高速无人驾驶车辆最优运动规划与控制的动力学建模分析

Dynamic Modeling Analysis of Optimal Motion Planning and Control for High-speed Self-driving Vehicles

在高速无人驾驶车辆的运动规划与跟踪控制过程中,滑移和侧倾是很难克服的高度非线性约束,特别是在复杂地形条件下,容易导致车辆失稳甚至侧翻。通过研究地形因素对车辆转向特性和稳定性的影响,建立高速车辆的等效动力学模型,并提出了一种变步长的模型离散化方法,能够在保证及时动态响应的基础上,实现较长的轨迹预测时域以及计算的实时性。针对高速无人驾驶车辆的滑移和侧倾等动力学安全因素,通过对车辆稳定行驶状态进行分析,推导了基于包络线和零力矩点的高速车辆稳定性约束条件。根据在高速、滑移、侧倾等复杂约束下车辆安全行驶的要求,运用模型预测控制算法求解最优运动轨迹及跟踪控制序列,在保证道路环境约束的同时满足车辆的滑移和侧倾等稳定性约束。仿真试验表明,该方法可以有效的考虑道路曲率和地形对高速车辆动力学特性的影响,保证车辆无碰撞行驶,同时防止车辆出现滑移和侧倾等现象。

Motion planning and control for high-speed self-driving vehicles is complicated since it involves highly nonlinear constraints such as sideslip and rollover. Inappropriate handling of these constraints, particularly under complex terrain conditions, will lead to loss control of vehicles or even fatal accidents. Through studies on the effect of road curvature and terrain to the vehicle steering characteristics and handling stability, a simplified equal dynamic model is developed for high-speed self-driving vehicles. And a model discretization method with variable time-steps in the prediction horizon is proposed to ensure immediate dynamical response while attaining a long enough prediction horizon and computational feasibility. Taking dynamical safety related concerns such as sideslip and rollover into account, vehicle handling stability constraints, including sideslip envelope and zero moment point, are concluded through vehicle steady-state analysis. A model predictive control problem is formulated and solved to find the optimal motion trajectory and control sequence, satisfying the road environmental constraints while ensuring handling stability. Simulation results validated the capability of the proposed approach under the influence of complex road curvature and terrain.