Improving small-signal stability of inverter-based microgrids using fractional-order control

Abstract

Augmenting the range of the active droop gain in inverter-based microgrids (IBMGs) is required for faster power sharing and improved control at the secondary level. However, IBMG stability is degraded when active droop gain is increased, which reveals an obvious tradeoff. Therefore, fractional-order control (FOC) is used in this paper to increase the inverter-based (IB) MGs’ stability margin by increasing the stable range of the active droop gain. So, a thorough small-signal model of IBMGs is developed to assess the MG stability and tune the control parameters for the case of using FOCs. Also, a fractional-order low-pass filter (FO-LPF) is proposed for the outer control loop which increases the damping factor and reduces the power oscillations at the same active droop gain. Moreover, a further boost in stability margin is achieved by combining the proposed FO-LPF in the power control loop with FO-PI controllers in the inner control loops. The stability results of the developed FO small-signal model are validated on a MATLAB/SIMULINK MG stability benchmark system. Also, a comparative case study has shown the superiority of the proposed approach over recent ones in the case of a reconfigured and meshed network. Moreover, the discretization scheme of FOCs is outlined and tested under a load disturbance event.

Keywords

• Fractional-order control
• Droop control
• Small signal stability
• Islanded microgrid
• Microgrid stability improvement
• Inverter control