Microcontroller-based fuzzy logic active filter for selective harmonic compensation

The half-bridge converter can be successfully employed as active filter in single-phase systems. The reduced number of semiconductor switches together with the need of balancing the capacitor voltages makes its control challenging especially if the aim is to have a simple digital algorithm easy to be implemented on an industrial microcontroller. Thus it has been chosen to adopt a fuzzy logic control the design of which is based on the dead-beat theory. The objective is to establish a link between the dead-beat control and the fuzzy logic control so as to provide dead-beat control with more intelligence and to reduce the trial and error attempts for the fuzzy controller tuning. The analysis developed and the consequent control include all the phenomena using no knowledge of the load, of the coupling filter or of the grid parameters thanks to the fuzzy logic computing. The proposed single phase active filter is controlled by the 7045F Hitachi microcontroller. Three techniques have been implemented in order to have a comparison: a classical hysteresis control and two predictive ones. The experimental results are discussed to better appreciate the impact of fuzzy logic in the design of controllers for low cost applications.