60kW DC-AC Inverter with Internal Isolation using GaN Devices

The amount of renewable energy installations is expected to grow substantially during the foreseeable future. Renewable energy harvested from PV, wind or hydrokinetic sources is intermittent and the most energy is not generally produced when the consumers need it most. Grid-tied storage can help to solve both of these problems. Stored energy can be used to smooth out an intermittent source; it can also be used to time-shift between the peak production and peak consumption of energy. In addition grid-tied energy storage can also provide grid stability by performing smart-grid services like frequency regulation and/or Volt/Var control. To enable these functions, it is important to improve the efficiency and power density of current inverters. Improving the efficiency of an inverter is immediately beneficial as it reduces the losses when converting energy while transmitting it between energy storage unit and the grid. Increasing power density allows building smaller inverters. In industrial scenarios this means that the installation cost for example for pouring concrete slabs can be reduced, but it also means that it will become easier to use grid-tied storage in smaller installations like residential cases. During the proposed project PPS, FSU, and Transphorm will design an inverter for grid-tied storage applications. The inverter will be rated at 60kW and will connect to 480V 3-phase grid without using a grid- side isolation transformer. Isolation will be built into the DC stage of the inverter. The isolating DC stage will use GaN devices made by Transphorm. The reduced losses of these wide-bandgap devices will compensate for the increased number of switch devices. The devices will be switched at frequencies above 200 kHz to reduce the size and weight of the reactive components, which – together with omitting the grid-side isolation transformer – will reduce the overall installation size in increase power density of the system. A successful completion of this project will increase the power density of grid-tied storage inverters, and decrease the system installation cost. During phase 1 the team will base the new design on an existing, industry-proven inverter by PPS. The DC stage of this inverter will be replaced with a new design that will incorporate isolation by using multiple, isolating DC-DC converters with included isolation that will be using GaN switching devices operated at above 200 kHz. This new DC stage will be integrated into the design of the existing inverter. The team wil also demonstrate a functional GaN device gate driver. The project team will design (phase 1) and build (phase 2) a DC-AC inverter for grid-tied energy storage applications. The inverter will use GaN devices inside one of the inverter stages to integrate isolation. The overall power density of the system will be increased by 40%. The overall efficiency of the inverter and isolation component will be increased, and the overall system cost will be reduced by 25%.