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电动拖拉机双轮边电机非线性预测协同驱动控制策略研究

Nonlinear predictive coordinated drive control for dual wheel-side motors of electric tractors

  • 摘要: 以轮边电机为核心的分布式电动拖拉机因高效节能、布局灵活而成为重要发展方向,其驱动系统在复杂农田作业中需实现高精度同步与强抗扰控制,但传统控制策略难以兼顾稳定性与同步性能,易导致同步失准与轨迹偏移,严重制约了作业精度与效率。针对上述问题,该研究从协同控制与单电机控制角度出发,提出基于负载前馈转矩差补偿非线性预测的协同控制策略,旨在兼顾系统同步精度与单轮边电机抗扰能力,提升电动拖拉机在复杂农田工况下的作业稳定性与轨迹跟踪精度。搭建试验平台对所提控制策略进行试验验证,结果表明:相比基于比例-积分的交叉耦合控制(PI based Cross-Coupling Control, PI-CCC),本文所提策略在直线行驶变负载试验中,同步误差波动减少68%,同步误差调节时间减少53.4%;在曲线行驶变负载试验中,同步误差波动减少64.3%,同步误差调节时间减少42.1%。所提策略有效提升了双轮边电机协同精度与抗扰性能,可为电动拖拉机在复杂农田工况下的高精度、高稳定作业控制提供参考。

     

    Abstract: Tractors have been one of the core pieces of equipment in the rapid transition towards electrification and intelligence in modern agriculture. Electric tractors can be the major direction in recent years, due to their zero emissions, high energy efficiency, and high precision. The distributed drive system with wheel-side motors can be used to further enhance the adaptability of electric tractors in complex terrain, such as high efficiency and precise control. Permanent magnet synchronous motors (known for their high-power density and reliability) can serve as the drive system. However, the cooperative control of dual wheel-side motors cannot fully meet the various agronomic requirements under complex terrain. Existing disturbances (like sudden soil variations and uneven loads) can easily lead to uneven ploughing depth and trajectory deviation, which seriously constrain the operational quality and efficiency. In this study, a coordinated drive control was proposed for the dual wheel-side motors of electric tractors using the load feedforward torque difference compensation with nonlinear predictive cooperative control (FTC-NPCC). Response speed and anti-interference were improved under variable working conditions. Current control was used as the motor torque equation. The intermediate conversion of voltage commands was eliminated to directly generate q axis current reference values, which were closely related to torque requirements. Thereby, the torque pulsations were effectively suppressed from the voltage error accumulation in the conventional system. The disturbance resistance was enhanced in the sliding mode load torque observer, where the feedforward compensation of disturbances was embedded in the obtained load torque into the control system. A feedforward compensation term was used to offset the load disturbances. The amplitude of the discontinuous terms was significantly reduced in the sliding mode control, thereby effectively suppressing chattering for the system's robustness. The control input was optimized in real time to adjust the q axis current reference value for the response speed. A nonlinear prediction cooperative control architecture was designed using torque difference compensation. Optimal torque difference commands were directly generated to effectively enhance the synchronization accuracy and disturbance rejection. An experimental platform was constructed to validate the effectiveness of the control strategy under multiple operations. Three control strategies were evaluated during the straight-line and curve driving tests: Strategy 1 was the PI-based cross-coupling control (PI-CCC), Strategy 2 was the load feedforward nonlinear predictive current-based cross-coupling control (FNPC-CCC), and Strategy 3 was the FTC-NPCC. The experimental results indicate that the FNPC-CCC reduced the synchronization error fluctuation from 3.47 to 2.37 r/min under straight-line driving with variable load conditions, which was reduced by 31.7%, compared with the PI-CCC. The synchronization error settling time was shortened from 4.3 to 3.1 s, which was reduced by 27.9%. Compared with the PI-CCC, the FTC-NPCC reduced the synchronization error fluctuation from 3.47 to 1.11 r/min, with a reduction of 68%; The synchronization error settling time was shortened from 4.3 s to 2.0 s, with a reduction of 53.4%. Under curve driving with variable load conditions, the FNPC-CCC reduced the synchronization error fluctuation from 6.11 to 2.61 r/min, with a reduction of 57.2%; The synchronization error settling time was shortened from 3.8 s to 3.2 s, with a reduction of 15.8%. The FTC-NPCC reduced the synchronization error fluctuation from 6.11 to 2.18 r/min, with the reduction of 64.3%; The synchronization error settling time was shortened from 3.8 s to 2.2 s, with the reduction of 42.1%. In conclusion, the FTC-NPCC significantly enhanced the cooperative control precision and disturbance resistance of the dual wheel-side motor system. The finding can provide an effective control approach for the high-precision and high-stability operation of electric tractors in complex field environments.

     

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