Analysis And Modeling Of LCC Resonant Converter

High frequency operation is an important method to achieve high power density and high integration in power electronic converters. Resonant converter possesses a good soft switching characteristic of utilizing inductor and capacitor to realize zero voltage switching or zero current switching. The LCC type series parallel resonant converter is a widely used high voltage DC power supply for acquiring the respective advantages of two elements resonant converter, be compatible with parasitic capacitance of high frequency step up transformer, and the ability to resist open load or short load.This dissertation study the analysis and model of LCC resonant converter in different current response condition, especially concentrate on the non-linearity resulting from the parallel capacitor behavior in one switching period. An analytical model based on the successive state space solving has been proposed, for obtaining mathematic relation among the various parameters of converter.The research will start with the general topology equivalent procedure. The state equations involved each variable in resonant tank have been deduced. Since the inverter can be realized by different structures, the response trajectory has been discussed within or without initial energy storage. In order to establish the interaction relationship between the load and the resonant tank, the energy transfer process is analyzed, and then a detailed expression of energy balance is given.Considering the series parallel characteristic in high power resonant charging application, the converter operated in discontinuous current mode (DCM) is analyzed. For a better understanding of voltage gain and soft switching environment, a sequence distinguishing method of equivalent topologies alternating has been proposed according to the different ranges of output voltage. Because the load impact on resonant tank is not direct, we can conveniently work out the analytical expressions of inductor current, capacitor voltage, and the rectifier current. By the response time of current in each sequence, an optimal driving signal width satisfying zero current switching is proposed. Accurate voltage gain with switching frequency and load has been given. An excellent agreement is obtained when comparing numerical values calculated by the proposed model to the simulation and to the experimental results.To achieve a high precision model of converter operated in continuous current mode (CCM), a pure analytical solving process is presented. Since the CCM response is more complicated than DCM, the sequence of equivalent topologies alternating is firstly distinguished by relation between turn off time and rectifier turn on time. Moreover, the analytical expressions of inductor current, capacitor voltage, and the rectifier current are deduced. The mapping relation about switching frequency, load, and output voltage in two particular situations is analyzed. Analytic constraint equations in general condition is proposed by the extending of particular situations. The study explains why the converter will show capacitive waves under lower switching frequency. The strict range of output voltage and load that makes converter in inductive operation is proposed. The steady state solving procedure of converter in CCM is generalized. The dissertation analyses the load and switching frequency influence on voltage gain, and acquires an analytical model of the three variables. The power factor performance is also discussed.