基于变权重系数的分布式驱动无人车轨迹跟踪

为了提高分布式无人车轨迹跟踪的精度，提出了基于自主与差动协调转向控制的轨迹跟踪方法。首先，在车辆三自由度模型基础上，基于模型预测控制（MPC）实时计算前轮转角以控制车辆进行自主转向轨迹跟踪。在此过程中，为了提高自主转向下车辆的轨迹跟踪精度与行驶的稳定性，考虑多种因素，利用经验公式及神经网络控制对MPC的预瞄步数和预瞄步长进行多参数调整，实现预瞄时间的自适应控制。其次，在恒转矩需求的情况下，以轨迹偏差为PID控制器的输入及左右轮毂电机转矩为输出进行差动转向控制，实现了差动转向下的轨迹跟踪控制。然后，通过设置权重系数的方法将自主与差动转向相结合。考虑到车辆横纵向动力学因素，采用模糊控制及经验公式对权重系数进行了调整，从而在提高车辆转向灵活性与轨迹跟踪效果的同时保证车辆行驶的稳定性。CarSim与Simulink联合仿真以及实车试验结果表明：与自主转向轨迹跟踪相比，采用变权重系数的协调控制可以在不同的工况下提高车辆的转向灵活性与轨迹跟踪的精度，轨迹跟踪偏差的均方根值改善率达到了11%。所提出的协调转向控制方法可为分布式驱动车辆转向灵活性的提高及轨迹跟踪精度的改善提供一种新的思路。

Varied Weight Coefficients Based Trajectory Tracking of Distributed Drive Self-driving Vehicle

In order to improve the tracking accuracy of distributed drive self-driving vehicles, a method based on the coordinated control of autonomous and differential steering was proposed. Firstly, based on the three degrees-of-freedom vehicle model and model predictive control, the front wheel angle was calculated in real time to realize the trajectory tracking of autonomous steering. In this process, many factors were considered to improve the trajectory tracking accuracy and driving stability of the vehicle under autonomous steering. Multiparameter adjustment of preview step numbers and sizes was also conducted using an empirical formula and neural network control to realize the adaptive control of preview time. Secondly, differential steering controlled by PID controller, with path deviation as input and torques of in-wheel motors as output for trajectory tracking, was realized with constant torque demand. Then, autonomous steering was combined with differential steering by setting the weight coefficient. Taking various factors of lateral and vertical dynamics into account, the weight coefficient was adjusted by fuzzy control and the empirical formula to improve the vehicle steering flexibility and trajectory tracking effect while ensuring the stability of vehicle. The joint simulation of CarSim and Simulink and the vehicle road testing results showed that compared with autonomous steering trajectory tracking, coordinated control with changing weight coefficients can improve the steering flexibility and trajectory tracking accuracy of the vehicle under different driving conditions. The improvement of the RMS value of the trajectory tracking deviation was approximately 11%. The proposed coordinated steering control provides new insights for the improvement of the steering flexibility of distributed driving vehicles and trajectory tracking accuracy.