A high frequency link direct dc-ac converter for residential fuel cell power systems

This paper describes a boost converter cascaded high frequency link direct dc-ac converter suitable for fuel cell power sources. A new multi-loop control for a boost converter to reduce the low frequency input current harmonics drawn from the fuel cell is proposed. A new PWM technique for the cycloconverter at the secondary to reject the low order harmonics in the output voltages is presented in detail. The front-end boost converter regulates the dc bus voltage effectively where the fuel cell voltage varies widely depending on the power demand, and provides a constant dc voltage to the high frequency link dc-ac converter. The proposed multi-loop control reduces the low frequency (120 Hz) input current harmonic of the boost converter without additional filter requirement in order to improve the performance of fuel cell system. The proposed PWM technique for the cycloconverter cancels the low order harmonics in the output voltage caused by the low frequency voltage ripple in the dc bus and guarantees the high quality of the output voltage. The trade-offs of proposed scheme are described in detail with mathematical evaluation approach.