A. Lecci

Implementation issues of a fuzzy-logic-based three-phase active rectifier employing only Voltage sensors

Switch-mode rectifiers are becoming more and more interesting in those applications where bidirectional power flow, power-factor correction, and electromagnetic interference reduction are required. Typical active rectifiers include current or voltage sensors, however, in order to obtain low-cost systems, their number should be reduced. In this paper, a current-sensorless active rectifier with feedforward fuzzy logic control is presented and discussed. The mathematical description of the system and the design of the fuzzy logic controller are introduced and analyzed; moreover the implementation on a SH7047 microcontroller is presented with emphasis on the most significant implementation issues. Experimental results are reported and discussed.

Fuzzy controlled active filter driven by an innovative current reference for cost reduction

The aim of this work is to minimize the active power filters prime and operating costs by the means of a new current reference. Such a current reference is able to share the responsibilities in power quality deterioration between supply and customer, making the filter to deliver a current with a lower harmonic content, which means a lower power delivered and a lower switching frequency. The use of fuzzy logic may be helpful to achieve a good current control since this approach allows a control action to be carried out independent of electrical parameters. Fuzzy control has been designed in order to have different direct actions in each critical point of reference waveform using the nonlinear input-output mapping.

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.

Design of the optimum duty cycle for a fuzzy controlled active filter

The paper presents a CC-PWM shunt active filter. A fuzzy control acts on the inverter devices duty cycles ensuring an optimum current tracking. A new controller design procedure has been adopted: with a mathematical analysis a rough outline of the fuzzy rules has been possible, then they have been modified during the simulation campaign to compensate the neglected phenomena. Moreover a compensating factor has been introduced to include the mains voltage effect on the current control. In short the analysis developed and the consequent control includes all the phenomena using no knowledge of load, coupling filter or grid parameters thanks to fuzzy logic computing. The results show a very high reduction of the line current harmonic distortion with medium switching frequency.

Optimal tuning of a fuzzy logic-based single-phase active power filter via the Nelder-Mead method

This paper describes an optimisation method for fuzzy logic-based single-phase active power filters (APFs). A two-step optimisation technique using the Nelder-Mead simplex (or Amoeba) method has been adopted for the real-time tuning of the controller. Simulations and experimental results obtained with a low cost microcontroller (SH7045) demonstrate the capability of the system to achieve fast convergence rate, power factor correction and low harmonics content.

A technique to balance a half-bridge single-phase active filter

The half-bridge converter can be successfully employed as an active filter in single-phase systems. The impact of this configuration becomes particularly relevant if the power level is limited and the cost reduction becomes a key point. In fact the half-bridge is made by only two bi-directional switches and two capacitors, being anyway able to ensure proper compensation even of the low order harmonics generated by a diode bridge. In this paper, the problem of the balancing of the voltages of the two capacitors is investigated, aiming to do not use a separate controller but only a simple combination logic that exploits the redundancies of the configuration. The simulation and the experimental results show that the voltages can not be controlled in all the conditions but this lack of performance does not affect very much the behavior of the active filter; the compensation of the selected harmonic currents is still good.

A shunt active filter control for one-phase and three-phase four-wire systems

The proposed active filter is based on a shunt configuration made up of three one-phase current controlled VSI-PWM inverters. A deep analysis of reference and filtering waveforms during a sampling period has been carried out to obtain a relationship between electrical feedback parameters and duty cycle of switching waveform. This analysis provides a design equation for switching signal generation and effective current tracking. Simulations have been carried out to show active filter performance under highly polluting load operation. Simulation results highlight a high reduction of line current harmonic distortion with an acceptable switching frequency as well as a sensible reduction of line neutral current.

Optimized Resonant Control for Shunt Active Power Filters

This paper presents an optimization technique of the resonant controller based on the minimization of an objective function through the Nelder-Mead method. This function allows to evaluate the behavior of the system in steady state and transient conditions. The optimized controller has been compared with the Naslin polynomial based one. The results show that by means of the optimization technique it is possible to achieve better performances also in presence of harmonics the control system has not been designed for.

A Two-phase Induction Motor Back-to-back Drive

This paper investigates a two-phase induction motor drive with active front-end. The aim is to conjugate high efficiency (through active shaping the grid current), high performance (implementing vector control) and low cost (using a common six-transistors bridge). The main theoretical aspects of the two-phase induction motor drive are pointed out and the possibility to adopt more complex converter and control structures are investigated. Particularly, the paper proposes a double current controller, with the goal of torque ripple optimization. Numerical results demonstrate the effectiveness of the proposed controller

A comparison between two predictive controllers for single-phase active filter

Predictive controllers can be successfully adopted for active filter due to their fast response and simple algorithm that allows a short execution time. In this paper two different predictive controllers are compared. The first controller aims to lower the switching frequency; the second one aims to the minimum possible current error and is based on a simpler algorithm. The two controllers are analyzed taking into consideration their digital implementation, via simulation and experimental results.