A method for estimating rotor position and speed of permanent magnet synchronous motor based on Hall sensor

Abstract

A method for estimating the rotor position and speed of a permanent magnet synchronous motor based on a Hall sensor comprises the following steps: 1) obtaining a series of discrete electrical angle values ​​according to the signal output by the Hall sensor installed on the stator of the permanent magnet synchronous motor; 2) fitting six continuous discrete electrical angle values ​​by the least squares algorithm to obtain continuous electrical angle information for coordinate transformation and as input of a sliding mode observer; 3) obtaining d-axis current value and q-axis current value by coordinate transformation of the sampled three-phase current value, and calculating the electromagnetic torque according to the electromagnetic torque equation in a synchronous coordinate system; 4) designing a sliding mode observer according to the mechanical motion equation of the motor to observe the electrical angular velocity and load torque of the rotor; 5) using the electrical angular velocity observed by S4 as feedback of the speed loop, and feeding the observed load torque value forward to the q-axis current loop. The present invention effectively estimates the rotor position and load torque, reduces the estimation errors of the position and speed, and enhances the robustness of the system.

Description

Technical Field

[0001] The invention relates to the field of industrial electric vehicle motor control, and in particular to a permanent magnet synchronous motor rotor position and speed estimation method based on a Hall sensor. Background Art

[0002] In recent years, permanent magnet synchronous motors have gradually become popular in the field of industrial electric vehicles due to their many advantages such as high power density, high efficiency and small size. Permanent magnet synchronous motor vector control requires accurate position and speed information to ensure control performance. High-precision position sensors such as photoelectric encoders and resolvers are usually installed on the shaft end of the motor rotor, but they are also susceptible to environmental interference, which reduces the reliability of the system and is limited by the system scale and cost. The speed sensorless control scheme is sensitive to motor parameters and is affected by the current sampling accuracy, and low speed will cause additional motor losses, noise and vibration. Therefore, the use of Hall sensors as position sensors in permanent magnet synchronous motors can ensure motor performance, effectively control system costs and improve system reliability. In one electrical cycle, three Hall sensors can only provide six discrete position signals. The traditional average speed estimation method will deteriorate when the motor runs at a non-uniform speed. The speed estimation noise is large at high speeds, and there is a time lag in speed estimation at low speeds. Compared with high-precision encoders and speed sensorless control, Hall sensors are a guarantee of low cost and control performance. Low-resolution Hall sensors will reduce the accuracy of position and speed calculation in vector control schemes. Therefore, this patent proposes a new position and speed estimation scheme to improve the estimation accuracy of position and speed. At the same time, the estimated load torque is used as the feedforward of the current loop to improve the anti-interference performance of the system. Summary of the invention

[0003] In order to solve the above problems, the present invention provides a permanent magnet synchronous motor rotor position and speed estimation method based on Hall sensor, which combines the non-model-based least squares algorithm and the model-based sliding mode observer to effectively estimate the rotor position and load torque, reduce the estimation error of position and speed, and enhance the robustness of the system.

[0004] The present invention provides a method for estimating the rotor position and speed of a permanent magnet synchronous motor based on a Hall sensor, and the specific steps are as follows:

[0005] S1. Obtain a series of discrete electrical angle values ​​according to the signal output by the Hall sensor installed on the stator of the permanent magnet synchronous motor;

[0006] S2, fitting the six continuous discrete electrical angle values ​​by the least squares algorithm to obtain continuous electrical angle information for coordinate transformation and as input of the sliding mode observer;

[0007] S3, obtaining the d-axis current value and the q-axis current value by coordinate transformation of the sampled three-phase current values, and calculating the electromagnetic torque according to the electromagnetic torque equation in the synchronous coordinate system;

[0008] S4. Design a sliding mode observer based on the mechanical motion equation of the motor to observe the electrical angular velocity and load torque of the rotor;

[0009] S5. The electrical angular velocity observed by S4 is used as feedback of the speed loop, and the observed load torque value is fed forward to the q-axis current loop.

[0010] As a further improvement of the present invention, the step S2 is specifically as follows:

[0011] S2.1. Select six continuous Hall discrete electrical angle values ​​as fitting data, and the fitting window moves with the rotation of the motor.

[0012] S2.2. Considering the estimation efficiency and estimation accuracy, the number of fittings is set to two times. Specifically, the fitting expression is as follows:

[0013] θ(t)=a2t 2 +a1t+a0 (1)

[0014] Where a0, a1, a2 are the coefficients to be solved, t is the time, and θ(t) is the continuous electrical angle value obtained by fitting.

