Interconnection inverter consisting of large capacity DC/DC converter and HF PWM inverter fuel cell power plant

The authors describe recently developed power system interconnection inverters applied to an onsite fuel cell power plant. A 50 kW prototype and a 100 kW prototype have been developed that consist of a MOSFET-type DC/DC power converter and a IGBT (insulated-gate bipolar transistor)-type PWM (pulse width modulation) inverter. Compared to the conventional bipolar transistor type PWM inverter and commercial transformer insulation system, major downsizing to about 1/3~1/5 volume and weight was achieved in addition to reduction of acoustic noise level by the application of a high-frequency PWM inverter and a large-capacity DC/DC converter consisting of a snubberless inverter stack. Furthermore, through application of a novel instantaneous waveform control method, the output voltage distortion with nonlinear load during stand-alone operation, and the output current distortion during line-paralleled operation are reduced to 5% THD (total harmonic distortion) or less