A Load Torque Observer for Permanent Magnet Synchronous Motor

Abstract

The present invention discloses a load torque observer for a permanent magnet synchronous motor, the output of which is used to perform load torque compensation on the output of a sliding mode speed controller. The load torque observation adopts an algorithm in which the feedback gain is automatically adjusted according to the change amount of the load torque given value and the change amount of the load torque observed value. When the motor speed is adjusted, the system parameters change, or the load is disturbed, resulting in a change in the load torque given value or / and a change in the load torque observed value, the observation error of the load torque can be quickly reduced, and the load torque observed value is fed forward and compensated to the current regulator, effectively weakening the chattering of the system, having a fast dynamic response speed, high robustness, and improving the control accuracy of the permanent magnet synchronous motor.

Description

[0001] This invention patent application is a divisional application. The original application number is 202010918598.8, the application date is September 4, 2020, and the invention title is a driving control method for a mine traction permanent magnet synchronous motor. Technical Field

[0002] The present invention relates to the technical field of permanent magnet synchronous motors, and more specifically, particularly relates to a load torque observer for a permanent magnet synchronous motor. Background Art

[0003] Permanent magnet synchronous motors have the advantages of high efficiency, large torque, and good speed performance, and are widely used in fields such as manufacturing, electric vehicles, and industrial production. The working environment of mine traction motors is complex and changeable, with large load torque variations, a wide speed regulation range, and the requirement of being able to start with a large torque. The robustness of the vector control method for permanent magnet synchronous motors based on PI controllers is not as good as that of the sliding mode control method. However, when there are load disturbances or internal parameter perturbations in the sliding mode control method, it will cause obvious chattering of the motor speed. Summary of the Invention

[0004] The object of the present invention is to provide a load torque sliding mode observer for a permanent magnet synchronous motor that can improve the response speed of load torque observation and quickly reduce the load torque observation error, thereby reducing the motor speed chattering, in view of the large load torque variations and wide speed regulation range of the permanent magnet synchronous motor. It includes:

[0005] Adjust the feedback gain according to the changes in the load torque given value and the load torque observed value, and observe the load torque based on the rotor angular velocity ω and the current i q to obtain a new load torque observed value; the load torque observer is

[0006]

[0007] where J is the moment of inertia, p is the number of pole pairs of the motor, ψ f is the permanent magnet flux linkage, is the estimated value of the rotor angular velocity, is the first derivative of; is the load torque observed value, is the first derivative of; g is the feedback gain of the load torque observer and g < 0; kw is the proportional gain of the load torque observer and it is required that k W < 0.

[0008] The speed of the permanent magnet synchronous motor is controlled by a sliding mode speed controller, and the output of the load torque observer is used to perform load torque compensation on the output of the sliding mode speed controller; the load torque given value Output from the sliding mode speed controller.

[0009] The feedback gain g is adjusted according to the load torque set value and the observed value of the load torque The method of adjustment is as follows:

[0010] Step ①: The load torque observer observes the load torque according to the existing value of the feedback gain g, and obtains the observed value of the load torque The sliding mode speed controller performs control operations to obtain the load torque set value

[0011] Step ②: Calculate

[0012] Step ③: Determine whether ΔT is greater than ε2; when ΔT is greater than ε2, take the feedback gain g equal to g min and exit; when ΔT is less than or equal to ε2, enter Step ④;

[0013] Step ④: Determine whether ΔT is less than ε1; when ΔT is less than ε1, take the feedback gain g equal to g max and exit; when ΔT is greater than or equal to ε1, enter Step ⑤;

[0014] Step ⑤: The feedback gain g is calculated according to

[0015]

[0016] where ε1 is the low limit comparison threshold of torque change, ε2 is the high limit comparison threshold of torque change, and 0 < ε1 < ε2; g max is the high value of the feedback gain, g min is the low value of the feedback gain, and g min < g max <0.

[0017] The method of selecting the values of g min , g max , ε1, and ε2 is as follows:

[0018] Step (1), both the load torque observer and the sliding mode speed controller are in a steady state, keeping the given rotor angular velocity unchanged and the load torque unchanged;

[0019] Step (2), let the feedback gain g gradually decrease from a relatively large value. When the steady-state error of the load torque observation reaches the limit value of the steady-state error of the load torque observation, determine the value of the feedback gain g at this time as g max ;

[0020] Step (3), keep the given rotor angular velocity unchanged and the load torque unchanged, and let the feedback gain g be equal to gmax Measure the ΔT value continuously for n times, and take the average value of the sum of the largest m ΔT values among the n measurements at this time as the lower limit comparison threshold ε1 of torque change;

[0021] Step (4), finely adjust and change the feedback gain g. When the load torque observer and the sliding mode speed controller are both in a steady state, keep the given rotor angular velocity unchanged and make the load torque suddenly change. On the premise of ensuring that the torque observation tracking overshoot of the output observation value of the load torque observer is within the torque observation tracking overshoot limit value, measure the tracking adjustment time of the load torque observer.

[0022] Step (5), repeat step (4), and select the feedback gain g value with the shortest tracking adjustment time as the g min value;

[0023] Step (6), keep the given rotor angular velocity unchanged and the load torque unchanged again, and make the feedback gain g equal to g min , measure the ΔT value continuously for n times, and take the average value of the sum of the largest m ΔT values among the n measurements at this time as the upper limit comparison threshold ε2 of torque change.

