A method for suppressing commutation failure of a converter, a coupling voltage circuit and a converter

Abstract

The present invention provides a method for suppressing converter commutation failure, a coupling voltage circuit, and a converter. The method comprises: when an AC voltage drop occurs during the converter commutation process, applying an induced voltage to the bridge arm of the converter to compensate for the AC voltage and thereby facilitate commutation completion. The method, coupling voltage circuit, and converter of the present invention are capable of suppressing high-voltage direct current (HVDC) commutation failure. To address the commutation failure problem existing in existing HVDC converters, the use of the converter of the present invention can improve the converter's ability to resist commutation failure, thereby reducing the number of commutation failures and improving the safety and stability of power grid operation.

Description

Technical Field

[0001] The present invention belongs to the technical field of power electronics, and in particular relates to a method for suppressing commutation failure of a converter, a coupling voltage circuit and a converter. Background Art

[0002] High Voltage Direct Current (HVDC) technology is currently widely used around the world due to its advantages such as large transmission capacity, low loss and high reliability.

[0003] Commutation failure is one of the most common faults in HVDC transmission systems. In a converter, if a valve that has been deactivated fails to restore its blocking capacity within a period of reverse voltage, or if commutation is not completed during the reverse voltage period, the valve that was deactivated will reverse phase to the valve that was originally deactivated when the valve voltage returns to the positive direction. This is called a commutation failure. Commutation failure can cause the converter valve to lock, interrupting the DC system's transmission path and, in severe cases, potentially leading to grid collapse.

[0004] Traditional HVDC converters use thyristors to form the basic three-phase bridge rectifier unit. Each bridge arm is composed of a thyristor valve string. Since the thyristor valve string cannot actively control the current shutdown, the converter has a large commutation current and reactive power support, which poses a risk of commutation failure and its reliability needs to be improved. Summary of the Invention

[0005] In view of the above problems, the present invention provides a method for suppressing commutation failure of a converter, comprising:

[0006] When an AC voltage drop occurs during the commutation process of the converter, an induced voltage is applied to the bridge arm of the converter to compensate for the AC voltage and complete the commutation.

[0007] Furthermore, a coupling voltage circuit is provided on the bridge arm of the converter, and the coupling voltage circuit is controlled to apply an induced voltage to the bridge arm by controlling a power electronic switch of the coupling voltage circuit;

[0008] By controlling the discharge of the energy storage capacitor of the coupling voltage circuit, an induced voltage is applied to the bridge arm where the coupling voltage circuit is located.

[0009] Furthermore, the induced voltage is generated by two coupled inductors in the coupled voltage circuit, one of which is an anode current limiting inductor on the converter bridge arm.

[0010] The present invention also provides a coupling voltage circuit, comprising:

[0011] a first inductor, a second inductor, an energy storage capacitor, and a power electronic switch;

[0012] Wherein, the first inductor and the second inductor constitute a coupled reactance;

[0013] The second inductor, the energy storage capacitor and the power electronic switch are connected in series to form a loop.

[0014] Furthermore, the two ends of the first inductor are used to connect the coupling voltage circuit to the DC converter or the first inductor is an anode current limiting inductor on the bridge arm;

[0015] The current input terminal of the power electronic switch when it is turned on is connected to the second inductor, and the current output terminal of the power electronic switch when it is turned on is connected to the energy storage capacitor;

[0016] The two ends of the first inductor are used to connect the coupling voltage circuit to the DC converter.

[0017] Furthermore, the coupling voltage circuit includes:

[0018] The power electronic switch is a thyristor, an IGCT, an IGBT or an IEGT.

[0019] The present invention also provides a converter, comprising: a bridge arm and the above-mentioned coupling voltage circuit connected in series with the bridge arm.

[0020] Furthermore, the converter is a three-phase DC converter, comprising:

[0021] There are three AC side ports and two DC side ports, and the coupling voltage circuit is connected in series with the bridge arm between the DC side port and the AC side port.

[0022] Furthermore, the coupling voltage circuit is connected between the bridge arm and the DC side port.

[0023] Furthermore, the bridge arm between each phase AC side port and the positive electrode port in the DC side port is the upper bridge arm, and the bridge arm between each phase AC side port and the negative electrode port in the DC side port is the lower bridge arm;

[0024] Each bridge arm of the converter is composed of a thyristor valve string and / or a turn-off valve string composed of fully controllable devices;

[0025] The upper bridge arm and the lower bridge arm are respectively connected to a coupling voltage circuit.

[0026] The present invention's converter commutation failure suppression method, coupled voltage circuit, and converter can suppress high-voltage direct current (HVDC) commutation failures. Addressing the commutation failure issues inherent in existing HVDC converters, the present invention improves the converter's ability to withstand commutation failures, thereby reducing the frequency of commutation failures and improving the safety and stability of power grid operations.

