Turn-off control method and system for controllable turn-off current source type converter
By judging the arc extinguishing area and zero-sequence voltage conditions during the phase commutation process in a controllable shutdown current source converter, it predicts that the phase commutation failure will occur and the shutdown is controlled in advance, which solves the problem of difficult to grasp the shutdown timing in the prior art, and improves safety and current transmission efficiency.
Patent Information
- Application Number
- CN202411992834.5
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-12-31
- Publication Date
- 2025-04-25
AI Technical Summary
The prior art is difficult to effectively control the shutdown timing of the controllable shutdown current source converter, which can easily lead to a reduction in current transmission efficiency or failure in phase commutation, which poses safety hazards.
By determining whether the arc extinguishing area during the phase commutation process is smaller than the minimum arc extinguishing area of normal phase commutation, and combining with the zero-sequence voltage condition, it is predicted whether the phase commutation failure is about to occur, and the inverter is turned off in advance to avoid phase commutation failure.
It realizes that when predicting that the commutation failure is about to occur, the inverter is turned off in advance, avoiding the commutation failure and current and voltage shocks, and improving safety and current transmission efficiency.
Smart Images
Figure CN119891338A_ABST
Abstract
Description
Technical Field
[0001] The invention relates to a controllable shutdown current source converter shutdown control method and system, belonging to the technical field of direct current transmission. Background Art
[0002] At present, HVDC transmission is the main form of large-capacity and long-distance power transmission in my country. Based on the different core power devices used in the converter, HVDC transmission technology is divided into current source converter HVDC transmission (LCC-HVDC) and voltage source converter HVDC transmission (VSC-HVDC). Traditional LCC-HVDC projects use line commutated converters (LCCs) based on thyristors, which have the advantages of low cost, low loss, high reliability, and mature technology. They play an important role in large-capacity long-distance power transmission, asynchronous grid interconnection, and submarine cable power transmission. However, there is a risk of commutation failure on the inverter side of LCC, and a large number of reactive compensation and filtering devices need to be installed, and it is not suitable for power transmission to weak systems or passive networks. The DC transmission system using voltage source converters (VSCs) based on fully controlled devices has the advantages of small filter capacity requirements, flexible control, no commutation failure, and can transmit power to passive networks. It has been increasingly widely used in recent years. However, compared with LCC, VSC has disadvantages such as large operating losses, high manufacturing costs, and small capacity. When used for remote distributed renewable energy transmission, it has the problem of large inverter platform, large footprint and large weight.
[0003] IGCT has lower on-state voltage and loss (30% to 50% lower than IGBT loss), and has significant advantages such as higher voltage level and current carrying capacity, greater fault surge current carrying capacity, more reliable failure short-circuit mode, low cost and controllable manufacturing process. In view of the shortcomings of LCC and VSC, the controllable off-state current source converter based on IGCT devices can solve the passive starting problem of the current LCC DC technology and can also effectively suppress commutation failure.
[0004] However, the timing of shutting down of most existing controlled controllable shutdown current source converters is set according to actual operating conditions or experience, and the timing of shutting down of the controlled controllable shutdown current source converter is difficult to grasp. If the controlled controllable shutdown current source converter is shut down too early, it may cause the current transmission efficiency to decrease and increase the risk of commutation failure; and if the controlled controllable shutdown current source converter is shut down too late, for example, the controlled shutdown current source converter is shut down only after the commutation failure has occurred, it will still cause excessive current and voltage shocks, and therefore there are safety hazards. Summary of the invention
[0005] The purpose of the present invention is to provide a controllable shutdown current source converter shutdown control method and system to solve the current controllable shutdown current source converter shutdown timing is difficult to grasp the problem of potential safety hazards.