[0024] The n is an integer greater than or equal to 20, and the m is an integer greater than or equal to 5 and less than or equal to 0.5n.

[0025] The state variables of the sliding mode speed controller are:

[0026]

[0027] Among them, ω is the rotor angular velocity, and ω * is the given rotor angular velocity; the sliding mode surface of the sliding mode speed controller is s = cx1 + x2, c is the sliding mode surface parameter, and c > 0; the given value of the load torque output by the sliding mode speed controller and the given component i′ of the torque current q are

[0028]

[0029] Among them, D = 1.5pψ f / J, the coefficients k1, k2, k3, k4 are the exponential reaching rate coefficients of the speed sliding mode control, and k1 > 0, k2 > 0, 1 < k3 < 2, k4 > 0.

[0030] The given value of the q-axis torque current is the sum of the given component i′ of the torque current q and the compensation component i″ of the torque current q , and is

[0031]

[0032] wherein the torque current compensation component i″ output by the load torque observer q is

[0033]

[0034] the proportional gain k w is selected according to

[0035]

[0036] where T N is the rated torque of the motor, and β > 0; further, 1 ≤ β ≤ 20.

[0037] The speed of the permanent magnet synchronous motor is controlled by a sliding mode speed controller. The method includes detecting the rotor position θ and the three-phase current i a , i b and i c of the permanent magnet synchronous motor; performing Clark transformation on the permanent magnet synchronous motor according to the three-phase current i a , i b and i c to obtain the current i α , i β in the α-β axis coordinate system, and performing Park transformation according to the current i α , i β and the rotor position θ to obtain the current i d , i q in the d-q axis coordinate system. Further, the speed control of the permanent magnet synchronous motor is realized by a permanent magnet synchronous motor speed control system including a sliding mode speed controller, a load torque observer, a q-axis current controller, a d-axis current controller, a Clark e transformation module, a position and speed detection module, a Park transformation module, a Park inverse transformation module, an SVPWM module and a three-phase inverter.

[0038] The beneficial effects of the present invention are as follows. For the load torque observation, an algorithm is adopted in which the feedback gain is automatically adjusted according to the change in the load torque given value and the change in the load torque observed value. This avoids the problems that when a fixed small feedback gain is selected for the load torque observer, the torque observation fluctuates greatly, and when a fixed large feedback gain is selected, the convergence time is long. When the control parameters, model parameters, etc. of the system change, or when the load is disturbed, resulting in changes in the load torque given value or / and the load torque observed value, the observation error of the load torque can be quickly reduced, improving the observation effect and the rapidity and accuracy of the motor speed control. The feedback gain is automatically adjusted when the load torque given value changes. When the load torque observed value has not changed significantly, but the load torque given value changes due to the change in the rotor angular velocity given value or / and the actual value of the rotor angular velocity, or when the load torque given value changes due to the change in the system model parameters, which will cause large fluctuations in the load torque observed value, the feedback gain can be adjusted in advance. When the observation error of the load torque actually occurs, the response speed of the observer can be accelerated, the observation error of the load torque observed value can be quickly reduced, and the rapidity and accuracy of the motor speed control can be further improved. By feeding forward the load torque observed value to the given value of the current regulator, the relevant effects caused by load disturbances or changes in system parameters can be offset without a large adjustment in the given current part output by the sliding mode speed controller, effectively weakening the chattering of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 FIG. 1 is a block diagram of Embodiment 1 of a permanent magnet synchronous motor speed control system;

[0040] Figure 2 FIG. 2 is a flowchart of Embodiment 1 of a method for automatically adjusting the feedback gain. DETAILED DESCRIPTION OF THE INVENTION

[0041] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0042] The permanent magnet synchronous motor speed control system for implementing the driving control method of a mine traction permanent magnet synchronous motor includes a permanent magnet synchronous motor load torque observer. Figure 1 FIG. 1 is a block diagram of Embodiment 1 of the permanent magnet synchronous motor speed control system. Figure 1 In FIG. 1, the Clarke transformation module inputs the three-phase currents i a , i b and i c of the permanent magnet synchronous motor (i.e., PMSM), and outputs the currents i α , i β; The position sensor in the position and speed detection module detects the rotor position θ of the permanent magnet synchronous motor and then converts it into the rotor angular velocity ω for output; The Park transformation module inputs the current iα, i β and the rotor position θ, and outputs the current i d 、i q in the rotating d-q axis coordinate system; The sliding mode speed controller SMC inputs the given rotor angular velocity ω * and the rotor angular velocity ω, and outputs the given load torque value T L * and the given torque current component i′ g ; The load torque observer inputs the given load torque value T L * 、the rotor angular velocity ω and the current i q , and outputs the torque current compensation component i″ q ; The given torque current component i′ q and the torque current compensation component i″ q are added together and used as the given q-axis torque current value i * q ; The q-axis current PI controller inputs the given q-axis torque current value i * q and the current i d , and outputs the control voltage U q in the q-axis coordinate system; The d-axis current PI controller inputs the given q-axis torque current value i * d and the current i d , and outputs the control voltage U d in the d-axis coordinate system. The given d-axis torque current value i * d is equal to 0; The Park inverse transformation module inputs the control voltages U d 、U q in the d-q axis coordinate system, and outputs the control voltages U α 、U β in the α-β axis coordinate system; The SVPWM module (i.e., the space vector pulse width modulation module) inputs the control voltages U α 、U β , and outputs pulse signals to the three-phase inverter. The three-phase inverter converts the DC voltage U dc into three-phase AC power supplies U a 、U b 、U c , thus driving the permanent magnet synchronous motor to operate.

