Collaborative Research: Modular Multilevel Converter with Parallel Connectivity -- Novel Topology, Control, and Applications

可充电电池系统对两项有助于减少化石燃料消耗的技术至关重要：电力运输系统和电网储能系统。尽管电池的性能有了很大的提高，但电池与系统的集成仍然面临着巨大的挑战。现有解决方案通常与目标应用程序高度集成，不能重新调整用途。这些系统通常不可扩展，单个电池单元的故障可能会导致整个系统发生故障。此外，此类系统的电力电子设备针对额定负载进行了优化，而不是针对系统通常运行的部分负载进行优化。这项工作探索了一种全新的设计能量存储和能量转换系统的方法，通过将电池与电力电子设备模块化和集成，以使用相同的半导体芯片面积提供多种功能。拟议的电池技术将使用一种新的多电平逆变器拓扑，允许动态重新配置串并连接：模块化多电平串并转换器(MMSPC)。相同子系统的模块化设计将使相同的模块能够用于多种应用，利用规模经济来降低系统成本。在电动汽车中，该系统可以用灵活的、可动态重新配置的交流电池取代硬连线的电池组，并取代多个电力电子单元，如驱动逆变器、电池充电器和电池平衡电路，以直接从交流电池提供输出。对于电网储能，所提出的技术可以改变不同应用的模块的用途，例如电动汽车，将不同容量或年龄的电池整合到一个系统中，通过大幅减少或消除磁元件来获得高输出质量，快速的动态响应，以及通过简单地添加交流电池模块来轻松扩展存储和功率转换器系统。为了利用MMSPC的优势，必须开发高效的控制策略来优化性能，同时将系统的复杂性和成本降至最低。模块化多电平转换器(MMC)的控制既带来了挑战，也带来了与大量可能的开关状态相关的机遇。MMSPC的自由度更大，这是因为增加了并行状态，允许广泛灵活地进行电路的串-并联配置，从而放大了对相干控制策略的需求。例如，在MMC和MMSPC中，可以通过多种模块配置实现相同的输出电压，从而提供了基于各种附加约束和目标(例如模块平衡、效率、输出质量、电磁发射以及开关和存储元件应力)来优化开关状态的机会。然而，现有的控制方法没有充分利用这一机会，因为它们通常减少目标的数量，并独立地处理各种限制和目标。关键的是，既定的战略并不是为了利用并行连接而设计的，这排除了对MMSPC优势的开发。针对这些局限性，我们提出了一种实时预测多目标优化框架，该框架系统地统一了多个系统约束和目标的处理，并克服了自由度随系统规模和预测范围指数增长的问题。该控制框架将同时适用于MMC和MMSPC，并将考虑这些转换器系列中的其他拓扑变化。新型MMSPC拓扑和控制策略的优势将在模块化交流电池的开发中得到展示，该电池集成了多个电池单元、电池管理和逆变器功能，适用于储能系统和电动汽车驱动系统等应用。这一创新的概念将提高电池系统的寿命、效率和成本，只有在利用MMSPC和相关控制的能力时才是实用的。

Rechargeable-battery systems are critical to two technologies that will help reduce the consumption of fossil fuels: electrically-powered transportation systems and energy storage systems for the grid. Despite great improvements in battery cell performance, battery integration into systems still faces significant challenges. Existing solutions are typically highly integrated with the target application, and cannot be repurposed. The systems are often not scalable, and the failure of a single battery cell can cause the entire system to fail. In addition, the power electronics of such systems is optimized for the nominal load, not for partial load, where the system typically operates. This work explores a radically new approach to designing energy storage and energy conversion systems by modularizing and integrating the battery with the power electronics to provide multiple functions using the same semiconductor chip area. The proposed battery technology will use a new multilevel inverter topology that allows dynamically reconfigurable series and parallel connectivity: the modular multilevel series-parallel converter (MMSPC). Modular design of identical sub-systems will enable the same modules to be used in multiple applications, making use of economies of scale to reduce system cost. In electric vehicles, the proposed system can replace hard-wired battery packs with a flexible, dynamically reconfigurable AC battery and replace multiple power electronics units, such as the drive inverter, battery charger, and battery balancing circuits, to provide the output directly from the AC battery. For grid energy storage, the proposed technology enables repurposing modules from various applications, such as electric vehicles, incorporation of cells of different capacity or age into one system, high output quality with substantially reduced or eliminated magnetic components, rapid dynamic response, and easy scaling of the storage and power converter systems by simple addition of AC battery modules.To leverage the advantages of MMSPC, efficient control strategies have to be developed to optimize performance while minimizing system complexity and cost. The control of modular multilevel converters (MMCs) presents both challenges and opportunities associated with the large number of possible switch states. The MMSPC degrees of freedom are even more due to the additional parallel state, which allows widely flexible series-parallel configuration of the circuit, amplifying the need for a coherent control strategy. For instance, in both MMC and MMSPC the same output voltage can be achieved with a multitude of module configurations, providing the opportunity to optimize the switch states based on various additional constraints and objectives such as module balancing, efficiency, output quality, electromagnetic emissions, and switch and storage-element stress. Existing control approaches, however, do not fully exploit this opportunity as they typically reduce the number of objectives and treat the various constraints and objectives independently. Critically, established strategies are not designed to utilize parallel connectivity, precluding exploitation of the MMSPC advantages. Addressing these limitations, we propose to develop a real-time predictive multi-objective optimization framework that systematically unifies the treatment of multiple system constraints and objectives, and overcomes the exponential growth of degrees of freedom with system size and prediction horizon. This control framework will be applicable to both MMC and MMSPC, and will consider additional topology variations within each of these converter families. The advantages of the novel MMSPC topology and control strategy will be demonstrated with the development of a modular AC battery that incorporates multiple battery units, battery management, and inverter functionality for applications such as energy storage systems and electric vehicle drive trains. This innovative concept will improve lifetime, efficiency, and cost of battery systems, and is practical only when the capabilities of the MMSPC and the associated control are leveraged.