Research On Resonant Converter With Capacitive Output Filter

Soft-switching of resonant converter can be realized by its own resonant process, so as toimprove the switching frequency, make power and electronic equipment of high frequency bein line with the development trend of power and electronic technology. At present theapplication of resonant converters has become more and more widely, such as static dustremoval medical devices and so on. However, resonant converter is popularly a strongnonlinear system, its modeling, circuit analysis and design are very difficult, so the study ofresonant converter is more and more urgent in terms of the accurate mathematical model fastsimulation technology and optimization technique. According to the topology characteristicsof resonant converters in high-voltage applications, the modeling optimization method andcontrol method of parallel resonant converter&LCC resonant converter with capacitiveoutput filter have been studied in this paper, and the research basis is provided for itsapplication in high-voltage applications.The graph theory is applied to multiple resonant modes analysis of resonant converters.Firstly all operating paths of parallel resonant converter&LCC resonant converter withcapacitive output filter are found by graph theory. Then the valid paths are derived in terms ofcircuit topology characteristics and operating law of the resonant converters. Finally the validresonant modes are obtained by these valid paths. The analysis method which is based ongraphic theory is verified by the simulation and experimental process. This proposed methodcan be used for analysis of resonant states of resonant converters easily and intuitively.In this paper, the time-domain mathematic models of parallel resonant converter&LCCresonant converter with capacitive output filter are studied in detail. Based on thetime-domain mathematic models, the circuit characteristics are studied, the relation betweenthe resonant tank component value choices and the circuit characteristics is obtained, theanalytic expressions are deduced to meet the requirements of circuit design, and the generalsteps of time-domain modeling and analysis is summarized.The state track diagram of LCC resonant converter is drew, the trajectory equations ofthe inductance current&the capacitance voltage are derived in this paper, the circuit topologystructure of LCC resonant converter is simply studied by a geometric analysis method, so thedynamic variation process of the state variables is more intuitive, more definite physicalmeaning. Based on the steady state trajectory, a simple and effective trajectory control methodis given, the trajectory control system has excellent transient performance and can achieve thenew steady state in minimum time by this method. Based on Fourier series, a large-signal model and a steady mathematic model of the LCCresonant circuit are established using dynamic phasor. This modeling method of large-signalmodel avoids the limitation that the circuit model which is established by the quasi-stationaryassumption can't simulate the vertiginous transient process, the excellent tracking behaviorand fast simulation speed of the large-signal model are verified by comparison withtime-domain model. Then, based on the large-signal model, a small-signal model is set upconsidering perturbation of the duty cycle and switching angular frequency, the systemperformance can be analyzed by this small-signal model. Finally, the small-signal model isverified by comparison with the perturbation simulation results of the linear model. Dynamicphasor modeling can simulate the vertiginous transient process, speed up the simulation speedgreatly, and realize the dynamic characteristics analysis of the resonant converters.In order to improve the system characteristics of LCC resonant converter with capacitiveoutput filter, the applications of multi-objective genetic algorithm are studied in detail. Firstly,the calculation expressions of the circuit characteristics are obtained based on the steadymathematic model. Then, a Pareto multi-objective optimization with genetic algorithm isapplied to improve the system characteristics of LCC resonant converter. With fine-grainedfitness assignment strategy and density estimation, the algorithm can achieve massive andwell-distributed optimal solutions by the minimization of objective functions, these optimalsolutions can be used to direct design of the circuit. In the condition of not relying on decisionpreference information, multi-objective optimization of the research objects can be completedby multi-objective genetic algorithm, so design deviation of the optimal scheme caused byman-made factors can be avoided. This proposed multi-objective genetic algorithm has goodapplicable value. Finally, it is verified by the results of simulation and experiment.