MMC fault diagnosis method, system and device based on sorting and balancing voltage algorithm

Abstract

The present invention relates to the technical field of modular multi-level converters, and provides an MMC fault diagnosis method, system, and device based on a sorting voltage balancing algorithm. The method comprises: calculating the theoretical value and actual value of the bridge arm voltage of the modular multi-level converter based on the measurement data of the modular multi-level converter, comparing the values ​​with a first alarm threshold, and determining the corresponding bridge arm fault and fault type; calculating the number of faulty submodules based on the actual value of the bridge arm voltage and the theoretical value of the bridge arm voltage; determining the number of switches of the faulty bridge arm submodule, and controlling and adjusting the opening of the bridge arm submodule based on the fault type and the number of faulty submodules; calculating the minimum value difference of the capacitor voltage, comparing the values ​​with a second alarm threshold, and determining the faulty submodule. The present invention designs a multi-tube fault diagnosis method, which solves the problem of poor fault location performance under light-load conditions and improves the submodule location performance within the full power range.

Description

Technical Field

[0001] The present invention relates to the technical field of modular multi-level converters, and provides an MMC fault diagnosis method, system and device based on a sorting voltage sharing algorithm. Background Art

[0002] Modular multilevel converters (MMCs), with their modular topology, are easy to expand and implement fault-tolerant control. They also offer advantages such as high-quality output waveforms, low switching frequency, and low power losses. Furthermore, MMCs possess strong fault ride-through capability, making them a promising core component of flexible HVDC transmission. However, MMCs are systems composed of a large number of cascaded submodules. During operation, submodules are constantly switched on and off, and switching devices frequently operate. This increases the probability of failures over time. Open-circuit faults in submodules may not affect overall system operation for a short period of time. However, if untreated, these open-circuit faults can damage other system components, ultimately leading to system downtime. Therefore, research on MMC open-circuit fault diagnosis is crucial for reliable system operation.

[0003] Existing methods for diagnosing open-circuit faults in submodule IGBTs are commonly categorized into two main categories: hardware circuit detection and software algorithms. These methods generally involve two steps: fault detection and fault location. The capacitor voltage deviation between the faulty and normal submodules is widely used to identify open-circuit faults. Existing methods rarely investigate fault analysis under specific operating conditions. When the system operates under light load conditions, using the submodule capacitor voltage deviation as a fault signature for open-circuit fault diagnosis can lead to degraded location performance, delayed diagnosis, or even missed detections due to the strong coupling between the fault arm current, the voltage deviation between the faulty and normal submodules, and the load conditions. Summary of the Invention

[0004] The present invention aims to address at least one of the technical problems existing in the related art. To this end, the present invention provides a method, system, and device for MMC fault diagnosis based on a sorting voltage balancing algorithm, which solves the problem of poor fault localization performance under light load conditions and improves submodule localization performance over the full power range.

[0005] The present invention provides an MMC fault diagnosis method based on a sorting and voltage-sharing algorithm, comprising:

[0006] S1: Calculate the theoretical value and actual value of the bridge arm voltage of the modular multilevel converter based on the measured data of the modular multilevel converter;

[0007] S2: Compare the actual bridge arm voltage value, the theoretical bridge arm voltage value and the first alarm threshold to determine whether the corresponding bridge arm has an IGBT open circuit fault;

[0008] S3: Calculate the number of faulty submodules according to the actual value of the bridge arm voltage and the theoretical value of the bridge arm voltage;

[0009] S4: Determine the number of switches in the faulty bridge arm submodule, and control and adjust the opening of the upper and lower bridge arm submodules of the faulty phase according to the fault type and the number of faulty submodules;

[0010] S5: Calculate the difference between the capacitor voltage of each submodule and the minimum capacitor voltage of the bridge arm submodule, and compare it with the second alarm threshold to determine the faulty submodule.

[0011] According to an MMC fault diagnosis method based on a sorting and voltage balancing algorithm provided by the present invention, step S1 includes:

[0012] S11: Calculating a theoretical bridge arm voltage value according to a DC side voltage value, an AC side voltage value, an inductance value of a bridge arm, and a bridge arm current value of the modular multilevel converter;

[0013] S12: Calculate the actual value of the bridge arm voltage according to the relationship between the submodule switching function and the submodule capacitor voltage.

[0014] According to an MMC fault diagnosis method based on a sorting and voltage balancing algorithm provided by the present invention, step S2 includes:

[0015] The first alarm threshold includes a bridge arm voltage error threshold and a first time threshold;

[0016] When the difference between the theoretical value of the bridge arm voltage and the actual value of the bridge arm voltage is greater than the bridge arm voltage error threshold, and the duration is greater than the first time threshold, it is determined that a fault exists in the corresponding bridge arm;

[0017] When the difference between the theoretical value of the bridge arm voltage and the actual value of the bridge arm voltage is greater than the bridge arm voltage error threshold, and the duration is greater than the first time threshold, determining that the fault type of the fault submodule is an upper tube fault;

[0018] When the difference between the actual bridge arm voltage value and the theoretical bridge arm voltage value is greater than the bridge arm voltage error threshold, and the duration is greater than the first time threshold, it is determined that the fault type of the fault submodule is a lower tube fault.

