Research On The Modulation Strategy Of DC/DC Converter In Micro Wind Power System

With the rapid development of wind power generation,micro-wind power grid-connected systems used in cities,homes and other places will become a major development trend.However,due to the influence of climate and weather,the output voltage range of the micro-fan is wide.In order to provide a stable DC bus voltage to the rear-stage converter,it is necessary to add a first-stage DC/DC converter between the fan and the post-stage converter.Therefore,DC/DC converters suitable for a wide range of input in micro wind power generation systems have certain research value.LLC resonant converter is widely used in resonant converter because it has good voltage regulation characteristics and can realize soft switching.However,when the input voltage varies widely,the traditional LLC resonant converter with variable frequency modulation strategy has a wide range of switching frequency variation.Based on LLC DC/DC converter,this paper studies a variable mode hybrid combining variable frequency and asymmetric PWM.The modulation strategy uses a variable frequency modulation strategy to boost when the input voltage is less than the switching voltage;and uses an asymmetric PWM strategy to step down when the input voltage is greater than the switching voltage.In this paper,the working principle and working characteristics of LLC DC/DC converters operating in variable frequency and asymmetric PWM strategies are analyzed in detail.The fundamental equivalent model of the converter is established.The voltage gain characteristics,input impedance characteristics and soft switching implementation conditions of the circuit are analyzed.The influence of the resonant network parameters on the hybrid modulation strategy is also discussed,and the circuit design and parameter design are given.In order to verify the rationality of the scheme,this paper establishes a closed-loop simulation model of LLC DC/DC converter in MATLAB/Simulink simulation software,and builds a small power hardware experimental platform with DSP as the control chip.According to the simulation and experimental results,the LLC DC/DC converter under the hybrid modulation strategy can achieve output voltage regulation with a wide input voltage range,and the switching frequency range is narrow,and zero voltage turn-on of the primary switching and zero current turn-off of the secondary side rectifier diode are realized.