NPC type three-level inverter single tube open circuit fault diagnosis method for motor drive

Abstract

The application discloses a kind of NPC type three-level inverter single tube open circuit fault diagnosis method for motor drive, in view of some conditions in permanent magnet synchronous motor closed loop driving system, three-level NPC inverter inner and outer tube fault phenomenon is highly similar, it is difficult to effectively distinguish the problem, a two-step diagnosis scheme is proposed: first, by constructing time domain fault diagnosis variable F x ( t ) It realizes the rapid determination of fault half bridge arm;Then, for the physical mechanism that back electromotive force leads to the consistent characteristics of inner and outer tube faults at high speed, a fault diagnosis algorithm based on d-axis current injection is proposed, which distinguishes between inner and outer tube faults by injecting d-axis current. Theoretical derivation and experimental analysis show that the method has strong real-time diagnosis and good robustness under complex conditions such as variable speed and variable torque, effectively avoiding misdiagnosis.

Description

Technical Field

[0001] This invention belongs to the field of electric drive technology for new energy vehicles, and specifically relates to a method for diagnosing single-tube open-circuit faults in NPC-type three-level inverters used for motor drives. Background Technology

[0002] In motor drive systems, the inverter is a core component, but its internal power devices are highly susceptible to open-circuit faults, which can lead to distortion of current and voltage waveforms, reduced system performance, and even safety accidents. Compared to two-level inverters, three-level NPC (neutral point clamped) inverters have advantages such as lower harmonic content in the output waveform, but the increased number of power switching devices significantly increases the probability of failure. Furthermore, the current path after a fault is more complex, making diagnosis more difficult.

[0003] Currently, inverter fault diagnosis methods can be mainly divided into three categories: signal processing methods, analytical model methods, and data-driven methods. Signal processing directly utilizes the sampled current signal, requiring no additional hardware. The method is simple and easy to implement. The sampled current is processed to extract fault features, thereby completing fault diagnosis. Although the analytical model method does not require additional hardware measurement equipment, greatly reducing the hardware investment of the fault diagnosis system, and can monitor the system in real time (see reference [Zhao Jintao. Research on open circuit fault diagnosis method of inverter in permanent magnet synchronous motor drive system [D]. Anhui University of Science and Technology, 2025]), this method is difficult to establish an accurate system analytical model due to many random factors in actual system operation. The accuracy of the system analytical model will directly affect the diagnosis results. The data-driven method has poor real-time and speed of diagnosis, and requires a large dataset as a training set. It has not been widely adopted in practical engineering applications and will increase the complexity of the system to a certain extent. It requires certain digital processors and other hardware support (see reference [Ma Mingyao, Ling Feng, Sun Yarong, et al. Review of intelligent fault diagnosis methods for three-phase voltage-source inverters [J]. Proceedings of the CSEE, 2020, 40(23):7683-7698].

[0004] Existing diagnostic methods for open-circuit faults in NPC inverters under PMSM (Permanent Magnet Synchronous Motor) loads, whether data-driven, analytical model-based, or traditional signal processing methods, sometimes exhibit identical symptoms for both internal and external transistor faults. For example, as seen in the literature [Chen Yu, Zheng Yu, Xu Gaoman. A Diagnostic Method for Open-Circuit Faults of Switching Transistors in Marine NPC Three-Level Inverters [J / OL]. China Shipbuilding Research, 2026, 1-10], these methods cannot accurately distinguish between internal and external transistor faults. Furthermore, unlike resistive-inductive loads, actual motor loads require consideration not only of closed-loop regulation and back electromotive force but also of varying speeds and torques. This places higher demands on the accuracy and robustness of inverter fault diagnosis methods.

[0005] Therefore, a new fault diagnosis algorithm for single-transistor open circuit in NPC-type three-level inverters for motor drive is urgently needed. Designing a fault diagnosis algorithm for single-transistor open circuit in NPC-type three-level inverters for motor drive that can be applied to different operating conditions and realize the fault diagnosis of power devices remains a challenge. Summary of the Invention

[0006] In view of the above, the present invention provides a method for diagnosing single-tube open-circuit faults in NPC-type three-level inverters for motor drives, which can realize the diagnosis of single-tube open-circuit faults in NPC-type three-level inverters for permanent magnet synchronous motors.