[0019] According to an MMC fault diagnosis method based on a sorting and voltage balancing algorithm provided by the present invention, step S3 includes:

[0020] S31: summing the capacitance and voltage of the bridge arm submodules and dividing the sum by the number of the bridge arm submodules to obtain an average capacitance and voltage of the submodules;

[0021] S32: Obtain the number of faulty submodules according to the difference between the actual bridge arm voltage value and the theoretical bridge arm voltage value and the average value of the bridge arm submodule capacitor voltage.

[0022] According to an MMC fault diagnosis method based on a sorting and voltage balancing algorithm provided by the present invention, step S4 includes:

[0023] According to the fault type and the number of faults, the control is adjusted in combination with the sorting voltage balancing algorithm to open or cut off the same number of submodules as the number of faulty submodules in the bridge arm on the same opposite side.

[0024] According to an MMC fault diagnosis method based on a sorting and voltage balancing algorithm provided by the present invention, step S5 includes: the second alarm threshold includes: a submodule fault characteristic value error threshold and a second time threshold;

[0025] When the difference between the bridge arm submodule capacitor voltage value and the bridge arm submodule capacitor voltage minimum value is greater than the fault characteristic value error threshold, and the duration is greater than the second time threshold, the corresponding bridge arm submodule has a fault.

[0026] According to the present invention, a method for diagnosing MMC faults based on a sorting and voltage balancing algorithm is provided, wherein the sorting and voltage balancing algorithm comprises:

[0027] When a tube failure occurs on a submodule of a faulty bridge arm, the submodules on the bridge arm opposite to the faulty bridge arm on the same phase are controlled to open the submodules corresponding to the number of submodules with tube failure on the faulty bridge arm;

[0028] When a submodule lower tube failure occurs in a faulty bridge arm, the submodules on the bridge arm opposite to the faulty bridge arm on the same phase are controlled to remove submodules equal to the number of submodules with lower tube failures on the faulty bridge arm.

[0029] According to the MMC fault diagnosis method based on the sorting voltage balancing algorithm provided by the present invention, the bridge arm voltage error threshold is the theoretical mean value of the submodule capacitor voltage.

[0030] The present invention also provides an MMC fault diagnosis method system based on a sorting and voltage balancing algorithm, comprising:

[0031] Deviation value calculation module: calculates the theoretical value and actual value of the bridge arm voltage of the modular multilevel converter based on the measurement data of the modular multilevel converter;

[0032] Fault judgment module: compares the actual value of the bridge arm voltage, the theoretical value of the bridge arm voltage and the first alarm threshold to determine whether the corresponding bridge arm has a fault and the fault type;

[0033] Fault number judgment module: calculates the number of fault submodules according to the actual value of the bridge arm voltage and the theoretical value of the bridge arm voltage;

[0034] Fault repair and adjustment module: determines the number of switches in the faulty bridge arm submodule, and controls and adjusts the opening of the upper and lower bridge arm submodules of the faulty phase according to the fault type and the number of faulty submodules;

[0035] Fault location judgment module: calculates the difference between the capacitor voltage of each submodule and the minimum value of the capacitor voltage of the bridge arm submodule, and compares it with the second alarm threshold to determine the faulty submodule.

[0036] The present invention also provides an electronic device, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor. When the processor executes the program, the steps of the MMC fault diagnosis method based on the sorting and voltage balancing algorithm as described above are implemented.

[0037] The above one or more technical solutions in the embodiments of the present invention have at least one of the following technical effects:

[0038] The present invention provides an MMC fault diagnosis method, system and device based on a sorting voltage-sharing algorithm. The theoretical value and actual value of the bridge arm voltage of each bridge arm are calculated by a constructed equation, and the deviation between the two is used to determine whether the corresponding bridge arm has a fault. The average value of the capacitor voltage of the submodule on the bridge arm with a fault is calculated, and the number of faulty submodules in the faulty bridge arm is calculated based on the difference between the theoretical value and the actual value of the bridge arm voltage. According to the fault type and the number of faulty submodules, the number of switches of the bridge arm submodule on the opposite side of the faulty bridge arm on the same phase is controlled and adjusted to reduce the current distortion of the faulty arm, so that the capacitor voltage of the faulty submodule and the normal submodule quickly deviates, and then the capacitor voltage value of each submodule on the faulty bridge arm is directly compared with the minimum capacitor voltage to locate the fault.

[0039] The present invention discloses a multi-tube fault diagnosis method applicable to any working conditions, which solves the problem of poor fault location performance under light-load conditions, effectively improves the sub-module location performance within the full power range, and reduces the data and calculation required for fault location, while having a certain fault tolerance capability.

[0040] Additional aspects and advantages of the present invention will be set forth in part in the description which follows and, in part, will be obvious from the description which follows, or may be learned by practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0042] Figure 1 It is a flow chart of the MMC fault diagnosis method based on the sorting and voltage balancing algorithm provided by the present invention.

[0043] Figure 2 This is a topology diagram of a single-phase MMC system.

[0044] Figure 3 This is the principle diagram of the sorting and equalizing pressure control method.

[0045] Figure 4 This is a status diagram of the upper tube failure and lower tube failure of the submodule.

[0046] Figure 5 This is an example diagram of the open circuit judgment of the upper tube IGBT of the upper bridge arm submodule.

[0047] Figure 6 This is an example diagram of the open circuit judgment of the lower tube IGBT of the upper bridge arm submodule.

[0048] Figure 7 This is an example diagram of fault diagnosis when faults occur simultaneously in different sub-modules.

[0049] Figure 8 This is an example diagram of judging the open circuit of the lower tube IGBT of the upper bridge arm submodule under the low-profile system.