[0027] Other features and advantages of the present invention will be described in the following description, and in part will become apparent from the description, or will be understood by practicing the present invention. The purpose and other advantages of the present invention can be realized and obtained by the structures pointed out in the description, claims and drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following is a brief introduction to the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0029] Figure 1 A schematic diagram of the circuit structure of a coupling voltage circuit for a DC converter according to an embodiment of the present invention is shown;

[0030] Figure 2 A schematic diagram of the circuit structure of a converter including a coupling voltage circuit according to an embodiment of the present invention is shown. DETAILED DESCRIPTION

[0031] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts shall fall within the scope of protection of the present invention.

[0032] An embodiment of the present invention provides a method for suppressing commutation failure of a converter, comprising:

[0033] When an AC voltage drop occurs during the commutation process of the converter, an induced voltage is applied to the bridge arm of the converter to compensate for the AC voltage and complete the commutation.

[0034] Specifically, a coupling voltage circuit is provided on the bridge arm of the converter, and the power electronic switch of the coupling voltage circuit is controlled to control the coupling voltage circuit to apply an induced voltage to the bridge arm. That is, the power electronic switch is controlled to be turned on, a current is generated in the coupling voltage circuit, and the electric energy in the coupling voltage circuit is applied to the bridge arm by means of an induced voltage. The electric energy source of the induced voltage can be generated by discharging the charging capacitor of the coupling voltage circuit. The induced voltage is generated by two coupled inductors in the coupling voltage circuit, one of which is the positive current limiting inductor on the bridge arm of the converter. In another embodiment, a controllable power supply can also be provided in the coupling voltage circuit for discharge, and accordingly, the discharge control can also be controlled by means of a mechanical switch or the like. Preferably, the converter commutation failure suppression method of the present invention is implemented using the following coupling voltage circuit.

[0035] like Figure 1 As shown, the coupling voltage circuit includes: a first inductor L1, a second inductor L2, an energy storage capacitor C and a power electronic switch. The first inductor L1 and the second inductor L2 form a coupling reactance. The second inductor L2, the energy storage capacitor C and the power electronic switch Tc are connected in series to form a loop. The current input terminal (anode) of the power electronic switch Tc when it is turned on is connected to the second inductor L2, and the current output terminal (cathode) of the power electronic switch Tc when it is turned on is connected to the energy storage capacitor C. The two ends of the first inductor L1 are used to connect the coupling voltage circuit to the DC converter, specifically, to the bridge arm of the DC converter, and multiple coupling voltage circuits can be connected in series. Furthermore, the first inductor L1 can be an independent inductor, or the anode current limiting inductor in the bridge arm of the DC converter can be directly used. In this case, to implement the coupling voltage circuit in the DC converter, only the second inductor L2 needs to be added, which is more simple and economical.

[0036] The self-inductance values ​​of the first inductor L1 and the second inductor are L1 and L2, respectively, and the mutual inductance value is M. The first inductor L1 is preferably directly adopted as the positive current limiting inductor of the high-voltage direct current transmission converter (i.e., the DC converter), and the self-inductance value of the first inductor L1 is the value of the positive current limiting inductor; the value of the second inductor self-inductance value L2 is determined according to the voltage level and tolerable current rise rate of the power electronic switch Tc and the pre-charge value of the energy storage capacitor C, and the value of the mutual inductance value M is determined according to the coupling voltage value to be generated and the voltage level of the bridge arm valve string. When the coupling voltage circuit is applied in the DC converter, according to the coupling voltage value to be generated by the bridge arm of the converter, based on the above-mentioned performance parameter relationship, the mutual inductance coefficient of the second inductor L2, the energy storage capacitor C, the first inductor, and the second inductor (determining their mutual inductance value M) is adjusted to meet the requirements for generating the coupling voltage.

[0037] The power electronic device Tc may be selected from, but is not limited to, a thyristor, an IGCT (Integrated Gate-Commutated Thyristor), an IGBT (Insulated Gate Bipolar Transistor), an IEGT (Injection Enhanced Gate Transistor), or other power electronic devices. For example, the power electronic device Tc is a turn-off thyristor.

[0038] The coupling voltage circuit according to the embodiment of the present invention can be used in a DC converter.

[0039] Illustratively, an embodiment of the present invention further provides a DC converter, which includes the above-mentioned coupling voltage circuit.

[0040] like Figure 2 As shown, the converter of the embodiment of the present invention is a three-phase DC converter, including three AC side ports and two DC side ports. The coupling voltage circuit is arranged in series with the bridge arm between the DC side ports and the AC side ports. Multiple coupling voltage circuits can be connected in series to each bridge arm.

[0041] The three AC side ports are the first phase AC port (Port A), the second phase AC port (Port B), and the third phase AC port (Port C). The two DC side ports include a positive port (Port P) and a negative port (Port N).

