Improved Droop Control Strategy for Single Phase Micro-Grid Inverters in Stand-Alone Mode

This paper deals with the control strategy of two single phase voltage source inverters that are operating parallelly. In case of conventional droop control scheme, the parrallelly operated inverters must have the same per-unit output impedance. In addition to that, the reference voltage also has to be same so that the load could be shared in proportion to their respective rating. The above mentioned conditions are very difficult to meet in practical situation, so there will be always some errors for proportional load sharing. In this paper, an improved droop control has been proposed to achieve an error free load sharing according to their droop ratio while avoiding the above mentioned conditions. Even the output voltage drop has been improved which was occurring earlier due to the load and droop effect. In the proposed droop control, two inverter modules have the different output impedance where each module contains two loops. The first one is inner current loop whereas the later is outer voltage loop. Here the best thing is that the power sharing of each inverter does not depend on their output impedance. By adjusting the frequency and fundamental voltage droop one can control active and reactive power. As a result, the output current of each inverter can be accurately limited to its maximum rating. The whole study has been simulated with resistive load and inductive load. The hardware setup also has been developed to verify the simulation results.