Simulation And Analysis On Medium-frequency Power Supply

Along with the development of steel industry in recent years, the high-power intermediate frequency inductive stoves are adopted in steel-making factory. Medium-frequency power supply as its main constituent is widely used. It can reduce the pollution of steel industry and energy loses, improve steel worker's working conditions and create higher economic efficiency and the social efficiency. On the other hand, as a result of non-linearity of the rectification and inversion equipment, massive harmonics appears in the electrical network, the security of electrical equipment and electrical network is threatened. User's economic efficiency is also influenced. Thus, it is extremely necessary to carry on the test and research towards medium-frequency power supply's harmonics.Each constituent of medium-frequency power supply is introduced particularly in this thesis. Medium-frequency power supply's principle, basic concepts and analytical method of harmonics and its damaging to power system are introduced. Characteristic harmonic currents of 6-pulsating and 12-pulsating rectifier are discussed. The curves which indicate relations between trigger angle, commutation angle and characteristic harmonic current ratio are presented. Commutation angle's change caused by transformer's leakage inductance is analyzed, whose relation curves are also given. The conclusion indicates that with appropriate increasing of transformer's leakage inductance, the process of commutation is prolonged and harmonic content of input currents is reduced. Taking from trigger angle of rectifier can also decrease the total harmonic ratio of input currents.Model of medium-frequency power supply is constructed with simulation software of MATLAB. Simulations about input currents are done time after time through adjusting transformer's leakage inductance. The simulation results indicated that increasing transformer's leakage inductance can improve waveform of input currents obviously, which coincides with the foregoing analysis. In order to grasp the harmonic currents injected by medium-frequency power supply accurately, harmonic tests are carried on towards the 8000kW medium-frequency power supply of Henan Jinhui Steel Plant. Its frequency spectrum and tested datum are presented. According to the harmonic characteristics of medium-frequency power supply, some suggestions about suppression of harmonics are put forward.The high-power medium-frequency power supply is the main harmonic source in power system. In this thesis, the springhead of the medium-frequency power supply is analyzed, which provides the technical support for the harmonic suppression. The conclusion has the practical significance on improving medium-frequency power supply's performance and suppression of harmonic pollution.