Current source converter valve protection system and current source converter

Abstract

The invention relates to a current source converter valve and a current source converter, an alternating current filter capacitor and a converter transformer are respectively connected to an alternating current outlet end of the current source converter valve, and a second end of the converter transformer is connected to an alternating current power grid, so that alternating current and direct current conversion can be carried out in a power transmission process. Moreover, according to the scheme, a capacitor protection module is connected to the alternating current filter capacitor, and through the capacitor protection module, overvoltage protection can be performed on the alternating current filter capacitor under the condition that the alternating current side fault of the current source converter valve occurs, and / or oscillation suppression can be performed on the alternating current filter capacitor under the condition that the alternating current side fault is recovered. Thus, it can be ensured that the AC filter capacitor is not in overvoltage when the current source converter valve has an AC side fault, and / or it can be ensured that the AC filter capacitor rapidly returns to a steady state when the AC side fault is recovered, and then the operation risk of the filter capacitor in the current source converter valve is greatly reduced.

Description

Technical Field

[0001] The present application relates to the field of commutation technology, and in particular to a current source commutation valve protection system and a current source converter. Background Art

[0002] A current source converter valve is a device that controls current conduction and cutoff by controlling the trigger angle of a thyristor device. It can convert alternating current into direct current or convert direct current into alternating current, achieving efficient conversion and long-distance transmission of electric energy. It is widely used in high-voltage direct current transmission systems (HVDC).

[0003] The current source converter valve is generally connected to an AC filter capacitor at the AC outlet to provide a phase-changing circuit. However, in the related art, the operation risk of the AC filter capacitor is relatively high. Summary of the invention

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

[0005] The present application provides a current source converter valve protection system, comprising: a current source converter valve, an AC filter capacitor and a capacitor protection module, wherein the AC filter capacitor is connected to the AC outlet end of the current source converter valve and the first end of a converter transformer; the capacitor protection module is connected to the AC filter capacitor; the capacitor protection module is used to perform overvoltage protection on the AC filter capacitor in the event of an AC side fault, and / or to suppress oscillation of the AC filter capacitor in the event of recovery from the AC side fault.

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

[0007] In one embodiment, the capacitor protection module includes a first protection submodule, a first end of the first protection submodule is connected to a first end of the AC filter capacitor, a second end of the first protection submodule is connected to a first end of the converter transformer and a one-phase AC outlet end of the current source converter valve, and a 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-passing switch device and a first overvoltage protection device connected in parallel; wherein, when the AC side fault is recovered, the first bidirectional current-passing switch device is turned off to generate additional damping through the first overvoltage protection device to suppress oscillation of the AC filter capacitor.

[0009] In one of the embodiments, the duration of the shutdown of the first bidirectional current-passing switch device is determined according to the oscillation period of the oscillation of the AC filter capacitor.

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

[0011] In one embodiment, the capacitor protection module includes a second protection submodule, a first end of the second protection submodule is connected to the first end of the AC filter capacitor, a second end of the second protection submodule 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 flow switch device 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 AC filter capacitor is protected from overvoltage by the second overvoltage protection device, and in the event of a fault in the AC filter capacitor, the second bidirectional flow switch device is turned on to bypass the faulty AC filter capacitor.

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

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

[0015] The present application also provides a current source converter, including a converter transformer and the above-mentioned current source converter valve protection system.

[0016] The above-mentioned current source converter valve protection system and current source converter are respectively connected to an AC filter capacitor and a converter transformer at the AC outlet end of the current source converter valve, and the second end of the converter transformer is connected to the AC power grid, so that AC-DC conversion can be performed during power transmission. In addition, the scheme also connects a capacitor protection module to the AC filter capacitor. Through the capacitor protection module, the AC filter capacitor can be protected from overvoltage in the event of an AC side fault, and / or the AC filter capacitor can be suppressed from oscillation in the event of an AC side fault recovery. The above scheme can perform overvoltage protection and / or oscillation suppression on the AC filter capacitor when an AC side fault occurs and when the AC side fault is restored. In this way, it can be ensured that the AC filter capacitor will not be over-voltage when an AC side fault occurs, and / or that the AC filter capacitor quickly returns to a steady state when the AC side fault is restored, thereby greatly reducing the operating risk of the filter capacitor connected to the AC outlet of the current source converter valve. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the conventional technology, the drawings required for use in the embodiments or the conventional technology descriptions are briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0018] Figure 1 This is a structural schematic diagram of a current source converter valve protection system in an embodiment of the present application;

