A Magnetically Coupled Feedback-Clamped Optimal Bidirectional Battery Charger

This paper presents a magnetically coupled feedback-clamped optimal bidirectional battery charger. The proposed charger acts as a current source, i.e., acts in constant-current (CC) mode with a controlled output current in case of deep discharge of a battery, and as a voltage source, i.e., acts in constant-voltage (CV) mode with a controlled output voltage for near-100% battery state of charge. The proposed circuit is universal from the battery voltage point of view, i.e., can charge a battery with any given voltage rating, and adaptive from the optimum charging current requirement viewpoint, i.e., can adapt to the optimum battery charging current. The presented solution uses a magnetically coupled bidirectional converter topology. In order to make the system feedback controlled during the whole cycle of charging, the regulation loop is clamped, and hence, automatic and smooth transition from the CC to CV mode is achieved without the need of any extra switching circuit or control loop. Experimental and simulation results for a 250-W prototype are presented to verify the proposed system. The prototype shows maximum efficiencies of 90.24% under boost mode and 92.7% under buck mode of operation. The performance of the charger is verified using two different 12-V-7-Ah and 12-V-32-Ah lead-acid batteries.