Submodule open-circuit fault judging and positioning method for modular multilevel converter

Abstract

The invention discloses a sub-module open-circuit fault judging and positioning method for a modular multilevel converter. The method comprises the following steps: calculating to obtain a bridge arm current observation value of each bridge arm; determining whether the corresponding bridge arm has a fault or not; calculating to obtain a capacitive current ideal value of each bridge arm sub-module on the bridge arm with the fault; the actual capacitance current value of each bridge arm sub-module on the bridge arm with the fault is obtained through calculation; and determining whether the corresponding bridge arm sub-module has a fault or not. The invention discloses a sub-module open-circuit fault judging and positioning method for a modular multilevel converter, which does not need to additionally increase system hardware cost and has the characteristics of accurate fault judging and positioning, small calculated amount and high fault positioning speed.

Description

Technical Field

[0001] The invention belongs to the field of modular multi-level converters, and in particular relates to a sub-module open circuit fault judgment and positioning method for a modular multi-level converter. Background Art

[0002] Modular multilevel converter (MMC) is widely used in battery energy storage systems, static synchronous compensators, motor drive systems and other fields due to its modular structure, scalability, low switching frequency and good harmonic performance. However, since MMC is usually composed of a large number of sub-modules connected in series, the number of insulated gate bipolar transistors (IGBT) also increases exponentially with the increase in the number of sub-modules. Although this can improve the harmonic performance of the system, it also increases the risk of potential failures. The open circuit fault inside the modular multilevel converter is usually caused by physical reasons such as unavailable drive signals or internal damage to the wiring, which will not immediately damage the sub-module. Therefore, it has always been a difficult problem to determine and locate the open circuit fault of the modular multilevel converter.

[0003] Under the existing technical conditions, the existing open-circuit fault judgment methods of modular multi-level converters are divided into two types: a hardware-based fault judgment method and a software algorithm-based fault judgment method. The hardware-based fault judgment method requires the addition of additional hardware circuits to collect fault signals for fault detection, which requires additional hardware costs. The software algorithm-based fault judgment method has the problem of poor robustness and is easily affected by model parameters. Summary of the invention

[0004] In view of this, the present invention aims to overcome the defects in the prior art and proposes a method for determining and locating an open circuit fault of a submodule of a modular multi-level converter.

[0005] To achieve the above object, the technical solution of the present invention is achieved as follows:

[0006] In a first aspect, a method for determining and locating a submodule open circuit fault of a modular multilevel converter comprises:

[0007] According to the DC side voltage value, AC side voltage value, bridge arm inductance value, bridge arm submodule switching function and bridge arm submodule capacitance voltage value of the modular multilevel converter, the bridge arm current observation value of each bridge arm is calculated;

[0008] Obtain the actual value of the bridge arm current of each bridge arm, and compare it with the corresponding bridge arm current observation value to determine whether the corresponding bridge arm has a fault;

[0009] According to the switching function of the bridge arm submodule on the bridge arm with the fault and the actual value of the bridge arm current, the ideal value of the capacitor current of each bridge arm submodule on the bridge arm with the fault is calculated;

[0010] According to the capacitor voltage value, the capacitance value and the sampling period of the capacitor voltage value of the bridge arm submodule on the bridge arm with the fault, the actual value of the capacitor current of each bridge arm submodule on the bridge arm with the fault is calculated;

[0011] The ideal capacitor current value is compared with the corresponding actual capacitor current value to determine whether the corresponding bridge arm submodule has a fault.

[0012] In another embodiment of the present invention, the bridge arm current observation value of each bridge arm is calculated according to the DC side voltage value, AC side voltage value, bridge arm cross-arm inductance value, bridge arm sub-module switching function and bridge arm sub-module capacitor voltage value of the modular multi-level converter, including: according to Kirchhoff's voltage law, an observer equation for the bridge arm current observation value is established, and the observer equation includes an injection term for improving the observation tracking effect.

[0013] In another embodiment of the present invention, the actual value of the bridge arm current of each bridge arm is obtained, and compared with the corresponding bridge arm current observation value to determine whether the corresponding bridge arm has a fault, including: presetting a bridge arm current error threshold and a first time threshold; when the difference between the actual value of the bridge arm current and the bridge arm current observation value is greater than the bridge arm current error threshold, and the duration is greater than the time threshold, it is determined that the corresponding bridge arm has a fault.

[0014] In another embodiment of the present invention, based on the switching function of the bridge arm sub-module on the faulty bridge arm and the actual value of the bridge arm current, the ideal value of the capacitor current of each bridge arm sub-module on the faulty bridge arm is calculated, including: the ideal value of the capacitor current is equal to the product of the switching function of the bridge arm sub-module and the corresponding actual value of the bridge arm current.

[0015] In another embodiment of the present invention, the ideal value of the capacitor current is compared with the corresponding actual value of the capacitor current to determine whether the corresponding bridge arm sub-module has a fault, including: comparing the average value of the ideal value of the capacitor current within a switching cycle of the bridge arm sub-module with the average value of the corresponding actual value of the capacitor current.

