Open-circuit fault diagnosis method for permanent magnet synchronous motor inverter based on current vector

Abstract

The present invention provides a current vector-based open-circuit fault diagnosis method for a permanent magnet synchronous motor inverter, belonging to the technical field of motor fault diagnosis. The method is applicable to a two-level voltage source inverter; it is implemented by three steps: the first step is to use the Lagrange interpolation method to predict the current in the two-phase rotating coordinate system and monitor the actual current value at the same time; the second step is to determine whether a switch tube fault has occurred based on the residual difference between the actual current and the predicted current. This fault judgment method is independent of the load and still has high diagnostic accuracy under sudden load conditions; the third step is to locate the fault. By separating the current vectors of the three-phase current, the fault of each phase current is calculated and located, which can simplify the fault location method and quickly determine the location of the fault. Fault diagnosis performed by the above method greatly improves the accuracy of diagnosis and can reduce diagnosis time.

Description

Technical Field

[0001] The present invention belongs to the technical field of motor fault diagnosis, and in particular relates to a current vector-based open-circuit fault diagnosis method for a permanent magnet synchronous motor inverter. Background Art

[0002] Permanent magnet synchronous motors (PMSMs) boast lightweight construction, high reliability, and high power density, making them widely applicable in electric vehicles, renewable energy generation, and aerospace. The inverters used with PMSMs contain numerous semiconductor devices, many of which operate in a high-frequency switching state for extended periods. This can lead to malfunctions and failures over time. Open-circuit failures in power devices are the most common type of failure and have the greatest impact on the entire drive system. To effectively and quickly locate the fault point in the drive system, inverter open-circuit fault diagnosis has become a research hotspot in the field of PMSM fault diagnosis.

[0003] Current is an important basic parameter of a motor drive system and can reflect the operating status and health of the motor drive system. Permanent magnet synchronous motor inverters can achieve motor current conversion, so the inverter operating status can be obtained from the current of each phase.

[0004] Fault diagnosis methods based on current prediction are currently widely used. Current vectors offer a more intuitive approach, quickly reflecting the operating status of motor drive systems. However, many current prediction methods rely on motor models, resulting in prediction accuracy that depends on the accuracy of motor parameters. Furthermore, diagnostic methods relying solely on current vectors are slow and cannot accurately reflect the health of the drive system. Summary of the Invention

[0005] The purpose of the present invention is to solve the problems of slow speed and low fault location accuracy in the existing inverter fault diagnosis using current vector, and to provide a permanent magnet synchronous motor inverter open circuit fault diagnosis method based on current vector.

[0006] To achieve the above objectives, the technical solutions provided by the present invention are:

[0007] A method for diagnosing open-circuit faults of a permanent magnet synchronous motor inverter based on current vector is provided, comprising the following steps:

[0008] Step 1: Use the Lagrange prediction method to predict the d-axis current value and q-axis current value of the permanent magnet synchronous motor in the two-phase rotating coordinate system to obtain the d-axis current prediction value at the current time k and the predicted q-axis current ; and monitor the d-axis current value at the same time in real time and q-axis current value ;

[0009] Step 2: Based on the predicted value of the d-axis current at time k obtained in step 1 and the predicted q-axis current And the d-axis current value at the same time and q-axis current value , determine whether an inverter open circuit fault occurs. If an inverter open circuit fault occurs, proceed to step 3 and save the time when the fault occurs. If no inverter open circuit fault occurs, return to step 1 and proceed to the next moment processing;

[0010] Step 3: If an inverter open-circuit fault occurs at time k, the following judgment is performed on each phase current of the permanent magnet synchronous motor to locate the fault:

[0011] Step 3.1: Based on the phase current angle at the moment before the fault occurs and the current value of the phase , according to the formula

[0012]

[0013] Calculate and save the phase current amplitude ;

