Fault diagnosis method, device and equipment of NPC three-level inverter and medium

Abstract

The application discloses a kind of NPC three-level inverter fault diagnosis method, device, equipment and medium, it is related to inverter fault diagnosis technical field, comprising: according to inverter fault stator current variation law, establish fault stator current analytical model;Utilize sliding window mean value method feature extraction and locate fault phase and fault bridge arm;The fault positioning reference value under the condition of setting ideal is calculated, and the fault positioning actual value of actual situation is compared to locate the IGBT that fails.Through establishing fault stator current analytical model, the current variation condition under the condition of setting ideal is simulated, and the deviation between the fault positioning reference value and the fault positioning actual value of actual situation distinguishes whether actual fault condition and setting ideal fault condition are consistent, whether the fault is positioned as inner tube or outer tube.In calculation, the current mean value from fault time to first zero-crossing time is used, and fault IGBT can be positioned in a fundamental cycle, and fault diagnosis positioning is carried out quickly and efficiently.

Description

Technical Field

[0001] This invention relates to the field of inverter fault diagnosis, and more particularly to a fault diagnosis method, apparatus, equipment and medium for an NPC three-level inverter. Background Technology

[0002] With the rapid development of electronic power technology, NPC three-level inverters, due to their advantages such as low output voltage harmonics and low switching losses, are widely used in industrial automation, new energy power generation, and electric vehicle drive systems, especially in motor stators. However, the increased number of power switching devices in its topology can affect the reliability of the system. For example, the open-circuit failure rate of IGBTs increases significantly. IGBT open-circuit failures not only cause inverter output voltage distortion and increased motor torque ripple, but may also lead to problems such as midpoint potential drift and DC bus voltage imbalance, seriously threatening the stability and safety of drive systems such as motors.

[0003] Current fault diagnosis for NPC three-level inverters primarily focuses on detection methods based on current feature extraction, harmonic analysis, or model residuals. However, these methods cannot accurately distinguish open-circuit faults in the inner / outer IGBTs. When an open-circuit fault occurs in either the inner or outer IGBT, the current waveform of the motor stator exhibits nonlinear distortion due to current path reconstruction. In the case of an inner IGBT fault, there is often a midpoint potential shift, leading to complex current harmonic components; in the case of an outer IGBT fault, abrupt switching changes cause high-frequency oscillations and transient energy concentration. This nonlinear distortion renders traditional steady-state characteristic-based diagnostic methods ineffective, and the non-stationarity of the fault signal and multi-source interference further complicate feature extraction. The fault current patterns of the inner and outer IGBTs are also quite similar, especially under high-noise conditions where the overlap between fault characteristics and normal operating conditions increases significantly, easily leading to misjudgments of fault location and type. Summary of the Invention

[0004] This invention discloses a fault diagnosis method, apparatus, equipment, and medium for NPC three-level inverters, in order to solve the technical problem of insufficient accuracy in fault diagnosis and location of IGBTs in NPC three-level inverters.

[0005] In a first aspect, embodiments of the present invention provide a fault diagnosis method for an NPC three-level inverter, comprising:

[0006] S101. Based on the current variation law of the motor stator under different fault conditions of the NPC three-level inverter, establish an analytical model of fault stator current to simulate the change of three-phase current when a fault occurs.

[0007] S102, the sliding window mean method is used to extract the features of the three-phase current of the motor stator to obtain the sliding window fault features, and the fault phase and fault bridge arm of the NPC three-level inverter are located based on the sliding window fault features.

[0008] S103. Based on the fault stator current analytical model, calculate the average current from the fault time to the zero crossing time, and use it as a fault location reference value.

[0009] S104: Obtain the actual current of the stator of the motor that has failed, and calculate the average current from the time of the fault to the time of zero crossing, as the actual value for fault location.

[0010] S105 calculates the fault location deviation value using the fault location reference value and the actual fault location value, and locates the faulty IGBT based on the fault location deviation value.

[0011] Furthermore, S103 includes:

[0012] Obtain the current values ​​of the three phases and the control vector output by the closed-loop controller, respectively;

[0013] Based on the fault stator current analytical model, the fault current analytical waveform is obtained by using the current values ​​of the three-phase currents and the control vector output by the closed-loop controller.

[0014] By analyzing the fault current waveform, the average current of the fault phase from the fault time to the first zero crossing time is calculated, which serves as a reference value for fault location.

[0015] Furthermore, S104 includes:

[0016] Obtain the actual three-phase current values ​​of the faulty stator and extract the current values ​​of the faulty phase;

[0017] Based on the current value of the faulty phase, calculate the average current from the time of the fault to the time of the first zero crossing, and use it as the actual value for fault location.

[0018] Furthermore, S105 includes:

[0019] Calculate the fault location deviation value using the fault location reference value and the actual fault location value;

[0020] The fault location deviation value is compared with a preset threshold, and the faulty IGBT is located as either the inner tube or the outer tube based on the comparison result.

[0021] Furthermore, S101 includes:

[0022] Based on the changes in fault phase current when an NPC three-level inverter experiences a fault, a hybrid logic dynamic model is established.

[0023] Based on the hybrid logic dynamic model, a model for instantaneous current change information is derived.

[0024] Based on the instantaneous change information model of current, the waveform of current change within one fundamental cycle is calculated to form an analytical model of fault stator current.

[0025] Furthermore, the step of calculating the current change waveform within one fundamental cycle based on the instantaneous current change information model to form an analytical model of the fault stator current includes:

[0026] Obtain the control vector output by the closed-loop controller, and calculate the waveform action vector and vector action time based on the control vector;

[0027] Calculate the three-phase instantaneous current at the start of the next switching cycle based on the waveform action vector and the vector action time;

[0028] The control feedback current is calculated based on the three-phase instantaneous current, and the control vector of the closed-loop controller at the next moment is calculated based on the control feedback current.

[0029] Based on the control vector at the next moment, the waveform action vector and the vector action time are recalculated, and iterative calculations are performed until a current change waveform of one fundamental cycle is formed, thus forming an analytical model of the fault stator current.

[0030] Furthermore, S102 also includes:

[0031] Obtain the actual three-phase current values ​​of the faulty stator and perform preprocessing;

[0032] The sliding window mean value is used to extract features from the actual three-phase current values ​​to obtain sliding window fault features;

[0033] Based on the characteristics of the sliding window failure, the faulty phase and the faulty bridge arm were identified.

[0034] Secondly, embodiments of the present invention provide a fault diagnosis device for an NPC three-level inverter, comprising:

[0035] The fault stator current analytical model construction module is used to establish a fault stator current analytical model based on the current variation law of the motor stator under different fault conditions of the NPC three-level inverter.

[0036] The sliding window mean feature extraction module is used to extract features from the three-phase current of the motor stator using the sliding window mean method to obtain sliding window fault features;

[0037] The fixed positioning reference calculation module is used to calculate the average current from the time of the fault to the time of zero crossing based on the fault stator current analytical model.

[0038] The fault location value calculation module is used to obtain the actual current of the stator of the motor that has failed, and to calculate the average current from the time of the fault to the time of zero crossing.

[0039] The fault IGBT location module is used to calculate the fault location deviation value using the fault location reference value and the actual fault location value, and to locate the faulty IGBT based on the fault location deviation value.

[0040] Thirdly, embodiments of the present invention provide an electronic device, including:

[0041] One or more processors;

[0042] Storage device for storing one or more programs.

[0043] When the one or more programs are executed by the one or more processors, the one or more processors implement the above-described fault diagnosis method for NPC three-level inverters.

[0044] Fourthly, embodiments of the present invention provide a storage medium containing computer-executable instructions, which, when executed by a computer processor, are used to perform the fault diagnosis method for the above-described NPC three-level inverter.

