A modular multilevel dc / dc converter switching device open circuit fault diagnostic method

Abstract

The application provides a modular multilevel DC / DC converter switch device open-circuit fault diagnosis method, comprising: collecting each phase output current in the converter; comparing each phase output current in the converter with a preset threshold value in sequence, if the kth phase output current is lower than the threshold value, locking all the fully controlled switch devices of the kth phase and marking the kth phase as a fault phase, calculating the total output current of each phase of the converter, and setting a reference value; if the total output current of each phase reaches the reference value, injecting an optimal switch action sequence into each H-bridge unit in the fault phase kth phase, and outputting a fault positioning result; the application can diagnose and position the open-circuit fault of the switch device of the modular multilevel DC / DC converter on the basis of only relying on the collection of the output current of each phase of the circuit, low sampling frequency and small calculation power.

Description

Technical Field

[0001] This invention belongs to the field of power electronics technology, specifically relating to a method for diagnosing open-circuit faults in switching devices of a modular multilevel DC / DC converter. Background Technology

[0002] In the field of power electronics, the development of multilevel converters is of great significance for achieving high power and improving voltage levels. Compared with traditional two-level converters, multilevel converters can reduce the voltage stress on power switching devices, reduce harmonic distortion of output voltage and current, and lower switching frequency. Therefore, research on multilevel converters is still ongoing. Cascaded H-bridge multilevel converters do not require passive components such as clamping diodes and flying capacitors, have a simple structure, and synthesize high-quality multilevel stepped waves by connecting multiple H-bridge power units powered by independent DC sources in series on the output side. They are widely used in microgrids, railway traction power supply, new energy power generation and other systems [1-4]. However, modular multilevel converters based on cascaded H-bridges contain a large number of power semiconductor switching devices. The electrical / thermal stress and reliability limitations of these devices make them weak links and major sources of failure in the system. The operational reliability of modular multilevel converters has become a focus of attention. Among them, open-circuit (OC) faults of individual devices may cause a decline in device performance, system shutdown or even catastrophic damage. Therefore, establishing an efficient and accurate online fault diagnosis and location system is an indispensable key technology for achieving high reliability and high availability operation of this type of converter [5]. It is not only an emergency rescue measure after a fault occurs, but also the core foundation for achieving intelligent fault-tolerant operation, predictive maintenance and leveraging the advantages of modular design.

[0003] In terms of device open-circuit fault diagnosis and location for cascaded H-bridge multilevel converters, existing technologies can be mainly divided into the following categories: (1) Spectral analysis of the acquired AC grid-connected current signal is performed by frequency domain analysis methods such as Fast Fourier Transform (FFT), harmonic components are extracted as fault features, and fault diagnosis criteria are constructed based on the amplitude changes of different harmonic components. Then, the fault unit is located by adjusting the carrier frequency and the characteristics of specific harmonic components. This type of method only needs to acquire AC grid-connected current signals to complete fault diagnosis and location, but it can only locate the fault unit and cannot accurately locate the specific fault switch, which has certain limitations. Moreover, online spectrum analysis requires high computing power from the controller, resulting in poor real-time performance of fault diagnosis and location. (2) A mathematical model is established to estimate the residual of grid-connected current or DC side current before and after the device open-circuit fault occurs. Fault feature variables are constructed based on the current residual and compared with the threshold as the basis for the occurrence of open-circuit fault. Then, a counter corresponding to each switch is defined, and logical judgment and fault state counting are performed by combining the drive signal combination after the open-circuit fault occurs with the polarity of the grid-connected current. The fault switch is identified by the counter value. Although this type of method can effectively locate specific faulty switching devices, it requires sampling the AC side grid current and the DC side voltage of each level of H bridge for current estimation. Moreover, since it is necessary to combine the high-frequency switching state for fault location, the sampling frequency is required to be much higher than the system switching frequency, which makes the entire hardware system more complex, requires high sensor performance, and is difficult to implement. (3) Reference

[16] judges whether a fault has occurred by detecting the grid current oscillation characteristics and the change trend of the H bridge DC capacitor voltage, and locates the faulty switching group according to the half-cycle of the grid current oscillation, and then combines the connection between the switch drive signal and the current path to achieve the final location of the faulty switch. This type of method still requires simultaneous sampling of the AC side grid current and the DC side voltage of each level of H bridge, and requires the sampling frequency to be much higher than the system switching frequency, which makes high sensor performance and difficult to implement. (3) Estimate the AC side voltage of the cascaded H bridge based on the drive signal of the previous control cycle, and obtain the voltage error by subtracting it from the actual voltage and normalizing it. This method uses voltage error as a detection variable and combines it with the counting comparator of each unit to construct fault diagnosis logic. By judging the relationship between the detected variable and a threshold, and the counting comparison result, the faulty unit is located. The fault characteristics are then directly matched with the corresponding faulty unit's drive signal to locate the faulty switch. This type of method requires additional cascaded H-bridge AC-side voltage sensors in the system, leading to increased system complexity.

