Protection method and device for short-circuit fault of bridge arm reactor

Abstract

The invention relates to a protection method and device for a short-circuit fault of a bridge arm electric reactor, and belongs to the field of flexible direct-current power transmission system.The current upper bridge arm current and the current lower bridge arm current of any phase of bridge arm of a flexible direct-current converter on the direct-current side are obtained, and the effective value of a fundamental component in current bridge arm circulating current is calculated according to the current upper bridge arm current and the current lower bridge arm current; determining a current protection constant value under the current upper and lower bridge arm current levels according to a linear relationship between a pre-obtained bridge arm current effective value and a protection constant value used for judging the fault of the reactor; and when the effective value of the fundamental component in the current bridge arm circulating current is greater than the current protection constant value, determining that the bridge arm reactor at the direct current side has a fault, and triggering a protection action, so that short-circuit fault identification and processing of the bridge arm reactor at the direct current side can be realized under any operation condition, and operation and maintenance personnel can conveniently and timely find the fault.

Description

Technical Field

[0001] The invention relates to a method and a device for protecting a bridge arm reactor from short-circuit fault, and belongs to the field of flexible direct current transmission systems. Background Art

[0002] Flexible DC transmission systems based on modular multilevel converters (MMCs) offer advantages such as flexible structure, high controllability, and low output voltage distortion. They play an important role in large-scale renewable energy integration, asynchronous interconnection of regional power grids, and long-distance, high-capacity power transmission. Arm reactors are a key component of flexible DC transmission systems, suppressing the rate of rise of fault currents. Arm reactors are deployed in the upper and lower arms of the three-phase modular multilevel converter. Arm reactors can be located between the AC connection point and the converter valve, or between the DC pole line and the converter valve.

[0003] Regardless of whether the flexible DC transmission system's wiring method is pseudo-bipolar or true bipolar, fault detection in the flexible DC transmission system is particularly critical due to the poor ability of the flexible DC converter valve equipment to withstand electrical stresses such as overcurrent and overvoltage. For flexible DC systems with arm reactors installed on the AC side, short-circuit faults in the arm reactor area can be quickly isolated through the differential protection and overcurrent protection configured in that area. However, for flexible DC systems with arm reactors installed on the DC side, when a valve-side short-circuit fault occurs in the arm reactor, the arm voltage changes slightly. When a single-phase end-to-end short-circuit fault occurs in the arm reactor, the circulating current suppression effect occurs, resulting in unclear characteristics of both faults. This makes the fault difficult to reliably detect, making it impossible to detect the reactor fault in time and provide circuit protection, posing a threat to equipment and operators within the converter station. Summary of the Invention

[0004] The object of the present invention is to provide a method and device for protecting a bridge arm reactor from short circuit faults, so as to solve the problem that the reactor faults cannot be detected in time when the bridge arm reactor is installed on the DC side.

[0005] To achieve the above object, the present invention provides a method for protecting a bridge arm reactor from a short-circuit fault, comprising the following steps:

[0006] 1) Obtain the current upper and lower arm currents of any phase bridge arm of the flexible DC converter on the DC side, and calculate the effective value of the fundamental component of the current arm circulating current based on the current upper and lower arm currents;

[0007] 2) determining the current protection setting at the current upper and lower bridge arm current levels based on the linear relationship between the pre-obtained bridge arm current effective value and the protection setting used to determine whether the reactor has failed;

[0008] 3) When the effective value of the fundamental component in the current arm circulating current is greater than the current protection setting, it is determined that the bridge arm reactor on the DC side is faulty and the protection action is triggered.

[0009] Furthermore, the linear relationship is generated by the following method:

[0010] Within the actual operating power range of the flexible HVDC transmission system, the minimum effective value of the fundamental component of the arm circulating current after first-order smoothing filtering during the fault period is calculated when the arm reactor fails at different actual operating powers. Based on the minimum effective value of the fundamental component of the arm circulating current after first-order smoothing filtering, the protection setting value corresponding to the effective value range of the arm current at the actual operating power is calculated.

[0011] The bridge arm current effective value intervals and protection settings corresponding to all actual operating powers are integrated to generate the linear relationship.

