A method and system for zero position correction of a position sensor for a salient pole permanent magnet motor

Abstract

The application discloses a position sensor zero correction method and system for a salient pole permanent magnet motor, and belongs to the field of motor control. The application considers the characteristics that permanent magnet torque and reluctance torque of the salient pole permanent magnet motor change with current, and implements different correction steps for motors with different salient pole rates, rated currents and magnetic flux sizes, so that the beneficial effects of reducing the interference of load torque on the zero deviation correction process and improving the zero deviation correction precision of the motor can be achieved. The application has higher correction precision on the salient pole permanent magnet synchronous motor with smaller permanent magnet flux, and is convenient to operate. The application can be realized on a general motor frequency converter, and does not need to add new hardware.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of motor control, and more particularly, relates to a position sensor zero correction method and system for salient-pole permanent magnet motors. BACKGROUND

[0002] Permanent magnet motors are widely used in modern drive systems due to their high power density, high efficiency and simple structure. In situations where cost is not very sensitive but control performance is required, a high-precision sensor such as a rotary transformer, an optical encoder, a magnetic encoder, etc. is installed in the motor to measure the rotor position and accurately measure the mechanical angle position of the rotor, and then the electrical angle position of the rotor is calculated. Due to the manufacturing cost and installation process, the actual position sensor of the motor has a certain mechanical angle deviation from the actual position of the rotor when installed, which is called zero deviation. For mass-produced motor models, a zero adjustment detection process is generally performed before shipment, and the deviation value is recorded for software algorithm correction by the motor controller; for experimental prototypes, the deviation can sometimes be an arbitrary angle, and the zero deviation needs to be measured and calibrated. Motor disassembly and repair, position sensor failure, drive controller replacement, and software data update may cause the position sensor zero information to be lost or invalid, and need to be recalibrated. In practical applications, the motor used is generally a high-pole motor, and the calibration error of the mechanical angle zero deviation of the rotor is converted into electrical angle, which will be multiplied. Therefore, a high-precision permanent magnet motor position sensor zero deviation correction method with high operability is of great significance for permanent magnet motor control.

[0003] At present, the main position sensor zero deviation correction methods mainly include the following: one is pre-positioning method, namely, in the case of motor no-load, a given voltage or current is inputted, so that the motor rotor rotates to the design position under the action of constant stator magnetic field, and the zero deviation can be obtained from the position sensor measurement value at this time. This method is simple to operate and is most widely used, but the estimation accuracy is affected by the motor load torque, and the estimation process will cause the rotor to rotate in an undetermined direction. Two is to estimate the rotor initial position through the position sensorless control technology, and then obtain the zero deviation, the main principle is to obtain the rotor position information contained in the motor saturation effect or saliency effect through pulse voltage injection. This algorithm can keep the motor stationary, but the algorithm is relatively complex, and the controller requires high computing performance, and the precision is low due to the nonlinear characteristics of the inverter and the motor and the noise problem of the electric sensor. Three is to use external bench to reverse the motor, and to calibrate the zero deviation through the motor back electromotive force or three-phase short-circuit current. This method has high accuracy, but it requires high external equipment, and the application range is limited. Four is to calculate the zero deviation through the motor current in the vector control, which requires the motor to run in the design working condition, and the accuracy is limited by the current sampling accuracy, and the initial deviation cannot be too large. The key to correction is to determine the rotor position and compare it with the measurement value of the position sensor corresponding to the rotor position.

[0004] In recent years, permanent magnet motors with saliency, such as embedded permanent magnet synchronous motors and permanent magnet auxiliary synchronous reluctance motors, have attracted more and more attention due to their higher rotor mechanical strength, lower magnet cost, wider constant power range, stronger fault tolerance and other advantages compared with the hidden pole synchronous motor. When using the traditional pre-positioning algorithm on this type of motor, the electromagnetic torque of the motor has a reluctance component in addition to the permanent magnet component. The reluctance component torque will reduce the positioning accuracy of the traditional method, making the method less effective on certain motors. SUMMARY

[0005] In view of the defects of the prior art and the improvement needs, the present application provides a position sensor zero correction method and system for salient pole permanent magnet motor, which aims to improve the accuracy of the position sensor zero deviation correction of the salient pole permanent magnet motor, and to facilitate the actual engineering site implementation as much as possible.

