Stability analysis of three-loop control for three phase voltage source inverter interfacing to the grid based on state variable estimation

Abstract

Grid tied inverters and associated control techniques have gained importance in the domain of distributed generation. Different methods of control have been compared in literature depending upon the ability to meet THD limits, damping offered to resonant oscillations and stable operation. Multiple loop methods compared to their single-loop counterparts have proved to be highly effective for meeting the grid regulations. This paper shows that amongst multi loop topologies, a three-loop structure gives more robust performance. However, in literature, it has generally not been preferred due to the hardware complexity and cost imparted by the increase in the number of sensors. In this paper a three-loop control structure is proposed for grid connected inverters and is analysed for stability and parametric variations. Robustness of three-loop control as compared to a single-loop grid-current feedback control is studied. An approach to estimate the state variables is proposed in this paper which cuts down the number of sensors and cost of implementation. The algorithm is validated through MATLAB/SIMULINK results, under dynamic and steady state conditions.