An Electrolytic-Capacitor-Free Single-Phase High-Power Fuel Cell Converter With Direct Double-Frequency Ripple Current Control

This paper proposes a direct double-frequency ripple current control in a single-phase high-power fuel cell converter that can achieve low-frequency ripple-free input current without using large electrolytic capacitors. To eliminate the double-frequency ripple current disturbance introduced by the single-phase inverter load, a proportional-resonant controller is developed to achieve an extra high control gain at designed resonant frequency. This high gain can be viewed as the virtual high impedance for blocking the double-frequency ripple energy propagation from inverter load to fuel cell stack. More particularly, the proposed control system can realize the utilization of all capacitive ripple energy sources in the system by regulating all the capacitors to have large voltage swing. In addition, this voltage swing is synchronized to keep real-time balancing of the transformer primary- and secondary-side voltages. As a result, the zero-voltage-switching operation for all switching devices in the dc-dc stage can be guaranteed. The controller design guidelines are derived based on the system small-signal model. The experimental results are presented to validate the theoretical analysis and proposed technology.