Practical development of a high-performance UPS with a novel buck-boost chopper circuit

In UPS without transformers, a boost chopper circuit is of the greatest importance for stepping up battery voltage and feeding it to the inverter. Problems with conventional boost chopper circuits are that a high step-up ratio worsens efficiency, and that there is a voltage imbalance between the high side and the low side of DC link voltage. The circuit type proposed here overcomes the conventional circuit type's shortcomings by employing a buck-boost chopper circuit with two magnetically coupled coils. Further, with this circuit type as a bi-directional chopper, the authors added a battery charging function, which allowed them to omit the independent charging circuit that has been necessary until now. They used this circuit type in developing a 1 kVA UPS and achieved excellent characteristics.