[0004] Based on the above-mentioned existing technologies, the following technical problems exist: (1) Most existing fault diagnosis and location technologies are developed for cascaded H-bridge grid-connected converters. (2) Existing fault diagnosis and location technologies rely on sampling and estimation of multiple electrical quantities such as AC side grid-connected current, H-bridge DC side voltage, and cascaded H-bridge AC voltage. This places high demands on the types and number of sensors, and requires the sampling frequency to be much higher than the system switching frequency, which increases the difficulty of technical implementation and deployment. (3) Some technologies rely on frequency domain characteristic analysis of key electrical quantities. These methods can generally only locate the faulty H-bridge unit rather than the specific faulty switching device, and the computational load is large, resulting in poor real-time fault location. Summary of the Invention

[0005] To address the problems existing in the prior art, this invention proposes a method for diagnosing open-circuit faults in the switching devices of a modular multilevel DC / DC converter. This method includes: the modular multilevel DC / DC converter has n phases, each phase consisting of three cascaded H-bridges; the specific steps are as follows:

[0006] S1. Acquire the output current of each phase in the converter;

[0007] S2. Compare the output current of each phase in the converter with the preset threshold in sequence. If the output current of the k-th phase is lower than the threshold, block all fully controlled switching devices of the k-th phase and mark the k-th phase as a faulty phase, and execute step S3. Otherwise, return to step S1.

[0008] S3. Calculate the total output current of each phase of the converter and set the reference value; if the total output current of each phase reaches the reference value, proceed to step S4; otherwise, repeat step S3.

[0009] S4. Inject the preferred switching action sequence into each H-bridge unit in the k-th phase of the faulty phase, and output the fault location result.

[0010] The beneficial effects of this invention are:

[0011] This invention provides a method for diagnosing open-circuit faults in switching devices of modular multilevel DC / DC converters. It solves the problems of existing fault diagnosis and location technologies for cascaded multilevel converters, such as relying on the acquisition of a large number of electrical quantities such as voltage and current, high sampling frequency, large algorithm computation, and inability to be directly applied to the circuit topology of modular multilevel DC / DC converters. This invention enables the diagnosis and location of open-circuit faults in switching devices of modular multilevel DC / DC converters based solely on the acquisition of output current of each phase of the circuit, low sampling frequency, and relatively small computing power. Attached Figure Description

[0012] Figure 1 This is a flowchart of a method for diagnosing open-circuit faults in switching devices of a modular multilevel DC / DC converter according to the present invention.

[0013] Figure 2 This is a flowchart of the preferred switching action sequence injected into each H-bridge unit in the k-th phase of the faulty phase according to the present invention;

[0014] Figure 3 This is a topology diagram of the modular multilevel DC / DC converter of the present invention;

[0015] Figure 4 The fault phase bridge arm current i during the entire process of k_2 open circuit fault location in this invention is... sk The trend chart;

[0016] Figure 5 This is a detailed waveform diagram of the entire process of Sk_2 open circuit fault location in this invention;

[0017] Figure 6 i, the present invention sk Schematic diagram of current single closed-loop control generating switch action sequence;

[0018] Figure 7 i, the present invention sk_com Schematic diagram of generating a switching action sequence by comparing with a triangular carrier wave. Detailed Implementation

[0019] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] This patent invention provides a method for diagnosing open-circuit faults in the switching devices of a modular multilevel DC / DC converter. It solves the problems of existing fault diagnosis and location technologies for cascaded multilevel converters, such as relying on the acquisition of a large number of electrical quantities such as voltage and current, high sampling frequency, large algorithm computation, and inability to be directly applied to the circuit topology of modular multilevel DC / DC converters. It realizes the diagnosis and location of open-circuit faults in the switching devices of modular multilevel DC / DC converters based on only relying on the acquisition of the output current of each phase of the circuit, low sampling frequency, and relatively small computing power.

[0021] The proposed method, on the one hand, relies solely on the output current information of the cascaded H-bridges in each phase for fault diagnosis and location, eliminating the need for additional voltage and current sensors and significantly reducing the hardware complexity of the system. On the other hand, by actively injecting an optimized switching action sequence into the faulty phase and combining it with the characteristics of output current changes, it achieves rapid location of open-circuit faulty devices, effectively reducing the computational load of the algorithm.

