4.1. Simulations in Saber
The simulated waveforms of the inductor current, switch voltage and diode voltage are shown in Figure 13
. The inductor current waveform shows a trend of first rising and then falling. The inductor current, MOSFET voltage, and diode voltage waveforms are all resonant. Compared with ideal conditions, the voltage amplitudes of MOSFETs and diodes are increased due to the influences of resonance when considering parasitic parameters under high-frequency conditions.
The simulation waveforms show that, due to the high-frequency resonance under high-frequency conditions, the amplitudes of inductor currents, MOSFET voltage and diode voltage all increases due to the parasitic capacitors resonate with the inductors in the sneak circuit, in line with the previous analysis.
4.3. Comparative Analysis of Simulation and Experimental Waveforms
The resonance current amplitudes values in experimental waveforms Figure 15
a are iL1
= 8.8 A, iL2
= 8.7 A, and resonance current amplitudes values in simulation waveforms Figure 13
a are iL1
= 8.9 A, iL2
= 8.7 A. The amplitudes are almost the same.
By comparing the experimental waveforms, the simulation waveforms, and theoretical analysis of the inductor currents, it can be known that the analysis of the influences of the parasitic parameters on the inductor currents is in line with the actual working situations.
The resonance voltage amplitudes values in experimental waveforms Figure 15
b are UCds1
= 188 V, UCds2
= 183 V, and voltage amplitudes values in simulation waveforms Figure 13
b are UCds1
= 187 V, UCds2
= 184 V. The experimental waveforms of MOSFETs resonant voltages are consistent with the simulated waveforms.
From above analysis, it can be known that the parasitic capacitors and the inductors in the circuit resonate under high-frequency conditions, and the amplitudes of the voltages are increased by the influences of resonance, which is consistent with the conclusions obtained from theoretical analysis.
From the above experimental waveform Figure 17
a, it can be seen that the resonance current peak value of the inductor current iL2
is enhanced by 0.64 A compared to iL1
, and the appearance time is advanced by 8.3 us. Since the inductor currents iL1
no longer maintain the same phase and amplitude, the centerline will have charge and discharge currents. Experimental waveform Figure 17
b shows the current in the converter centerline to prove this conclusion. Through the above analysis of the experimental waveforms of the inductor currents iL1
in the asymmetric condition, it can be known that the symmetry of the ideal symmetric dual switch high-gain converter will be destroyed and the dynamic balance characteristics of converters will be affected when considering parasitic parameters under high-frequency conditions.
From the experimental waveform Figure 17
c, it can be seen that the peak value of the resonance voltage UCds2
increases by 7 V than UCds1
, and the phases of the two voltages UCds1
are no longer the same. From the waveform Figure 17
d, it can be seen that the peak value of the resonance voltage UCD02
increases by 13 V than UCD01
, and the phases of the two voltages UCD01
are different. Through the above analysis, it can be known that the amplitudes of the resonance voltages of MOSFETs and diodes no longer maintains the same values after considering the parasitic parameters values asymmetry, which puts more precise requirements for the selection of devices and the selection of device-rated voltages in actual applications.
From the above experimental waveforms, it can be seen when the values of the parasitic parameters become larger, the voltage stress values of the corresponding switches will be greater. Through the comparisons of experimental waveforms with the same and different parasitic parameter values, it can be seen that when the parasitic parameter values of the devices are different, the symmetry of the ideal symmetric dual switch high-gain converter will be destroyed and the dynamic balance characteristics of converters will be affected and the resonance voltages amplitudes of the MOSFETs are no longer the same, which puts more precise requirements for the selections of devices and the selections of device rated voltages in actual high-frequency application conditions.
A comparison of voltage gains obtained from the experiment and calculation is shown in Figure 18
In Condition 1, the values of parasitic parameters are: Cds
= 232 pF, CD
= 60 pF, Rs
= 0.05 Ω, Le
= 147 nH. In Condition 2, the values of parasitic parameters are: Cds
= 232 pF, CD
= 120 pF, Rs
= 0.1 Ω, Le
= 147 nH. The different values in Figure 18
are acquired by adding external capacitors, inductors, and resistors across the device terminals. Figure 18
proves that by varying the values of parasitic parameters while other parameters remain unchanged, the greater the parasitic parameter values, the more obvious the impacts on the output gain, which consistent with theoretical results. The results of the theoretical analysis and experiments verify that the sneak circuit phenomena can be reduced by choosing the value of parameters appropriately, which means higher requirements for the selection and optimization of power devices.