[0050] Figure 9 It is a structural block diagram of the MMC fault diagnosis system based on the sorting and voltage balancing algorithm provided by the present invention.

[0051] Figure 10 It is a structural schematic diagram of the electronic device provided by the present invention.

[0052] Figure 11 This is a simulation diagram of the impact of the present invention on system circulation.

[0053] Reference numerals:

[0054] 101. Deviation value calculation module; 102. Fault judgment module; 103. Fault number judgment module; 104. Fault repair adjustment module; 105. Fault location judgment module; 810. Processor; 820. Communication interface; 830. Memory; 840. Communication bus. DETAILED DESCRIPTION

[0055] To make the purpose, technical solutions and advantages of the present invention clearer, the technical solutions in the present invention will be clearly and completely described below. Obviously, the embodiments described are part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention. The following embodiments are used to illustrate the present invention, but are not used to limit the scope of the present invention.

[0056] In the description of the embodiments of the present invention, it should be noted that the terms "center", "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating the orientation or positional relationship, are based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing the embodiments of the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operate in a specific orientation, and therefore should not be understood as limiting the embodiments of the present invention. In addition, the terms "first", "second", and "third" are used for descriptive purposes only and should not be understood as indicating or implying relative importance.

[0057] In the description of the embodiments of the present invention, it should be noted that, unless otherwise specified or limited, the terms "connected" and "connection" should be understood in a broad sense. For example, they can refer to fixed connections, detachable connections, or integral connections; mechanical connections, electrical connections; and direct connections or indirect connections through an intermediary. Those skilled in the art will understand the specific meanings of the above terms in the embodiments of the present invention based on the specific circumstances.

[0058] In the description of this specification, the reference terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" mean 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 embodiment of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art can combine and combine different embodiments or examples described in this specification and features of different embodiments or examples without contradiction.

[0059] The following combination Figures 1 to 11 The present invention is described.

[0060] Example 1

[0061] like Figure 1 As shown, Figure 1 The flowchart of the MMC fault diagnosis method based on the sorting and voltage balancing algorithm provided by the present invention includes the following steps:

[0062] S1: Calculate the theoretical value and actual value of the bridge arm voltage of the modular multilevel converter based on the measured data of the modular multilevel converter;

[0063] S2: Compare the actual bridge arm voltage value, the theoretical bridge arm voltage value and the first alarm threshold to determine whether the corresponding bridge arm has an IGBT open circuit fault;

[0064] S3: Calculate the number of faulty submodules according to the actual value of the bridge arm voltage and the theoretical value of the bridge arm voltage;

[0065] S4: Determine the number of switches in the faulty bridge arm submodule, and control and adjust the opening of the upper and lower bridge arm submodules of the faulty phase according to the fault type and the number of faulty submodules;

[0066] S5: Calculate the difference between the capacitor voltage of each submodule and the minimum capacitor voltage of the bridge arm submodule, and compare it with the second alarm threshold to determine the faulty submodule.

[0067] like Figure 2 As shown, the MMC single-phase structure diagram of the present invention is as shown Figure 2 As shown in (a), the submodule structure diagram is as follows Figure 2 As shown in (b), when the MMC operates as an inverter unit, one side is connected to the DC bus as the input terminal; the other side is used to output three-phase AC power. Each phase of the MMC consists of two upper and lower bridge arms with the same structure. Each bridge arm consists of N cascaded half-bridge submodules and a bridge arm inductor. The topology of the half-bridge module consists of two complementary IGBTs, with S1 being the upper transistor and S2 being the lower transistor, two anti-parallel diodes, VD1 being the first anti-parallel diode, VD2 being the second anti-parallel diode, and a DC energy storage capacitor C. is the DC side voltage, is half of the DC side voltage, For the AC side voltage, by changing the number of upper and lower bridge arm submodules put into and removed, the AC side multi-level output can be achieved. Indicates the upper arm voltage; represents the lower bridge arm voltage, Represents the upper arm current, represents the lower arm current, For the upper arm Capacitor voltage of each submodule; The first The output voltage of each submodule. , is the total number of modules. is the external equivalent resistance, is the external equivalent inductance, For the submodules, For the The upper arm current of each submodule.

[0068] From the MMC topology, we can see that each sub-module is connected in parallel with a capacitor. During normal operation, the sub-module switching is controlled by a modulation strategy to continuously charge and discharge the capacitor. This nonlinear process is difficult to control accurately. In addition, there are losses in actual operation, which will lead to unstable capacitor voltages in each sub-module. Therefore, maintaining capacitor voltage balance is the basis for the normal operation of the MMC system.

[0069] like Figure 3 As shown, the sorting and voltage balancing algorithm solves this problem. The basic principle is: first, based on the modulation strategy, determine the number of sub-modules (Non) required for each bridge arm of the MMC system at any time. Then, the capacitor voltages of each sub-module in the bridge arm are sorted in ascending or descending order, and the order of sub-module input is determined based on the direction of the bridge arm current sampling. Specifically, a judgment output is performed: when the bridge arm current is positive, the sub-modules with lower capacitor voltages are prioritized for charging according to the ascending order of the sub-module capacitor voltages; if the bridge arm current is negative, the sub-modules with higher capacitor voltages are prioritized for discharge according to the descending order of the sub-module capacitor voltages. Comparison output is performed to achieve balanced control of the capacitor voltages of each sub-module in each bridge arm.