[0022] A method for diagnosing open-circuit faults in switching devices of a modular multilevel DC / DC converter, such as... Figure 1 As shown, the modular multilevel DC / DC converter has n phases, each phase consisting of three cascaded H-bridges. The method is characterized by the following steps:

[0023] Step 1: Sample the converter output current, proceed to Step 2;

[0024] Step 2: Convert the output current i of each phase s1 to i sn sequentially with the preset threshold i s,thr Comparison, if the output current i of phase k... sk Below the threshold i s,thr Then, all fully controlled switching devices in phase k are locked out and phase k is marked as a faulty phase. Then proceed to Step 3. Otherwise, if the output current i of all phases is... s1 to i sn All are above the threshold i s,thr Then proceed to Step 1;

[0025] Step 3: If the total output current i of each phase of the converter is TF Reaching reference value i TF,ref If so, proceed to Step 4; otherwise, if the total output current i of each phase of the converter is... TF Less than the reference value i TF,ref Then proceed to Step 3; Step 4: Inject the preferred switching action sequence into each H-bridge unit in the k-th phase of the faulty phase, and output the fault location result.

[0026] In this embodiment, the sampling converter output current includes the first phase output current i of the converter. s1 Output current i up to the nth phase sn and the total output current i of each phase of the converter TF .

[0027] Threshold i s,thr It should be set to 0, taking into account factors such as electrical interference and sampling signal interference in the actual system. The threshold i s,thr It should be preset to a value slightly greater than 0, depending on the actual situation.

[0028] In this embodiment, the reference value is set to meet the actual load current requirements.

[0029] In this embodiment, as Figure 2 As shown, to inject the preferred switching action sequence into each H-bridge unit within the k-th phase of the faulty phase and output the fault location result, the following steps and order should be followed:

[0030] Step 4.1: Inject switch action sequence 1 into each H-bridge unit in the k-th phase of the faulty phase, and calculate the output current i of the faulty phase according to equation (1). sk The average value i over time T sk_avg :

[0031] (1)

[0032] If 0 sk_avg < i sk,ref1 Then, inject switch action sequence 2 into each H-bridge unit in the k-th phase of the faulty phase, and proceed to Step 4.2;

[0033] If i sk,ref1 < i sk_avg < i sk,ref2 Then, inject switch action sequence 2 into each H-bridge unit in the k-th phase of the faulty phase, and proceed to Step 4.3;

[0034] If i sk,ref2 < i sk_avg Then, inject switch action sequence 3 into each H-bridge unit in the k-th phase of the faulty phase, and proceed to Step 4.4;

[0035] Step 4.2: Calculate i after waiting time T. sk_avg :

[0036] If 0 sk_avg < i sk,ref1 Then, inject the switching action sequence 4 into each H-bridge unit in the k-th phase of the faulty phase, and proceed to Step 4.5;

[0037] If i sk,ref1 < i sk_avg < i sk,ref2 Then, inject switch action sequence 3 into each H-bridge unit in the k-th phase of the faulty phase, and proceed to Step 4.6;

[0038] Step 4.3: After waiting for time T, calculate i according to formula (1). sk_avg :

[0039] If 0 sk_avg < i sk,ref1 Then, inject the switching action sequence 5 into each H-bridge unit in the k-th phase of the faulty phase, and proceed to Step 4.7;

[0040] If i sk,ref1 < i sk_avg < i sk,ref2 Then, inject the switching action sequence 6 into each H-bridge unit in the k-th phase of the faulty phase, and proceed to Step 4.8;

[0041] If i sk,ref2 < i​​​sk_avg Then, inject switch action sequence 3 into each H-bridge unit in the k-th phase of the faulty phase, and proceed to Step 4.9;

[0042] Step 4.4: After waiting for time T, calculate i according to formula (1). sk_avg :

[0043] If 0 sk_avg < i sk,ref1 This indicates that the faulty phases Sk_3 and Sk_5 switches are open-circuited. The fault location is now complete, and the fault location result is output.

[0044] If i sk,ref1 < i sk_avg < i sk,ref2 Then, inject switch action sequence 2 into each H-bridge unit in the k-th phase of the faulty phase, and proceed to Step 4.10;

[0045] Step 4.5: After waiting for time T, calculate i according to formula (1). sk_avg :

[0046] If i sk,ref1 < i sk_avg < i sk,ref2 Then inject the switching action sequence 8 into each H-bridge unit in the k-th phase of the faulty phase, and proceed to Step 4.11;

[0047] If i sk,ref2 < i sk_avg This indicates an open circuit fault in switches Sk_1 and Sk_6. The fault location process is complete, and the fault location result is output.

[0048] Step 4.6: After waiting for time T, calculate i according to formula (1). sk_avg :

[0049] If i sk,ref1 < i sk_avg < i sk,ref2 Then inject the switching action sequence 7 into each H-bridge unit in the k-th phase of the faulty phase, and proceed to Step 5.12;

[0050] If i sk,ref2 < i sk_avg This indicates an open circuit fault in switches Sk_4 and Sk_6. The fault location process is complete, and the fault location result is output.

[0051] Step 4.7: After waiting for time T, calculate i according to formula (1). sk_avg :

[0052] If i sk,ref1 < i sk_avg < i sk,ref2 ​Then, inject the switching action sequence 9 into each H-bridge unit in the k-th phase of the faulty phase, and proceed to Step 4.13;

[0053] If i sk,ref2 < i sk_avg This indicates an open circuit fault in switches Sk_3 and Sk_6. The fault location process is complete, and the fault location result is output.