[0006] To achieve the above-mentioned purpose, the present application provides a position sensor zero correction method for salient pole permanent magnet motor, comprising the following steps:

[0007] The first threshold value I sThd1 and the second threshold value I sThd2 of the stator current are calculated by the permanent magnet flux linkage ψ m , the direct axis inductance L d , and the quadrature axis inductance L q .

[0008] Determine the rated stator current I N With the I sThd1 and I sThd2 Based on the relationship, salient pole permanent magnet motors are divided into three types: if I N ≤I sThd1 Classified as type 1; if I sThd1 <I N ≤I sThd2 Classified as type 2; if I sThd2 <I N Classified as type 3;

[0009] For type 1: setting the electrical angle of the given value of the stator current. Amplitude i s * =I N This causes the controller to enter a current closed loop and maintain the current for time T1; then set... i s * =I N This causes the controller to enter a current closed loop and maintain the current for time T1; then set... i s * =I N This causes the controller to enter a current closed loop and maintain this position for time T2; the mechanical angle value of the rotor is then read, which is the zero-position deviation angle θ. ms ;

[0010] For type 2: setting the electrical angle of the given value of the stator current. Amplitude i s * =I sThd1 This causes the controller to enter a current closed loop and maintain the current for time T1; then set... i s * =I sThd1 This causes the controller to enter a current closed loop and maintain the current for time T1; then set... i s * =I sThd1 This causes the controller to enter a current closed loop and maintain this position for time T2; the mechanical angle value of the rotor is then read, which is the zero-position deviation angle θ. ms ;

[0011] For type 3: setting the electrical angle of the given value of the stator current. Amplitude i s * =I sThd1 This causes the controller to enter a current closed loop and maintain the current for time T1; then set... i s * =IsThd1 entering current closed loop, keeping T1 time; setting again i s * = I N entering current closed loop, keeping T2 time; reading mechanical angle value θ of rotor m1 ; setting again i s * = I sThd1 entering current closed loop, keeping T1 time; setting again i s * = I N entering current closed loop, keeping T2 time; finally reading mechanical angle value θ of rotor m2 ; then zero deviation angle

[0012] wherein the first threshold I sThd1 and the second threshold I sThd2 are:

[0013] In particular, if θ m1 and θ m2 are distributed at both ends of the angle interval [0, 2π), at this time,

[0014] Further, θ s1 is expressed as:

[0015] Further, T1 is 2-5 seconds.

[0016] Further, T2 is 3-10 seconds.

[0017] Another aspect of the present application provides a position sensor zero correction system for a salient pole permanent magnet motor, comprising: a computer readable storage medium and a processor;

[0018] The computer readable storage medium is used to store executable instructions.

[0019] The processor is used to read the executable instructions stored in the computer readable storage medium, and execute the above-mentioned position sensor zero correction method for a salient pole permanent magnet motor.

[0020] Compared with the prior art, the above technical scheme conceived by the present application can reduce the interference of load torque on the zero deviation correction process and improve the zero deviation correction accuracy of the motor, because the characteristics of the permanent magnet torque and the reluctance torque of the salient pole permanent magnet motor varying with the current are considered, and different correction steps are implemented for motors with different salient pole rates, rated currents and magnetic flux sizes. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 is a schematic diagram of the dq current expressed as the torque angle;

[0022] Figure 2 is a torque angle characteristic curve diagram of a typical PMa-SynRM under different stator currents;

[0023] Figure 3 is a schematic diagram of the position relationship between the stator and the rotor of the permanent magnet motor;

[0024] Figure 4 is a structural schematic diagram of the zero deviation correction system;

[0025] Figure 5 is a correction algorithm flowchart. DETAILED DESCRIPTION

[0026] In order to make the purpose, technical scheme and advantages of the present application clearer, the present application is further described in detail below in combination with the drawings and examples. It should be understood that the specific examples described herein are only used to explain the present application and do not limit the present application. In addition, the technical features involved in each embodiment of the present application described below can be combined with each other as long as they do not conflict with each other.

