Two-step on-line diagnosis strategy for open-circuit fault of doubly salient motor inverter

Abstract

The application discloses a two-step online diagnosis strategy for open-circuit fault of a doubly salient motor inverter, and relates to the field of motor control. In the first step, the method realizes open-circuit fault detection of the inverter switch tube by sampling phase current and the driving signal of the switch tube. In the second step, the method realizes fault positioning according to the phase current and the winding neutral point voltage. Compared with the existing diagnosis methods for open-circuit fault of the switch tube of the doubly salient motor inverter, the method does not need to change the inverter topology structure, can be applied to different working conditions, can realize positioning of 26 kinds of open-circuit faults of the switch tube, and the diagnosis time is less than one electrical angle period. This not only widens the diagnosis range, but also helps to switch to a fault-tolerant control strategy in time, and further improves the reliability of the doubly salient motor driving system.

Description

Technical Field

[0001] This invention relates to the field of motor control, and in particular to a two-step online diagnostic strategy for open-circuit faults in a doubly salient pole motor inverter. Background Technology

[0002] Like other motor drive systems, the duo-cam motor drive system consists of an inverter, sensors, a controller, and the motor itself. Due to factors such as temperature, overvoltage, overcurrent, and vibration, various components in the drive system are prone to failure. Reports indicate that in existing failure cases, inverter switching transistor failures account for the largest proportion. Open-circuit faults increase torque ripple and severe mechanical vibration; prolonged operation may lead to secondary failures in the system. Therefore, to improve the reliability of the motor drive system, it is necessary to conduct research on open-circuit faults in switching transistors.

[0003] The patent "A Method for Diagnosing Open Circuit Faults in an Electrically Excited Double Salient Pole Motor Power Converter" (China, Authorization Date: April 18, 2023, Authorization No.: CN115508742B) published by Chen Weiqian et al. discloses a method for locating single-tube and dual-tube faults under the same conduction logic by sampling the current at a specific rotor position.

[0004] Fang Wenjing et al. disclosed in their patent "Diagnosis Method for Open Circuit Fault of Power Transistor and Winding of Electrically Excited Double Salient Pole Motor Converter" (China, Authorization Date: March 24, 2023, Authorization No.: CN114487917B) that by adding a voltage sensor, the fault of a single transistor and a dual transistor under the same conduction logic can be located based on the difference between the neutral point voltage of the motor winding and ground before and after the fault.

[0005] However, the above method has a narrow diagnostic range, capable of diagnosing only 6 types of single-tube open circuits and 3 types of double-tube open circuits, totaling 9 fault types. In reality, the characteristics of different faults are very similar, and misdiagnosis can easily occur if they are not distinguished. Summary of the Invention

[0006] To address the aforementioned problems and technical needs, and to broaden the scope of fault diagnosis, this invention proposes a two-step diagnostic strategy for open-circuit faults in doubly salient pole motor inverters. The technical solution of this invention is as follows:

[0007] A two-step diagnostic strategy for open-circuit faults in a doubly salient pole motor inverter is characterized by: firstly, detecting open-circuit faults in the inverter switching transistors by sampling the phase current and the drive signal of the switching transistors; and secondly, locating the fault based on the phase current and the neutral point voltage of the windings.

[0008] A further technical solution involves the first step of detecting open-circuit faults in the inverter's switching transistors by sampling the phase currents and the drive signals of the switching transistors. Let the currents of phase A, phase B, and phase C be i...a i b and i c Switch T k The driving signal is P k (k=1, 2, 3, 4, 5, 6), and define P k =1 and P k =0 respectively indicates that the switching transistor T k Turning on and off.

[0009] When the system is operating normally, the specific analysis is as follows: One electrical angle cycle is divided into three intervals: 0°~120°, 120°~240°, and 240°~360°. When the rotor is in the 0°~120° interval, switching transistors T1 and T2 are working, and the drive signals P1 and P2 change between 0 and 1, with the phase current i... a =-i c >0、i b =0; When the rotor is in the 120°~240° range, switching transistors T3 and T4 operate, and drive signals P3 and P4 vary between 0 and 1, with phase current i b =-i a >0、i c =0; When the rotor is in the 240°~360° range, switching transistors T5 and T6 operate, and drive signals P5 and P6 vary between 0 and 1, with phase current i c =-i b >0、i a =0.

[0010] When a switching transistor malfunctions, the specific analysis is as follows: When the rotor is in the 0°~120° range, an open circuit in T1 or T2 will prevent the A and C phase windings from forming a circuit with the bus voltage, causing the phase current i to... a =i b =i c =0, according to the current closed-loop effect, the corresponding drive signal P1=P2=1; when the rotor is in the 120°~240° range, the open circuit of T3 or T4 will cause the A and B phase windings to be unable to form a loop with the bus voltage, resulting in the phase current i a =i b =i c =0, according to the current closed-loop effect, the corresponding drive signal P3=P4=1; when the rotor is in the 240°~360° range, the open circuit of T5 or T6 will cause the B and C phase windings to be unable to form a loop with the bus voltage, resulting in the phase current i a =i b =i c =0, according to the current closed-loop effect, the corresponding drive signal P5=P6=1.

