Single-Phase Inverter-Control Techniques for Interfacing Renewable Energy Sources With Microgrid—Part II: Series-Connected Inverter Topology to Mitigate Voltage-Related Problems Along With Active Power Flow Control

In this paper (Part II), a control strategy for a single-phase series-connected inverter with the microgrid is proposed to interface ac loads not only to regulate the load voltage under voltage disturbances, but also to control the load power drawn from the microgrid. The inverter compensating voltage works in such a way that, irrespective of any type of disturbances in the microgrid voltage (such as sag, swell, or harmonic distortions), the load voltage is maintained at its rated voltage level with low total harmonic distortion (THD) in voltage. The proposed control strategy also facilitates a specific amount of active power flow (from renewable energy source) to the load irrespective of the microgrid voltage condition. The rest of the load power is supplied by the microgrid. To facilitate this control strategy, a spatial repetitive controller (SRC) is proposed and implemented in microgrid phase (θ) domain to make the controller independent of the microgrid frequency. The proposed controller ensures dynamic stability of the system even if there is a sudden change in the microgrid frequency. Detailed experimental results are presented to show the efficacy of the proposed series inverter system along with the controller under different operating conditions.