In recent years, the research interest in off-grid (standalone mode) and hybrid (capable of both standalone and grid-connected modes) charging systems for electric vehicles (EVs) has increased. The main reason is to provide a seamless charging infrastructure in urban and rural areas where the electrical grid is unreliable or unavailable so that EV adoption can be increased worldwide. In this regard, this article reviews the state-of-the-art architectures of the off-grid and hybrid charging systems and investigates their various subsystems, such as single or multiple energy sources, power electronics converters, energy storage systems, and energy management strategies. These subsystems should be optimally integrated and operated to achieve low-cost and efficient EV charging. Moreover, each subsystem is explored in detail to find the current status and technology trends. Furthermore, EV charging connectors, their power level, and standards for all kinds of EVs (ranging from one-wheeler to four-wheelers) are reviewed, and suggestions are discussed related to the non-standardization of charging plugs. Finally, conclusions show the continuous efforts of the researchers in improving the systems in various aspects, such as cost reduction, performance improvement, longevity, negative environmental effect, system size minimization, and efficient operation, and highlight challenges for both charging systems.

中文翻译：

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电动汽车离网和混合充电系统的综合评价

近年来，对电动汽车（EV）的离网（独立模式）和混合动力（能够独立和并网模式）充电系统的研究兴趣有所增加。主要原因是在电网不可靠或不可用的城市和农村地区提供无缝充电基础设施，以便在全球范围内增加电动汽车的采用率。在这方面，本文回顾了离网和混合充电系统的最新架构，并研究了它们的各种子系统，例如单个或多个能源、电力电子转换器、储能系统和能源管理策略。这些子系统应优化集成和运行，以实现低成本和高效的电动汽车充电。而且，详细探索每个子系统，以了解当前状态和技术趋势。此外，还对电动汽车充电连接器、其功率等级和各种电动汽车（从单轮车到四轮车）的标准进行了审查，并就充电插头的非标准化提出了建议。最后，结论显示了研究人员在降低成本、提高性能、寿命、负面环境影响、系统尺寸最小化和高效运行等各个方面改进系统的持续努力，并突出了两种充电系统面临的挑战。就充电插头的非标准化问题进行了讨论和建议。最后，结论显示了研究人员在降低成本、提高性能、寿命、负面环境影响、系统尺寸最小化和高效运行等各个方面改进系统的持续努力，并突出了两种充电系统面临的挑战。就充电插头的非标准化问题进行了讨论和建议。最后，结论表明研究人员在降低成本、提高性能、寿命、负面环境影响、系统尺寸最小化和高效运行等各个方面改进系统的持续努力，并突出了两种充电系统面临的挑战。