Current source converter protection system and current source converter

Abstract

The application relates to a current source converter valve protection system and a current source converter. An AC filter capacitor and a converter transformer are connected to an AC outlet end of the current source converter valve respectively, and a second end of the converter transformer is connected to an AC power grid. Thus, AC-DC conversion can be performed in the process of power transmission. Moreover, a capacitor protection module is connected to the AC filter capacitor. Through the capacitor protection module, overvoltage protection can be performed on the AC filter capacitor in the case of an AC side fault of the current source converter valve, and / or oscillation suppression can be performed on the AC filter capacitor in the case of recovery of the AC side fault. Thus, it can be ensured that the AC filter capacitor will not be overvoltage in the case of the AC side fault of the current source converter valve, and / or the AC filter capacitor can quickly return to a steady state in the case of recovery of the AC side fault, thereby greatly reducing the operation risk of the filter capacitor in the current source converter valve.

Description

Technical Field

[0001] This application relates to the field of converter technology, and in particular to a current source converter valve protection system and a current source converter. Background Technology

[0002] A current source converter valve is a device that controls the conduction and cutoff of current by controlling the firing angle of a silicon controlled rectifier (SCR) device. It can convert alternating current (AC) to direct current (DC) or vice versa, achieving efficient energy conversion and long-distance transmission. It is widely used in high-voltage direct current (HVDC) transmission systems.

[0003] Current source converter valves typically connect an AC filter capacitor at the AC outlet to provide the commutation circuit. However, in related technologies, the operation of the AC filter capacitor carries a relatively high risk. Summary of the Invention

[0004] Therefore, it is necessary to provide a current source converter valve protection system and a current source converter to reduce the operational risk of the AC filter capacitor connected to the AC outlet of the current source converter valve.

[0005] This application provides a current source converter valve protection system, including: a current source converter valve, an AC filter capacitor, and a capacitor protection module. The AC filter capacitor is connected to the AC outlet terminal of the current source converter valve and the first terminal of the converter transformer. The capacitor protection module is connected to the AC filter capacitor. The capacitor protection module is used to provide overvoltage protection for the AC filter capacitor in the event of an AC side fault, and / or to suppress oscillation of the AC filter capacitor when the AC side fault is recovered.

[0006] In one embodiment, the AC outlet of the current source converter valve includes a three-phase AC outlet. Each phase AC outlet of the current source converter valve is connected to the first end of the converter transformer and an AC filter capacitor. The number of capacitor protection modules is less than or equal to the number of AC filter capacitors, and each capacitor protection module is connected to an AC filter capacitor.

[0007] In one embodiment, the capacitor protection module includes a first protection submodule, a first end of which is connected to the first end of the AC filter capacitor, a second end of which is connected to the first end of the converter transformer and one phase AC outlet of the current source converter valve, and the second end of each AC filter capacitor is connected to a common connection point.

[0008] In one embodiment, the first protection submodule includes a first bidirectional current-carrying switch and a first overvoltage protection device connected in parallel; wherein, in the event of recovery of the AC side fault, the first bidirectional current-carrying switch is turned off to generate additional damping through the first overvoltage protection device to suppress oscillation of the AC filter capacitor.

[0009] In one embodiment, the duration of the first bidirectional current-carrying switch being turned off is determined based on the oscillation period of the AC filter capacitor.

[0010] In one embodiment, the method for determining AC-side fault recovery includes: acquiring the AC-side voltage of the current source converter valve in real time when an AC-side fault occurs in the current source converter valve; and determining that the AC-side fault has been recovered when the AC-side voltage recovers to a preset multiple of the rated voltage.

[0011] In one embodiment, the capacitor protection module includes a second protection submodule, the first end of which is connected to the first end of the AC filter capacitor, the second end of which is connected to the second end of the AC filter capacitor, and the second end of each AC filter capacitor is connected to a common connection point.

[0012] In one embodiment, the second protection submodule includes a second bidirectional current-passing switch and a second overvoltage protection device connected in parallel; wherein, in the event of an AC side fault in the current source converter valve, the second overvoltage protection device provides overvoltage protection for the AC filter capacitor, and in the event of a fault in the AC filter capacitor, the second bidirectional current-passing switch is turned on to bypass the faulty AC filter capacitor.

