Modelling and control of the single-phase dc-ac PWM converter for grid-connected applications including a loop for average primary current controlling

This work presents a complete analysis of the single-phase bidirectional PWM dc-ac converter for grid-connected applications. Traditionally, this converter contains two control loops (instantaneous grid current and dc bus voltage), but, as in this work a low frequency transformer is employed for the grid-connection, a third control loop is proposed, in order to compensate any primary transformer average current. This additional control loop is added to avoid the transformer saturation, since the grid current sensor, placed at the secondary, cannot measure the primary average current component, impeding the traditional control system to compensate it. The dc-ac converter modeling is performed considering the low frequency transformer dynamic and simulation results are presented to validate the analysis.