[0015] S2.3. According to the principle of minimizing the sum of squares of the errors between the fitted electrical angle and the actual electrical angle, the following equation is constructed to solve the coefficients:

[0016] Ax=B (2)

[0017]

[0018] Among them, t k is the Hall discrete angle value θ k At the corresponding moment, A is the coefficient matrix, and x and B are column vectors.

[0019] S2.4. Limit the continuous electrical angle value obtained by formula (1) so that its value is between two consecutive Hall discrete electrical angle values. The limiting formula is as follows:

[0020]

[0021] As a further improvement of the present invention, step S3 is specifically as follows:

[0022] S3.1. The current sensor samples the three-phase current of the permanent magnet synchronous motor, and obtains the current in the two-phase stationary coordinate system through stationary coordinate transformation. Specifically, the calculation process is as follows:

[0023]

[0024] Among them, i a 、i b 、i c is the three-phase stator current sampled by the current sensor; i α 、i β is the two-phase stationary coordinate system current.

[0025] S3.2. Based on the static two-phase current obtained in S3.1 and the electrical angle value obtained in step S2, the two-phase current in the rotating coordinate system is obtained through synchronous rotating coordinate transformation. Specifically, the calculation process is as follows:

[0026]

[0027] Wherein, θ is the rotor electrical angle value obtained in step S2; i d 、i q It is the two-phase synchronous rotating coordinate system current.

[0028] S3.3. For a surface-mounted permanent magnet synchronous motor, the electromagnetic torque of the permanent magnet synchronous motor is calculated in a two-phase synchronous rotating coordinate system. Specifically, the calculation process is as follows:

[0029]

[0030] Among them, T e is the electromagnetic torque of the motor; n p is the number of pole pairs of the motor; ψ f It is the permanent magnet flux of the motor rotor.

[0031] As a further improvement of the present invention, step S4 is specifically as follows:

[0032] S4.1. Design the sliding mode observer equation based on the mechanical motion equation of the motor. Ignoring the influence of friction, the mechanical motion state equation of the motor is:

[0033]

[0034] Where ω is the electrical angular velocity of the rotor, T L is the load torque, J is the moment of inertia of the motor, and the designed sliding mode observer equation is as follows:

[0035]

[0036] in, is the estimated value of the sliding mode observer, P and U represent the sliding mode control law, and g represents the feedback coefficient.

[0037] S4.2. Subtract equation (8) from equation (9) to obtain the observation error equation of the system:

[0038]

[0039] Among them, e1 is the observation error of the rotor electrical angle, e2 is the observation error of the load torque, is the first-order derivative of e1, is the second-order derivative of e1, is the first derivative of e2.

[0040] S4.3. In order to achieve finite time convergence and stable convergence accuracy, the sliding surface is selected as:

[0041]

[0042] Where s is the sliding mode function and c is a constant. The derivative of (11) is:

[0043]

[0044] in, is the first derivative of the sliding mode function.

[0045] S4.4. Design the sliding surface approach law and the sliding mode control rate. Specifically, the sliding mode control rate P is designed as:

[0046]

[0047] Where k is a positive constant, when the observer enters the sliding mode, s = 0 and Combining equation (12) and equation (13), we can obtain:

[0048]

[0049] Among them, C1 is a constant. Reasonable design parameters make the exponential term converge quickly to zero, and the sliding surface reaching law is designed as:

[0050]

[0051] Where k1 is the control rate gain, n p is the number of pole pairs of the permanent magnet synchronous motor, a is a positive constant, exp(-as) is an exponential term with e as the base, and combining (12), (13), and (15), we get the sliding mode control rate U:

[0052]

[0053] As a further improvement of the present invention, the step S5 is specifically as follows:

[0054] S5.1, the estimated value of the rotor electrical angular velocity obtained in step S4 Feedback to the speed loop.

[0055] S5.2, the load torque estimation value obtained in step S4 Feed forward to the d-axis current loop.