[0045] This invention provides a fault diagnosis method, apparatus, device, and medium for an NPC three-level inverter. The method establishes an analytical model of the fault stator current based on the stator current variation patterns under different fault conditions. This model simulates the ideal three-phase current changes during a fault and calculates a fault location reference value. Then, based on the actual three-phase current changes, the actual fault location value is calculated. A fault location deviation value is formed by comparing the deviation between the reference value and the actual value. This deviation value is compared with a preset fault location threshold to determine whether the actual fault condition matches the ideal fault condition, thus identifying whether the faulty IGBT is an inner or outer tube. Simultaneously, a sliding window averaging method is used to extract fault features from the three-phase current, and the faulty phase and bridge arm are located based on the changes in these features. Because the NPC three-level inverter has three phases, each with an upper and lower bridge arm, and each bridge arm with an outer and inner IGBT, locating the faulty phase and bridge arm allows for identification of whether the fault is an outer or inner IGBT. Simultaneously, based on the fault stator current analytical model and the current waveform of a fundamental cycle formed by iterative calculation of the control signal of the closed-loop controller, the average current value from the fault time to the first zero crossing time is used in the calculation, and the faulty IGBT can be located within one fundamental cycle. This allows for rapid and efficient diagnosis and location of IGBT open-circuit faults in NPC three-level inverters. Attached Figure Description

[0046] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0047] Figure 1 This is a flowchart of a fault diagnosis method for an NPC three-level inverter according to Embodiment 1 of the present invention;

[0048] Figure 2 This is a flowchart of a fault diagnosis method for an NPC three-level inverter according to Embodiment 2 of the present invention;

[0049] Figure 3 This is a flowchart of a fault diagnosis method for an NPC three-level inverter according to Embodiment 3 of the present invention;

[0050] Figure 4 This is a schematic diagram of the topology of the NPC three-level inverter described in Embodiment 3 of the present invention;

[0051] Figure 5 This is a schematic diagram of the current flow path under the three switching states described in Embodiment 3 of the present invention;

[0052] Figure 5 (a) is the current flow path under the switch state P as described in Embodiment 3 of the present invention;

[0053] Figure 5 (b) is the current flow path under switch state O as described in Embodiment 3 of the present invention;

[0054] Figure 5 (c) is the current flow path under switch state N as described in Embodiment 3 of the present invention;

[0055] Figure 6 The switching transistor S described in Embodiment 3 of the present invention a1 A schematic diagram of the current conduction path when an open circuit fault occurs;

[0056] Figure 6 (a) S as described in Embodiment 3 of the present invention a1 The current flow path under switch state P when an open circuit fault occurs;

[0057] Figure 6 (b) is the S described in Embodiment 3 of the present invention. a1 The current flow path under switch state O when an open circuit fault occurs;

[0058] Figure 6 (c) S as described in Embodiment 3 of the present invention a1The current flow path under switch state N when an open circuit fault occurs;

[0059] Figure 7 The switching transistor S described in Embodiment 3 of the present invention a2 A schematic diagram of the current conduction path when an open circuit fault occurs;

[0060] Figure 7 (a) S as described in Embodiment 3 of the present invention a2 The current flow path under switch state P when an open circuit fault occurs;

[0061] Figure 7 (b) is the S described in Embodiment 3 of the present invention. a2 The current flow path under switch state O when an open circuit fault occurs;

[0062] Figure 7 (c) S as described in Embodiment 3 of the present invention a2 The current flow path under switch state N when an open circuit fault occurs;

[0063] Figure 8 This is a schematic diagram of the three-phase current simulated using the fault stator current analytical model as described in Embodiment 3 of the present invention;

[0064] Figure 8 (a) S as described in Embodiment 3 of the present invention a1 A schematic diagram of the distorted waveform during an open-circuit fault;

[0065] Figure 8 (b) is the S described in Embodiment 3 of the present invention. a2 A schematic diagram of the distorted waveform during an open-circuit fault;

[0066] Figure 9 This is a schematic diagram of the sliding window mean method described in Embodiment 3 of the present invention;

[0067] Figure 10 This is a schematic diagram of the structure of a fault diagnosis device for an NPC three-level inverter according to Embodiment 4 of the present invention;

[0068] Figure 11 This is a structural diagram of the electronic device described in Embodiment 5 of the present invention. Detailed Implementation

[0069] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and not intended to limit it. Furthermore, it should be noted that, for ease of description, the accompanying drawings show only the parts relevant to the present invention, and not all of the structures.

[0070] The NPC three-level inverter (neutral-point clamped three-level inverter) is a type of inverter that achieves three-level output (+) through series-connected IGBT switching transistors and clamping diodes. V dc / 2、0、- V dc / 2) is a converter that converts DC-side electrical energy into three-phase AC electrical energy and transmits it to the stator windings of the motor to provide the power required for motor operation. Due to the significantly increased number of power switching devices in its topology, including clamping diodes, an IGBT open-circuit fault refers to a situation where a single IGBT switch fails to conduct due to device damage or abnormal control signal. When an open-circuit fault occurs in the IGBT power switching device of an NPC three-level inverter, it leads to an interruption of the current path, abnormal output voltage, and consequently, problems such as system waveform distortion, midpoint potential imbalance, and decreased power output. The current in the faulty stator will enter a clamping state. Therefore, the instantaneous current change of the faulty phase can be analyzed based on the current clamping effect of the faulty stator. This type of fault may be caused by overvoltage, overheating, short circuit evolution, or device aging. If not handled promptly, it may cause inverter shutdown or even equipment damage. Fault diagnosis technology is needed to quickly identify and locate the fault point. Because the nonlinear distortion of fault current varies greatly, noise can also interfere with the current shape. Especially under complex operating conditions such as high noise and multi-source interference, the difficulty of extracting fault characteristics formed by current distortion is significantly increased. It is difficult to locate specific faulty IGBTs based on the current distortion. If complex analysis and calculation methods are used, a large number of derivation and calculation processes will be generated, which is not conducive to quickly and accurately locating faulty IGBTs.

[0071] Example 1

[0072] Figure 1 This is a flowchart of a fault diagnosis method for an NPC three-level inverter according to Embodiment 1 of the present invention. This embodiment establishes a fault stator current analytical model, compares the instantaneous current change information of the actual fault stator with the theoretical fault situation simulated by the model, and locates the IGBT with an open-circuit fault. The specific steps include the following:

[0073] S101. Based on the current variation law of the motor stator under different fault conditions of the NPC three-level inverter, an analytical model of fault stator current is established to simulate the change of three-phase current when a fault occurs.

[0074] Based on the current variation pattern of the NPC three-level inverter, an MLD (Mixed Logic Dynamic Model) can be established using the instantaneous changes in the three-phase stator current under normal conditions. The MLD model can represent the regular changes in the three-phase stator current of the NPC three-level inverter during normal operation. The MLD model can be expressed as a formula:

[0075]

[0076] in, Indicates three-phase current. Represents the switching function. This represents the three back electromotive forces, and , Indicates stator resistance. Indicates stator inductance, Indicates time, The sign indicates the partial derivative. Indicates the DC bus voltage. This indicates the instantaneous change information of the three-phase current under normal operating conditions. This change information is related to the instantaneous value of the three-phase current, the inverter status, and the motor back electromotive force.

[0077] When an open-circuit fault occurs in the IGBT of an NPC three-level inverter, the current flow path of the faulty phase stator changes, entering a clamping state. At this time, the stator current of the faulty phase is distorted. Using the MLD model, a model of the instantaneous current change is derived. This instantaneous current change model can be expressed as a formula:

[0078]

[0079] in, Indicates three-phase current. Represents the switching function. This represents the three back electromotive forces, and , Indicates stator resistance. Indicates stator inductance, Indicates time, The sign indicates the partial derivative. Indicates the DC bus voltage. This indicates the three-phase current after the fault. This indicates the instantaneous changes in the three-phase current under fault stator current clamping conditions.

[0080] Because the closed-loop controller outputs corresponding control signals according to the set control algorithm to maintain three-phase current balance, but in reality, the IGBT power switch of the faulty phase is open-circuited, and current cannot conduct, resulting in a change in the current path. At this time, under the control signal of the closed-loop controller, the current of the healthy phase will gradually increase, which can easily lead to current overload. The clamping diode will conduct to control the current and enter the clamping state, indicating that the NPC three-level inverter has failed. By using the instantaneous current change information and combining it with the output parameters of the closed-loop controller, the three-phase current change over a period of time can be generated through repeated iterative calculations. This allows the construction of an analytical model of the faulty stator current, used to simulate the change in three-phase current when a fault occurs. Based on the current change within one fundamental cycle, the faulty IGBT can be further analyzed. At the same time, to avoid severe system imbalance leading to collapse, it is necessary to quickly locate the faulty IGBT for maintenance.

