Grid Interfaced Distributed Generation System With Modified Current Control Loop Using Adaptive Synchronization Technique

Abstract

This paper presents real-time implementation of a grid interfaced distributed generation (DG) system with modified current control loop using three phase amplitude adaptive notch filter (AANF) based synchronization tool. A grid current feedback based modified dq-current control technique for interfacing inverter is developed in order to achieve constant loading on the grid, transient-free operation, and power factor improvement close to unity power factor (UPF) of the utility grid during sudden load variations. This technique does not require separate calculation of reference reactive component and harmonics component of currents hence reduces control circuit complexity. In addition, it requires only three voltage and three current sensors. Three phase AANF is developed and is used for online extraction of utility voltage phase angle to generate synchronized reference current signals for interfacing inverter. AANF is used because of its adjustable accuracy and amplitude adaptability even under unbalanced voltage sag and swell, frequency variation, and distorted grid conditions. Fast and accurate behavior of three phase AANF improves the dynamic response of entire DG system control performance for sudden load variations. The dynamic behavior of the proposed grid interfaced DG system is experimentally evaluated in maintaining constant loading on grid, transient-free operation, and power factor improvement close to UPF operation of the utility grid, by compensating total reactive power and harmonic current demanded by variable linear as well as nonlinear load.