[0043] Ignoring the effects of core eddy current and hysteresis loss, etc., and adopting the PMSM rotor magnetic field orientation control with i d = 0, the mathematical model of the PMSM in the d-q axis rotating coordinate system is established, and the voltage equation is:

[0044]

[0045] For the use of i d =0 control mode of salient pole PMSM vector control system, the electromagnetic torque equation is:

[0046]

[0047] The PMSM motion equation is:

[0048]

[0049] In formula (1), (2), and (3), u d 、u q are the voltages of the dq axes respectively; i d 、i q are the currents of d and q axes respectively; L d , L q are the inductance of d and q axes respectively; T e is the electromagnetic torque; T L is the load torque; R is the stator resistance; p is the number of motor poles; ω e is the rotor electrical angular velocity, i.e. angular frequency; ω is the rotor angular velocity, i.e. the motor rotor mechanical angular velocity; ψ f is the permanent magnet flux; J is the moment of inertia; B is the friction coefficient; t is time.

[0050] Let the motor's rotor angular velocity error e = ω*-ω, where ω* is the motor's given rotor angular velocity. Define the state variables of the permanent magnet synchronous motor speed control system embodiment 1 as:

[0051]

[0052] From equations (2), (3) and (4), we can get:

[0053]

[0054] Simplify equation (5) and let D = 1.5pψf / J. The state space equation of the system in Example 1 can be obtained as follows:

[0055]

[0056] Select the sliding surface function as:

[0057] s=cx1+x2 (7)

[0058] In Equation (7), s is the sliding mode surface, c is the sliding mode surface parameter, and c > 0. In Equation (7), c is the coefficient of the rotor angular velocity error term, and its magnitude mainly affects the control action similar to the proportional coefficient in PID control. The value of c also takes into account balancing the rotor angular velocity error and the change rate of the rotor angular velocity. Usually, it is selected in the range greater than 0 and less than 1000. For example, c = 60 is taken. Differentiating Equation (7) gives:

[0059]

[0060] The expression of the traditional exponential reaching law is:

[0061]

[0062] In Equation (9), sgn() is the sign function, -k1sgn(s) is the constant velocity reaching term, -k2s is the exponential reaching term. The two coefficients k1 and k2 respectively determine the chattering of the sliding mode surface and the motion quality of the reaching process, and both k1 and k2 are greater than 0. To improve the system response speed, based on the traditional exponential reaching law, the constant velocity reaching term is changed to a variable velocity reaching term. The improved reaching law is:

[0063]

[0064] where k1 > 0, k2 > 0, 1 < k3 < 2, k4 > 0. When |s| is relatively large, the approaching speed of the variable velocity reaching term is relatively large, which can accelerate the sliding mode approaching motion speed; when |s| is relatively small, the approaching speed of the variable velocity reaching term is relatively small, which can weaken the chattering. The value of k4 can be selected with reference to the change rate of the rotor angular velocity when the permanent magnet synchronous motor starts under rated load, and is selected near this change rate of the rotor angular velocity. Further, it is taken in the range of 80% to 120% of this change rate of the rotor angular velocity. For example, assume that the time taken for a certain permanent magnet synchronous motor to start from rated load to the rated speed of 1500 r / min is 0.21 s, and the average change rate of the rotor angular velocity is 750 rad / s 2 , it is recommended that k4 be taken in the range of 600 - 900 at this time. The larger k3 is, the greater the variable speed is. Generally, k3 is taken in the range of 1.05 - 1.3. Generally, the values of the coefficient k1 and the coefficient k2 are both less than 2000; the larger the coefficient k2 is, the faster the system state can approach the sliding mode; the coefficient k1 determines the speed of reaching the switching surface, and the smaller k1 is, the smaller the distance and jitter of crossing the switching surface are. k1 and k2 are the variable velocity reaching term coefficient and the exponential reaching term coefficient respectively. Since The value varies near 1. Therefore, the variable-speed approaching term coefficient k1 and the exponential approaching term coefficient k2 in Equation (10) can be tuned in the same way as the constant-speed approaching term coefficient and the exponential approaching term coefficient in the traditional exponential approaching rate. k3 is the variable-speed coefficient, and its magnitude changes the speed of variable speed; k4 is the migration coefficient, and its magnitude changes the variable-speed critical point.

[0065] Combining Equations (8) and (10), the calculated q-axis current command is used as the torque current command component i′ q , and the load torque command value T output by the sliding-mode speed controller can be obtained L * and the torque current command component i′ q are:

[0066]

[0067] In Embodiment 1 of the permanent magnet synchronous motor speed control system, the output of the sliding-mode speed controller contains an integral term, which filters the control quantity, can weaken the system chattering, and reduce the steady-state error of the system. Define the Lyapunov function as:

[0068]

[0069] From Equations (10) and (12), we can get:

[0070]

[0071] In Equation (13), k1>0, k2>0, s·sgn(s)≥0, Therefore It shows that the system tracking error can converge to zero within a finite time, and the system can operate stably.