[0056] Compared with the prior art, the present invention has the following beneficial effects:

[0057] Compared with the problem of large estimation error and hysteresis caused by using the average speed method to process low-resolution discrete Hall signals, the present invention divides angle estimation and speed estimation into two parts. The least squares algorithm does not depend on any motor parameters and can output the electrical angle value stably and smoothly. The sliding mode observer is based on the motor motion model, has good dynamic performance and strong robustness, can update the estimated value of the speed in each control cycle, has a small speed estimation error, and can quickly and accurately estimate the load torque of the motor, thereby improving the rapidity of the current loop. It meets the angle and speed information requirements of the closed-loop vector control of the permanent magnet synchronous motor, guarantees the system cost and control accuracy, and has application prospects in low-cost motor drivers. BRIEF DESCRIPTION OF THE DRAWINGS

[0058] Figure 1 A flowchart of the method according to an embodiment of the present invention;

[0059] Figure 2 The installation position and output waveform of the Hall sensor;

[0060] Figure 3 is a specific schematic diagram of step S2;

[0061] Figure 4 A control block diagram of a permanent magnet synchronous motor having a new solution proposed by the present invention;

[0062] Figure 5 , Figure 6 , Figure 7 It is a simulation comparison chart of the traditional scheme and the new estimation scheme;

[0063] Figure 8 A diagram of the load torque simulation results estimated for the solution proposed in the present invention. DETAILED DESCRIPTION

[0064] The present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments:

[0065] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0066] The embodiment of the present invention provides a method for estimating the rotor position and speed of a permanent magnet synchronous motor based on a Hall sensor. Figure 1, is a flow chart of the method described in an embodiment of the present invention, and the specific steps are as follows:

[0067] Step S1, obtaining a series of discrete electrical angle values ​​according to the signal output by the Hall sensor installed on the stator of the permanent magnet synchronous motor;

[0068] See also Figure 2 The three Hall sensors installed on the motor will output a series of waveforms during the rotation of the motor rotor. According to the characteristics of the high and low levels of the waveforms, the sectors of the electrical angle range of the rotor are divided to obtain the discrete electrical angle values ​​at the sector switching points. Specifically, the discrete electrical angle values ​​at the switching points are 30°, 90°, 150°, 210°, 270°, and 330°.

[0069] Step S2, fitting six continuous discrete electrical angle values ​​by least squares algorithm to obtain continuous electrical angle information for coordinate transformation and as input of sliding mode observer;

[0070] See also Figure 3 , is a specific schematic diagram of step S2. Step S2 includes:

[0071] S2.1. Select the first six consecutive Hall discrete electrical angle values ​​of the current rotor sector as fitting data, and the fitting window moves with the rotation of the motor rotor. Specifically, Figure 3 When the fitting window is located, θ4, θ5, θ6 of the previous electrical cycle and θ1, θ2, θ3 of the current electrical cycle are selected as fitting data.

[0072] S2.2. Considering the estimation efficiency and estimation accuracy, the number of fittings is set to two times. Specifically, the fitting expression is as follows:

[0073] θ(t)=a2t 2 +a1t+a0 (1)

[0074] Where a0, a1, a2 are the coefficients to be solved, t is the time, and θ(t) is the continuous electrical angle value obtained by fitting.

[0075] S2.3. According to the principle of minimizing the sum of squares of the errors between the fitted electrical angle and the actual electrical angle, the following equation is constructed to solve the coefficients:

[0076] Ax=B (2)

[0077]

[0078] Among them, t k is the Hall discrete electrical angle value θ kAt the corresponding moment, A is the coefficient matrix, x and B are column vectors. After solving the coefficients, the electrical angle value before the next Hall discrete electrical angle point appears can be predicted by formula (1).

[0079] S2.4. Limit the continuous electrical angle value obtained by formula (1) so that its value is between two consecutive Hall discrete electrical angle values. The limiting formula is as follows:

[0080]

[0081] Step S3, obtaining the d-axis current value and the q-axis current value by coordinate change of the sampled three-phase current value, and calculating the electromagnetic torque according to the electromagnetic torque equation in the synchronous coordinate system; Step S3 includes:

[0082] S3.1. The current sensor samples the three-phase current of the permanent magnet synchronous motor, and obtains the current in the two-phase stationary coordinate system through stationary coordinate transformation. Specifically, the calculation process is as follows:

[0083]

[0084] Among them, i a 、i b 、i c is the three-phase stator current sampled by the current sensor; i α 、i β is the two-phase stationary coordinate system current.

[0085] S3.2, according to the static two-phase current obtained in S3.1 and the electrical angle value obtained in step S2, the two-phase current in the rotating coordinate system is obtained through synchronous rotating coordinate transformation. Specifically, the calculation process is as follows:

[0086]

[0087] Wherein, θ is the rotor electrical angle value obtained in step S2; i d 、i q It is the two-phase synchronous rotating coordinate system current.

[0088] S3.3. For a surface-mounted permanent magnet synchronous motor, calculate the electromagnetic torque of the permanent magnet synchronous motor in a two-phase synchronous rotating coordinate system. Specifically, the calculation process is as follows:

[0089]

[0090] Among them, T e is the electromagnetic torque of the motor; n p is the number of pole pairs of the motor; ψ f It is the permanent magnet flux of the motor rotor.