[0012] Furthermore, the protection setting value corresponding to the effective value range of the bridge arm current under the actual operating power is calculated based on the minimum effective value of the fundamental component in the bridge arm circulating current after the first-order smoothing filter by the following method:

[0013] I set =k*MIN(Icir x _50_PT1)

[0014] Among them, I set is the protection value; k is the reliability coefficient; Icir x _50_PT1 is the effective value of the fundamental component of the circulating current in the x-phase bridge arm after first-order smoothing filtering.

[0015] Furthermore, the reliability coefficient ranges from 0.8 to 0.9.

[0016] Furthermore, when the arm reactor fault is an interphase short circuit fault on the valve side of the arm reactor, the effective value of the fundamental component of the arm circulating current after the first first-order smoothing filter during the interphase short circuit fault on the valve side of the arm reactor is calculated;

[0017] When the arm reactor fault is a single-phase short-circuit fault at the beginning and end of the arm reactor, calculate the effective value of the fundamental component of the arm circulating current after the second first-order smoothing filter during the single-phase short-circuit fault of the arm reactor;

[0018] A smaller value is selected from the effective value of the fundamental wave component in the bridge arm circulating current after the first first-order smoothing filter and the effective value of the fundamental wave component in the bridge arm circulating current after the second first-order smoothing filter as the minimum value.

[0019] On the other hand, the present invention also provides a protection device for a bridge arm reactor short circuit fault, comprising a processor, wherein the processor is configured to perform the following steps:

[0020] 1) Obtain the current upper and lower arm currents of any phase bridge arm of the flexible DC converter on the DC side, and calculate the effective value of the fundamental component of the current arm circulating current based on the current upper and lower arm currents;

[0021] 2) determining the current protection setting at the current upper and lower bridge arm current levels based on the linear relationship between the pre-obtained bridge arm current effective value and the protection setting used to determine whether the reactor has failed;

[0022] 3) When the effective value of the fundamental component in the current arm circulating current is greater than the current protection setting, it is determined that the bridge arm reactor on the DC side is faulty and the protection action is triggered.

[0023] Furthermore, the linear relationship is generated by the following method:

[0024] Within the actual operating power range of the flexible HVDC transmission system, the minimum effective value of the fundamental component of the arm circulating current after first-order smoothing filtering during the fault period is calculated when the arm reactor fails at different actual operating powers. Based on the minimum effective value of the fundamental component of the arm circulating current after first-order smoothing filtering, the protection setting value corresponding to the effective value range of the arm current at the actual operating power is calculated.

[0025] The bridge arm current effective value intervals and protection settings corresponding to all actual operating powers are integrated to generate the linear relationship.

[0026] Furthermore, the protection setting value corresponding to the effective value range of the bridge arm current under the actual operating power is calculated based on the minimum effective value of the fundamental component in the bridge arm circulating current after the first-order smoothing filter by the following method:

[0027] I set =k*MIN(Icir x _50_PT1)

[0028] Among them, I set is the protection value; k is the reliability coefficient; Icir x _50_PT1 is the effective value of the fundamental component of the circulating current in the x-phase bridge arm after first-order smoothing filtering.

[0029] Furthermore, the reliability coefficient ranges from 0.8 to 0.9.

[0030] Furthermore, when the arm reactor fault is an interphase short circuit fault on the valve side of the arm reactor, the effective value of the fundamental component of the arm circulating current after the first first-order smoothing filter during the interphase short circuit fault on the valve side of the arm reactor is calculated;

[0031] When the arm reactor fault is a single-phase short-circuit fault at the beginning and end of the arm reactor, calculate the effective value of the fundamental component of the arm circulating current after the second first-order smoothing filter during the single-phase short-circuit fault of the arm reactor;

[0032] A smaller value is selected from the effective value of the fundamental wave component in the bridge arm circulating current after the first first-order smoothing filter and the effective value of the fundamental wave component in the bridge arm circulating current after the second first-order smoothing filter as the minimum value.