[0014] Step 3.2: Construct the current vector of the phase current and use the phase current value as the horizontal coordinate value of the rectangular coordinate system , the phase current value after 1 / 4 cycle delay is used as the vertical axis value :

[0015]

[0016]

[0017] in is the phase current angle at the time of fault occurrence;

[0018] Step 3.3: Based on the horizontal coordinate value of the phase current obtained in step 3.2 , vertical coordinate value , construct the space vector of the phase current :

[0019]

[0020] in The unit space vector representing the ordinate direction, Represents the angle of the phase current space vector;

[0021] Step 3.4: Taking the time k at which the fault occurs as the starting point, calculate the space vector of the phase current within the time t0. The fault current area enclosed by the coordinate axes in the rectangular coordinate system , and according to the current amplitude Calculate the healthy current area of ​​the inverter at the healthy moment :

[0022]

[0023]

[0024] Step 3.5: Calculate the fault current area for this phase current and healthy current area Ratio , determine whether the upper switch or the lower switch of the phase is faulty according to the following logic:

[0025] If the ratio Less than or equal to the set current ratio threshold, and each phase current angle If the ratio is between [0,π), it is determined that the switch on this phase is faulty; if the ratio is between [0,π], it is determined that the switch on this phase is faulty. Less than or equal to the set current ratio threshold, and the phase current angle If the ratio is between [π, 2π), it is determined that the switch tube in this phase is faulty; if the ratio is between [π, 2π], it is determined that the switch tube in this phase is faulty. If the current ratio is greater than the set current ratio threshold, the process returns to step 1 to perform diagnosis on the next current cycle.

[0026] Furthermore, in step 1, the predicted value of the d-axis current at the current k moment is and the predicted q-axis current for:

[0027]

[0028]

[0029] in 、 、 Respectively represent the 、 、 The d-axis current value at the moment, 、 、 Respectively represent the 、 、 The q-axis current value at the moment.

[0030] Furthermore, the process of obtaining the d-axis current value and the q-axis current value in step 1 is as follows:

[0031] Step 1.1: Measure the three-phase current value of the permanent magnet synchronous motor at the current moment 、 、 ;

[0032] Step 1.2: According to the formula

[0033] [ i α i β ] = [ 1 0 0 1 3 2 3 0 ] [ i A i B i C ]

[0034] The three-phase current values ​​in the three-phase stationary coordinate system 、 、 Converted to the α-axis current value in the two-phase stationary coordinate system , β-axis current value ;

[0035] According to the formula

[0036] [ i d i q ] = [ cos θ sin θ − sin θ cos θ ] [ i α i β ]

[0037] The α-axis current value in the two-phase stationary coordinate system , β-axis current value Converted to the d-axis current value in the two-phase rotating coordinate system , q-axis current value ,in Indicates the electrical angle of the permanent magnet synchronous motor rotor.

[0038] Furthermore, in step 2, for the kth moment, the d-axis current prediction value obtained in step 1.3 is , q-axis current prediction value The actual d-axis current value at the same time , q-axis current value For comparison; if the d-axis current prediction value and the actual d-axis current value The difference between the two, and the predicted value of the q-axis current and the actual q-axis current value If any difference between the current difference and the inverter difference is greater than or equal to the set current difference threshold, it is determined that an inverter open circuit fault occurs; otherwise, the inverter is determined to be normal, and the process returns to step 1 to continue measuring.

[0039] Furthermore, in step 2, the current difference threshold is set to 23.

[0040] Furthermore, in step 3.5, the current ratio threshold is set to 0.8.

