Research on zero low-speed control and dead zone compensation of drive motor for agricultural tracked vehicle

Hilly and mountainous areas serve as important production bases for grain, oil, sugar and distinctive agricultural products in China. However, restricted by complex topography and landforms, the level of agricultural mechanization in these regions is roughly 20% lower than the national average, posing a huge challenge to the promotion of agricultural mechanization. At present, agricultural production in hilly and mountainous areas still relies mainly on manual labor, which is inconsistent with the actual demand due to population aging and the loss of young and middle-aged labor force. As a power platform in hilly and mountainous areas, electric tracked vehicles feature excellent trafficability and environmental friendliness. Nevertheless, the existing motor control theories are difficult to meet the operational requirements of tracked vehicles in such scenarios. Specifically, permanent magnet synchronous motors (PMSM), which is viewed as power core of agricultural tracked vehicle, exhibit unsatisfactory control performance in the zero and low-speed range, making it difficult for agricultural tracked vehicles to achieve precise operation in hilly and mountainous areas. To address this issue, a hybrid control strategy combining the high-frequency signal injection method and a nonlinear observer is proposed based on existing research foundations and the actual operating conditions of hilly and mountainous regions. Through a systematic analysis of the impacts of inverter dead time and nonlinear factors on the motor operating characteristics, a corresponding compensation scheme is designed to effectively attenuate the adverse effects caused by the aforementioned factors. The mathematical model of a PMSM is established, and the three-phase current waveforms of the motor under the non-compensation scheme and the hybrid compensation strategy for dead time and nonlinear factors are compared. The results demonstrate that the dead-time effect and chattering phenomenon in the motor current are significantly suppressed after compensation, and the stability of the current waveform is greatly improved. An experimental platform is built, and motor starting and operating condition switching tests are carried out under set load conditions. The experimental results verify the effectiveness of the proposed hybrid control strategy; the system can maintain stable operation even during the switching process between the high-frequency signal injection method and the flux observer. Data comparison reveals that compared with non-compensation control, the total harmonic distortion (THD) of the motor current is reduced by 6.34 percentage points under no-load conditions and by 5.26 percentage points under load conditions after adopting the hybrid compensation strategy. Meanwhile, a comparative test of super-twisting sliding mode active disturbance rejection control shows that the control strategy can basically eliminate the speed overshoot during motor operation and further enhance the control precision of the system. It should be acknowledged that satisfactory progress has been made in the present research. However, limited by experimental conditions, only simulations and tests under partial operating conditions have been completed. Further optimization of the switching strategy and improvement of the field test scheme are required in future work, so as to fully verify the robustness of the hybrid algorithm.