[0091] Step S4, designing a sliding mode observer according to the mechanical motion equation of the motor to observe the electrical angular velocity and load torque of the rotor; Step S4 includes:

[0092] S4.1. Design the sliding mode observer equation based on the mechanical motion equation of the motor. Ignoring the influence of friction, the mechanical motion state equation of the motor is:

[0093]

[0094] Where ω is the electrical angular velocity of the rotor, T L is the load torque, and J is the moment of inertia of the motor. The designed sliding mode observer equation is as follows:

[0095]

[0096] in, is the estimated value of the sliding mode observer, P and U represent the sliding mode control law, and g represents the feedback coefficient.

[0097] S4.2. Subtract equation (8) from equation (9) to obtain the observation error equation of the system:

[0098]

[0099] Among them, e1 is the observation error of the rotor electrical angle, e2 is the observation error of the load torque, is the first-order derivative of e1, is the second-order derivative of e1, is the first derivative of e2.

[0100] S4.3. In order to achieve finite time convergence and stable convergence accuracy, the sliding surface is selected as:

[0101]

[0102] Where s is the sliding mode function and c is a constant. By taking the derivative of (11), we can get:

[0103]

[0104] S4.4. Design the sliding surface reaching law and sliding mode control rate. Specifically, the sliding mode control rate P is designed as:

[0105]

[0106] in, is the first-order derivative of the sliding mode control rate P, and k is a positive constant. When the observer enters the sliding mode, s=0 and Combining equation (12) and equation (13), we can obtain:

[0107]

[0108] Among them, C1 is a constant, and the parameters are reasonably designed to make the exponential term converge quickly to zero. The sliding surface reaching law is designed as:

[0109]

[0110] Where k1 is the control rate gain, n p is the number of pole pairs of the permanent magnet synchronous motor, a is a positive constant, and exp(-as) is an exponential term with e as the base. Combining equations (12), (13), and (15), we get the sliding mode control rate U:

[0111]

[0112] Step S5: Use the electrical angular velocity observed in S4 as feedback of the speed loop, and feed forward the observed load torque value to the q-axis current loop. Figure 4 , step S5 comprises:

[0113] S5.1, the estimated value of the rotor electrical angular velocity obtained in step S4 Feedback to the speed loop.

[0114] S5.2, the load torque estimation value obtained in step S4 Feedforward to the d-axis current loop. For the surface-mounted permanent magnet synchronous motor, the feedforward coefficient is:

[0115]

[0116] Where k is the torque coefficient.

[0117] use Figure 4 The new solution shown is used to simulate a permanent magnet synchronous motor system based on Hall sensors. Figure 5 In the figure, the dotted line represents the actual electrical angle value θ real When the motor is accelerating, it can be seen that the electrical angle value θ estimated by the traditional average speed method is avg There is a time lag and a large error, and when the solution of the present invention is adopted, the estimated electrical angle value θ ppsd The actual electrical angle value θ real The closer, the smaller the error. In terms of speed estimation, Figure 6 , Figure 7 It can be seen that no matter at low speed or high speed, the speed value ω output by the speed estimation scheme proposed by the present invention is ppsd The actual speed ω can be accurately estimated in each control cycle real , while the speed ω estimated by the traditional average speed method avg There are large fluctuations at high speeds and serious lags at low speeds, which are not conducive to the adjustment of the speed loop. Figure 8In the figure, the dotted line represents the given torque T L ,The simulation results show that the sliding mode observer can quickly and accurately estimate the ,load torque and its changes of the motor, thus accelerating the ,dynamic performance of the system.

[0118] At this point, the basic operation of the present invention is completed. The present invention proposes a new rotor position and load torque estimation method, which combines the non-model-based least squares algorithm and the model-based sliding mode observer to effectively estimate the rotor position and load torque, reduce the estimation error of position and speed, and enhance the robustness of the system.

[0119] The above description is only a preferred embodiment of the present invention and does not constitute any other form of limitation to the present invention. Any modification or equivalent change made based on the technical essence of the present invention still falls within the scope of protection required by the present invention.

Claims

1. A method for estimating the rotor position and speed of a permanent magnet synchronous motor based on a Hall sensor, the specific steps are as follows, and the method is characterized in that: S1. Obtain a series of discrete electrical angle values ​​according to the signal output by the Hall sensor installed on the stator of the permanent magnet synchronous motor; S2, fitting the six continuous discrete electrical angle values ​​by the least squares algorithm to obtain continuous electrical angle information for coordinate transformation and as input of the sliding mode observer; The step S2 is specifically as follows: S2.

