A 160-kW high-efficiency photovoltaic inverter with paralleled SiC-MOSFET modules for large-scale solar power

To reduce the life cycle cost of solar power plants, high conversion efficiency for inverters is necessary. The advantages of SiC MOSFETs include not only lower conduction loss but also the ability of high-speed switching. Lower switching loss is derived from high-speed switching. Especially with SiC MOSFETs, the tail current and switching recovery loss can be drastically reduced compared with Si IGBTs because of unipolar device operation. However, high-speed switching with SiC MOSFETs creates technical problems such as erroneous ignition at higher dv/dt and di/dt and device failure due to surge voltage. Therefore, we focused on high-speed, stable switching techniques for SiC-MOSFET-based modules. To solve the problems, the following steps were taken. 1) A compact gate driver output stage including a Miller clamp circuit was developed and arranged on the gate and the source terminals of each module directly. 2) A low inductance busbar configuration between the P terminal and the N terminal was developed. 3) For the 4-paralleled SiC-MOSFET modules, the modules having similar Vds characteristics were selected. To confirm the contribution of these techniques to the improvement in efficiency, a 160-kW prototype photovoltaic inverter (2-level) with SiC-MOSFET modules for large-scale solar power plants was developed. A higher peak efficiency (greater than 99.1%) was obtained for an input voltage of 470 VDC, an output voltage of 300 VAC, and a load factor of 30-60%. Our findings show that inverters with a SiC-MOSFET-based module have higher efficiency than 2- and 3-level single-stage inverters with a Si-IGBT-based module.