[0007] A method for diagnosing single-transistor open-circuit faults in an NPC-type three-level inverter for motor drive includes the following steps: (1) Collect the three-phase stator current in the permanent magnet synchronous motor drive system and normalize the three-phase stator current to obtain the normalized three-phase current; (2) Construct a three-phase time-domain fault diagnosis variable based on the three-phase normalized current. This variable is used to characterize the cumulative characteristics of the normalized current distortion within a preset electrical angle window. (3) Compare the three-phase time-domain fault diagnosis variables with the first diagnosis threshold, and determine the fault phase and fault arm of the inverter according to the sign relationship of the three-phase time-domain fault diagnosis variables; (4) Detect the fault phase current of the corresponding polarity of the faulty bridge arm, compare it with the second diagnostic threshold, and determine the open circuit fault of the power switching device on the outside of the faulty bridge arm or perform d-axis current injection based on the comparison result. (5) After short-term injection, detect the fault phase current of the corresponding polarity of the fault arm again, compare it with the second diagnostic threshold, and determine the open circuit fault of the power switching device on the outside or inside of the fault arm based on the comparison result.

[0008] Furthermore, in step (1), the three-phase stator current is normalized using the following expression: in: i x for x Phase stator current, for x Phase normalized current, x =a,b,c i q_ref This is the reference value for the q-axis current.

[0009] Furthermore, in step (2), the three-phase time-domain fault diagnosis variables are constructed using the following expression: in: F x ( t )for t time x Phase-time domain fault diagnosis variables, i e The electrical angle of the PMSM at the current moment. Indicates the electrical angle i Below x Phase normalized current, x =a,b,c.

[0010] Furthermore, in step (3), the faulty phase and faulty arm of the inverter are determined by the following criteria: When phases a, b, and c all satisfy | F x ( t )|≤ e At time 1, the inverter is determined to be fault-free; When phases a, b, and c all satisfy | F x ( t )|> e At time 1, it is determined that the inverter has malfunctioned, and at this time: like F a ( t ) < 0, F b ( t ) > 0, F c ( t If ) > 0, it is determined that the upper arm of phase a of the inverter has a fault; like F a ( t ) > 0, F b ( t ) < 0, F c ( tIf the value is less than 0, it is determined that a fault has occurred in the lower arm of phase a of the inverter. like F a ( t ) > 0, F b ( t ) < 0, F c ( t If ) > 0, it is determined that the upper arm of phase b of the inverter has a fault; like F a ( t ) < 0, F b ( t ) > 0, F c ( t If the value is less than 0, it is determined that a fault has occurred in the lower arm of phase b of the inverter. like F a ( t ) > 0, F b ( t ) > 0, F c ( t If the value is less than 0, it indicates a fault in the upper arm of phase c of the inverter. like F a ( t ) < 0, F b ( t ) < 0, F c ( t If ) > 0, it is determined that a fault has occurred in the lower arm of phase c of the inverter; in: e 1 is the first diagnostic threshold. F x ( t )for t time x Phase-time domain fault diagnosis variables, x =a,b,c.

[0011] Furthermore, in step (4), if the fault phase current of the corresponding polarity of the faulty bridge arm is greater than the second diagnostic threshold, it is determined that the power switching device on the outer side of the faulty bridge arm (the side relatively far from the output port of the bridge arm) has an open circuit fault; if the fault phase current is less than or equal to the second diagnostic threshold, then d-axis current injection is performed near the zero-crossing point of the back electromotive force of the fault.

[0012] Furthermore, the injection duration and amplitude of the d-axis current are preset values, and the preset values ​​are determined based on at least one of the following: DC bus voltage, voltage vector limiting, controller parameters, current sampling accuracy, and system safety margin.

[0013] Furthermore, in step (5), if the fault phase current of the corresponding polarity of the faulty bridge arm is detected again as being greater than the second diagnostic threshold, it is determined that the power switching device on the outer side of the faulty bridge arm has an open circuit fault; if the fault phase current is less than or equal to the second diagnostic threshold, it is determined that the power switching device on the inner side (relative to the side closer to the output port of the bridge arm) of the faulty bridge arm has an open circuit fault.