[0013] In one embodiment, the method for determining that the AC filter capacitor has failed includes: obtaining the voltage value of the AC filter capacitor; and determining that the AC filter capacitor has failed when the voltage value is less than a preset voltage threshold for a preset duration.

[0014] In one embodiment, the method for determining that the current source converter valve has an AC side fault includes: acquiring the AC side voltage of the current source converter valve in real time; and determining that the current source converter valve has an AC side fault when the AC side voltage drops to a preset fault voltage.

[0015] This application also provides a current source converter, including a converter transformer and the aforementioned current source converter valve protection system.

[0016] The aforementioned current source converter valve protection system and current source converter connect an AC filter capacitor and a converter transformer to the AC outlet of the current source converter valve, respectively. The second end of the converter transformer is connected to the AC power grid, thus enabling AC-DC conversion during power transmission. Furthermore, this scheme incorporates a capacitor protection module at the AC filter capacitor. This module provides overvoltage protection for the AC filter capacitor in the event of an AC-side fault and / or oscillation suppression for the AC filter capacitor upon recovery from an AC-side fault. This scheme provides overvoltage protection and / or oscillation suppression for the AC filter capacitor during both AC-side fault occurrence and recovery. This ensures that the AC filter capacitor will not experience overvoltage during an AC-side fault and / or that it quickly returns to a steady state upon recovery from an AC-side fault, thereby significantly reducing the operational risk of the filter capacitor connected to the AC outlet of the current source converter valve. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of this application or the conventional technology, the drawings used in the description of the embodiments or the conventional technology will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a schematic diagram of the structure of a current source converter valve protection system in one embodiment of this application;

[0019] Figure 2 This is a schematic diagram of the current source converter circuit topology in one embodiment of this application;

[0020] Figure 3 This is a schematic diagram of the topology of a current source converter valve protection system in one embodiment of this application;

[0021] Figure 4 This is a schematic diagram of the topology of the current source converter valve protection system in another embodiment of this application;

[0022] Figure 5 This is a schematic diagram of the topology of a current source converter valve protection system in another embodiment of this application.

[0023] Explanation of reference numerals in the attached figures:

[0024] 110 - Current source converter valve, 111 - Power unit, Ldc - DC smoothing reactor, C - AC filter capacitor, 120 - Converter transformer, 131 - First protection submodule, T1 - First bidirectional current-carrying switch device, B1 - First overvoltage protection device, 132 - Second protection submodule, T2 - Second bidirectional current-carrying switch device, B2 - Second overvoltage protection device, L - Leakage inductance of converter transformer. Detailed Implementation

[0025] To facilitate understanding of this application, a more complete description will be provided below with reference to the accompanying drawings. Preferred embodiments of this application are shown in the drawings. However, this application can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a thorough and complete understanding of the disclosure of this application.

[0026] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application.

[0027] It is understood that the terms "first," "second," etc., used herein may be used to describe various elements, but these elements are not limited by these terms. These terms are only used to distinguish one element from another. For example, without departing from the scope of this application, a first resistor may be referred to as a second resistor, and similarly, a second resistor may be referred to as a first resistor. Both the first resistor and the second resistor are resistors, but they are not the same resistor.

[0028] It is understood that the term "connection" in the following embodiments should be understood as "electrical connection," "communication connection," etc., if the connected circuits, modules, units, etc., have electrical signal or data transmission with each other.

[0029] It is understandable that "at least one" refers to one or more, and "multiple" refers to two or more. "At least a part of an element" refers to part or all of an element.

[0030] When used herein, the singular forms of “a,” “an,” and “the” may also include the plural forms unless the context clearly indicates otherwise. It should also be understood that the terms “comprising / including” or “having,” etc., specify the presence of the stated features, wholes, steps, operations, components, parts, or combinations thereof, but do not preclude the possibility of the presence or addition of one or more other features, wholes, steps, operations, components, parts, or combinations thereof. Meanwhile, the term “and / or” as used in this specification includes any and all combinations of the associated listed items.

[0031] With the continuous development of science and technology, high-voltage direct current (HVDC) transmission systems have gradually gained widespread application due to their advantages such as long transmission distance, low loss, high transmission efficiency, good stability, and ease of dispatching. However, the AC filter capacitors located on the AC side of the converter valves in HVDC transmission systems pose significant operational risks, specifically due to their susceptibility to damage from overvoltage or the tendency to oscillate.

