The Design and Processor-In-The-Loop Implementation of a Super-Twisting Control Algorithm Based on a Luenberger Observer for a Seamless Transition between Grid-Connected and Stand-Alone Modes in Microgrids

Abstract

The abrupt transfer from grid-connected (GC) to stand-alone (SA) operation modes is one of the major issues that may threaten the stability of a distributed generation (DG) system. Furthermore, if the islanding mode happens, it is vital to take into consideration the load voltages or load current waveforms as soon as feasible. This paper develops an advanced control technique based on a super-twisting sliding mode controller (ST-SMC) for a three-phase inverter operating in both the GC and SA modes. This control scheme is proposed to ensure a smooth transition from the GC to SA mode and enhance the load voltage waveforms under the islanding mode. In addition, to minimize the operational costs of the system and the complexity of the studied model, a digital Luenberger observer (DLO) with a proper design is adopted for estimating the inverter-side current. The control scheme of the whole system switches between a current control mode during the GC mode and a voltage control mode during the SA mode. The super-twisting control algorithm is applied to the outer voltage control loop involved in the cascaded voltage/current control scheme in the SA mode. Simulation tests of a three-phase inverter are performed for the purpose of assessing the suggested control performance by using the PowerSim (PSIM) software and comparing it with a classical PI controller. Furthermore, a processor-in-the-loop (PIL) implementation in a DSP board TMS32F28335 while debugging is conducted using code composer studio 6.2.0. The obtained results show efficient control properties, such as a smooth transition among the microgrid (MG) operating modes, as well as effectiveness and robustness during both the GC and SA operation modes.

Linear, Nonlinear, and Distributed-Parameter Observers Used for (Renewable) Energy Processes and Systems—An Overview

“…Reference [196] presents the use of observers for DC-DC converters. Several recent papers have dealt with the emerging issues in observer design: observers were used to solve various aspects of gridconnected inverters [197][198][199][200], in a neutral-point clamped (NPC) converter that acts as an interface between the grid and many energy systems [201], as well as in microgrids, as demonstrated in papers [202,203], where linear discrete-time (digital) Luenberger observers were used. The most recent advances and potential challenges in the use of nonlinear observers for energy systems were nicely discussed in a very recent dissertation [204] published in 2023.…”

A Review on Mode Transition Strategies between Grid-Connected and Standalone Operation of Voltage Source Inverters-Based Microgrids

“…Numerous current studies have been performed to deal with the transition issue based on the SCS process strategy [38][39][40][41][42][43]. In [38], a smooth transition approach based on SCS was proposed for a three-phase DG inverter application.…”

“…An enhanced transition from the SA mode to the GC mode using process control switching was designed for DG systems [40]. During the GC mode, the proposed method Indeed, the SCS is assigned to change the mode of control from the current controller to the voltage controller.…”

“…An enhanced transition from the SA mode to the GC mode using process control switching was designed for DG systems [40]. During the GC mode, the proposed method employed combination of a PI regulator and a Luenberger observer to regulate the power fluctuation on the main grid.…”