| A general description of development of harmonic around the world and the importance of the evaluation of the harmonics are given in this thesis at first. Then the harmonic characteristics of the VFD, the arc furnace, and the electric locomotive are analyzed. According to their different characteristics, the concrete evaluation methods are proposed respectively. The fitting function of the load rate and harmonics in the VFD is got through the results of the simulation in the MATLAB. In order to give more details of the evaluation, two examples are given in the paper. Finally, the inter-harmonics of the thyristor rectifier system are analyzed. The switching function method is applied, and the modulation theory of the switching function applied in inter-harmonics is verified by the simulation in the MATLAB. The PLL's influence in the system's inter-harmonics is proposed. The inter-harmonics in the open-loop system and close-loop, in the system with different background inter-harmonics and the influence of the harmonics are analyzed.
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