[0072] When designing the sliding-mode speed controller, the method for tuning the parameters c, k1, k2, k3, and k4 is to first determine the values of k3 and k4; let the q-axis torque current command value i * q only includes the input torque current command component i′ q (that is, no load torque compensation control is performed), and then adjust the sliding-mode surface parameter c and the variable-speed approaching term coefficient k1 from small to large in the sliding mode of the system until obvious chattering appears in the system. On this basis, taking into account the suppression of chattering and the system state convergence speed, appropriately reduce the sliding-mode surface parameter c and the variable-speed approaching term coefficient k1; finally, while taking into account the suppression of the sliding-mode chattering, mainly adjust the exponential approaching term coefficient k2 according to the rapidity of the system reaching section (for example, the motor starting stage of the step response), and make appropriate fine-tuning of the other parameter values of the sliding-mode speed controller.

[0073] According to the electromagnetic torque and motion equation of PMSM, for a constant step load, it can be considered as a constant value within the change period, that is Taking the motor rotor angular velocity and load torque as state variables, the PMSM state equation is:

[0074]

[0075] Based on Equation (14), taking the load torque and the motor rotor angular velocity as the observation objects, the first embodiment of the load torque observer is established as:

[0076]

[0077] In Equation (15), is the observed value of the load torque, is the estimated value of the rotor angular velocity, g is the feedback gain of the load torque observer, k g is the sliding mode gain of the first embodiment of the load torque observer, and the first embodiment of the load torque observer is a sliding mode observer. Comparing the motor friction with the load torque, the proportion is small. Let B = 0 and ignore the influence of friction, then the first embodiment of the load torque observer in Equation (15) becomes:

[0078]

[0079] Based on Equation (14) and Equation (16) when B = 0, the error equation of the first embodiment of the load torque observer is obtained as:

[0080]

[0081] In Equation (17), is the rotor angular velocity estimation error, is the load torque observation error, and the observer sliding mode surface is defined as According to the sliding mode reachability condition, the stability condition of the observer system in Equation (16) is k g ≤ -|e2 / J|, and g < 0.

[0082] Based on Equation (14), taking the load torque and the motor rotor angular velocity as the observation objects, the second embodiment of the load torque observer can also be established as:

[0083]

[0084] Comparing the motor friction with the load torque, the proportion is small. Let B = 0 and ignore the influence of friction, then the second embodiment of the load torque observer in Equation (18) becomes:

[0085]

[0086] In formula (18) and (19), is the observed value of the load torque, is the estimated value of the rotor angular velocity, g is the feedback gain of the load torque observer, k W is the proportional gain of the load torque observer embodiment 2, and the load torque observer embodiment 2 is a state observer. According to equation (14) and equation (19) when B=0, the error equation of the load torque observer embodiment 2 is obtained as follows:

[0087]

[0088] In formula (20), is the rotor angular velocity estimation error, is the load torque observation error. The state observer of equation (19) is an autonomous linear system. W <0, and g<0, the observer is asymptotically stable. Formula (15) of the load torque observer embodiment 1 and formula (18) of the load torque observer embodiment 2 both take into account the friction factor of the motor. The addition of small friction damping will have an adverse effect on the rapidity of the system response, but can increase the stability based on formula (16) and formula (19), respectively.

[0089] When the observer embodiment 1 of equations (15) and (16) is selected, the sliding mode gain k g The setting method is to follow

[0090]

[0091] In formula (21), α≥1; generally, the value of α is selected in the range of 1 to 5, for example, α is selected to be equal to 1.5. Load torque observer embodiment 1 In the process of observing the load torque, k g The absolute value of |e2| is too small. When |e2| is large, the observer cannot enter the sliding mode state. g The absolute value of is large enough to ensure that the observer enters the sliding mode state, but the steady-state observation fluctuation of the load torque becomes larger; k g The value of changes with the load torque observation error, which can simultaneously increase the stability of the observer and reduce the steady-state observation fluctuation of the load torque.

[0092] When the observer embodiment 2 of equations (18) and (19) is selected, the proportional gain k W The setting method is to follow

[0093]

[0094] In formula (22), T Nis the rated torque of the motor, β > 0; generally, the value of β is selected within the range of 1 to 20. For example, β = 10 is selected. When β is selected to increase, the steady-state fluctuation of the load torque observation becomes larger, but the overshoot of the torque observation tracking becomes smaller; when β is selected to decrease, the steady-state fluctuation of the load torque observation becomes smaller, but the overshoot of the torque observation tracking becomes larger.

[0095] In the observer represented by Equation (15), (16) or Equation (18), (19), the value of the feedback gain g has a great influence on the load torque observation result. The larger the feedback gain g, the smaller the fluctuation of the observed torque, but the slower the identification speed of the observed torque; the smaller the feedback gain g, the faster the observed torque speed, but the larger the fluctuation of the observed torque. Considering this problem, in the traditional load torque observer, considering the observation speed and fluctuation of the load torque comprehensively, the feedback gain g is taken as a compromise value, but this will discard the advantages of small fluctuation at large feedback gain and fast observation speed at small feedback gain.

[0096] The motor sliding mode speed control mainly suppresses the influence of parameter changes and external load disturbances on the system by increasing the amplitude of the discontinuous term in the controller, but the increase in amplitude will cause the inherent chattering of the sliding mode. To solve the contradiction between chattering and disturbance rejection in the sliding mode control system, the observer is used to observe the change of the load disturbance in real time, and the observed value of the load torque is fed forward and compensated to the current regulator to reduce the amplitude of the discontinuous term in the sliding mode control, weaken the change of the given torque caused by parameter changes, or the chattering of the system caused by load disturbances. In order to make full use of the advantages of the feedback gain g at high and low values, according to the change of the load torque observed value and the change of the load torque given value at two adjacent moments, when the change of the load torque given value is small and the change of the load torque observed value is small, a larger value of the feedback gain g is given to make the observation result have small fluctuation and stronger stability; when the change of the load torque given value is large or the change of the load torque observed value is large, a smaller value of the feedback gain g is given to make the observation speed faster. Finally, through the adjustment of the feedback gain g, a comprehensive result of fast observation speed, small fluctuation and stronger stability is obtained.