[0041] The advantages of the present invention are:

[0042] The open-circuit fault diagnosis method for a permanent magnet synchronous motor inverter designed in the present invention is applicable to two-level power supply inverters. It predicts the current in a two-phase rotating coordinate system as a reference for whether a fault has occurred. It separates the current vectors of the three-phase stator windings of the permanent magnet synchronous motor to construct a current vector for each phase current. The fault current vector area is compared with the healthy vector area to serve as a reference value for fault point location. This not only simplifies the fault location method and speeds up the fault location time, but also improves the accuracy of fault location. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] The features and advantages of the present invention will become more readily understood with reference to the following description of the accompanying drawings, which are not drawn to scale and in which some features are exaggerated or minimized to show details of particular components:

[0044] Figure 1 is a topology diagram of a two-level voltage source inverter according to an embodiment of the present invention;

[0045] Figure 2 1 is a schematic diagram of the principle structure of the open circuit fault diagnosis of the permanent magnet synchronous motor inverter in an embodiment of the present invention;

[0046] Figure 3 is a flow chart of a method for diagnosing an open-circuit fault of a permanent magnet synchronous motor inverter according to the present invention;

[0047] Figure 4 1 is a simulation verification result diagram of the maximum rated speed change in an embodiment of the present invention;

[0048] Figure 5 1 is a simulation verification result diagram of the maximum rated torque change in an embodiment of the present invention;

[0049] Figure 6 It is a simulation verification result diagram of fault diagnosis and location in an embodiment of the present invention. DETAILED DESCRIPTION

[0050] The present invention will be described in detail below with reference to the accompanying drawings by means of exemplary embodiments of the present invention. It should be noted that the following detailed description of the present invention is only for the purpose of illustration and is not intended to limit the present invention.

[0051] The present invention provides a method for diagnosing open-circuit faults of permanent magnet synchronous motor inverters based on current vectors, which is used to judge and locate open-circuit faults of permanent magnet synchronous motor inverters. The diagnostic process is as follows: Figure 3 As shown, the following steps are included:

[0052] Step 1: In order to detect whether the permanent magnet synchronous motor is working in a healthy state, the Lagrange prediction method is used to predict the d-axis current value and q-axis current value of the permanent magnet synchronous motor in the two-phase rotating coordinate system to obtain the d-axis current prediction value at the current time k and the predicted q-axis current ; and monitor the d-axis current value at the same time in real time and q-axis current value The specific process includes the following:

[0053] Step 1.1: Measure the three-phase current value of the permanent magnet synchronous motor at the current moment 、 、 ;

[0054] Step 1.2: Substitute the three-phase current values ​​obtained in step 1.1 、 、 Perform coordinate transformation to obtain the d-axis current value in the two-phase rotating coordinate system , q-axis current value ;

[0055] Step 1.3: Use the Lagrangian prediction method to calculate the d-axis current value obtained in step 1.2. , q-axis current value Make a prediction and get the predicted value of the d-axis current at the next moment , q-axis current prediction value .

[0056] Among them, in step 1.2: first use the following formula to convert the three-phase current value in the three-phase stationary coordinate system 、 、 Converted to the α-axis current value in the two-phase stationary coordinate system , β-axis current value :

[0057] [ i α i β ] = [ 1 0 0 1 3 2 3 0 ] [ i A i B i C ]

[0058] Then use the following formula to convert the α-axis current value in the two-phase stationary coordinate system into , β-axis current value Converted to the d-axis current value in the two-phase rotating coordinate system , q-axis current value :

[0059] [ i d i q ] = [ cos θ sin θ − sin θ cos θ ] [ i α i β ]

[0060] in, Indicates the electrical angle of the permanent magnet synchronous motor rotor.

[0061] Through the above two coordinate transformations, the three-phase current values 、 、 Converted into two-phase rotating d-axis current value , q-axis current value , the transformed d-axis current value , q-axis current value Contains three-phase current values 、 、 All the information of the ,reduce the amount of calculation in subsequent predictions.

[0062] Through the above process, the three-phase current value of the permanent magnet synchronous motor can be 、 、 Calculate the d-axis current value at each moment and q-axis current value .

