信号时滞对NMPC路径跟踪系统的影响机理与消减方法

Influence mechanism and elimination method of signal time delay on NMPC-based path tracking systems

  • 摘要: 目前已有一些针对路径跟踪控制中信号时滞问题的研究工作,但这些工作大多针对某种特定的控制方法,而在路径跟踪控制方法中,非线性模型预测控制(Nonlinear model predictive control, NMPC)具有能够显式处理系统约束、便于实现多目标优化、能够有效利用被控对象前方参考路径信息等优势,但是针对NMPC路径跟踪控制系统中时滞问题的研究较不成熟,制约了这种控制方法的实际应用。为解决上述问题,开展了以下研究工作。首先构建了能够较好地孤立出时滞影响的类车机器人路径跟踪控制系统。接着分析了信号时滞对NMPC路径跟踪控制系统的影响机理,即时滞会导致控制器产生的控制信号不能适应类车机器人在执行控制信号时所处的位置。然后提出了基于增长NMPC预测时域的时滞影响消减方法,即在迭代周期不变的情况下,在无时滞系统较优预测步数的基础上增加二倍时滞周期比以上的整数。最后通过计算机仿真和实验验证了提出方法的有效性。仿真和实验结果表明,信号时滞对NMPC路径跟踪控制系统存在影响,未考虑时滞的NMPC控制算法能够在无时滞系统中实现高精确性路径跟踪,而在有时滞系统中控制失效。通过增长预测时域可以有效消减信号时滞的影响,在信号时滞为0.2s以上的仿真与实验系统中,基于该方法的NMPC控制器可以保证路径跟踪控制的位移误差幅值不超过0.1002m,航向误差幅值不超过0.0291rad。

     

    Abstract: There have been some research works on the signal time delay (STD) problem in path tracking control, but most of these works are aimed at a specific control method. Among the path tracking control methods, nonlinear model predictive control (NMPC) has the advantage of dealing with the system's constraints explicitly, realizing multi-objective optimization easily, and effectively utilizing the reference path information in front of the controlled object, etc. However, the research on the STD problem in the path tracking control system based on NMPC is relatively immature, which restricts the practical application of this control method. The following research has been carried out to address the above issues. First, a path tracking control system for car-like robots that can better isolate the influence of STD is constructed. Next, the mechanism of STD on the NMPC path tracking control system is analyzed, i.e., the STD causes the position of the car-like robot to be used for generating the control signals by the controller to not correspond to the position of the car-like robot at the time of execution of those control signals. Then, an STD influence abatement method based on growing the NMPC prediction horizon is proposed, i.e., with the iteration period unchanged, the number of the better prediction steps of the STD-free system is added by an integer number above the ratio of the STD and period by a factor of two. Finally, the effectiveness of the proposed method is verified by computer simulation and experiment. The simulation and experiment results show that the STD affects the NMPC path tracking control system, and the NMPC control algorithm that does not consider STD can achieve highly accurate path tracking in STD-free systems, whereas control failure in STD systems. The influence of the STD can be effectively reduced by increasing the prediction horizon. The NMPC controller based on this method can ensure that the displacement error amplitude of the path tracking control is not more than 0.1002m and the heading error amplitude is not more than 0.0291rad in the simulation and experiment systems where the STD is not smaller than 0.2s.

     

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