[0011] Based on the above analysis, the phase current and drive signal after a fault can be used as features for fault detection. Therefore, let F be the open-circuit fault detection flag for the switching transistor, and its expression is as follows:

[0012] (1)

[0013] In the formula, F=1 indicates that the switching transistor has an open circuit fault; otherwise, it indicates that the system is normal.

[0014] A further technical solution is that the second step involves fault location based on the phase current and the winding neutral point voltage. Taking the open circuit of switch T1 in the 0°~120° range as an example, the analysis is as follows: When the rotor is in the 0°~120° range, the phase current i a =i b =i c =0, combining the phase winding voltage equation and Kirchhoff's voltage law, we can obtain the winding neutral point voltage U under zero current. N-zero dc / 2, where U dc This is the DC bus voltage; when the rotor is in the 120°~240° range, the phase current i b =-i a >0、i c =0; when the rotor is in the 240°~360° range, the phase current i c =-i b >0、i a =0. Therefore, the fault location characteristics of T1 open circuit are: U within the range of 0°~120° N-zero dc / 2, within the 120°~240° range i b >0 and within the 240°~360° range i c >0.

[0015] Using a similar analysis method to T1 open-circuit fault location, the location characteristics under different faults are shown in Table 1.

[0016] Table 1 Fault Location Table

[0017]

[0018] The beneficial technical effects of this invention are:

[0019] This invention discloses a two-step online diagnostic strategy for open-circuit faults in doubly salient pole motor inverters. The inputs to this method are only the phase current, the drive signal of the switching transistor, and the neutral point voltage of the winding under zero current. The output is the location of the faulty transistor. This method does not require changes to the inverter topology, is applicable to different operating conditions, can locate 26 types of open-circuit faults, and the diagnostic time is less than one electrical angle cycle. Attached Figure Description​​

[0020] Figure 1 This is the inverter topology diagram of a dual salient pole motor drive system.

[0021] Figure 2 It shows the inductance curve of a doubly salient pole motor and the switching logic diagram of the switching transistor.

[0022] Figure 3 It is the phase current waveform before and after the switch transistor T1 is opened within the range of 0°~120°.

[0023] Figure 4 This is the circuit diagram with T1 open within the 0°~120° range.

[0024] Figure 5 This is the circuit diagram when T1 and T2 are conducting under normal system operation.

[0025] Figure 6 This is a flowchart of the open-circuit fault diagnosis process for the switching transistor of the present invention. Detailed Implementation

[0026] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings.

[0027] This invention discloses a two-step online diagnostic strategy for open-circuit faults in a doubly salient pole motor inverter. The strategy mainly consists of the following two steps:

[0028] first step:

[0029] like Figure 1 As shown, where i p U is the phase current, and its positive direction is defined as shown by the arrow in the figure; p The voltage across the winding is expressed as follows:

[0030] (2)

[0031] In the formula, L p and L pf These are the self-inductance of the phase winding and the mutual inductance between the phase winding and the excitation winding, i f This is the excitation current. Since the excitation current i f Controlled by a constant current, therefore di in equation (2) f / dt can be approximated as 0, that is, equation (2) can be simplified to:

[0032] (3)

[0033] When the motor is working normally, the switching logic of the transistor within one electrical angle cycle is as follows: Figure 2As shown. It can be observed that the 0°~120°, 120°~240°, and 240°~360° intervals are symmetrical. Therefore, the following analysis will use the 0°~120° interval as an example. The analysis of the other two intervals is similar and can be derived by analogy. When the fault occurs in the 0°~120° interval, taking an open-circuit fault in T1 as an example, as... Figure 3 As shown, after the fault, the phase current drops to 0. According to the current closed-loop effect, the drive signal P1=P2=1, that is, the fault detection characteristic i a =i b =i c =0&P1=P2=1. Based on this, the expression for the fault detection flag F within one electrical angle cycle can be generalized as follows:

[0034] (4)

[0035] In the formula, F=1 indicates that the switching transistor has an open circuit fault; otherwise, it indicates that the system is normal.

[0036] Step Two:

[0037] Taking T1 open circuit as an example, the circuit state after a fault in the 0°~120° range is as follows: Figure 4 As shown, according to Kirchhoff's voltage law and equation (3), we can obtain:

[0038] (5)

[0039] In the formula, U N-zero This is the voltage at the neutral point N of the winding under zero current.