[0006] In order to solve the above technical problems, the present invention provides a controllable shutdown current source converter shutdown control method. In the commutation process of the controllable shutdown current source converter at the receiving end, when at least one set condition is met, the single valve that is expected to be shut down in the current commutation process of the converter is controlled to be shut down;
[0007] The setting condition includes a first setting condition; the first setting condition is: the arc extinguishing area of the current commutation process is smaller than the minimum arc extinguishing area of the normal commutation of the converter;
[0008] The arc extinguishing area of the current commutation process is determined based on the integral of the product of the commutation voltage and the commutation current in the arc extinguishing area over the angle corresponding to the time; the minimum arc extinguishing area of the normal commutation of the converter is determined based on the ratio of the commutation angle to the sine value of the trigger angle in the current commutation process plus the product of the ratio and the cosine value of the trigger angle, minus twice the product of the rated DC current of the converter and the rated relative inductive voltage drop.
[0009] Furthermore, the setting condition also includes a second setting condition; the second setting condition is: the zero-sequence voltage of the AC system at the receiving end is greater than the zero-sequence voltage setting value.
[0010] Furthermore, the zero-sequence voltage setting value is greater than or equal to 0.02pu.
[0011] Beneficial effect: The present invention provides a new controllable shutdown current source converter shutdown control method, which determines whether the integral of the product of the commutation voltage and the commutation current in the arc extinguishing area at the time corresponding angle (i.e., the arc extinguishing area) during the commutation process of the controllable shutdown current source converter at the receiving end is less than the minimum arc extinguishing area of the converter in normal commutation (i.e., the ratio of the commutation angle to the sine value of the trigger angle plus the product of the ratio and the cosine value of the trigger angle minus the product of the rated DC current of the converter and the rated relative inductive voltage drop). The value obtained by doubling the product of the two products) is used to predict whether a commutation failure may occur. When it is predicted that a commutation failure may occur in the current commutation process, the valve that is expected to be shut down in the current commutation process of the converter is controlled in advance to be shut down; considering that in the commutation process, when the commutation current passes through zero, sufficient arc extinguishing time is required for the power electronic device to restore its blocking ability, otherwise a commutation failure may occur. If the arc extinguishing area is less than the minimum value of the arc extinguishing area of the converter in the current commutation process, it means that the power electronic device has time to restore its blocking ability. The arc extinguishing time of the blocking capacity is insufficient, and a commutation failure may be about to occur. At this time, the corresponding single valve of the controllable shut-off current source converter (that is, the single valve that is expected to be shut down in the current commutation process) is controlled to be shut down in advance to avoid the occurrence of commutation failure. It can be seen that this method can control the single valve that is expected to be shut down in the current commutation process of the controllable shut-off current source converter to be shut down in advance when it is predicted that a commutation failure may occur, thereby controlling the current interruption and avoiding the timing of controlling the single valve that is about to be shut down of the controllable shut-off current source converter to be shut down too late (for example, at After a commutation failure has occurred, controlling the single valve of the controllable shut-off current source converter to be shut down to be shut down will still cause excessive current and voltage shocks due to the commutation failure, or controlling the single valve of the controllable shut-off current source converter to be shut down to be shut down too early, resulting in reduced current transmission efficiency and increased risk of commutation failure. Therefore, a more appropriate time can be selected to control the single valve of the controllable shut-off current source converter that is expected to be shut down in the current commutation process to avoid commutation failure and provide higher safety.
[0012] The present invention also provides a controllable shutdown current source converter shutdown control system, comprising a processor, wherein the processor is used to execute computer program instructions to implement the steps of the above-mentioned controllable shutdown current source converter shutdown control method.
