Two-step off-line diagnosis strategy for high resistance connection fault of open-winding electrically excited doubly salient motor

Abstract

The application discloses a two-step offline diagnosis strategy for high-resistance connection fault of open-winding electrically excited doubly salient motor, and belongs to the technical field of motor fault monitoring. In the first step, the rotor is positioned at a commutation point by injecting a predetermined positioning pulse; in the second step, based on the characteristics that the self-inductances of two phases at the commutation point are equal, current pulses are injected into the two-phase windings, and the detection and positioning of the high-resistance connection fault are realized according to the difference of response currents. The application fills the blank of the high-resistance connection fault diagnosis technology of the open-winding electrically excited doubly salient motor, is suitable for the initial debugging and regular maintenance of the motor, and can effectively improve the reliability of the motor driving system.

Description

Technical Field

[0001] This invention belongs to the field of motor fault monitoring technology, and in particular to a two-step offline diagnostic strategy for high-resistance connection faults in an open-winding electrically excited doubly salient pole motor. Background Technology

[0002] Open-winding electrically excited doubly salient pole motors combine the advantages of simple structure and high reliability of doubly salient pole motors with the flexible and adjustable magnetic field of the electrically excited method. Furthermore, the open-winding topology allows for independent control of each phase winding, improving the fault tolerance and control freedom of the drive system, making it a promising candidate for applications in fields with high reliability requirements, such as aviation and electric vehicles. However, during actual operation and maintenance, high-resistance connection faults can easily occur at the connection terminals between the windings and the power converter due to long-term vibration, oxidation corrosion, or improper installation. This fault manifests as an abnormally increased equivalent contact resistance at the connection point, but without forming a complete open circuit. High-resistance connection faults can lead to phase current distortion, increased torque ripple, and decreased system efficiency. In severe cases, it can cause localized overheating or even burn out the connector, threatening the safe operation of the motor drive system. Therefore, to improve the reliability of motor drive systems, it is necessary to study high-resistance connection faults in open-winding electrically excited doubly salient pole motors.

[0003] However, there are currently no literature reports on the diagnosis of high-resistance connection faults in open-winding electrically excited doubly salient pole motors. While some common offline detection methods (such as infrared measuring instruments) can detect high-resistance connection faults, they are time-consuming and costly. Furthermore, the self-inductance of open-winding electrically excited doubly salient pole motors exhibits a certain degree of nonlinearity, which makes traditional observer-based methods unsuitable for application.

[0004] In summary, there is currently a lack of a fault diagnosis method for high-resistance connection of open-winding electrically excited doubly salient pole motors that does not rely on motor parameters and has low diagnostic costs. Summary of the Invention

[0005] To address the aforementioned problems and technical requirements, the inventors have proposed a two-step offline diagnostic strategy for high-resistance connection faults in open-winding electrically excited doubly salient pole motors. The technical solution of this invention is as follows:

[0006] A two-step offline diagnostic strategy for high-resistance connection faults in an open-winding electrically excited doubly salient pole motor is characterized by: in the first step, injecting a rotor prepositioning pulse to position the rotor at the commutation point; in the second step, based on the characteristic that the self-inductance of the two phases at the commutation point is equal, injecting current pulses into the two-phase windings, and detecting and locating the high-resistance connection fault based on the difference in response current.

[0007] A further technical solution involves injecting a rotor pre-positioning pulse to position the rotor at the commutation point in the first step. One electrical angle cycle is divided into three intervals: 0°~120°, 120°~240°, and 240°~360°, where 0° (360°), 120°, and 240° are the rotor commutation points. According to the electromagnetic torque expression of an open-winding electrically excited doubly salient pole motor, current flowing through the inductance region generates torque, while current flowing through the inductance region does not generate torque. Based on this, the following example uses the injected rotor pre-positioning pulse A+C- (where A+ represents the conduction of the upper left tube and the lower right tube of phase A, and C- represents the conduction of the lower left tube and the upper right tube of phase C), as shown in Table 1. It can be seen that the injection of the pre-positioning pulse A+C- will position the rotor at 120°. Similar conclusions are drawn for the pre-positioning pulses of the other two energized phases, as shown in Table 2.

[0008] Table 1. Output torque characteristics in each range under rotor prepositioning pulse A+C-injection.

[0009]

[0010] Table 2. Final rotor position under different rotor prepositioning pulse injections

[0011]

[0012] The further technical solution is that, in the second step, based on the characteristic that the self-inductance of the two phases at the commutation point is equal, a current pulse is injected into the two-phase winding, and the high-resistance connection fault is detected and located according to the difference in response current.