[0054] Step 4.8: After waiting for time T, calculate i according to formula (1). sk_avg :

[0055] If 0 sk_avg < i sk,ref1 This indicates an open circuit fault in switches Sk_3 and Sk_4. The fault location process is complete, and the fault location result is output.

[0056] If i sk,ref1 < i sk_avg < i sk,ref2 Then, inject switch action sequence 10 into each H-bridge unit in the k-th phase of the faulty phase, and proceed to Step 4.14;

[0057] If i sk,ref2 < i sk_avg Then inject the switching action sequence 8 into each H-bridge unit in the k-th phase of the faulty phase, and proceed to Step 4.15;

[0058] Step 4.9: After waiting for time T, calculate i according to formula (1). sk_avg :

[0059] If i sk,ref1 < i sk_avg < i sk,ref2 This indicates an open circuit fault in switches Sk_4 and Sk_5. The fault location process is complete, and the fault location result is output.

[0060] If i sk,ref2 < i sk_avg This indicates an open circuit fault in phase Sk_4 switch. The fault location process is now complete, and the fault location result is output.

[0061] Step 4.10: After waiting for time T, calculate i according to formula (1). sk_avg :

[0062] If i sk,ref1 < i sk_avg < i sk,ref2 This indicates an open circuit fault in phase Sk_3 switch. The fault location process is now complete, and the fault location result is output.

[0063] If i sk,ref2 < i sk_avg ​This indicates an open circuit fault in phase Sk_5 switch. The fault location process is now complete, and the fault location result is output.

[0064] Step 4.11: After waiting for time T, calculate i according to formula (1). sk_avg :

[0065] If i sk,ref1 < i sk_avg < i sk,ref2 This indicates an open circuit fault in switches Sk_1 and Sk_2. The fault location process is complete, and the fault location result is output.

[0066] If i sk,ref2 < i sk_avg This indicates an open circuit fault in switches Sk_2 and Sk_6. The fault location process is complete, and the fault location result is output.

[0067] Step 4.12: After waiting for time T, calculate i according to formula (1). sk_avg :

[0068] If i sk,ref1 < i sk_avg < i sk,ref2 This indicates an open circuit fault in switches Sk_2 and Sk_4. The fault location process is complete, and the fault location result is output.

[0069] If i sk,ref2 < i sk_avg This indicates an open circuit fault in switches Sk_1 and Sk_4. The fault location process is complete, and the fault location result is output.

[0070] Step 4.13: After waiting for time T, calculate i according to formula (1). sk_avg :

[0071] If i sk,ref1 < i sk_avg < i sk,ref2 This indicates an open circuit fault in switches Sk_2 and Sk_3. The fault location process is complete, and the fault location result is output.

[0072] If i sk,ref2 < i sk_avg This indicates that the faulty phases Sk_1 and Sk_3 switches are open-circuited. The fault location is then completed and the fault location result is output.

[0073] Step 4.14: After waiting for time T, calculate i according to formula (1). sk_avg :

[0074] If i sk,ref1 < i sk_avg < i sk,ref2Then inject switch action sequence 8 into each H-bridge unit in the k-th phase of the faulty phase, and proceed to Step 4.16;

[0075] If i sk,ref2 < i sk_avg Then inject switch action sequence 8 into each H-bridge unit in the k-th phase of the faulty phase, and proceed to Step 4.17;

[0076] Step 4.15: After waiting for time T, calculate i according to formula (1). sk_avg :

[0077] If 0 sk_avg < i sk,ref1 This indicates an open circuit fault in switches Sk_1 and Sk_5. The fault location process is complete, and the fault location result is output.

[0078] If i sk,ref1 < i sk_avg < i sk,ref2 This indicates an open circuit fault in phase Sk_1 switch. The fault location process is now complete, and the fault location result is output.

[0079] Step 4.16: After waiting for time T, calculate i according to formula (1). sk_avg :

[0080] If i sk,ref1 < i sk_avg < i sk,ref2 This indicates an open circuit fault in switches Sk_5 and Sk_6. The fault location process is complete, and the fault location result is output.

[0081] If i sk,ref2 < i sk_avg This indicates an open circuit fault in phase Sk_6 switch. The fault location process is now complete, and the fault location result is output.

[0082] Step 4.17: After waiting for time T, calculate i according to formula (1). sk_avg :

[0083] If i sk,ref1 < i sk_avg < i sk,ref2 This indicates an open circuit fault in switches Sk_2 and Sk_5. The fault location process is complete, and the fault location result is output.

[0084] If i sk,ref2 < i sk_avg This indicates an open circuit fault in phase Sk_2 switch. The fault location process is now complete, and the fault location result is output.