1. Select six continuous Hall discrete electrical angle values ​​as fitting data, and the fitting window moves with the rotation of the motor rotor; S2.

2. Considering the estimation efficiency and estimation accuracy, the number of fittings is set to two times. Specifically, the fitting expression is as follows: θ(t)=a2t 2 +a1t+a0(1) Where a0, a1, a2 are the coefficients to be solved, t is the time, and θ(t) is the continuous electrical angle value obtained by fitting; S2.

3. According to the principle of minimizing the sum of squares of the errors between the fitted electrical angle and the actual electrical angle, the following equation is constructed to solve the coefficients: Ax=B(2) Among them, t k is the Hall discrete angle value θ k At the corresponding moment, A is the coefficient matrix, x and B are column vectors; S2.

4. Limit the continuous electrical angle value obtained by formula (1) so that its value is between two consecutive Hall discrete electrical angle values. The limiting formula is as follows: S3, obtaining the d-axis current value and the q-axis current value by coordinate transformation of the sampled three-phase current values, and calculating the electromagnetic torque according to the electromagnetic torque equation in the synchronous coordinate system; The step S3 is specifically as follows: S3.

1. The current sensor samples the three-phase current of the permanent magnet synchronous motor, and obtains the current in the two-phase stationary coordinate system through stationary coordinate transformation. Specifically, the calculation process is as follows: Among them, i a 、i b 、i c is the three-phase stator current sampled by the current sensor; i α 、i β is the two-phase stationary coordinate system current; S3.

2. Based on the static two-phase current obtained in S3.1 and the electrical angle value obtained in step S2, the two-phase current in the rotating coordinate system is obtained through synchronous rotating coordinate transformation. Specifically, the calculation process is as follows: Wherein, θ is the rotor electrical angle value obtained in step S2; i d 、i q is the two-phase synchronous rotating coordinate system current; S3.

3. For a surface-mounted permanent magnet synchronous motor, the electromagnetic torque of the permanent magnet synchronous motor is calculated in a two-phase synchronous rotating coordinate system. Specifically, the calculation process is as follows: Among them, T e is the electromagnetic torque of the motor; n p is the number of pole pairs of the motor; ψ f is the permanent magnet flux of the motor rotor; S4. Design a sliding mode observer based on the mechanical motion equation of the motor to observe the electrical angular velocity and load torque of the rotor; The step S4 is specifically as follows: S4.

1. Design the sliding mode observer equation based on the mechanical motion equation of the motor. Ignore the influence of friction. The mechanical motion state equation of the motor is: Where ω is the electrical angular velocity of the rotor, θ is the electrical angle of the rotor, T L is the load torque, J is the moment of inertia of the motor; the designed sliding mode observer equation is as follows: in, is the estimated value of the sliding mode observer, P and U represent the sliding mode control law, and g represents the feedback coefficient; S4.

2. Subtract equation (8) from equation (9) to obtain the observation error equation of the system: Among them, e1 is the observation error of the rotor electrical angle, e2 is the observation error of the load torque, is the first-order derivative of e1, is the second-order derivative of e1, is the first derivative of e2; S4.

3. In order to achieve finite time convergence and stable convergence accuracy, the sliding surface is selected as: Where s is the sliding mode function and c is a constant. The derivative of (11) is: in, is the first derivative of the sliding mode function; S4.

4. Design the sliding surface approach law and the sliding mode control rate. Specifically, the sliding mode control rate P is designed as: in, is the first-order derivative of the sliding mode control rate P, k is a positive constant, when the observer enters the sliding mode, s = 0 and Combining equation (12) and equation (13), we can obtain: Among them, C1 is a constant. Reasonable design parameters make the exponential term converge quickly to zero, and the sliding surface reaching law is designed as: Where k1 is the control rate gain, n p is the number of pole pairs of the permanent magnet synchronous motor, a is a positive constant, exp(-as) is an exponential term with e as the base, and combining (12), (13), and (15), we get the sliding mode control rate U: S5. The electrical angular velocity observed by S4 is used as feedback of the speed loop, and the observed load torque value is fed forward to the q-axis current loop.

2. The method for estimating the rotor position and speed of a permanent magnet synchronous motor based on a Hall sensor according to claim 1, characterized in that: The step S5 is specifically as follows: S5.1, the estimated value of the rotor electrical angular velocity obtained in step S4 Feedback to the speed loop; S5.2, the load torque estimation value obtained in step S4 Feed forward to the d-axis current loop.

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