[0033] The beneficial effects of the present invention are: obtaining the current upper and lower arm currents of any phase bridge arm on the DC side of the flexible DC converter, and calculating the effective value of the fundamental component in the current bridge arm circulating current based on the current upper and lower arm currents; determining the current protection setting under the current upper and lower arm current levels from the linear relationship between the pre-obtained bridge arm current effective value and the protection setting used to determine whether the inductor has failed; when the effective value of the fundamental component in the current bridge arm circulating current is greater than the current protection setting, it is determined that the bridge arm inductor on the DC side has failed, triggering the protection action, and realizing the selection of setting different protection settings according to different bridge arm currents, so that the short-circuit fault of the bridge arm inductor on the DC side can be identified and processed under any operating conditions, avoiding the problem of no fault being discovered due to weak changes in the bridge arm voltage or the circulating current suppression effect, and facilitating operation and maintenance personnel to discover faults in a timely manner, which not only protects the safety of equipment and personnel, but also simplifies the fault judgment process, occupies less memory resources during the operation process, and facilitates engineering implementation. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 This is a flow chart of a method for protecting a bridge arm reactor from short-circuit faults proposed by the present invention;

[0035] Figure 2 This is a partial circuit topology diagram of a bridge arm reactor short-circuit fault protection method proposed by the present invention when a pseudo-bipolar wiring method is used in an actual application scenario;

[0036] Figure 3 This is a partial circuit topology diagram of a bridge arm reactor short-circuit fault protection method proposed by the present invention when a true bipolar wiring method is used in an actual application scenario;

[0037] Figure 4 This is a flow chart of a protection method for a bridge arm reactor short-circuit fault proposed by the present invention in an actual application scenario;

[0038] Figure 5 This is a flow chart of triggering a protection action in an actual application scenario of a protection method for a bridge arm reactor short-circuit fault proposed by the present invention;

[0039] Figure 6 The present invention provides a schematic diagram of the internal system structure of a protection device for a bridge arm reactor short-circuit fault in an actual application scenario. DETAILED DESCRIPTION

[0040] In order to make the objectives, technical solutions and advantages of the present invention more clear, the present invention is further described in detail below with reference to the accompanying drawings and embodiments.

[0041] The inventive concept of the present invention is: in order to accurately monitor the faults of the bridge arm reactor installed on the DC side, by collecting the upper and lower arm currents of any bridge arm of the converter on the DC side, the effective value of the fundamental component in the current bridge arm circulating current is calculated, and then the linear relationship between the pre-obtained bridge arm current effective value and the protection setting used to determine whether the reactor has a fault is obtained is combined to obtain the current protection setting, so as to use the current protection setting to determine whether the bridge arm reactor is faulty, timely discover the operating status of the DC side bridge arm reactor, and trigger the protection action when the reactor fails, breaking through the technical barrier of the inability to timely monitor the faults of the DC side reactor.

[0042] Example 1 of a protection method for a bridge arm reactor short-circuit fault:

[0043] like Figure 1 FIG. 1 is a flow chart of a method for protecting a bridge arm reactor from a short-circuit fault according to the present invention, which includes steps S11, S12, and S13. Specifically,

[0044] Regardless of whether the flexible DC transmission system adopts the pseudo-bipolar connection method or the true bipolar limit method, step S11 is executed to obtain the current upper and lower arm currents of any phase bridge arm on the DC side of the flexible DC converter, and calculate the effective value of the fundamental component of the current arm circulating current based on the current upper and lower arm currents; here, the effective value of the fundamental component in the arm circulating current refers to the effective value of the 50Hz component in the arm circulating current; when calculating the arm circulating current, the calculation is performed based on the upper and lower arm currents (such as Figure 2 and Figure 3 As shown, VSC is a converter; L is an arm reactor, and the arm reactor L is installed on the DC side of the converter VSC. The arm circulating current is calculated based on the sampled values of IbP and IbN). In actual application, the arm circulating current can be calculated by the following formula:

[0045] Icir x =(IbP x +IbN x )*0.5

[0046] Among them, Icir x is the x-phase bridge arm circulation; x is phase a, phase b, or phase c; IbP x is the sampling value of the upper bridge arm current of phase x; IbN x is the sampling value of the x-phase lower arm current.

[0047] The current upper and lower bridge arm currents obtained in step S11 are used to determine the current bridge arm current according to the current upper and lower bridge arm currents, and the effective value of the current bridge arm current is calculated, so that step S12 is executed according to the current effective value of the bridge arm current. The current protection setting at the current upper and lower bridge arm current levels is determined from the linear relationship between the pre-obtained effective value of the bridge arm current and the protection setting used to determine whether the inductor has failed, so as to achieve different protection settings according to different bridge arm currents, form a dynamic adjustment of the protection setting according to the operating status of the circuit, and expand the scope of application.

