Study Of Harmonic Suppression Technology Based On Triple Harmonics Injection

Progress in the power electronics technology has led to a significant increase of nonlinear loads' application in industry. These loads act as harmonic current sources and cause harmonic distortion of line current and grid voltage, energy consumption and equipment malfunction even damage etc. The rectifiers both controllable and uncontrollable ones are very typical nonlinear loads. The improvement of harmonics of the rectifiers is necessary and important. Third harmonic current injection is a novel method of harmonic suppression. The basic concept is using the third harmonic source of the diode rectifier to produce the third harmonic current, and injected it into three-phase inputs, which reduce the input current harmonics.This paper produced a third serial resonant circuit to form the third harmonic current, and a set of star-connected capacitors are used as injection circuit, instead of popular star/delta transformer, to divide and injected the third harmonic current into three-phase inputs separately, which is the passive approach of third harmonic current injection. The method has advantages of less power dissipation, device bulk and also easier implementation. Principle and characteristics of the injection circuit are analyzed in details in this paper, which including the condition of optimal injection, the effect of component parameters' deviation and the load varying range with optimal component parameters.; the influence of fundamental phase displacement, the work modes of the circuit, and the analysis of changing injection current under varying load by controlling the inductance are also explained reasonedly. The results show that: This approach has better harmonic suppression performance than passive filter's and more simple and reliable than active power filters, has a noticeable application potential. Results of simulation and experiments validate the feasibility of the method and analysis.Additionally, this paper introduced two active approaches of third harmonic current injection: phase-control method and PWM chopping control method. The circuit diagram, the work principle and the circuit characteristics are introduced severally. The advantages and disadvantages of both of the methods are compared with each other, which also show the application situations of the two methods. For phase-control method, this paper analyses the complete points of the circuit, and compares the ambivalent relation of the circuit energy loss and THD under load dynamic control, which indicates the application drawbacks of phase-control method. For PWM chopping control method, this paper gives a particular analyses of voltage regulation, using a AC voltage regulation circuit to control the injection circuit based on the passive method. The results and conclusions of simulation experiments are introduced also.This paper gives an advance and exploring study of third harmonic current injection technology, discusses the application characteristics. The results of analyses show that the third harmonic current injection method is a novel harmonic suppression technology deserving study and having an extended application potential.