[0014] Furthermore, the second diagnostic threshold is a preset value, and the preset value is determined based on at least one of the fault phase current before and after injection, normal current ripple, dead zone effect, and sampling error.

[0015] A computer device includes a memory and a processor, wherein the memory stores a computer program, and the processor executes the computer program to implement the above-described method for diagnosing single-transistor open-circuit faults in an NPC-type three-level inverter for motor drive.

[0016] A computer-readable storage medium storing a computer program, which, when executed by a processor, implements the above-described method for diagnosing single-transistor open-circuit faults in an NPC-type three-level inverter for motor drive.

[0017] This invention addresses the problem in closed-loop drive systems of permanent magnet synchronous motors (NPC) where the fault phenomena of the internal and external transistors of a three-level NPC inverter are highly similar and difficult to distinguish at high speeds. It proposes a two-step diagnostic scheme: first, by constructing time-domain fault diagnosis variables... F x ( t This invention enables rapid identification of faulty half-bridge arms. Then, addressing the physical mechanism by which back EMF at high speeds causes identical fault characteristics in both inner and outer tubes, a fault diagnosis algorithm based on d-axis current injection is proposed. This algorithm distinguishes between inner and outer tube faults by injecting d-axis current. Theoretical derivation and experimental analysis show that the method of this invention has strong real-time diagnostic performance and good robustness under complex operating conditions such as variable speed and variable torque, effectively avoiding misdiagnosis. Therefore, this invention has the following beneficial technical effects: 1. Achieving differentiation between internal and external tube faults: This invention innovatively employs d-axis current injection to differentiate between internal and external tube faults when the fault symptoms are identical.

[0018] 2. Simple engineering implementation: This invention is based on the existing three-phase current, electrical angle and q-axis current reference values ​​of the motor drive system for diagnosis, without the need to add additional hardware measurement devices, nor does it rely on a large number of fault samples for training.

[0019] 3. Good robustness and avoidance of false diagnosis: The method of this invention reduces the influence of load torque changes on the amplitude of diagnostic variables by normalizing the current, and reduces the influence of speed changes on the diagnostic results by constructing diagnostic variables. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the equivalent circuit structure topology of the three-phase NPC inverter and PMSM system in an embodiment of the present invention.

[0021] Figure 2 This is a schematic diagram of a three-level voltage vector sector in an embodiment of the present invention.

[0022] Figure 3 This is a flowchart illustrating the single-transistor open-circuit fault diagnosis method for an NPC-type three-level inverter used in motor drive according to an embodiment of the present invention.

[0023] Figure 4 This is a schematic diagram of the experimental results of increasing the rotational speed from 500 r / min to 1000 r / min in an embodiment of the present invention.

[0024] Figure 5 In this embodiment of the invention, the power switch T is used when the rotational speed is 500 r / min. a1 A schematic diagram of the experimental results when an open-circuit fault occurs. Detailed Implementation

[0025] To describe the present invention in more detail, the technical solution of the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0026] In this embodiment, the main circuit of the three-phase NPC inverter and the equivalent circuit of the PMSM system are as follows: Figure 1 As shown, each phase arm of an NPC-type three-level inverter contains four switching transistors. Taking phase a as an example, it includes four switching transistors T. a1 ~T a4 T a1 ~T a4 Each has an anti-parallel diode D a1 ~D a4 There are also two diodes D a5 D a6 T a1 The collector is connected to the DC bus voltage. V dc The positive electrode, T a1 emitter and T a2 The collector and D a5 The cathodes are connected, T a2 emitter and T a3 The collector of D is connected as the output port of this phase bridge arm. a5 anode and Da6 The cathode is connected to the midpoint of the DC bus, T a3 emitter and T a4 The collector and D a6 The anode is connected, T a4 The emitter is connected to the negative terminal of the DC bus voltage, T a1 ~T a4 The gate is connected to the drive signal provided by the control system; where C1 and C2 are supporting capacitors. R and L For the stator resistance and stator inductance of the PMSM, i a ~ i c The output current of the three-phase bridge arm is the three-phase stator current. e a ~ e c T is the three back electromotive force of PMSM. a1 T a4 T b1 T b4 T c1 T c4 The part located on the outside of the inverter is called the outer tube, T a2 T a3 T b2 T b3 T c2 T c3 Located inside the inverter, known as the inner tube, the bridge arm has three switching states and can output a + level. V dc / 2, 0 and - V dc / 2, where P, O, and N represent the corresponding bridge arm states, respectively. The output ports of phases a, b, and c are connected to the stator windings of phases u, v, and w of the motor, respectively. The PMSM variable frequency speed control system uses a classic PI controller, and the control parameters are usually tuned according to linear control theory or engineering design methods. The control system includes an outer speed loop and an inner current loop, with the d-axis current command value being... i d_ref The q-axis current command value is i q_ref .