[0085] In this embodiment, the switching action sequence includes 10 switching action sequences.

[0086] ​Preferably, the switching action sequence 1 refers to: the switching actions of Sk_1 and Sk_2 are caused by i sk Current is generated by a single closed-loop control, with Sk_3 kept off, Sk_4 kept on, Sk_5 kept off, and Sk_6 kept on.

[0087] Preferably, the switching action sequence 3 refers to: the switching actions of Sk_1 and Sk_2 are caused by i sk Current single closed-loop control is generated, Sk_3 remains on, Sk_4 remains off, Sk_5 remains on, and Sk_6 remains off;

[0088] Preferably, the switching action sequence 4 refers to: Sk_1 remaining off, Sk_2 remaining on, and the switching actions of Sk_3 and Sk_4 being controlled by i sk Current is generated by a single closed-loop control, with Sk_5 kept on and Sk_6 kept off.

[0089] Preferably, the switching action sequence 5 refers to: the switching actions of Sk_1 and Sk_2 are caused by i sk Current single closed-loop control is generated, Sk_3 remains off, Sk_4 remains on, Sk_5 remains on, and Sk_6 remains off;

[0090] Preferably, the switching action sequence 6 refers to: Sk_1 remaining off, Sk_2 remaining on, and the switching actions of Sk_3 and Sk_4 being controlled by i sk Current is generated by a single closed-loop control, with Sk_5 kept off and Sk_6 kept on.

[0091] Preferably, the switching action sequence 7 refers to: Sk_1 remaining off, Sk_2 remaining on, Sk_3 remaining on, Sk_4 remaining off, and the switching actions of Sk_5 and Sk_6 being determined by i sk Current single-closed-loop control generation;

[0092] Preferably, the switching action sequence 8 refers to: Sk_1 remaining on, Sk_2 remaining off, and the switching actions of Sk_3 and Sk_4 being controlled by i sk Current is generated by a single closed-loop control, with Sk_5 kept on and Sk_6 kept off.

[0093] Preferably, the switching action sequence 9 refers to: Sk_1 remaining off, Sk_2 remaining on, Sk_3 remaining off, Sk_4 remaining on, and the switching actions of Sk_5 and Sk_6 being determined by i sk Current single-closed-loop control generation;

[0094] Preferably, the switching action sequence 10 refers to: Sk_1 remaining on, Sk_2 remaining off, and the switching actions of Sk_3 and Sk_4 being controlled by i skCurrent is generated by a single closed-loop control, with Sk_5 kept off and Sk_6 kept on.

[0095] In this embodiment, i sk,ref1 and i sk,ref2 The value should be based on i observed after the actual injection of the preferred switching action sequence. sk The actual waveform phenomenon was determined, taking into account factors such as electrical interference and sampling signal interference in the actual system. sk,ref1 It should be set to a value slightly greater than 0, i sk,ref2 It should be set to slightly less than i TF,ref The value of / n.

[0096] The switching action of the specified switching device is determined by i sk The steps for generating a single closed-loop current control are as follows:

[0097] Step 1: Calculate the comparison value i sk_com ;

[0098]

[0099] Where, k p1 For i TF The proportional gain, k, of a current-controlled single-loop PI controller i1 For i TF The integral coefficient, k, of a current-controlled single-loop PI controller p2 For i sk The proportional gain, k, of a current-controlled single-loop PI controller i2 For i sk The integral coefficient, i, of the current single-loop PI controller TF,ref i is the reference value for the total current. TF denoted as the total output current, and n as the number of parallel phases of the device.

[0100] Step 2, i sk_com The switching action sequence of the specified switching device is generated by comparing it with a triangular carrier wave of a given switching frequency: if i sk_com When the value is greater than 0, Sk_1 / Sk_3 / Sk_5 are turned on, and i sk_com If the triangular carrier frequency is greater than the given switching frequency, then Sk_2 / Sk_4 / Sk_6 will be turned on, and i sk_com If the triangular carrier frequency is less than the given switching frequency, then Sk_2 / Sk_4 / Sk_6 are turned off; if i sk_com When the value is less than 0, Sk_1 / Sk_3 / Sk_5 are turned off, i sk_com If the triangular carrier frequency is less than the given switching frequency, then Sk_2 / Sk_4 / Sk_6 are turned off, i sk_com If the triangular carrier frequency is greater than the given switching frequency, then Sk_2 / Sk_4 / Sk_6 will be turned on.

[0101] A specific implementation of a modular multilevel DC / DC converter topology. For example... Figure 3 As shown, the system consists of n parallel phases, with each phase composed of three cascaded H-bridge units. Each H-bridge consists of two diodes D and two fully controlled power electronic switching devices S. For example, the two diodes in the first H-bridge unit of the k-th phase are Dk_1 and Dk_2, and the two fully controlled switching devices in the first H-bridge unit of the k-th phase are Sk_1 and Sk_2. L1~L n For the inductance of each phase bridge arm, i s1 ~ i sn For the output current of each phase, v c1_1 v c1_2 v c1_3 ~ v cn_1 v cn_2 v cn_3 For DC side voltage, i TF R is the total output current of all phases of the converter. TF L is the resistance of the load coil. TF This is the inductance of the load coil.