[0013] The controllable shutdown current source converter shutdown control system can achieve the same beneficial effects as the above-mentioned controllable shutdown current source converter shutdown control method. BRIEF DESCRIPTION OF THE DRAWINGS
[0014] Figure 1 It is a schematic diagram of the electrical topology structure of a controllable shutdown current source type converter in an embodiment of a controllable shutdown current source type converter shutdown control method of the present invention;
[0015] Figure 2 is a commutation equivalent circuit diagram in an embodiment of a controllable shutdown current source converter shutdown control method of the present invention;
[0016] Figure 3 It is a logic block diagram of a controllable shutdown current source type converter shutdown control method in an embodiment of the controllable shutdown current source type converter shutdown control method of the present invention;
[0017] Figure 4 It is an example diagram of the arc extinction area of the commutation process in the embodiment of the controllable shutdown current source converter shutdown control method of the present invention. DETAILED DESCRIPTION
[0018] The specific implementation of the present invention will be further described below in conjunction with the accompanying drawings.
[0019] Embodiment of a controllable shutdown current source converter shutdown control method
[0020] The present embodiment provides a technical solution for a controllable shutdown current source converter shutdown control method. The method predicts whether a commutation failure is about to occur by judging whether, during the commutation process of the controllable shutdown current source converter at the receiving end, the arc extinguishing area of the current commutation process is less than the set condition of the minimum arc extinguishing area of the normal commutation of the converter. When it is predicted that the commutation process is about to fail, the single valve that is expected to be shut down in the current commutation process of the converter is controlled to be shut down; a more appropriate time can be selected to control the single valve that is expected to be shut down in the current commutation process of the converter to be shut down before the commutation failure occurs, thereby avoiding the occurrence of commutation failure and providing higher safety.
[0021] The method specifically comprises: in a commutation process of a controllable shut-off current source converter at a receiving end, when at least one set condition is met, controlling a single valve that is expected to be shut down in the current commutation process of the converter to be shut down;
[0022] The setting conditions include a first setting condition; the first setting condition is: the arc extinguishing area of the current commutation process is less than the minimum arc extinguishing area of the normal commutation of the converter;
[0023] The arc extinguishing area of the current commutation process is determined based on the integral of the product of the commutation voltage and the commutation current in the arc extinguishing area over the angle corresponding to the time; the minimum arc extinguishing area of the normal commutation of the converter is determined based on the ratio of the commutation angle to the sine value of the trigger angle in the current commutation process plus the product of the ratio of the commutation angle to the sine value of the trigger angle in the current commutation process and the cosine value of the trigger angle, minus twice the product of the rated DC current of the converter and the rated relative inductive voltage drop.
[0024] The method determines whether there is enough arc extinguishing area in the current commutation process to enable the power electronic device to restore its blocking capability by judging whether the arc extinguishing area in the current commutation process is smaller than the minimum arc extinguishing area for normal commutation of the converter, thereby judging whether a commutation failure is about to occur. When it is judged that a commutation failure is about to occur, the method actively controls the single valve that is expected to be shut down in the current commutation process of the converter to shut down. The method can select a more appropriate time (i.e., when it is judged that a commutation failure may be about to occur) to control the single valve that is expected to be shut down in the current commutation process of the controllable shutdown current source converter to shut down, thereby avoiding commutation failure and improving safety.
[0025] The existing converter valves are mainly divided into voltage source converter valves and current source converter valves. Since the voltage source converter valve does not have the problem of commutation failure, this method is a shutdown control method for a controllable shutdown current source converter. The electrical topology structure principle diagram of the controllable shutdown current source converter in this embodiment is as follows: Figure 1 As shown in FIG. 1 , the electrical topology of the controllable shutdown current source converter includes six single valves V1 to V6, a DC filter reactor L d , AC equivalent inductance per phase L r And the equivalent potential u of the three-phase AC of A, B, and C a 、u b 、u c , Figure 1 middleu d Refers to DC voltage, I d Refers to direct current (direct current can also be expressed as i d ).
