Optimized Design for Proportional Resonant Control Strategy for Power Quality Improvement in Grid Connected Three Phase Power Converters
A. U. Essien *
Department of Electrical/Electronic Engineering, Akanu Ibiam Federal Polytechnic Unwana, P.M.B. 1007, Afikpo, Ebonyi State, Nigeria.
F. U. Ilo
Department of Electrical and Electronic Engineering, Enugu State University of Science and Technology, P.M.B. 01660, Agbani, Enugu State, Nigeria.
*Author to whom correspondence should be addressed.
Abstract
This work focuses on the modelling and simulation of a Proportional Resonant (PR) current controller designed to mitigate, to an acceptable limit, the current harmonics that distort the output current of the Voltage Source Inverter (VSI) tied to the utility grid. To achieve this, an LCL filter was designed to filter out harmonics at the kilohertz level in the output current of the Photovoltaic (PV) inverter system. The effectiveness of the designed LCL filter was confirmed by the reduction in the Total Harmonic Distortion (THD) of the PV inverter system from 85.17% to 1.27%. This satisfies the requirements for harmonic control in electrical power systems. Secondly, a conventional Proportional Integral (PI) current controller was developed for comparison with the proposed Proportional Resonant (PR) current controller. Both controllers were designed and optimised using Particle Swarm Optimization (PSO). The results show that the proposed PR current controller provides better power quality and tracking capability than the conventional PI controller. A THD of 0.36% was achieved with the PR controller, compared with 0.62% for the PI controller. To assess the effectiveness of the PR controller, the open-loop and closed-loop transfer functions of the entire system were determined. Bode and root-locus plots were used for the stability analysis of the PR-current-controlled inverter system. The system has gain and phase margins of 3.94 dB and 4.4 deg, respectively.
Keywords: LCL filter, voltage source inverter, Total Harmonic Distortion (THD), PI controller, PR controller