An analysis of three-phase low-harmonic rectifiers applying the third-harmonic current injection

An analysis of the three-phase low-harmonic rectifiers applying passive third-harmonic current injection networks is presented in this paper. Optimal amplitude of the injected current to minimize the input current total-harmonic distortion (THD) is derived as a function of the injected current phase displacement. Power aspects of the third-harmonic current injection are analyzed, and it is shown that improvement in the input current THD could be obtained at the expense of the power taken by the current injection network. In the case of optimal current injection, the power taken by the current injection network is shown to be equal to 8.571% of the input power, resulting in the input current THD of 5.125%. Effects of unwanted higher order harmonics in the injected currents are studied for two previously proposed passive current injection networks. The current injection networks are compared under the constraint that volt-ampere ratings of applied components are the same. Analytically obtained results are experimentally verified.