[0027] For the aforementioned NPC-type inverters and PMSM systems, this embodiment provides a method for diagnosing single-transistor open-circuit faults in NPC-type three-level inverters used for motor drives. The specific implementation process is as follows: Figure 3 As shown: (1) Collect stator phase current i xAnd by combining the q-axis current reference value provided by the speed regulator, the normalized current is calculated. : in: i x for x Phase stator current, x =a,b,c i q,ref This is the reference value for the q-axis current.

[0028] (2) Constructing time-domain fault diagnosis variables And complete the calculation.

[0029] in: i e The electrical angle of the PMSM at the current moment. i e ∈[0,2π).

[0030] (3) Based on time-domain diagnostic variables F x ( t Identify the faulty bridge arm.

[0031] Since the characteristics of time-domain diagnostic variables differ between healthy and faulty states, the faulty half-bridge arm can be identified. The current characteristics of the time-domain diagnostic variables under healthy and faulty states are as follows: a. In a healthy state: b with T a2 Taking a fault as an example, The distortion characteristics of the positive half-wave make F a ( t When the forward current of phase a is completely eliminated, and the forward current is less than 0, we have: outer tube T a1 During a fault, the positive half-wave of the fault phase current will also be significantly attenuated, with -2≤ F a (t) < 0.

[0032] Therefore, a first diagnostic threshold is set. e 1. Real-time monitoring of the values ​​of time-domain fault diagnosis variables for each phase; when phases a, b, and c all satisfy | F x ( t )|≤ e When 1, it is determined that no fault has occurred; when all three phases a, b, and c meet the condition | Fx ( t )|> e At time 1, a fault is determined to have occurred, and at this time: like F a ( t ) < 0, F b ( t ) > 0, F c ( t If ) > 0, it is determined that the upper arm of phase a of the inverter has a fault; like F a ( t ) > 0, F b ( t ) < 0, F c ( t If the value is less than 0, it is determined that a fault has occurred in the lower arm of phase a of the inverter. like F a ( t ) > 0, F b ( t ) < 0, F c ( t If ) > 0, it is determined that the upper arm of phase b of the inverter has a fault; like F a ( t ) < 0, F b ( t ) > 0, F c ( t If the value is less than 0, it is determined that a fault has occurred in the lower arm of phase b of the inverter. like F a ( t ) > 0, F b ( t ) > 0, F c ( t If the value is less than 0, it indicates a fault in the upper arm of phase c of the inverter. like F a ( t ) < 0, F b ( t ) < 0, F c ( tIf ) > 0, it is determined that a fault has occurred in the lower arm of phase c of the inverter; Therefore, it can be seen that fault diagnosis variables in the three-phase time domain can be used as a basis. F x ( t The sign of the faulty bridge arm is used to determine the faulty phase. The phase with the opposite sign is considered faulty. A time-domain fault diagnosis variable greater than 0 indicates a fault in the lower half of the bridge arm of that phase, while a value less than 0 indicates a fault in the upper half of the bridge arm. If the time-domain fault diagnosis variables of phases a, b, and c do not simultaneously meet the above-mentioned non-fault or fault criteria, the phase current continues to be collected and the time-domain fault diagnosis variables are updated. No fault location result is output, or the previous diagnostic state is maintained. In this embodiment... e 1 is set to 0.2.

[0033] (4) After identifying the faulty phase and the faulty bridge arm, detect the faulty phase current response of the corresponding polarity of the faulty bridge arm; when the faulty phase current response is greater than the second diagnostic threshold... e At time 2, it is determined that the outer power device in the faulty bridge arm has an open-circuit fault; when the faulty phase current response is less than or equal to the second diagnostic threshold. e At time 2, d-axis current injection is performed near the zero-crossing point of the opposite electromotive force of the fault; in this embodiment... e 2 is set to 0.5.

