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

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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.