[0027] Generally, considering the ideal linear model of the permanent magnet motor, the electromagnetic torque of the motor can be expressed in the synchronous rotating coordinate system as follows:

[0028]

[0029] where p0 is the number of motor pole pairs, ψ m is the permanent magnet flux, ψ d and ψ q respectively represent the dq-axis flux, i d and i q respectively represent the dq-axis current, L d and L q respectively represent the dq-axis inductance. is the permanent magnet torque component, which is derived from the interaction of the permanent magnet and the current; is the reluctance torque component, which is derived from the asymmetry of the dq-axis magnetic circuit. The following discussion is directed to the salient pole permanent magnet motor, i.e., L q >L d .

[0030] To simplify the mathematical expression, the current in equation (1) can be transformed into the form of a resultant current plus a torque angle, such as... Figure 1 As shown. Then we can obtain:

[0031]

[0032] Where δ is the angle by which the stator current leads the d-axis, called the torque angle or load angle, and we have:

[0033]

[0034] It can be seen that the permanent magnet component of the electromagnetic torque varies sinusoidally with the angle of the composite current in the synchronous rotating coordinate system, and its amplitude is proportional to the stator current; the reluctance component varies sinusoidally with twice this angle, and its amplitude is proportional to the square of the stator current. Figure 2 The figure shows the torque-torque angle relationship curves (also known as torque-angle characteristic curves) of a typical permanent magnet assisted synchronous reluctance motor (PMa-SynRM) under different stator currents. Obviously, when the current is large, the reluctance torque amplitude will exceed the permanent magnet torque, and the relationship between the total electromagnetic torque and the torque angle δ will also change significantly.

[0035] The static stability point of the rotor is now considered when a constant current is passed through the stator to generate a constant magnetic field.

[0036] The stator and rotor position relationship of a salient pole permanent magnet motor is as follows: Figure 3 As shown. The number of pole pairs of the motor is defined as p0. For simplicity, the figure shows a motor with one pole pair. Due to the rotational symmetry of the motor stator, it can be assumed that the direction of the constant magnetic field generated by the constant current flowing through the stator coincides with the A-axis, i.e., the stator current i s >0, and i s electrical angle θ e * =0° (coinciding with the A-axis direction). Let θ be the angle (mechanical angle) between the d-axis and the A-axis of the rotating coordinate system (dq coordinate system) that is relatively stationary with the motor rotor at this time. mr For θ mr =θ / p0 (that is, converted to electrical angle is θ). Due to the rotational symmetry of the motor rotor, we only need to discuss the case of 0≤θ<2π.

[0037] will i s Transforming to a rotating coordinate system, we obtain the electromagnetic torque acting on the rotor at this point as follows:

[0038]

[0039] Compared to the result of equation (2), only the signs are reversed. Intuitively, if T e If T > 0, the rotor experiences a positive torque, and θ tends to increase; if T e< 0, the rotor is subject to a reverse torque and θ has a tendency to decrease.

[0040] If the rotor is stable at θ, the necessary condition is T e = 0, i.e. we have:

[0041]

[0042] This equation always has a solution:

[0043]

[0044] When there is an additional solution:

[0045]

[0046] Obviously, equation (7) gives two angle values, and they are symmetric about 0.