[0048] Step S13: When the effective value of the fundamental wave component in the current arm circulating current is greater than the current protection setting, it is determined that the DC-side arm reactor has a fault, and a protection action is triggered. Here, when the effective value of the fundamental wave component in the current arm circulating current is less than the current protection setting, it is determined that the DC-side arm reactor has not a fault.

[0049] Through the above steps S11 to S13, it is possible to determine a reactor fault and trigger a protection action based on the magnitude relationship between the effective value of the fundamental component in the arm circulating current of any bridge arm and the current protection setting, thereby enhancing the sensitivity of reactor fault judgment during flexible direct current transmission. In addition, the current protection setting is directly found from the pre-acquired linear relationship, greatly reducing the memory space required for fault judgment. While detecting reactor faults in a timely manner, it occupies fewer resources and facilitates engineering implementation.

[0050] In a preferred embodiment of the present invention, the upper arm current IbP of the flexible DC converter on the DC side X-phase bridge arm is obtained. x and the lower arm current IbP x ; According to the upper arm current IbP x and the lower arm current IbP x , calculate the x-phase bridge arm circulating current Icir x and the circulating current Icir from the x-phase bridge arm x Extract the effective value of the 50Hz component to obtain Icir x _50; According to the upper arm current IbP x and the lower arm current IbP x , obtain the current bridge arm current and calculate the effective value; use the linear relationship l1 between the pre-obtained bridge arm current effective value and the protection setting value used to judge whether the reactor has failed, and determine the current protection setting value I corresponding to the current bridge arm current effective value set ; preferably Icir x _50>I set , it is determined that the reactor of the X-phase bridge arm on the DC side is faulty, and the circuit is triggered to protect the reactor of the X-phase bridge arm.

[0051] Example 2 of the protection method for bridge arm reactor short circuit fault:

[0052] In a flexible direct current transmission system, the effective value of the fundamental component in the arm circulating current is related to the operating power of the flexible direct current system. The greater the active power, the higher the fundamental component value. Therefore, when establishing a linear relationship, the determination of the protection setting is related to different operating current ranges. In a protection method for arm reactor short-circuit faults proposed in the present invention, the linear relationship is generated by the following method:

[0053] Within the actual operating power range of the flexible DC transmission system, the minimum effective value of the fundamental component of the arm circulating current after first-order smoothing filtering during the fault period is calculated when the arm reactor fails under different actual operating powers; based on the minimum effective value of the fundamental component of the arm circulating current after first-order smoothing filtering, the protection setting corresponding to the effective value range of the arm current under the actual operating power is calculated.

[0054] The effective value intervals of the bridge arm current and their protection settings corresponding to all actual operating powers are integrated to generate the linear relationship. It should be noted that during normal operation, the flexible DC system will generate a certain fundamental circulating current component. In order to improve the reliability of the protection algorithm, all protection settings are greater than the maximum effective value of the fundamental circulating current component of the bridge arm after first-order smoothing filtering during normal operation of the flexible DC transmission system, so as to ensure that interference from non-fault conditions (i.e., system device disturbances) is excluded during the reactor fault judgment process.

[0055] Here, in order to cover all operating power conditions of the flexible direct current transmission system, it is preferred to represent different actual operating powers through different per-unit values. For example, 0.1pu, 0.2pu, ..., 0.9pu and 1pu are used to represent all operating power conditions. Of course, the above is only an example. Different actual operating powers can be represented according to the circuit operating conditions or operating power laws. The effective value of the fundamental component in the bridge arm circulating current after the first-order smoothing filter refers to the first-order smoothing filter of the effective value of the fundamental component in the bridge arm circulating current, wherein the filtering time constant can be 100ms-200ms, providing an undisturbed data basis for the subsequent calculation of protection constants.

[0056] At the same time, in order to avoid line errors / losses between components in the actual circuit and improve the sensitivity of electromechanical system protection, a reliability coefficient is introduced when calculating the protection setting value. Specifically, the protection setting value corresponding to the effective value range of the bridge arm current under the actual operating power is calculated based on the minimum effective value of the fundamental component in the bridge arm circulating current after first-order smoothing filtering using the following method:

[0057] I set =k*MIN(Icir x _50_PT1)

[0058] Among them, I setis the protection value; k is the reliability coefficient; Icir x _50_PT1 is the effective value of the fundamental component of the circulating current in the x-phase bridge arm after first-order smoothing filtering. The reliability coefficient ranges from 0.8 to 0.9.