[0097] The load torque observer Embodiment 1, or the load torque observer Embodiment 2 is used for Figure 1 In the permanent magnet synchronous motor speed control system Embodiment 1, the load torque observer adjusts the feedback gain g according to the change of the load torque given value and the load torque observed value q observes the load torque based on the rotor angular velocity ω and the current i

[0098] Figure 2Flowchart of Embodiment 1 of the method for automatically adjusting feedback gain. In Embodiment 1 of the load torque observer, or when Embodiment 2 of the load torque observer is used in Figure 1 Embodiment 1 of the permanent magnet synchronous motor speed control system, the feedback gain is automatically adjusted. During a periodic control process of the motor speed, Figure 2 As shown in (b) therein, the adjustment of the feedback gain g is later than the observation of the load torque and the calculation of the output of the sliding mode speed controller, and there is:

[0099] Step ①: The load torque observer observes the load torque T according to the existing value of the feedback gain g L to obtain the observed value of the load torque The sliding mode speed controller performs control operations to obtain the given value of the load torque At this time is is Until the next adjustment of the feedback gain g, this time becomes becomes

[0100] Step ②: Calculate

[0101] Step ③: Judge whether ΔT is greater than ε2; when ΔT is greater than ε2, take the feedback gain g equal to g min and exit; when ΔT is less than or equal to ε2, enter Step ④;

[0102] Step ④: Judge whether ΔT is less than ε1; when ΔT is less than ε1, take the feedback gain g equal to g max and exit; when ΔT is greater than or equal to ε1, enter Step ⑤;

[0103] Step ⑤: The feedback gain g is calculated according to

[0104]

[0105]

[0106] wherein, ε1 is the low limit comparison threshold of torque change, ε2 is the high limit comparison threshold of torque change, and 0 < ε1 < ε2; g max is the high value of the feedback gain, g min is the low value of the feedback gain, and g min max <g max <0.

[0107] During a periodic control process of the motor speed, Figure 2The adjustment of the feedback gain g shown in (a) in [reference] precedes the observation of the load torque and the calculation of the output of the sliding mode speed controller. The method for adjusting the feedback gain g changes step ① above to step ⑤, and steps ② - ⑤ to steps ① - ④. The exits in each step are changed to enter step ⑤, and

[0108] Figure 2 in which, the sum of the changes in the load torque reference value and the changes in the observed load torque value for the last two times ΔT L * is the difference between the last two load torque reference values, is the difference between the last two observed load torque values. When ΔT is greater than ε2, it indicates that the observed load torque value fluctuates greatly, or due to changes in system model parameters, changes in the rotor angular velocity reference value, and changes in the actual rotor angular velocity value, the load torque reference value changes greatly and will cause large fluctuations in the observed load torque value. The feedback gain g is selected to be equal to g min for rapid identification and observation of the load torque; when ΔT is less than ε1, it indicates that the change in the load torque reference value is small and the observed load torque value of the state fluctuates little. The feedback gain g is selected to be equal to g max for load torque identification and observation mainly focused on stability; when ΔT is greater than or equal to ε1 and less than or equal to ε2, the feedback gain g is calculated according to Equation (23), so that the feedback gain g decreases with the increase of ΔT in this interval, avoiding the adverse impact on the working stability of the torque observer caused by the drastic change of the feedback gain g due to small changes in ΔT. Figure 2 in which, the specific values of ε1 and ε2 are related to the sampling control period (cycle time) of the sliding mode speed controller, the permanent magnet synchronous motor and its load conditions. ε2 generally takes values in the range less than 5% of the rated torque. For example, when the rated torque is 22 N·m, take ε1 = 0.1 N·m and ε2 = 0.6 N·m. The value of the feedback gain g satisfies g min <g max <0. Generally, g min ≥ -5000. g min should be such that when the load torque suddenly changes, the torque observation tracking overshoot of the torque observer is within the torque observation tracking overshoot limit value; g max should be such that when the load torque remains unchanged and both the torque observer and the sliding mode speed controller are in a steady state, the sum of the changes in the load torque reference value and the changes in the observed load torque value for the last two times ΔT is less than ε1; for example, select the feedback gain g max = -0.5, g min = -10. Select g min 、g max, the specific method for ε1 and ε2 values is as follows:

[0109] Step (1), both the load torque observer and the sliding mode speed controller are in a steady state, keeping the given rotor angular velocity unchanged and the load torque unchanged;

[0110] Step (2), let the feedback gain g start to gradually decrease from a relatively large value. For example, let the feedback gain g gradually decrease from -0.01. When the steady-state error of the load torque observation reaches the limit value of the steady-state error of the load torque observation, determine the feedback gain g value at this time as g max ;

[0111] Step (3), keep the given rotor angular velocity unchanged and the load torque unchanged, and let the feedback gain g be equal to g max , continuously measure the ΔT value n times, and take the average value of the sum of the largest m ΔT values in these n measurements at this time as the low-limit comparison threshold ε1 of the torque change;

