# Ferrites and Nanocrystalline Alloys Applied to DC-DC Converters for Renewable Energies
## 6 Discussion  
Table 13 presents relevant recent research focused on MFTs with high power density and in the mid-frequency range (600-20 kHz).  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Reference**} & \multirow{2}{*}{**Material**} & \multirow{2}{*}{\begin{tabular}{c} \(B_{ac}\) \\ **(T)** \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} **Frequency** \\ **(kHz)** \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} **Power** \\ **(kVA)** \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} **Efficiency** \\ **(\%)** \\ \end{tabular} } & \multirow{2}{*}{\
\begin{tabular}{c} **Year** \\ **(kW/L)** \\ \end{tabular} } & \multirow{2}{*}{
\begin{tabular}{c} **Power Density** \\ **(kW/L)** \\ \end{tabular} } \\ \hline
[9] & Silicon Steel & 0.6 & 0.6 & 0.8 & 99 & 2017 & 1.29 \\
[19] & Nanoc./Silic. Steel & 0.9/0.1 & 1 & 1 & 80.2/99.1 & 2019 & 2.50/0.25 \\
[10] & Silicon Steel & 0.5 & 1 & 35 & 99.4 & 2017 & 2.96 \\
[21] & Nanocrystalline & 0.46 & 10 & 200 & 99.4 & 2020 & 8.00 \\
[18] & Ferrite & 0.35 & 20 & 10 & 99.2 & 2017 & 9.25 \\
[17] & Nanocrystalline & 0.9 & 5 & 50 & 99.5 & 2016 & 11.50 \\
[16] & Nanocrystalline & 0.9 & 5 & 1 & 99.4 & 2018 & 15.01 \\
[15] & Nanocrystalline & 0.3 & 10 & 5 & 96 & 2017 & 19.90 \\
[22] & Nanoc./Ferrite & 0.3/0.2 & 10 & 35 & 99.2/99.5 & 2016 & 23.30/11.7 \\
[14] & Nanocrystalline & 0.3 & 10 & 35 & 98 & 2017 & 23.30 \\ This proposal & Nanocrystalline & 0.8 & 20 & 1 & 99.8 & 2021 & 36.91 \\ \hline \hline \end{tabular}
\end{table}
Table 13: MFTs with high power density within the mid-frequency range (600–20 kHz).  
Figure 16: Thermography of the MFT-DAB lab prototype: (a) ferrite, (b) Nanocrystalline alloys.  
The flux density in the silicon steel MFTs at 1 kHz [10], 0.5 T, is higher than the one in the ferrite MFT at 20 kHz [18], 0.2 T; therefore, the former would be 2.5 times smaller in dimensions than the latter, if both were designed at the same frequency. Nevertheless, ferrites have a relative advantage compared to silicon steel in this case, higher flux density at higher frequency (>10 kHz); however, the former is preferable for designs in the medium frequency range, around 20 kHz.  
Collaterally, a relatively higher power density can be reached with the ferrite MFT, as shown in Table 13, as a result of designing the MFT at a higher frequency. In [19], a comparison of two MFTs, designed for the same frequency (1 kHz), one with nanocrystalline alloys and silicon steel the other, the first MFT evidences better characteristics in terms of power density, total cost, and efficiency. Moreover, in the 5 kHz range, the design option is also nanocrystalline alloys [16; 17].  
However, around the 20 kHz range, ferrite cores [18] have been the standard option. In addition to the main objective of obtaining a high power density MFT, the work presented in this paper challenges and tackles this presumption by designing and building MFTs with nanocrystalline cores at 20 kHz, and comparing performances with a ferrite MFT.  
The analysis and results presented in this paper highlight the better performance, 56.4% higher in terms of the power density, for instance, of the nanocrystalline MFT compared to the ferrite MFT. However, in terms of construction cost, the ferrite MFT is 46% lower than nanocrystalline MFT. Regarding efficiency, both transformers have an efficiency higher than 98% at 20 kHz and 1 kVA.  
On the other hand, nanocrystalline alloys have also been designed at a frequency of 10 kHz [14; 15; 21; 22], obtaining high efficiencies (>98%) [14; 21; 22], and power densities of up to 23.3 kW/L [14; 22]. As shown in Table 13, in the present proposal a transformer efficiency of 99.8% and a power density of 36.91 kW/L are obtained. The present power density obtained from the MFT contributes to the development of a higher power density in DC-DC converters. These converters are key in applications such as fuel cell supplied systems, electric vehicles, solid state transformers, and photovoltaic systems.