Optimization Design Of High-power High-frequency Transformer

Within the promising power conversion fields as new energy DC Grid-connected system,electric locomotive traction system and power electric transformer and so on,the high frequency high power transformer is the key component and has great impact on the converter efficiency and power density.The high frequency transformer losses,parasitic parameters,insulation and heat dissipation should be taken into consideration when designing the high transformers with the increment of transformer capacity and working frequency.This paper focuses on the high frequency high power transformer optimization design from three aspects as shown below.Firstly,this paper discusses the core materials used in the high frequency transformers.The nanocrystalline magnetic core CN138*95*45*30 has been chosen to measure the basic magnetizing curve and core losses under sinusoidal excitation for transformer core losses calculation within nonsinusoidal excitation.And the IGSE algorithm is verified with lower relative calculation errors and is suitable for calculating the core losses under nonsinusoidal excitation based on the experiments.Three different winding conductor losses,foil conductor,round conductor and litz wire conductor,are analyzed with the generally available winding losses calculation methods and the relationship among the winding losses and winding structure parameters are also given.For the round conductor,the relative calculation errors of different winding losses analytical methods are compared based on two transformer prototype AC resistance measurements.The experiment results have shown that the listed Modified Ferreira algorithm is suitable for the round conductor winding loss calculation and analysis with lower relative calculation errors.Meanwhile,the Modified Ferreira algorithm can be used to select the winding conductor as reference.Secondly,as the transformer parasitic parameters have significant impact on the converter performances,the high frequency transformer leakage and parasitic capacitance are discussed separately.For the high frequency transformer leakage calculation,this paper shows different analytical algorithms used in leakage calculation and the relationship among the transformer structure parameters and leakage values as reference in adjusting the transformer leakage.Meanwhile,the transformer parasitic capacitance model is also discussed and the transformer six-capacitance or three-capacitance equivalent models are derived based on the relevant transformer structure capacitances calculation.Finally,for the optimization of high frequency high power transformers,an optimal design method with limited multi-objective genetic algorithm,NSGA-II,has presented based on the high frequency transformer losses and parasitic parameters calculation given consideration of transformer insulation,losses and leakage value control and so on.An220V/3.52 kV,3.52kW/20 kHz nanocrystalline transformer prototype has built and the measurement results have verified the validity and correctness of the transformer losses and leakage calculation.