Estimated Droop Control for Parallel Connected Voltage Source Inverters

Renewable Energy Sources (RES) are considered as the replacement of conventional energy sources. These RES can use wind energy, solar light, bio waste and can also be in the form of small hydro power units. These RES has very poor power quality and contains voltage fluctuations and variable frequency. These factors make RES a stability risk for the main utility grid. As a solution, currently inverters with different design techniques are being used as an interface between RES and main utility grid. The current study proposed a new technique "estimated droop control" for inverter design. 

The conventional droop control technique which was already used in inverter design, has difficulty in synchronizing parallel connected inverters with different droop gains and line impedances. 

The proposed "estimated droop control" does not use any predefined droop values for inverters and all inverters are responsible for the estimation of their own droop values with respect to their output power. This problem has been successfully solved with estimated droop control as in this method each inverter set its droop gains according to its output power, which helps an inverter to operate at nominal values with different droop gains and line impedance. The performance of droop control with different conditions as same line impedance, different line impedance and estimated droop with same line impedance and different line impedance evaluated the results by using Matlab/Simulink software.

Keywords: Renewable Energy Sources (RES), Estimated Droop Control