High power density medium voltage photovoltaic grid-forming inverter with soft-switching

到2021年，加拿大的光伏总装机容量已达到2.4吉瓦，预计到2040年将增加到近5吉瓦。为了便于大规模转换为光伏发电，输电网络由一个中压交流电网组成，该电网收集来自单个光伏阵列的电力。由于光伏阵列的输出电压过低（如300-750V输出），无法实现有效的远距离输电，因此采用线频（即60Hz）中压升压变压器（如充液垫式电力变压器）将输出电压升压到中压级（> 20kv）。然而，这些升压变压器又大又重。与北方变压器公司（NT）合作，拟议的研究伙伴关系的目标是开发一种完全集成的高功率密度光伏升压并网逆变器。特别是，将研究一种新的基于多级的逆变器拓扑结构，该拓扑结构在整个功率范围内具有无损开关特性。所开发的电网形成控制方案将允许所提出的逆变器拓扑模拟为电网中的虚拟同步发电单元，这样所设计的拓扑将能够：(1)在电网故障导致的电压骤降期间提供故障穿越能力以维持正常的机组运行；(2)提供电网频率调节，保证系统稳定；(3)支持并网模式与孤岛模式无缝切换；(4)输出过流保护。NT是安大略省液体填充电力变压器的领先制造商，服务的客户包括：Hydro One， Fortis, Toronto Hydro， Alectra等。随着所提出的PV升压逆变技术的尺寸和重量的显著减小，它将成为中压电网中用于PV能量转换的传统垫装升压变压器的理想替代品。这项无变压器并网发电技术的成功开发将为NT提供一个独特的营销机会，为全球光伏能源市场创造收入，并利用最先进的电力解决方案。

The total installed photovoltaic (PV) capacity in Canada has reached to 2.4 GW in 2021, and it is projected to increase to almost 5 GW by 2040. To facilitate large-scale power conversion to electricity from PV energy, the power transmission network consists of a medium voltage (MV) AC grid that collects power from individual PV arrays. As the output voltage of the PV arrays is too low (e.g. 300-750V output) for effective long-distance power transmission, a line frequency (i.e. 60Hz) MV step-up transformer (such as the liquid-filled pad mount power transformer) is used to step up the output voltage to the MV level (> 20 kV). These step-up transformers, however, are bulky and heavy. Collaborating with Northern Transformer Corporation (NT), the goal of the proposed research partnership is to develop a fully integrated high power density PV step-up grid-forming inverter. In particular, a new multi-level based inverter topology that exhibits lossless switching characteristics over the entire power range will be investigated. The developed grid-forming control scheme will allow the proposed inverter topology to emulate as a virtual synchronous generation unit in the power grid, such that the devised topology will be able to: (1) provide fault-ride through capability to maintain normal unit operation during a voltage sag resulted from the grid faults; (2) provide grid frequency regulation to ensure system stability; (3) support seamless transition between grid-connected and islanded modes; and (4) perform output over current protection. NT is a leading manufacturer of liquid-filled power transformers in Ontario, it serves clients such as: Hydro One, Fortis, Toronto Hydro, Alectra, etc. With the significant reduction in size and weight of the proposed PV step-up inversion technology, it will be an ideal replacement for the conventional pad mounted step-up transformer used for PV energy conversion in the MV power grid. Successful development of the proposed transformer-less, step-up grid-forming power technology will provide NT a unique marketing opportunity to create revenue and capitalize on state-of-the-art power solutions for the global PV energy market.