[0032] In-depth research revealed that overvoltage damage to AC filter capacitors often occurs during AC-side faults. Oscillation of the AC filter capacitors, however, primarily occurs after the fault has occurred, i.e., after the AC-side fault has been resolved. Specifically, this is because the AC side of the current source converter valve is equipped with a converter transformer, which has a certain leakage inductance. Since both the capacitance of the current source converter valve and the leakage inductance of the converter transformer are relatively large, they are prone to LC resonance after a fault, and the recovery process is lengthy.

[0033] To alleviate the above phenomenon, research has shown that a capacitor protection module can be connected to the AC filter capacitor to monitor AC side faults of the current source converter valve. When an AC side fault is detected, the capacitor protection module is activated to provide overvoltage protection for the AC filter capacitor. When the AC side fault is detected to have recovered, the capacitor protection module is activated to suppress oscillations in the AC filter capacitor, thereby rapidly attenuating the resonant current and allowing the AC filter capacitor to quickly return to a steady state, reducing operational risks.

[0034] Based on this, please refer to Figure 1 This application provides a current source converter valve protection system, including: a current source converter valve 110, an AC filter capacitor C, and a capacitor protection module 130. The AC filter capacitor C is connected to the AC outlet terminal of the current source converter valve 110 and the first terminal of the converter transformer 120. The second terminal of the converter transformer 120 is used to connect to the AC power grid (not shown). The capacitor protection module 130 is connected to the AC filter capacitor C. The capacitor protection module 130 is used to provide overvoltage protection for the AC filter capacitor C in the event of an AC side fault, and / or to suppress oscillation of the AC filter capacitor C when the AC side fault is recovered.

[0035] Specifically, the current source converter valve 110 is a device that converts alternating current (AC) to direct current (DC) or vice versa through the on / off control of switching devices. The converter transformer 120 is the transformer used in the current source converter to perform the transformation function. The AC filter capacitor C is located on the AC side of the current source converter valve 110 and provides capacitance for the commutation circuit. The capacitor protection module 130 is a functional module used to protect the AC filter capacitor C. An AC side fault refers to a fault occurring on the AC side of the current source converter valve, which is the side equipped with AC power.

[0036] It should be noted that the specific type of the current source converter valve 110 is not unique; in one embodiment, please refer to [reference needed]. Figure 2 The current source converter valve 110 includes a DC smoothing reactor Ldc and a power unit 111. The DC terminal of the power unit 111 is connected to a DC power supply via the DC smoothing reactor Ldc, while the AC output terminal of the power unit 111 serves as the AC output terminal of the current source converter valve 110. Furthermore, the type of power unit 111 is not unique. In one embodiment, the AC power supply connected to the current source converter valve 110 is three-phase AC, and correspondingly, the power unit 111 should also be a three-phase power unit 111. More specifically, the power unit 111 is a three-phase six-arm power unit, but the specific type is not limited.

[0037] It is understood that, in one embodiment, the capacitor protection module 130 is connected to the AC filter capacitor C, and when an AC side fault is detected in the current source converter valve 110, or when the AC side fault is recovered, the capacitor protection module 130 can be manually turned on by the user to achieve overvoltage protection and / or oscillation suppression.

[0038] In another embodiment, the current source converter may further include a controller that monitors the current source converter valve 110 for faults in real time during operation. When an AC side fault is detected in the current source converter valve 110, the controller controls the capacitor protection module 130 to operate to provide overvoltage protection for the AC filter capacitor C; and / or when the AC side fault is detected to be resolved, the controller controls the capacitor protection module 130 to operate to suppress oscillations in the AC filter capacitor C.

