Model predictive control of DSTATCOM employing a single DC source cascaded H-bridge multilevel inverter in a weak distribution system

Abstract

This paper presents the performance of distribution static compensator (DSTATCOM) for load compensation in a weak distribution system. The DSTATCOM topology is realized using a single DC source based cascaded H-bridge multilevel inverter (SDCHBMLI). In SDCHBMLI, the multilevel waveform is generated by cascading the output of the transformers connected to individual full-bridge cells. The use of single DC source eliminates the requirement for capacitor voltage balancing, which is one of the limitations of diode-clamped and flying-capacitor based multilevel inverters. Also, the transformers in SDCHBMLI provide inbuilt isolation between the DSTATCOM and the distribution system. In a weak distribution system, feeder impedances make the voltages at point of common coupling (PCC) susceptible to distortions. To improve the PCC voltage waveform, shunt filter capacitors are incorporated in each phase, which make the system more complex to control. In this paper, the DSTATCOM is controlled using Finite Control Set Model Predictive Control (FCS-MPC) technique, which can independently ensure desired compensator current tracking and PCC voltage improvement simultaneously. The operation of proposed DSTATCOM has been verified using PSCAD/EMTDC. The system behavior is simulated for load step changes and voltage sag condition. The robustness of the control algorithm is also validated with variations in model parameters.