This study provides a detailed analysis of a dc to ac conversion unit as a building block of a modular multilevel converter for grid integration of photovoltaic (PV) systems. Each conversion unit contains a PV-linked multi-active-bridge (MAB) dc–dc converter followed by a grid-connected single-phase cascaded inverter. Using MAB topology can reduce the size and cost of the entire system as more conversion cells are connected to the same transformer. To integrate the PV outputs and maintain the maximum power point tracking (MPPT), different conversion cell topologies are feasible for the MAB converter. This study provides a comparison between the feasible topologies of the conversion cells in terms of the conversion efficiency, reliability, power transfer ability, cost, size, control complexity and generated ripple. The steady-state operation and the control technique of the selected topology are presented in detail. Some control techniques are introduced to improve the system's efficiency and MPPT performance of the conversion cell. A prototype of the conversion cell is developed to validate the proposed topology and the control techniques.

中文翻译：

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DC-AC转换单元在PV链接的并网模块式多级串联转换器中的比较分析

这项研究提供了对直流到交流转换单元的详细分析，该转换单元是用于光伏（PV）系统并网的模块化多电平转换器的组成部分。每个转换单元都包含一个光伏链接的多有源桥（MAB）dc-dc转换器，然后是一个并网的单相级联逆变器。使用MAB拓扑可以减少整个系统的尺寸和成本，因为更多的转换单元连接到同一变压器。为了集成光伏输出并维持最大功率点跟踪（MPPT），MAB转换器可以采用不同的转换单元拓扑。这项研究在转换效率，可靠性，功率传输能力，成本，尺寸，控制复杂度和产生的纹波方面对转换单元的可行拓扑进行了比较。详细介绍了所选拓扑的稳态操作和控制技术。引入了一些控制技术来提高转换单元的系统效率和MPPT性能。开发了转换单元的原型以验证所提出的拓扑和控制技术。