[0059] For example, when the actual operating power of the bridge arm current is 0.1 pu, calculate the effective value of the fundamental component Icir of the bridge arm circulating current after the first-order smoothing filter during the duration of the bridge arm reactor fault. x _50_PT1 minimum value; in accordance with Icir x The minimum value of _50_PT1 is used to calculate the protection setting value I in the 0.1pu lower bridge arm current effective value range. set1 When the actual operating power of the bridge arm current is 0.2 pu, calculate the effective value of the fundamental component Icir of the bridge arm circulating current after the first-order smoothing filter during the duration of the bridge arm reactor fault. x _50_PT1 minimum value; in accordance with Icir x The minimum value of _50_PT1 is used to calculate the protection setting value I in the 0.2pu lower bridge arm current effective value range. set2 Similarly, when the bridge arm current is running at the actual operating power of 0.3pu, ... 1.0pu, the Icir when the bridge arm reactor fault occurs is calculated. x _50_PT1 minimum value, and the corresponding bridge arm current effective value range is obtained respectively. With the bridge arm current operating value as the horizontal axis and the corresponding protection setting value as the vertical axis, the linear relationship l1 is obtained.

[0060] Example 3 of the protection method for bridge arm reactor short circuit fault:

[0061] Following the above embodiment of the present invention, no matter whether the flexible DC transmission system adopts the pseudo bipolar connection method or the true bipolar limit method, the bridge arm reactor fault includes the bridge arm reactor valve side phase short circuit fault and the bridge arm reactor single-phase head-tail short circuit fault (such as Figure 2 and Figure 3 As shown, F1 is the interphase short circuit fault of the bridge arm reactor valve side; F2 is the single-phase head-tail short circuit fault of the bridge arm reactor), within each different operating power, when the bridge arm reactor fault is the interphase short circuit fault of the bridge arm reactor valve side, the effective value of the fundamental component of the bridge arm circulating current after the first-order smoothing filter during the bridge arm reactor valve side phase short circuit fault is calculated.

[0062] When the arm reactor fault is a single-phase short-circuit fault at the beginning and end of the arm reactor, the effective value of the fundamental component of the arm circulating current after the second first-order smoothing filter during the single-phase short-circuit fault at the beginning and end of the arm reactor is calculated.

[0063] A smaller value is selected from the effective value of the fundamental wave component in the bridge arm circulating current after the first first-order smoothing filter and the effective value of the fundamental wave component in the bridge arm circulating current after the second first-order smoothing filter as the minimum value.

[0064] For example, when the bridge arm current is at an actual operating power of 0.1 pu, calculate the first Icir during the fault period when a bridge arm reactor valve side interphase short circuit fault occurs. x _50_PT1; calculate the second Icir during the fault period when the bridge arm reactor single-phase short circuit fault occurs x _50_PT1; take the first Icir x _50_PT1 and the second Icir x The smaller value of _50_PT1 is determined as the bridge arm current Icir when the actual operating power is 0.1pu x _50_The minimum value of PT1.

[0065] Example 4 of the protection method for bridge arm reactor short circuit fault:

[0066] like Figure 4 As shown, it is a flow chart of a protection method for a bridge arm reactor short-circuit fault proposed by the present invention in an actual application scenario, wherein the upper (bridge arm current IbP) and lower bridge arm current (IbN) of any phase bridge arm of the converter on the DC side are collected; the bridge arm circulating current is calculated according to the upper and lower bridge arm currents, and the effective value of the polar wave component in the bridge arm circulating current is extracted from the bridge arm circulating current; the protection criterion is determined from the preset linear relationship (that is, the current protection setting is determined); it is judged whether the effective value of the polar wave component in the bridge arm circulating current meets the protection criterion, and if so, it is determined that the bridge arm reactor on the DC side has a fault and the protection action is triggered; if not, the upper and lower bridge arm currents continue to be collected to monitor the bridge arm reactor on the DC side of the flexible DC transmission system.

[0067] Example 5 of the protection method for bridge arm reactor short circuit fault:

[0068] like Figure 5 The figure shows a flow chart of triggering a protection action in an actual application scenario of a bridge arm reactor short-circuit fault protection method proposed by the present invention, wherein the upper and lower bridge arm currents of the flexible DC converter on the DC side are collected; and the bridge arm circulating current is calculated based on the positive and negative fixed values of the upper and lower bridge arm currents; the effective value of the 50Hz component is extracted from the bridge arm circulating current to obtain Icir x _50; When Icir x _50>Iset (current protection setting), when the fault delay reaches T1, an alarm signal about the X-phase bridge arm reactor fault is sent; when the fault delay reaches T2, the control system is switched to protect the equipment and system in the flexible DC transmission system.