[0042] Among them, each phase AC side port of the DC converter is connected to the two ports on the DC side through a bridge arm. Specifically, the bridge arm between each phase AC side port and the positive port of the DC side port is the upper bridge arm, and the bridge arm between each phase AC side port and the negative port of the DC side port is the lower bridge arm.

[0043] Specifically, there is a bridge arm Ap between port A and port P, a bridge arm Bp between port B and port P, a bridge arm Cp between port C and port P, a bridge arm An between port A and port N, a bridge arm Bn between port B and port N, and a bridge arm Cn between port C and port N. Each bridge arm is connected in series with a coupling voltage circuit, specifically, the coupling voltage circuit is connected between the bridge arm and the DC side port. When the coupling voltage circuit is connected to the DC side, it is easier to improve and the anode current limiting inductor on the existing bridge arm can be utilized to achieve greater economy. The anode current limiting inductor is arranged on the DC side (not shown in the figure) of each bridge arm (including the upper bridge arm and the lower bridge arm) of the converter.

[0044] Without loss of generality, each bridge arm of the converter consists of a thyristor valve string (S1…S k ) and / or a shut-off valve train (Q1…Qm ), the ratio of thyristor valve string to shut-off valve string can be 0%-100%, and the fully controlled devices include but are not limited to high-power power electronic devices such as IGCT, IGBT, IEGT with bidirectional pressure-bearing capacity and shut-off capability.

[0045] The DC converter of the embodiment of the present invention can suppress commutation failure. The specific process is as follows: When the AC system voltage fails, the commutation voltage of the bridge arm commutation is insufficient, and commutation failure may occur. Therefore, the power electronic switch Tc in the coupling voltage circuit is controlled to conduct, and the energy storage capacitor C discharges through the second inductor L2. Through the coupling effect of the coupling reactance, an induced voltage is induced on the first inductor L1. The induced voltage compensates for the drop in the AC voltage, supplements and raises the voltage, thereby ensuring the completion of the commutation process and suppressing the occurrence of commutation failure. Specifically, the detection of insufficient commutation voltage can be implemented using a commutation failure prediction algorithm. For example, the depth of the three-phase fault is determined by abc-αβ conversion monitoring, and the depth of the single-phase fault is determined by detecting the zero-sequence voltage. The possibility of commutation failure is predicted based on the three-phase fault depth and the single-phase fault depth.

[0046] The present invention proposes a DC converter containing a coupling voltage circuit that can suppress commutation failure. The implementation method can be to modify and add a coupling voltage circuit to each bridge arm of an existing conventional high-voltage DC converter. The implementation is simple and easy, the overall cost of the coupling voltage circuit is low, the operating reliability is high, and it only operates when a commutation failure is likely to occur and does not intervene during normal operation.

[0047] The beneficial effects of the present invention are as follows: by utilizing a topological structure with a coupling voltage circuit, which is connected in series in each phase bridge arm of the converter, at the moment when commutation failure is about to occur, the coupling voltage circuit is utilized to additionally create commutation voltage and increase the commutation voltage, thereby striving for a larger commutation area, enhancing the commutation immunity of the converter, reducing the number of commutation failures, and improving the hybrid converter's ability to resist commutation failures, thereby ultimately further improving the reliability of the DC power grid, reducing the failure rate, increasing the transmission capacity, and enhancing the role of promoting the national economy.

[0048] Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A coupling voltage circuit, characterized in that: include: A first inductor, a second inductor, an energy storage capacitor, and a power electronic switch, wherein the first inductor and the second inductor form a coupled reactance, and the second inductor, the energy storage capacitor, and the power electronic switch are connected in series to form a loop; The two ends of the first inductor are used to connect the coupling voltage circuit to the bridge arm of the DC converter, or the first inductor is an anode current limiting inductor on the bridge arm; The current input terminal of the power electronic switch when it is turned on is connected to the second inductor, and the current output terminal of the power electronic switch when it is turned on is connected to the energy storage capacitor.

2. The coupling voltage circuit according to claim 1, wherein: include: The power electronic switch is a thyristor, an IGCT, an IGBT or an IEGT.

3. A converter, characterized in that: include: A bridge arm and a coupling voltage circuit as claimed in claim 1 or 2 connected in series with the bridge arm.

4. The converter according to claim 3, characterized in that The converter is a three-phase DC converter, comprising: There are three AC side ports and two DC side ports, a coupling voltage circuit and a bridge arm are connected in series between the DC side port and the AC side port, and the coupling voltage circuit is connected between the bridge arm and the DC side port.

5. The converter according to claim 4, characterized in that The bridge arm between each phase AC side port and the positive port in the DC side port is the upper bridge arm, and the bridge arm between each phase AC side port and the negative port in the DC side port is the lower bridge arm; Each bridge arm of the converter is composed of a thyristor valve string and / or a turn-off valve string composed of fully controllable devices; The upper bridge arm and the lower bridge arm are respectively connected to a coupling voltage circuit.

Images