Current vector-based open-circuit fault diagnosis method for inverter of permanent magnet synchronous motor

Abstract

The invention provides a permanent magnet synchronous motor inverter open-circuit fault diagnosis method based on a current vector, belongs to the technical field of motor fault diagnosis, and is suitable for a two-level voltage source type inverter. The method comprises the following three steps of: 1, performing current prediction on current under a two-phase rotating coordinate system by using a Lagrange interpolation method, and monitoring an actual current value at the same moment; secondly, whether a switch tube fault occurs or not is judged according to the residual error of the actual current and the predicted current, and the fault judgment method does not depend on a load and still has high diagnosis precision under the working condition of the abrupt change load; and step 3, fault positioning is carried out, current vectors of the three-phase current are separated, and fault calculation and positioning are carried out on each phase of current, so that the fault positioning method can be simplified, and the fault occurrence position can be rapidly judged. The fault diagnosis is carried out through the method, so that the diagnosis accuracy is greatly improved, and the diagnosis time can be shortened.

Description

Technical Field

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

[0002] Permanent magnet synchronous motors have the advantages of light structure, high reliability and high power density, and can be widely used in electric vehicles, new energy power generation, and aerospace fields. There are a large number of semiconductor devices in the inverter used with permanent magnet synchronous motors. Among them, the power devices run in a high-frequency switching state for a long time. After a long period of work, they will inevitably fail to work normally and fail. Among them, the open circuit failure of the power device is the type of failure with the highest incidence rate and the greatest impact on the entire drive system. In order to effectively and quickly find the fault point of the drive system, inverter open circuit fault diagnosis has become a research hotspot in the field of permanent magnet synchronous motor fault diagnosis.

[0003] As an important basic parameter of the motor drive system, current can reflect the working state and health of the motor drive system. The permanent magnet synchronous motor inverter can realize the motor current conversion function, so the inverter working state can be obtained from each phase current.

[0004] At present, fault diagnosis methods based on current prediction have been widely used in the field of fault diagnosis. At the same time, current vector has a more intuitive feature and can reflect the working condition of the motor drive system more quickly. However, so far, a large number of current prediction methods are still based on motor models, so the prediction accuracy depends on the accuracy of motor parameters, and the diagnostic method that relies solely on current vector has a relatively slow diagnostic speed and cannot reflect the health of the drive system in a timely manner. Summary of the invention

[0005] The purpose of the present invention is to solve the problems of slow inverter fault diagnosis speed and low fault location accuracy 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 purpose, the technical solution provided by the present invention is:

[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 Lagrangian 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 predicted d-axis current 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, enter step 3 and save the time when the fault is determined to occur. 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 the kth moment, 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 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 a delay of 1 / 4 cycle is used as the ordinate 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 is the unit space vector in 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 Area with healthy current 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 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 If the current ratio is greater than the set current ratio threshold, the process returns to step 1 to diagnose the next current cycle.

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

[0027]

[0028]

[0029] in , , Respectively represent , , The d-axis current value at time , , Respectively represent , , 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:

[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 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 ;

[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 The actual d-axis current value The difference between the two, and the predicted value of the q-axis current The actual q-axis current value If any 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 permanent magnet synchronous motor inverter open circuit fault diagnosis method designed by the present invention is applicable to a two-level power supply inverter. The current prediction is performed on the current in a two-phase rotating coordinate system as a reference for whether a fault occurs. The current vector of the three-phase stator winding of the permanent magnet synchronous motor is separated to construct the current vector of each phase current. The fault current vector area is compared with the healthy vector area to serve as a reference value for locating the fault point. This can not only simplify the fault locating method and speed up the fault locating time, but also improve the accuracy of fault locating. 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 in an embodiment of the present invention;

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

[0046] Figure 3 It is a flow chart of the permanent magnet synchronous motor inverter open circuit fault diagnosis method of the present invention;

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

[0048] Figure 5 is a simulation verification result diagram of the large 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 permanent magnet synchronous motor inverter open circuit fault diagnosis method based on current vector, which is used to judge and locate the permanent magnet synchronous motor inverter open circuit fault. The diagnosis 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 information can be used to reduce the amount of calculation for 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 time k 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 substituted 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 d-axis current value at time , , Respectively represent , , 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 occurs; otherwise, it is determined that the inverter is normal, and the process returns to step 1 to continue measuring. In this embodiment, the current difference threshold is 23.

