Reduction in size and weight of transformer for grid tie applications is demanded and can be achieved by applying SST to the transformer. However, SST application to PCS for sunlight requires the following: handle a wide variation range of the voltage of solar power generation; reduce switching losses of power devices, DC/DC converter and inverter, in the power circuit to implement high frequency for SST application; increase voltage to the grid voltage; and reduce the dimensions of the high current path prior to step-up. Thus, LLC resonant converter configuration is applied with an inverter placed in the output, and series connected configuration is applied to the inverter. The LLC resonant converter is subject to constant frequency regulation with large output, step-up control with low output, and step-down control with the upper limit voltage according to MPPT voltage from sunlight, in order to achieve drive loss reduction and voltage range handling.