[0081] S102, the sliding window mean method is used to extract the features of the three-phase current of the motor stator to obtain the sliding window fault features, and the fault phase and fault arm of the NPC three-level inverter are located based on the sliding window fault features.

[0082] Because the current in the faulty phase will be distorted when a fault occurs, the phase and arm of the bridge that is faulty can be determined by analyzing the changes in the three-phase current. First, the harmonic state of the three-phase stator current is collected. The three-phase current is then preprocessed to remove interference terms and form a data format suitable for feature extraction. Then, the sliding window mean method is used to extract features from the three-phase current. Since it is necessary to maintain the amplitude balance of the three-phase current to ensure stable motor torque, the current waveform is symmetrical across the three phases and is sinusoidal. Under normal conditions, the sliding window mean should strictly approach 0. After a fault, the current becomes distorted. For example, when an open-circuit fault occurs in the outer tube IGBT of the upper arm, the fault phase current will undergo a nonlinear commutation dynamic process such as commutation and clamping. During this process, the current is in a nonlinear distorted form, so the sliding window mean will decrease significantly. Meanwhile, the non-fault phase current is affected by the closed-loop controller and will be consistent with the trend of the lower tube open-circuit fault of the upper arm in a short period of time, showing a significant increase. Therefore, the phase (fault phase) and the arm (fault arm) where the fault occurred can be determined based on the change of the sliding window mean after the fault.

[0083] S103, based on the fault stator current analytical model, calculate the average current from the fault time to the zero crossing time, and use it as a fault location reference value.

[0084] The fault stator current analytical model can simulate the changes in three-phase current during a fault. It collects the three-phase current and the output signal of the closed-loop controller, inputs them into the model, and generates the current analytical waveform of the faulty phase. The average current of the faulty phase from the fault time to the zero-crossing time is used as the fault location reference value. The current analytical waveform simulated by the model represents an ideal situation of instantaneous current changes during a fault. This simulated ideal situation is used as a reference for locating the faulty IGBT. Furthermore, based on the degree of similarity between the actual situation and the simulated ideal situation, the IGBT experiencing an open-circuit fault can be further identified.

[0085] S104: Obtain the actual current of the stator of the faulty motor and calculate the average current from the time of the fault to the time of zero crossing, as the actual value for fault location.

[0086] The fault location reference value calculated using the fault stator current analytical model represents the stator current change after a fault under ideal conditions. The actual fault location value, calculated from the average current from the fault time to the zero-crossing time, is compared with the fault location reference value under ideal conditions to determine their similarity. This allows analysis of whether the actual and ideal fault types are the same, and can be used to locate IGBTs with open-circuit faults. Furthermore, by calculating the average current from the fault time to the first zero-crossing time, the time required for fault location can be reduced to within one fundamental frequency cycle. One fundamental frequency cycle refers to the period of the current's analytical waveform from one zero-crossing point to the next. The time from the fault time to the first zero-crossing time is necessarily less than or equal to one fundamental frequency cycle, meaning that at most one fundamental frequency cycle is needed to locate an IGBT with an open-circuit fault.

[0087] S105 calculates the fault location deviation value using the fault location reference value and the actual fault location value, and locates the faulty IGBT based on the fault location deviation value.

[0088] The deviation between the fault location reference value and the actual fault location value is calculated as the fault location deviation value. This deviation value reflects the degree of difference between the actual fault location value and the fault location reference value. The deviation value is compared with a preset threshold. If the deviation value exceeds the threshold, it is determined whether the ideal situation represented by the fault location reference value and the actual situation represented by the fault location value belong to the same fault type, thereby locating the faulty IGBT. For example, in S103, when the faulty phase is in the P state and the current direction is positive, the fault stator current analytical model is used to calculate the waveform distortion of the positive half-wave current of the faulty phase caused by the interruption of the original forward conduction path and the current commutation to the O state when the external IGBT experiences an open-circuit fault. The average current value from the moment of the first zero crossing is used as the fault location reference value under ideal conditions. In this case, the external IGBT open-circuit fault has no effect on the O and N states, so the obtained fault location reference value is always non-negative. The average actual current of the fault phase from the moment of the fault to the moment of its first zero crossing is then directly calculated as the actual fault location value, representing the actual instantaneous change in current after the fault. The actual value is compared with the ideal value, and the deviation between the two is calculated. This deviation is then compared with a preset fault location threshold, which is determined empirically and has a certain tolerance to avoid minor deviations caused by noise and other interference factors affecting the judgment result. If the fault location deviation falls within the tolerance range where the fault location reference value and the actual fault location value are close, the fault can be located as an external IGBT. If it falls within the tolerance range where the two are not close and there is a deviation, the fault can be located as an internal IGBT. The ideal situation can be defined based on the conditions set when calculating the fault location reference value. By analyzing the consistency between the actual situation and the ideal situation, the faulty IGBT can be quickly located.

[0089] This embodiment establishes an analytical model of the fault stator current based on the current variation patterns of the motor stator under different fault conditions in an NPC three-level inverter. This model simulates the ideal changes in the three-phase current during a fault and calculates a fault location reference value. Then, based on the actual changes in the three-phase current, the actual fault location value is calculated. A fault location deviation value is generated by comparing the deviation between the fault location reference value and the actual fault location value. This deviation value is compared with a preset fault location threshold to determine whether the actual fault condition matches the ideal fault condition, thus identifying whether the faulty IGBT is an inner or outer tube. Simultaneously, a sliding window averaging method is used to extract fault features from the three-phase current. By analyzing the changes in these fault features, the faulty phase and faulty bridge arm are located in advance, narrowing down the fault range. Because the topology of the NPC three-level inverter has three phases, each with an upper and lower bridge arm, and each bridge arm with an outer and inner IGBT, the faulty phase and faulty bridge arm can be identified as either an outer or inner IGBT after locating the faulty phase and faulty bridge arm. Simultaneously, based on the fault stator current analytical model and the current waveform of a fundamental cycle formed by iterative calculation of the control signal of the closed-loop controller, the average current value from the fault time to the first zero crossing time is used in the calculation, and the faulty IGBT can be located within one fundamental cycle. This allows for rapid and efficient diagnosis and location of IGBT open-circuit faults in NPC three-level inverters.

[0090] Example 2

[0091] Figure 2 This is a flowchart of a fault diagnosis method for an NPC three-level inverter according to Embodiment 2 of the present invention. This embodiment is based on the above embodiment and optimized. In this embodiment, S105 is specifically optimized as follows:

[0092] Calculate the fault location deviation value using the fault location reference value and the actual fault location value;

[0093] The fault location deviation value is compared with a preset threshold, and the faulty IGBT is located as either the inner tube or the outer tube based on the comparison result.

[0094] Accordingly, the fault diagnosis method for the NPC three-level inverter provided in this embodiment specifically includes:

[0095] S201. Based on the current variation law of the motor stator under different fault conditions of the NPC three-level inverter, an analytical model of fault stator current is established to simulate the change of three-phase current when a fault occurs.

[0096] S202, the sliding window mean method is used to extract the features of the three-phase current of the motor stator to obtain the sliding window fault features, and the fault phase and fault arm of the NPC three-level inverter are located based on the sliding window fault features.

[0097] S203. Based on the fault stator current analytical model, calculate the average current from the fault time to the zero crossing time, and use it as a fault location reference value.

[0098] Specifically, the current values ​​of the three phases and the control vector output by the closed-loop controller are obtained respectively.

[0099] During fault location, based on the determined faulty phase and faulty bridge arm, it is also necessary to analyze and locate the IGBT that has an open-circuit fault step by step according to the distortion of the three-phase current. By obtaining the current values ​​of the three-phase current and the control vector output by the closed-loop controller, the fault-customized current analytical model is constructed. The model is used to simulate the changes in the three-phase current after the fault, which serves as a reference for subsequent fault location.

[0100] Based on the fault stator current analytical model, the fault current analytical waveform is obtained by using the current values ​​of the three-phase currents and the control vector output by the closed-loop controller.