[0016] In another embodiment of the present invention, comparing and judging by the mean of the ideal value of the capacitor current in one switching cycle of the bridge arm submodule and the mean of the corresponding actual value of the capacitor current, including: obtaining an upper tube fault characteristic value for judging an upper tube fault of the bridge arm submodule and a lower tube fault characteristic value for judging a lower tube fault according to a ratio relationship between the mean of the ideal value of the capacitor current and the mean of the corresponding actual value of the capacitor current;

[0017] A fault characteristic value error threshold and a second time threshold are preset; when the actual value of the bridge arm current is greater than zero, and the upper tube fault characteristic value is greater than the fault characteristic value error threshold and the duration is greater than the second time threshold, the upper tube of the corresponding bridge arm submodule is faulty;

[0018] When the actual value of the bridge arm current is less than zero, the fault characteristic value of the lower tube is greater than the fault characteristic value error threshold, and the duration is greater than the second time threshold, the lower tube of the corresponding bridge arm submodule is faulty.

[0019] In another embodiment of the present invention, the method further comprises setting a flag bit, where the flag bit is used to identify a fault location of the bridge arm submodule.

[0020] In a second aspect, the present invention discloses a submodule open circuit fault judgment and positioning device for a modular multi-level converter, the device comprising:

[0021] The bridge arm current observation value calculation module is used to calculate the bridge arm current observation value of each bridge arm according to the DC side voltage value, AC side voltage value, bridge arm cross-arm inductance value, bridge arm submodule switching function and bridge arm submodule capacitor voltage value of the modular multilevel converter;

[0022] The first judgment module is used to obtain the actual value of the bridge arm current of each bridge arm, and compare and judge with the corresponding bridge arm current observation value to determine whether the corresponding bridge arm has a fault;

[0023] A capacitor current ideal value calculation module, used to calculate the capacitor current ideal value of each bridge arm submodule on the bridge arm with the fault according to the switch function of the bridge arm submodule on the bridge arm with the fault and the actual value of the bridge arm current;

[0024] A capacitor current actual value calculation module is used to calculate the capacitor current actual value of each bridge arm submodule on the bridge arm with the fault according to the capacitor voltage value, the capacitance value and the sampling period of the capacitor voltage value of the bridge arm submodule on the bridge arm with the fault;

[0025] The second judgment module is used to compare and judge the ideal value of the capacitor current with the corresponding actual value of the capacitor current to determine whether the corresponding bridge arm submodule has a fault.

[0026] In a third aspect, the present invention discloses an electronic device, comprising: one or more processors; a storage device for storing one or more programs, wherein when the one or more programs are executed by the one or more processors, the one or more processors execute the above method.

[0027] According to a fourth aspect, a computer program product comprises a computer program, wherein the computer program implements the above method when executed by a processor.

[0028] Compared with the prior art, the present invention has the following advantages:

[0029] The present invention discloses a method for determining and locating a submodule open circuit fault for a modular multi-level converter, comprising: calculating and obtaining an observed bridge arm current value of each bridge arm; determining whether the corresponding bridge arm has a fault; calculating and obtaining an ideal value of a capacitor current of each bridge arm submodule on the bridge arm with the fault; calculating and obtaining an actual value of a capacitor current of each bridge arm submodule on the bridge arm with the fault; and determining whether the corresponding bridge arm submodule has a fault. The present invention discloses a method for determining and locating a submodule open circuit fault for a modular multi-level converter, which does not require additional system hardware costs, and has the characteristics of accurate fault determination and locating, small calculation amount, and fast fault locating speed. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The accompanying drawings, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0031] In the attached picture:

[0032] Figure 1 A schematic diagram of an application scenario of a method for determining and locating a submodule open circuit fault of a modular multi-level converter according to an embodiment of the present invention;

[0033] Figure 2 A schematic diagram of a method for determining and locating a submodule open circuit fault in a modular multi-level converter according to an embodiment of the present invention;

[0034] Figure 3 A schematic diagram of a fault bridge arm judgment method for judging and locating a submodule open circuit fault of a modular multi-level converter according to an embodiment of the present invention;

[0035] Figure 4 A schematic diagram of a faulty bridge arm submodule judgment method for judging and locating a submodule open circuit fault of a modular multi-level converter according to an embodiment of the present invention;

[0036] Figure 5 This is an example diagram of a submodule upper tube open circuit fault judgment method for a modular multi-level converter according to an embodiment of the present invention;

[0037] Figure 6 This is an example diagram of a method for determining and locating a submodule open circuit fault of a modular multi-level converter according to an embodiment of the present invention, and a submodule lower tube open circuit fault determination example;

[0038] Figure 7 This is an example diagram of a submodule double-tube open circuit fault judgment method for a modular multi-level converter according to an embodiment of the present invention;

[0039] Figure 8 A schematic diagram of a submodule open circuit fault judgment and location device for a modular multi-level converter according to an embodiment of the present invention;

[0040] Fig. 9 The present invention is a schematic diagram of an electronic device for determining and locating an open circuit fault of a submodule of a modular multi-level converter according to an embodiment of the present invention. DETAILED DESCRIPTION

[0041] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments may be combined with each other.

