Optimal Design For High Frequency High Voltage Transformers Based On Lagrange Multiplier Approach

The high energy density developing and the size reduction trend of power electronic equipment require higher operating frequency, which promotes the continuous development of High frequency high voltage transformers(HFHV transformers)for they are the critical block of the power electronics systems. In this paper, a design of a high power HFHV transformer is introduced considering its operation in the LC resonant converter, which is applied as a capacitor charging power supply(CCPS).The reliability and stability of HFHV transformers play a decisive role on the performance of CCPS.There are many factors affecting the performance of HFHV transformers, such as parasitic capacitance, leakage inductance, temperature rise, etc. Among them the parasitic capacitance of the winding and loss of the transform reduction are the main objectives of this CCPS system. A novel optimization design of HFHV transformers based on the Lagrange multiplier approach is firstly put forward. This design could reach the minimum value of the parasitic capacitance within the required loss range by modifying the winding structures, including the number of slots, layers, turns. The design facilitates an iterative design procedure and is suitable for computer calculation.The HFHV transformer life span depends heavily on insulation – its condition, materials, composition, etc. The high voltage transformer insulation requires a very focused analysis in the design stage. A comprehensive electrostatic analysis is conducted to improve the electric field distribution and optimize the insulation strategy and calculate parasitic capacitance the by finite element analysis(FEA). In addition, thermal analysis results from FEA is also presented to validate the proposed design. At last, a prototype transformer has been designed and built, of which the input and output voltages of the transformer are 500 V and 10 kV, respectively. Normal operation frequency is 15 k Hz and power of the transformer is 30 kVA with an efficiency of better than 98%. Experimental measurements are presented to validate the loss and parasitic capacitance are consistent with the calculation results and the reliability of the designed HFHV transformer in the application of a LC resonant CCPS.