A Local Power Control Scheme for Electronically Interfaced Distributed Generators in Islanded Microgrids

The conventional real power-frequency and reactive power-voltage droop characteristics are commonly employed to share the electric power among parallel distributed generation (DG) units. Despite some advantages such as easy implementation and no need for communication infrastructure, inaccurate reactive power sharing is one of the main disadvantages of conventional droop control. This paper presents a modified droop control scheme based on changing the y-intercept of the voltage droop characteristic. In this method, the initial control of the inverter-based DG units is performed using conventional droop characteristics. Then, the reactive power sharing error for each DG unit is determined by injecting a small real power disturbance and making a coupling between the real and reactive powers. Accordingly, the modified reactive power controller modifies the generated reactive power of each DG unit by changing the output voltage. As this process should be simultaneously implemented in all DG units and employment of the central controller and the communication link for activation of the modification procedure has some disadvantages, this paper presents a local activation mechanism. The proposed scheme operates based on a significant change of reactive power and ensures the execution of all stages of modified droop control and its reactivation to respond to the microgrid power changes. Several simulation case studies using a low voltage microgrid network verify the effectiveness of the proposed control scheme.