Complex disturbance compensation control strategy for VLF-PM motor in the e-PTO system of electric tractors

In recent years electric tractors are widely used in automated agricultural production, among which the type of decoupling structure adopts electric power-take-off (e-PTO)system, which has the advantage of flexible control. In order to improve the efficiency of the Power Take Off (PTO) system for electric tractors, this paper proposes a Variable Leakage Flux Permanent Magnet(VLF-PM) Motor as the driving motor for the PTO system. It has the advantages of light load wide speed regulation and high torque for heavy loads, which can meet the needs of different working conditions. However, the VLF-PM motor drive system under the PTO system of electric tractors often faces complex disturbances such as changes in motor parameters, load shocks, and system failures, which seriously affect the operational accuracy and efficiency of the PTO system. This article proposes a complex disturbance compensation control strategy for the VLF-PM motor drive system under electric tractor PTO to solve the issues above. Firstly, considering the characteristics of VLF-PM motor electromagnetic parameter changes, as well as uncertain external disturbances such as load shocks, soil conditions, and different crops, the control performance of the motor will be affected to varying degrees, A sliding mode anti-disturbance control strategy based on Nonlinear Disturbance Observer (NDO) was designed, in which the sliding mode control part adopts a separate design, greatly reducing the complexity of parameter adjustment and improving the dynamic and steady-state performance of the motor. PTO motor failure, as an unavoidable problem, has a greater and more fatal impact on click work efficiency. Traditional NDO often performs poorly in the event of a fault, and the control system cannot have strong anti-disturbance performance to resist the impact of the fault. On this basis, this article proposes an analysis method for perturbing system faults, which suppresses the impact of faults and improves the robustness of motor systems by compensating for the lumped disturbances after faults. A quasi resonant feedforward nonlinear disturbance observer was designed based on this, which can ensure the stability of VLF-PM motor speed and torque output under faults. To verify the effectiveness of the proposed algorithm, we carried out experimental validation of the control strategy at different PTO standard speeds.During the experiment, we first conducted a load test on the VLF-PM motor to verify its feasibility as a PTO motor. The results demonstrated that the motor could maintain a typical standard speed output during the loading process and exhibited higher efficiency compared to traditional interior permanent magnet synchronous motors. Secondly, we compared the performance of three control methods—PID, traditional ADRC, and the proposed SMC-NDO under parameter and load disturbances. The results showed that the SMC-NDO method reduced speed oscillation and adjustment time by 60.0% and 13.4%, respectively, exhibiting the most effective anti-interference performance. Therefore, it can meet the high operational accuracy requirements of electric tractors; The frequency of the fault disturbance signal during current sensor faults and motor phase loss faults conforms to theoretical analysis, and under improved observer control, the disturbance observation level returns to normal state, meanwhile the q-axis feedback current ripple is suppressed. When the current sensor fails, the output torque ripple under three operating conditions decreases by 33.6%, 69.0%, and 49.7%, respectively. When the motor has a phase loss fault, the output torque ripple under three operating conditions decreases by 68.5%, 51.4%, and 52.8%, respectively. It is worth noting that under this control method, there is almost no pulsation in the speed when the motor fails. This control strategy effectively improves the anti-disturbance ability and system robustness of the PTO motor, providing new ideas and references for the research on anti- disturbance and efficient operation of electric tractors.