[0019] Figure 2 This is a schematic diagram of the topological structure of a current source converter circuit in an embodiment of the present application;

[0020] Figure 3 A schematic diagram of the topological structure of a current source converter valve protection system in an embodiment of the present application;

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

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

[0023] Description of reference numerals:

[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-converter transformer leakage inductance. DETAILED DESCRIPTION

[0025] In order to facilitate the understanding of the present application, the present application will be described more fully below with reference to the relevant drawings. The preferred embodiments of the present application are provided in the drawings. However, the present application can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the understanding of the disclosure of the present application more thorough and comprehensive.

[0026] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which this application belongs. The terms used herein in the specification of this application are only for the purpose of describing specific embodiments and are not intended to limit this application.

[0027] It is understood that the terms "first", "second", etc. used in this application may be used herein to describe various elements, but these elements are not limited by these terms. These terms are only used to distinguish a first element from another element. 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 can be understood that the “connection” in the following embodiments should be understood as “electrical connection”, “communication connection”, etc. if the connected circuits, modules, units, etc. have electrical signals or data transmission between each other.

[0029] It can be understood that “at least one” means one or more, “plurality” means two or more, and “at least a portion of an element” means a part or all of an element.

[0030] When used herein, the singular forms "a", "an", and "said / the" may also include plural forms, unless the context clearly indicates otherwise. It should also be understood that the terms "include / comprise" or "have" and the like specify the presence of stated features, wholes, steps, operations, components, parts, or combinations thereof, but do not exclude the possibility of the presence or addition of one or more other features, wholes, steps, operations, components, parts, or combinations thereof. At the same time, the term "and / or" used in this specification includes any and all combinations of the relevant listed items.

[0031] With the continuous development of science and technology, high-voltage direct current transmission systems have gradually been widely used due to their advantages such as long transmission distance, low loss, high transmission efficiency, good stability, and easy dispatch. However, in the converter valve of the high-voltage direct current transmission system, the AC filter capacitor located on the AC side has a greater operating risk, which is manifested in that it is easy to be damaged due to overvoltage or prone to oscillation.

[0032] Through in-depth research, it is found that overvoltage damage of AC filter capacitors often occurs during the process of AC side faults. The oscillation of AC filter capacitors mainly occurs after the AC filter capacitors experience a fault, that is, after the AC side fault is restored. Specifically, because the AC side of the current source converter valve is equipped with a converter transformer with a certain converter transformer leakage inductance, and because the capacitance of the current source converter valve and the leakage inductance of the converter transformer are both relatively large, it is easy for the two to produce LC resonance after a fault, and the recovery process is long.

[0033] In order to alleviate the above phenomenon, it was found through research that a capacitor protection module can be connected to the AC filter capacitor, and the AC side fault of the current source converter valve can be monitored. When an AC side fault is detected, the capacitor protection module is turned on to protect the AC filter capacitor from overvoltage; and when the AC side fault recovery is detected, the capacitor protection module is turned on to suppress the oscillation of the AC filter capacitor, so as to quickly attenuate the resonant current, so that the AC filter capacitor can quickly return to a steady state and reduce the operating risk.

[0034] Based on this, see Figure 1 The present 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 end of the current source converter valve 110 and the first end of the converter transformer 120, and the second end of the converter transformer 120 is used to access 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 perform overvoltage protection on the AC filter capacitor C in the event of an AC side fault, and / or to suppress oscillation of the AC filter capacitor C in the event of an AC side fault recovery.

