Research On ZVZCS Three-level Circuit With Narrow Duty Cycle Loss

Power electronic technology mainly studies the transformation and control of high-efficiency electric energy,which is closely related to people's daily life and industrial production.Among them,DC power conversion technology plays an irreplaceable role in human production and life.In order to improve the input voltage level of DC converter,scholars put forward a variety of solutions,among which three-level DC converter is widely concerned in the field of high input voltage DC converter because the voltage stress of its transformer primary side switch device is only half of the input voltage.In order to improve the power conversion efficiency of three-level DC converter in high frequency operation,and improve the soft switching operation of switching devices,this paper proposes a narrow duty cycle loss ZVZCS three-level circuit topology and studies it.In this paper,traditional zero voltage(ZVS)and traditional zero voltage zero current(ZVZCS)three-level DC converters are deeply studied.The advantages and problems of these two three-level circuit topologies are analyzed,and the load range of their soft switches is compared.In view of the problems existing in the original three-level DC converter,such as the difficulty in soft switching of the lagging bridge arm switch device,the imbalance of the input capacitance current,the imbalance of the current stress of the primary side switch device and the serious loss of the primary and secondary side duty cycle of the transformer,a circuit topology of the narrow duty cycle loss zero voltage zero current(ZVZCS)three-level circuit is proposed.The narrow duty cycle loss ZVZCS three-level circuit proposed in this paper.The circuit adds two auxiliary switching devices to the original ZVS clamp free three-level circuit topology.The auxiliary switching device does not flow current in the power transmission stage,so the on state loss is very low.In the auxiliary commutation stage,the reverse current can be blocked to realize the zero current switching of the switching device.The working principle of the circuit is described in detail,and the clamping mechanism of the auxiliary switch to the primary current is emphasized.This paper analyzes the reasons for the improvement of duty cycle loss in the circuit,and points out that the original side current is clamped in the continuous current stage,under the same condition of transformer leakage inductance,the loss of duty cycle of the original and secondary side voltage of the transformer is improved,which can optimize the working characteristics of the converter.The other advantages of the new circuit are analyzed,such as equalizing the current stress of the input capacitor,equalizing the current stress of each switch device on the original side,etc.On the basis of theoretical analysis,this paper designs and selects the transformer,switch device,rectifier diode,isolation capacitance,input capacitance,filter inductance,filter capacitance and other components involved in the circuit in detail,and introduces the design of the software and hardware part of the control circuit.According to the design parameters of each component in the circuit,this paper builds a simulation circuit through PSIM software,analyzes the simulation results and verifies the theoretical feasibility of the designed circuit.On the basis of the simulation results,this paper designs and makes an experimental prototype with a switching frequency of 100kHz,an input voltage of 400V and an output power of 500W,and carries out experiments.The experimental results are compared with the theoretical analysis to verify the correctness of the proposed circuit topology.