[0034] (5) After a short injection, the fault phase current response of the corresponding polarity of the faulty half-bridge arm is detected again. If the fault phase current response of the corresponding polarity of the faulty half-bridge arm is greater than the second diagnostic threshold after injection, the response is positive. e At time 2, it is determined to be an open-circuit fault in the external power device; when the fault phase current response of the corresponding polarity of the faulty half-bridge arm after short-time injection is less than or equal to the second diagnostic threshold. e At time 2, it was determined to be an open circuit fault in the internal power device.

[0035] The voltage vector of the three-level inverter in this embodiment is as follows: Figure 2 As shown, each sector can be further divided into 6 smaller regions, and the three-phase switch level state corresponding to each voltage vector is represented by P, O, or N.

[0036] To verify the effectiveness and superiority of the method of the present invention, experimental verification was carried out in this embodiment. The parameters of the surface-mounted high-speed permanent magnet synchronous motor used in the embodiment are shown in Table 1: Table 1 The experimental results, taking the change in rotational speed as an example, are as follows: Figure 4 As shown, the motor speed increased from 500 r / min to 1000 r / min, and the time-domain fault diagnosis variable never exceeded the threshold, indicating a fault. F A value consistently of 0 indicates a healthy state and no misdiagnosis has occurred. The zoomed-in area displays the three-phase current.i a ~ i c The waveform.

[0037] With power switch T a1 The experimental results of an open-circuit fault are as follows: Figure 5 As shown, the fault occurred during operation when the motor speed was 500 r / min and the load torque was 6 N·m. Under healthy conditions, i a , i b and i c All are symmetrical sine values, fault signs F The value remains 0, and the time-domain fault diagnosis variable remains at the threshold. e 1 and e The fault occurred between 1 and 1. ωt =near 0, after the fault occurred i a Initially, the current remained at 0. After a period of time, a weak positive current fault characteristic appeared, reaching the threshold. e After 1, fault sign F An output of -1 indicates that a fault has occurred in the upper half of phase a, and subsequently, the positive current fault characteristics of phase a reach a threshold. e 2. Fault indicator F An output of 1 indicates that the judgment is T. a1 The fault diagnosis results are accurate; the experimental diagnosis speed in this embodiment is fast, with the first step diagnosis time being 0.222 fundamental frequency periods (T), the second step diagnosis time being 0.083 fundamental frequency periods (T), and a total of 0.306 fundamental frequency periods (T).

[0038] The above description of the embodiments is provided to enable those skilled in the art to understand and apply the present invention. Those skilled in the art can readily make various modifications to the above embodiments and apply the general principles described herein to other embodiments without creative effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made to the present invention by those skilled in the art based on the disclosure thereof should be within the scope of protection of the present invention.

Claims

1. A method for diagnosing single-transistor open-circuit faults in an NPC-type three-level inverter for motor drive, characterized in that, Includes the following steps: (1) Collect the three-phase stator current in the permanent magnet synchronous motor drive system and normalize the three-phase stator current to obtain the normalized three-phase current; (2) Construct a three-phase time-domain fault diagnosis variable based on the three-phase normalized current. This variable is used to characterize the cumulative characteristics of the normalized current distortion within a preset electrical angle window. (3) Compare the three-phase time-domain fault diagnosis variables with the first diagnosis threshold, and determine the fault phase and fault arm of the inverter according to the sign relationship of the three-phase time-domain fault diagnosis variables; (4) Detect the fault phase current of the corresponding polarity of the faulty bridge arm, compare it with the second diagnostic threshold, and determine the open circuit fault of the power switching device on the outside of the faulty bridge arm or perform d-axis current injection based on the comparison result. (5) After short-term injection, detect the fault phase current of the corresponding polarity of the fault arm again, compare it with the second diagnostic threshold, and determine the open circuit fault of the power switching device on the outside or inside of the fault arm based on the comparison result.