[0102] In this embodiment, the parameters of the modular multilevel DC / DC converter include: bridge arm inductance of 25uH, DC-side voltage of 800V, and load coil resistance R. TF =2mΩ, load coil inductance L TF =16mH, preset threshold i s,thr =2A, i TF,ref =200kA, i sk,ref1 =5A, i sk,ref2 =1000A, setting the k-th phase Sk_2 to have an open circuit fault.

[0103] A method for rapid diagnosis and location of open-circuit faults in modular multilevel DC / DC converters, with key waveforms shown in the specific implementation process. Figure 4 and Figure 5 As shown in the figure, Sk_1~Sk_6 are the drive signals for the six fully controlled switching devices in the faulty phase, i sk This refers to the output current of the faulty phase. This method can be applied to digital signal processors or controllers such as DSPs / FPGAs / ARMs. Its principle is as follows: Figure 6 and Figure 7 As shown.

[0104] The above-described embodiments further illustrate the purpose, technical solution, and advantages of the present invention. It should be understood that the above-described embodiments are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made to the present invention within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for diagnosing open-circuit faults in switching devices of a modular multilevel DC / DC converter, wherein the modular multilevel DC / DC converter has n phases, each phase consisting of 3 cascaded H-bridges, characterized in that... include: S1. Acquire the output current of each phase in the converter; S2. Compare the output current of each phase in the converter with the preset threshold in sequence. If the output current of the k-th phase is lower than the threshold, block all fully controlled switching devices of the k-th phase and mark the k-th phase as a faulty phase, and execute step S3. Otherwise, return to step S1. S3. Calculate the total output current of each phase of the converter and set the reference value; if the total output current of each phase reaches the reference value, proceed to step S4; otherwise, repeat step S3. S4. Inject the preferred switching action sequence into each H-bridge unit in the k-th phase of the faulty phase, and output the fault location result.

2. The method for diagnosing open-circuit faults in switching devices of a modular multilevel DC / DC converter according to claim 1, characterized in that, The preset threshold is 0.

