Design of a Full-Bridge Converter for Lead-Acid Battery Charging and Powering DC Loads

This paper presents a design procedure for a hard switched full-bridge ac-dc converter for constant voltage / current controlled charging of Lead-Acid Batteries. The converter is designed to operate in two-stage charging control or Constant Current Constant Voltage (CC/CV). The converter also acts as a regulated dc power supply for dc loads connected in parallel with the battery at the secondary side of the converter. Initially, the battery charges with the constant current set manually, as and when the battery terminal voltage reaches a threshold value corresponding to the battery's full voltage, the control method changes to constant voltage mode to keep the battery voltage constant near its float voltage. Step by step method for converter design is illustrated along with the load v/s efficiency comparison for various switching frequency designs. The results show that losses at partial loading are higher when the operating frequency increases; to overcome this, low-medium switching frequency and lower saturation flux density in the magnetics can be chosen, but at the expense of larger sized transformer and inductor in the circuit. Finally, the converter design is simulated in MATLAB Simulink to verify the output as per the specification.