[0040] To further determine the amplitude range of equation (5), the following can be combined with the circuit diagram of T1T2 conducting under normal system operation, such as... Figure 5 As shown. According to Kirchhoff's laws, we can obtain:

[0041] (6)

[0042] Combination formula (3) and Figure 2 We can obtain:

[0043] (7)

[0044] Combining equations (5) and (7), we can obtain U under open circuit T1. N-zero as follows:

[0045] (8)

[0046] When the rotor is in the 120°~240° range, Figure 2It can be seen that T3 and T4 are working within this interval, which means that opening T1 does not affect the circuit state of this interval, that is, i can be detected in this interval. b >0; Similarly, when the rotor is in the 240°~360° range, the current i can be detected. c >0.

[0047] Using a similar analysis method to that for the T1 open-circuit fault described above, the location characteristics of open-circuit faults for different switching transistors are shown in Table 1. It can be seen that this invention can locate 26 types of open-circuit faults. Finally, the diagnostic flowchart of this invention is as follows: Figure 6 As shown, the inputs are only the phase current, the switching transistor drive signal, and the winding neutral point voltage, and the output is the fault location.

[0048] Table 1 Fault Location Table

[0049]

[0050] The above descriptions are merely preferred embodiments of this application, and the present invention is not limited to the above embodiments. It is understood that other improvements and variations directly derived or conceived by those skilled in the art without departing from the spirit and concept of the present invention should be considered to be included within the protection scope of the present invention.

Claims

1. A two-step online diagnostic strategy for open-circuit faults in a doubly salient pole motor inverter, characterized in that: The first step is to detect open-circuit faults in the inverter switching transistors by sampling the phase current and the drive signal of the switching transistors. The second step is to locate the fault based on the phase current and the neutral point voltage of the winding.

2. The method according to claim 1, characterized in that: The first step is to detect open-circuit faults in the inverter switching transistors by sampling the phase current and the drive signal of the switching transistors. Let the currents of phase A, phase B, and phase C be i, respectively. a i b and i c Switch T k The driving signal is P k (k=1, 2, 3, 4, 5, 6), and define P k =1 and P k =0 respectively indicates that the switching transistor T k Turning on and off. When the system is operating normally, the specific analysis is as follows: One electrical angle cycle is divided into three intervals: 0°~120°, 120°~240°, and 240°~360°. When the rotor is in the 0°~120° interval, switching transistors T1 and T2 are working, and the drive signals P1 and P2 change between 0 and 1, with the phase current i... a =-i c >0、i b =0; When the rotor is in the 120°~240° range, switching transistors T3 and T4 operate, and drive signals P3 and P4 vary between 0 and 1, with phase current i b =-i a >0、i c =0; When the rotor is in the 240°~360° range, switching transistors T5 and T6 operate, and drive signals P5 and P6 vary between 0 and 1, with phase current i c =-i b >0、i a =0. When a switching transistor malfunctions, the specific analysis is as follows: When the rotor is in the 0°~120° range, an open circuit in T1 or T2 will prevent the A and C phase windings from forming a circuit with the bus voltage, causing the phase current i to... a =i b =i c =0, according to the current closed-loop effect, the corresponding drive signal P1=P2=1; when the rotor is in the 120°~240° range, the open circuit of T3 or T4 will cause the A and B phase windings to be unable to form a loop with the bus voltage, resulting in the phase current i a =i b =i c =0, according to the current closed-loop effect, the corresponding drive signal P3=P4=1; when the rotor is in the 240°~360° range, the open circuit of T5 or T6 will cause the B and C phase windings to be unable to form a loop with the bus voltage, resulting in the phase current i a =i b =i c =0, according to the current closed-loop effect, the corresponding drive signal P5=P6=1. Based on the above analysis, the phase current and drive signal after a fault can be used as features for fault detection. Therefore, let F be the open-circuit fault detection flag for the switching transistor, and its expression is as follows: （1） In the formula, F=1 indicates that the switching transistor has an open circuit fault; otherwise, it indicates that the system is normal.

3. The method according to claim 1, characterized in that: The second step is to locate the fault based on the phase current and the winding neutral point voltage. Taking the open circuit of switch T1 in the 0°~120° range as an example, the analysis is as follows: When the rotor is in the 0°~120° range, the phase current i a =i b =i c =0, combining the phase winding voltage equation and Kirchhoff's voltage law, we can obtain the winding neutral point voltage U under zero current. N-zero dc / 2, where U dc This is the DC bus voltage; when the rotor is in the 120°~240° range, the phase current i b =-i a >0、i c =0; when the rotor is in the 240°~360° range, the phase current i c =-i b >0、i a =0. Therefore, the fault location characteristics of T1 open circuit are: U within the range of 0°~120° N-zero dc / 2, within the 120°~240° range i b >0 and within the 240°~360° range i c >0.​​ Using a similar analysis method to T1 open-circuit fault location, the location characteristics under different faults are shown in Table 1. Table 1 Fault Location Table

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