[0070] The switching function generated by the sorting and voltage-sharing algorithm is applied to the submodule switches. During normal operation, there are two operating states: on and off. The on state is when the upper switch S1 is on and the lower switch S2 is off. In this state, the submodule output voltage equals the submodule capacitor voltage. The off state is when the upper switch S1 is off and the lower switch S2 is on. In this state, the submodule output voltage equals zero. If an open circuit fault occurs in either the upper switch S1 or the lower switch S2 in a submodule, current cannot flow through the faulty IGBT, causing the submodule output voltage to differ from that of a normal submodule.

[0071] When the upper tube of the submodule is turned on and the lower tube is turned off, the submodule switching function is 1 and the bridge arm current is negative. During normal operation, the bridge arm current passes through C and S1, the submodule is in the input state and the capacitor is discharged. The submodule output voltage Equal to the capacitor voltage .

[0072] like Figure 4 As shown in (a), if S1 has an open circuit fault, the bridge arm current cannot flow through S1, the capacitor cannot discharge, and the current is forced to flow only through the anti-parallel diode VD2. The submodule is in the cut-off state, and the submodule output voltage Equal to 0. When the upper tube of the submodule is turned off and the lower tube is turned on, the submodule switching function is 0 and the bridge arm current is positive, the bridge arm current passes through S2 during normal operation, the submodule is in the cut-off state, and the submodule output voltage Equal to 0.

[0073] like Figure 4 As shown in (b), if S2 has an open circuit fault, the bridge arm current cannot flow through S2, and the current is forced to flow through the anti-parallel diode VD1 to charge the capacitor. The submodule switches from the cut-off state to the on-state, and the submodule output voltage Equal to the submodule capacitor voltage . Other operating states are the same as normal operating states.

[0074] Specifically, step S1 includes:

[0075] S11: Calculate a theoretical bridge arm voltage value according to a DC side voltage value, an AC side voltage value, an inductance value of a bridge arm, and a bridge arm current value of the modular multilevel converter.

[0076] In this embodiment, taking phase a of the MMC system as an example, the actual value of the bridge arm voltage can be obtained by calculation according to the discrete-time mathematical model of the MMC based on Kirchhoff's voltage law, as follows:

[0077]

[0078] in, is the upper arm current Taking the derivative with respect to time, is the lower arm current Taking the derivative with respect to time, is the actual value of the upper tube voltage, is the actual value of the lower tube voltage.

[0079] S12: Calculate the theoretical value of the bridge arm voltage based on the relationship between the submodule switching function and the submodule capacitor voltage:

[0080]

[0081] in, The upper arm is The switch function of each submodule, The lower bridge arm is The switch function of each submodule, is the theoretical value of the upper tube voltage, is the theoretical value of the lower tube voltage, The first The output voltage of each submodule For the lower arm The capacitor voltage of each submodule.

[0082] Specifically, step S2 includes:

[0083] The first alarm threshold includes a bridge arm voltage error threshold and a first time threshold; the bridge arm voltage error threshold is a theoretical mean value of the submodule capacitor voltage.

[0084] When the difference between the theoretical value of the bridge arm voltage and the actual value of the bridge arm voltage is greater than the bridge arm voltage error threshold, and the duration is greater than the first time threshold, it is determined that a fault exists in the corresponding bridge arm;

[0085] When the difference between the theoretical value of the bridge arm voltage and the actual value of the bridge arm voltage is greater than the bridge arm voltage error threshold, and the duration is greater than the first time threshold, determining that the fault type of the fault submodule is an upper tube fault;

[0086] When the difference between the actual bridge arm voltage value and the theoretical bridge arm voltage value is greater than the bridge arm voltage error threshold, and the duration is greater than the first time threshold, it is determined that the fault type of the fault submodule is a lower tube fault.

[0087] Specifically, step S3 includes:

[0088] S31: Sum the capacitance and voltage of the bridge arm submodules and divide the sum by the number of the bridge arm submodules to obtain an average capacitance and voltage of the submodules. ;

[0089] The calculation formula for the average value of the submodule capacitor voltage is as follows:

[0090]

[0091] S32: Obtain the number of faulty submodules according to the difference between the actual bridge arm voltage value and the theoretical bridge arm voltage value and the average value of the bridge arm submodule capacitor voltage.

[0092]

[0093] in, is the actual value of the bridge arm voltage, Theoretical value of bridge arm voltage, is the number of upper tube failures in the bridge arm, is the number of lower tube failures in the bridge arm, is the rounding function.

[0094] Specifically, step S4 includes: according to the fault type and the number of faults, combining the sorting and balancing voltage algorithm to control and adjust the same opposite side bridge arm to open or cut off the same number of submodules as the number of faulty submodules.

[0095] When a tube failure occurs on a submodule of a faulty bridge arm, the submodules on the bridge arm opposite to the faulty bridge arm on the same phase are controlled to open the submodules corresponding to the number of submodules with tube failure on the faulty bridge arm;

[0096] When a submodule lower tube failure occurs in a faulty bridge arm, the submodules on the bridge arm opposite to the faulty bridge arm on the same phase are controlled to remove submodules equal to the number of submodules with lower tube failures on the faulty bridge arm.