[0112] Step (4), finely adjust and change the feedback gain g. When both the load torque observer and the sliding mode speed controller are in a steady state, keep the given rotor angular velocity unchanged and let the load torque mutate. On the premise that the torque observation tracking overshoot of the output observation value of the load torque observer is within the limit value of the torque observation tracking overshoot, measure the tracking adjustment time of the load torque observer;

[0113] Step (5), repeat Step (4), and select the feedback gain g value with the shortest tracking adjustment time as the g min value; Usually, when the torque observation tracking overshoot is close to the limit value of the torque observation tracking overshoot, the tracking adjustment time of the load torque observer is shorter;

[0114] Step (6), once again keep the given rotor angular velocity unchanged and the load torque unchanged, and let the feedback gain g be equal to g min , continuously measure the ΔT value n times, and take the average value of the sum of the largest m ΔT values in these n measurements at this time as the high-limit comparison threshold ε2 of the torque change.

[0115] After observing the load torque observation value and converting the observed value of the load torque q into the torque current compensation component i″ q and feeding it forward to the input of the q-axis current PI controller to compensate the torque current given component i′ * q output by the sliding mode speed controller. The q-axis torque current given value i

[0116]

[0117] In Equation (24), k q = 1 / (1.5pψf) is the torque observation compensation coefficient. By comparing Equation (11) and Equation (24), it can be seen that when the load is disturbed or the system parameters change, no load torque compensation is added in Equation (11). It is necessary to select larger values of k1 and k2 to provide a large enough change in the given current to offset the relevant effects of load disturbance or system parameter change, so as to ensure that the motor speed can be quickly stabilized; while Equation (24) feeds forward the observed value of the load torque to the current regulator. Without the need for large values of k1 and k2, when the load is disturbed or the system parameters change, it can provide a large enough change in the given current to offset the relevant effects of load disturbance or system parameter change, reduce the output pressure of the sliding mode speed controller and the amplitude of the discontinuous term, and effectively weaken the chattering of the system.

[0118] When the fixed feedback gain value is set, the smaller the feedback gain g, the larger the oscillation amplitude of the load torque observation and the stronger the volatility; the larger the feedback gain g, the smaller the oscillation amplitude of the load torque observation and the higher the observation accuracy. The automatic gain adjustment algorithm solves the problems of large torque observation fluctuations caused by small feedback gains in the load torque observer and long convergence times for large feedback gains. The convergence time and fluctuation amplitude indicators are better than those of the compromise gain algorithm. It can quickly track the change value of the load torque and quickly reduce the observation error caused by given changes or parameter changes, with a small oscillation amplitude and high observation accuracy, achieving a good observation effect.

[0119] When changing the given speed under the rated load torque, although the actual load torque remains unchanged, from the load torque observer constructed by Equation (15), (16) or Equation (18), (19), it can be seen that when the rotor angular velocity ω changes, even if the load torque remains unchanged, the observed torque value will change, resulting in an observation error. When changing the given speed under the rated load torque, the control adjustment process of the permanent magnet synchronous motor sliding mode control system is that first, the sliding mode speed controller makes the output given value T of the load torque change according to the given speed change L * change, so that the given value i of the torque current * q changes, and then the electromagnetic torque T of the permanent magnet synchronous motor e changes, driving the motor to change the rotor angular velocity ω; if the feedback gain g is only automatically adjusted according to the change amount of the observed value of the load torque, then at this time, only when the rotor angular velocity ω changes and the observed value of the load torque changes, the feedback gain g is adjusted; the feedback gain g is based on the change amount ΔT of the given value of the load torque L *and the change in the observed value of the load torque The sum of the absolute values is automatically adjusted. When the given speed changes to make the given value of the load torque T L * change, and the observed value of the load torque has not changed yet, the feedback gain g is adjusted in advance. When the observed error of the load torque truly occurs, the response speed of the observer can be accelerated, and the observed error of the observed value of the load torque can be eliminated (reduced) as soon as possible, thereby improving the rapidity and accuracy of the motor speed control. Similarly, when the system model parameters change to make the given value of the load torque T L * change prior to the observed value of the load torque the feedback gain g is simultaneously adjusted according to the change amount ΔT of the given value of the load torque L * and the change amount of the observed value of the load torque to be able to adjust the feedback gain g in advance, accelerate the response speed of the observer, eliminate (reduce) the observed error of the observed value of the load torque as soon as possible, and further improve the rapidity and accuracy of the motor speed control. Of course, if the load is disturbed and causes the observed value to change, when it changes greatly, it can be seen from Figure 2 that the feedback gain g can also be automatically adjusted to eliminate (reduce) the observed error of the observed value of the load torque as soon as possible, so that the observed value of the load torque can catch up with the change of the load torque T L as soon as possible.

