1-MW PV Power RD&D Using SiC-based qZS Cascade Multilevel Inverter and Battery Energy Storage

Regardless the importance of photovoltaic (PV) power conversion systems, they are still too expensive, unreliable, bulky, and have difficulty reaching utility-scale (e.g., 1 MW at 11 kV). The drastic advances in semiconductor materials, devices, and circuits are needed to reach Utility-Scale Solar Power. Therefore, we propose a silicon carbide (SiC)-based (IGBT/SiC-diode) cascade quasi-impedance-source inverter (qZSI) for a utility-scale PV power with a transformative holistic approach – from developing low-cost SiC wafers, high voltage/power SiC devices, to LC filter-/transformer-less low-cost high-reliability inverter topology. The RD&D (Reseach, Development, and Demonstration) project will provide the following advances: 1) LC filter-/transformer-less qZS cascade multilevel inverter for direct medium voltage grid connected PV system. The power modules will be reduced to two-thirds when compared with traditional solutions. 2) Low-cost, utility-scale power conversion technology with distributed maximum power point tracking to maximize energy production. 3) Defect-free 6''-diameter SiC wafers to reduce the cost. 4) Distributed energy storage systems. 5) The use of the pulse width amplitude modulation will further reduce switching frequency and minimize the capacitance and inductance in the qZS network, so as to lower power loss and cost, smaller volume, and lighter weight. A 1 MW 11kV qZS CMI will be designed and demonstrated in the PV system connected to the real grid.

Power electronics; Quazi Z source inverter - qZSI; PV power generation; Cascade Multilevel Inverter; Silicon Carbide SiC

A full-scale qZS CMI product is interfaced between an existing 0.5-MW PV farm and an 11-kV utility grid. The product is developed, fabricated, and tested, which is done to verify the control functions, operating modes, dynamic performance, efficiency, and protection for fail-safe operation. The interfacing power converter will be a CMI
made from the Si-IGBT/SiC-diode power modules. Due to the cascaded multilevel topology, no transformers is used for connecting to the real MV grid. The power converter will make the PV panels operating at their own MPPs; all of this functionality is embedded in each single unit. The proposed qZS CMI combines the advantages of qZSI, CMI, and a battery energy storage system with the proposed PWAM technology, resulting in a new, integrated PV inverter that isachieved a lower power loss, lower cost, lighter weight, and smaller volume, with higher reliability while remaining transformer-less.