode of the DC transmission system; 5. DC transmission line; 6. Smoothing reactor. Specific implementation mode

[0021] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0022] As Figure 1 shown in Figure 2 In one embodiment, an adaptive line restoration method for an LCC-HVDC system using DC source injection includes the following steps:

[0023] Step S110: After the high-voltage DC transmission line protection device detects line fault information when a fault occurs in the line, it quickly sends the line fault information to the pole control system of the system. After receiving the line fault information, the pole control system executes a phase shift instruction, and the system enters the phase shift stage. In this stage, the control protection system quickly shifts the firing angle of the rectifier side to 120°. The valve control system maintains the normal triggering of the pulses, causing the rectifier station to operate in an inverter mode. At this time, the energy stored in the DC system is transmitted to the AC system through the converters at both ends, resulting in a rapid decrease in the DC current. The firing angle of the inverter side quickly shifts to the limit value of 95°. When the DC line current drops close to zero, the pole control system shifts the firing angle of the rectifier side to the fully closed state of 160°; since the maximum value selection is used on the inverter side, in this stage, the extinction angle control is selected, and the firing angle is quickly shifted to the limit value. When the current is very small, the current controller is selected, and the angle is moved to 120°. The DC line enters the preset deionization stage. In this stage, the firing angle of the rectifier side is 160°, and the firing angle of the inverter side is 120°; the DC currents on both sides are close to zero, and the DC voltages on both sides are at a very low level. The deionization time is generally set to 100 - 500 ms, and the operator can determine the length of this period according to the physical characteristics of the line to ensure that the insulation of the line can recover to the normal level when the line fault is restarted.

[0024] Step S120: Inject a DC voltage source with an amplitude of 0.1 p.u. on the valve side of the smoothing reactor at the rectifier side of the HVDC transmission system. The reason for selecting a DC voltage source with an amplitude of 0.1 p.u. is as follows: 1) Generally, the lower limit of general electronic current and voltage transformers is greater than 0.05 p.u., and the amplitude of the injected signal should be greater than the lower limit range of measurement. 2) To facilitate injection and reduce the secondary impact on the system and avoid affecting the line insulation recovery, the selected amplitude should be small. The valve side of the smoothing reactor at the rectifier side is namely Figure 2 point a in

[0025] Step S130: Collect the real-time voltage value and real-time current value on the line side of the smoothing reactor at the rectifier side of the HVDC transmission system; use a filter to extract the DC component of the real-time voltage and the DC component of the real-time current. A voltage divider and a shunt are installed on the line side of the smoothing reactor at the rectifier side, which can measure the real-time voltage and real-time current signals at this location. The selected filter is a Chebyshev filter. The line side of the smoothing reactor at the rectifier side is namely Figure 2 point m in

[0026] Step S140: According to the formula R m = U m(DC) / I m(DC) , the resistance value on the line side of the smoothing reactor at the rectifier side of the HVDC transmission system can be calculated.

[0027] Step S150: Compare and determine the resistance value on the line side of the smoothing reactor at the rectifier side of the HVDC transmission system with the threshold value to realize the judgment of the fault type and whether to execute the restart instruction. Specifically, refer to Figure 3 , determine whether the resistance value on the line side of the smoothing reactor at the rectifier side of the HVDC transmission system is greater than the threshold value. If it is, it is determined that the line fault type is a transient fault, and the pole control system can execute the restart instruction; if not, continue to collect the voltage and current information on the line side of the smoothing reactor at the rectifier side of the HVDC transmission system, calculate the resistance value on the line side of the smoothing reactor at the rectifier side of the HVDC transmission system and then compare it with the threshold value; when the injection time ends and the resistance value on the line side of the smoothing reactor at the rectifier side of the HVDC transmission system is still less than the threshold value, it is determined that the DC line fault is a permanent fault, and the pole control system executes the blocking instruction.

[0028] The above LCC-HVDC system adaptive line restoration method using DC source injection judges the fault type of the HVDC transmission line by using single-ended electrical quantities, does not require data from the opposite converter station, has good speed, a sampling rate of 2 kHz can meet the requirements, has low requirements for the device sampling rate, is easy to implement in hardware, and has good ability to resist transition resistance.

[0029] Such as Figure 4As shown in the figure, through the simulation analysis of the protection device in this embodiment when a permanent fault of high-resistance grounding occurs in the DC transmission line, it can be known that the resistance value on the line side of the smoothing reactor at the rectifier side of the HVDC system is always lower than the threshold value. Therefore, according to step S150, it is determined that the DC line fault is a permanent fault.

[0030] The following table gives the simulation results of the adaptive line restoration method of the ±500kV LCC-HVDC system using DC source injection involved in this embodiment when a permanent fault occurs with different transition resistances at different positions on the line.

[0031]

[0032] It can be seen from the table that the proposed adaptive line restoration method of the LCC-HVDC system using DC source injection in the present invention can accurately operate when a permanent fault occurs with different transition resistances at different fault positions, avoiding a large impact on the secondary side due to blind restart of the system, and having good reliability. The proposed solution in the present invention has better ability to withstand transition resistance, with a transition resistance of up to 500Ω. It has low requirements for the sampling rate of the device, is easy to implement in hardware, can complete fault type identification without the data of the opposite converter station, and has stronger quick-acting performance.

[0033] The above-described embodiments only represent several implementation manners of the present invention, and the description thereof is relatively specific and detailed, but it should not be construed as a limitation on the scope of the patent of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the appended claims.

Claims

1. A method for adaptive line fault recovery of LCC-HVDC system using DC source injection, characterized in that: The method comprises: After the DC line protection device detects a line fault, it sends the fault information to the control system, which executes the phase shift command and line de-ionization; After the line is de-ionized, a DC voltage source is injected into the valve side of the smoothing reactor on the rectifier side; The resistance value here is calculated by measuring the DC component of the voltage and current on the line side of the rectifier-side smoothing reactor; The resistance value is compared with the threshold value to determine the type of fault and whether the system executes a restart command.

2. The adaptive line fault recovery method of LCC-HVDC system using DC source injection according to claim 1, characterized in that: The amplitude of the DC voltage source is selected to be 0.1 pu; For the electronic current and voltage transformer, the amplitude of the injected signal is a DC voltage source of 0.1 pu.

3. The adaptive line fault recovery method of LCC-HVDC system using DC source injection according to claim 1, characterized in that: The resistance value R is calculated by measuring the DC component of the voltage and current on the line side of the rectifier side smoothing reactor. m , whose expression is: R m =U m(DC) / I m(DC) , Where m is the measurement point on the line side of the smoothing reactor of the rectifier station; U m(DC) is the measured DC component of the line-side voltage of the rectifier-side smoothing reactor; I m(DC) is the measured DC component of the line-side current of the rectifier-side smoothing reactor; R m The resistance value calculated for the line side of the rectifier-side smoothing reactor.

4. The adaptive line fault recovery method of LCC-HVDC system using DC source injection according to claim 1, characterized in that: The comparison between the resistance value and the threshold value can determine the type of fault and whether the system executes a restart command, which specifically includes: Determine the R value of the smoothing reactor circuit measured and calculated on the rectifier side m Is it greater than the threshold value? If so, the line fault is determined to be a transient fault, and the system executes the restart instruction; if not, the DC voltage source signal is continuously injected, and the measured R m Constantly compare with the threshold value. If within a period of time, R m If the value of is continuously less than the threshold value, the line fault is determined to be a permanent fault and the system executes the locking instruction.

Images