[0035] Specifically, the current source converter valve 110 is a device that can convert AC power into DC power, or convert DC power into AC power, by controlling the on-off of a switch device. The converter transformer 120 is a transformer used to implement a voltage transformation function in a current source converter. The AC filter capacitor C is arranged on the AC side of the current source converter valve 110 to provide capacitance for a commutation circuit. The capacitor protection module 130 is a functional module used to protect the AC filter capacitor C. An AC side fault is a fault that occurs on the AC side of the current source converter valve, and the AC side of the current source converter valve is the side that is equipped with an AC power supply.

[0036] It should be noted that the specific type of the current source converter valve 110 is not unique. In one embodiment, see Figure 2 The current source converter valve 110 includes a DC smoothing reactor Ldc and a power unit 111, wherein the DC end of the power unit 111 is connected to the DC power supply through the DC smoothing reactor Ldc, and the AC outlet end of the power unit 111 serves as the AC outlet end of the current source converter valve 110. Further, the type of the 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 power, and correspondingly, the power unit 111 should also be a three-phase type of power unit 111. In more detail, the power unit 111 is a three-phase six-bridge arm power unit, which is not specifically limited.

[0037] It can be understood that in one embodiment, the capacitor protection module 130 is connected to the AC filter capacitor C. When an AC side fault is detected in the current source converter valve 110, or the AC side fault is restored, 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. During the operation of the current source converter valve 110, the controller is used to monitor the fault of the converter valve in real time. When an AC side fault is detected in the current source converter valve 110, the controller controls the capacitor protection module 130 to operate so as to perform overvoltage protection on the AC filter capacitor C; and / or when the AC side fault recovery is detected, the controller controls the capacitor protection module 130 to operate so as to suppress oscillation of the AC filter capacitor C.

[0039] In the above-mentioned current source converter valve protection system, an AC filter capacitor C and a converter transformer 120 are respectively connected to the AC outlet end of the current source converter valve 110, and the second end of the converter transformer 120 is connected to the AC power grid, so that AC-DC conversion can be performed during power transmission. In addition, the scheme also connects a capacitor protection module 130 to the AC filter capacitor C. Through the capacitor protection module 130, when an AC side fault occurs in the current source converter valve 110, the AC filter capacitor C can be over-voltage protected, and / or when the AC side fault is restored, the AC filter capacitor C can be oscillated. The above-mentioned scheme can respectively perform over-voltage protection and / or oscillation suppression on the AC filter capacitor C when an AC side fault occurs in the current source converter valve 110 and when the AC side fault is restored. In this way, it can be ensured that when an AC side fault occurs in the current source converter valve 110, the AC filter capacitor C will not be over-voltaged, and / or, it can be ensured that when the AC side fault is restored, the AC filter capacitor C quickly returns to a steady state, thereby greatly reducing the operating risk of the AC filter capacitor C connected to the AC outlet end of the current source converter valve 110.

[0040] See also Figure 2 In one embodiment, the AC outlet end of the current source converter valve 110 includes a three-phase AC outlet end, each phase AC outlet end of the current source converter valve 110 is correspondingly connected to the second end 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 correspondingly connected to an AC filter capacitor C.

[0041] Specifically, the solution of this embodiment is explained by taking the current source converter valve 110 as a three-phase current source converter valve, and the AC end of the current source converter valve 110 includes a three-phase AC outlet end, that is, an AC outlet end corresponding to A, an AC outlet end corresponding to B, and an AC outlet end corresponding to C. In order to achieve reliable transmission of AC power, an AC filter capacitor C (which may be a single capacitor or a capacitor group formed by connecting multiple capacitors in series and / or in parallel) needs to be configured at each phase AC outlet end.

[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, which means that a capacitor protection module 130 can be configured for at least one AC filter capacitor C to protect the AC filter capacitor C. It can be understood that in actual scenarios, the number of capacitor protection modules 130 is not unique, and can be selected in combination with actual needs. In more detail, in one embodiment, the number of capacitor protection modules 130 can be set to be consistent with the number of AC filter capacitors C, that is, each AC filter capacitor C is configured with a capacitor protection module 130 to achieve protection of all AC filter capacitors C at the AC outlet end of the current source converter valve 110.

