Research On Unbalanced Voltage Analysis Of Modular LCC Resonant Converter And Fuzzy PI Control Strategy

Series-parallel(LCC)resonant converters combines the advantages of series resonant converters and parallel resonant converters,and have the advantages of high efficiency,high power density,strong voltage regulation capability,strong parasitic parameter compatibility,and strong load short circuit resistance.In high-voltage and high-power applications,modular cascading technology is used to achieve high power density and large capacity.Input Parallel Output Series(IPOS)multi-module LCC resonant converters are easy to expand,with high voltage levels and high power.The advantages of density,large capacity,and high reliability.In this paper,theoretical research,simulation analysis and experimental verification have been done for several problems of modular LCC resonant converter.Although the multi-module LCC converter cascade topology has significant advantages over the single-module topology,it also has the problem of unbalanced output voltage.This paper analyzes the distributed parameters of the LCC converter,establishes a large-signal model of the multi-module LCC converter with distributed parameters,and uses this model to analyze the impact on the output voltage imbalance between the modules.Transformer leakage inductance,winding distributed capacitance,and diode distributed capacitance affect the resonance parameters to cause uneven voltage between modules,while the distributed capacitance between the primary and secondary windings of the transformer causes uneven voltage between modules through common mode interference.The proposed large signal model also provides a theoretical basis for the voltage equalization control between modules.For modular LCC converters,a dual-loop control strategy of frequency modulation and H-bridge duty cycle modulation is usually adopted.The system gain is changed by changing the switching frequency,and the total output voltage is controlled;the gain of each module is adjusted by changing the H-bridge duty cycle of the unit module to achieve the purpose of voltage equalization.Since traditional PI controllers cannot adapt to complex working conditions,fuzzy control can imitate the engineer’s thinking process through empirical data,and by establishing appropriate fuzzy rules,traditional PI control parameters can be modified.Finally,based on theoretical analysis and simulation,a two-module IPOS-type LCC converter experimental prototype platform was built.The accuracy of the large-signal model of the two-module LCC converter is verified through experiments.The proposed model can be used for circuit tolerance design and analysis of uneven voltage between modules.It also verifies the superiority of the fuzzy PI controller compared to the traditional PI controller.For the two-module LCC converter,the voltage imbalance and the load severity between the modules are selected as input variables to correct the voltage stabilization loop and the equalization loop.PI parameters.Therefore,the fuzzy PI control,which is a combination of fuzzy control and traditional PI control,is very suitable for dual-loop control of modular LCC resonant converters.