Enhanced Internal Model Control and Harmonics Mitigation in Three-Phase Voltage Source Converters

This paper deals with the problem of voltage and current control of voltage source converters (VSCs) with LC output filter. The objective is to achieve voltage regulation and reference tracking while ensuring current stability and regulation despite the unknown disturbances and to mitigate voltage harmonics. In this work, an enhanced internal model-based control system proposed for voltage and current control and harmonics compensation in three-phase VSCs with LC output filter. The proposed control system has a cascade structure and it is designed in the synchronous reference frame d-q. The outer loop is for voltage control and the inner loop is for current control. A three-degree-of-freedom internal model controller (IMC) is developed for robust voltage regulation and reference tracking despite the unknown disturbances and voltage harmonics elimination. The current controller uses PI controllers for current regulation and feedforward terms to enable the d-q components of voltage and current to be fully decoupled. A comparative simulation study with the conventional PI-based synchronous reference frame VSC control system is conducted to highlight the efficiency of the proposed approach. Unlike conventional control, The IMC based control system provides faster reference tracking with less fluctuating output voltage. The proposed method also provides individual harmonics distortion (IHD) and total harmonics distortion (THD) withing the maximum level defined by the standard IEEE 519-2014.