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

[0044] Specifically, in the solution of this embodiment, the capacitor protection module 130 includes a first protection submodule 131, and the first protection submodule 131 is connected in series with the AC filter capacitor C, specifically connected in series between the AC filter capacitor C and the converter transformer 120. In this way, when LC resonance occurs between the AC filter capacitor C and the leakage inductance L of the converter transformer, oscillation suppression can be performed to reduce the oscillation duration of the AC filter capacitor C and improve the operating stability of the AC filter capacitor C.

[0045] It should be noted that the number of the first protection submodules 131 is not unique, and 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, a 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 device T1 and a first overvoltage protection device B1 connected in parallel; wherein, when the AC side fault is restored, the first bidirectional current-carrying switch device T1 is turned off to generate additional damping through the first overvoltage protection device B1 to suppress the oscillation of the AC filter capacitor C.

[0047] Specifically, the structure of the first protection submodule 131 is not unique, as long as it can generate a certain amount of additional damping to achieve oscillation suppression of the AC filter capacitor C when the AC side fault of the current source converter valve 110 is restored. The solution of this embodiment is explained by taking the first protection submodule 131 as including a first bidirectional through-current switch device T1 and a first overvoltage protection device B1 connected in parallel. In this solution, the first end and the second end of the first bidirectional through-current switch device T1 are respectively connected to the first end and the second end of the first overvoltage protection device B1, and the control end of the first bidirectional through-current switch device T1 is connected to the controller, and the protection of the capacitor protection module 130 is achieved under the action of the controller.

[0048] Specifically, when the current source converter valve 110 is operating normally, or when the current source converter valve 110 has an AC side fault, the controller controls the first bidirectional flow switch device T1 to be in the on state, at which time the current is transmitted through the first bidirectional flow switch device 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 the AC side fault recovery is monitored, the controller controls the first bidirectional flow switch device T1 to be turned off, and the current flows through the first overvoltage protection device B1. Afterwards, the first overvoltage protection device B1 will generate a clamping voltage, which is opposite to the current direction of the AC filter capacitor C and can be regarded as a reverse voltage. The reverse voltage hinders the further charging of the AC filter capacitor C, so it can be regarded as a damping effect, that is, additional damping is generated to suppress the oscillation of the AC filter capacitor C.

[0049] The above scheme adopts the first bidirectional current-passing switch device T1 and the first overvoltage protection device B1 to build the first protection submodule 131, which generates additional damping in the form of a reverse clamping voltage to achieve oscillation suppression 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-passing switch device T1 is not unique, and any current-passing switch device that can realize on-off control under the action of the controller can be used. For example, in a more detailed embodiment, the first bidirectional current-passing switch device T1 can be any one of an IGBT (Insulate-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 lightning arrester, a transient voltage suppression diode, an avalanche diode and a Zener diode, and the selection can be made based on 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 put the first bidirectional flow switch device T1 into operation between the AC filter capacitor C and the converter transformer 120, that is, restore the first bidirectional flow switch device T1 to the on state. Therefore, after the first bidirectional flow switch device T1 is turned off and meets certain conditions, the controller needs to control the first bidirectional flow switch device T1 to be turned on to end the oscillation suppression.

[0053] It should be pointed out that the conditions satisfied by the shutdown operation of the first bidirectional current-passing switch device T1 are not unique. In one embodiment, the oscillation state of the AC filter capacitor C can be detected by the controller. When the oscillation of the AC filter capacitor C disappears, the first bidirectional current-passing switch device T1 is controlled to be turned on to end the oscillation suppression.

[0054] In another embodiment, the allowed duration of the turn-off configuration of the first bidirectional current-passing switch device T1 can be configured. When the duration of the turn-off of the first bidirectional current-passing switch device T1 reaches a certain value, the first bidirectional current-passing switch device T1 is controlled to be turned on to end the oscillation suppression.

