Loss Calculation,Heat Sink Design And Optimization Of High Frequency Transformers

With the development of High Voltage DC(HVDC)Transmission System,the capacity of the transmission system is increasing rapidly,which is the same with transformers.The traditional line frequency transformers have the disadvantage of low power density,large volume and mass.They occupy much space of the HVDC system.Therefore,the high frequency transformer with high power density,small volume and mass is becoming the development tendency.At present,the model and design method of high frequency transformers are not that mature,which are still hot researching fields.In this essay,the core loss calculation method under the excitation of sinusoidal and non-sinusoidal is described.In addition,the Ferreira's winding loss calculation method has been modified and supplemented to make it suitable for more winding configurations and wider frequency.By using ANSYS finite element simulation,it is validated that compared with a maximum error of 107%,the new method merely has a maximum error 1.6%.In the next chapter,the thermal resistance model of high frequency transformer is established,and the algorism for steady state temperature calculation is proposed.By using the model and algorism,the steady state temperature rise of windings and cores is calculated in the condition of both natural and force convection with the consideration of heat radiation.The results are validated by experiment and Fluent simulation.The maximum deviation of the results is 6?,much smaller than traditional empirical formulas method.Finally,by focusing on the high loss density of high frequency transformers which usually causes over temperature,the fin heat sinks and force convection are used.The model of fin heat sinks is described,and an algorism for the acquisition of optimal dimension of fin heat sinks is proposed,which saves much time to reach for the optimal results.The algorism is validated by comparing its results with the results of exhaustive method.At the end of this chapter,the equation to calculate the thermal resistance of the fin heat sinks is derived and modified,and it can be used in the calculation of steady state temperature rise of high frequency transformer by using thermal resistance method when it is equipped with fin heat sinks.