Control And Simulation Of LLC Resonant Converter

At present,the use of new energy sources is becoming more and more widespread for environmental pollution.Photovoltaic power generation is the main way to use a kind of new energy,and the resonant power converter plays an important role in photovoltaic power generation,especially the LLC resonant converter.For example,the LLC resonant converter can be used in a two stage short time photovoltaic system.The unstable DC voltage is converted to a steady DC voltage.General power converter increases the switching frequency in order to improve the efficiency of energy transfer,but switching loss will increase when the switching frequency is increased.Besides the cost of magnetic capacitor will be very high when the switching frequency is low.The parasitic capacitance of the photovoltaic panels due to the lack of isolation may lead to leakage current,but the LLC resonance converter can overcome these problems well for this kind of system.In this paper,the modeling,control algorithm and simulation of LLC resonant converter are studied.A relatively accurate nonlinear dynamic model is necessary to determine the small signal model as well as the transfer function for a typical LLC converter.In the modeling process,first the basic differential equations are obtained by circuit law;The voltage and current LLC resonant circuit is quasi sinusoidal current and voltage waveform,voltage of the electromagnetic induction current and resonant capacitor is composed of basic cosine part;the large signal model is obtained by separating sine and cosine components;the large signal model of harmonic balance can be used to obtain the steady state operating point by setting the derivative to zero;in the end the first order approximation equations and transfer function are obtained.A reasonable controller is designed to adjust the gain of the resonant pool under the disturbance of input voltage,resonant parameter and output load,so that the output voltage of the system always follows the reference voltage.In the control research of LLC resonant converter,a single loop or double loop feedback control loop is designed to adjust the output voltage according to the reference voltage.The output of the LLC resonant converter controller is used to control the switching frequency in this paper,so this is a method to control the gain of the resonant cell by changing the switching frequency.The double loop controller with compensator,fuzzy logic controller and sliding mode controller are designed and the simulation model is built to make comparisons of control effect.