[0026] The commutation equivalent circuit diagram in this embodiment is as follows Figure 2 As shown in the figure, the energy conversion process during the phase change from V5 valve to V1 valve is actually to convert the V5 valve phase change inductor L r The energy stored in the valve is transferred to the inductor L of the V1 valve. r According to the circuit principle, the current through the inductor is continuous and will not change suddenly. Therefore, a certain amount of time must pass during the phase change from the V5 valve to the V1 valve. This time is called the phase change time, which is converted into an electrical angle as the phase change angle μ. During the phase change time, the current of the V1 valve changes from zero to a DC current i d , the current of valve V5 is from i d becomes zero, i d is the commutation current.
[0027] This embodiment takes the commutation process from the V5 valve to the V1 valve as an example to specifically illustrate the controllable shutdown current source type converter shutdown control method:
[0028] The logic block diagram of the controllable shutdown current source converter shutdown control method in this embodiment is as follows Figure 3As shown, in the commutation process of the controllable shutdown current source converter at the receiving end, when at least one set condition is met, the single valve that is expected to be shut down in the current commutation process of the converter is controlled to be shut down;
[0029] The setting conditions include a first setting condition (such as Figure 3 As shown, the first setting condition is also called the arc extinction area criterion); the first setting condition is: the arc extinction area of the current commutation process is less than the minimum arc extinction area of the normal commutation of the converter;
[0030] The arc extinction area of the current commutation process is determined according to the integral of the product of the commutation voltage and the commutation current in the arc extinction region at an angle corresponding to time (i.e., ωt, ω refers to the angular frequency, and t refers to time); since the angular frequency ω of the commutation current and the commutation voltage of the converter is a constant in this embodiment, the integral of the product of the commutation voltage and the commutation current in the arc extinction region at an angle corresponding to time is essentially the integral of the product of the commutation voltage and the commutation current in the arc extinction region over time;
[0031] An example of the arc extinction region in the commutation process of this embodiment is shown in FIG. Figure 4 As shown, Figure 4 i5 is the current passing through valve V5, i1 is the current passing through valve V1, and u ca is the commutation voltage, α is the trigger angle, μ is the commutation angle, γ is the arc extinction angle, ωt represents the angle corresponding to time, specifically, ω refers to the angular frequency. In this embodiment, the angular frequency ω of the commutation current and commutation voltage of the converter is a constant, and t refers to time; Figure 4 The area indicated by the arrow at the arc extinction angle γ in the current commutation process is the arc extinction area, and the area indicated by the arrow at the commutation angle μ is the commutation area of the current commutation process. Figure 4 The shaded part in the figure represents the integral of the commutation voltage in the arc extinction area over the angle corresponding to the time, and the product of the area of the shaded part and the commutation current in the arc extinction area is the arc extinction area of the current commutation process (i.e., the integral of the product of the commutation voltage and the commutation current in the arc extinction area over the angle corresponding to the time).
[0032] The minimum arc extinguishing area for normal commutation of the converter is determined based on the value obtained by adding the ratio of the commutation angle to the sine value of the trigger angle in the current commutation process multiplied by the ratio of the commutation angle to the sine value of the trigger angle in the current commutation process and the cosine value of the trigger angle, minus twice the product of the rated DC current of the converter and the rated relative inductive voltage drop.
[0033] In this embodiment, the method of determining the arc extinguishing area of the current commutation process according to the integral of the product of the commutation voltage and the commutation current in the arc extinguishing area over the angle corresponding to the time is specifically:
[0034]
[0035] Where S is the arc extinction area of the current commutation process, u ca is the commutation voltage (in this embodiment, it is the commutation voltage between phase c and phase a), i d is the commutation current, ωt represents the angle corresponding to time, α is the trigger angle, μ is the commutation angle, and γ is the arc extinction angle;
[0036] In this embodiment, the method for determining the minimum arc extinguishing area for normal commutation of the converter is specifically as follows: the product of the ratio of the commutation angle to the sine value of the trigger angle in the current commutation process plus the ratio of the commutation angle to the sine value of the trigger angle in the current commutation process and the cosine value of the trigger angle, minus twice the product of the rated DC current of the converter and the rated relative inductive voltage drop:
[0037]
[0038] In the formula, S min is the minimum arc extinguishing area of the normal commutation of the converter, α is the trigger angle, μ is the commutation angle, I dN is the rated DC current, D xN is the rated relative inductive voltage drop of the converter;
[0039] In this embodiment, the setting condition also includes a second setting condition (such as Figure 3 As shown, the second setting condition is also called the zero-sequence criterion); the second setting condition is: the zero-sequence voltage of the AC system at the receiving end is greater than the zero-sequence voltage setting value.