[0097] Specifically, such as Figure 11 As shown in the figure, since the interphase circulating current is caused by the imbalance between the fault phase bridge arm voltage and the DC side voltage due to the open circuit fault of the submodule, the fault phase bridge arm voltage and the DC side voltage can be balanced by adjusting the number of submodule switches, thereby reducing the fault phase circulating current and thus reducing the bridge arm current distortion. Figure 11 The black arrow in (a) indicates the error signal of the corresponding fault submodule. Figure 11 The Fault in (b) is a fault signal. Detection signal of SM1 fault, This is the fault location signal of SM1. Figure 11 (c) is the capacitor voltage of the first submodule of the upper bridge arm of phase a, is the capacitor voltage of the first submodule in the lower bridge arm of phase a, is the capacitor voltage of the first submodule of the upper bridge arm of phase b, is the capacitor voltage of the first submodule of the lower bridge arm of phase b, is the capacitor voltage of the first submodule of the upper bridge arm of phase C, is the capacitor voltage of the first submodule in the lower bridge arm of phase c. and When the signal is on, each submodule can charge and discharge according to the sorting and equalizing algorithm, and the system does not crash. However, since the subsequent images are simulation images, it is impossible to replace the wrong modules in reality, which leads to larger fluctuations in the circulation. In actual production life, and After the signal is received, the faulty submodule is repaired.

[0098] from Figure 11It can be seen that adjusting the number of submodule switches can reduce the three-phase circulating current, thereby minimizing its impact on the current in the non-faulty bridge arm. Due to the use of a sorted voltage-sharing algorithm, each submodule charges and discharges according to the direction of the bridge arm current and the sorting results. The strategy of adjusting the number of submodule switches is intended to reduce the impact of the circulating current generated by the open-circuit IGBT fault in the factor module on the bridge arm current, thereby reducing the impact on the operating status of the normal submodules in the faulty bridge arm. As can be seen from the submodule charging and discharging patterns in the figure, a significant deviation quickly develops between the faulty submodule and the normal submodule, allowing the faulty submodule to be quickly located. Since adjusting the number of submodule switches effectively reduces the circulating current in the system, the distortion of the current in each bridge arm is reduced, and the impact of the circulating current on the charging and discharging status of each bridge arm submodule is reduced, adjusting the number of submodule switches will not adversely affect the system during fault diagnosis.

[0099] Specifically, step S5 includes:

[0100] The second alarm threshold includes: a submodule fault characteristic value error threshold and a second time threshold;

[0101] When the difference between the bridge arm submodule capacitor voltage value and the bridge arm submodule capacitor voltage minimum value is greater than the fault characteristic value error threshold, and the duration is greater than the second time threshold, the corresponding bridge arm submodule has a fault.

[0102] Among them, the second time threshold is artificially set, and in the embodiment of the present invention, it is set to one-fifth of the fundamental wave period. Since the system adopts a sorting and equalizing voltage algorithm, the minimum value of the submodule capacitor voltage in the bridge arm is the capacitor voltage value of the normal submodule at a certain sampling moment, and the capacitor voltage value of the normal submodule is not much different from the minimum value of the submodule capacitor voltage. The error threshold is artificially set. Since the error threshold and the difference between the bridge arm submodule capacitor voltage value and the minimum value of the bridge arm submodule capacitor voltage are close to each other, the calculation of the capacitor voltage change rate is faster.

[0103] In particular, when the submodule switching function is 1 and the bridge arm current is negative and an upper tube fault occurs, the faulty submodule cannot discharge, the capacitor voltage remains constant, and the capacitor voltage change rate is 0. However, the normal submodule discharges normally, the submodule capacitor voltage drops, and the absolute value of the capacitor voltage change rate is a positive number. This can be used as a fault feature for fault location. Because the submodule with the lowest capacitor voltage in the bridge arm must be a normal submodule, the value obtained by dividing the change rate of the lowest capacitor voltage in the bridge arm by the change rate of each submodule capacitor voltage is recorded as The expression is as follows.

[0104]

[0105] in, Indicates the minimum change in the bridge arm capacitor voltage, is the change in capacitor voltage, Indicates taking the absolute value, is the change time, The minimum value of the bridge arm capacitor voltage at the detection moment To detect the judgment time After time, the bridge arm capacitor voltage reaches its minimum value. To detect the capacitor voltage value at the judgment moment, Detection and judgment time Capacitor voltage value after time.

[0106] When the normal submodule discharges normally, the absolute value of the capacitor voltage change rate is a positive number, which can be obtained by the above formula. is also a positive number. The absolute value of the fault submodule capacitor voltage change rate is 0 and is used as the denominator, and the obtained is a large number, when Greater than the set threshold When the fault is detected, the submodule is located.

[0107] like Figure 8 As shown, Figure 8 (a) is the capacitance-voltage curve. Figure 8 (b) is the capacitance voltage change rate curve. When the normal submodule is discharged normally, the absolute value of the capacitance voltage change rate is a number that is not much different from the numerator. The above formula can be used to calculate It is also a very small positive number (close to zero, so it is not shown in the figure). The absolute value of the voltage change rate of the faulty submodule capacitor is 0 and is used as the denominator, so the obtained is a large number, when Greater than the set threshold When the fault is detected, the submodule is located.

[0108] When the submodule switching function is 0 and the bridge arm current is positive, a lower tube fault occurs. The faulty submodule continues to charge, while the normal submodule charges much slower than the faulty submodule. The absolute value of the capacitor voltage change rate is very small, which can be used as a fault feature for fault location. The value obtained by dividing the change rate of each submodule capacitor voltage by the change rate of the lowest bridge arm capacitor voltage is recorded as The expression is as follows.