[0120] In the periodic control process of the permanent magnet synchronous motor speed control system embodiment 1, the given value of the load torque T calculated at the k-th moment (or the k-th step) of the current time L * is denoted as T L * (k), and the observed value of the load torque is denoted as The k - 1 moment is the previous moment of the periodic control process of the k-th moment. The given value of the load torque T L * is denoted as T L * (k - 1), and the observed value of the load torque is denoted as The k - 2 moment is the previous moment of the periodic control process of the k - 1 moment. The given value of the load torque T L * is denoted as T L* (k - 2), observed value of load torque denoted as Figure 2 In (b) of, load torque observation and speed control are first performed, and then automatic adjustment of feedback gain is carried out. The periodic control process of the motor speed is as follows:

[0121] Step 1: Detect the rotor position θ, rotor angular velocity ω, and three-phase current i a , i b and i c ;

[0122] Step 2: Perform Clark transformation on the permanent magnet synchronous motor according to the three-phase current i a , i b and i c to obtain the current i α , i β in the α-β axis coordinate system. According to the current i α , i β and the rotor position θ, perform Park transformation to obtain the current i d , i q in the d-q axis coordinate system;

[0123] Step 3: The load torque observer observes the load torque according to the rotor angular velocity ω and the current i q to obtain the observed value of load torque and the torque current compensation component i″ q ;

[0124] Step 4: The sliding mode speed controller performs control calculations according to the input rotor given angular velocity ω * and the rotor angular velocity ω to obtain the given value of load torque and the given component of torque current i′ q ;

[0125] Step 5: The feedback gain g of the load torque observer is adjusted according to the change of the given value of load torque T L * and the observed value of load torque ;

[0126] Step 6: Calculate the given value of q-axis torque current i q according to the given component of torque current i′ q and the torque current compensation component i″ q * ; The d-axis current controller is based on the given value of d-axis torque current i d * and the current i d in the d-axis coordinate system.Perform PI control operation on the difference to obtain the control voltage U in the d-axis coordinate system d ; The q-axis current controller is based on the given value i of the q-axis torque current q * and the current i in the q-axis coordinate system q Perform PI control operation on the difference to obtain the control voltage U in the q-axis coordinate system q ; According to the control voltages U d and U q in the d-q axis coordinate system, perform Park inverse transformation to obtain the control voltages U α and U β in the α-β axis coordinate system; The given value i of the d-axis torque current d * is equal to 0;

[0127] Step seven: Use the control voltages U α and U β in the α-β axis coordinate system as the inputs of the SVPWM module, and the SVPWM module controls the three-phase inverter to generate three-phase AC power supplies U a and U b and U c , thereby driving the permanent magnet synchronous motor to operate.

[0128] Figure 2 In (a) of , first perform feedback gain automatic adjustment, and then perform load torque observation and speed control. In the above steps, the order of step five and steps three and four should be interchanged, that is, first perform step five, and then perform steps three and four.

[0129] In the specific methods of selecting the values of g min and g max and the comparison thresholds ε1 and ε2 above, they are all realized under the condition that the parameters in the sliding mode speed controller have been tuned and the load torque compensation control is performed; it is recommended that n be an integer greater than or equal to 20, and m be an integer greater than or equal to 5 and less than or equal to 0.5n.

[0130] In the above embodiments, the overshoot limit value of torque observation and tracking is generally 1% to 10% of the rated torque of the motor. Specifically, the overshoot limit value of torque observation and tracking is 2% of the rated torque, or 5% of the rated torque, or 10% of the rated torque, and so on. When the load torque suddenly changes from one fixed value to another, the time from the start of the mutation to the time when the observed value output by the load torque observer stably enters the range of the steady-state error limit of the load torque observation is the torque observation transition process, and the tracking adjustment time refers to the time of this transition process; the steady-state error of the load torque observation refers to the error between the instantaneous value of the observed torque and the load torque when the load torque is constant and the load torque observer is in a steady state. This error includes the observation error caused by the chattering of the sliding mode observer itself and the observation error caused by interference reasons other than load fluctuations, or the observation error caused by the chattering of the rotor angular velocity of the state observer and the observation error caused by interference reasons other than load fluctuations; the steady-state error limit of the load torque observation is the maximum absolute value of the steady-state error of the load torque observation allowed by the load torque observer; the steady-state error limit of the load torque observation is generally 1% to 5% of the rated torque of the motor. Specifically, the steady-state error limit of the load torque observation is 1% of the rated torque, or 2% of the rated torque, or 5% of the rated torque, and so on. The overshoot of torque observation and tracking refers to the maximum deviation value of the observed value output by the load torque observer exceeding the load torque after the mutation when the load torque suddenly changes from one fixed value to another. When the steady-state error of the load torque observation is within the vicinity range of the steady-state error limit of the load torque observation, for example, within the range of 95% to 105%, or within the range of 98% to 102%, it is considered that the steady-state error of the load torque observation increases to the steady-state error limit of the load torque observation. The sliding mode speed controller being in a steady state means that the sliding mode speed controller is stably in the sliding mode; the steady-state error of the rotor angular velocity refers to the difference between the instantaneous value of the rotor angular velocity of the motor and the steady-state value at steady state, and the steady-state error limit of the rotor angular velocity is the maximum absolute value of the steady-state error of the rotor angular velocity allowed by the system. In the load torque observer, the sliding mode observer of Embodiment 1 being in a steady state means that the sliding mode observer is stably in the sliding mode; the state observer of Embodiment 2 being in a steady state means that the state observer is in the working state after the torque observation transition process. The steady-state error of the rotor angular velocity refers to the difference between the instantaneous value of the rotor angular velocity of the motor and the steady-state value at steady state, and the steady-state error limit of the rotor angular velocity is the maximum absolute value of the steady-state error of the rotor angular velocity allowed by the system.

[0131] The permanent magnet synchronous motor speed control system and the permanent magnet synchronous motor drive control method including the load torque observer of the permanent magnet synchronous motor of the present invention can be used in other application occasions of permanent magnet synchronous motors in addition to the control of mine traction motors.

