Switch Fault Tolerant Model-Based Predictive Control of a VSC Connected to the Grid

Abstract

During IGBT breakdowns, the grid side converter (GSC) of a renewable power plant must be disconnected from the grid. In the recent past, topological modifications propose the faulty phase to be connected to the midpoint of the dc bus as a solution. In this configuration, the converter can generate only four vectors. Moreover, since the capacitor voltages carry a voltage ripple at the grid frequency, the magnitude and angle of the vectors become variable during post-fault scenarios. The recent model predictive control (MPC) approaches select the vectors to be used in the cost function based on the location of the reference vector in a post-fault unsymmetrical vector diagram or by checking the effect of all of them, which is time consuming. This article proposes a simplified approach, which reduces the computing time by avoiding successive iterations to obtain the correct vector pairs. Furthermore, an approach to rebuild a regular hexagon from the four post-fault vectors is proposed. Hence, the proposed controller retains the advantages of the conventional space vector modulation (SVM) approach with minimal additions to handle post-fault scenarios. Finally, this article studies the limitations in the VSC output voltage and power magnitudes during post-fault scenarios. The approaches presented in this article have been verified using simulation and experimental results.