[0101] exist Three-phase currents collected at all times The back electromotive force of the motor ,as well as Three-phase switch status during the time period (Switch function) and vector action time (Control vector of closed-loop electromotive force), input the above data into the fault stator current analytical model, and use the model for iterative calculation to obtain The information on current changes within a time period is used to gradually construct the current change within a fundamental cycle, i.e., the fault current analytical waveform.

[0102] By analyzing the fault current waveform, the average current of the fault phase from the fault time to the first zero crossing time is calculated, which serves as a reference value for fault location.

[0103] Calculate the fault occurrence time based on the fault current waveform. until the fault phase current first crosses zero The average current, i.e., the change in fault phase current simulated by the fault stator current analytical model under ideal conditions, is the average current from the start of the fault until the fault current analytical waveform first crosses zero. This average current is used as a fault location reference value for consistency comparison with the actual situation. For example, since the NPC three-level inverter is three-phase symmetrical, each phase has upper and lower bridge arms, and each bridge arm has two IGBTs (upper and lower transistors). Based on the determined fault phase and fault bridge arm, a faulty IGBT can be set between the upper and lower transistors as the ideal situation. For example, when the fault phase is phase A and the faulty bridge arm is the upper bridge arm, an open-circuit fault can be set for the outer IGBT of the upper bridge arm. In this case, if the A phase switch is in the P state and the current direction is positive... An open-circuit fault in the outer IGBT will interrupt the original forward conduction path (outer tube → inner tube → load side). At this time, the current will commutate to the 0 state, flowing through the capacitor midpoint O, the clamping diode, and the inner tube to the load side. Compared to the path before the fault, this current commutation will cause distortion of the positive half-wave current waveform in phase A. This distortion will depend on the timing of the fault. until the fault phase current first crosses zero The average A-phase current is used to determine the fault location reference value. It should be noted that when the switch is in the O or N state, an open circuit fault in the external IGBT of the upper bridge arm has no effect on the current path, so the obtained fault location reference value is always non-negative.

[0104] S204: Obtain the actual current of the stator of the faulty motor and calculate the average current from the time of the fault to the time of zero crossing, as the actual value for fault location.

[0105] Specifically, obtain the actual three-phase current values ​​of the faulty stator and extract the current values ​​of the faulty phase.

[0106] Based on the fault current analytical waveform generated by the fault stator current analytical model, the ideal fault location reference value is calculated. The actual three-phase current value of the fault stator is obtained, and the current value of the fault phase is extracted. The average current value is used to calculate the consistency comparison with the fault location reference value.

[0107] Based on the current value of the faulty phase, calculate the average current from the time of the fault to the time of the first zero crossing, and use it as the actual value for fault location.

[0108] Using the actual obtained fault phase current value, calculate the current from the time the fault occurred. until the fault phase current first crosses zero The average current is used as the actual value for fault location and is used to compare its consistency with the fault location reference value.

[0109] S205, calculate the fault location deviation value using the fault location reference value and the actual fault location value.

[0110] If the actual fault condition matches the ideal condition (similar IGBT faults), the fault location reference value and the actual fault location value will be close, indicating that the actual situation matches the set ideal condition. For example, if the set ideal condition is an external IGBT fault in S203, when the actual fault is an internal IGBT, the forward current conduction path in both the P and O states will be blocked. When the internal IGBT cannot conduct current, in the P state, it relies on the external IGBT and clamping diode to form a circuit. However, the open circuit of the internal IGBT interrupts the current path. The O state is similarly blocked, and current can only conduct in the N state. Therefore, if the actual fault is in the internal IGBT, the actual fault location value will deviate from the fault location reference value calculated by the model under the ideal condition. This indicates an internal IGBT fault, inconsistent with the external IGBT fault type in the ideal condition. Conversely, if the actual fault is in the external IGBT, the actual fault location value will approach the fault location reference value, consistent with the ideal condition, allowing for the location of the faulty IGBT. The fault location deviation between the fault location reference value and the actual fault location value is calculated, representing the degree of deviation. The formula is as follows:

[0111]

[0112] in, This indicates the actual value for fault location. Indicates the fault location reference value. To prevent the denominator from being zero, use a small positive number. If an open-circuit fault actually occurs in the external pipe, then... Fault location deviation value It will approach 0 if an open circuit fault actually occurs in the inner tube. Close to 0, and The model generated values ​​for open-circuit faults in external pipes, and the fault location deviation values. It will approach 1.

[0113] S206, compare the fault location deviation value with the preset threshold, and locate whether the faulty IGBT is the inner tube or the outer tube based on the comparison result.

[0114] Because the calculation of actual current is affected by noise and other interference factors, the calculated current value may have a slight deviation. Strictly comparing using only 0 or 1 values ​​may result in unsuccessful comparisons. Based on past experience, a reasonable tolerance threshold is preset. This tolerance threshold is then used to compare the fault location deviation value with the actual fault location deviation value, ultimately determining whether the faulty IGBT is an outer or inner tube. The formula for calculating the fault location deviation value using the tolerance threshold is as follows:

[0115]

[0116] in, This represents the tolerance threshold, and , This indicates the fault location deviation value. This represents the fault location value for the IGBT, where 1 indicates an outer tube fault and 2 indicates an inner tube fault. If the fault location deviation value is between 0 and the tolerance threshold, it can be considered that the actual fault matches the set ideal situation, and the result is 1; if the fault location deviation value is between 1 and 2, it indicates a fault. Tolerance threshold The result between 1 and 2 can be considered as the actual fault not matching the set ideal situation, resulting in 2.

[0117] This embodiment simulates and calculates the current changes under ideal conditions to obtain a fault location reference value representing the ideal situation. Then, it uses actual current changes to obtain the actual fault location value. The fault location reference value and the actual fault location value are compared to identify the deviation, forming a fault location deviation value. This deviation value, along with a preset reasonable tolerance threshold, defines the consistency between the actual and ideal situations. If the actual current changes are consistent with the ideal fault conditions, the actual fault type is determined to be the same type of IGBT fault as the one set in the ideal situation. If they are not consistent, the actual fault type is determined to be different from the one set in the ideal situation. Since a single bridge arm only has two IGBTs (upper and lower), the IGBT with the open-circuit fault can be directly located by identifying consistency or inconsistency. Furthermore, only the current change data from the fault occurrence time to the first zero crossing time is needed to directly calculate and locate the fault, meaning the faulty IGBT can be located within less than or at most one fundamental frequency cycle. This results in high accuracy and speed in fault location.

[0118] Example 3

[0119] Figure 3 This is a flowchart of a fault diagnosis method for an NPC three-level inverter according to Embodiment 3 of the present invention. This embodiment is an optimization based on the above embodiment. In this embodiment, S101 includes:

[0120] Based on the changes in fault phase current when an NPC three-level inverter experiences a fault, a hybrid logic dynamic model is established.

[0121] Based on the hybrid logic dynamic model, a model for instantaneous current change information is derived.

[0122] Based on the instantaneous change information model of current, the waveform of current change within one fundamental cycle is calculated to form an analytical model of fault stator current.

[0123] Accordingly, the fault diagnosis method for the NPC three-level inverter provided in this embodiment specifically includes:

[0124] S301 establishes a hybrid logic dynamic model based on the change in fault phase current when a fault occurs in the NPC three-level inverter.

[0125] The topology of the NPC three-level inverter is as follows: Figure 4 As shown, it is widely used in high power density permanent magnet synchronous motor (PMSM) drive systems. By introducing a midpoint clamping mechanism, it achieves three-level output (+) based on the traditional two-level inverter. V dc / 2、0、- V dc / 2), thereby significantly reducing the harmonic content of the output voltage and reducing switching losses. Figure 4 The NPC-type PMSM drive system shown includes a DC side, an inverter bridge, and a load side. The DC side uses two equal-value capacitors. C 1. C 2) Series voltage division forms a symmetrical DC bus voltage. V dc It provides positive, negative, and neutral point voltage references for the inverter. The inverter bridge (inverter) is three-phase symmetrical, and each phase bridge arm contains four power switching devices (IGBTs). Four freewheeling diodes and two clamping diodes Multi-level output is achieved by controlling the combination of switching states. Clamping diodes limit neutral point voltage fluctuations and provide a current path during the freewheeling phase. On the load side, a modulation strategy generates a near-sinusoidal three-phase output voltage to drive the PMSM for efficient operation. The inverter ultimately outputs three switching states: P, O, and N, which represent the inverter bridge arm outputs. Table 1 shows the relationship between the inverter voltage, bridge arm operating states, and the on / off state of the switching transistors.