[0069] Example 6 of the protection method for bridge arm reactor short circuit fault:

[0070] For example, the upper arm current and lower arm current of any phase arm (any phase A, B, C) of the flexible DC converter on the DC side are collected; the x-phase arm circulating current is calculated based on the upper and lower arm currents; the effective value of the 50Hz component in the arm circulating current is extracted for logical judgment; when the protection criterion is met (any phase A, B, C), that is, the effective value of the 50Hz component in the arm circulating current is greater than the protection set value Iset, in response to the fault delay T1, an alarm signal is sent; in response to the fault delay T2, the control system is switched. Since the arm reactor failure will not directly cause the flexible DC equipment to suffer severe overvoltage or overcurrent, the flexible DC system can still operate for a long time. Therefore, the operating personnel can choose to shut down the converter as planned when the load is small to repair the fault according to the DC power transmission situation of the flexible DC transmission system.

[0071] The protection criteria are constructed as follows: considering that the 50Hz fundamental component is related to the operating power level of the flexible DC system, the greater the active power, the higher the fundamental component. The protection setting needs to be adjusted in different operating current ranges, that is, the protection setting is adjusted according to different bridge arm current operating ranges, and the setting curve is fitted. Finally, different protection settings are determined according to the curve. Specifically: when the bridge arm current is 0.1pu, the minimum effective value of the fundamental component in the bridge arm circulating current after the first-order smoothing filter during the period when the bridge arm reactor valve-side phase-to-phase short-circuit fault and the bridge arm reactor single-phase head-to-tail short-circuit fault occur is determined, and the minimum value is multiplied by the reliability coefficient to obtain the safe setting of the bridge arm current at 0.1pu.

[0072] Similarly, with the arm current operating at 0.2 pu, 0.3 pu, …, and 1.0 pu, the minimum RMS value of the fundamental component of the arm circulating current after first-order smoothing filtering during the duration of an arm reactor valve-side phase-to-phase short-circuit fault and an arm reactor single-phase end-to-end short-circuit fault is determined. Based on the reliability coefficient, the fixed values for the corresponding current intervals are obtained. All protection setting points should be greater than the maximum RMS value of the fundamental component of the arm circulating current after first-order smoothing filtering during normal operation of the flexible DC system to ensure that the set values can avoid system disturbances under non-fault conditions. With the arm current operating value as the horizontal axis and the corresponding protection setting value as the vertical axis, curve fitting is performed to obtain a protection setting curve that shows the linear relationship between the arm current and the protection setting used to determine reactor faults. The protection setting is then determined based on the actual operating arm current value.

[0073] Protection device for bridge arm reactor short circuit fault:

[0074] On the other hand, the present invention provides a bridge arm reactor short circuit fault protection device, comprising a processor, wherein the processor is configured to perform the following steps:

[0075] 1) Obtain the current upper and lower arm currents of any phase bridge arm of the flexible DC converter on the DC side, and calculate the effective value of the fundamental component of the current bridge arm circulating current based on the current upper and lower arm currents.

[0076] 2) Determine the current protection settings of the upper and lower bridge arm currents from the linear relationship between the pre-obtained effective value of the bridge arm current and the protection setting used to determine whether the reactor has failed.

[0077] 3) When the effective value of the fundamental component in the current arm circulating current is greater than the current protection setting, it is determined that the bridge arm reactor on the DC side is faulty and the protection action is triggered.

[0078] At the same time, the linear relationship described in step 2) is generated by the following method:

[0079] Within the actual operating power range of the flexible DC transmission system, the minimum effective value of the fundamental component of the arm circulating current after first-order smoothing filtering during the fault period is calculated when the arm reactor fails under different actual operating powers; based on the minimum effective value of the fundamental component of the arm circulating current after first-order smoothing filtering, the protection setting corresponding to the effective value range of the arm current under the actual operating power is calculated.

[0080] The bridge arm current effective value intervals and protection settings corresponding to all actual operating powers are integrated to generate the linear relationship.