[0063] The predicted value of the d-axis current at the current k moment is obtained and the predicted q-axis current The process is:

[0064] The predicted current value at the current moment is obtained by predicting the current value at the previous moment. For the predicted current at the kth moment, The expression is:

[0065] i k p = A [ k − ( k − 1 )][ k − ( k − 2 )] + B [ k − ( k − 2 )][ k − ( k − 3 )] + C [ k − ( k − 1 )][ k − ( k − 3 )]

[0066] Among them, the specific values ​​of A, B, and C are: , , , 、 、 Corresponding to the 、 、 The current value at the moment, the values ​​of A, B, and C are brought into the predicted current In the expression of , we get:

[0067] i k p = i k − 1 [ k − ( k − 2 )][ k − ( k − 3 )] 2 − i k − 2 [ k − ( k − 1 )][ k − ( k − 3 )] + i k − 3 [ k − ( k − 1 )][ k − ( k − 2 )] 2

[0068] Simplify to get the predicted current The expression is as follows:

[0069]

[0070] Based on the above method, the predicted value of the d-axis current at the kth moment can be calculated respectively and the predicted q-axis current :

[0071]

[0072]

[0073] in 、 、 Respectively represent the 、 、 The d-axis current value at the moment, 、 、 Respectively represent the 、 、 The q-axis current value at the moment.

[0074] Step 2: Based on the predicted value of the d-axis current at time k obtained in step 1 and the predicted q-axis current And the d-axis current value at the same time and q-axis current value , determine whether an inverter open circuit fault occurs. If an inverter open circuit fault occurs, go to step 3 and save the time when the fault occurs. If no inverter open circuit fault occurs, return to step 1 and proceed to the next moment. The specific process is:

[0075] For the kth moment, the predicted d-axis current value obtained in step 1.3 is , q-axis current prediction value The actual d-axis current value at the same time , q-axis current value For comparison; if the d-axis current prediction value The actual d-axis current value The difference between the q-axis current and the predicted value and q-axis current value If one of the differences is greater than or equal to the set current difference threshold, it is determined that an inverter open circuit fault has occurred; otherwise, the inverter is determined to be normal and the process returns to step 1 for further measurement. In this embodiment, the current difference threshold is 23.

[0076] When an open-circuit fault occurs in the inverter, the current in the three-phase stator windings of the permanent magnet synchronous motor will show abnormal values. By performing coordinate transformation on the three-phase current, the current in the two-phase rotating coordinate system is obtained. The transformed current is then predicted using the Lagrange interpolation method. The residual difference between the actual current value and the predicted current value is then used to determine whether a switch failure has occurred. This fault diagnosis method is independent of the load, not only reducing the computational effort but also maintaining high diagnostic accuracy even under sudden load changes.

[0077] Step 3: If an inverter open-circuit fault occurs at time k, the following judgment is performed on each phase current of the permanent magnet synchronous motor to locate the fault:

[0078] Step 3.1: Based on the phase current angle at the moment before the fault occurs and the current value of the phase , according to the formula

[0079]

[0080] Calculate and save the phase current amplitude .

[0081] To simplify calculations, it is generally assumed that the starting angle of the A-phase current is 0°, the starting angle of the B-phase current is 120°, and the starting angle of the C-phase current is -120°.

[0082] Step 3.2: Construct the current vector of the phase current, and in order to obtain the position of the current vector in the rectangular coordinate system, expand the current value of the phase into horizontal and vertical coordinate values, where the phase current value is used as the horizontal coordinate value , the phase current value after 1 / 4 cycle delay is used as the vertical axis value :

[0083]

[0084]

[0085] in is the phase current angle at the time of fault occurrence.

[0086] Step 3.3: Based on the horizontal coordinate value of the phase current obtained in step 3.2 , vertical coordinate value , construct the space vector of the phase current :

[0087]

[0088] in The unit space vector representing the ordinate direction, Represents the angle of the phase current space vector.

