Combining droop and direct current vector control for control of parallel inverters in microgrid

Traditionally, active and reactive power sharing between parallel inverters based on droop control method is considered as a high priority for operating an islanded microgrid. An issue in droop control of parallel inverters in the islanding mode is the voltage drop associated with reactive power sharing within a microgrid. However, maintaining microgrid voltage stability while sharing active power between parallel inverters should be the primary objective for a microgrid. This study proposes to integrate droop and direct-current vector control (DCVC) techniques for active power sharing and bus voltage control within a microgrid. The proposed approach consists of a droop-only controlled unit whose function is similar to a traditional slack bus generator and the rest inverters controlled by using a combined droop-DCVC technique. The droop-DCVC controlled units provide active power sharing among parallel inverters and at the same time maintain microgrid voltage level by injecting the needed reactive power that is determined automatically from the droop-DCVC controllers. Parallel inverter units with loads for a microgrid in the islanding mode are simulated using Matlab/Simulink and Opal-RT real-time simulation system. The hardware experiment is also conducted for two parallel inverters. Results show the effectiveness and excellent performance of parallel inverters in the microgrid by combining DCVC and droop methods.