Current Loop Control with Admittance Compensation for a Single-Phase Grid-Tie Fuel Cell Power Conditioning System

Current loop transfer function of a single-phase grid-tie inverter has been systematically derived with representations of conventional transfer function format and admittance terms for the sake of controller design and feed-forward compensation. A 5 kW grid-tie fuel cell power conditioning system (PCS) example is used in paper to show current loop controller design and admittance compensation technique. A second order lead-lag compensator is proposed to avoid low stability margin while maintaining sufficient gain at the fundamental frequency. The proposed current loop controller and admittance compensation have been simulated, and the same parameters have been used for a DSP-based PCS inverter controller. Simulation results indicate that without the admittance path compensation, the duty cycle of the current loop controller is largely offset by the admittance path. At light load settings, the power flow may be erratically fed back to the inverter that can cause dc bus over voltage and subsequently a catastrophe failure. With admittance path compensation and the designed lead-lag compensator, the output power shows a steady-state offset that coincidently is required by the fuel cell. Experimental results well matched the mathematical design and simulation results.