[0039] The aforementioned current source converter valve protection system connects an AC filter capacitor C and a converter transformer 120 to the AC outlet of the current source converter valve 110. The second end of the converter transformer 120 is connected to the AC power grid, thus enabling AC-DC conversion during power transmission. Furthermore, this system integrates a capacitor protection module 130 at the AC filter capacitor C. This module provides overvoltage protection for the AC filter capacitor C in the event of an AC-side fault in the current source converter valve 110, and / or oscillation suppression for the AC filter capacitor C upon recovery from the AC-side fault. This design provides overvoltage protection and / or oscillation suppression for the AC filter capacitor C in the event of an AC-side fault in the current source converter valve 110 and upon recovery from the AC-side fault. This ensures that the AC filter capacitor C will not experience overvoltage during an AC-side fault in the current source converter valve 110, and / or that the AC filter capacitor C quickly returns to a steady state upon recovery from the AC-side fault, thereby significantly reducing the operational risk of the AC filter capacitor C connected to the AC outlet of the current source converter valve 110.

[0040] Please see Figure 2 In one embodiment, the AC outlet of the current source converter valve 110 includes a three-phase AC outlet. Each phase AC outlet of the current source converter valve 110 is connected to the second terminal of the converter transformer 120 and an AC filter capacitor C. The number of capacitor protection modules 130 is less than or equal to the number of AC filter capacitors C, and each capacitor protection module 130 is connected to an AC filter capacitor C.

[0041] Specifically, in this embodiment, the current source converter valve 110 is explained as a three-phase current source converter valve. The AC terminals of the current source converter valve 110 include three-phase AC output terminals, namely the AC output terminal corresponding to A, the AC output terminal corresponding to B, and the AC output terminal corresponding to C. To achieve reliable AC power transmission, an AC filter capacitor C needs to be configured at each phase AC output terminal (which can be a single capacitor or a capacitor bank formed by multiple capacitors connected in series and / or in parallel).

[0042] It should be noted that the number of capacitor protection modules 130 is less than or equal to the number of AC filter capacitors C, meaning that at least one AC filter capacitor C can be configured with a capacitor protection module 130 to protect that AC filter capacitor C. It is understood that in practical scenarios, the number of capacitor protection modules 130 is not unique; it can be selected based on actual needs. More specifically, in one embodiment, the number of capacitor protection modules 130 can be set to be the same as the number of AC filter capacitors C, that is, a capacitor protection module 130 is configured for each AC filter capacitor C, thereby protecting all AC filter capacitors C at the AC outlet of the current source converter valve 110.

[0043] Please see Figure 3 In one embodiment, the capacitor protection module 130 includes a first protection submodule 131. The first end of the first protection submodule 131 (i.e., the S1 end in the figure) is connected to the first end of the AC filter capacitor C (i.e., the 1 end in the figure). The second end of the first protection submodule 131 (i.e., the S2 end in the figure) is connected to the second end of the converter transformer 120 (not shown) and one phase AC outlet end of the current source converter valve 110. The second end of each AC filter capacitor C (i.e., the 2 end in the figure) is connected to a common connection point.

[0044] Specifically, in this embodiment, the capacitor protection module 130 includes a first protection submodule 131, which is connected in series with the AC filter capacitor C, specifically between the AC filter capacitor C and the converter transformer 120. This allows for oscillation suppression when LC resonance occurs between the AC filter capacitor C and the leakage inductance L of the converter transformer, reducing the oscillation duration of the AC filter capacitor C and improving its operational stability.

[0045] It should be noted that the number of first protection submodules 131 is not unique. In one embodiment, the first protection submodule 131 may be provided between at least one AC filter capacitor C and the converter transformer 120. More specifically, in one embodiment, one first protection submodule 131 may be provided between each AC filter capacitor C and the converter transformer 120.

[0046] Please continue reading. Figure 3 In one embodiment, the first protection submodule 131 includes a first bidirectional current-carrying switch T1 and a first overvoltage protection device B1 connected in parallel; wherein, in the event of AC side fault recovery, the first bidirectional current-carrying switch T1 is turned off to generate additional damping through the first overvoltage protection device B1 to suppress oscillation of the AC filter capacitor C.

[0047] Specifically, the structure of the first protection submodule 131 is not unique. Any submodule can generate additional damping to suppress the oscillation of the AC filter capacitor C when the AC side of the current source converter valve 110 recovers from a fault. In this embodiment, the first protection submodule 131 includes a first bidirectional current-carrying switch T1 and a first overvoltage protection device B1 connected in parallel. In this scheme, the first and second terminals of the first bidirectional current-carrying switch T1 are connected to the first and second terminals of the first overvoltage protection device B1, respectively. The control terminal of the first bidirectional current-carrying switch T1 is connected to a controller, and the capacitor protection module 130 is protected under the control of the controller.

