Electromagnetic Characteristics Analysis And Optimal Design Of High-Power Three-Winding High-Frequency Transformer

With the development of power electronic devices and the gradual diversification of applications,the demand for high-power three-winding high-frequency transformers in engineering has gradually increased.Accurately calculating the electromagnetic parameters of three-winding high-frequency transformers and optimizing their structure have important engineering values.This paper studies the loss characteristics,leakage inductance calculation and optimization design method of high-power three-winding high-frequency transformer.The main work and results are as follows:(1)The current calculation formulas of AC resistance factor of the winding of double winding high frequency transformer are derived from the premise that the winding magnetomotive force rises from zero.Because of the existence of inner winding,the magnetomotive force of the winding arranged in the middle position is not rising from zero,but depends on the actual load of the inner winding.Based on Dowell algorithm and Tourkhani algorithm,the paper deduces the calculation formulas of AC resistance factor arranged in the middle position of foil and Litz wire three winding high frequency transformer respectively,and verifies the correctness of the results by finite element simulation.(2)During the short circuit test of the inner and outer windings of three winding high-frequency transformer,the proximity effect eddy current will be induced in the middle winding,which will change the distribution of magnetic field in the winding.In this paper,the calculation formula of leakage magnetic field intensity along the conductor thickness direction of the winding arranged in the middle position in the open circuit state is derived by equivalent multi-layer multi-turn winding to a single-layer single-turn winding,thus the calculation formula of leakage magnetic field energy of the winding in this region is derived,which can be used to calculate the leakage inductance between two non adjacent windings of three winding high frequency transformer.The correctness of the formula is verified by finite element simulation.(3)A method of controlling two leakage inductors of three winding high-frequency transformer at the same time is proposed,and it is embedded in the design of three winding high frequency transformer based on non dominated sorting genetic algorithm Ⅱ(NSGA-Ⅱ).According to the optimal design results,a shell type nanocrystalline core three winding high-frequency transformer model with rated parameters of 5KHz/1OkVA is made.The leakage inductance,AC resistance,core loss,temperature rise and AC resistance factor of medium voltage winding are extracted by experiment and finite element simulation.which verifies the effectiveness of the optimization design method.