[0047] Consider the stability of the solution (6):

[0048] When we have:

[0049] k1= ψ m - i s (L q - L d ) cos(θ) > 0 (8)

[0050]

[0051] When θ is near 0: if θ > 0, then T e < 0; if θ < 0, then T e > 0. The rotor is always subject to a torque opposite to the direction of the deviation, and has a tendency to return to the original position, so θ = 0 is a stable equilibrium point. When θ is near π: if θ > π, then T e > 0; if θ < π, then T e < 0. The rotor is always subject to a torque in the same direction as the direction of the deviation, and has a tendency to move away from the original position, so θ = π is an unstable equilibrium point. Ideally, the rotor cannot remain stationary at this point, but in practical applications, the rotor can remain at this point after energization due to friction torque and the like.

[0052] When we have:

[0053]

[0054] When θ is near 0, in the neighborhood of θ = 0, there always exists θ1> 0 such that there always exists θ2< 0 such that The rotor is always subjected to a torque in the same direction as the offset, and tends to move away from its original position; therefore, θ = 0 is an unstable equilibrium point. When θ is near π, Similarly, it can be proven that θ = π is an unstable equilibrium point.

[0055] Consider the stability of solution (7):

[0056] Let θ s1 satisfy but:

[0057]

[0058] Obviously, when At that time, there is i s 2 (L q -L d ) 2 -ψ m 2 >0, we can get Similarly, it can be proved that θ = θ s1 It is a stable equilibrium point.

[0059] In summary, the electrical angles at which the rotor may reach a stable equilibrium position are:

[0060]

[0061] As the stator current gradually increases, the equilibrium point changes from θ within one electrical cycle. s0 Split into θ s1 (Two solutions). The absolute values ​​of the electrical angles corresponding to these two equilibrium points are less than... It is symmetric about 0.

[0062] The following discussion covers an approximate calculation method for the angular offset of the rotor due to load torque when it is in equilibrium.

[0063] Considering the torque acting on the rotor, the mechanical motion equation of the rotor is:

[0064]

[0065] At static equilibrium, we have:

[0066] T e =T L +T f =T L ′ (14)

[0067] Generally, the total disturbance torque T L The angle '' remains largely unchanged and is generally small. Therefore, in reality, the stationary position is near the ideal equilibrium point. T can be... eAt the ideal equilibrium point θ0, the Taylor expansion of the electrical angle is given by

[0068]

[0069] Substituting (14) into (16) gives

[0070]

[0071] Although it is difficult to measure the specific value of T L in (16), (16) can be used to compare the relative size of the error at different positioning points. Substituting (12) into (16) gives an estimate of the angle error at different positioning currents:

[0072]

[0073] It can be seen that when the positioning current is small, the angle error is large. For a general salient-pole machine, the angle error can be reduced by increasing the positioning current. However, for a salient-pole machine, blindly increasing the positioning current does not reduce the angle error, but rather can increase the error or introduce a new equilibrium point. The optimal positioning method needs to be further discussed according to the machine parameters.

[0074] The following electrical parameters of the salient-pole permanent magnet machine to be measured are required: permanent magnet flux linkage ψ m , direct-axis inductance L d , quadrature-axis inductance L q , number of pole pairs p0, rated stator current I N .

[0075] When performing zero offset correction, the d-axis current at equilibrium is always greater than zero, i.e. the machine is always in a magnetizing state, and demagnetization does not need to be considered.

[0076] The minimum value of the angle error given by (17) at different i s is analyzed below.

[0077] For θ = θ s0 , the denominator is a quadratic function of i s , and it can be proved that the denominator 3p0i s [ψ m -i s (L q -L d )] has a maximum value at i s . Therefore, Δθ has a minimum value at this i s , and the value is:

[0078]

[0079] That is, Δθ decreases with increasing i s , and when i s = 0, Δθ = 0. the minimum is reached, and then increases with i s

[0080] For θ = θ s1 , the denominator increases with i s , so that the larger i s is, the smaller Δθ is. Substituting into equation (17) gives the critical current value for which Δθ equals that of equation (18) in this case:

[0081]

[0082] That is, in this case, Δθ increases with i s . When i , the maximum value of the previous case is reached.

