Application of fuzzy logic controller to input power control of integrated rectifier/inverter servo drive systems

The objective of this paper is to apply fuzzy logic controller to instantaneous power balancing control for a three-phase induction motor drive system. The system, which is composed of a cascade of pulse-width-modulation rectifier and inverter separated by a dc-link capacitor, has the characters of unity power factor and low harmonics in ac input side. By the feedforward control with output power estimation, the input power can be controlled to match the required power dynamically. A dc-link voltage control loop is introduced to remedy the unbalanced power caused by estimation errors. The FLC is adopted in dc-link voltage control loop to suppress voltage variations due to its inherent merit of design convenience in nonlinear control system. The proposed system is implemented by a digital signal processor based single board and is evaluated with a 1.5-kW three-phase induction motor. Performance comparisons are given with a traditional proportional-integral controller. The experimental results show that not only the current harmonics in steady-state can be reduced but also the dynamic responses of dc-link voltage become superior by the proposed scheme.