Inter-turn fault diagnosis method for high-speed permanent magnet motors based on the third harmonic of back EMF

Abstract

This invention discloses a method for diagnosing inter-turn faults in high-speed permanent magnet motors based on the third harmonic of back electromotive force (EMF), relating to the field of motor control technology. High-speed permanent magnet motors can be diagnosed online using their voltage and back EMF information. When a permanent magnet synchronous motor (PMSM) operates in a healthy state, the third harmonic content in the back EMF is low and the three phases are symmetrical. However, when an inter-turn short-circuit fault occurs in the PMSM, the three-phase windings are no longer symmetrical, and an asymmetrical third harmonic component is introduced into the back EMF. The method diagnoses inter-turn short-circuit faults by estimating the back EMF of the PMSM in real time and based on the difference in the amplitude of the third harmonic in the three-phase back EMF. This method only requires adding a back EMF estimation algorithm and a third harmonic extraction algorithm to the motor control software to complete the diagnosis of inter-turn faults, without increasing hardware costs.

Description

Technical Field

[0001] This invention relates to the field of motor control technology, and in particular to a method for diagnosing inter-turn faults in high-speed permanent magnet motors based on the third harmonic of back EMF. Background Technology

[0002] With the widespread application of high-speed permanent magnet motors in aerospace and other applications requiring high reliability, fault diagnosis of permanent magnet synchronous motors has attracted considerable attention from researchers. Faults in permanent magnet synchronous motors can be mainly categorized into winding faults, permanent magnet faults, and rotor faults. Among these, inter-turn winding faults have a high failure rate and pose a significant threat; therefore, diagnosing inter-turn winding faults in permanent magnet synchronous motors is of great importance.

[0003] Currently, most methods for diagnosing inter-turn faults in permanent magnet synchronous motor windings rely on detecting voltage or current. However, these methods are susceptible to transient processes, leading to misdiagnosis and affecting the normal operation of the permanent magnet synchronous motor drive system. Furthermore, because inter-turn short-circuit currents are affected by motor load and operating speed, fault characteristics are less obvious when the motor is running at low load and low speed, potentially causing missed diagnoses with conventional methods. To improve the robustness of fault diagnosis methods and achieve reliable diagnosis of inter-turn faults, it is necessary to conduct in-depth research on fault diagnosis methods covering the entire motor operating cycle. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a method for diagnosing inter-turn faults of high-speed permanent magnet motors based on the third harmonic of back EMF. The present invention does not require additional hardware costs, and the method can be used to diagnose inter-turn faults of permanent magnet synchronous motors. Moreover, the diagnosis method is simple and reliable.

[0005] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0006] A method for diagnosing inter-turn faults in a high-speed permanent magnet motor based on the third harmonic of back electromotive force, according to the present invention, includes the following steps:

[0007] Real-time estimation of the three-phase back EMF of a permanent magnet synchronous motor;

[0008] The difference between the third harmonic amplitudes of the three back electromotive forces yields ε. ab ε bc ε ca ; where ε ab ε is the difference in the amplitude of the third harmonic of the opposite potentials of a and b. bc ε is the difference in the amplitude of the third harmonic of the opposite potentials of b and c. ca The difference between the amplitudes of the third harmonics of the opposite potentials of c and a;

[0009] Define the maximum value e of the third harmonic amplitude of the three back electromotive forces. max and minimum value e min e max =max{ε ab ε bc ε ca}、e min =min{ε ab ε bc ε ca}; If e max -e min If ≥ε, where ε is the threshold for fault diagnosis, then the motor has an inter-turn short circuit fault.

[0010] As a further optimization of the inter-turn fault diagnosis method for high-speed permanent magnet motors based on the third harmonic of back EMF described in this invention, the specific steps for estimating the three back EMFs of the permanent magnet synchronous motor are as follows:

[0011] Step 1: Obtain the three-phase current i a i b i c and the control voltage u output by the current loop controller d * and u q * ; where i a i b i c These are the currents of phase a, phase b, and phase c, respectively. d * u q * These are the d-axis control voltage and the q-axis control voltage, respectively.

[0012] Step 2: Convert the three-phase current i according to the Park transformation. a i b i c Transform to the dq axis coordinate system to obtain i d i q ; where i d i q These are the d-axis current and the q-axis current, respectively.

