## 4 DC-DC Converter Topologies for LEV Charging
### On-Board Charging
#### 4.1.2 Non-Isolated Converters
[56] present a two-stage non-isolated bidirectional onboard charger LEV. The front-end includes a voltage source converter which converts the AC supply to DC, and controls grid current power quality. The following stage is an interleaved buck-boost converter, which regulates the battery charging current. The bidirectional nature of the given topology makes it suitable for vehicle to grid (V2G) operation. However, this circuit suffers from a high switch count. Another recent development in non-isolated topologies is the development of quadratic topologies. These topologies have the advantage of achieving high currents at the battery end. [PERSON] et al. [57] developed a quadratic buck boost converter for LEV charging. This has the advantage of operation at discontinuous conduction, helping to further reduce component size. However, the number of passive components is comparatively high. Additionally, there may be scope for reduction in supply current THD due to DBR front end. This topology is shown in Figure 14.  
Finally, [58] presents a detailed review of on-board bidirectional DC-DC converters for EV charging, which also include Level 1 (up to 3.7 kW) and Level 2 (3.7-7 kW) chargers. This work investigates two-stage and single-stage charger topologies in detail--standards, major components and some converters for PFC and DC-DC stage. The authors emphasize some of the challenges pertaining to single stage on-board chargers: complex control strategy, large output current ripple and sophisticated design. Furthermore, some future trends are highlighted such as advances in topology (use of interleaved converters), semiconductor electronics (wide bandgap devices) and thermal design, to name a few. A comparison of all the isolated and non-isolated on-board chargers is shown in Table 2.  
Figure 14: Quadratic buck-boost converter [57]. \begin{table}
\begin{tabular}{c c c c c c c c c c c c} \hline \hline  & & & \multicolumn{8}{c}{**Isolated Topologies**} \\ \hline \hline
**Ref. ** & **Topology** & \multicolumn{8}{c}{**Component Count 1**} & \multicolumn{1}{c}{**Salient Features**} & \multicolumn{1}{c}{**Areas of Improvement**} \\ \cline{2-10}  & **L** & **C** & **S** & **D** & **Tr. ** & & & & & & \\ \hline
[35] & Isolated Cuk converter + interleaved canonical switching cell (CSC) front-end & 4 & 7 & 3 & 3 & 1 & \(\bullet\) & Unity power & \(\bullet\) & No efficiency data \\  & Isolated SEPIC converter + diode bridge rectifier front-end & 1 & 3 & 1 & 1 & \(\bullet\) & Positive output polarity & \(\bullet\) & Charging current ripples increase with battery voltage \\  & Isolated Cuk converter + diode bridge rectifier front-end & 1 & 3 & 1 & 1 & 1 & \(\bullet\) & Positive output polarity & \(\bullet\) & Substantial charging \\  & & & & & & \(\bullet\) & Unity power & \(\bullet\) & current ripple \\  & & & & & & & \(\bullet\) & 81\% efficiency & \(\bullet\) & No output inductance \\  & & & & & & & \(\bullet\) & Simple design & \(\bullet\) & Efficiency may be improved \\  & Flyback converter with interleaved Zeta + SEPIC converter front-end & 3 & 4 & 3 & 3 & 1 & \(\bullet\) & Unity power & \(\bullet\) & Conduction losses may be optimized \\  & & & & & & & \(\bullet\) & Indoor operation & \(\bullet\) & The DC link voltage and \\  & & & & & & & \(\bullet\) & Low current ripple & & capacitance may be optimized \\  & & & & & & & & \(\bullet\) & Unity power & \\  & & & & & & & & & & \\  & & & & & & & & & & \\  & Flyback converter with modified Bridgeless Landsman converter front-end & 4 & 4 & 4 & 5 & 1 & \(\bullet\) & Unity power & \(\bullet\) & Energy operation