[0126] Table 1. Relationship between bridge arm status and output voltage and transistor on / off state.

[0127]

[0128] Define power switching transistor When conducting When shut down For example, when phase A bridge arm is in state P, the outer switch S of the upper bridge arm... a1 (Outer IGBT) and inner switching transistor S a2(Inner IGBT) is on; in the 0 state, the inner switch S of the upper bridge arm is on. a2 (Inner IGBT) and the inner switch S of the lower bridge arm a3 (Inner IGBT) is on; in the N state, the inner switch S of the lower bridge arm is on. a3 (Inner IGBT) and outer switching transistor S a4 When the external IGBT is turned on, the current flow path in the three switching states is as follows: Figure 5 As shown, Figure 5 (a) shows the current flow path under switch state P. Figure 5 (b) shows the current flow path in switch state O. Figure 5 (c) shows the current flow path in switch state N, where the red line represents the positive current flow path and the blue line represents the negative current flow path. From this, the hybrid logic dynamic model (MLD model) of the inverter can be obtained. The MLD model can be expressed as a formula:

[0129]

[0130] in, Indicates three-phase current. Represents the switching function. This represents the three back electromotive forces, and , Indicates stator resistance. Indicates stator inductance, Indicates time, The sign indicates the partial derivative. Indicates the DC bus voltage. This indicates the instantaneous change information of the three-phase current under normal operating conditions. This change information is related to the instantaneous value of the three-phase current, the inverter status, and the motor back electromotive force.

[0131] S302, based on the hybrid logic dynamic model, derives the instantaneous change information model of current.

[0132] The hybrid logic dynamic model represents the operating state and variation patterns of the inverter under normal operating conditions. Each of the A, B, and C phase arms of the inverter may experience a single power switching device failure (single IGBT open-circuit fault), resulting in 12 possible fault modes. Since the three phase arms of the inverter are symmetrical pairwise, the three-phase outputs have a high degree of similarity. When the fault current enters the clamping state, the instantaneous current change information under the clamping state can be derived from the hybrid logic dynamic model, represented as the instantaneous current change information model, as shown in the following formula:

[0133]

[0134] in, Indicates three-phase current. Represents the switching function. This represents the three back electromotive forces, and , Indicates stator resistance. Indicates stator inductance, Indicates time, The sign indicates the partial derivative. Indicates the DC bus voltage. This indicates the three-phase current after the fault. This indicates the instantaneous changes in the three-phase current under fault stator current clamping conditions. For example, when the switching transistor S... a1 In the event of an open circuit fault, the current conduction path is as follows: Figure 6 As shown, Figure 6 (a) shows the current flow path under switch state P. Figure 6 (b) shows the current flow path in switch state O. Figure 6 (c) shows the current flow path in switch state N. Switch S a2 In the event of an open circuit fault, the current conduction path is as follows: Figure 7 As shown, Figure 7 (a) shows the current flow path under switch state P. Figure 7 (b) shows the current flow path in switch state O. Figure 7 (c) shows the current flow path in switch state N. The red line in the figure represents the positive current conduction path, and the blue line represents the negative current conduction path. Under the vector action of the closed-loop controller, when the current increases in the positive direction, the instantaneous rate of change is positive, and the action vector is a positive vector; conversely, when the current decreases, the instantaneous rate of change is negative, and the action vector is a negative vector.

[0135] For example, when the current in phase A flows in the forward direction and the switch is in state P, if the outer tube S of the upper bridge arm... a1 In the event of an open-circuit fault, current can only continue to conduct by switching to the 0 state to achieve commutation. At this time, the A-phase switching function... S a =0, substitute into the MLD model to calculate the instantaneous change of the A-phase current at the commutation moment. k a_nom ,at this time:

[0136] (1) If the instantaneous change information of the current k a_nom If the value is greater than 0, then the action vector is a positive vector, and the current... The path to the O state continues to increase;

[0137] (2) If the instantaneous change information of the current k a_nom If the value is less than 0, the action vector is a negative vector, and in this case, it is necessary to determine the current. Will a clamping state occur: Let the current vector action time be... T Calculate the time required for the current to decay to 0. :

[0138]

[0139] in Indicates the current of phase A. This indicates the change in phase A current. If at this time... t n > T If the current does not decay to 0 within the current vector's cycle, the A-phase current gradually decreases along the O-state path. Although it can continue to conduct, the gradual decrease also indicates a fault has occurred. t n ≤ T Then the current will decay to 0 within the current vector's period, and the current path of phase A will pass through the anti-parallel diode D. a1 and D a2 Switching to the inverter's P state, according to the switching function S a =1 calculation Instantaneous change information of phase A current at time =0 k a_cl :

[0140] If the instantaneous change information of the current k a_cl <0, then the current Connect to state P and increase it in the opposite direction;

[0141] If the instantaneous change in current information k a_cl If the current is greater than 0, then a clamping state will occur because the current should continue to decrease in the O state. At this time, the current... The clamping value is zero. S a1 Open circuit fault The actual operating state of phase A when the current is greater than 0 is shown in Table 2. The instantaneous change information of phase B and phase C current can be calculated based on the instantaneous change information model of current.

[0142] Table 2 S a1 Open circuit fault >0 Hour A Phase Actual Working Status

[0143]

[0144] For example, when the current in phase A is 0, it enters the clamping state, and the switch state is in the P state (i.e., S a When =1), if the change information of phase A current ka_nom1 <0, then the current Continue to conduct negatively according to the P state; if k a_nom1 If the value is >0, then due to an open-circuit fault in the external tube, the inverter commutates to state O. At this time, state O (i.e., S a Instantaneous current change information under (=0) k a_nom2 ,like k a_nom2 If >0, then the current in phase A will be connected to the O state and forward conduction will occur in the next moment; if k a_nom2 If the value is less than 0, it is considered that the current is positively conducting in the P state and negatively conducting in the O state. Therefore, the current remains in a clamped state, meaning that the current repeatedly switches between the P and O states but still cannot conduct. a1 Open circuit fault and The actual working state of phase A when = 0 is shown in Table 3:

[0145] Table 3 S a1 Open circuit fault =0, actual working state of phase A

[0146]

[0147] For example, when the current in phase A flows in the negative direction and the switch is in state P, the current conducts in the negative direction along the P state, and at this time the switching function will... S a Substituting 1 into the MLD model, we can calculate the instantaneous change of the A-phase current at the commutation moment. k a_nom :

[0148] (1) If the instantaneous change information of the current k a_nom If the current in phase A is less than 0, then the current in phase A is less than 0. Continue to flow in the negative direction according to state P;

[0149] (2) If the instantaneous change information of the current k a_nom If the value is greater than 0, then it is necessary to determine the current of phase A. Will the current increase from negative conduction to zero trigger a clamping state? If so, what is the time required for the current to decay to zero? Greater than the time of action of the previous vector T ,Right now t n > T If the current does not increase from negative conduction to 0 within the current vector period; if t n ≤ T，The current will then increase to 0, and the current path will pass through the anti-parallel diode D. a5 and switching transistor S a2 Switch to inverter state O according to the switching function S a =0 calculation Instantaneous change in current at time =0 k a_cl :

[0150] If the instantaneous change information of the current k a_cl >0, then the current of phase A Connect to the 0 state and conduct in the forward direction; if the current changes instantaneously... k a_cl If the current is less than 0, then since the current should continue to increase under state P, a clamping state is determined to have occurred, and the current in phase A is... The clamped value is zero, S a1 Open circuit fault and The actual working status of phase A when <0 is shown in Table 4:

[0151] Table 4 S a1 Open circuit fault <0 Time A Phase Actual Working Status

[0152]

[0153] For example, if the inner tube S of the upper bridge arm a2 If an open-circuit fault occurs, the actual operating status of phase A is shown in Table 5:

[0154] Table 5 S a2 Open circuit fault, actual working state of phase A

[0155]

[0156] Similarly, those skilled in the art can observe that, based on the topology of the NPC three-level inverter, since the inverter is three-phase symmetrical, the fault patterns of the three-phase circuit are also consistent; and since the upper and lower bridge arms of each current phase are also symmetrical, the faults of the external IGBT and the internal IGBT are also symmetrical.

