Active and reactive power control of single phase inverter with seamless transfer between grid-connected and islanded mode

In this paper, a seamless transfer control strategy or algorithm for single phase grid-tied inverter is proposed using synchronous frame PLL. The inverter is controlled using the Direct-Quadrature synchronous reference frame transformation for active and reactive power control in the grid connected mode and output voltage control in the islanded mode of operation. The breaker status is responsible for the switching between the two control modes and the breaker status is decided by the proposed algorithm. The seamless transfer algorithm observes the PCC voltage on the grid side and the frequency of the grid and decides an action based on the whether the two parameters are within a particular limit. The SF-PLL is responsible for the synchronization process, it takes the reference from the grid or from a constant d-q component of the voltage depending on the output setting of the algorithm. The output of the SF-PLL will determine the frequency and phase angle of the inverter. Simulations verify the operation of this algorithm and the control modes used on the single phase inverter.