[0042] In the description of the present invention, it should be further explained that the terms "first", "second", etc. are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Thus, a feature defined as "first", "second", etc. may explicitly or implicitly include one or more of the features. In the description of the present invention, unless otherwise specified, "plurality" means two or more.

[0043] Under the existing technical conditions, the existing open-circuit fault judgment methods of modular multi-level converters are divided into two types: a hardware-based fault judgment method and a software algorithm-based fault judgment method. The hardware-based fault judgment method requires the addition of additional hardware circuits to collect fault signals for fault detection, which requires additional hardware costs. The software algorithm-based fault judgment method has the problem of poor robustness and is easily affected by model parameters.

[0044] The application scenario of the method for determining and locating a submodule open circuit fault of a modular multi-level converter disclosed in the present invention is as follows: Figure 1 As shown in Figure 2, the structure of a modular multilevel converter (MMC) is as follows: Figure 1As shown in the figure, the MMC consists of three-phase six bridge arms, each of which is composed of N half-bridge sub-modules of the same structure cascaded and together with the cross-arm inductor. In practical applications, each bridge arm of the MMC system may have hundreds of bridge arm sub-modules. Each bridge arm sub-module consists of two switches with anti-parallel diodes and a capacitor C for energy storage. The switch symbol is T juip and T jlip , where j represents each phase of the MMC system, j∈{a,b,c}, that is, three phases; u represents the upper bridge arm, l represents the upper bridge arm; i=1,2,…,N represents the number of submodules; p=1 represents the upper tube in the submodule, p=2 represents the lower tube in the submodule, and the switching pulse S ju and S jl Control the on / off state of the upper and lower tubes. In normal operation, the upper and lower tubes are complementary to each other. In each phase of the MMC system, the upper and lower bridge arms are connected through the arm inductance L ju and L jl Interconnection, DC side voltage is represented by U dc , the AC side voltage is represented by u jo By changing the number of upper and lower bridge arm submodules put into and removed, the AC side voltage u jo Multi-level output. ju and u jl are the voltages of the upper bridge arm and the lower bridge arm of phase j respectively, and the capacitor voltage is expressed as U cju ,i ju and i jl are the bridge arm currents of the upper bridge arm and the lower bridge arm of phase j, respectively. Since the current and voltage are continuous and the switch pulse is discrete in the MMC system, the MMC system is a nonlinear multivariable hybrid system. The following uses phase a as an example to represent the embodiment, and the other phases are the same as phase a.

[0045] The present invention discloses a method for determining and locating a submodule open circuit fault for a modular multi-level converter, comprising: calculating and obtaining an observed bridge arm current value of each bridge arm; determining whether the corresponding bridge arm has a fault; calculating and obtaining an ideal value of a capacitor current of each bridge arm submodule on the bridge arm with the fault; calculating and obtaining an actual value of a capacitor current of each bridge arm submodule on the bridge arm with the fault; and determining whether the corresponding bridge arm submodule has a fault. The present invention does not require additional system hardware costs, and has the characteristics of accurate fault determination and positioning, small calculation amount, and fast fault positioning speed.

[0046] The present invention will be described in detail below with reference to the accompanying drawings and in conjunction with embodiments.

[0047] like Figure 1 to Figure 2 As shown, a method for determining and locating a submodule open circuit fault of a modular multi-level converter comprises:

[0048] Step 201, calculating the bridge arm current observation value of each bridge arm according to the DC side voltage value, AC side voltage value, bridge arm cross-arm inductance value, bridge arm submodule switching function and bridge arm submodule capacitance voltage value of the bridge arm submodule of the modular multilevel converter;

[0049] In this embodiment, taking the upper bridge arm of phase a of the MMC system as an example, the DC side voltage value is expressed as U dc , the AC side voltage value is expressed as u ao , the inductance across the arm is represented by L au , the switching function of the bridge arm submodule is expressed as S au , the capacitor voltage value of the bridge arm submodule is expressed as U cau .

[0050] Step 202, obtaining the actual bridge arm current value of each bridge arm, and comparing it with the corresponding bridge arm current observation value to determine whether the corresponding bridge arm has a fault;

[0051] In this embodiment, the method first determines the bridge arm where the fault occurs, for example, Figure 1 As shown, among all 6 bridge arms, the faulty bridge arm is located.

[0052] Step 203, calculating the ideal value of the capacitor current of each bridge arm submodule on the bridge arm with the fault according to the switch function of the bridge arm submodule on the bridge arm with the fault and the actual value of the bridge arm current;

[0053] In this embodiment, after the failed bridge arm is determined in step 202, it is further determined which bridge arm submodule in the failed bridge arm is faulty.

[0054] Step 204, calculating the actual value of the capacitor current of each bridge arm submodule on the bridge arm with the fault according to the capacitor voltage value, the capacitance value and the sampling period of the capacitor voltage value of the bridge arm submodule on the bridge arm with the fault;

[0055] In this embodiment, if Figure 1 As shown, the capacitor in the ideal value of the capacitor current and the actual value of the capacitor current refers to the capacitor C in the bridge arm submodule.