3. The method for diagnosing open-circuit faults in switching devices of a modular multilevel DC / DC converter according to claim 1, characterized in that, The preferred switching action sequence injected into each H-bridge unit within the k-th phase of the faulty phase includes: S401. Inject switch action sequence 1 into each H-bridge unit within the k-th phase of the faulty phase, and calculate the output current i of the faulty phase. sk The average value i over time T sk_avg ; S402, Compare the average value with the reference value i sk,ref1 and reference value i sk,ref2 Compare, if 0 sk_avg < i sk,ref1 Then, for each H-bridge unit in the k-th phase of the faulty phase, a switching action sequence 2 is injected, and step S403 is executed; if i sk,ref1 < i sk_avg sk,ref2 Then, for each H-bridge unit in the k-th phase of the faulty phase, a switching action sequence 2 is injected, and step S404 is executed; if i sk,ref2 sk_avg Then, for each H-bridge unit in the k-th phase of the faulty phase, a switching action sequence 3 is injected, and step S405 is executed;​​​ S403, calculate i after waiting time T. sk_avg If 0 sk_avg < i sk,ref1 Then, for each H-bridge unit in the k-th phase of the faulty phase, a switching action sequence 4 is injected, and step S406 is executed; if i sk,ref1 < i sk_avg < i sk,ref2 Then, a switching action sequence 3 is injected into each H-bridge unit in the k-th phase of the faulty phase, and step S407 is executed.​ S404, calculate i after waiting time T. sk_avg If 0 sk_avg < i sk,ref1 Then, for each H-bridge unit in the k-th phase of the faulty phase, a switching action sequence 5 is injected, and step S408 is executed; if i sk,ref1 < i sk_avg < i sk,ref2 Then, for each H-bridge unit in the k-th phase of the faulty phase, a switching action sequence 6 is injected, and step S409 is executed; if i sk,ref2 < i sk_avg Then, a switching action sequence 3 is injected into each H-bridge unit in the k-th phase of the faulty phase, and step S410 is executed.​ S405, calculate i after waiting time T. sk_avg If 0 sk_avg < i sk,ref1 If the faulty phases Sk_3 and Sk_5 are open circuit faults, the fault location is completed and the fault location result is output; if i sk,ref1 < i sk_avg < i sk,ref2 Then, for each H-bridge unit in the k-th phase of the faulty phase, a switching action sequence 2 is injected, and step S411 is executed;​ S406, calculate i after waiting time T. sk_avg ; if i sk,ref1 < i sk_avg < i sk,ref2 Then, for each H-bridge unit in the k-th phase of the faulty phase, a switching action sequence 8 is injected, and step S412 is executed; if i sk,ref2 < i sk_avg If the faulty phase Sk_1 and Sk_6 switches are open circuit faults, the fault location is completed and the fault location result is output. S407, calculate i after waiting time T. sk_avg ; if i sk,ref1 < i sk_avg < i sk,ref2 Then, for each H-bridge unit in the k-th phase of the faulty phase, a switching action sequence 7 is injected, and step S413 is executed; if i sk,ref2 < i sk_avg If the faulty phases Sk_4 and Sk_6 are open circuit faults, the fault location is completed and the fault location result is output. S408, calculate i after waiting time T. sk_avg ; if i sk,ref1 < i sk_avg < i sk,ref2 Then, for each H-bridge unit in the k-th phase of the faulty phase, a switching action sequence 9 is injected, and step S414 is executed; if i sk,ref2 < i sk_avg If the faulty phases Sk_3 and Sk_6 are open circuit faults, the fault location is completed and the fault location result is output. S409, calculate i after waiting time T. sk_avg If 0 sk_avg < i sk,ref1 If the faulty phases Sk_3 and Sk_4 are open circuit faults, the fault location is completed and the fault location result is output; if i sk,ref1 < i sk_avg < i sk,ref2 Then, for each H-bridge unit in the k-th phase of the faulty phase, a switching action sequence 10 is injected, and step S415 is executed; if i sk,ref2 < i sk_avg Then, a switching action sequence 8 is injected into each H-bridge unit in the k-th phase of the faulty phase, and step S416 is executed.​ S410, calculate i after waiting time T. sk_avg ; if i sk,ref1 < i sk_avg < i sk,ref2 If the faulty phases Sk_4 and Sk_5 are open circuit faults, the fault location is completed and the fault location result is output; if i sk,ref2 < i sk_avg If the faulty phase Sk_4 switch is open-circuited, the fault location is completed and the fault location result is output. S411, calculate i after waiting time T. sk_avg ; if i sk,ref1 < i sk_avg < i sk,ref2 If the faulty phase Sk_3 switch is open-circuited, the fault location is completed and the fault location result is output; if i sk,ref2 < i sk_avg If the faulty phase Sk_5 switch is open-circuited, the fault location is completed and the fault location result is output. S412, calculate i after waiting time T. sk_avg ; if i sk,ref1 < i sk_avg < i sk,ref2 If the faulty phases Sk_1 and Sk_2 are open circuit faults, the fault location is completed and the fault location result is output; if i sk,ref2 < i sk_avg If the faulty phase Sk_2 and Sk_6 switches are open circuit faults, the fault location is completed and the fault location result is output. S413, calculate i after waiting time T. sk_avg ; if i sk,ref1 < i sk_avg < i sk,ref2 If the faulty phases Sk_2 and Sk_4 are open circuit faults, the fault location is completed and the fault location result is output; if i sk,ref2 < i sk_avg If the faulty phase Sk_1 and Sk_4 switches are open circuit faults, the fault location is completed and the fault location result is output. S414, calculate i after waiting time T. sk_avg ; if i sk,ref1 < i sk_avg < i sk,ref2 If the faulty phases Sk_2 and Sk_3 are open circuit faults, the fault location is completed and the fault location result is output; if i sk,ref2 < i sk_avg If the faulty phase Sk_1 and Sk_3 switches are open circuit faults, the fault location is completed and the fault location result is output. S415, calculate i after waiting time T. sk_avg ; if i sk,ref1 < i sk_avg < i sk,ref2 Then, for each H-bridge unit in the k-th phase of the faulty phase, a switching action sequence 8 is injected, and step S417 is executed; if i sk,ref2 < i sk_avg Then, a switching action sequence 8 is injected into each H-bridge unit in the k-th phase of the faulty phase, and step S418 is executed. S416, calculate i after waiting time T. sk_avg If 0 sk_avg < i sk,ref1 If the faulty phases Sk_1 and Sk_5 are open circuit faults, the fault location is completed and the fault location result is output; if i sk,ref1 < i sk_avg < i sk,ref2 If the faulty phase Sk_1 switch is open-circuited, the fault location is completed and the fault location result is output.​ S417, calculate i after waiting time T. sk_avg ; if i sk,ref1 < i sk_avg < i sk,ref2 If the faulty phases Sk_5 and Sk_6 are open circuit faults, the fault location is completed and the fault location result is output; if i sk,ref2 < i sk_avg If the faulty phase Sk_6 switch is open-circuited, the fault location is completed and the fault location result is output. S418, calculate i after waiting time T. sk_avg ; if i sk,ref1 < i sk_avg < i sk,ref2 If the faulty phases Sk_2 and Sk_5 are open circuit faults, the fault location is completed and the fault location result is output; if i sk,ref2 < i sk_avg If the faulty phase Sk_2 switch is open-circuited, the fault location is completed and the fault location result is output.

