A method to apply current source inverter to single-phase UPS.

Abstract

At present, most of all inverters used in UPS are voltage-source types. In this case, a series reactor is an essential component of the output filter of the inverter because the waveforms of the output voltages consist of trains of voltage pulses. One of major issues of this type of system is magnetic noises, which are produced by the output voltage and appear at the series reactor and the output transformer.The use of the current-source inverter has merits not only reducing noises when compared to the case of voltage-source type but also getting a quasi-sinusoidal output voltage without any series reactors. However, there are few cases of applying the current-source inverters to the UPSs because built-in batteries of constant voltage are utilized as a voltage supply in the system.The feasibility of applying the current-source inverter to the UPSs is attempted in this paper, and a new circuit topology suitable for the UPSs is proposed. At the output terminal of the inverter only a capacitor is connected in parallel with a load, and the output voltage of the inverter is controlled so as to make it coincide with reference sinusoidal voltage. In order to realize this strategy, two choppers have to be connected between the DC input voltage source and the inverter.After showing the circuit configuration, the validity of the proposed method is confirmed by means of both simulation and measurement. When this type of the inverter is applied to an UPS, the waveforms of the inverter output voltage and the switching frequency depend strongly on the circuit constants and output voltage error. Then, these are discussed in quantity to get a design guide. A comparison with conventional current-source inverters shows that the new inverter system has a plenty of merits.