[0048] Specifically, during normal operation of the current source converter valve 110, or during an AC-side fault in the current source converter valve 110, the controller controls the first bidirectional current-carrying switch T1 to be in the conducting state. At this time, current is transmitted through the first bidirectional current-carrying switch T1 and does not pass through the first overvoltage protection device B1. When an AC-side fault is detected in the current source converter valve 110 and its recovery is observed, the controller controls the first bidirectional current-carrying switch T1 to be turned off. At this time, current flows through the first overvoltage protection device B1. Subsequently, the first overvoltage protection device B1 generates a clamping voltage. This clamping voltage is opposite in direction to the current in the AC filter capacitor C, and can be considered a reverse voltage. This reverse voltage hinders further charging of the AC filter capacitor C, thus acting as a damping effect, i.e., generating additional damping to suppress the oscillation of the AC filter capacitor C.

[0049] The above scheme uses a first bidirectional current-carrying switch device T1 and a first overvoltage protection device B1 to build a first protection submodule 131, which generates additional damping by using a reverse clamping voltage to suppress the oscillation of the AC filter capacitor C. The circuit structure is simple and has a good oscillation suppression effect.

[0050] It should be noted that the type of the first bidirectional current-carrying switch device T1 is not unique; any current-carrying switch device capable of on / off control under the action of the controller is acceptable. For example, in a more detailed embodiment, the first bidirectional current-carrying switch device T1 can be any one of an IGBT (Insulated-Gate Bipolar Transistor) and a bidirectional thyristor.

[0051] Similarly, the type of the first overvoltage protection device B1 is not unique. In a more detailed embodiment, the first overvoltage protection device B1 can be any one of a surge arrester, transient voltage suppressor diode, avalanche diode, and Zener diode, and the specific choice can be made according to actual needs.

[0052] After the AC side fault of the current source converter valve 110 is gradually restored, in order to ensure the reliable operation of the current source converter valve 110, it is necessary to switch the first bidirectional current-carrying switch device T1 between the AC filter capacitor C and the converter transformer 120, that is, to restore the first bidirectional current-carrying switch device T1 to the conducting state. Therefore, after the first bidirectional current-carrying switch device T1 is turned off under certain conditions, the controller needs to control the first bidirectional current-carrying switch device T1 to turn on, thereby ending the oscillation suppression.

[0053] It should be noted that the conditions for the first bidirectional current-carrying switch T1 to turn off are not unique. In one embodiment, the controller can detect the oscillation state of the AC filter capacitor C, and when the oscillation of the AC filter capacitor C disappears, the controller controls the first bidirectional current-carrying switch T1 to turn on, thereby ending the oscillation suppression.

[0054] In another embodiment, an allowable duration can be configured for the turn-off of the first bidirectional current-carrying switch device T1. When the turn-off duration of the first bidirectional current-carrying switch device T1 reaches a certain value, the first bidirectional current-carrying switch device T1 is controlled to turn on, thereby ending the oscillation suppression.

[0055] More specifically, in one embodiment, the duration of the first bidirectional current-carrying switch T1 being turned off is determined based on the oscillation period of the AC filter capacitor C.

[0056] Specifically, the oscillation period of the AC filter capacitor C can be calculated using the LC resonance period calculation formula, combined with the capacitance value of the AC filter capacitor C and the leakage inductance L value of the converter transformer at this time, which will not be elaborated here. In practical scenarios, the duration of the first bidirectional current-carrying switch T1 being turned off can be set to be greater than a preset multiple of the oscillation period. More specifically, in one embodiment, the duration of the first bidirectional current-carrying switch T1 being turned off can be set to be greater than or equal to 5 times the oscillation period. In other embodiments, the duration can be set to other values, as long as it can effectively suppress the oscillation of the AC filter capacitor C.

[0057] The above scheme determines the duration of the first bidirectional current-carrying switch T1 being turned off by the oscillation period of the AC filter capacitor C. In this way, while accurately suppressing the oscillation of the AC filter capacitor C, it can also ensure that the current source converter valve 110 quickly returns to normal operation.