[0040] Among them, the calculation formula of the zero-sequence voltage of the AC system at the receiving end is:
[0041]
[0042] Where U0 refers to the zero-sequence voltage of the AC system at the receiving end. Refers to the AC voltage of phase A, Refers to the AC voltage of phase B, Refers to the AC voltage of phase C;
[0043] In this embodiment, the zero-sequence voltage setting value is greater than or equal to 0.02pu, and 0.02pu (per unit value) means that the ratio of the zero-sequence voltage setting value to the voltage level of the high-voltage direct current transmission project is 0.02; the zero-sequence voltage setting value is adjusted according to the actual voltage level of the high-voltage direct current transmission project, and the zero-sequence voltage setting value of the high-voltage direct current transmission project with a voltage level of ±800KV is 0.03pu.
[0044] When a single-phase ground fault (asymmetric fault) occurs in the receiving-end AC system, a zero-sequence voltage component will appear in the commutation bus voltage. This fault will cause the inverter-side commutation bus voltage to drop, thereby increasing the risk of commutation failure. Therefore, when the zero-sequence voltage of the receiving-end AC system exceeds the zero-sequence voltage setting value, commutation failure may be imminent. In this case, controlling the controllable shutdown current source converter to shut down can avoid commutation failure.
[0045] Controllable shutdown current source converter shutdown control system embodiment
[0046] This embodiment provides a technical solution for a controllable shutdown current source converter shutdown control system, the system comprising a processor, the processor being used to execute a computer program to implement the steps of a controllable shutdown current source converter shutdown control method.
[0047] Since the specific implementation process and principle of the controllable shutdown current source converter shutdown control system of this embodiment have been described in detail in the controllable shutdown current source converter shutdown control method embodiment, no further details will be given here.
[0048] It should be understood that the above specific embodiments of the present invention are only used to illustrate or explain the principles of the present invention, but do not constitute a limitation to the present invention.
Claims
1. A controllable shutdown current source converter shutdown control method, characterized in that: During the commutation process of the controllable shut-off current source converter at the receiving end, when at least one set condition is met, controlling the single valve that is expected to be shut down during the current commutation process of the converter to be shut down; The setting condition includes a first setting condition; the first setting condition is: the arc extinguishing area of the current commutation process is smaller than the minimum arc extinguishing area of the normal commutation of the converter; The arc extinguishing area of the current commutation process is determined based on the integral of the product of the commutation voltage and the commutation current in the arc extinguishing area over the angle corresponding to the time; the minimum arc extinguishing area of the normal commutation of the converter is determined based on the ratio of the commutation angle to the sine value of the trigger angle in the current commutation process plus the product of the ratio and the cosine value of the trigger angle, minus twice the product of the rated DC current of the converter and the rated relative inductive voltage drop.
2. The controllable shutdown current source converter shutdown control method according to claim 1, characterized in that: The setting condition also includes a second setting condition; the second setting condition is: the zero-sequence voltage of the AC system at the receiving end is greater than the zero-sequence voltage setting value.
3. The controllable shutdown current source converter shutdown control method according to claim 2, characterized in that: The zero-sequence voltage setting value is greater than or equal to 0.02pu.
4. A controllable shutdown current source converter shutdown control system, comprising a processor, characterized in that: The processor is used to execute computer program instructions to implement the steps of the controllable shutdown current source converter shutdown control method according to any one of claims 1-3.