Research On Optimal Modulation Technology Of Multilevel Converter

This paper analyzes the equivalence relationship between carrier modulation and vector modulation in multilevel converters.It is the basis for the research on the relationship between traditional carrier stacked modulation strategy(LSPWM)and carrier phase shift modulation strategy(CPSPWM)and the law of gradual evolution.Above,a new dynamic grouping hybrid modulation strategy was proposed,and a 17-level modular multilevel converter(MMC)hardware platform based on DSP and FPGA collaborative control was designed for experimental verification.Firstly,the related topology of the multilevel converter is introduced,the MMC topology with the most flexible control degree of freedom is selected as the main research object,and its working principle is briefly analyzed.The implementation steps of carrier modulation and vector modulation,which are both the principle of volt-second pulse balance,are described in detail,and the equivalence of vector modulation and carrier modulation is studied.It is pointed out that injecting common mode components into carrier modulation can achieve high vector modulation.DC bus utilization.After that,a detailed theoretical analysis of dual Fourier series was carried out on LSPWM and CPSPWM,and the multiple voltage equalization control strategy to ensure the stable operation of the MMC system was introduced.Aiming at the disadvantages of traditional LSPWM modulation with high distortion rate of output voltage and high switching loss of CPSPWM modulation,a new dynamic grouping hybrid modulation strategy based on the intermediate transition state of the two and combining their respective advantages is proposed,which realizes the unification of carrier modulation strategy;The corresponding dynamic sorting grouping strategy,the voltage equalization strategy between groups,and the voltage equalization strategy within the group are presented,which completes the capacitor voltage equalization control strategy based on carrier modulation.Finally,based on the MATLAB/SIMULINK simulation platform and the17-level hardware experiment platform,the new dynamic grouping hybrid modulation strategy proposed in this paper is verified,and it is proved that the modulation strategy and sub-module voltage equalization strategy proposed in this paper can meet the requirements of output voltage distortion.Under the premise,the number of packets is dynamically switched in real-time during the operation of the system to minimize the switching loss of the system and improve efficiency.