Discrete-time Three-phase Current Harmonic Stuff Estimator

Abstract

In order to compensate the higher order current harmonics caused by the operation of a number of non-linear loads, the modern semiconductor converters called active power filters are used. The principle of operation of active power filter is to generate to the electrical grid a compensation current which is equal to the distortion currents in magnitude and opposite to the sign. To form the compensation current, it is necessary to perform an analysis of the harmonic stuff of the distorted current in real time. In this paper, the results of design of discrete-time harmonic stuff estimator for three-phase network are presented. Proposed estimator is based on isolation of positive and negative sequences of each harmonics and provides asymptotic estimation of mains current harmonic stuff. During this study, the current of the network has a non-sinusoidal form, and in its spectrum consists of 20 higher harmonics. It is shown that observer tuning, based on the choice of a damping factor, provides selectivity properties of the estimator, but the time of harmonic currents estimation is increased. In order to preserve the selectivity properties and provide faster convergence of the estimation to zero, an approach to estimator tuning based on the estimator poles location is proposed. Estimator behavior implemented in a discrete form coincides with the behavior of a similar estimator implemented in a continuous form. The properties of proposed solution are confirmed by simulations. The results of the study can be used in the practical implementation of active power filters based on digital signal processors.