Design of Reactive Power and Voltage Controllers for Converter-interfaced ac Microgrids

This paper aims at presenting design of two controllers for the study of a microgrid testbed. The response of the microgrid testbed to different short circuits would be investigated under these two control regimes, namely, reactive power and voltage controls. This paper therefore presents design of active power, reactive power and voltage regulators for a converter-interfaced ac microgrid. The design was performed using Simulink Control Design® in the Department of Electrical and Computer Engineering, Curtin University, Sarawak, Malaysia between May 2015 and December 2015. The microgrid consists of two 5.5kW, 575V wind turbines based on doubly-fed induction generators (DFIGs). The systems designed are pitch control system, active power regulator, reactive power regulator, grid ac voltage regulator, dc bus voltage regulator, grid-side converter current regulator and rotor-side converter current regulator. The time-domain step response analysis for each modeled plant indicated stable performance but poor response. Therefore, regulators were realized in closed-loop feedback architecture. Each regulator was designed using small signal frequency response analysis, resulting in stable systems with satisfactory response. The regulators have been combined to implement two mutually exclusive control regimes: the active power-voltage (PV) control and the active-reactive power (PQ) control. Microgrid short circuit studies have been performed while the effect of control is decoupled, a highly simplified method which does not sufficiently mimic real systems. While attempting to study the microgrid short circuit response under different control regimes in a project which is still ongoing, this paper presents an attempt to design two control regimes for the ac microgrid testbed.