*4.2. Steady-State Waveforms*

The steady-state experimental waveforms of the proposed converter at the maximum input voltage are given in Figure 8a–c. The operating power was 300 W and the bidirectional switch was turned <sup>o</sup>ff. The primary switches *S*1,2,3,4 were driven with a nearly 0.5 duty cycle, so the primary winding voltage of the transformer had the square shape in Figure 8a. The proposed converter operated in the DC transformer (DCX) mode. The peak-to-peak voltage of the transformer primary was 60 V and the input current equaled 10 A. The primary current was a periodic sine wave with a peak value of 8 A. The oscillations appeared in the primary winding voltage and current due to the parasitic capacitances of the semiconductors. In Figure 8b, the bidirectional switch had zero current and the peak-to-peak voltage of 350 V. The secondary winding voltage had the same shape of the primary winding voltage, but the magnitude was multiplied by *n* (i.e., 180 V). The peak value of the secondary winding current was 2.4 A. The theoretical and measured peak-to-peak of the resonance capacitor voltage was 174 and 175, respectively. These values are well-matched, which proves the theoretical analysis. The output voltage was constant at 350 V and *C*1 had half of the output voltage (i.e., 175 V). The voltage swing of the resonant capacitor equaled 300 V, which was slightly higher than the calculated value of 280 V.

**Figure 8.** Steady-state experimental waveforms of the proposed converter operating at (**<sup>a</sup>**–**<sup>c</sup>**) *PIN* = 300 W, *VIN* = 30 V, *Db* = 0, and (**d**–**f**) *PIN* = 300 W, *VIN* = 25 V, *Db* = 0.215.

For the converter operation in the boost mode, the steady-state voltage and current waveform are given in Figure 8d–f. The operating power was *PIN* = 300 W and the input voltage equaled *VIN* = 25 V. The cumulative duty cycle of the bidirectional switch equaled *Db* = 0.215. The drawn current from the supply equaled 12 A. The average voltage of the resonance capacitor was zero and the peak-to-peak ripple voltage equaled roughly 230 V. The output voltage was constant at *VOUT* = 350 V. Small parasitic oscillations occurred due to hard-switching of the output transistors.

The state-plane trajectory of the converter in the DCX and the boost modes are presented in Figure 9. In the case of the DCX mode, the state-plane trajectory has a circular shape because the voltages and currents of the resonant tank are virtually sinusoidal. The radius of each curve corresponds to Δ*VCr*.

**Figure 9.** Experimental state-plane trajectory for the proposed converter at *PIN* = 300 W corresponding to (**a**) the DCX mode and (**b**) the boost mode.
