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arXiv 2309.03069math.OC
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一种用于Bang-Bang最优控制问题的新平滑技术

A New Smoothing Technique for Bang-Bang Optimal Control Problems

Kun Wang, Zheng Chen, Zhenyu Wei, Fangmin Lu, Jun Li

AI总结:

针对bang-bang最优控制问题中控制不连续导致的间接法数值困难,提出用归一化L2范数函数近似符号函数进行平滑,并在最短时间振子和多圈低推力轨迹优化问题上验证了其简单性和更优性能。

摘要:

Bang-bang控制在最优控制问题(OCPs)中普遍存在,其中受约束的控制变量在动力学和代价函数中线性出现。基于庞特里亚金极小值原理,间接法被广泛用于数值求解OCPs,因为它能够推导出最优控制的理论结构。然而,bang-bang控制结构中的不连续性可能会给基于梯度的间接法带来数值困难。在这种情况下,通常采用平滑或正则化程序来消除bang-bang控制的不连续性。传统的平滑或正则化程序通常通过添加一个依赖于小参数的项来修改代价函数,或在状态方程中引入一个小误差。这些程序可能会使数值算法复杂化或降低收敛性能。为了克服这些问题,我们提出了一种有界光滑函数,称为归一化L2范数函数,以根据切换函数来近似符号函数。由此得到的最优控制是光滑的,并且可以容易地嵌入到间接法中。然后,通过一个最短时间振子问题和一个涉及多圈飞行的最小燃料低推力轨迹优化问题,数值上证明了所提方法相对于一些现有方法的简单性和改进的性能。

英文摘要:

Bang-bang control is ubiquitous for Optimal Control Problems (OCPs) where the constrained control variable appears linearly in the dynamics and cost function. Based on the Pontryagin's Minimum Principle, the indirect method is widely used to numerically solve OCPs because it enables to derive the theoretical structure of the optimal control. However, discontinuities in the bang-bang control structure may result in numerical difficulties for gradient-based indirect method. In this case, smoothing or regularization procedures are usually applied to eliminating the discontinuities of bang-bang controls. Traditional smoothing or regularization procedures generally modify the cost function by adding a term depending on a small parameter, or introducing a small error into the state equation. Those procedures may complexify the numerical algorithms or degenerate the convergence performance. To overcome these issues, we propose a bounded smooth function, called normalized L2-norm function, to approximate the sign function in terms of the switching function. The resulting optimal control is smooth and can be readily embedded into the indirect method. Then, the simplicity and improved performance of the proposed method over some existing methods are numerically demonstrated by a minimal-time oscillator problem and a minimal-fuel low-thrust trajectory optimization problem that involves many revolutions.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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