[0013] Step 3, based on i d i q and u d * u q * The back potential e is observed using a sliding membrane observer. d e q ; where e d e q These are the d-axis back EMF and the q-axis back EMF, respectively.

[0014] Step 4: Convert the observed back potential e using the inverse Park transform. d e q Transforming to a three-phase coordinate system, we obtain the three-phase back electromotive force e. a e b e c ; where e a e b e c The opposite potentials are a, b, and c, respectively.

[0015] As a further optimization of the high-speed permanent magnet motor inter-turn fault diagnosis method based on the third harmonic of back EMF described in this invention, step 3 involves observing the back EMF e using a sliding diaphragm observer. d e q The details are as follows:

[0016] Step 3.1: Based on the voltage equation, the state equation for the current is expressed as follows:

[0017]

[0018] In this context, both A and B are intermediate variables.

[0019]

[0020] Among them, R s L is the phase resistance. d For the d-axis inductance, ω e L is the electric angular velocity. q It is the q-axis inductance;

[0021] Step 3.2: Design the synovial membrane observer as follows:

[0022]

[0023] in, These are the observed values ​​of the d-axis current and the q-axis current, respectively; u d u q These are the control inputs for the d-axis observer and the q-axis observer, respectively. d v q These are the observed d-axis back EMF and q-axis back EMF, respectively.

[0024] Step 3.3: Subtract formula (1) from formula (2) to get:

[0025]

[0026] in, The observation error of the d-axis and q-axis currents;

[0027] Step 3.4: Design the slippage control rate as follows:

[0028]

[0029] Where k is a coefficient;

[0030] When the observer's state variable reaches the sliding surface Afterwards, the observer will remain on the sliding surface, and the control quantity at this time is considered as the equivalent control quantity, thus obtaining...

[0031]

[0032] in,[*] eq (*) eq This indicates that when the observer's state variable reaches the sliding surface... Then, the corresponding variable values.

[0033] As a further optimization of the high-speed permanent magnet motor inter-turn fault diagnosis method based on the third harmonic of back EMF described in this invention, the third harmonic amplitudes of the three back EMFs are a, b, and c, and the third harmonic amplitude E of the back EMFs is... a3 E b3 E c3 ;

[0034]

[0035]

[0036]

[0037] Where, θ a θ b θ c The initial phases of phases a, b, and c are respectively, E a Let E be the magnitude of the opposite potential of a. b E is the magnitude of the opposite potential of b. c Let c be the magnitude of the opposite potential.

[0038] As a further optimization of the inter-turn fault diagnosis method for high-speed permanent magnet motors based on the third harmonic of back EMF described in this invention, the amplitude E of the third harmonic of the three-phase back EMF is obtained. p3 The method is as follows, where variables p = a, b, c:

[0039] Step A: Convert the three back potentials e p Multiplying by sin3θ and cos3θ respectively, we get:

[0040]

[0041] Where θ is the rotor position, θp For the initial phase of phase p, E p Let p be the magnitude of the opposite potential.

[0042] Step B: Find e p sin3θ and e p The average value of cos3θ over one period is given by the fact that the average value of the sixth harmonic component over one period is zero, thus the DC component is obtained as follows: and

[0043] Step C: The obtained DC component and Find the root mean square value, sum the results, and multiply by 2 to obtain the third harmonic amplitude E of the back electromotive force of phase p. p3 :

[0044]

[0045] This is a further optimization of the inter-turn fault diagnosis method for high-speed permanent magnet motors based on the third harmonic of back EMF described in this invention.

[0046] ε ab ε bc ε ca They are respectively:

[0047] Compared with the prior art, the present invention, employing the above technical solution, has the following technical effects:

[0048] (1) This invention diagnoses inter-turn short circuit faults by estimating the back EMF of a permanent magnet synchronous motor in real time and by considering the difference in the amplitude of the third harmonic in the three back EMFs.

[0049] (2) This method only requires adding back EMF estimation algorithm and third harmonic extraction algorithm to the motor control software to complete the diagnosis of inter-turn faults without increasing hardware costs.

[0050] (3) The diagnostic method of the present invention is simple, reliable and robust. Attached Figure Description

[0051] Figure 1 This is a flowchart of the fault diagnosis method.

