| With the realization of the national "double carbon" goal,battery energy storage technology is the core equipment of new energy power generation and microgrids,mainly used for stabilizing and absorbing fluctuating power.However,the input voltage range is not wide enough.In this thesis,a PFM(frequency)and PSM(phase shift)hybrid modulation lifting method is adopted to solve the problems of narrow working range of conventional PFM modulation converter and difficult voltage regulation when no load is loaded.Based on the extended description function method,transfer functions of PFM and PSM modulation modes are established respectively.Given the current situation where the small signal model has no guidance under the PSM control mode,a small signal model is derived for reference,and a hybrid modulation adaptive PI control strategy of the LLC resonant converter PFM and PSM is proposed to achieve a wide input voltage range of the converter and improve the efficiency of the converter.The main work of this paper can be summarized into the following four aspects.Ⅰ.Analysis of working principle and gain characteristics of LLC resonant converterFor the switching mode analysis of the LLC resonant converter,the steadystate characteristics of the LLC converter in PFM mode are analyzed using the fundamental wave analysis method.Different operating modes such as under-resonant,critical resonance,and over-resonant are analyzed in PFM modulation mode.The under-resonant operating mode is taken as the model for detailed inference,and its gain characteristic curve is drawn and analyzed.The formula of the five operating modes in the second half cycle of PSM modulation mode is derived.By analyzing the relationship between duty ratio and each variable under each mode,the implicit function equation of voltage gain with respect to duty ratio is obtained.Ⅱ.The small signal model of PFM and PSM modulation mode is establishedFor the PFM modulation mode,a small signal model of the LLC resonant converter is established based on the extended description function method,and it is verified by the sweep frequency method.For PSM modulation mode,the extended description function method modeling is introduced into LLC resonant converter modeling in PSM modulation mode.The small signal model of the resonant capacitor is equivalent to series inductance,and its small signal model is finally obtained.MATLAB sweep code is used to verify the transfer function of PFM and PSM control modes.Ⅲ.Adaptive PI control strategies for PFM and PSM modulation modes in piecewise and continuous modeAccording to the different transfer functions of discrete PFM and PSM modulation modes,a PFM and PSM hybrid adaptive PI controller is designed.Two kinds of piecewise adaptive PI control strategies based on switching function and continuous functional adaptive PI control method based on gain function are proposed.The PFM modulation mode and PSM modulation mode can be switched adaptively according to load changes,and the output voltage remains stable.IV.Simulation and experimentThe simulation and experimental platform were built,and the experiment verified that the proposed PFM and PSM hybrid control adaptive PI control strategy could realize a wide range of input voltage of the converter and could realize adaptive switching between PFM modulation mode and PSM modulation mode.The efficiency of the converter under PFM modulation mode and the hybrid adaptive modulation strategy proposed in this paper were compared to verify that the hybrid adaptive modulation strategy proposed in this paper can significantly improve the efficiency of the converter.In this thesis,a hybrid modulation adaptive PI control strategy of LLC resonant converter PFM and PSM is proposed to solve the problems of a narrow working range of conventional PFM modulation converter,low voltage regulation,and low efficiency under no-load conditions.The simulation and experimental results show that the maximum efficiency can reach about 94.5%under a wide input voltage range. |
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