Study of Reduction Method of Harmonic Currents in Power Systems Generated by Switching Regulators

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For rectifier circuits with small capacity such as those for consumer electronics and appliances, capacitor input type rectifier circuits are generally used. It is well known that the generation of the harmonics in the power system becomes a social problem. For such power supply, various switching regulators with capacitor input rectifiers have become more common, typically for the television set. Consequently, as the application of those equipment is expanded, various harmonics are much generated in the power system. The harmonics problem will become more serious in the future. Such equipment will be more used similarly in industrial applications.Under such circumstances, various improved circuits to reduce harmonics have been studied and reported. However, their purposes are intended to make the input current waveform sinusoidal, thereby increasing the cost. The harmonics generated by the capacitor input type rectifier circuit, except the third and fifth harmonics, do not increase in proportion to the number of the equipment in the power system, and are kept constant a certain value. Considering that the third harmonics eliminated by the transformer of the power system and the cost is high for sinusoidalizing the input current, we need not persist on making the input current sinusoida 1wave.From such point of view, we have studied a method to reduce the harmonics for the rectifier circuit of the forward converter, which is more used in a variety switching regulators. The proposed switching regulators do not only reduce their own harmonics but also eliminate other harmonics in the power system which are generated by other rectifier circuits. The authors have reported various harmonic eliminating techniques to reduce the harmonics in the power system in various periodicals.