[0013] Phase voltage u of an open-winding electrically excited doubly salient pole motor p The expression is as follows:

[0014] (1)

[0015] In the formula, p = a, b, c; R p Let R be the internal resistance of the phase winding, and satisfy R a =R b =R c L p For the self-inductance of the phase winding, L pf The mutual inductance between the phase winding and the excitation winding; i p and i f These are the phase current and the magnetizing current, respectively; R HRC-P R is the resistance value of the P-phase winding with a high-resistance connection fault, under normal system conditions. HRC-P =0, R under P-phase fault HRC ≠0; θ and ω are the rotor position angle and rotor angular velocity, respectively. Combining equation (1), it can be seen that ω and i are the rotor position angle and rotor angular velocity when the motor is stationary.f Both are 0; simultaneously, the self-inductance of the two phases at the commutation point is equal; therefore, by injecting current pulses into the two phase windings with equal self-inductance and judging the relationship of the response currents, the fault location can be detected and located. Taking the rotor at the commutation point of 0° as an example, the DSEM inductance curve shows that L at this time... a =L b By injecting current pulses into the A and B phase windings, the response current relationships are as follows: If i a =i b This indicates that neither phase A nor phase B has experienced a high-resistance connection fault; if i a >i b This indicates that a high-resistance connection fault has occurred in phase A; if i a b This indicates that a high-resistance connection fault has occurred in phase B. Using a similar analysis method, the location characteristics of the high-resistance connection fault are shown in Table 3.

[0016] Table 3. Fault Location Characteristics of High-Resistance Connections

[0017] The beneficial technical effects of this invention are:

[0018] This invention discloses a two-step offline diagnostic strategy for high-resistance connection faults in open-winding electrically excited doubly salient pole motors. The input to this method is only the existing three-phase current information of the system, and the output is the location of the fault. This method requires no additional diagnostic costs, is independent of motor parameters, and is effectively applied to the initial commissioning and periodic maintenance phases of the motor. Attached Figure Description

[0019] Figure 1 This is the inverter topology diagram of an open-winding electrically excited doubly salient pole motor drive system.

[0020] Figure 2 It is the self-inductance curve of an open-winding electrically excited doubly salient pole motor. Detailed Implementation

[0021] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings.

[0022] This invention discloses a two-step offline diagnostic strategy for high-resistance connection faults in an open-winding electrically excited doubly salient pole motor. The strategy mainly consists of the following two steps:

[0023] first step:

[0024] Figure 1 This is the inverter topology diagram for an open-winding electrically excited doubly salient pole motor drive system, where U dc The voltage is the DC bus voltage, and A, B, and C are three-phase windings. p (p=a, b, c) represents the phase current.​ Figure 2 For the self-inductance L of an open-winding electrically excited doubly salient pole motor p The curve has one electrical angle period divided into three intervals: 0°~120°, 120°~240°, and 240°~360°, with 0° (360°), 120°, and 240° representing the rotor commutation points. According to the electromagnetic torque expression for an open-winding electrically excited doubly salient pole motor, current flowing through the inductance region will generate torque, while current flowing through the inductance region will not generate torque. Based on this, the following discussion uses the injected rotor pre-positioning pulse A+C- (where A+ indicates the conduction of the upper tube T on the left side of phase A) as an example. A1 And the lower tube T on the right side of phase A A4 C- indicates that the lower tube T on the left side of phase C is conducting. C2 And the upper tube T on the right side of phase C C3 Taking the example of a rotor, the output torque in different ranges is shown in Table 1. It can be seen that the injection of the prepositioning pulse A+C- will position the rotor at 120°. Similar conclusions are reached for the prepositioning pulses of the other two energized phases, as shown in Table 2.

[0025] Table 1. Output torque characteristics in each range under rotor prepositioning pulse A+C-injection.

[0026]

[0027] Table 2. Final rotor position under different rotor prepositioning pulse injections

[0028]

[0029] Step Two:

[0030] Phase voltage u of an open-winding electrically excited doubly salient pole motor p The expression is as follows:

[0031] (1)

[0032] In the formula, R p Let R be the internal resistance of the phase winding, and satisfy R a =R b =R c L pf The mutual inductance between the phase winding and the excitation winding; i f It is the magnetizing current; R HRC-P R is the resistance value of the P-phase winding with a high-resistance connection fault, under normal system conditions. HRC-P =0, R under P-phase fault HRC ≠0; θ and ω are the rotor position angle and rotor angular velocity, respectively.

[0033] Table 3 shows the self-inductance information at the commutation point during the electrical cycle.