[0052] Figure 2 This is a block diagram of the dual closed-loop control of a permanent magnet synchronous motor.

[0053] Figure 3 This is a cross-sectional view of a permanent magnet synchronous motor. Detailed Implementation

[0054] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0055] The fault diagnosis process of this invention is as follows: Figure 1 As shown, the permanent magnet synchronous motor being targeted is as follows: Figure 2 As shown, the control strategy used by the permanent magnet synchronous motor is as follows: Figure 3 As shown.

[0056] The specific implementation steps of this invention are as follows:

[0057] A method for diagnosing inter-turn short-circuit faults in high-speed permanent magnet motors based on the third harmonic of back EMF includes the following steps:

[0058] When a permanent magnet synchronous motor is running healthily, the third harmonic content in the back EMF is low and the three phases are symmetrical. However, when an inter-turn short-circuit fault occurs in the permanent magnet synchronous motor, the three-phase windings are no longer symmetrical, and an asymmetrical third harmonic component is introduced into the back EMF. Therefore, the inter-turn fault can be diagnosed based on the third harmonic of the three-phase back EMF, including the following steps:

[0059] Step 1.1: Obtain the three-phase current i a i b i c and the control voltage u output by the current loop controller d * and u q * ;

[0060] Step 1.2: Convert the three-phase current i according to the Park transformation. a i b i c Transform to dq axis coordinate system i d i q ;

[0061] Step 1.3: Based on i d i q and u d * u q * The back potential e is observed using a sliding membrane observer. d e q ;

[0062] Step 1.4: Convert the observed back potential e using the inverse Park transform. d e q Transform to three-phase coordinate system e a e b e c ;

[0063] Step 1.5: Extract the three-phase back potential e a e b e c The third harmonic amplitude E a3 E b3 E c3 ;

[0064] Step 1.6: Divide the amplitude of the third harmonic of the three back EMFs, and determine the inter-turn fault based on the amplitude difference of the third harmonic of the three back EMFs.

[0065] Step 1.3 describes the observation of the back potential e using a sliding diaphragm observer. d e q It includes the following steps:

[0066] Step 1.3.1: Based on the voltage equation, the state equation for the current can be obtained as follows:

[0067]

[0068] in:

[0069]

[0070] Step 1.3.2: Design the synovial membrane observer as follows:

[0071]

[0072] in: The observed value of the current; u d u q It is the control input of the observer.

[0073] Step 1.3.3: Subtracting the above equation, we get:

[0074]

[0075] in

[0076] Step 1.3.4: Design the sliding control rate as follows:

[0077]

[0078] When the observer's state variable reaches the sliding surface Afterwards, the observer will remain on the sliding surface, and the control quantity at this time can be regarded as the equivalent control quantity, which can be obtained.

[0079]

[0080] Step 1.5 Obtain the third harmonic amplitude E of the three back electromotive forces. p3The method is as follows, where variables p = a, b, c:

[0081] Step A: Convert the three back potentials e p Multiplying by sin3θ and cos3θ respectively, we get:

[0082]

[0083] Where θ is the rotor position, θ p For the initial phase of phase p, E p Let p be the magnitude of the opposite potential.

[0084] Step B: Find e p sin3θ and e p The average value of cos3θ over one period is given by the fact that the average value of the sixth harmonic component over one period is zero, thus the DC component is obtained as follows: and

[0085] Step C: The obtained DC component and Find the root mean square value, sum the results, and multiply by 2 to obtain the third harmonic amplitude E of the back electromotive force of phase p. p3 :

[0086]

[0087] Step 1.6, which involves subtracting the third harmonic amplitudes of the three back EMFs and diagnosing inter-turn faults based on these differences, includes the following steps:

[0088] Step 1.6.1: Define the amplitude difference of the third harmonic of the three back potentials as ε ab ε bc ε ca :

[0089]

[0090] Step 1.6.2: Define the maximum and minimum values ​​of the third harmonic amplitude of the three-phase back electromotive force as e max =max{ε ab ε bc ε ca}、e min =min{ε ab ε bc ε ca}; If e max -e min If e < ε, the permanent magnet synchronous motor will operate normally; if e < ε < ε, the permanent magnet synchronous motor will operate normally. max -e min If ≥ε, where ε is the threshold for fault diagnosis, then the motor has an inter-turn short circuit fault.