[0132] Except for the technical features described in the specification, other technologies involved in the present invention are all conventional technologies mastered by those skilled in the art. For example, the q-axis current controller and the d-axis current controller are controlled by a PI controller and the selection of controller parameters, the selection of control parameters for the sliding mode speed controller, the position and speed detection module uses a resolver or an optical encoder, etc. to detect the rotation angle and rotation speed of the permanent magnet synchronous motor rotor, and for the Clarke transformation module, Park transformation module, Park inverse transformation module, SVPWM module, the transformation method and application method of the three-phase inverter, etc., are all conventional technologies mastered by those skilled in the art.

Claims

1. A load torque observer for a permanent magnet synchronous motor, characterized in that Adjust the feedback gain according to the changes in the load torque given value and the load torque observed value, based on the rotor angular velocity ω and the current i q Observe the load torque to obtain a new observed value of the load torque; The load torque observer is where J is the moment of inertia, p is the number of pole pairs of the motor, ψ f is the permanent magnet flux linkage, is the estimated value of the rotor angular velocity, is the first derivative of; is the observed value of the load torque, is the first derivative of; g is the feedback gain of the load torque observer and g < 0; k W is the proportional gain of the load torque observer and it is required that k W < 0; The speed of the permanent magnet synchronous motor is controlled by a sliding mode speed controller, and the output of the load torque observer is used to compensate the load torque for the output of the sliding mode speed controller; the load torque set value is output by the sliding mode speed controller.

2. The permanent magnet synchronous motor load torque observer according to claim 1, wherein The feedback gain g is adjusted according to the given value of the load torque and the observed value of the load torque The method of adjustment is as follows: Step ①: The load torque observer observes the load torque based on the existing feedback gain g value to obtain the observed value of the load torque The sliding mode speed controller performs control operations to obtain the given value of the load torque Step ②, calculate Step ③: Determine whether ΔT is greater than ε2; when ΔT is greater than ε2, take the feedback gain g equal to g min and exit; when ΔT is less than or equal to ε2, proceed to Step ④; Step ④: Determine whether ΔT is less than ε1; when ΔT is less than ε1, take the feedback gain g equal to g max and exit; when ΔT is greater than or equal to ε1, proceed to Step ⑤; Step ⑤, the feedback gain g is calculated according to as follows; Among them, ε1 is the lower limit comparison threshold of torque change, ε2 is the upper limit comparison threshold of torque change, and 0 < ε1 < ε2; g max is the high value of feedback gain, g min is the low value of feedback gain, and g min < g max < 0.

3. The permanent magnet synchronous motor load torque observer according to claim 2, wherein Select g min and g max The method for the values of ε1 and ε2 is as follows: Step ⑴, both the load torque observer and the sliding mode speed controller are in a steady state, keeping the given rotor angular velocity unchanged and the load torque unchanged; Step ⑵, let the feedback gain g start to gradually decrease from a large value. When the steady-state error of the load torque observation reaches the load torque When determining the steady-state error limit of the moment observation, the feedback gain g value at this time is determined to be g max ; Step ⑶, keeping the given rotor angular velocity and load torque unchanged and setting the feedback gain g equal to g max , continuously performing n measurements of the ΔT value, and taking the average value of the sum of the largest m ΔT values among the n measurements at this time as the low-limit comparison threshold ε1 for torque change; Step ⑷, finely adjust the feedback gain g. When both the load torque observer and the sliding mode speed controller are in a steady state, keep the given rotor angular velocity unchanged and make the load torque mutate. On the premise of ensuring that the torque observation tracking overshoot of the output observation value of the load torque observer is within the torque observation tracking overshoot limit, measure the tracking adjustment time of the load torque observer; Step ⑸, repeat Step ⑷, and select the feedback gain g value with the shortest tracking adjustment time as the g min value; Step (6), again keep the given rotor angular velocity constant and the load torque constant and let the feedback gain g be equal to g min , continuously perform n measurements of the ΔT value, and take the average value of the sum of the largest m ΔT values in these n measurements at this time as the torque change upper limit comparison threshold ε2; where n is an integer greater than or equal to 20, and m is an integer greater than or equal to 5 and less than or equal to 0.5n.

4. The permanent magnet synchronous motor load torque observer according to any one of claims 1-3, characterized in that, The state variable of the sliding mode speed controller is where ω is the rotor angular velocity, and ω * is the given rotor angular velocity; the sliding mode surface of the sliding mode speed controller is s = cx1 + x2, where c is the sliding mode surface parameter and c > 0; the given value of the load torque output by the sliding mode speed controller and the given component i′ q of the torque current are where D = 1.5pψ f / J, the coefficients k1, k2, k3, k4 are the exponential reaching law coefficients of the speed sliding mode control, and k1 > 0, k2 > 0, 1 < k3 < 2, k4 > 0.

5. The load torque observer of the permanent magnet synchronous motor according to claim 4, wherein q-axis torque current reference value It is the sum of the torque current reference component i′ q and the torque current compensation component i″ q and is where k q = 1 / (1.5pψ f ).

6. The load torque observer of the permanent magnet synchronous motor according to claim 1, wherein The speed of the permanent magnet synchronous motor is controlled by a sliding mode speed controller. The method includes Detect the rotor position θ and three-phase currents i of the permanent magnet synchronous motor a 、i b and i c ; According to the three-phase currents i a 、i b and i c perform Clark transformation on the permanent magnet synchronous motor to obtain the currents i α 、i β in the α-β axis coordinate system. According to the currents i α 、i β and the rotor position θ, perform Park transformation to obtain the currents i d 、i q .

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