[0081] The protection setting value of the bridge arm current effective value range corresponding to the actual operating power is calculated based on the minimum value of the fundamental component effective value of the bridge arm circulating current after first-order smoothing filtering using the following method:

[0082] I set =k*MIN(Icir x _50_PT1)

[0083] Among them, I set is the protection value; k is the reliability coefficient; Icir x _50_PT1 is the effective value of the fundamental component of the x-phase bridge arm circulating current after first-order smoothing filtering. The reliability coefficient ranges from 0.8 to 0.9.

[0084] Regardless of whether the flexible DC transmission system adopts the pseudo-bipolar connection mode or the true bipolar connection mode, the arm reactor fault includes the arm reactor valve side phase short circuit fault and the arm reactor single-phase head-tail short circuit fault (such as Figure 2 and Figure 3As shown, F1 is the bridge arm reactor valve side phase-to-phase short circuit fault; F2 is the bridge arm reactor single-phase head-to-tail short circuit fault), within each different operating power, when the bridge arm reactor fault is the bridge arm reactor valve side phase-to-phase short circuit fault, calculate the effective value of the fundamental component in the bridge arm circulating current after the first first-order smoothing filter during the bridge arm reactor valve side phase-to-phase short circuit fault; when the bridge arm reactor fault is the bridge arm reactor single-phase head-to-tail short circuit fault, calculate the effective value of the fundamental component in the bridge arm circulating current after the second first-order smoothing filter during the bridge arm reactor single-phase head-to-tail short circuit fault; select the smaller value from the effective value of the fundamental component in the bridge arm circulating current after the first first-order smoothing filter and the effective value of the fundamental component in the bridge arm circulating current after the second first-order smoothing filter as the minimum value.

[0085] like Figure 6 As shown, a schematic diagram of the internal system structure of a protection device for a bridge arm reactor short-circuit fault proposed by the present invention in an actual application scenario, wherein the system for protecting the bridge arm reactor short-circuit fault includes a data acquisition unit, a data processing unit, a logic judgment unit and a protection output unit, wherein the data acquisition unit is used to obtain the current upper and lower arm currents of any phase bridge arm of the flexible DC converter on the DC side; the data processing unit is used to calculate the circulating current of each phase bridge arm, extract the effective value of the 50Hz component, and fit the linear relationship between the bridge arm current and the protection constant used to determine whether the inductor fault has occurred; the logic judgment unit is used to determine whether the effective value of the fundamental wave component of the bridge arm circulating current meets the judgment criterion; the protection output unit is used to determine the protection action signal output after the bridge arm reactor on the DC side fails.

[0086] In summary, the present invention is suitable for a flexible direct current transmission system in which the arm reactor is configured on the DC side of the converter. Based on the collection of the upper and lower arm currents of the converter, the protection criterion is constructed by calculating the arm circulating current and extracting the 50Hz component in the arm circulating current. A preset protection setting method is also provided. The short-circuit fault of the arm reactor can be reliably identified, and operation and maintenance personnel can discover and repair the fault in time to protect the safety of equipment and personnel. At the same time, the protection algorithm is simple, the protection setting is easy to set, and the CPU resources are small. The sampling frequency requirement of the protection device is not high (generally 10kHz can meet the requirements), which facilitates engineering implementation.

Claims

1. A method for protecting a bridge arm reactor from short circuit fault, characterized in that: The steps include: 1) Obtain the current upper and lower arm currents of any phase bridge arm of the flexible DC converter on the DC side, and calculate the effective value of the fundamental component of the current arm circulating current based on the current upper and lower arm currents; 2) determining the current protection setting at the current upper and lower bridge arm current levels based on the linear relationship between the pre-obtained bridge arm current effective value and the protection setting used to determine whether the reactor has failed; 3) When the effective value of the fundamental component in the current arm circulating current is greater than the current protection setting, it is determined that the bridge arm reactor on the DC side is faulty and the protection action is triggered.

2. The method for protecting a bridge arm reactor from a short-circuit fault according to claim 1, wherein: The linear relationship is generated by the following method: Within the actual operating power range of the HVDC Flexible system, the minimum effective value of the fundamental component of the arm circulating current after first-order smoothing filtering during the fault period is calculated when the arm reactor fails at different actual operating powers. Based on the minimum value of the effective value of the fundamental component in the bridge arm circulating current after first-order smoothing filtering, the protection setting value corresponding to the effective value range of the bridge arm current under the actual operating power is calculated; The bridge arm current effective value intervals and protection settings corresponding to all actual operating powers are integrated to generate the linear relationship.

