A Decentralized Robust Mixed $H_{{2}}/ H_{{{\infty }}}$ Voltage Control Scheme to Improve Small/Large-Signal Stability and FRT Capability of Islanded Multi-DER Microgrid Considering Load Disturbances

This paper presents a decentralized robust mixed
$H_{{2}}/ H_{{{\infty }}}$
control strategy for autonomous/islanded multidistributed energy resources (multi-DER) voltage-sourced converter based microgrids. The power management system specifies voltage set points for local controllers and the frequency of each DER unit is specified by hierarchical droop-based control structure. A robust mixed
H
₂
/
H
${}_{\infty}$
control system is designed for set point tracking and disturbance rejection, and also improves fault-ride through capability of microgrid and enhances its performance for small- and large-signal disturbances and nonlinear loads. Unlike some of the previous research works, here the load current is modeled as the disturbance. The controller design problem is formulated by a set of linear matrix inequalities and then solved as a multi-objective optimization problem. Fuzzy decision making tool is used to choose the best tradeoff solution for robust mixed
$H_{{2}}/ H_{{{\infty }}}$
controller design problem. The theoretical concept of the proposed robust mixed
H
₂
/
H
${}_{\infty}$
control strategy, including the mathematical modeling of microgrid, basic lemma, and controller design procedure, is outlined. To demonstrate the effectiveness of the proposed robust control scheme, offline time-domain simulation studies are performed on a microgrid consisting of three DERs with local loads in MATLAB/Simulink environment and also results are experimentally verified by OPAL-RT real-time digital simulator.