# TAB Series-Resonant DC-DC Converter and Multi-Phase-Shift Based Global Optimization Modulation
## 4 Experimental Results and Analysis
In state 1, the input voltages of port 1 and port 2 are set as 120 V and 140 V. \(k_{1}\) and \(k_{2}\) are accordingly 0.83 and 0.71. The corresponding experimental waveforms of state 1 with \(P_{13}\) = 800 W and \(P_{23}\) = 1 kW are shown in Figure 9. Figure 9a shows the experimental results of the optimized modulation. \(D_{1}\), \(D_{2}\), \(\varphi_{13}\) and \(\varphi_{23}\) calculated by the optimal conditions in (25) are 0.15, 0.33, 0.16, and 0.19, respectively. \(i_{\rm r1}\), \(i_{\rm r2}\), and \(i_{\rm r3}\) are all in a phase of \(\varphi_{\rm EF}\). Hence, the converter operates at the minimum RMS value of the transformer current. In contrast, the experimental results of the SPS modulation under the same transfer power are shown in Figure 9b. There is a phase difference between \(i_{\rm r1}\), \(i_{\rm r2}\), \(i_{\rm r3}\), and \(\varphi_{\rm EF}\). The RMS value of the transformer current under the SPS modulation is greater than that of the optimized modulation. The experimental results verify under the same transfer power, the optimized modulation effectively reduces the RMS value of the transformer current, thereby reducing the power loss of the converter, compared with the SPS modulation. In addition, the power switching transition types are marked in the corresponding experimental results. All power switches of the three ports realize the soft-switching under the proposed modulation. In state 2, there are two cases according to the range of \(k_{1}\). First, the performance of the optimized modulation in the case of \(k_{1}\) < 1 is tested. The transfer power of port 1 is set as 1 kW. Figure 10a,b show the experimental results of the optimized modulation and those of the SPS modulation, respectively. \(D_{1}\), \(D_{2}\), \(\varphi_{13}\), and \(\varphi_{23}\) calculated by the optimal  
Figure 8: Experimental results of power decoupling in the forward mode. (**a**) TAB converter without decoupling tank, (**b**) Proposed converter. Figure 9: Experimental results of state 1 in the forward mode. (**a**) Optimized modulation, (**b**) SPS modulation. conditions in (27) are 0, 0.33, 0.2, and 0.19, respectively. It can be seen that, under the proposed modulation, port 2 operates at the unity power factor. The rms value of \(i_{\rm{r2}}\) of the optimized modulation is smaller than that of the SPS modulation. For port 1, as the transfer power increases, \(D_{1}\) reduces to 0 and port 1 operates with the maximum RMS value of \(v_{\rm{AB}}\). The modulation of port 1 is simplified to SPS modulation. Hence, the overall power loss and the RMS value of the transformer current of the optimized modulation are reduced compared with the SPS modulation. In the case of \(k_{1}>1\), the voltage of port 1 and port 2 are 60 V and 140 V, and \(k_{1}\) and \(k_{2}\) are 1.67 and 0.71, accordingly. The transfer power of port 1 and port 2 is 500 W and 1 kW, respectively. \(D_{1}\), \(D_{2}\), \(\varphi_{13}\), and \(\varphi_{23}\) calculated by the optimal conditions in (27) are 0, 0.33, 0.20, and 0.19, respectively. In this case, the magnitude of \(v_{\rm{AB}}\) is always smaller than \(v_{\rm{EF}}\), thus the modulation of port 1 is also simplified to the SPS modulation to minimise the RMS value of \(i_{\rm{r1}}\). The corresponding experimental waveforms of the two modulations are shown in Figure 11. It can be seen that \(i_{\rm{r2}}\) is in a phase of \(v_{\rm{EF}}\) of the optimized modulation. The RMS value of \(i_{\rm{r2}}\) and \(i_{\rm{r3}}\) of the optimized modulation are smaller than those of the SPS modulation. Since the topologies of port 1 and port 2 are exactly the same, the experimental results of state 3 are similar to those of state 2. They are not shown here. The experimental waveforms of state 4 of the optimal modulation are shown in Figure 12. The input voltage of port 1 and port 2 is 60 V and 80 V, and \(k_{1}\) and \(k_{2}\) are 1.67 and 1.25, accordingly.