Autonomous micro-grid operation by employing weak droop control and PQ control

This paper presents an autonomous operation of a micro-grid by employing a droop control and PQ control strategy. The local distributed generation (DG) is modeled by a grid-tied inverter with LCL filter. A proportional-resonant controller is adopted to control the inverter. A new control scheme based on a combination of weak droop control and PQ control is proposed in this paper. Droop control aims to share the load change after islanding occurs. Meanwhile, weak droop control equations with a small power-dependent variation are used for generating the reference signal for PQ control after islanding has occurred. These are implemented using code in the Simulink environment. The simulations show that the proposed scheme which combines droop control with PQ control could operates well in both grid-connected and islanded conditions. By employing such a scheme the transition of the micro-grid from grid-connected operation to autonomous operation or vice versa is smooth.