[0055] In more detail, in one embodiment, the duration of the shutdown of the first bidirectional current-passing switch device T1 is determined according to the oscillation period of the oscillation of the AC filter capacitor C.

[0056] Specifically, the oscillation period of the oscillation of the AC filter capacitor C can be calculated according to the period calculation formula of LC resonance, 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 repeated here. In an actual scenario, the duration of the first bidirectional current-passing switch device T1 being turned off can be set to be greater than a preset multiple of the oscillation period. In more detail, in one embodiment, the duration of the first bidirectional current-passing switch device 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 also be set to other sizes, as long as it can ensure that the oscillation of the AC filter capacitor C is effectively suppressed.

[0057] The above scheme determines the duration of the shutdown of the first bidirectional current-passing switch device T1 through 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 of the embodiments, the method for determining the recovery of the AC side fault includes: when an AC side fault occurs in the current source converter valve 110, obtaining the AC side voltage of the current source converter valve 110 in real time; when the AC side voltage recovers to a preset multiple of the rated voltage, determining that the AC side fault is recovered.

[0059] Specifically, the method for judging whether the AC side fault of the current source converter valve 110 has been restored is not unique. In the scheme of this embodiment, after the AC side fault occurs, the controller monitors the AC side voltage in real time, that is, the AC side voltage is obtained in real time by a voltage detection device arranged on the AC side, and compared and analyzed with the rated voltage of the current source converter valve 110. When the AC side voltage is analyzed to be restored to a preset multiple of the rated voltage, that is, the AC side voltage gradually increases to a preset multiple greater than or equal to the rated voltage, it is considered that the AC side fault disappears, that is, the AC side fault is restored. This scheme, which judges whether the AC side fault is restored based on the AC side voltage of the current source converter valve 110, has a high judgment accuracy.

[0060] It should be noted that the size of the preset multiple is not unique, as long as it can reasonably represent the disappearance of the AC side fault. For example, in a more detailed embodiment, the preset multiple can be set to 90%, that is, when the AC side voltage recovers to 90% of the rated voltage, it is considered that the AC side fault has recovered. In other embodiments, the preset multiple can also be set to 85%, 95%, etc., without specific limitation.

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

[0062] Specifically, in the solution of this embodiment, the capacitor protection module 130 includes a second protection submodule 132 connected in parallel with the AC filter capacitor C. Thus, through the setting of the second protection submodule 132, the voltage of the AC filter capacitor C can be clamped, thereby preventing the voltage flowing through the AC filter capacitor C from being too large, thereby achieving overvoltage protection.

[0063] Specifically, in an actual scenario, the capacitor protection module 130 may 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 , and may be configured according to actual needs.

[0064] It should be noted that the number of the second protection submodules 132 is not unique, and in one embodiment, the second protection submodule 132 may be connected in parallel at both ends of at least one AC filter capacitor C. In more detail, in one embodiment, a second protection submodule 132 may be connected in parallel at both ends of 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 flow switch device 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 protected from overvoltage by the second overvoltage protection device B2, and in the event of a fault in the AC filter capacitor C, the second bidirectional flow switch device T2 is turned on to bypass the faulty AC filter capacitor C.

[0066] Specifically, in the solution of this embodiment, the second protection submodule 132 has a similar structure to the first protection submodule 131, and both include a bidirectional through-current switch device and an overvoltage protection device connected in parallel, wherein the control end of the second bidirectional through-current switch device T2 is connected to the controller, and the types of the second bidirectional through-current switch device T2 and the second overvoltage protection device B2 are similar to the above-mentioned first bidirectional through-current switch device T1 and the first overvoltage protection device B1, and are not repeated here. In the actual operation process, the controller performs real-time detection of AC side faults and AC filter capacitor C faults. When the AC filter capacitor C fault is not detected, regardless of whether the AC side fault occurs, the controller controls the second bidirectional through-current switch device T2 to be in a disconnected state, which is equivalent to the second overvoltage protection device B2 being connected in parallel with the AC filter capacitor C, and overvoltage protection of the AC filter capacitor C can be achieved (overvoltage protection is performed when the AC side fault occurs, or overvoltage protection is performed when the non-AC side fault occurs). When a fault in the AC filter capacitor C is detected, the controller can control the second bidirectional current-carrying switch device T2 to be turned on. At this time, the AC filter capacitor C is short-circuited, and the current is transmitted through the second bidirectional current-carrying switch device T2, thereby realizing fault bypass of the AC filter capacitor C without affecting the operation of other AC filter capacitors C that are not faulty.

