Research On Temperature Rise Modeling And Insulation Optimization Of Power Electronic Transformer

With the development of science and technology in China,great changes have taken place in people’s travel modes.High-speed rail vehicles have gradually become an indispensable means of transportation in our daily life.In order to further i mprove the speed and passenger capacity of high-speed rail vehicles,it is urgent to further reduce the weight of high-speed rail vehicles.Among them,the transformer,as one of the essential electrical equipment of high-speed rail vehicles,its weight and volume need to be further reduced.Power electronic transformer is widely used in high-speed railway vehicles because of its small size and light weight.However,power electronic transformers have advantages,but also brought some shortcomings.Due to its small size,it is difficult to centralize the heat generation inside the transformer,and the structure between the winding and the iron core is compact,so the electric field intensity is high.In this case,the insulation of the transformer may be dam aged under the combined action of high temperature and electric field,so it is necessary to conduct temperature rise modeling and insulation optimization of power electronic transformer.In this paper,the leakage inductance and loss of power electronic t ransformers with different structures are analyzed,and the optimal structure of power electronic transformers is obtained.The transient electromagnetic field simulation of power electronic transformers with this structure is carried out,and the magnetic flux density distribution and core loss distribution under different excitations are analyzed.Furthermore,the core loss and winding loss of power electronic transformers working under square wave excitation are further calculated as the loads in the subsequent electromagnetic field-temperature field-flow field multi-physics coupling calculation.The temperature field of a shell-type hollow winding oil-immersed power electronic transformer is calculated,and the internal temperature distribution and flow field distribution are analyzed.The temperature field under different oil pump velocity,different deionized water velocity and different oil outlet is compared.Finally,using the principle of thermoelectric analogy,the corresponding transient thermal circuit structures are constructed for d ifferent internal structures of shell-type hollow staggered winding oil-immersed power electronic transformer,and the overall transient thermal circuit model of the transformer is further constructed.For the thermal parameters in the transient thermal ci rcuit model of the transformer,this paper uses the results of electromagnetic field and steady-state temperature field of the transformer to accurately calculate the thermal parameters,so as to construct a refined transient thermal circuit model.Furthermore,the existing transient thermal circuit model is optimized by using the REI equivalent method,namely the radial equivalent independent power supply method,so that it can quickly calculate the temperature change of each point in the transformer while using the overall loss of the transformer winding and the core.The transient thermal circuit model optimized by REI equivalent method has both the accuracy of steady-state temperature field calculation and the rapidity of thermal circuit model calculatio n,and makes it more suitable for the actual working state of power electronic transformer through the overall introduction winding loss and core loss.