[0083] Therefore, the value of i N can be determined according to its relationship with the following two thresholds:

[0084]

[0085]

[0086] 1) When I N ≤ I sThd1 , take i s = I N , in which case the motor will be positioned at θ = θ s0 .

[0087] 2) When I sThd1 <I N ≤ I sThd2 , take i s = I sThd1 , in which case the motor will be positioned at θ = θ s0 .

[0088] 3) When I sThd2 <I N , take i s = I N , in which case the motor will be positioned at θ = θ s1 .

[0089] In case 3) above, θ s1 has two possible values, and the value depends on the motor parameters. In practical engineering, due to inaccurate parameters and nonlinear effects such as saturation, the actual equilibrium point angle θ s1 ' will deviate from the calculated value θ s1 . However, due to the symmetry of the relationship between the motor torque and the angle, θ s1 ​The two values ​​of θ' are also symmetrical about θ = 0. Therefore, the motor can be positioned at two equilibrium points, and the angle between the two points can be taken as θ = 0.

[0090] Since the mechanical time constant of a real motor is generally much larger than its electrical time constant, the motor can be positioned at the two equilibrium points mentioned above using the following approach: First, under a smaller stator current, the motor rotor is positioned at θ = θ using a pre-positioning method. s0 Equilibrium point. After the rotor position stabilizes, set the stator composite current electrical angle to... And its amplitude i s * >i sThd2 Because the stator current changes extremely rapidly, the rotor cannot rotate in time. Influenced by the torque generated by the new current, the rotor reaches a new equilibrium point near its original position, corresponding to an electrical angle of ±θ. s1 ′, and will stabilize at this equilibrium point.

[0091] Assume the motor has a stator resultant current electrical angle When in equilibrium, the angle value read by the position sensor is θ. m1 (From a mechanical perspective), the zero-position deviation of the position sensor is θ. ms (From a mechanical perspective) these quantities satisfy the following relationship:

[0092]

[0093] Similarly, for The angle value θ read by the position sensor when the system is in equilibrium. m2 ,have:

[0094]

[0095] Solving equations (22) and (23) simultaneously yields:

[0096]

[0097] In particular, it is necessary to consider the case where the angles are distributed at both ends of the angular interval. In this case, it can be expressed as:

[0098]

[0099] In the above formula, when (θ m1 +θ m2 When (θ) / 2 ≥ π / 2, the sign is negative; when (θ) / 2 ≥ π / 2, the sign is negative. m1 +θ m2 When π / 2 < π / 2, the sign is positive.

[0100] Based on the above discussion, the following method is proposed to complete the position sensor zero correction to improve the correction accuracy. The method is based on the widely used motor vector control (FOC) current loop, and the system structure block diagram is shown in Figure 4 The flow chart of the correction method is shown in Figure 5 In general, it can be divided into the following two steps:

[0101] Step 1: Calculate the motor parameters and determine the motor type.

[0102] According to formula (20), formula (21), calculate I sThd1 And I sThd2 . Determine the relationship between the rated stator current I N And I sThd1 And I sThd2 , divide the salient pole permanent magnet motor into three types: if I N ≤I sThd1 , it belongs to type 1; if I sThd1 <I N ≤I sThd2 , it belongs to type 2; if I sThd2 <I N , it belongs to type 3, and calculate θ s1 According to formula (26) below.

[0103]

[0104] Step 2: Use different correction schemes according to different motor types.

[0105] Type 1:

[0106] Pre-positioning step: set the given value of the synthesized stator current to the electric angle Amplitude I s * = I N , so that the controller enters current closed loop and keeps T1 time; then set I s * = I N , so that the controller enters current closed loop and keeps T1 time.

[0107] Deviation correction step: set I s * = I N , so that the controller enters current closed loop and keeps T2 time, and then read the stable mechanical angle value θ m1 Measured by the position sensor.

[0108] Calculate the correction result: θ m1 That is, the zero deviation angle θms .