[0056] Step 205 , comparing the ideal capacitor current value with the corresponding actual capacitor current value to determine whether the corresponding bridge arm submodule has a fault.

[0057] The present embodiment discloses a method for determining and locating a submodule open circuit fault for a modular multi-level converter, which does not require additional system hardware costs and has the characteristics of accurate fault determination and locating, small calculation amount, and fast fault locating speed.

[0058] Based on the previous embodiment, in another embodiment disclosed by the present invention, according to the DC side voltage value, AC side voltage value, bridge arm inductance value, bridge arm sub-module switching function and bridge arm sub-module capacitor voltage value of the modular multi-level converter, the bridge arm current observation value of each bridge arm is calculated, including: according to Kirchhoff's voltage law, an observer equation for the bridge arm current observation value is established, and the observer equation includes an injection term for improving the observation tracking effect.

[0059] In this embodiment, if Figure 1 As shown, according to Kirchhoff's voltage law, exemplary, the dynamic characteristic equation of the MMC system a phase is as follows:

[0060]

[0061] Among them, the upper and lower bridge arm currents are expressed as (i au ,i al )∈R, the cross-arm inductance of the upper and lower bridge arms is expressed as (L au ,L al )∈R, the switching pulse of the switching function of the upper and lower bridge arm submodules is expressed as S au ∈R N×1 and S al ∈R N×1 , the capacitor voltage of the upper and lower bridge arm submodules is expressed as U cau ∈R N×1 and U cal ∈R N×1 , the phase AC side voltage is expressed as u ao ∈R;

[0062] Wherein, R represents a real number set, t represents a sampling time, and N represents the number of submodules on a bridge arm.

[0063] According to the dynamic characteristic equation, the observer equation is further established as follows:

[0064] The dynamic equation of the bridge arm current can be expressed as: Assuming that the physical quantity of the MMC can be measured every microsecond, considering the very low sampling time T s (i.e. 10 -6 The dynamic equation of the bridge arm current is discretized using the shift operator as follows:

[0065]

[0066] Furthermore, the observer equation of the bridge arm current observation value is established as follows:

[0067]

[0068] Among them, η iuis the injection term of the upper arm current observer, k represents the sampling point, T s Indicates the sampling period.

[0069] In this embodiment, the sliding mode observer does not consider the tracking effect of the observer required by the system before and after the fault. Generally, when the MMC system is operating normally, the smaller the error between the observed value and the actual value, the better. However, after the MMC system fails, the larger the error between the observed value and the actual value, the easier it is to detect the fault. At the same time, the chattering of the MMC system will seriously affect the control accuracy and stability. To solve the above problems, an adaptive reaching law is proposed, η iu The calculation process is as follows:

[0070]

[0071] Among them, i au (k) is the actual value of the bridge arm current. is the observed value of the bridge arm current; e iau (k) represents the residual between the actual value of the bridge arm current and the observed value of the bridge arm current, and k represents the sampling point;

[0072] When a submodule fault occurs on the bridge arm, the bridge arm current will be distorted. In order to ensure the robustness of the observer during normal operation of the system and the rapidity of post-fault detection, the boundary layer h(e iau ) is set to:

[0073]

[0074] Among them, N fault is the number of faulty submodules on the bridge arm. For example, when a submodule fails on the bridge arm, N fault The value is 1;

[0075]

[0076] Among them, exemplary, n iu is the injection term of the upper arm current observer, k represents the sampling point, k1 is a constant and k1>0, which controls the overall amplitude of the reaching law; λ controls the decay rate of the exponential function, λ=1,3,6,12…, usually λ needs to be adjusted according to the dynamic response speed of the system, the larger the value, the faster the decay rate. When the error is large, 1-e -λei au Close to 1, the approach speed is close to a constant, h(e iau ) is the boundary layer thickness, which determines the response speed of the sliding mode observer. The larger the value, the stronger the system's anti-interference ability. As the error decreases, the approach rate gradually decreases, and the approach speed is slower near the sliding surface. This dynamic adjustment can significantly weaken the chattering phenomenon near the sliding surface, and the system performs more smoothly and stably near the sliding surface.

[0077] Based on the previous embodiment, Figure 2 and Figure 3 As shown, step 202, obtain the actual value of the bridge arm current of each bridge arm, and compare and judge with the corresponding bridge arm current observation value to determine whether the corresponding bridge arm has a fault, including: presetting a bridge arm current error threshold and a first time threshold; when the difference between the actual value of the bridge arm current and the bridge arm current observation value is greater than the bridge arm current error threshold, and the duration is greater than the time threshold, it is determined that the corresponding bridge arm has a fault.

[0078] In this embodiment, the bridge arm current error threshold is expressed as ΔI th , the first time threshold is denoted as ΔT th1 , initialize timer T1, that is, T1=0;

[0079] Exemplarily, the residual error e between the actual bridge arm current value and the observed bridge arm current value is calculated. iau , if e iau The absolute value is less than the threshold ΔI th , it is determined that this bridge arm has no fault; otherwise, timer T1 is enabled to record the fault duration. If T1>ΔT th1 , it is determined that a fault has occurred on the bridge arm, and the submodule on the bridge arm is further determined to have a fault.