3. The method for protecting a bridge arm reactor from a short-circuit fault according to claim 2, wherein: The protection setting value of the bridge arm current effective value range corresponding to the actual operating power is calculated based on the minimum value of the fundamental component effective value of the bridge arm circulating current after first-order smoothing filtering using the following method: I set =k*MIN(Icir x _50_PT1) Among them, I set is the protection value; k is the reliability coefficient; Icir x _50_PT1 is the effective value of the fundamental component of the circulating current in the x-phase bridge arm after first-order smoothing filtering.

4. The method for protecting a bridge arm reactor from a short circuit fault according to claim 3, wherein: The reliability coefficient ranges from 0.8 to 0.

9.

5. The method for protecting a bridge arm reactor from short-circuit fault according to any one of claims 2 to 4, characterized in that: When the arm reactor fault is an interphase short circuit fault on the valve side of the arm reactor, calculate the effective value of the fundamental component of the arm circulating current after the first-order smoothing filter during the interphase short circuit fault on the valve side of the arm reactor; When the arm reactor fault is a single-phase short-circuit fault at the beginning and end of the arm reactor, calculate the effective value of the fundamental component of the arm circulating current after the second first-order smoothing filter during the single-phase short-circuit fault of the arm reactor; A smaller value is selected from the effective value of the fundamental wave component in the bridge arm circulating current after the first first-order smoothing filter and the effective value of the fundamental wave component in the bridge arm circulating current after the second first-order smoothing filter as the minimum value.

6. A protection device for bridge arm reactor short circuit fault, characterized in that: The device comprises a processor configured to perform the following steps: 1) Obtain the current upper and lower arm currents of any phase bridge arm of the flexible DC converter on the DC side, and calculate the effective value of the fundamental component of the current arm circulating current based on the current upper and lower arm currents; 2) determining the current protection setting at the current upper and lower bridge arm current levels based on the linear relationship between the pre-obtained bridge arm current effective value and the protection setting used to determine whether the reactor has failed; 3) When the effective value of the fundamental component in the current arm circulating current is greater than the current protection setting, it is determined that the bridge arm reactor on the DC side is faulty and the protection action is triggered.

7. The protection device for bridge arm reactor short circuit fault according to claim 6, characterized in that: The linear relationship is generated by the following method: Within the actual operating power range of the HVDC Flexible system, the minimum effective value of the fundamental component of the arm circulating current after first-order smoothing filtering during the fault period is calculated when the arm reactor fails at different actual operating powers. Based on the minimum value of the effective value of the fundamental component in the bridge arm circulating current after first-order smoothing filtering, the protection setting value corresponding to the effective value range of the bridge arm current under the actual operating power is calculated; The bridge arm current effective value intervals and protection settings corresponding to all actual operating powers are integrated to generate the linear relationship.

8. The protection device for bridge arm reactor short circuit fault according to claim 7, characterized in that: The protection setting value of the bridge arm current effective value range corresponding to the actual operating power is calculated based on the minimum value of the fundamental component effective value of the bridge arm circulating current after first-order smoothing filtering using the following method: I set =k*MIN(Icir x _50_PT1) Among them, I set is the protection value; k is the reliability coefficient; Icir x _50_PT1 is the effective value of the fundamental component of the circulating current in the x-phase bridge arm after first-order smoothing filtering.

9. The protection device for bridge arm reactor short circuit fault according to claim 8, characterized in that: The reliability coefficient ranges from 0.8 to 0.

9.

10. The protection device for bridge arm reactor short circuit fault according to any one of claims 6 to 9, characterized in that: When the arm reactor fault is an interphase short circuit fault on the valve side of the arm reactor, calculate the effective value of the fundamental component of the arm circulating current after the first-order smoothing filter during the interphase short circuit fault on the valve side of the arm reactor; When the arm reactor fault is a single-phase short-circuit fault at the beginning and end of the arm reactor, calculate the effective value of the fundamental component of the arm circulating current after the second first-order smoothing filter during the single-phase short-circuit fault of the arm reactor; A smaller value is selected from the effective value of the fundamental wave component in the bridge arm circulating current after the first first-order smoothing filter and the effective value of the fundamental wave component in the bridge arm circulating current after the second first-order smoothing filter as the minimum value.

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