Research and application of zero voltage and zero current switching power supply

    Abstract: A new soft-switching circuit topology is proposed. Through simulation analysis and experimental verification, it achieves the zero-voltage and zero-current switching characteristics of the converter, reduces switching losses, and has been applied to communication switching power supplies.

    Keywords: converter, zero voltage and zero current switch, simulation

1 Introduction

    At present, the phase-shifted full-bridge zero-voltage PWM (FBZVSPWM) converter with the characteristics of resonant soft switching and PWM control has been widely used. Since the power switching device realizes zero-voltage switching, switching losses are reduced. Improved power system stability. However, the FBZVSPWM converter still has shortcomings such as serious loss of duty cycle and large loop conduction loss. To this end, based on the above research, this paper proposes a new zero-voltage zero-current topology, which improves the operating status of the device. Through simulation analysis and experimental research, the zero-voltage and zero-current switching characteristics of the converter are realized , and has been successfully used in communication switching power supplies.

2 Working principle

    The structure of the phase-shifted full-bridge zero-voltage zero-current PWM (FBZVZCSPWM) inverter circuit is shown in Figure 1. S1~S4 are power switching devices, D1~D4 are the antiparallel diodes of the device itself, D5 and D6 are blocking diodes, C1~C2 are the bypass capacitors of S1 and S2, and Cb is the DC blocking capacitor. The relevant waveforms of the zero-voltage zero-current inverter circuit are shown in Figure 2.

    During the working process of the zero-voltage zero-flow soft-switching inverter circuit, there are six working modes in half a cycle, as shown in Figure 3. The specific working process is as follows:

    Mode1:

    During [t0~t1], S1 and S4 are turned on, uAB=Ui, transformer T transfers energy to the secondary, and the voltage of DC blocking capacitor Cb rises linearly.

    Mode2:

    During [t1~t2], S1 is turned off, S4 is still turned on, the parallel capacitor C1 at both ends of S1 is charged to Ui, and when the parallel capacitor at both ends of S2 is discharged to zero, the anti-parallel diode D2 of S2 is turned on. If S2 is turned on subsequently , that is, zero voltage conduction.

    Mode3:

    During [t2~t3], S1 and S4 are turned on, uAB=0, the voltage of DC blocking capacitor Cb is all added to the leakage inductance of transformer T, and the primary current linearly drops to zero.

    During [t3~t4], S2 and S4 are turned on, and the blocking diode D6 prevents the primary current from flowing in the reverse direction. No current flows through the primary of the transformer and will remain zero.

    Mode5:

    During [t4~t5], S4 is turned off and S2 is turned on. Since no current flows through the primary, the shutdown of S4 is zero current shutdown, and the circuit is in an open circuit state.

    Mode6:

    During [t5~t6], S2 and S3 are turned on, and the primary current remains zero instantaneously. Subsequently, the primary current increases, the DC blocking capacitor voltage decreases linearly, and the transformer primary transfers energy to the secondary.

3 Circuit Characteristics

    The zero-voltage zero-current soft switching inverter circuit utilizes the blocking operating characteristics of the blocking diode in series with the lagging arm, and can realize zero-voltage switching of super-forearm power devices and zero-current switching of delay arm power devices in a wide load range.

3.1 Zero-voltage switching of super forearm power devices

    Like the zero-voltage soft-switching inverter circuit, the zero-voltage turn-on of the super forearm power device of the zero-voltage zero-flow soft-switching inverter circuit can be achieved by outputting the energy in the filter inductor. The degree of soft switching mainly depends on the bypass capacitor and the original edge current.

    The charging and discharging time of the bypass capacitor is:

    t=2CU i / I p

    where: U i ——input DC voltage;

    C——Super forearm power device bypass capacitance;

    I p - primary current, similar to a constant current source.

    When the power device is turned on, the primary current of the transformer has flowed through the antiparallel diode of the device, and the voltage between the collector and the emitter is zero. If the bypass capacitance is large, the circuit can not only achieve zero-voltage conduction within a wide load range, but also reduce the IGBT turn-off loss.

3.2 Zero-current switching of delay arm power devices

    During the freewheeling phase, the primary current of the transformer remains zero, and the turn-on and turn-off of the delay arm power device will be completed under zero current conditions, reducing the switching losses of the IGBT. If the delay arm implements zero-current switching, the primary current must decrease from the load current to zero before the delay arm turns off and remain at zero thereafter.

    The time for the primary current to decrease from the load current to zero is:

    t=4L lk C b / DT s

    where: L lk - the leakage inductance of the main transformer;

    C b - DC blocking capacitance;

    D——Duty cycle;

    T s ——switching period.

    As can be seen from the above formula, the current drop time has nothing to do with the load. Therefore, if the switching time is set appropriately, the delay arm can achieve zero current switching in any load range.

4 Experimental research

    Using FB-ZVZCS-PWM converter, a high-power communication switching power supply was successfully developed. The specific technical parameters are as follows:

    Input voltage: three-phase 380V

    Switching frequency: 25kHz

    Output power: ≥3kW

    Efficiency: ≥92%

    The current waveform and collector-emitter voltage waveform of the super forearm power device, the current waveform and collector-emitter voltage waveform of the delay arm power device, the primary current waveform of the transformer and the midpoint voltage waveform of the inverter circuit are shown in Figure 4, where, (a) (c) (e) are simulation waveforms, (b) (d) (f) are test waveforms.

5 Conclusion

    Through the above analysis and experimental research, the following conclusions are drawn:

    (1) The FB-ZVZCS-PWM inverter circuit can achieve zero voltage of super forearm power devices and zero current switching of delay arm power devices in a wide load range;

    (2) During the freewheeling stage, the primary current of the transformer is zero, effectively reducing loop losses;

    (3) Compared with the FB-ZVS-PWM inverter circuit, the efficiency is significantly improved.