[0080] Based on the previous embodiment, Figure 2 and Figure 4 As shown, step 203, based on the switching function of the bridge arm sub-module on the bridge arm with the fault and the actual value of the bridge arm current, the ideal value of the capacitor current of each bridge arm sub-module on the bridge arm with the fault is calculated, including: the ideal value of the capacitor current is equal to the product of the switching function of the bridge arm sub-module and the corresponding actual value of the bridge arm current.

[0081] In this embodiment, according to Kirchhoff's voltage law, illustratively, Figure 1 As shown, the relationship between the phase a capacitor current and the bridge arm current is:

[0082] i cau (t) = S au (t)·i au (t)

[0083] Among them, i cau (t) is the capacitive current of the bridge arm submodule, S au (t) is the switching function of the bridge arm submodule, i au (t) is the actual current of the bridge arm, and t is the sampling time.

[0084] The ideal value of capacitor current is discretized using the shift operator It is expressed as follows:

[0085]

[0086] Where k represents the sampling point.

[0087] In this embodiment, each bridge arm in an actual MMC system often has hundreds or thousands of submodules, which greatly increases the system cost. Therefore, without increasing the hardware cost, the actual capacitor voltage is used to estimate the actual capacitor current value i cau , the actual value of capacitor current i cau It is expressed as follows:

[0088]

[0089] Among them, U cau is the collected capacitance voltage value of the bridge arm submodule, C is the capacitance value of the bridge arm submodule, T s is the sampling period, and k represents the sampling point.

[0090] Based on the previous embodiment, in another embodiment of the present invention, the ideal value of the capacitor current is compared with the corresponding actual value of the capacitor current to determine whether the corresponding bridge arm sub-module has a fault, including: comparing the average value of the ideal value of the capacitor current within a switching cycle of the bridge arm sub-module with the average value of the corresponding actual value of the capacitor current.

[0091] In this embodiment, the ideal value of the capacitor current is And the actual value of the capacitor current i cau Both contain discrete quantities, and sensor measurement errors or system control delays will cause errors in the sampling of capacitor voltage and bridge arm current, so the calculated capacitor current is not accurate. In each switching cycle, the submodule may be in the input and output states. Therefore, in order to reduce the error, the average capacitor current in a switching cycle is used, as follows:

[0092]

[0093] Where M is the number of sampling periods in a switching cycle, T f Represents a switching cycle, T s represents the sampling period, n represents the nth sampling period in a switching period, is the mean of the actual values ​​of the capacitor current, is the mean of the ideal values ​​of the capacitor current.

[0094] On the basis of the previous embodiment, in another embodiment of the present invention, the average value of the ideal capacitor current in a switching cycle of the bridge arm submodule is compared with the average value of the corresponding actual capacitor current, including: obtaining an upper tube fault characteristic value for judging an upper tube fault of the bridge arm submodule and a lower tube fault characteristic value for judging a lower tube fault according to a ratio relationship between the average value of the ideal capacitor current and the average value of the corresponding actual capacitor current;

[0095] In this embodiment, when the upper tube of the submodule fails, the actual capacitor current of the faulty submodule is 0; the ideal capacitor current is the bridge arm current, so the result of dividing the actual capacitor current by the ideal capacitor current is infinite, while the actual capacitor current of the normal submodule is equal to the bridge arm current, and the result of dividing the two is very small; when the lower tube of the submodule fails, the actual capacitor current of the faulty submodule is the bridge arm current, and the ideal capacitor current is 0, so the result of dividing the ideal capacitor current by the actual capacitor current is infinite, while the result of dividing the ideal capacitor current of the normal submodule by the actual capacitor current is very small. Since the divisor cannot be 0, the divisor is processed separately in two cases, and the expressions are as follows:

[0096]

[0097] Among them, μ1 is the upper tube fault characteristic value, μ2 is the lower tube fault characteristic value, and ε is a very small value.

[0098] A fault characteristic value error threshold and a second time threshold are preset; when the actual value of the bridge arm current is greater than zero, and the upper tube fault characteristic value is greater than the fault characteristic value error threshold and the duration is greater than the second time threshold, the upper tube of the corresponding bridge arm submodule is faulty;

[0099] When the actual value of the bridge arm current is less than zero, the fault characteristic value of the lower tube is greater than the fault characteristic value error threshold, and the duration is greater than the second time threshold, the lower tube of the corresponding bridge arm submodule is faulty.

[0100] For example, Figure 4 As shown, the fault characteristic value error threshold is expressed as Δμ th , the second time threshold is represented by ΔT th2 , initialize timer T2, that is, T2=0;

[0101] If the bridge arm current i au >0, that is, when the current flows into the submodule in the reverse direction, it continues to determine whether μ2 is greater than the threshold Δμ th , and whether the timing duration of timer T2 is greater than the time threshold ΔT th2 , if yes, it is determined that the lower tube of the submodule is faulty;

[0102] If the bridge arm current i au<0, that is, when the current flows into the submodule in the positive direction, it continues to determine whether μ1 is greater than the threshold Δμ th , and whether the timing duration of timer T2 is greater than the time threshold ΔT th2 , if yes, it is determined that the upper tube of the submodule is faulty;

[0103] In this embodiment, if Figure 4 As shown, the method also includes setting a flag bit, which is used to identify the fault location of the bridge arm submodule.

