A Guideline for Modeling Voltage and Frequency Controls in AC Microgrids: The Influence of Line Impedance on Transient Time

Microgrids (MG) were first conceived as small-scale grids working in an islanding-mode. However, they can be operated in a grid-connected mode too. MGs can easily host a large number of paralleled-connected distributed generations (DGs). The increased penetration of the renewable energy sources (RESs) is raising new concerns about redesigning the role of MGs for supporting and regulation services of power grids at the system level. The operation of MGs could provide support for voltage and frequency regulation while ensuring uniform power flow in both directions. In this regard, MGs can relieve the stress of the main transmission system, decrease feeder losses, and increase system power quality. In order to inject current, a proper design of the control system parameters of the AC MGs is needed to ensure the exact parameters of the amplitude and synchronized frequency. In this paper, we present a step-by-step methodology for designing control systems for MGs. The primary and secondary control loops of the voltage and frequency of the three-phase paralleled connected voltage source inverter-based (VSI) MG are derived. In addition, we study the impact of DGs remoteness. The primary and secondary control loops are based on the droop control and autonomous frequency control system. The control systems are modeled and simulated in MATLAB/Simulink.