EXPERIMENTAL RESULTS
To verify and test the presented converter, Table 2 demonstrates the
experimental parameters.
From (15), the curves of voltage gain versus duty cycle in various turns
ratio are plotted in Fig. 7. Considering the converter operate in the
step-up mode and step-down mode with suitable duty cycle, the turns
ratio n is selected as 1.
The experiment waveforms under step-up mode underVin = 15 V, Vo = 48 V, andPo = 100 W are illustrated in Fig. 8. Fig. 8 (a)
and (b) show the voltage stresses of power switches
(Vds 1 andVds 2) which are 31 V and 62 V,
respectively, verifying (19) and (20). The voltage spike of power
switches can be inhibited by clamp circuit. The current waveform of
inductor L 1 matches the expected behavior based
on theoretical analysis. Fig. 8 (c), (d) and (e) show the voltage
waveforms and current waveforms of the diodes D 1,D 2, and D 3, respectively.
The voltage stresses of VD 1,VD 2, andVD 3 are about 30V, 30V, and 94V,
respectively. Therefore, the (16), (17) and (18) are evidenced. The
current of D 2 achieves ZCS whenD 2 is turned off. At the same time, the leakage
inductor on the secondary side of the coupled inductor is resonant with
the parasitic capacitor of D 2. Thus, the voltage
of diode D 2 have resonance phenomena, affecting
the current and voltage of Lk .Lk resonates with the parasitic capacitors of the
diodes and power switches during diodes are turn-on, resulting in the
resonance of the voltages and currents of the semiconductor.
The waveforms of experiment under step-down mode underVin = 75 V, Vo = 48 V, andPo = 100 W are shown in Fig. 9. Fig. 9 (a) and
(b) show the voltage stresses of power switches
(Vds 1 andVds 2) which are 103 V and 76 V,
respectively, verifying (19) and (20). Similar to the step-up mode, the
voltage spike can be suppressed. Fig. 9 (c), (d) and (e) show the
voltage waveforms and current waveforms of the diodesD 1, D 2, andD 3, respectively. (16), (17) and (18) are
evidenced with the voltage stresses ofVD 1,VD 2, andVD 3 which are about 103 V, 103V,
and 180 V. Considering the parasitic capacitor of diodeD 2, the voltage of D 2 will
resonate with the leakage inductor on the secondary side of the coupled
inductor, also affecting the primary side current of the coupled
inductor. Therefore, the current of Lk has
resonance phenomena during the rising time. Moreover, the value ofiD 2 is related to the slope of
currents of Lm and Lk . In
both step-up and step-down modes, the currents ofLm and Lk have significant
differences so that iD 2 has
different waveforms. The voltages and currents of the semiconductor have
resonance phenomena because Lk resonates with the
parasitic capacitance of the semiconductor at the turn-off time of power
switches.
The experimental results in the closed-loop for output voltage under
both step-up and step-down modes are given in Fig. 10 (a) and (b),
respectively. The load current changes from 50% of the rated value to
100% and then back to 50% of the rated value. The stability
performances of the dynamic response are presented.
Fig. 11 (a) and (b) show the block diagram of power losses distributions
in step-up mode under Vin = 15 V,Vo = 48 V, and Po = 100 W
and step-down mode under Vin = 75 V,Vo = 48 V, and Po = 100 W,
respectively. Both of these modes, the diodes loss is the highest part
of the total losses. To improve the efficiency, the lower forward
voltage drops and resistance of diodes can be selected.
The curves of measured efficiency
versus output power in both step-up and step-down modes are plotted in
Fig. 12. The maximum efficiency when the converter operates in the
step-up mode and step-down mode are 95.7% and 96.8%, respectively. The
full load efficiency of the step-up mode and step-down mode are 86.8%
and 96.2%, respectively.
Table
the experimental parameters