[0109]

[0110] A small positive parameter to prevent the denominator from being zero.

[0111] The charging speed of the normal submodule is much slower than that of the faulty submodule, so according to the above formula, the charging speed of the faulty submodule is much faster than that of the normal submodule. When the value of Greater than the set threshold When the fault is detected, the submodule is located.

[0112] The results of the upper IGBT open circuit fault diagnosis of the upper bridge arm submodule are as follows: Figure 5 shown. Figure 5 (a) shows the theoretical value of the bridge arm voltage and the actual value of the bridge arm voltage ,

[0113] Figure 5 (b) shows the number of faulty submodules , number of sub-modules invested The number of sub-modules invested after the investment strategy ;

[0114] Figure 5 (c) shows the bridge arm current ;

[0115] Figure 5 (d) shows the capacitor voltage of each submodule in the fault bridge arm and ;

[0116] Figure 5 (e) shows all the signals, among which Fault is the fault signal. Detection signal of SM1 fault, This is the fault location signal of SM1.

[0117] When the bridge arm current is positive, the faulty submodule has no fault characteristics. When the bridge arm current changes from positive to negative, the submodule 1 in the on state is mistakenly bypassed through the diode VD2, resulting in the theoretical value of the bridge arm voltage being greater than the actual value of the bridge arm voltage. When the deviation between the two is greater than the bridge arm voltage error threshold and the duration is greater than the time threshold, it is determined that the corresponding bridge arm has a fault. The number of faulty submodules is obtained by the ratio of the difference between the two and the average value of the capacitor voltage of each submodule in the bridge arm. After the holding time exceeds the time threshold, the strategy is quickly put into use to increase the number of lower bridge arm switch tubes turned on by 1 to offset the capacitor voltage of the submodule in the upper bridge arm that is mistakenly shut down due to upper tube failure. This allows the bridge arm current to pass through zero normally to a negative value, and the normal submodule can discharge normally, causing the capacitor voltage of the faulty submodule to quickly deviate from the other normal submodules, causing the voltage of the faulty submodule to be far away from the normal submodule, thereby reducing the diagnostic requirements and improving the diagnostic capability. Figure 5 As shown in (a) to (e), the faulty submodule can be quickly located. Figure 5Figures (f) through (i) show the waveforms of the fault diagnosis experiment without the strategy. As can be seen, when a submodule's upper IGBT fails in a bridge arm, the current in the faulty arm drops to zero. Normal submodules cannot discharge properly, making it impossible to quickly distinguish the capacitor voltages of the faulty and normal SMs, preventing the rapid location of the faulty SM.

[0118] Similarly, Figure 6 This is an example diagram of the open circuit judgment of the lower tube IGBT of the upper bridge arm submodule.

[0119] Figure 6 (a) shows the theoretical value of the bridge arm voltage and the actual value of the bridge arm voltage ,

[0120] Figure 6 (b) shows the number of faulty submodules , number of sub-modules invested The number of sub-modules invested after the investment strategy ;

[0121] Figure 6 (c) shows the bridge arm current ;

[0122] Figure 6 (d) shows the capacitor voltage of each submodule in the fault bridge arm and ;

[0123] Figure 6 (e) shows all the signals, among which Fault is the fault signal. Detection signal of SM1 fault, This is the fault location signal of SM1.

[0124] like Figure 6 As shown in (a) to (e), the faulty submodule can be quickly located. Figure 6 Figures (f) through (i) show the waveforms from the fault diagnosis experiment without the strategy. As can be seen, when a submodule's lower IGBT fails in a bridge arm, the current in the faulty arm drops to zero. Normal submodules cannot charge properly, making it impossible to quickly distinguish the capacitor voltages of the faulty and normal SMs, preventing the rapid location of the faulty SM.

[0125] It can be seen from the simulation waveform that compared with the traditional fault diagnosis method, the method proposed in the present invention balances the energy in the bridge arm by controlling the number of switches in the bridge arm sub-module, which can effectively reduce the current distortion of the faulty arm, thereby quickly distinguishing the capacitor voltage of the faulty sub-module from the capacitor voltage of the normal sub-module, and realizing rapid fault location.

[0126] like Figure 7 As shown, Figure 7 This is an example diagram of fault judgment when different submodules fail at the same time.

[0127] Figure 7 (a) shows the theoretical value of the bridge arm voltage and the actual value of the bridge arm voltage ,

[0128] Figure 7 (b) shows the number of faulty submodules , number of sub-modules invested The number of sub-modules invested after the investment strategy ;

[0129] Figure 7 (c) shows the bridge arm current ;

[0130] Figure 7 (d) shows the capacitor voltage of each submodule in the fault bridge arm and ;

[0131] Figure 7 (e) shows all the signals, among which Fault is the fault signal. Detection signal of SM1 fault, This is the fault location signal of SM1.

[0132] When multiple tube faults occur in different phases, since the submodule open-circuit faults occur in different bridge arms of different phases, the fault diagnosis strategy is parallel, without affecting the individual fault diagnosis processes. Similarly, after detecting the type and number of faults in the bridge arm submodules, the corresponding strategy is implemented to reduce bridge arm current distortion, which benefits the charging and discharging processes of the normal submodules. This allows the faulty submodule to quickly deviate from the normal submodule, significantly improving fault location speed.

