## 5 Experimental Validation, Using Power-Cycling Converters
### Experimental Losses Measure  
A set of Frequency-Ripple-Output-Inductor (F-R-Oi) operating points have been defined and characterized by the opposition method in order to check if they are actually optimal. Losses have been measured for these points and are presented in Figures 27 and 28. Figure 27 represents converter losses curves for the following operating point: step down 30 V to 20 V under <2.5 A> output current for various inductor values. These values have been chosen to be compliant with the bench limits (switching frequency) and the limits of inductors (saturation). These inputs have been validated by the simulation results as Figure 28 presents the same curves for <1 A> output current. The model calculations and measures are plotted and compared with respect to current ripples, keeping in mind that for the same inductor value, frequency and ripple are linked. In the plots, dashed curves with circles are coming from measurements whereas full lines are modelling results coming from previous parts. Not all inductors have been measured since this is representing a lot of operating points and measurement set-up. These measures are highly sensitive to the output DC current level. This variable can hardly be measured with better precision than 2% (50 mA in our case) and made it difficult to set precisely the operating point. Combined with high \(R_{DC}\), this lack of precision is the weakest spot of the measurement process. Nonetheless, the results provide that the model calculations are in satisfactory accordance with the experimental results. Also, the different curves prove the ability of the modelling and design optimization method to identify the best inductor value and the minimum total losses with respect to ripple current magnitude since both theoretical and experimental curves are pointing to the same optimal point. Figure 26: Picture of the test bench with the two TI controllers, one for each converter and in between the two converters, one feeding the other. In Figure 27, it appears clearly in the plot for XGL6060 that lowering the value for the main inductor down to 10 uH, with a ripple current magnitude of about 80% of the average output current is almost leading to the minimum total losses in the converter. In addition to being the smaller component series, the smallest component in the series appears to be the best compromise in terms of volume and total losses, keeping in mind that the output filter has been taken into account. Again, in Figure 27, it is clearly visible that there is always an inductor value which is optimal for a significant ripple current magnitude, more in the range of 40 to 80%, significantly larger than the ripple current magnitude usually considered in best practice designs. This clearly outlines the interest to add knowledge on the inductor characteristics in order to really explore the solution space and look for the best compromises. Using an  
Figure 28: Optimization results compared with experimental measurements (curves with circles). For one converter processing, 20 W from 30 V to 20 V. Measures are carried out with the back-to-back method. The results are plotted with respect to the current ripple magnitude into the main inductors. Figure 27: Optimization results compared with experimental measurements (curves with circles). For one converter processing, 50 W from 30 V to 20 V. Measure are carried out with back-to-back method. The results are plotted with respect to current ripples into the main inductors. off-the-shelf component series. Implementing AC loss characterizations is a useful generic work in order to later carry on multiple design optimizations. In Figure 28, with a lower average output current, it is still possible to see that large ripple currents are leading to optimal tradeoff for each component series.