Adaptive Higher-Order Sliding Mode Control for Islanding and Grid-Connected Operation of a Microgrid

Abstract

Grid-connected and islanding operations of a microgrid are often influenced by system uncertainties, such as load parameter variations and unmodeled dynamics. This paper proposes a novel adaptive higher-order sliding mode (AHOSM) control strategy to enhance system robustness and handle an unknown uncertainty upper bounds problem. Firstly, microgrid models with uncertainties are established under islanding and grid-connected modes. Then, adaptive third-order sliding mode and adaptive second-order sliding mode control schemes are respectively designed for the two modes. Microgrid models' descriptions are divided into nominal part and uncertain part, and higher-order sliding mode (HOSM) control problems are transformed into finite time stability problems. Again, a scheduled law is proposed to increase or decrease sliding mode control gain adaptively. Real higher-order sliding modes are established, and finite time stability is proven based on the Lyapunov method. In order to achieve smooth mode transformation, an islanding mode detection algorithm is also adopted. The proposed control strategy accomplishes voltage control and current control of islanding mode and grid-connected mode. Control voltages are continuous, and uncertainty upper bounds are not required. Furthermore, adjustable control gain can further whittle control chattering. Simulation experiments verify the validity and robustness of the proposed control scheme.

Design of a Finite-Time Terminal Sliding Mode Controller for a Nonlinear Hydro-Turbine Governing System

“…Particularly for the rapid transition process of an HGS, the control system requires a faster response [25][26][27]. Finite-time control can improve the transient characteristics of the system, including reducing the overshoot and stabilization time [28][29][30][31][32]. Terminal sliding mode (TSM) is an advanced finite-time control algorithm, which enables nonlinear systems to be stable in a finite-time.…”

Control Method of Parallel Inverters with Self-Synchronizing Characteristics in Distributed Microgrid

“…A microgrid is an integrated system composed of DGs, energy storage, loads, as well as control and protection devices. It can be connected to the user side directly, which contributes to improving the users' power quality and the reliability of the power supply [4][5][6].…”

“…(3) In the case of grid-connection switching, the control strategies of the inverters have to be changed [6,9], which has low reliability and success rate. Moreover, there can be transient surge during the switching process, and the equipment will be damaged in severe cases.…”

Adaptive-Gain Second-Order Sliding Mode Direct Power Control for Wind-Turbine-Driven DFIG under Balanced and Unbalanced Grid Voltage

“…Among all the nonlinear control approaches, sliding mode control, which is used in wind turbine systems, is a robust control method capable of providing finite-time convergence, disturbance suppression, fast response, and simple implementation [20,21]. Some studies have evaluated the direct power sliding mode control for DFIG [22][23][24][25][26][27].…”