Soft Starter Harmonic Suppression Method

Three-phase asynchronous motor has been used widely in all kinds of industrial fields and mine areas because of their low cost, high reliability and easy maintenance features. For its start-up process exist too much starting current, this paper analyze the three-phase asynchronous motor soft-start method which based on three-phase voltage modulation circuit, the simulation results show that this soft-start method can effectively limit three-phase asynchronous motor's start current. Since the main circuit of the soft starter use power electronic devices to realize voltage-modulation, so this method will be producing harmonics in the course of their work, which affects the quality of electric power energy. In order to effectively improve the quality of electric power energy, this paper using active harmonic filtering method to reduce the harm of harmonics.Active power filter which makes up the shortcomings of the traditional passive filter can compensates the harmonic and reactive current which frequency and amplitude are variation. Therefore this device rapidly makes more widespread in lots of fields. The two key technologies of active power filter are harmonic and reactive current detection, and compensation current control, therefore its very significance to choose harmonic current detection technique for improving the performance of active power filter.This paper describes the active power filter device working principle, research the harmonic current detection method which based on the instantaneous reactive power theory, in the view of the limitations of this method, the paper introduces the concept of unity power factor to the control of active power filter, describes the harmonic current detection method based on unity power factor in detail, this detection technique applied to a variety of circuit structure.Apply MATLAB software to simulation the two harmonic current detection methods. The results show that the harmonic current detection method which based on unity power factor is correctly and more effectively.This paper also consider the influence on the harmonic current detection method which based on unity power factor when the work environment mutation. The simulation results show that this program still be able to accurate, real-time detection of the load fundamental current and harmonic current when the work environment mutation. It has a good tracking performance.Finally, this paper use the active power filter which harmonic current detection method based on unity power factor to simulation, and the nonlinear load based on the soft-start model, the simulation results show that the active power filter can effectively suppress the harm of harmonic current to the quality of electric power energy, and show the feasibility of active power filter which harmonic current detection method based on unity power factor.