[0089] Step 3.4: Taking the time k at which the fault occurs as the starting point, calculate the space vector of the phase current within the time t0. The fault current area enclosed by the coordinate axes in the rectangular coordinate system , and according to the current amplitude Calculate the healthy current area of ​​the inverter at the healthy moment :

[0090]

[0091]

[0092] In this embodiment, t0 is selected as 5% of the current cycle.

[0093] Step 3.5: Calculate the fault current area for this phase current and healthy current area Ratio , determine whether the upper switch or the lower switch of the phase is faulty according to the following logic:

[0094] If the ratio Less than or equal to the set current ratio threshold, and the phase current angle If the ratio is between [0,π), it is determined that the switch on this phase is faulty; if the ratio is between [0,π], it is determined that the switch on this phase is faulty. Less than or equal to the set current ratio threshold, and the phase current angle If the ratio is between [π, 2π), it is determined that the switch tube in this phase is faulty; if the ratio is between [π, 2π], it is determined that the switch tube in this phase is faulty. If the current ratio is greater than the set threshold, it means that the inverter fault occurred too late and cannot be located. It is necessary to perform another diagnosis in the next current cycle to determine the location of the inverter fault. In this embodiment, the current ratio threshold is selected as 0.8.

[0095] Next, we take a three-phase four-pole permanent magnet synchronous motor as an example, and use a two-level voltage source inverter to form a motor drive system for experiment. The topology of the two-level voltage source inverter is shown in the figure below. Figure 1 As shown, the principle structure of the fault diagnosis system is as follows Figure 2 shown.

[0096] Figure 4 In order to verify that the method proposed in this embodiment can effectively avoid misdiagnosis experiments when the reference speed of the permanent magnet synchronous motor suddenly changes, the reference speed is changed to 150 rpm after the speed of the permanent magnet synchronous motor stabilizes at 15000 rpm. The experimental waveforms show that neither of the two fault diagnosis variables exceeds the current difference threshold.

[0097] Figure 5 In order to verify that the method proposed in this embodiment can effectively avoid misdiagnosis experiments in the case of sudden load changes in the permanent magnet synchronous motor, the load of the permanent magnet synchronous motor is stabilized at 1.25 Nm and then the load is increased to 0.25 Nm. The experimental waveforms show that neither of the two fault diagnosis variables exceeds the current difference threshold.

[0098] Figure 6 When the permanent magnet synchronous motor is running at a rated speed of 15000rpm and a load of 1.25Nm, the switch tube T1 suddenly fails to open circuit. The experimental waveform shows that the fault location can be effectively diagnosed.

[0099] In summary, the method proposed in this paper is applicable to two-level voltage source inverters. Compared to traditional methods, the proposed diagnostic method is load-independent and requires only coordinate transformation of the three-phase currents and current prediction of the transformed currents to determine whether a fault has occurred. This not only reduces the computational effort but also maintains high diagnostic accuracy even in the presence of sudden load changes. Combined with the predicted current fault diagnosis, the three-phase current vectors are separated to obtain the current vector for each phase. This not only simplifies the fault location method and accelerates fault location time, but also improves fault location accuracy.

[0100] Finally, it should be noted that various changes and improvements may be made to the present invention without departing from the spirit and scope of the present invention, and such changes and improvements shall fall within the scope of the invention claimed for protection. The features mentioned and / or illustrated in the above description of the exemplary embodiments of the present invention may be incorporated into one or more other embodiments in the same or similar manner, combined with features in other embodiments, or substituted for corresponding features in other embodiments. The technical solutions obtained by such combination or substitution shall also be deemed to be included within the scope of protection of the present invention.