[0058] In one embodiment, the method for determining AC side fault recovery includes: in the event of an AC side fault in the current source converter valve 110, acquiring the AC side voltage of the current source converter valve 110 in real time; and determining AC side fault recovery when the AC side voltage recovers to a preset multiple of the rated voltage.

[0059] Specifically, the method for determining whether an AC side fault in the current source converter valve 110 has been resolved is not unique. In this embodiment, after an AC side fault occurs, the controller monitors the AC side voltage in real time. That is, it acquires the AC side voltage in real time through a voltage detection device installed on the AC side and compares it with the rated voltage of the current source converter valve 110. When the AC side voltage recovers to a preset multiple of the rated voltage, that is, when the AC side voltage gradually rises to a level greater than or equal to a preset multiple of the rated voltage, the AC side fault is considered to have disappeared, i.e., the AC side fault has been resolved. This method, which uses the AC side voltage of the current source converter valve 110 to determine whether an AC side fault has been resolved, has high accuracy.

[0060] It should be noted that the preset multiple is not unique; any value that can reasonably represent the disappearance of the AC side fault is acceptable. For example, in a more detailed embodiment, the preset multiple can be set to 90%, meaning that the AC side fault is considered to have been resolved when the AC side voltage recovers to 90% of the rated voltage. In other embodiments, the preset multiple can be set to 85%, 95%, etc., and there is no specific limitation.

[0061] Please refer to the following: Figure 4 or Figure 5 In one embodiment, the capacitor protection module 130 includes a second protection submodule 132, the first end of the second protection submodule 132 (i.e., Figure 4 As shown, terminal M1 is connected to the first terminal of the AC filter capacitor C (i.e., terminal C). Figure 4 As shown in Figure 1), the second end of the second protection submodule 132 (i.e. Figure 4 The M2 terminal shown is connected to the second terminal of the AC filter capacitor C (i.e., ...). Figure 4 As shown in Figure 2, the second terminal of each AC filter capacitor C is connected to the common connection point.

[0062] Specifically, in this embodiment, the capacitor protection module 130 includes a second protection submodule 132 connected in parallel with the AC filter capacitor C. Thus, by setting the second protection submodule 132, voltage clamping can be performed on the AC filter capacitor C, thereby preventing excessive voltage flowing through the AC filter capacitor C and achieving overvoltage protection.

[0063] Specifically, in actual scenarios, the capacitor protection module 130 can include only the first protection submodule 131, only the second protection submodule 132, or both the first protection submodule 131 and the second protection submodule 132. The configuration can be made according to actual needs.

[0064] It should be noted that the number of second protection submodules 132 is not unique. In one embodiment, a second protection submodule 132 may be connected in parallel across at least one AC filter capacitor C. More specifically, in one embodiment, one second protection submodule 132 may be connected in parallel across each AC filter capacitor C.

[0065] Please continue reading. Figure 4 or Figure 5 In one embodiment, the second protection submodule 132 includes a second bidirectional current-passing switch T2 and a second overvoltage protection device B2 connected in parallel; wherein, in the event of an AC side fault in the current source converter valve 110, the AC filter capacitor C is overvoltage protected by the second overvoltage protection device B2, and in the event of a fault in the AC filter capacitor C, the second bidirectional current-passing switch T2 is turned on to bypass the faulty AC filter capacitor C.

[0066] Specifically, in this embodiment, the second protection submodule 132 has a similar structure to the first protection submodule 131, both including a bidirectional current-carrying switch device and an overvoltage protection device connected in parallel. The control terminal of the second bidirectional current-carrying switch device T2 is connected to the controller. The types of the second bidirectional current-carrying switch device T2 and the second overvoltage protection device B2 are similar to those of the first bidirectional current-carrying switch device T1 and the first overvoltage protection device B1, and will not be repeated here. During actual operation, the controller performs real-time detection of AC side faults and AC filter capacitor C faults. When no AC filter capacitor C fault is detected, regardless of whether an AC side fault occurs, the controller controls the second bidirectional current-carrying switch device T2 to be in the open state. This is equivalent to the second overvoltage protection device B2 being connected in parallel with the AC filter capacitor C, enabling overvoltage protection for the AC filter capacitor C (overvoltage protection during AC side faults or non-AC side faults). When a fault is detected in the AC filter capacitor C, the controller can turn on the second bidirectional current-carrying switch T2. At this time, the AC filter capacitor C is short-circuited, and the current is transmitted through the second bidirectional current-carrying switch T2, which can realize the fault bypass of the AC filter capacitor C without affecting the operation of other non-faulty AC filter capacitors C.

