Starting from Fliess's model-free control (MFC) technique developed 15 years ago, this article aims to provide a systematic framework for characterizing, benchmarking, and generalizing this emerging control technique, with a particular focus on power electronics (PE). It examines the performance of MFC in terms of dynamic response, stability, and robustness, using the classical control theory as a basic tool. A theoretical comparison is conducted with the conventional linear control techniques on dynamic response and performance robustness. A generalized MFC theory and means to enhance its robustness performance are also highlighted. This article suggests that MFC, in contrast to the conventional understanding based on model-independent error dynamics, is practically a model-based control technique. Such model dependence characteristics under MFC become more severe for PE systems. However, following a new design principle, MFC is found possible to possess extraordinarily robust performance against model variations as compared to most existing model-based control methods. On top of that, stability margin is found to be the key bottleneck hindering the performance robustness of the existing MFC techniques. A new MFC with greater stability margin and performance robustness is proposed in this article. Comprehensive Pareto fronts analysis, simulations, and experiments are conducted on a buck converter system to verify the new understandings and conclusions drawn from the framework. With the new design principle and the new MFC, the system is able to demonstrate an almost constant dynamic response despite 25-fold circuit parameter (R, C, and L) variations and 1.85-fold input voltage variations.

中文翻译：

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重新审视无模型控制


本文从 Fliess 15 年前开发的无模型控制 (MFC) 技术开始，旨在提供一个系统框架来表征、基准测试和推广这种新兴控制技术，特别关注电力电子 (PE)。它以经典控制理论为基本工具，从动态响应、稳定性和鲁棒性方面检验MFC的性能。与传统线性控制技术的动态响应和性能鲁棒性进行了理论比较。还重点介绍了广义的 MFC 理论和增强其鲁棒性性能的方法。本文认为，与基于模型无关误差动力学的传统理解相反，MFC 实际上是一种基于模型的控制技术。 MFC 下的这种模型依赖特性对于 PE 系统来说变得更加严重。然而，遵循新的设计原则，与大多数现有的基于模型的控制方法相比，MFC 被发现可以针对模型变化拥有异常鲁棒的性能。最重要的是，稳定性裕度被发现是阻碍现有 MFC 技术性能鲁棒性的关键瓶颈。本文提出了一种具有更大稳定性裕度和性能鲁棒性的新型 MFC。在降压转换器系统上进行了全面的帕累托前沿分析、仿真和实验，以验证从该框架中得出的新理解和结论。凭借新的设计原理和新的 MFC，尽管电路参数（R、C 和 L）变化 25 倍，输入电压变化 1.85 倍，系统仍能够表现出几乎恒定的动态响应。