Claims

1. A method for diagnosing open-circuit faults of a permanent magnet synchronous motor inverter based on current vector, characterized in that: The following steps are involved: Step 1: Use the Lagrange prediction method to predict the d-axis current value and q-axis current value of the permanent magnet synchronous motor in the two-phase rotating coordinate system to obtain the d-axis current prediction value at the current time k and the predicted q-axis current ; and monitor the d-axis current value at the same time in real time and q-axis current value ; The predicted value of the d-axis current at the current time k and the predicted q-axis current for: in 、 、 Respectively represent the 、 、 The d-axis current value at the moment, 、 、 Respectively represent the 、 、 The q-axis current value at the moment; Step 2: Based on the predicted value of the d-axis current at time k obtained in step 1 and the predicted q-axis current And the d-axis current value at the same time and q-axis current value , determine whether an inverter open circuit fault occurs. If an inverter open circuit fault occurs, proceed to step 3 and save the time when the fault occurs. If no inverter open circuit fault occurs, return to step 1 and proceed to the next moment processing; Among them, for the kth moment, the d-axis current prediction value obtained in step 1 is , q-axis current prediction value The actual d-axis current value at the same time , q-axis current value For comparison; if the d-axis current prediction value Compared with the actual d-axis current value The difference between the two, and the predicted value of the q-axis current and the actual q-axis current value If any difference between the two values ​​is greater than or equal to the set current difference threshold, it is determined that an inverter open circuit fault has occurred; otherwise, the inverter is determined to be normal and the process returns to step 1 to continue measuring. Step 3: If an inverter open-circuit fault occurs at time k, the following judgment is performed on each phase current of the permanent magnet synchronous motor to locate the fault: Step 3.1: Based on the phase current angle at the moment before the fault occurs and the current value of the phase , according to the formula Calculate and save the phase current amplitude ; Step 3.2: Construct the current vector of the phase current and use the phase current value as the horizontal coordinate value of the rectangular coordinate system , the phase current value after 1 / 4 cycle delay is used as the vertical axis value : in is the phase current angle at the time of fault occurrence; Step 3.3: Based on the horizontal coordinate value of the phase current obtained in step 3.2 , vertical coordinate value , construct the space vector of the phase current : in The unit space vector representing the ordinate direction, Represents the angle of the phase current space vector; Step 3.4: Taking the time k at which the fault occurs as the starting point, calculate the space vector of the phase current within the time t0. The fault current area enclosed by the coordinate axes of the rectangular coordinate system , and according to the current amplitude Calculate the healthy current area of ​​the inverter at the healthy moment : Step 3.5: Calculate the fault current area for this phase current and healthy current area Ratio , determine whether the upper switch or the lower switch of the phase is faulty according to the following logic: If the ratio Less than or equal to the set current ratio threshold, and each phase current angle If the ratio is between [0,π), it is determined that the switch on this phase is faulty; if the ratio is between [0,π], it is determined that the switch on this phase is faulty. Less than or equal to the set current ratio threshold, and the phase current angle If the ratio is between [π, 2π), it is determined that the switch tube in this phase is faulty; if the ratio is between [π, 2π], it is determined that the switch tube in this phase is faulty. If the current ratio is greater than the set current ratio threshold, the process returns to step 1 to perform diagnosis on the next current cycle.

2. The method for diagnosing open-circuit faults of a permanent magnet synchronous motor inverter according to claim 1, wherein: The process of obtaining the d-axis current value and the q-axis current value in step 1 is: Step 1.1: Measure the three-phase current value of the permanent magnet synchronous motor at the current moment 、 、 ; Step 1.2: According to the formula The three-phase current values ​​in the three-phase stationary coordinate system 、 、 Converted to the α-axis current value in the two-phase stationary coordinate system , β-axis current value ; Then according to the formula The α-axis current value in the two-phase stationary coordinate system , β-axis current value Converted to the d-axis current value in the two-phase rotating coordinate system , q-axis current value ,in Indicates the electrical angle of the permanent magnet synchronous motor rotor.

3. The method for diagnosing open-circuit faults of a permanent magnet synchronous motor inverter according to claim 1, wherein: In step 2, the current difference threshold is set to 23.

4. The method for diagnosing open-circuit faults of a permanent magnet synchronous motor inverter according to claim 1, wherein: In step 3.5, the current ratio threshold is set to 0.8.

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