Development of a novel parallel redundant UPS

Generally, in case parallel operation of UPS is analyzed, an inverter is assumed to be an ideal voltage source, and a line resistance is disregarded. Therefore, the reactive current of UPS connected in parallel is generated by voltage difference, and active current is generated by phase difference. It shows that phase difference and amplitude difference are controllable by reactive current and active current respectively. However, since an inverter is not an ideal voltage source and a line resistance is not disregarded, it is difficult to distinguish active current and reactive current and to control them. In this paper, influence control of an inverter and line resistance affect the cross current between inverters is analyzed. And especially focusing attention on a line resistance, the method of utilizing this for parallel operation control positively is proposed. Moreover, UPS was connected in parallel using the control based on this method, and operation was confirmed in the experiment. By using the method proposed in this paper, parallel operation control of UPS can be realized comparatively easily with few information exchanges between UPS.