Induction Motor Starting in Islanded Microgrids

Motor loads require high amount of reactive power for a short period during their startup. The high reactive power drawn from the system causes voltage dips at startup time and potentially overvoltage after motor startup is over. The voltage dip and overvoltage may cause the relays to trip and the system to go unstable. This phenomenon is more challenging in weak distribution systems and isolated systems such as microgrids due to the limited inertia of the master generator. This paper presents a dynamic voltage controller that coordinates all the reactive power sources in the system to provide the necessary reactive power during motor startup. The presented Model Predictive Control (MPC) based dynamic Volt/Var Control (VVC) scheme considers the dynamics of the microgrid in the VVC formulation to overcome the voltage dip caused by motor startup. This method uses predictions of voltage behavior of the system based on a simplified system model and tries to eliminate the effect of motor startup by coordinating the reactive power sources in the system.