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