Single phase utility interface inverter based on digital hysteresis current controller - Operational characteristics both grid-connected mode and islanding mode -

Current control of single phase utility interface is one of the problems because current reference contains frequency components and dq transformation cannot be applicable. Several methods have been proposed to overcome this problem such as deadbeat control, inner model method and so on. Hysteresis control is one of the current control method which can realize robust current controller with simple hardware. On the other hand, LC output filter is required in some cases. In this case, a simple hysteresis control may cause oscillations or current error due to LC filter. Authors have proposed a new current control method suitable for single phase utility interface inverter using digital hysteresis controller with PI controller and state feedback. On the other hands, utility interface inverter has to have voltage control function in islanding mode. In this paper, operational characteristics of islanding mode are discussed at first as well as operational characteristics in grid-connected mode. Then hybrid switching filter is introduced to realize further improvement of switching ripple of output voltage.