Three-Phase Active Power Filter with Predictive Structure for Reference Current Determination

Abstract

This paper describes a parallel active power filter that cancels higher harmonics of current in the electrical network. The active filter uses a three-phase inverter to inject into the network an appropriate current waveform that will cancel harmonic distortions so that the network current is practically a sinusoidal waveform. Control is performed in the time domain using three independent hysteresis regulators that generate control signals for the inverter based on reference currents. The reference current is defined as the difference between the actual load current and its fundamental harmonic. In order to obtain a reference current without time delay, a filter system with a predictive structure consisting of a cascade connection of a low-pass digital Chebyshev filter and a predictive digital filter was used to determine the fundamental harmonic. The low-pass filter extracts its fundamental harmonic from the load current, and the predictive filter cancels the delay introduced by the low-pass filter. The coefficients of the predictive FIR filter for predicting a sinusoidal signal were determined using Lagrange multipliers. By subtracting the extracted fundamental harmonic of the load current from its current value, the reference current of the active filter is obtained without time delay. Computer simulation of the mathematical model of the filter system with a predictive structure has confirmed its applicability in the system for determining the reference current of the active filter. Simulation of the operation of a single-phase and three-phase active power filter with predictive determination of the reference current in stationary and dynamic operating modes has determined the basic characteristics of the active filter. For the purpose of experimental verification of the results, a laboratory model of a parallel active power filter with a nominal power of 16.5 kVA was created based on an inverter implemented using an intelligent power module (IPM) with 6 IGBTs. The algorithm for determining the reference current using the filter system with a predictive structure has been implemented on a DSP, and current regulation has been achieved using three independent hysteretic current regulators. The efficiency of the implemented laboratory model of the active power filter has also been confirmed experimentally. The measurements obtained by connecting the active filter to the electrical network with different types of consumers were compared with the simulation results. A very good agreement between the experimental and simulation results is observed. It has been shown that the active filter successfully cancels current harmonics both in the stationary mode and in the dynamic mode of operation of the electrical network.

Tomislav Kilić

Full Professor | Department of Electrical Measurements

Full professor at the at the Faculty of Electrical Engineering, Mechanical Engineering and Naval Architecture in Split, with professional reserch focus on power quality, signal analysis in electrical power systems, and measurement of process variables, alongside a significant role in the academic and administrative life of the University of Split.