[0067] The above scheme uses a second bidirectional current-carrying switch T2 and a second overvoltage protection device B2 to build a second protection submodule 132. The second bidirectional current-carrying switch T2 is turned on to realize the fault bypass of AC filter capacitor C, and the second overvoltage protection device B2 realizes the overvoltage protection of AC filter capacitor C during operation. The circuit structure is simple and effectively saves circuit costs.

[0068] In one embodiment, the method for determining that the AC filter capacitor C has failed includes: obtaining the voltage value of the AC filter capacitor C; and determining that the AC filter capacitor C has failed when the voltage value is less than a preset voltage threshold for a preset duration.

[0069] Specifically, there is no single way to determine if the AC filter capacitor C has failed. In this embodiment, fault analysis is performed by detecting the voltage across the AC filter capacitor C. Specifically, the controller compares the real-time voltage across the AC filter capacitor C with a preset voltage threshold. When the voltage value is lower than the preset voltage threshold, a timer is started. If the voltage value remains lower than the preset voltage threshold for a preset duration, the AC filter capacitor C is considered to have failed, i.e., it has broken down.

[0070] The above scheme uses the voltage across the AC filter capacitor C to monitor the fault of the AC filter capacitor C, which has high accuracy in fault diagnosis.

[0071] In one embodiment, the method for determining that the current source converter valve 110 has an AC side fault includes: acquiring the AC side voltage of the current source converter valve 110 in real time; and determining that the current source converter valve 110 has an AC side fault when the AC side voltage drops to a preset fault voltage.

[0072] Specifically, during the operation of the current source converter valve 110, the controller acquires the AC side voltage of the current source converter valve 110 in real time to monitor whether an AC side fault has occurred. Specifically, the AC side voltage is compared and analyzed with a preset fault voltage. When the AC side voltage is detected to be less than or equal to (i.e., dropping to) the preset fault voltage, an AC side fault is determined to have occurred. This scheme achieves AC side fault monitoring by real-time detection of the AC side voltage of the current source converter valve 110, and has high monitoring accuracy.

[0073] To facilitate understanding of the technical solution of this application, the following detailed embodiments will be used to explain and illustrate this application.

[0074] The current source converter valve protection system of this application includes a controller, a current source converter valve 110, an AC filter capacitor C, and a first protection submodule 131 and a second protection submodule 132. The current source converter valve 110, the first protection submodule 131, and the second protection submodule 132 are respectively connected to the controller. The current source converter valve 110 includes a three-phase six-bridge power unit 111 and a DC smoothing reactor Ldc. The DC terminal of the three-phase six-bridge power unit 111 is connected to a DC power supply through the DC smoothing reactor Ldc. The three-phase output terminals of the three-phase six-bridge power unit 111 are respectively connected to a converter transformer 120 and an AC filter capacitor C. The first protection submodule 131 and the second protection submodule 132 have the same structure, both including parallel bidirectional current-carrying switching devices and overvoltage protection devices.

[0075] During actual operation, the controller acquires the AC side voltage of the current source converter valve 110 and the voltage value across the AC filter capacitor C in real time. Based on the analysis of the AC side voltage and voltage value, and assuming no AC side fault or AC filter capacitor C fault occurs, for each AC filter capacitor C, the controller controls the first bidirectional current-carrying switch T1 to turn on and the second bidirectional current-carrying switch T2 to turn off.

[0076] When the AC side voltage drops to the preset fault voltage, an AC side fault is determined. At this time, there is no need to control the first bidirectional current-carrying switch T1 and the second bidirectional current-carrying switch T2. The AC filter capacitor C can be over-voltage protected by the second overvoltage protection device B2.

[0077] After this, if an AC side voltage rise is detected and reaches a preset multiple of the rated voltage (e.g., 90% of the rated voltage), it is determined that the AC side fault has been resolved. At this time, the controller controls the first bidirectional current-carrying switch T1 to turn off, causing the first overvoltage protection device B1 to engage and generate additional damping to suppress oscillations. During this process, the controller can calculate the required duration for the first bidirectional current-carrying switch T1 to turn off by combining the leakage inductance L of the converter transformer and the capacitance value of the AC filter capacitor C. After the duration for which the first bidirectional current-carrying switch T1 is turned off is reached, the controller controls the first bidirectional current-carrying switch T1 to turn on, entering normal operation.

