Constant Power-Constant Voltage Battery Charging Based on a Loss-Free Resistor Approach

A constant power (CP)-constant voltage (CV) protocol for battery charging is implemented in a conventional boost converter with output filter (BOF) by imposing loss-free resistor (LFR) behavior during the CP phase. To compare on equal basis the performance of the new CP-CV technique with the classical constant current (CC)–CV protocol, the latter is also implemented in the same power stage. The CC phase in BOF is attained by imposing a G-gyrator of type II behavior to the converter. A versatile controller uses the same voltage regulation loop for both protocols during the CV phase and a slightly different loop for the CP and CC phases. The latter loop is based in both CP and CC phases on the sliding-mode control (SMC) of the input inductor current of BOF, which in steady-state is made proportional to the input voltage in the LFR case or to the output voltage in the gyrator implementation. To compensate for the slow variations of the battery voltage during the CC phase, a proportional-integral (PI) current regulator has been added in the gyrator realization. The comparison of the corresponding experimental results shows identical behavior in both approaches in the measured waveforms, component stress, efficiency and external temperature. The simplicity of the CP-CV implementation based on LFR allows the extension of the proposed protocol to other hard-switching converters.