[0104] In this embodiment, the flag bit is represented by F lagi , initial state F lagi = 0, the upper tube of the submodule fails F lagi =1, the lower tube of the submodule fails F lagi =-1.

[0105] Figure 5 This is an example diagram for judging the open circuit fault of the upper tube of the submodule. At 0.9s, the submodule has an open circuit fault. At 0.905s, the deviation between the observed value and the actual value of the bridge arm current of the upper bridge arm of phase a exceeds the error threshold ΔI th , timer T1 is greater than the first time threshold ΔT th1 At this time, the fault bridge arm location is completed (i.e. Figure 5 The fault detection flag in the fault submodule is that the fault submodule cannot discharge when the bridge arm flows through a negative current and the switch function value is 1. The actual value of its capacitor current is 0, and the ideal value is the bridge arm current. Therefore, the ratio of the ideal value of the capacitor current of the fault submodule to the actual value of the capacitor current is infinite. Finally, the fault submodule is located in 0.9065s (i.e. Figure 5 Fault location mark in the ).

[0106] Figure 6 This is an example diagram for judging the open circuit fault of the lower tube of the submodule. At 0.9s, the submodule has an open circuit fault. At 0.9005s, the deviation between the observed value and the actual value of the bridge arm current of the upper bridge arm of phase a exceeds the error threshold ΔI th , timer T1 is greater than the first time threshold ΔT th1 At this time, the fault bridge arm location is completed (i.e. Figure 6 The fault detection flag in the fault submodule is abnormally charged when the bridge arm flows through a positive current and the switch function value is 0. The actual value of the capacitor current is the bridge arm current, and the ideal value of the capacitor current is 0. Therefore, the ratio of the actual value of the capacitor current of the fault submodule to the ideal value of the capacitor current is infinite. Finally, the submodule fault location is completed in 0.9128s (i.e. Figure 6 Fault location mark in the ).

[0107] Figure 7This is an example diagram of the judgment of the double-tube open circuit fault of the submodule. At 0.9s, the submodule SM1 has an open circuit fault, and the submodule SM2 also has an open circuit fault. The submodule SM1 completes the fault location at 0.9069s (i.e. Figure 7 The fault location mark of SM1 in the submodule is shown in Figure 1), and the fault location of submodule SM2 is completed in 0.915s (i.e. Figure 7 SM2 fault location mark).

[0108] like Figure 8 As shown, the present invention also discloses a submodule open circuit fault judgment and positioning device for a modular multi-level converter, comprising:

[0109] The bridge arm current observation value calculation module 801 is used to calculate the bridge arm current observation value of each bridge arm according to the DC side voltage value, AC side voltage value, bridge arm cross-arm inductance value, bridge arm submodule switching function and bridge arm submodule capacitor voltage value of the modular multilevel converter;

[0110] The first judgment module 802 is used to obtain the actual value of the bridge arm current of each bridge arm, and compare and judge with the corresponding bridge arm current observation value to determine whether the corresponding bridge arm has a fault;

[0111] The capacitor current ideal value calculation module 803 is used to calculate the capacitor current ideal value of each bridge arm submodule on the bridge arm with the fault according to the switch function of the bridge arm submodule on the bridge arm with the fault and the actual value of the bridge arm current;

[0112] The capacitor current actual value calculation module 804 is used to calculate the capacitor current actual value of each bridge arm submodule on the bridge arm with the fault according to the capacitor voltage value, the capacitance value and the sampling period of the capacitor voltage value of the bridge arm submodule on the bridge arm with the fault;

[0113] The second judgment module 805 is used to compare the ideal capacitor current value with the corresponding actual capacitor current value to determine whether the corresponding bridge arm submodule has a fault.

[0114] The present invention also discloses an electronic device, such as Fig. 9 As shown, an embodiment is disclosed, which is a block diagram of an electronic device applicable to the above-mentioned method for determining and locating a sub-module open circuit fault of a modular multi-level converter.

[0115] The electronic device 90 of this embodiment includes a processor 901, which can perform various appropriate actions and processes according to the program stored in the ROM 902 or the program loaded from the storage part 908 into the RAM 903. The processor 901 may include, for example, a general-purpose microprocessor, an instruction set processor and / or a related chipset and / or a dedicated microprocessor, etc. The processor 901 may also include an onboard memory for caching purposes. The processor 901 may include a single processing unit or multiple processing units for performing different actions of the method flow according to an embodiment of the present invention.

[0116] In RAM903, various programs and data required for the operation of the electronic device 90 are stored. The processor 901, ROM902 and RAM903 are connected to each other through a bus 904, and the processor 901 performs various operations of the method flow according to the embodiment of the present invention by executing the program in ROM902 and / or RAM903. It should be noted that the program can also be stored in one or more memories other than ROM902 and RAM903, and the processor 901 can also perform various operations of the method flow according to the embodiment of the present invention by executing the program stored in one or more memories.