2. The method for diagnosing single-transistor open-circuit faults in NPC-type three-level inverters for motor drives according to claim 1, characterized in that, In step (1), the three-phase stator current is normalized using the following expression: in: i x for x Phase stator current, for x Phase normalized current, x =a,b,c i q_ref This is the reference value for the q-axis current.

3. The method for diagnosing single-transistor open-circuit faults in NPC-type three-level inverters for motor drives according to claim 1, characterized in that, In step (2), the three-phase time-domain fault diagnosis variables are constructed using the following expression: in: F x ( t )for t time x Phase-time domain fault diagnosis variables, θ e The electrical angle of the PMSM at the current moment. Indicates the electrical angle θ Below x Phase normalized current, x =a,b,c.

4. The method for diagnosing single-transistor open-circuit faults in NPC-type three-level inverters for motor drives according to claim 1, characterized in that, In step (3), the faulty phase and faulty bridge arm of the inverter are determined by the following criteria: When phases a, b, and c all satisfy | F x ( t )|≤ ε At time 1, the inverter is determined to be fault-free; When phases a, b, and c all satisfy | F x ( t )|> ε At time 1, it is determined that the inverter has malfunctioned, and at this time: like F a ( t ) < 0, F b ( t ) > 0, F c ( t If ) > 0, it is determined that the upper arm of phase a of the inverter has a fault; like F a ( t ) > 0, F b ( t ) < 0, F c ( t If the value is less than 0, it is determined that a fault has occurred in the lower arm of phase a of the inverter. like F a ( t ) > 0, F b ( t ) < 0, F c ( t If ) > 0, it is determined that the upper arm of phase b of the inverter has a fault; like F a ( t ) < 0, F b ( t ) > 0, F c ( t If the value is less than 0, it is determined that a fault has occurred in the lower arm of phase b of the inverter. like F a ( t ) > 0, F b ( t ) > 0, F c ( t If the value is less than 0, it indicates a fault in the upper arm of phase c of the inverter. like F a ( t ) < 0, F b ( t ) < 0, F c ( t If ) > 0, it is determined that a fault has occurred in the lower arm of phase c of the inverter; in: ε 1 is the first diagnostic threshold. F x ( t )for t time x Phase-time domain fault diagnosis variables, x =a,b,c.

5. The method for diagnosing single-transistor open-circuit faults in NPC-type three-level inverters for motor drives according to claim 1, characterized in that: In step (4), if the fault phase current of the corresponding polarity of the fault bridge arm is greater than the second diagnostic threshold, it is determined that the power switching device on the outer side of the fault bridge arm has an open circuit fault; if the fault phase current is less than or equal to the second diagnostic threshold, d-axis current injection is performed near the zero-crossing point of the back electromotive force of the fault.

6. The method for diagnosing single-transistor open-circuit faults in NPC-type three-level inverters for motor drives according to claim 1, characterized in that: The injection duration and amplitude of the d-axis current are preset values, and the preset values ​​are determined based on at least one of the following: DC bus voltage, voltage vector limiting, controller parameters, current sampling accuracy, and system safety margin.

7. The method for diagnosing single-transistor open-circuit faults in NPC-type three-level inverters for motor drives according to claim 1, characterized in that: In step (5), if the fault phase current of the corresponding polarity of the faulty bridge arm is detected again as being greater than the second diagnostic threshold, it is determined that the power switching device on the outer side of the faulty bridge arm has an open circuit fault; if the fault phase current is less than or equal to the second diagnostic threshold, it is determined that the power switching device on the inner side of the faulty bridge arm has an open circuit fault.

8. The method for diagnosing single-transistor open-circuit faults in NPC-type three-level inverters for motor drives according to claim 1, characterized in that: The second diagnostic threshold is a preset value, and the preset value is determined based on at least one of the fault phase current before and after injection, normal current ripple, dead zone effect, and sampling error.

9. A computer device comprising a memory and a processor, wherein the memory stores a computer program, characterized in that: The processor is used to execute the computer program to implement the single-tube open-circuit fault diagnosis method for NPC-type three-level inverters for motor drive as described in any one of claims 1 to 8.

10. A computer-readable storage medium storing a computer program, characterized in that: When the computer program is executed by the processor, it implements the single-transistor open-circuit fault diagnosis method for NPC-type three-level inverters for motor drive as described in any one of claims 1 to 8.

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