With the development of permanent magnet materials, semiconductor power devices, and control theory, permanent magnet synchronous motors (PMSMs) are playing an increasingly important role in current medium and low power motion control. They possess advantages such as compact structure, high power density, high air gap flux, and high torque-to-inertia ratio. Therefore, they are increasingly widely used in servo systems. However, a PMSM is a nonlinear system containing a product of angular velocity ω and current id or iq. Therefore, to achieve accurate control performance, angular velocity and current must be decoupled. For high-precision speed tracking control, load disturbances can affect speed fluctuations. Therefore, load disturbances need to be estimated to reduce their impact. Consequently, general linear control methods are not ideal. To address this control problem, current nonlinear control methods mainly include variable structure control, feedback linearization, and passive control. However, the design methods for these nonlinear controls are complex and difficult to understand. This paper proposes a backstepping control strategy based on the coordinate transformation method of vector control. This strategy not only achieves complete decoupling of the PMSM system and has a simple design method, but also demonstrates significantly superior control performance compared to traditional PID control. In addition, the influence of load disturbance on speed fluctuation is reduced by designing a load torque disturbance observer [6]. Back-drive control of permanent magnet synchronous motor The mathematical model adopts a surface-type permanent magnet synchronous motor, and its dq model based on synchronous rotating rotor coordinates [1] is as follows: [img=27,26]http://www.ca800.com/uploadfile/maga/servo2006-5/____wm11.jpg[/img]（1） [img=201,55]http://www.ca800.com/uploadfile/maga/servo2006-5/1.jpg[/img]（2） [img=199,57]http://www.ca800.com/uploadfile/maga/servo2006-5/2.jpg[/img]（3） Where: ud, uq is the d-axis and q-axis stator voltage; id, iq is the d-axis and q-axis stator current; r is the stator resistance; l is the stator inductance; tl is the constant load torque; j is the moment of inertia; b is the viscous friction system; p is the number of pole pairs; ω is the rotor mechanical angular velocity; φf is the permanent magnet flux. Backstepping control is an effective nonlinear control design method. It is based on the Lyapunov function design. Therefore, the designed controller can ensure the global asymptotic stability of the system and achieve the effect of current tracking, so that the system has a fast response speed [2]. According to the backstepping design steps [3,4], the actual control ud and uq can be designed as follows: [img=187,33]http://www.ca800.com/uploadfile/maga/servo2006-5/____wmf4.jpg[/img][img=151,33]http://www.ca800.com/uploadfile/maga/servo2006-5/____wmf5.jpg[/img]（4） [img=154,23]http://www.ca800.com/uploadfile/maga/servo2006-5/____wmf6.jpg[/img]（5） Load disturbance observer design In some high-precision servo systems, load disturbances will change, causing speed fluctuations, which will lead to a decrease in the servo performance of the system. Therefore, in high-precision speed tracking control, it is necessary to estimate the load disturbance and compensate it online in real time. From equation (3), we get: [img=127,22]http://www.ca800.com/uploadfile/maga/servo2006-5/____wmf7.jpg[/img]（6） Where: [img=65,34]http://www.ca800.com/uploadfile/maga/servo2006-5/____wmf8.jpg[/img] Since load disturbance is not easy to measure directly, it can be observed here through the obtained iq and ω. Considering that the measurement of iq and ω will produce noise error, a filter is added to the output of the tl observer [img=36,35]http://www.ca800.com/uploadfile/maga/servo2006-5/____wmf9.jpg[/img]（,） to eliminate the above influence. Taking the Laplace transform of equation (6), we get: [img=212,35]http://www.ca800.com/uploadfile/maga/2006-10-18/2006101814363917607.jpg[/img] [img=212,47]http://www.ca800.com/uploadfile/maga/2006-10-18/2006101814365450813.jpg[/img][ img=212,51]http://www.ca800.com/uploadfile/maga/2006-10-18/2006101814372224062.jpg[/img][i mg=164,40]http://www.ca800.com/uploadfile/maga/2006-10-18/2006101814373683069.jpg[/img] (7) Let [img=143,41]http://www.ca800.com/uploadfile/maga/2006-10-18/200610181438855851.jpg[/img], take the inverse Laplace transform, and we get: [img=142,36]http://www.ca800.com/uploadfile/maga/2006-10-18/2006101814381798153.jpg[/img]（8） Equation (15) can be transformed into: [img=82,38]http://www.ca800.com/uploadfile/maga/2006-10-18/2006101814382853620.jpg[/img]（9） The designed load disturbance observer is shown in Figure 1. [align=center] Figure 1 Load Disturbance Observer System Example Simulation Figure 2 System Control Block Diagram The block diagram of the reverse thrust control of the permanent magnet synchronous motor based on torque disturbance estimation is shown in Figure 2. The system reaches a satisfactory configuration point by adjusting the parameters. The parameters of the permanent magnet synchronous motor are shown in the attached table. Attached Table Permanent Magnet Synchronous Motor Parameters Assuming the reference speed is 500 r/min, a sudden load of 20 nm is applied at 0.2 s, the reverse thrust control parameters are: k1 = 50000, k2 = 300, k3 = 20, t0 = 0.01 The simulation is shown in Figure 3. A partial magnification of the circle in Figure 3 is shown in Figure 4. Curve 1 in Figure 4 is the speed tracking curve under reverse thrust control, and curve 2 is the reverse thrust speed tracking curve with torque disturbance estimation. The simulation results show that reverse thrust control enables the system to achieve fast speed tracking while ensuring good dynamic performance. At the same time, the reverse thrust control with torque disturbance estimation further accelerates the system's tracking speed and reduces the impact of disturbances on speed fluctuations. Figure 3 Speed ​​Tracking Curve [align=center] Figure 4 Speed ​​Tracking Curve[/align] Conclusion and Implementation [align=center] Figure 5 Main Program [/align] [align=center] Figure 6 Timer Interrupt Subroutine[/align] To implement the reverse control method based on load disturbance estimation, the TMS320LF2810 dedicated DSP chip for motor control was selected as the digital controller, and the corresponding software was developed. As shown in Figure 5, Figure 6 shows the timer interrupt subroutine to implement the reverse control strategy and generate SVPWM. This paper applies the reverse control based on torque disturbance estimation to the speed tracking of permanent magnet synchronous motors. This design method reduces the adjustment parameters and simplifies the control design of the system. Through MATLAB simulation, it is shown that the system has good tracking performance, verifying the effectiveness and feasibility of the system design. In addition, this control strategy has been applied to the key project of Zhejiang Province: "All-Digital AC General-Purpose Servo Drive System". It shows that the adjustment parameters are relatively reduced compared to PID, the parameter tuning is easier, the programming work is reduced, and the system has achieved good results.