[0133] like Figure 9 As shown, Figure 9 The following is a block diagram of an MMC fault diagnosis method system based on a sorting and voltage balancing algorithm, including:

[0134] Deviation value calculation module 101: calculates the theoretical value and actual value of the bridge arm voltage of the modular multilevel converter according to the measurement data of the modular multilevel converter;

[0135] Fault judgment module 102: compares the actual bridge arm voltage value, the theoretical bridge arm voltage value and the first alarm threshold to determine whether the corresponding bridge arm has a fault and the fault type;

[0136] Fault number determination module 103: calculates the number of fault submodules according to the actual value of the bridge arm voltage and the theoretical value of the bridge arm voltage;

[0137] Fault repair and adjustment module 104: determines the number of switches in the faulty bridge arm submodule, and controls and adjusts the opening of the upper and lower bridge arm submodules of the faulty phase according to the fault type and the number of faulty submodules;

[0138] The fault location determination module 105 calculates the difference between the capacitor voltage of each submodule and the minimum capacitor voltage of the bridge arm submodule, and compares it with the second alarm threshold to determine the faulty submodule.

[0139] Figure 10 An example of a physical structure diagram of an electronic device is shown below. Figure 10 As shown, the electronic device may include: a processor 810, a communication interface 820, a memory 830, and a communication bus 840, wherein the processor 810, the communication interface 820, and the memory 830 communicate with each other via the communication bus 840. The processor 810 may call the logic instructions in the memory 830 to execute the MMC fault diagnosis method based on the sorting and voltage balancing algorithm, which includes:

[0140] S1: Calculate the theoretical value and actual value of the bridge arm voltage of the modular multilevel converter based on the measured data of the modular multilevel converter;

[0141] S2: Compare the actual bridge arm voltage value, the theoretical bridge arm voltage value and the first alarm threshold to determine whether the corresponding bridge arm has an IGBT open circuit fault;

[0142] S3: Calculate the number of faulty submodules according to the actual value of the bridge arm voltage and the theoretical value of the bridge arm voltage;

[0143] S4: Calculate the difference between the capacitor voltage of each submodule and the minimum capacitor voltage of the bridge arm submodule, and compare it with the second alarm threshold to determine the faulty submodule;

[0144] S5: Determine the number of switches of the faulty bridge arm submodules, and control and adjust the opening of the upper and lower bridge arm submodules of the faulty phase according to the fault type and the number of the faulty submodules.

[0145] Furthermore, the logic instructions in the aforementioned memory 830 can be implemented as software functional units and, when sold or used as independent products, can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present invention, or the portion that contributes to the prior art, or a portion of the technical solution, can be embodied in the form of a software product. This computer software product, stored in a storage medium, includes instructions for enabling a computer device (which can be a personal computer, server, or network device, etc.) to perform all or part of the steps of the methods described in various embodiments of the present invention. The aforementioned storage medium includes various media capable of storing program code, such as USB flash drives, mobile hard drives, read-only memories (ROMs), random access memories (RAMs), magnetic disks, or optical disks.

[0146] The device embodiments described above are merely illustrative. The units described as separate components may or may not be physically separate, and the components shown as units may or may not be physical units, i.e., they may be located in one location or distributed across multiple network units. Some or all of the modules may be selected based on actual needs to achieve the objectives of the present embodiment. Persons of ordinary skill in the art will be able to understand and implement the present invention without inventive effort.

[0147] Through the above description of the embodiments, those skilled in the art will clearly understand that each embodiment can be implemented using software plus a necessary general-purpose hardware platform, or of course, hardware. Based on this understanding, the essence of the above technical solution, or the portion that contributes to the prior art, can be embodied in the form of a software product. This computer software product can be stored in a computer-readable storage medium, such as ROM / RAM, a magnetic disk, or an optical disk, and includes a number of instructions for causing a computer device (such as a personal computer, server, or network device) to execute the methods described in each embodiment or certain portions of the embodiments.

[0148] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention.

[0149] It should be noted that the embodiments of the present disclosure can be implemented by hardware, software, or a combination of software and hardware. The hardware portion can be implemented using dedicated logic; the software portion can be stored in a memory and executed by an appropriate instruction execution system such as a microprocessor or dedicated hardware. Those skilled in the art will understand that the above-mentioned devices and methods can be implemented using computer-executable instructions and / or contained in processor control code, for example, such code is provided on a programmable memory or a data carrier such as an optical or electronic signal carrier.

[0150] In addition, although the operations of the method of the present disclosure are described in a particular order in the accompanying drawings, this does not require or imply that these operations must be performed in this particular order, or that all the operations shown must be performed to achieve the desired result. On the contrary, the steps depicted in the flow chart can change the order of execution. Additionally or alternatively, certain steps can be omitted, multiple steps can be combined into one step, and / or one step can be decomposed into multiple steps. It should also be noted that the features and functions of two or more devices according to the present disclosure can be embodied in one device. Conversely, the features and functions of a device described above can be further divided into being embodied by multiple devices.

[0151] Although the present disclosure has been described with reference to several specific embodiments, it should be understood that the present disclosure is not limited to the specific embodiments disclosed. The present disclosure is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.