[0157] S303 calculates the current change waveform within one fundamental cycle based on the instantaneous current change information model, forming an analytical model of the fault stator current.

[0158] Based on the instantaneous current change information model, the switching cycle can be divided into seven stages according to the SVPWM (Space Vector Pulse Width Modulation) strategy to calculate the current change information within this period. The instantaneous current change information model is used to repeatedly calculate the current change information within each time period, and then the current model within a fundamental cycle is calculated. Gradually, a current change waveform representing the current change within a fundamental cycle is constructed, which is the fault stator current analytical model.

[0159] Optionally, the control vector output by the closed-loop controller can be obtained, and the waveform action vector and vector action time can be calculated based on the control vector.

[0160] A closed-loop controller is a control component that regulates the three-phase current by outputting a control vector, thereby maintaining the balanced and stable operation of the motor. When a power switching device in the inverter malfunctions, the stator current of the faulty phase becomes distorted. Even without fault handling (fault elimination), the closed-loop controller will still issue control signals according to the previously programmed control logic, attempting to maintain stable system operation. If its monitoring and protection functions fail to react in time, it will forcibly increase the current to compensate for the total motor torque, easily leading to an imbalance in the two-phase current amplitude and causing severe torque oscillations in the motor. Therefore, it is necessary to obtain the control vector output by the closed-loop controller. and The process involves calculating the waveform vector and duration of the control vector's effect on the current waveform, which are then used to extrapolate current changes. For example, the intermediate value of the vector's effect is first calculated using the control vector. Then, the modulation index is calculated, and the sector containing the vector is determined based on the modulation index. Finally, the waveform vector and duration are determined by looking up the SVPWM table. The formula is as follows:

[0161]

[0162] in, and This represents the control vector output by the closed-loop controller. Indicates the angle of the current waveform. Indicates the α-axis reference voltage. This represents the β-axis reference voltage.

[0163]

[0164] in, This represents the intermediate value of the vector action. It represents the imaginary part of a complex number.

[0165]

[0166] in, Indicates adjustment system, This indicates the DC-side bus voltage.

[0167] Calculate the three-phase instantaneous current at the start of the next switching cycle based on the waveform action vector and the vector action time.

[0168] Based on the obtained waveform action vector and vector action time, the current change under each switching state under the vector action can be calculated based on the action vector and the three-phase instantaneous current. Furthermore, the change in the three-phase current can be calculated through the vector action time, thereby gradually forming the three-phase instantaneous current at the beginning of the next switching cycle.

[0169] The control feedback current is calculated based on the three-phase instantaneous current, and the control vector for the next moment of the closed-loop controller output is calculated based on the control feedback current.

[0170] The three-phase instantaneous current formed by the three-phase current after control vector regulation at the start of the next switching cycle will be fed back to the closed-loop controller. The closed-loop controller will then adjust the system's stable operation based on the feedback current. Since the closed-loop controller outputs two control vectors, it is necessary to convert the calculated three-phase instantaneous current into d-axis and q-axis currents, and combine this with the reference current to determine the new d-axis and q-axis voltages (control vectors) output by the current-loop PI controller at the next moment. and The formula is as follows:

[0171]

[0172] in, , , These are the three-phase instantaneous currents, Indicates the angle of the current waveform. , These are the d-axis and q-axis currents, respectively, representing the new d-axis and q-axis currents output at the next moment.

[0173] Based on the control vector at the next moment, the waveform action vector and the vector action time are recalculated, and iterative calculations are performed until a current change waveform of one fundamental cycle is formed, thus forming an analytical model of the fault stator current.

[0174] Based on the calculated control vector for the next moment, this is used as the new output of the closed-loop controller. The above process is repeated: calculating the waveform action vector and vector action time based on the control vector, then calculating the three-phase instantaneous current at the start of the next switching cycle, followed by calculating the control feedback current and the new control vector output for the next moment. This iterative calculation continues until the stator current changes for one fundamental cycle, forming a current change waveform for one fundamental cycle, i.e., the analytical model of the fault stator current. Using this model, the current change waveform for one fundamental cycle can be simulated and calculated using the three-phase current and the control vector of the closed-loop controller, such as... Figure 8 As shown, Figure 8 (a) is S a1 A schematic diagram of the distorted waveform during an open-circuit fault. Figure 8 (b) is S a2 A schematic diagram of the distorted waveform during an open-circuit fault, where the solid lines represent the actual three-phase current and the dashed lines represent the three-phase current calculated by the model, which is used to identify and locate the power switching device that has an open-circuit fault.

[0175] S304 uses the sliding window mean method to extract features of the three-phase current of the motor stator to obtain sliding window fault features, and locates the faulty phase and faulty bridge arm of the NPC three-level inverter based on the sliding window fault features.

[0176] One optional implementation of this embodiment is to obtain the current change information of the actual three-phase current of the faulty stator and perform preprocessing.

[0177] The actual three-phase current values ​​of the faulty stator are collected to form analytical waveforms of the three-phase currents, which are used to represent the changes in the three-phase currents. Since the actual collected data may contain noise and other interference, and to facilitate calculations while preserving as much of the data characteristics as possible, normalization preprocessing is required. The formula is as follows:

[0178]

[0179] in, This represents the normalized value of the three-phase current. These are the three-phase current values, and , This represents the amplitude of the three-phase current.

[0180] By using the sliding window mean to extract features from the actual three-phase current variation information, sliding window fault features are obtained.

[0181] Under normal operating conditions, the stator current of a motor is three-phase symmetrical, and this property can be used to identify abnormal situations. The sliding window mean method is a technique for smoothing time series data using a fixed-size window. It involves sliding a fixed-length window across the time series and calculating the average of all data within the window. Figure 9 As shown. The sliding window averaging method is used to extract features from the waveforms that reflect the changes in three-phase current. The formula is as follows:

[0182]

[0183] in, This represents the average current within the sliding window, i.e., the fault characteristics of the sliding window. This indicates the angle of the current waveform at the moment of the fault. This indicates the starting angle of the sliding window, that is, the initial position of the sliding window on the waveform graph. This indicates the final angle of the sliding window on the waveform graph, i.e., the ending position of the sliding window. Indicates the integral symbol, Indicates the angle of the current waveform. This represents the integral over the current angle. This represents the fault three-phase current, and The sliding window mean of the three-phase current is obtained by summing the integral values ​​of the average current under normal operating conditions and the average current under fault conditions.

[0184] Based on the characteristics of the sliding window failure, the faulty phase and the faulty bridge arm were identified.

[0185] Due to the characteristics of the sliding window mean method and the three-phase symmetry of current, the sliding window mean should strictly approach 0 under normal operating conditions. Using the extracted sliding window fault characteristics, the distorted faulty phase and faulty bridge arm are located based on the changes in the three-phase current. For example, the three-phase topology of a three-level inverter is identical, with each phase having an upper and lower bridge arm, and each bridge arm containing an external and an internal IGBT. If an open-circuit fault occurs in the external IGBT of the upper bridge arm, the current of the faulty phase... The dynamic process involves a nonlinear commutation process, including the transition from the P state to the O state and the entry into a clamping state due to the motor's back electromotive force. During commutation, the current... The waveform will exhibit nonlinear distortion, and the sliding window mean feature extracted by the sliding window mean method will be significantly reduced. Meanwhile, the current in the non-faulty phase is affected by the adjustment signal of the closed-loop controller, and its trend is consistent with that of the IGBT open-circuit fault in the short term, both increasing significantly after the fault. Based on this pattern, the variation of the sliding window mean after faults in different phases and bridge arms is shown in Table 6:

[0186] Table 6. Variation Pattern of Sliding Window Mean

[0187]

[0188] in, , , These represent the sliding window mean characteristics of phases A, B, and C, respectively. S represents the fault detection variable. a1 For the outer tube IGBT of phase A upper arm, S a2 For the inner tube IGBT of phase A upper arm, S a3 For the inner tube IGBT of the lower arm of phase A, S a4 For the outer IGBT of phase A's lower arm, the same logic applies. First, the sliding window mean characteristic is utilized. The fault detection reference value d is calculated using the following formula:

[0189]

[0190] in, Represents a sign function, if Then output 1, if Then the output is 0, if The output is -1. This represents the reference value for three-phase fault detection, and Then, the faulty bridge arm and faulty phase are determined using fault detection reference values, as shown in the following formula:

[0191]

[0192] in, , , These represent the fault detection reference values ​​for phases A, B, and C, respectively; that is, the fault detection variables when the average value of the three-phase current sliding window is 0. Output 0; if the average value of the three-phase current sliding window is not 0, then output 0. The sum of these values, combined with Table 1, can be used to locate the faulty phase and the faulty bridge arm.

