Direct grid connection of matrix converter with transition control for flywheel UPS

This paper discusses an uninterrupted power supply (UPS) with a flywheel and a matrix converter using a direct grid connection. A flywheel type UPS has a problem where a standby power is bigger than that of the battery or EDLC type UPS. To solve this problem, an operation known as direct grid connection mode is proposed, where a matrix converter is the interface converter between the flywheel and grid. In the direct grid connection mode, the matrix converter has no switching operation. Thus, the converter loss is remarkably low in the standby mode due to no switching loss. However, a rush output current will occur in when the matrix converter is transited from PWM to direct grid connection mode. In order to solve this problem, in this paper, a transition control which treats the output voltage to correspond to the input voltage is proposed. Additionally, the validity of the proposed control is demonstrated in the simulation and experimental results.