[0034] Table 3 Self-inductance information at the commutation point during the electrical cycle

[0035]

[0036] Taking the rotor at 0° as an example, as shown in Table 3, L a =L b Therefore, by injecting current pulses into the A-phase and B-phase windings, according to Kirchhoff's voltage law, we can obtain:

[0037] (2)

[0038] Combining ω and i when the motor is stationary f Both are 0, and R a =R b L a =L b We can obtain:

[0039] (3)

[0040] The expression for the response current is obtained as follows:

[0041] (4)

[0042] When the system is running normally, R HRC-A =R HRC-B =0, and combining with equation (4), we can see that the response current characteristics are as follows:

[0043] (5)

[0044] When a high-resistance connection fault occurs in phase A, i.e., R HRC-A ≠0、R HRC-B =0, and combining with equation (4), we can see that the response current characteristics are as follows:

[0045] (6)

[0046] When a high-resistance connection fault occurs in phase B, i.e., R HRC-A =0、R HRC-B ≠0, and combining with equation (4), we can see that the response current has the following characteristics:

[0047] (7)

[0048] Therefore, according to the response current i a and i b The magnitude relationship can be used to locate the location of high-resistance connection faults. Using a similar analysis method, the location characteristics of high-resistance connection faults in motors are shown in Table 4.

[0049] Table 4. Fault Location Characteristics of High-Resistance Connections

[0050]

[0051] 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 offline diagnostic strategy for high-resistance connection faults in an open-winding electrically excited doubly salient pole motor, characterized in that: In the first step, the rotor is positioned at the commutation point by injecting a rotor prepositioning pulse; in the second step, based on the characteristic that the self-inductance of the two phases at the commutation point is equal, a current pulse is injected into the two-phase winding, and the high-resistance connection fault is detected and located according to the difference in response current.

2. The method according to claim 1, characterized in that: In the first step, the rotor is positioned at the commutation point by injecting a rotor prepositioning pulse. One electrical angle cycle is divided into three intervals: 0°~120°, 120°~240°, and 240°~360°, where 0° (360°), 120°, and 240° are the rotor commutation points. According to the electromagnetic torque expression of an open-winding electrically excited doubly salient pole motor, current flowing through the region of changing inductance will generate torque, while current flowing through the region of constant inductance will not generate torque. Based on this, the following example uses the injected rotor prepositioning pulse A+C- (where A+ represents the conduction of the upper left tube and the lower right tube of phase A, and C- represents the conduction of the lower left tube and the upper right tube of phase C) as shown in Table 1. It can be seen that the injection of the prepositioning pulse A+C- will position the rotor at 120°. Similar conclusions are drawn for the prepositioning pulses of the other two energized phases, as shown in Table 2. Table 1. Output torque characteristics in each range under rotor prepositioning pulse A+C-injection. Table 2. Final rotor position under different rotor prepositioning pulse injections 3. The method according to claim 1, characterized in that: In the second step, based on the characteristic that the self-inductance of the two phases is equal at the commutation point, a current pulse is injected into the two-phase winding, and the high-resistance connection fault is detected and located according to the difference in response current. Phase voltage u of an open-winding electrically excited doubly salient pole motor p The expression is as follows: (1) In the formula, p = a, b, c; R p Let R be the internal resistance of the phase winding, and satisfy R a =R b =R c L p For the self-inductance of the phase winding, L pf The mutual inductance between the phase winding and the excitation winding; i p and i f These are the phase current and the magnetizing current, respectively; R HRC-P R is the resistance value of the P-phase winding with a high-resistance connection fault, under normal system conditions. HRC-P =0, R under P-phase fault HRC ≠0; θ and ω are the rotor position angle and rotor angular velocity, respectively. Combining equation (1), it can be seen that ω and i are the rotor position angle and rotor angular velocity when the motor is stationary. f Both are 0; at the same time, the self-inductance of the two phases at the commutation point is equal. Therefore, by injecting current pulses into two-phase windings with equal self-inductance and determining the relationship of the response currents, the fault location can be detected and pinpointed. Taking the rotor at the commutation point of 0° as an example, the DSEM inductance curve shows that L at this point... a =L b By injecting current pulses into the A and B phase windings, the response current relationships are as follows: If i a =i b This indicates that neither phase A nor phase B has experienced a high-resistance connection fault; if i a >i b This indicates that a high-resistance connection fault has occurred in phase A; if i a b This indicates that a high-resistance connection fault has occurred in phase B. Using a similar analysis method, the location characteristics of the high-resistance connection fault are shown in Table 3.​ Table 3. Fault Location Characteristics of High-Resistance Connections

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