An Improved Droop Control Method with ability of secondary frequency control for Micro-grid inverters

With the development of Distributed Generations (DGs), its inherent randomness and fluctuation in the power production is slowly demonstrated. The microgrid maybe solve the above problem. The traditional droop control technology is common in operation of DGs in Microgrids. But it presents a large frequency deviation when facing large load demand, which need to be solved. A new method is presented to merge the secondary control function into the traditional droop control for multi-inverters. The method can built the relation from frequency unqualified zone by the only primary control to the qualified zone by the secondary control with the help of projection function. The method can automatically find new nominal power output value to change the former operation point to reduce the frequency deviation range and even no deviation without the help of communication. It help the aim of plug and play in microgrids. The test in Matlab/Simulink environments were carried out and the results verified the validity of the new method with secondary control strategy in deal with the large load demand.