[0091] By following the steps above, the inter-turn faults in the windings of a permanent magnet synchronous motor can be diagnosed without adding any testing equipment.

[0092] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for diagnosing turn-to-turn fault of high-speed permanent magnet motor based on back EMF third harmonic, characterized in that, Includes the following steps: Real-time estimation of the three-phase back EMF of a permanent magnet synchronous motor; The difference between the third harmonic amplitudes of the three-phase counter electromotive force is obtained respectively , , ; wherein, is the difference between the third harmonic amplitudes of the counter electromotive forces of phases a and b, is the difference between the third harmonic amplitudes of the counter electromotive forces of phases b and c, is the difference between the third harmonic amplitudes of the counter electromotive forces of phases c and a; Define the maximum value of the third harmonic amplitude of the three back electromotive forces. and minimum value They are respectively ;like , If the threshold for fault diagnosis is set, then the motor will experience an inter-turn short circuit fault. The specific steps for estimating the three back EMFs of a permanent magnet synchronous motor are as follows: Step 1: Obtain the three-phase current , , and the control voltage output by the current loop controller and ;in, , , These are the currents of phase a, phase b, and phase c, respectively. , These are the d-axis control voltage and the q-axis control voltage, respectively. Step 2: Convert the three-phase current according to the Park transformation. , , Switch to Axis coordinate system obtained , ;in, , These are the d-axis current and the q-axis current, respectively. Step 3, according to , and Observing the back potential using a synovial observer , ;in, , These are the d-axis back EMF and the q-axis back EMF, respectively. Step 4: Calculate the observed back potential using the inverse Park transform. , Transforming to a three-phase coordinate system, we obtain the three-phase back electromotive forces. , , ;in, , , The opposite potentials are a, b, and c, respectively. In step 3, the back potential is observed using a synovial observer. , The details are as follows: Step 3.1: Based on the voltage equation, the state equation for the current is expressed as follows: （1）； In this context, both A and B are intermediate variables. ; in, For phase resistance, For d-axis inductance, Electric angular velocity, It is the q-axis inductance; Step 3.2: Design the synovial membrane observer as follows: (2); in, , These are the observed values ​​of the d-axis current and the q-axis current, respectively. , These are the control inputs for the d-axis observer and the q-axis observer, respectively. , These are the observed d-axis back EMF and q-axis back EMF, respectively. Step 3.3: Subtract formula (1) from formula (2) to get: ； in, , , , The observation error of the d-axis and q-axis currents; Step 3.4: Design the slippage control rate as follows: ； Where k is a coefficient; When the observer's state variable reaches the sliding surface , Afterwards, the observer will remain on the sliding surface, and the control quantity at this time is considered as the equivalent control quantity, thus obtaining... ； in, , This indicates that when the observer's state variable reaches the sliding surface... , Then, the corresponding variable values.

2. The method for diagnosing inter-turn faults in a high-speed permanent magnet motor based on the third harmonic of back EMF as described in claim 1, characterized in that, The third harmonic amplitudes of the three back electromotive forces are a, b, and c. , , ; ； ； ； in, , , These are the initial phases of phases a, b, and c, respectively. Let a be the magnitude of the opposite potential. Let b be the magnitude of the opposite potential. Let c be the magnitude of the opposite potential.

3. The method for diagnosing inter-turn faults in a high-speed permanent magnet motor based on the third harmonic of back EMF as described in claim 2, characterized in that, Obtain the third harmonic amplitude of the three back electromotive forces The method is as follows, where the variable : Step A: Convert the three back potentials Multiply by and get: ； in, For rotor position, This is the initial phase of phase p. Let p be the magnitude of the opposite potential. Step B: Find and The average value over one period is obtained because the average value of the sixth harmonic component over one period is zero, thus yielding the DC component as follows: and ; Step C: The obtained DC component and Find the root mean square value, sum the results, and multiply by 2 to get the result. The third harmonic amplitude of the phase back electromotive force : 。 4. The method for diagnosing inter-turn faults in a high-speed permanent magnet motor based on the third harmonic of back EMF according to claim 2, characterized in that, , , They are respectively: .

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