[0076] When an open-circuit fault occurs in the inverter, the current of the three-phase stator winding of the permanent magnet synchronous motor will have an abnormal value. By transforming the coordinates of the three-phase current, the current in the two-phase rotating coordinate system is obtained, and the Lagrange interpolation method is used to predict the transformed current. Then, the residual between the actual current value and the predicted current value is used to determine whether a switch tube fault has occurred. This fault judgment method does not depend on the load, which not only reduces the amount of calculation, but also has a high diagnostic accuracy in the case of sudden load changes.

[0077] Step 3: If an inverter open circuit fault occurs at the kth moment, 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 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] In order to simplify the calculation, it is usually considered 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 a delay of 1 / 4 cycle is used as the ordinate 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 is the unit space vector in 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 Area with healthy current 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 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 If the current ratio is greater than the set current ratio 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 4-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 diagram of the two-level voltage source inverter is as follows: Figure 1 As shown in the figure, 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 the misdiagnosis prevention experiment when the reference speed of the permanent magnet synchronous motor changes suddenly, the reference speed is changed to 150rpm after the speed of the permanent magnet synchronous motor stabilizes at 15000rpm. The experimental waveform shows 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 1.25Nm and then the load is increased to 0.25Nm. 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 at a rated speed of 15000rpm and a load of 1.25Nm, the switch tube T1 suddenly has an open circuit fault. The experimental waveform shows that the fault location can be effectively diagnosed.

[0099] In summary, the method proposed in the present invention is applicable to two-level voltage source inverters. Compared with the traditional method, the proposed diagnostic method does not rely on the load. It only needs to perform coordinate transformation on the three-phase current and predict the transformed current to determine whether a fault occurs. This not only reduces the amount of calculation, but also has a high diagnostic accuracy in the case of sudden load changes. Combined with the fault judgment of the predicted current, the current vector of the three-phase current is separated to obtain the current vector of each phase. This can not only simplify the fault location method and speed up the fault location time, but also improve the accuracy of fault location.

[0100] Finally, it should be noted that, without departing from the spirit and scope of the present invention, the present invention may be subject to various changes and improvements, all of which fall within the scope of the present invention to be protected. The features mentioned and / or shown in the above description of the exemplary embodiments of the present invention may be combined in the same or similar manner into one or more other embodiments, combined with features in other embodiments or substituted for corresponding features in other embodiments. The technical solutions obtained by these combinations or substitutions shall also be deemed to be included in the protection scope 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 Lagrangian 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 predicted d-axis current 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 ; 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, enter step 3 and save the time when the fault is determined to occur. If no inverter open circuit fault occurs, return to step 1 and proceed to the next moment processing; Step 3: If an inverter open circuit fault occurs at the kth moment, 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 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 a delay of 1 / 4 cycle is used as the ordinate 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 is the unit space vector in 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 Area with healthy current 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 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 If the current ratio is greater than the set current ratio threshold, the process returns to step 1 to diagnose the next current cycle.

2. The method for diagnosing open circuit faults of a permanent magnet synchronous motor inverter according to claim 1, characterized in that: In step 1, the predicted value of the d-axis current at the current time k is and the predicted q-axis current for: in , , Respectively represent , , The d-axis current value at time , , Respectively represent , , The q-axis current value at the moment.

3. The method for diagnosing open circuit faults of a permanent magnet synchronous motor inverter according to claim 1, characterized in that: 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 ; 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.

4. The method for diagnosing open circuit faults of a permanent magnet synchronous motor inverter according to claim 1, characterized in that: In step 2, 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 two, and the predicted value of the q-axis current The actual q-axis current value If any difference value among the differences is greater than or equal to the set current difference threshold, it is determined that an inverter open circuit fault occurs; otherwise, it is determined that the inverter is normal, and the process returns to step 1 to continue measuring.

5. The method for diagnosing open circuit faults of a permanent magnet synchronous motor inverter according to claim 4, characterized in that: In step 2, the current difference threshold is set to 23.

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

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