Parameters Global Optimization Design Method for LLC Converter with Planar Magnetic
Zhou Zihang1, Gao Yihan1, Liu Yijing1, Zhang Xin1,2, Ma Hao1,3
1. College of Electrical Engineering Zhejiang University Hangzhou 310027 China; 2. Hangzhou Global Scientific and Technological Innovation Center Hangzhou 310027 China; 3. University of Illinois at Urbana-Champaign Institute Zhejiang University Haining 314400 China
Abstract：Traditional step-by-step optimization design methods struggle with the large number, strong continuity, and mutual coupling of planar magnetic elements, which is challenging to achieve the highest overall efficiency. Therefore, this paper proposes a parameter global optimization design method for the LLC converter based on planar magnetic elements to enhance efficiency and power density, including the switching frequency, resonant parameters (parallel-to-series resonance inductance ratio, resonance capacitance), the size of planar magnetic elements (middle leg radius, winding linewidth, transformer and inductance middle leg length, middle leg height), and the output power at peak efficiency. The optimization objective is to maximize the peak efficiency of the converter, expressed as the optimization parameters. The optimization constraints are the working stress and volume of the converter related to the optimization parameters to meet practical engineering requirements. The optimization design is expressed as a single objective, multi-parameter, nonlinear problem. Genetic algorithm (GA), particle swarm optimization (PSO), simulated annealing algorithm (SA), traversal optimization, and other methods can be used to solve this problem. The theoretical global optimal design parameters for maximizing the peak efficiency can be obtained in a single step. Compared with the step-by-step design method, the parameter global optimization design method can improve the theoretical peak efficiency for a certain LLC converter by about 0.1%, with a reduction of more than 20% in the volume of the planar magnetic element. This improvement is achieved by reducing the switching loss of switching devices and the core loss of the magnetic element by an appropriate decrease in the switching frequency and allocating more of the total area of the magnetic element to the magnetic core rather than the winding. The efficiency at each working condition below half load is improved, validating the effectiveness of the parameter global optimization design method. A 3 kW high-efficiency and high-power density LLC converter is designed. Considering that the optimization parameters are variables with practical physical significance and processing technology constraints, the traversal optimization method can ensure that the optimization results are the actual values achieved in production by setting the appropriate step size. The power density of the converter is 510 W/in3, the peak efficiency is 99.0%, and the full load efficiency is 98.3%. The result is close to the theoretical results of the parameter global optimization design method, which proves the correctness and effectiveness of the design method. The idea is also applicable to other topologies using planar magnetic elements. The application to other topologies involves similar thinking, with specific optimization parameters and their relationships tailored to each case.
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2024, Vol. 39 
