The Study On Control Strategy Of Input Series Output Parallel Phase Shifted Full Bridge Converter

With the rapid development ofpower electronics,the power level of power electronic equipment is higher and higher,and the application of high voltage D C converters is numerous.It is difficult to design the converters and select device because of the high voltage.Instead of a single high power converter,using standard module units connectedin series at input and parallel at output(ISOP)can simplify the design of the converter,reduce the voltage and current stress of the switching device,improving the reliability.Based on the phase shifted full bridge converter,the control strategy of the input series parallel output combined converter is studied and verified by simulation and experiment.As the topology of each module unit,the full bridge circuit has less voltage stress under same power,and soft switching can be realized with phase-shift control.Through the detailed analysis of its working process,the par ameters such as the transformer and resonant inductance are designed,and the switching tube,diode and other devices are selected.In order to stabilize the ISOP converter,the power sharingamong the modules must be controlled.To solve this problem,the method of sensorless current mode control is used to make sure the voltage sharing and current sharingare achived among modules.In this method,the output of output voltage loop is treated as a reference signal,the inductor voltage integral signal can reflect current signal,there is no current sampling.Since the desired input voltage of each unit is the same and the reference signal is also same,each unit obtains the same driving signal.Based on the establishment of small signal model of ISOP system,the stability of this method to balance voltage sharing and current sharing is analyzed.The correctness of the theoretical analysis and the feasibility of this control method are verified by simulation.The control strategy is implemented in a digital waywith DSP.On the basis of realizing the basic functions such as expected duty cycle and soft start,in order to reduce the output ripple,interleaving control is adopted on the basis of voltage sharing and current sharing.Dynamic dead time is set to reduce the reverse recovery current of the MOSFET diode,and the dynamic shift of the carrier is also added to accelerate the dynamic response of the output when the load or the input voltage is abrupt.The input series output parallel prototype is build.Itconsists of three phase shifted full bridge units.The experimental results show that the phase shifted full bridge unit can achieve zero voltage switching from halfof rated current to rated current range;ISOP converter can achieve voltage sharing in steady and dynamic state,and afteraddinginterleaving control,the rippleof output voltage and currenteffectively reduce.