4. The method for diagnosing open-circuit faults in switching devices of a modular multilevel DC / DC converter according to claim 3, characterized in that, Calculate the output current i of the faulty phase sk The average value over time T is: ； Where T is the waiting time, i sk The output current is for the faulty phase.

5. The method for diagnosing open-circuit faults in switching devices of a modular multilevel DC / DC converter according to claim 3, characterized in that, The switching action sequence includes 10 switching action sequences.

6. The method for diagnosing open-circuit faults in switching devices of a modular multilevel DC / DC converter according to claim 5, characterized in that, The switching action sequence 1 is as follows: the switching actions of Sk_1 and Sk_2 are determined by i sk Current single closed-loop control is generated, Sk_3 remains off, Sk_4 remains on, Sk_5 remains off, and Sk_6 remains on. Switching action sequence 2 is: the switching actions Sk_1 and Sk_2 are initiated by i sk Current single closed-loop control is generated, Sk_3 remains on, Sk_4 remains off, Sk_5 remains off, and Sk_6 remains on. Switching action sequence 3 is as follows: the switching actions of Sk_1 and Sk_2 are determined by i sk Current single closed-loop control is generated, Sk_3 remains on, Sk_4 remains off, Sk_5 remains on, and Sk_6 remains off; The switching action sequence 4 is as follows: Sk_1 remains off, Sk_2 remains on, and the switching actions of Sk_3 and Sk_4 are determined by i. sk Current is generated by a single closed-loop control, with Sk_5 kept on and Sk_6 kept off. The switching action sequence 5 is as follows: the switching actions of Sk_1 and Sk_2 are determined by i sk Current single closed-loop control is generated, Sk_3 remains off, Sk_4 remains on, Sk_5 remains on, and Sk_6 remains off; The switching action sequence 6 is as follows: Sk_1 remains off, Sk_2 remains on, and the switching actions of Sk_3 and Sk_4 are determined by i. sk Current is generated by a single closed-loop control, with Sk_5 kept off and Sk_6 kept on. The switching action sequence 7 is as follows: Sk_1 remains off, Sk_2 remains on, Sk_3 remains on, Sk_4 remains off, and the switching actions of Sk_5 and Sk_6 are determined by i. sk Current single-closed-loop control generation; The switching action sequence 8 is as follows: Sk_1 remains on, Sk_2 remains off, and the switching actions of Sk_3 and Sk_4 are determined by i. sk Current is generated by a single closed-loop control, with Sk_5 kept on and Sk_6 kept off. The switching action sequence 9 is as follows: Sk_1 remains off, Sk_2 remains on, Sk_3 remains off, Sk_4 remains on, and the switching actions of Sk_5 and Sk_6 are determined by i. sk Current single-closed-loop control generation; The switching action sequence 10 is as follows: Sk_1 remains on, Sk_2 remains off, and the switching actions of Sk_3 and Sk_4 are determined by i. sk Current is generated by a single closed-loop control, with Sk_5 kept off and Sk_6 kept on.

7. The method for diagnosing open-circuit faults in switching devices of a modular multilevel DC / DC converter according to claim 6, characterized in that, The switching action of the fixed switching device is determined by i sk The specific steps for generating a single closed-loop current control are as follows: Step 1: Calculate the comparison value i sk_com ; Step 2, i sk_com The switching action sequence of the specified switching device is generated by comparing it with a triangular carrier wave of a given switching frequency: if i sk_com When the value is greater than 0, Sk_1 / Sk_3 / Sk_5 are turned on, and i sk_com If the triangular carrier frequency is greater than the given switching frequency, then Sk_2 / Sk_4 / Sk_6 will be turned on, and i sk_com If the triangular carrier frequency is less than the given switching frequency, then Sk_2 / Sk_4 / Sk_6 are turned off; if i sk_com When the value is less than 0, Sk_1 / Sk_3 / Sk_5 are turned off, i sk_com If the triangular carrier frequency is less than the given switching frequency, then Sk_2 / Sk_4 / Sk_6 are turned off, i sk_com If the triangular carrier frequency is greater than the given switching frequency, then Sk_2 / Sk_4 / Sk_6 will be turned on.

8. The method for diagnosing open-circuit faults in switching devices of a modular multilevel DC / DC converter according to claim 7, characterized in that, Calculate the comparison value i sk_com The formula is: ； Where, k p1 For i TF The proportional gain, k, of a current-controlled single-loop PI controller i1 For i TF The integral coefficient, k, of a current-controlled single-loop PI controller p2 For i sk The proportional gain, k, of a current-controlled single-loop PI controller i2 For i sk The integral coefficient, i, of the current single-loop PI controller TF,ref i is the reference value for the total current. TF denoted as the total output current, and n as the number of parallel phases of the device.

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