Claims

1. A MMC fault diagnosis method based on sorting and voltage balancing algorithm, characterized in that: The following steps are involved: S1: Calculate the theoretical value and actual value of the bridge arm voltage of the modular multilevel converter based on the measured data of the modular multilevel converter; S2: Compare the actual value of the bridge arm voltage, the theoretical value of the bridge arm voltage and the first alarm threshold to determine whether the corresponding bridge arm has an IGBT open circuit fault; Step S2 includes: the first alarm threshold includes a bridge arm voltage error threshold and a first time threshold; When the difference between the theoretical value of the bridge arm voltage and the actual value of the bridge arm voltage is greater than the bridge arm voltage error threshold, and the duration is greater than the first time threshold, it is determined that a fault exists in the corresponding bridge arm; When the difference between the theoretical value of the bridge arm voltage and the actual value of the bridge arm voltage is greater than the bridge arm voltage error threshold, and the duration is greater than the first time threshold, determining that the fault type of the fault submodule is an upper tube fault; When the difference between the actual bridge arm voltage value and the theoretical bridge arm voltage value is greater than the bridge arm voltage error threshold, and the duration is greater than the first time threshold, determining that the fault type of the fault submodule is a lower tube fault; S3: Calculate the number of faulty submodules according to the actual value of the bridge arm voltage and the theoretical value of the bridge arm voltage; S4: Determine the number of switches in the faulty bridge arm submodules, and control and adjust the opening of the upper and lower bridge arm submodules of the faulty phase according to the fault type and the number of faulty submodules. Step S4 includes: based on the fault type and the number of faults, combined with the sorting and voltage balancing algorithm, control and adjust the opening or removal of the same number of submodules in the bridge arm on the same opposite side as the number of faulty submodules; S5: Calculate the difference between the capacitor voltage of each submodule and the minimum capacitor voltage of the bridge arm submodule, and compare it with the second alarm threshold to determine the faulty submodule. Step S5 includes: The second alarm threshold includes: a submodule fault characteristic value error threshold and a second time threshold; When the difference between the bridge arm submodule capacitor voltage value and the bridge arm submodule capacitor voltage minimum value is greater than the fault characteristic value error threshold, and the duration is greater than the second time threshold, the corresponding bridge arm submodule has a fault; When the submodule switching function is 1 and the bridge arm current is negative and an upper tube fault occurs, the value obtained by dividing the change rate of the lowest capacitor voltage of the bridge arm by the change rate of the capacitor voltage of each submodule is recorded as ,when Greater than the set threshold When the fault occurs in the submodule, it is located; When the submodule switching function is 0 and the bridge arm current is positive and a lower tube fault occurs, the value obtained by dividing the change rate of each submodule capacitor voltage by the change rate of the lowest bridge arm capacitor voltage is recorded as ,when Greater than the set threshold When the fault is detected, the submodule is located.

2. The MMC fault diagnosis method based on the sorting and voltage balancing algorithm according to claim 1 is characterized in that: Step S1 includes: S11: Calculating a theoretical bridge arm voltage value according to a DC side voltage value, an AC side voltage value, an inductance value of a bridge arm, and a bridge arm current value of the modular multilevel converter; S12: Calculate the actual value of the bridge arm voltage according to the relationship between the submodule switching function and the submodule capacitor voltage.

3. The MMC fault diagnosis method based on the sorting and voltage balancing algorithm according to claim 1 is characterized in that: Step S3 includes: S31: summing the capacitor voltages of the bridge arm submodules and dividing the sum by the number of the bridge arm submodules to obtain an average value of the capacitor voltages of the submodules; S32: Obtain the number of faulty submodules according to the difference between the actual bridge arm voltage value and the theoretical bridge arm voltage value and the average value of the bridge arm submodule capacitor voltage.

4. The MMC fault diagnosis method based on the sorting and voltage balancing algorithm according to claim 1 is characterized in that: The combined sorting and pressure balancing algorithm includes: When a tube failure occurs on a submodule of a faulty bridge arm, the submodules on the bridge arm opposite to the faulty bridge arm on the same phase are controlled to open the submodules corresponding to the number of submodules with tube failure on the faulty bridge arm; When a submodule lower tube failure occurs in a faulty bridge arm, the submodules on the bridge arm opposite to the faulty bridge arm on the same phase are controlled to remove submodules equal to the number of submodules with lower tube failures on the faulty bridge arm.

5. The MMC fault diagnosis method based on the sorting and voltage balancing algorithm according to claim 1 is characterized in that: The bridge arm voltage error threshold is the theoretical mean value of the submodule capacitor voltage.

6. An MMC fault diagnosis system based on a sorting and voltage balancing algorithm, used to execute the MMC fault diagnosis method based on a sorting and voltage balancing algorithm as claimed in any one of claims 1 to 5, characterized in that: include: Deviation value calculation module: calculates the theoretical value and actual value of the bridge arm voltage of the modular multilevel converter based on the measurement data of the modular multilevel converter; Fault judgment module: compares the actual value of the bridge arm voltage, the theoretical value of the bridge arm voltage and the first alarm threshold to determine whether the corresponding bridge arm has a fault and the fault type; Fault number judgment module: calculates the number of fault submodules according to the actual value of the bridge arm voltage and the theoretical value of the bridge arm voltage; Fault repair and adjustment module: determines the number of switches in the faulty bridge arm submodule, and controls and adjusts the opening of the upper and lower bridge arm submodules of the faulty phase according to the fault type and the number of faulty submodules; Fault location judgment module: calculates the difference between the capacitor voltage of each submodule and the minimum value of the capacitor voltage of the bridge arm submodule, and compares it with the second alarm threshold to determine the faulty submodule.

7. An electronic device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein: When the processor executes the computer program, the steps of the MMC fault diagnosis method based on the sorting voltage balancing algorithm as claimed in any one of claims 1 to 5 are implemented.

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