Research On Isolated SWISS Rectifier Based On Phase-Shift Full-Bridge Topology

In the power supply system including the AC/DC rectifier,the characteristics of the entire system are determined by the performance of the rectifier.Although boost-type three-phase PWM rectifiers are used commonly,its application is limited by the disadvantages of starting shock,low output voltage and difficulty in achieving single-stage isolation.As a result,the reliability and safety of the power supply system will be affected.SWISS rectifier(SR)is a single-stage three-phase buck-type PWM rectifier with the characteristics of high efficiency and high-power density.What’s more,SR can make up for some of the shortcomings of the boost-type three-phase PWM rectifier.At present,the high frequency power devices of the SR are under the hard switching operation.This will not only bring the switching losses,but also limit the increase of the switching frequency.The power desinty of the rectifier can be improved with the decrease of the volume of magnetic elements by the increase of the switching frequency.This paper studies a single-stage isolated SR with soft switching named as SWISS phase-shifted full-bridge rectifier.According to the basic operation principles of SR and the characteristics of soft switching in the phase-shifted full-bridge converter,a modulation strategy of synchronous transmission is proposed,and the realization conditions of soft switching are derived.Considering the driving requirments of SWISS phase-shifted full-bridge rectifier and the limited driving resources of DSP,a DSP+FPGA digital control scheme is designed including the drive modulation method and software design.To solve the voltage oscillating problem of the secondary side of the transformer,the active clamp circuit is designed based on the comparative analysis of the passive absorption circuit.The problem of low harmonic current of the input current caused by the duty cycle loss of phase-shifted full-bridge converter is studied.The relationship between duty cycle loss and the load is analyzed and a related compensation method is proposed,which is simple and easy to implement.Finally,the experimental waveform of the 10kW prototype is shown in the paper,including soft start,closed-loop running and soft shutdown.Besides,the load efficiency curve of the rectifier is ploted based on the experimental data.It can be seen that the SWISS phase-shifted full-bridge rectifier is a low-THD,high-efficiency,high power-density single-stage isolated PWM rectifier.