The Research Of Two-stage Converter With APFC Based On LLC Resonant Circuit

The development of power electronic technology and power devices promotes the winged development of switching power supply. On the one hand, the decrease of cost, materials, volume and weight makes switch power supply to improve high frequency and high power density, on the other hand, environmental pollution and energy crisis require high power factor and high efficiency for switching power supply. So according to the development trendency of switch power supply and the demand of the topic, the paper adopts two-stage AC/DC converter to design switching power supply; the former is Boost circuit structure of one cycle control for active power factor correction(APFC), the latter is LLC resonant circuit structure of soft switching for the decrease of switching loss.The paper firstly analyzes the fundamental of one cycle control and implementation method of one cycle control in Boost APFC circuit, furthermore uses the theory of mathematics to detailedly analyze two modulaiton modes of one cycle control-the frontier modulation and the latter modulation and the stability of one cycle control, carry out the parameter design of main circuit; at the same time based on the state space average method builds the small-signal model of Boost circuit, and theoretical analysis and software simulation about average current control and one cycle control are carried out for the design of controllers; and combining with control chip IR1150, the paper completes the design of the whole control circuit.Secondly according to the operating principle of LLC resonant circuit in different switch frequency ranges, focuses on the analysis of every modal in the section less than the resonant frequency; adopts the fundamental wave analysis method to set up steady-state model of LLC resonant circuit; detailedly analyzes the relationship of voltage gain and input resistance of resonant network of three elements about switching frequency, and determine operating frequency domain of soft switching, meanwhile studies the influences on voltage gain, current gain, constant power output for the parameters of resonant network so as to provide theoretical guidance for parameter design of LLC resonant network in different output modes, thereby ensure LLC resonant circuit can always achieve the zero-voltageturn-on(ZVS) of original side MOSFET in different output modes. According to the steady state analysis and the corresponding design requirements, the paper realizes the parameter design of LLC main circuit, at the same time uses the expanded describing function method to set up small signal model of LLC and provides theoretical guidance for the controller design, finally completes the design of the whole control circuit combining with the control chip L6599.Finally on the basis of the research and analysis above, a experimental prototype of two-stage converter that its former’s maximum output is 300 W and its latter’s maximum output is 120 W is made, and the experiment tests and analysis are respectively conducted for the former-Boost APFC circuit and the latter- LLC resonant circuit to prove the accuracy and feasibility of entire design scheme, so as to easure high power factor and high efficiency of the prototype.