[0117] According to an embodiment of the present invention, the electronic device 90 may further include an I / O interface 905, which is also connected to the bus 904. The electronic device 90 may further include one or more of the following components connected to the I / O interface 905: an input portion 906 including a keyboard, a mouse, etc.; an output portion 907 including a cathode ray tube, a liquid crystal display, and a speaker; a storage portion 908 including a hard disk, etc.; and a communication portion 909 including a network interface card such as a LAN card, a modem, etc. The communication portion 909 performs communication processing via a network such as the Internet. A drive 9010 is also connected to the I / O interface 905 as needed. A removable medium 9011, such as a magnetic disk, an optical disk, a magneto-optical disk, a semiconductor memory, etc., is installed on the drive 9010 as needed, so that a computer program read therefrom is installed into the storage portion 908 as needed.

[0118] The present invention also provides a computer-readable storage medium.

[0119] The computer-readable storage medium may be included in the electronic device / device system described in the above embodiment; or it may exist independently without being assembled into the electronic device / device. The above computer-readable storage medium carries one or more programs, and when the above one or more programs are executed, the method according to the embodiment of the present invention is implemented.

[0120] According to an embodiment of the present invention, the computer-readable storage medium may be a non-volatile computer-readable storage medium. For example, it may include but is not limited to: a portable computer disk, a hard disk, a random access memory RAM, a read-only memory ROM, an erasable programmable read-only memory EPROM or a flash memory, a portable compact disk read-only memory CD-ROM, an optical storage device, a magnetic storage device, or any suitable combination thereof. In the present invention, the computer-readable storage medium may be any tangible medium containing or storing a program, which may be used by or in combination with an instruction execution system, apparatus, or device.

[0121] Embodiments of the present invention also include a computer program product.

[0122] The computer program product includes a computer program, which contains program codes for executing the method provided by the embodiment of the present invention. When the computer program product runs on an electronic device, the program codes are used to enable the electronic device to implement the method provided by the embodiment of the present invention.

[0123] In one embodiment, the computer program may rely on a tangible storage medium such as an optical storage device or a magnetic storage device. In another embodiment, the computer program may also be transmitted and distributed in the form of a signal on a network medium. The program code included in the computer program may be transmitted using any appropriate network medium, including but not limited to: wireless, wired, etc., or any suitable combination of the above.

[0124] According to an embodiment of the present invention, the program code for executing the computer program provided by the embodiment of the present invention can be written by any combination of one or more programming languages, and specifically, these computing programs can be implemented using high-level process and / or object-oriented programming languages. Programming languages ​​include but are not limited to programming languages ​​such as Java, C++, python, C language or similar. The program code can be executed completely on the user computing device, partially on the user device, partially on the remote computing device, or completely on the remote computing device or server. In the case of a remote computing device, the remote computing device can be connected to the user computing device through any type of network, including a local area network or a wide area network, or can be connected to an external computing device.

[0125] The flowcharts and block diagrams in the accompanying drawings illustrate the possible architecture, functions and operations of the systems, methods and computer program products according to various embodiments of the present invention. In this regard, each box in the flowchart or block diagram may represent a module, a program segment, or a part of a code, and the above-mentioned module, program segment, or a part of the code contains one or more executable instructions for implementing the specified logical function. It should also be noted that in some alternative implementations, the functions marked in the box may also occur in a different order from the order marked in the accompanying drawings. For example, two boxes represented in succession can actually be executed substantially in parallel, and they can sometimes be executed in the opposite order, depending on the functions involved. It should also be noted that each box in the block diagram or flowchart, and the combination of boxes in the block diagram or flowchart, can be implemented with a dedicated hardware-based system that performs the specified function or operation, or can be implemented with a combination of dedicated hardware and computer instructions. It can be understood by those skilled in the art that the features recorded in the various embodiments and / or claims of the present invention can be combined and / or combined in various ways, even if such a combination or combination is not explicitly recorded in the present invention. In particular, without departing from the spirit and teaching of the present invention, the features described in the various embodiments and / or claims of the present invention may be combined and / or combined in a variety of ways. All of these combinations and / or combinations fall within the scope of the present invention.

[0126] The embodiments of the present invention are described above. However, these embodiments are only for the purpose of illustration, and are not intended to limit the scope of the present invention. Although the embodiments are described above, this does not mean that the measures in the various embodiments cannot be used in combination. The scope of the present invention is limited by the attached claims and their equivalents. Without departing from the scope of the present invention, those skilled in the art may make various substitutions and modifications, which should all fall within the scope of the present invention.

Claims

1. A method for determining and locating a submodule open circuit fault in a modular multilevel converter, characterized in that: include: According to the DC side voltage value, the AC side voltage value, the arm inductance value of the bridge arm, the switching function of the bridge arm submodule and the capacitor voltage value of the bridge arm submodule of the modular multilevel converter, the bridge arm current observation value of each bridge arm is calculated; Obtaining the actual value of the bridge arm current of each bridge arm, and comparing it with the corresponding bridge arm current observation value to determine whether the corresponding bridge arm has a fault; According to the switching function of the bridge arm submodule on the bridge arm with fault and the actual value of the bridge arm current, the ideal value of the capacitive current of each bridge arm submodule on the bridge arm with fault is calculated; According to the capacitor voltage value, the capacitance value and the sampling period of the capacitor voltage value of the bridge arm submodule on the bridge arm with fault, the actual value of the capacitor current of each bridge arm submodule on the bridge arm with fault is calculated; The ideal capacitor current value is compared with the corresponding actual capacitor current value to determine whether the corresponding bridge arm submodule has a fault.

