Efficiency Optimization Based on LLC Cascaded Three-phase Inverter

Modern power electronic devices pay great attention to the index of efficiency. In the case of high voltage input, low voltage and high current output, if the inverter is directly inverted, the inverter efficiency is low and the power quality is poor. In order to solve this problem, LLC con-verter can be used to convert high voltage to low voltage and supply power to the inverter. This two-stage inverter has higher efficiency. For the former LLC power supply, the lower the output DC voltage, the lower the efficiency; for three-phase inverters, the higher the input voltage, the lower the efficiency. How to select the intermediate DC voltage is the key to achieve optimal system efficiency. From the perspective of the system, this paper analyzes the influence of the intermediate stage voltage on the efficiency of the pre-stage LLC converter and the post-stage three-phase inverter. The intermediate stage voltage with the best efficiency of the cascade system is obtained by theoretical calculation, and the simulation model is built to verify the calculation results. Compared with the traditional single-stage inverter, the efficiency of the cascaded system with optimized intermediate voltage is improved by 5%.