[0193] S305, based on the fault stator current analytical model, calculate the average current from the fault time to the zero crossing time, and use it as a fault location reference value.

[0194] S306: Obtain the actual current of the stator of the faulty motor and calculate the average current from the time of the fault to the time of zero crossing, as the actual value for fault location.

[0195] S307 calculates the fault location deviation value using the fault location reference value and the actual fault location value, and locates the faulty IGBT based on the fault location deviation value.

[0196] This embodiment establishes a hybrid logic dynamic model based on the inverter's normal operating conditions and the current changes of the faulty phase during a fault, and derives a current instantaneous change information model. Then, using the current instantaneous change information model combined with the control parameters of the closed-loop controller, iterative calculation of the current change waveform within one fundamental cycle is used to form an analytical model of the faulty stator current. This model can realistically simulate the changes in three-phase current during a fault. During fault location, an ideal fault condition can be set to simulate the current changes under that condition as a reference for identifying the fault location. This is used to compare the current changes with the actual situation to determine whether the actual fault matches the fault under the set condition, thus determining the actual fault type and locating the faulty IGBT. Furthermore, the sliding window mean method is used to extract features from the three-phase current of the motor stator. Based on the extracted sliding window fault features, the faulty phase and faulty bridge arm can be initially located, narrowing down the fault location range.

[0197] Example 4

[0198] Figure 10 This is a schematic diagram of a fault diagnosis device for an NPC three-level inverter according to Embodiment 4 of the present invention. In this embodiment, the fault diagnosis device for the NPC three-level inverter includes:

[0199] The fault stator current analytical model construction module 810 is used to establish a fault stator current analytical model based on the current variation law of the motor stator under different fault conditions of the NPC three-level inverter.

[0200] The sliding window mean feature extraction module 820 is used to extract features of the three-phase current of the motor stator using the sliding window mean method to obtain sliding window fault features;

[0201] The fault location reference calculation module 830 is used to calculate the average current from the fault time to the zero crossing time based on the fault stator current analytical model.

[0202] The fault location value calculation module 840 is used to obtain the actual current of the stator of the motor that has a fault, and to calculate the average current from the time of the fault to the time of zero crossing.

[0203] The fault IGBT location module 850 is used to calculate the fault location deviation value using the fault location reference value and the actual fault location value, and to locate the faulty IGBT based on the fault location deviation value.

[0204] This embodiment establishes a fault stator current analytical model through a fault stator current analytical model construction module, extracts sliding window fault features through a sliding window mean feature extraction module, calculates fault location reference values ​​through a fault location reference calculation module, calculates actual fault location values ​​through a fault location value calculation module, and locates the faulty IGBT based on the fault location deviation value through a fault IGBT location module. By establishing a fault stator current analytical model based on the current variation patterns of the motor stator under different fault conditions in an NPC three-level inverter, the model simulates the changes in three-phase current under ideal conditions during a fault and calculates fault location reference values. Then, based on the actual changes in three-phase current, the actual fault location value is calculated. A fault location deviation value is formed by comparing the deviation between the fault location reference value and the actual fault location value. This deviation value is compared with a preset fault location threshold to determine whether the actual fault condition matches the ideal fault condition, thereby locating whether the faulty IGBT is an inner or outer tube. Simultaneously, the sliding window mean method is used to extract fault features from the three-phase current, and the faulty phase and faulty bridge arm are located based on the changes in these fault features. Because of the topology of the NPC three-level inverter, it has three phases, each with an upper arm and a lower arm. Each arm has an external IGBT and an internal IGBT. After locating the faulty phase and arm, it is possible to distinguish whether the fault is in the external or internal IGBT. Simultaneously, based on the fault stator current analytical model and the current waveform generated by iterative calculation of the control signal from the closed-loop controller, a fundamental cycle is generated. The average current from the fault time to the first zero-crossing time is used in the calculation, allowing the faulty IGBT to be located within one fundamental cycle. This enables rapid and efficient diagnosis and location of IGBT open-circuit faults in NPC three-level inverters.

[0205] The fault diagnosis device for NPC three-level inverters provided in this embodiment of the invention can execute the fault diagnosis method for NPC three-level inverters provided in any embodiment of the invention, and has the corresponding functional modules and beneficial effects of the method.

[0206] Example 5

[0207] Figure 11 This is a structural diagram of an electronic device according to Embodiment 5 of the present invention. Figure 11 A block diagram of an exemplary device 12 suitable for implementing embodiments of the present invention is shown. Figure 11 The device 12 shown is merely an example and should not impose any limitations on the functionality and scope of use of the embodiments of the present invention.

[0208] like Figure 11As shown, device 12 is represented as a general-purpose computing device. Components of device 12 may include, but are not limited to: one or more processors or processing units 16, system memory 28, and a bus 18 connecting different system components (including system memory 28 and processing unit 16).

[0209] Bus 18 represents one or more of several bus architectures, including a memory bus or memory controller, a peripheral bus, a graphics acceleration port, a processor, or a local bus using any of the various bus architectures. For example, these architectures include, but are not limited to, the Industry Standard Architecture (ISA) bus, the Micro Channel Architecture (MAC) bus, the Enhanced ISA bus, the Video Electronics Standards Association (VESA) local bus, and the Peripheral Component Interconnect (PCI) bus.

[0210] Device 12 typically includes a variety of computer system readable media. These media can be any available media that can be accessed by device 12, including volatile and non-volatile media, removable and non-removable media.

[0211] System memory 28 may include computer system readable media in the form of volatile memory, such as RAM 30 (Random Access Memory) and / or cache 32. Device 12 may further include other removable / non-removable, volatile / non-volatile computer system storage media. By way of example only, storage system 34 may be used to read and write non-removable, non-volatile magnetic media (…). Figure 11 Not shown; usually referred to as a "hard drive"). Although Figure 11 Not shown, a disk drive for reading and writing to a removable non-volatile disk (e.g., a "floppy disk") and an optical disk drive for reading and writing to a removable non-volatile optical disk (e.g., a CD-ROM, DVD-ROM, or other optical media) may be provided. In these cases, each drive may be connected to bus 18 via one or more data media interfaces. System memory 28 may include at least one program product having a set (e.g., at least one) of program modules configured to perform the functions of the embodiments of the present invention.

[0212] A program / utility 40 having a set (at least one) of program modules 42 may be stored, for example, in system memory 28. Such program modules 42 include, but are not limited to, an operating system, one or more application programs, other program modules, and program data. Each or some combination of these examples may include an implementation of a network environment. Program modules 42 typically perform the functions and / or methods described in the embodiments of the present invention.

[0213] Device 12 can also communicate with one or more external devices 14 (e.g., keyboard, pointing device, display 24, etc.), and with one or more devices that enable a user to interact with the device 12 / server / computer, and / or with any device that enables the device 12 to communicate with one or more other computing devices (e.g., network interface card, modem, etc.). This communication can be performed through I / O interface 22 (input / output interface). Furthermore, device 12 can also communicate with one or more networks (e.g., local area network (LAN), wide area network (WAN), and / or public networks, such as the Internet) via network adapter 20. Figure 11 As shown, network adapter 20 communicates with other modules of device 12 via bus 18. It should be understood that, although... Figure 11 As not shown, other hardware and / or software modules can be used in conjunction with device 12, including but not limited to: microcode, device drivers, redundant processing units, external disk drive arrays, RAID systems, tape drives, and data backup storage systems.

[0214] The processing unit 16 executes various functional applications and data processing by running programs stored in the system memory 28, such as implementing the fault diagnosis method for the NPC three-level inverter provided in the embodiments of the present invention.

