A low cost flyback-based high power factor battery charger for UPS applications

This paper proposes a feasible low cost isolated battery charger converter, which is powered directly by the ac mains voltage, and with characteristics of high power factor for uninterruptible power systems (UPS) applications. The main advantage of this converter is due to the fact of its total independence of the UPS online power stage. Thus, if the batteries capacity of the system are changed (i.e., the output power of the battery charger), no such modification are required to the main power stage of the UPS, such as re-design of the input ac/dc power stage for an higher or lower output power capacity. This re-design commonly occurs in UPS topologies that the battery charger is directly fed by the dc-link bus voltage, such as common neutral connections UPS. Another advantage is that the energy supplied to charge the batteries is processed by only one power processing stage, increasing the system reliability. As disadvantage of such converter is the reasonable efficiency. Experimental results and relevant curves regarding the proposed converter operation are shown, confirming the viability of such circuit.