[0109] Type 2:

[0110] Pre-positioning step: set the electrical angle of the given value of the resultant stator current Amplitude i s * = I sThd1 , make the controller enter the current closed loop, keep Tl time; then set i s * = I sThd1 , make the controller enter the current closed loop, keep Tl time.

[0111] Deviation correction step: set i s * = I sThd1 , make the controller enter the current closed loop, keep T2 time, then read the stable mechanical angle value θ of the rotor measured by the position sensor m1 .

[0112] Calculate the correction result: θ m1 , which is the zero deviation angle θ ms .

[0113] Type 3:

[0114] Pre-positioning step: set the electrical angle of the given value of the resultant stator current Amplitude i s * = I sThd1 , make the controller enter the current closed loop, keep Tl time; then set i s * = I sThd1 , make the controller enter the current closed loop, keep Tl time.

[0115] Deviation correction step: set i s * = I N , make the controller enter the current closed loop, keep T2 time; then read the stable mechanical angle value θ of the rotor measured by the position sensor m1 . Set again i s * = I sThd1 , make the controller enter the current closed loop, keep Tl time; then set θ e * = - θ s1 , i s * = IN The controller enters current closed loop, keeps T2 time; finally reads the steady mechanical angle value θ of the rotor measured by the position sensor m2 .

[0116] The correction result is calculated: the zero deviation angle can be calculated by formula (24), formula (25).

[0117] Those skilled in the art can understand that the above description is only a preferred embodiment of the present application, and is not used to limit the present application, and any modification, equivalent replacement and improvement made within the spirit and principle of the present application should be included in the protection scope of the present application.

Claims

1. A method for zero-position calibration of a position sensor for a salient-pole permanent magnet motor, characterized in that, Includes the following steps: Composed of permanent magnet magnetic chain Direct-axis inductor quadrature axis inductance First threshold for calculating stator current Second threshold ; , ; Determine the rated stator current With the and Based on the relationship, salient pole permanent magnet motors are divided into three types: if Classified as type 1; if Classified as type 2; if Classified as type 3; For type 1: setting the electrical angle of the given value of the stator current. Amplitude This causes the controller to enter the current closed loop and maintain... Time; Reset , This causes the controller to enter the current closed loop and maintain... Time; Reset , This causes the controller to enter the current closed loop and maintain... Time; read the mechanical angle value of the rotor, which is the zero-position deviation angle. ; For type 2: setting the electrical angle of the given value of the stator current. Amplitude This causes the controller to enter the current closed loop and maintain... Time; Reset , This causes the controller to enter the current closed loop and maintain... Time; Reset , This causes the controller to enter the current closed loop and maintain... Time; read the mechanical angle value of the rotor, which is the zero-position deviation angle. ; For type 3: setting the electrical angle of the given value of the stator current. Amplitude This causes the controller to enter the current closed loop and maintain... Time; Reset , This causes the controller to enter the current closed loop and maintain... Time; Reset , This causes the controller to enter the current closed loop and maintain... Time; reading the rotor's mechanical angle value ; then set , This causes the controller to enter the current closed loop and maintain... Time; Reset , , This causes the controller to enter the current closed loop and maintain... Time; finally, read the rotor's mechanical angle value. Then the zero-position deviation angle .

2. The method according to claim 1, characterized in that, For type 3, if and Distributed in the angular range At both ends, at this time, .

3. The method according to claim 1, characterized in that, It lasts for 2 to 5 seconds.

4. The method according to claim 1, characterized in that, It lasts for 3 to 10 seconds.

5. A position sensor zero-position correction system for a salient-pole permanent magnet motor, characterized in that, include: Computer-readable storage media and processors; The computer-readable storage medium is used to store executable instructions; The processor is used to read executable instructions stored in the computer-readable storage medium and execute the zero-position correction method for a position sensor of a salient pole permanent magnet motor as described in any one of claims 1 to 4.

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