[0067] In the above scheme, a second bidirectional current-passing switch device T2 and a second overvoltage protection device B2 are used to build a second protection submodule 132. The second bidirectional current-passing switch device T2 is turned on to achieve fault bypass of the AC filter capacitor C, and the second overvoltage protection device B2 is used to achieve overvoltage protection during operation of the AC filter capacitor C. The circuit structure is simple and circuit costs are effectively saved.

[0068] In one of the embodiments, a method for determining whether an AC filter capacitor C has failed includes: obtaining a 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 time period.

[0069] Specifically, there is not only one way to determine whether the AC filter capacitor C has a fault. In this embodiment, the fault analysis is performed by detecting the voltage value at both ends of the AC filter capacitor C. Specifically, the controller compares and analyzes the voltage value at both ends of the AC filter capacitor C obtained in real time with the preset voltage threshold, and starts timing when the voltage value is less than the preset voltage threshold. If the duration of the voltage value being less than the preset voltage threshold reaches the preset duration, it is considered that the AC filter capacitor C has a fault, that is, the AC filter capacitor C is broken down.

[0070] The above scheme uses the voltage value across the AC filter capacitor C to perform fault monitoring on the AC filter capacitor C, which has a high fault judgment accuracy.

[0071] In one of the embodiments, a method for determining that an AC side fault occurs in the current source converter valve 110 includes: acquiring the AC side voltage of the current source converter valve 110 in real time; and determining that an AC side fault occurs in the current source converter valve 110 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 obtains the AC side voltage of the current source converter valve 110 in real time, and uses the AC side voltage to monitor whether an AC side fault occurs in the current source converter valve 110 in real time. Specifically, the AC side voltage is compared and analyzed with a preset fault voltage, and when it is detected that the AC side voltage is less than or equal to (that is, drops to) the preset fault voltage, it is determined that an AC side fault occurs at this time. This solution realizes AC side fault monitoring by detecting the AC side voltage of the current source converter valve 110 in real time, and has high monitoring accuracy.

[0073] In order to facilitate understanding of the technical solution of the present application, the present application is explained below in conjunction with more detailed embodiments.

[0074] The current source converter valve protection system of the present application includes a controller, a current source converter valve 110, an AC filter capacitor C, 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 arm power unit 111 and a DC smoothing reactor Ldc. The DC end of the three-phase six-bridge arm power unit 111 is connected to a DC power supply through the DC smoothing reactor Ldc. The three-phase output ends of the three-phase six-bridge arm 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, and both include a parallel bidirectional flow switch device and an overvoltage protection device.

[0075] During the actual operation, the controller obtains in real time the AC side voltage of the current source converter valve 110 and the voltage value across the AC filter capacitor C. When analyzing the AC side voltage and the voltage value and finding that there is no AC side fault or AC filter capacitor C fault, for each AC filter capacitor C, the controller controls the first bidirectional current-carrying switch device T1 to turn on and controls the second bidirectional current-carrying switch device T2 to turn off.

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

[0077] After that, if it is detected that the AC side voltage rises and reaches a preset multiple of the rated voltage (for example, 90% of the rated voltage), it is determined that the AC side fault has recovered. At this time, the controller controls the first bidirectional current-carrying switch device T1 to turn off, so that the first overvoltage protection device B1 is connected to generate additional damping for oscillation suppression. In this process, the controller can combine the leakage inductance L of the converter transformer and the capacitance value of the AC filter capacitor C to calculate the duration of the first bidirectional current-carrying switch device T1 to be turned off. After the duration of the first bidirectional current-carrying switch device T1 being turned off reaches the duration, the controller controls the first bidirectional current-carrying switch device T1 to be turned on and enter the normal operating state.

