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Harmonics Reduction in Three Phase System Using Current Injection Technique for Adjustable Speed Drive

This paper presents a new approach to mitigate harmonics and to improve the power factor of a three phase front-end uncontrolled rectifier. A high-power-factor could be achieved by injecting high-frequency triangular current from the output of the threephase inverter. The HF current modulates the rectifier input voltage resulting in conduction of diodes into each switching cycle. The resulting ac input line current is continuous and sinusoidal in shape with significant reduction in current harmonics. All the switches are operated at zero-voltage switching (ZVS). The diodes of the rectifier are also operated with soft switching at turn-on as well as at turn-off. Varying switching frequency with a fixed duty ratio regulates the output voltage. The main feature of the circuit is that it does not require any additional active devices for current injection. Results that are presented shows that improved power quality at AC mains.