[0078] If the detected voltage value is lower than the preset voltage threshold for a duration that reaches the preset duration, it is considered that the AC filter capacitor C has failed. At this time, it is necessary to control the second bidirectional current-passing switch T2 across the AC filter capacitor C to be turned on, and to bypass the faulty AC filter capacitor C, so as to ensure that the other AC filter capacitors C can continue to operate until the fault is eliminated.

[0079] In the description of this specification, references to terms such as "some embodiments," "other embodiments," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of this application. In this specification, the illustrative descriptions of the above terms do not necessarily refer to the same embodiments or examples.

[0080] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0081] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A current source converter valve protection system, characterized in that, include: Current source converter valve; An AC filter capacitor is connected to the AC outlet terminal of the current source converter valve and the first terminal of the converter transformer, and the second terminal of the converter transformer is used to connect to the AC power grid. A capacitor protection module is connected to the AC filter capacitor; the capacitor protection module is used to suppress oscillation of the AC filter capacitor in the event of AC side fault recovery. The current source converter valve has three-phase AC outlets, each of which is connected to the first terminal of the converter transformer and an AC filter capacitor. The capacitor protection module includes a first protection submodule, with its first terminal connected to the first terminal of the AC filter capacitor and its second terminal connected to the first terminal of the converter transformer and one phase of the current source converter valve. The second terminals of each AC filter capacitor are connected to a common connection point. The first protection submodule includes a first bidirectional current-carrying switch and a first overvoltage protection device connected in parallel. When the AC side fault is resolved, the first bidirectional current-carrying switch is turned off to generate additional damping through the first overvoltage protection device, suppressing oscillations in the AC filter capacitor.

2. The current source converter valve protection system according to claim 1, characterized in that, The number of capacitor protection modules is less than or equal to the number of AC filter capacitors, and each capacitor protection module is connected to one AC filter capacitor.

3. The current source converter valve protection system according to claim 1, characterized in that, The duration of the first bidirectional current-carrying switch being turned off is determined based on the oscillation period of the AC filter capacitor.

4. The current source converter valve protection system according to claim 1, characterized in that, The method for determining AC-side fault recovery includes: in the event of an AC-side fault in the current source converter valve, acquiring the AC-side voltage of the current source converter valve in real time; and determining that the AC-side fault has been recovered when the AC-side voltage recovers to a preset multiple of the rated voltage.

5. The current source converter valve protection system according to any one of claims 1-4, characterized in that, The capacitor protection module is also used to provide overvoltage protection for the AC filter capacitor in the event of an AC side fault.

6. The current source converter valve protection system according to claim 5, characterized in that, The capacitor protection module includes a second protection submodule. The first end of the second protection submodule is connected to the first end of the AC filter capacitor, and the second end of the second protection submodule is connected to the second end of the AC filter capacitor. The second ends of each AC filter capacitor are connected to a common connection point.

7. The current source converter valve protection system according to claim 6, characterized in that, The second protection submodule includes a second bidirectional current-passing switch and a second overvoltage protection device connected in parallel; wherein, in the event of an AC side fault in the current source converter valve, the second overvoltage protection device provides overvoltage protection for the AC filter capacitor, and in the event of a fault in the AC filter capacitor, the second bidirectional current-passing switch is turned on to bypass the faulty AC filter capacitor.

8. The current source converter valve protection system according to claim 7, characterized in that, The method for determining that the AC filter capacitor has failed includes: obtaining the voltage value of the AC filter capacitor; and determining that the AC filter capacitor has failed when the voltage value is less than a preset voltage threshold for a preset duration.

9. The current source converter valve protection system according to claim 5, characterized in that, The method for determining that the current source converter valve has an AC side fault includes: acquiring the AC side voltage of the current source converter valve in real time; and determining that the current source converter valve has an AC side fault when the AC side voltage drops to a preset fault voltage.

10. A current source converter, characterized in that, It includes a converter transformer and a current source converter valve protection system as described in any one of claims 1-9.

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