[0215] Example 6

[0216] Embodiment 6 of the present invention also provides a storage medium containing computer-executable instructions, which, when executed by a computer processor, are used to perform the fault diagnosis method for the NPC three-level inverter provided in the above embodiments.

[0217] The computer storage medium of this invention can be any combination of one or more computer-readable media. A computer-readable medium can be a computer-readable signal medium or a computer-readable storage medium. A computer-readable storage medium can be, for example,—but not limited to—an electrical, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device, or any combination thereof. More specific examples of computer-readable storage media (a non-exhaustive list) include: an electrical connection having one or more wires, a portable computer disk, a hard disk, random access memory (RAM), read-only memory (ROM), erasable programmable read-only memory (EPROM or flash memory), optical fiber, portable compact disk read-only memory (CD-ROM), optical storage device, magnetic storage device, or any suitable combination thereof. In this document, a computer-readable storage medium can be any tangible medium that contains or stores a program that can be used by or in conjunction with an instruction execution system, apparatus, or device.

[0218] Computer-readable signal media may include data signals propagated in baseband or as part of a carrier wave, carrying computer-readable program code. Such propagated data signals may take various forms, including but not limited to electromagnetic signals, optical signals, or any suitable combination thereof. Computer-readable signal media may also be any computer-readable medium other than computer-readable storage media, capable of sending, propagating, or transmitting programs for use by or in connection with an instruction execution system, apparatus, or device.

[0219] The program code contained on a computer-readable medium may be transmitted using any suitable medium, including—but not limited to—wireless, wire, optical fiber, RF, etc., or any suitable combination thereof.

[0220] Computer program code for performing the operations of this invention can be written in one or more programming languages ​​or a combination thereof, including object-oriented programming languages ​​such as Java, Smalltalk, and C++, as well as conventional procedural programming languages ​​such as "C" or similar programming languages. The program code can be executed entirely on the user's computer, partially on the user's computer, as a standalone software package, partially on the user's computer and partially on a remote computer, or entirely on a remote computer or server. In cases involving remote computers, the remote computer can be connected to the user's computer via any type of network—including a local area network (LAN) or a wide area network (WAN)—or can be connected to an external computer (e.g., via the Internet using an Internet service provider).

[0221] Note that the above description is merely a preferred embodiment of the present invention and the technical principles employed. Those skilled in the art will understand that the present invention is not limited to the specific embodiments described herein, and various obvious changes, readjustments, and substitutions can be made without departing from the scope of protection of the present invention. Therefore, although the present invention has been described in detail through the above embodiments, the present invention is not limited to the above embodiments, and may include many other equivalent embodiments without departing from the concept of the present invention, the scope of which is determined by the scope of the appended claims.

Claims

1. A fault diagnosis method for an NPC three-level inverter, characterized in that, include: S101. Based on the current variation law of the motor stator under different fault conditions of the NPC three-level inverter, establish an analytical model of fault stator current to simulate the change of three-phase current when a fault occurs. S102, the sliding window mean method is used to extract the features of the three-phase current of the motor stator to obtain the sliding window fault features, and the fault phase and fault bridge arm of the NPC three-level inverter are located based on the sliding window fault features. S103. Based on the fault stator current analytical model, calculate the average current from the fault time to the zero crossing time, and use it as a fault location reference value. S104: Obtain the actual current of the stator of the motor that has failed, and calculate the average current from the time of the fault to the time of zero crossing, as the actual value for fault location. S105, calculate the fault location deviation value using the fault location reference value and the actual fault location value, and locate the faulty IGBT based on the fault location deviation value; S101 includes: Based on the changes in fault phase current when an NPC three-level inverter experiences a fault, a hybrid logic dynamic model is established. Based on the hybrid logic dynamic model, a model for instantaneous current change information is derived. Based on the instantaneous change information model of current, the current change waveform within one fundamental cycle is calculated to form an analytical model of fault stator current; The step of calculating the current change waveform within one fundamental cycle based on the instantaneous current change information model to form an analytical model of the fault stator current includes: Obtain the control vector output by the closed-loop controller, and calculate the waveform action vector and vector action time based on the control vector; Calculate the three-phase instantaneous current at the start of the next switching cycle based on the waveform action vector and the vector action time; The control feedback current is calculated based on the three-phase instantaneous current, and the control vector of the closed-loop controller at the next moment is calculated based on the control feedback current. Based on the control vector at the next moment, the waveform action vector and the vector action time are recalculated, and iterative calculations are performed until a current change waveform of one fundamental cycle is formed, thus forming an analytical model of the fault stator current.

2. The method according to claim 1, characterized in that, S103 includes: Obtain the current values ​​of the three phases and the control vector output by the closed-loop controller, respectively; Based on the fault stator current analytical model, the fault current analytical waveform is obtained by using the current values ​​of the three-phase currents and the control vector output by the closed-loop controller. By analyzing the fault current waveform, the average current of the fault phase from the fault time to the first zero crossing time is calculated, which serves as a reference value for fault location.

3. The method according to claim 1, characterized in that, S104 includes: Obtain the actual three-phase current values ​​of the faulty stator and extract the current values ​​of the faulty phase; Based on the current value of the faulty phase, calculate the average current from the time of the fault to the time of the first zero crossing, and use it as the actual value for fault location.

4. The method according to claim 1, characterized in that, S105 includes: Calculate the fault location deviation value using the fault location reference value and the actual fault location value; The fault location deviation value is compared with a preset threshold, and the faulty IGBT is located as either the inner tube or the outer tube based on the comparison result.

5. The method according to claim 1, characterized in that, S102 further includes: Obtain the actual three-phase current change information of the faulty stator and perform preprocessing; By using the sliding window mean to extract features from the actual three-phase current variation information, sliding window fault features are obtained. Based on the characteristics of the sliding window failure, the faulty phase and the faulty bridge arm were identified.

6. A fault diagnosis device for an NPC three-level inverter, characterized in that, include: The fault stator current analytical model construction module is used to establish a fault stator current analytical model based on the current variation law of the motor stator under different fault conditions of the NPC three-level inverter. The sliding window mean feature extraction module is used to extract features from the three-phase current of the motor stator using the sliding window mean method to obtain sliding window fault features; The fixed positioning reference calculation module is used to calculate the average current from the time of the fault to the time of zero crossing based on the fault stator current analytical model. The fault location value calculation module is used to obtain the actual current of the stator of the motor that has failed, and to calculate the average current from the time of the fault to the time of zero crossing. The fault IGBT location module is used to calculate the fault location deviation value using the fault location reference value and the actual fault location value, and to locate the faulty IGBT based on the fault location deviation value. The fault stator current analytical model construction module includes: The hybrid logic dynamic model building unit is used to establish a hybrid logic dynamic model based on the change in fault phase current when a fault occurs in an NPC three-level inverter. The instantaneous change information model derivation unit is used to derive the instantaneous change information model of current based on the hybrid logic dynamic model. The fault stator current analytical model construction unit is used to calculate the current change waveform within one fundamental cycle based on the instantaneous current change information model, and form the fault stator current analytical model. The fault stator current analytical model construction unit includes: The control vector action calculation subunit is used to obtain the control vector output by the closed-loop controller and calculate the waveform action vector and vector action time based on the control vector. The next cycle instantaneous current calculation subunit is used to calculate the three-phase instantaneous current at the start of the next switching cycle based on the waveform action vector and the vector action time. The next moment control vector calculation subunit is used to calculate the control feedback current based on the three-phase instantaneous current, and to calculate the next moment control vector output by the closed-loop controller based on the control feedback current. The iterative calculation subunit is used to recalculate the waveform action vector and vector action time based on the control vector at the next moment, and perform iterative calculations until a current change waveform of one fundamental cycle is formed, thus forming an analytical model of the fault stator current.

7. An electronic device, characterized in that, The device includes: One or more processors; Storage device for storing one or more programs. When the one or more programs are executed by the one or more processors, the one or more processors implement the fault diagnosis method for the NPC three-level inverter as described in any one of claims 1-5.

8. A storage medium containing computer-executable instructions, which, when executed by a computer processor, are used to perform a fault diagnosis method for an NPC three-level inverter as described in any one of claims 1-5.

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