In this paper, it is introduced the composition of supply unit for 25 kg and 100 kg medium frequency induction furnace in a laboratory and the specific functions of each device, analyzed the changing rules of medium-frequency power supplies with parallel resonance and series resonance in rectification and contravariance, given the calculation formulas of main parameters as well as compared and analyzed combining with the actual use. The results showed that the medium-frequency power supply with series resonance was easy to be started, which was more suitable in workplace with frequent start; while the medium-frequency power supply with parallel resonance was more difficult to be started, which was not suitable to be used in workplace with frequent start, but it was with strong adaptive capacity to the load so that it was more used in workplace where the smelting steel grade changed at any time.

parallel resonance  /  series resonance  /  thyristor  /  IGBT