## 4 Innovative Micro-Grid with Bi-Directional Flows for RES and EV Charging
As shown in Table 1, for the same package (T0-247) and hence the same occupied area on a printed circuit board, and the same rated current \(\mathrm{I_{Dmax}}\), SiC power Mosfets double the sustained voltage vs. Si power Mosfets (1200 V vs. 600 V), improve the typical figure of merit \(\mathrm{R_{Dson}}\) x \(\mathrm{Q_{G}}\)[75] by reducing both the \(\mathrm{R_{Dson}}\) and the total gate charge (\(\mathrm{Q_{G}}\)), and remarkably reduce ton/off-delay time (\(\mathrm{t_{dON}}\)/\(\mathrm{t_{dOFF}}\)) and reverse recovery time (\(\mathrm{t_{rr}}\)) of the integrated diode. From a switching frequency point of view, the solutions proposed in [3; 71] for bidirectional DC/DC conversion are in the order of 100 kHz, more in detail up to 140 kHz in [71] and up to 150 kHz in [3]. As discussed in [72; 73; 74], by using wide bandgap power devices like SiC and GaN the typical frequencies of power Si devices of about 100 kHz can be increased above 300 kHz. For example, a 500 kHz switching frequency is used for a 6.6 kW CLLC DC/DC resonant converter in [72; 73; 74] where a bi-directional EV charger is proposed by cascading a first AC/DC stage (switching at 300 kHz) followed by the 500 kHz CLLC DC/DC converter stage. The higher the frequency, the lower the size and weight of the inductive passive devices (inductors, transformers). As far as the selection of the active devices is concerned the work in [72; 73; 74] proposes a mix of 650 V GaN and 1.2 kV SiC power switch devices. Particularly, since in [72; 73; 74] the power DC Bus of the EV charger is sized for values ranging from 500 V\({}_{\mathrm{DC}}\) to 840 V\({}_{\mathrm{DC}}\) (when the battery on board the EV is 250 V\({}_{\mathrm{DC}}\) to 420 V\({}_{\mathrm{DC}}\)) it is necessary to change the 650V GaN devices with 1.2 kV SiC Mosfets in the AC/DC stage and in the primary side of the DC/DC stage of the bidirectional EV charger. 650V GaN devices are used in [72; 73; 74] only for the secondary stage of the bidirectional DC/DC converter. A full \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Power Mosfets** & **Package** & \(\mathbf{I_{Dmax}}\) & \(\mathbf{V_{DSmax}}\) & \(\mathbf{R_{DSon}}\) & \(\mathbf{Q_{G}}\) & \(\mathbf{T_{dON}}\) & \(\mathbf{T_{dOFF}}\) & \(\mathbf{T_{rr}}\) \\ \hline SiC & & & & & & & & \\ C2M0040120D & & 60 A & 1200 V & 40 m\(\Omega\) & 115 nC & 15 ns & 26 ns & 54 ns \\ Si IPW60R045 CP & & 60 A & 60 V & 45 m\(\Omega\) & 150 nC & 30 ns & 100 ns & 600 ns \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Power Mosfets performance comparison (same package and current), SiC in [3] vs. Si in [71]. Figure 8: Bi-directional DC/DC converter: (**A**) half-bridge at the primary stage; (**B**) dual-active bridge topology. 650 V GaN devices solution is discussed in [74] but limited to applications where the DC power bus is 450 V at maximum. Summarizing, compared with Si devices, the absence of reverse recovery charge in wide-bandgap devices (GaN and SiC) enables bidirectional operation with simplified converter structures. Moreover, wide-bandgap devices have better figure of merit [75] than Si devices and hence for a given ON-resistance and breakdown voltage, wide-bandgap devices require smaller die size, which translates into smaller gate charge and junction capacitance. These characteristics allow increasing switching frequency (above the 100 kHz typical of converters with power SI devices) and reducing the switching loss. From reported results [3; 72; 73; 74] of recent bi-directional EV chargers, 650 V GaN devices may allow a higher switching frequency than 1.2 kV SiC devices, but the latter become mandatory to manage in a reliable and efficient manner DC power bus of 500 V\({}_{\text{DC}}\) or above. With the larger battery capability in EVs, power flow between the EV and the grid is exploited in a bi-directional fashion. It is especially useful in applications using renewables such as solar generation as in [3].