[0078] If it is detected that the voltage value is less than the preset voltage threshold for a continuous period of time that reaches the preset time, it is considered that the AC filter capacitor C has a fault. At this time, it is necessary to control the second bidirectional current-passing switch device T2 at both ends of the AC filter capacitor C to be turned on, and the faulty AC filter capacitor C to be bypassed to ensure that other AC filter capacitors C can operate continuously until the fault is eliminated.

[0079] In the description of this specification, the description with reference to the terms "some embodiments", "other embodiments", etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present application. In this specification, the schematic description of the above terms does not necessarily refer to the same embodiment or example.

[0080] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described 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 above-described embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be construed as limiting the scope of the patent application. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the patent application shall be subject to the attached claims.

Claims

1. A current source converter valve protection system, characterized in that: include: Current source commutation valve; An AC filter capacitor connected to the AC outlet end of the current source converter valve and the first end of the converter transformer, the second end of the converter transformer being used to access the AC power grid; A capacitor protection module is connected to the AC filter capacitor; the capacitor protection module is used to perform overvoltage protection on the AC filter capacitor in the event of an AC side fault, and / or to suppress oscillation of the AC filter capacitor in the event of AC side fault recovery.

2. The current source converter valve protection system according to claim 1, characterized in that: The AC outlet end of the current source converter valve includes a three-phase AC outlet end, each phase AC outlet end of the current source converter valve is correspondingly connected to the first end of the converter transformer and an AC filter capacitor, the number of the capacitor protection modules is less than or equal to the number of the AC filter capacitors, and each of the capacitor protection modules is correspondingly connected to an AC filter capacitor.

3. The current source converter valve protection system according to claim 2, characterized in that: The capacitor protection module includes a first protection submodule, a first end of the first protection submodule is connected to the first end of the AC filter capacitor, a second end of the first protection submodule is connected to the first end of the converter transformer and a one-phase AC outlet end of the current source converter valve, and the second end of each AC filter capacitor is connected to a common connection point.

4. The current source converter valve protection system according to claim 3, characterized in that: The first protection submodule includes a first bidirectional current-carrying switch device and a first overvoltage protection device connected in parallel; wherein, when the AC side fault is restored, the first bidirectional current-carrying switch device is turned off to generate additional damping through the first overvoltage protection device to suppress oscillation of the AC filter capacitor.

5. The current source converter valve protection system according to claim 4, characterized in that: The duration of the shutdown of the first bidirectional current-passing switch device is determined according to the oscillation period of the oscillation of the AC filter capacitor.

6. The current source converter valve protection system according to any one of claims 1 to 5, characterized in that: The method for determining the recovery of the AC side fault includes: when an AC side fault occurs in the current source converter valve, obtaining the AC side voltage of the current source converter valve in real time; when the AC side voltage recovers to a preset multiple of the rated voltage, determining that the AC side fault has been recovered.

7. The current source converter valve protection system according to any one of claims 2 to 5, characterized in that: The capacitor protection module includes a second protection submodule, a first end of the second protection submodule is connected to the first end of the AC filter capacitor, a second end of the second protection submodule 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.

8. The current source converter valve protection system according to claim 7, characterized in that: The second protection submodule includes a second bidirectional flow switch device 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 AC filter capacitor is protected from overvoltage by the second overvoltage protection device, and in the event of a fault in the AC filter capacitor, the second bidirectional flow switch device is turned on to bypass the faulty AC filter capacitor.

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

10. The current source converter valve protection system according to any one of claims 1 to 5, characterized in that: The method for determining whether an AC side fault occurs in the current source converter valve includes: acquiring the AC side voltage of the current source converter valve in real time; and determining that an AC side fault occurs in the current source converter valve when the AC side voltage drops to a preset fault voltage.

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

Images