Researching On The Control Strategies Of Three-Level-Full Bridge Dc Converter

As the development of novel energy field,multiple power converter have been reached and applied more and more widely so that requirements to the power level and charge technology of converters are rigorous,simultaneously a standard to the efficiency and volume of power electronic devices is needed.A type of three-level full bridge topology structure is proposed in this paper,it have features of better high-frequency performances,higher voltage level and transmission efficiency.Thus in this paper,circuit modeling,controller designing,experimental validation for three-level full bridge converters has been presented.Three-level full bridge converters have been modeled and analyzed,based on state-space the single module and paralled model are constructed,circuit parameters are confirmed.Open-loop transfer function and output-input impedance are analyzed,the topology structure of three-level full bridge converter is different from conventional Buck converter,it has the higher input impedance and lower output impedance,which provide a wide match grade in the application of cascade connection and parallel operation.Three mainstream control methods are compared so that full bridge phase shift is confirmed.The closed-loop controller,source voltage forwardfeed controller and current sharing controller are designed,as for some matters of converters the compensating controllers are also raised,then simulations are shown.Dynamic response and stability for disturbance of system are reached.Two type of current sharing strategies are contrasted so that current inner-loop method is regarded as a more appropriate choice.Using Matlab/Simulink tools the inner-loop current sharing strategy is validated and final results prove that current-sharing performance is almost ideal.The matters in converters including primary voltage of mid-frequency transformer duty cycle loss and divided-voltage capacitances voltage-sharing,as for above matters corresponding solutions are found and simulated.Several typical fault conditions are picked as research targets for Three-level full bridge converter for the sake of the safety and stability of operation.Related to the normal condition of three-level full bridge converter,some high probability fault conditions are existed,including DC output side short-circuit,capacitance in filter open-circuit fault and some one IGBT open-circuit fault.By simulation result for fault conditions,some critical fault characteristic can be obtained,which can become criterions for circuit protection.Finally,a hardware experimental platform about three-level full bridge converter has been constructed to validate the designed controller and circuit performance,main tasks include that component selection,design of sample and drive circuits and STM32 control procedures.Ultimately one 200 W three-level full bridge converter parallel system can realize 50V/4A output stability,voltage-divided capacitances are voltage-sharing and load currents is divided averagely.Besides several experimental waveform are analyzed which can present that sundry controllers designed are efficacious.