Robust adaptive H‐infinity based controller for islanded microgrid supplying non‐linear and unbalanced loads

Abstract

This study introduces a proposed control method for microgrids (MGs) in islanded (off-grid) mode. The proposed control method is developed by modifying the droop control method using H-infinity controller. In this control method, the droop control loop, current and voltage control loops are adjusted to respond to system load variation. The proposed method is an adaptive control one as it regulates the system voltage and frequency to their nominal values after system load variations. Also, it is a repetitive control method as it depends on the internal model principle that provides good performance for voltage and current error tracking. To prove the applicability and effectiveness of the proposed method, it is applied to a test system using MATLAB/Simulink under three different loading conditions. The results are compared with those of droop control and they prove the effectiveness of the proposed method in adjusting MGs under the off-grid mode of operation. Also, a system stability analysis is performed based on root locus and system step response. Robustness analysis is performed to prove the ability of the proposed controller to restore the system performance after the fault clearance.

Unbalance mitigation strategies in microgrids

“…A control strategy enabling seamless system transition during unbalanced dynamic MG reconfiguration, and ensuring proportional powersharing using a distributed secondary control strategy is developed in [213] for DGs with grid forming inverters in unbalanced dynamic MGs, which is validated through HIL. A novel control algorithm using double reduced-order generalised integrators for a four-leg shunt converter is presented in [214], while Sedhom et al [215] proposed another robust H ∞ based controller for unbalance mitigation in islanded MGs. Hoseinnia et al [216] proposed a double SRF (DSRF) control scheme without the need for load current sensors, while Hart et al [217] investigated the impact of harmonics and unbalance on the performance dynamics of gridforming converters modelled using the dynamic phasor approach.…”

“…A novel control algorithm using double reduced‐order generalised integrators for a four‐leg shunt converter is presented in [214], while Sedhom et al . [215] proposed another robust H ∞ based controller for unbalance mitigation in islanded MGs. Hoseinnia et al .…”

Validation of Novel PLL-driven PI Control Schemes on Supporting VSIs in Weak AC-Connections

“…However, this theory suffers from the lack of a systematic method of solving the resulting inequalities that arise in the case of complex nonlinear systems [16]. To overcome this obstacle, usually a small-signal model is used [17] or some kind of heuristic algorithms [18]. Certainly, in these cases, the control design once again is not based on the accurate nonlinear model and stable operation can be guaranteed only for predetermined operating points.…”

“…where in steady-state conditions, the angular frequency of the PLL is equal to the one of the utility ω 0 after a transient period starting at an arbitrary ω PLL (0). As one can easily see, in Equations (16) and (17), instead of using the varying original In Figure 2, the PLL operation is explained. In the process of aligning the q-axis reference voltage, it is initially observed that a small angle, θ B , appears between the q-axis reference voltage and the q-axis voltage at the PCC.…”

Analysis of Voltage and Reactive Power Algorithms in Low Voltage Networks

“…HIC is a repeated control approach for improving the performance of droop controllers, voltage, and current control loops. It has the ability to solve multi-objective and multivariate problems [97,98]. The goals of HIC synthesis include assuring system stability in the face of uncertainty, often known as robust stability [99].…”