2. A method for determining and locating a submodule open circuit fault for a modular multilevel converter according to claim 1, characterized in that: The method comprises: calculating the bridge arm current observation value of each bridge arm according to the DC side voltage value, the AC side voltage value, the bridge arm cross-arm inductance value, the bridge arm submodule switching function and the bridge arm submodule capacitor voltage value of the modular multilevel converter, including: establishing an observer equation for the bridge arm current observation value according to Kirchhoff's voltage law, and the observer equation includes an injection term for improving the observation tracking effect.

3. A method for determining and locating a submodule open circuit fault for a modular multilevel converter according to claim 1, characterized in that: The actual value of the bridge arm current of each bridge arm is obtained, and compared with the corresponding bridge arm current observation value to determine whether the corresponding bridge arm has a fault, including: presetting a bridge arm current error threshold and a first time threshold; when the difference between the actual value of the bridge arm current and the bridge arm current observation value is greater than the bridge arm current error threshold, and the duration is greater than the time threshold, it is determined that the corresponding bridge arm has a fault.

4. A method for determining and locating a submodule open circuit fault for a modular multilevel converter according to claim 1, characterized in that: The ideal value of the capacitor current of each bridge arm submodule on the bridge arm with a fault is calculated based on the switching function of the bridge arm submodule on the bridge arm with a fault and the actual value of the bridge arm current, including: the ideal capacitor current value is equal to the product of the switching function of the bridge arm submodule and the corresponding actual value of the bridge arm current.

5. The method for determining and locating a submodule open circuit fault of a modular multilevel converter according to claim 1, characterized in that: The ideal capacitor current value is compared with the corresponding actual capacitor current value to determine whether the corresponding bridge arm submodule has a fault, including: comparing the average value of the ideal capacitor current value within a switching cycle of the bridge arm submodule with the average value of the corresponding actual capacitor current value.

6. A method for determining and locating a submodule open circuit fault in a modular multilevel converter according to claim 5, characterized in that: The comparing and judging by the mean of the ideal value of the capacitor current within a switching cycle of the bridge arm submodule with the mean of the corresponding actual value of the capacitor current includes: obtaining an upper tube fault characteristic value for judging an upper tube fault of the bridge arm submodule and a lower tube fault characteristic value for judging a lower tube fault according to a ratio relationship between the mean of the ideal value of the capacitor current and the mean of the corresponding actual value of the capacitor current; A fault characteristic value error threshold and a second time threshold are preset; when the actual value of the bridge arm current is greater than zero, and the upper tube fault characteristic value is greater than the fault characteristic value error threshold and the duration is greater than the second time threshold, the upper tube of the corresponding bridge arm submodule is faulty; When the actual value of the bridge arm current is less than zero, the lower tube fault characteristic value is greater than the fault characteristic value error threshold, and the duration is greater than the second time threshold, the lower tube of the corresponding bridge arm submodule is faulty.

7. A method for determining and locating a submodule open circuit fault for a modular multilevel converter according to claim 6, characterized in that: The method further comprises setting a flag bit, wherein the flag bit is used to identify a fault position of the bridge arm submodule.

8. A submodule open circuit fault judgment and positioning device for a modular multi-level converter, characterized in that: The device comprises: A bridge arm current observation value calculation module is used to calculate the bridge arm current observation value of each bridge arm according to the DC side voltage value, AC side voltage value, bridge arm cross-arm inductance value, bridge arm submodule switching function and bridge arm submodule capacitor voltage value of the modular multilevel converter; A first judgment module is used to obtain the actual value of the bridge arm current of each bridge arm, and compare and judge with the corresponding bridge arm current observation value to determine whether the corresponding bridge arm has a fault; A capacitor current ideal value calculation module, used for calculating the capacitor current ideal value of each of the bridge arm submodules on the bridge arm with a fault according to the switching function of the bridge arm submodule on the bridge arm with a fault and the actual value of the bridge arm current; A capacitor current actual value calculation module, used to calculate the capacitor current actual value of each of the bridge arm submodules on the bridge arm with a fault according to the capacitor voltage value, the capacitance value and the sampling period of the capacitor voltage value of the bridge arm submodule on the bridge arm with a fault; The second judgment module is used to compare and judge the ideal value of the capacitor current with the corresponding actual value of the capacitor current to determine whether the corresponding bridge arm submodule has a fault.

9. An electronic device, characterized in that: include: one or more processors; A storage device for storing one or more programs, wherein when the one or more programs are executed by the one or more processors, the one or more processors are caused to perform the method according to any one of claims 1 to 7.

10. A computer program product, comprising a computer program, characterized in that When the computer program is executed by a processor, the method according to any one of claims 1 to 7 is implemented.

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