An ac-dc converter with reduced electromagnetic interference

The circuit proposed in this paper causes considerably reduced ElectroMagnetic Interference (EMI) and harmonic current distortion on the utility supply network in comparison to existing power supplies that are used in electronic equipment (computers, television sets, etc.). The proposed circuit can also be used in providing variable-voltage power supplies for the control of motors and other applications in electrotechnologies. The effect of a distorted mains current waveform in distribution systems is to increase the heating of distribution transformers and interfere with radio-frequency equipment such as radios and TVs, and even to disturb the reliable operation of other electronic equipment. The multiphase commutation concept proposed for the circuit topology permits an appreciable reduction in the amplitude of current harmonics generated by modern switching power supplies. The proposed circuit thereby operates at a higher efficiency and reduces the constraints on the switching elements. The multiphase commutation concept can be applied to the development of dc-ac converters that are used mainly in Uninterruptible Power Supplies (UPSs), where it makes possible an output current with very low distortion by using low-weight and less bulky filter elements.