Electric Vehicle On-Board Charging Systems
On-board charging systems (OBCs) convert AC power from an external charging source into a DC voltage that is used to charge the battery pack in the vehicle. OBCs also perform other functions including charge rate monitoring and protection. Industry charging standards for OBC systems are shown in the table below. AC Level 2 OBCs and some Level 1 systems require isolation. With DC Fast Chargers, which plug directly into the quick charging connector, OBCs are bypassed.
|Level||AC Level 1||AC Level 2||DC Fast Charge|
|Voltage||120V||220V or 208V||480V DC|
|Current||15A max||40A max||125A max|
The Importance of Isolation in On-Board Charging Systems
On-board charging systems take the AC input source, convert it to high voltage DC through the rectifier and provide Power Factor Correction (PFC). The resulting DC signal is chopped into a switched square wave, driving a transformer to create the required output DC voltage. The chopping of the input signal is accomplished using isolated gate drivers, such as Si8239x, Si823x, Si823Hx, and Si827x.
The output voltage is filtered to the final DC voltage using sync FETs under the control of additional isolated gate drivers. The output voltage can be monitored to provide closed-loop feedback to the system controller using isolated analog sensors, for example: Si892x
The entire system can be monitored and controlled via an Isolated CAN bus. The CAN is isolated with digital isolators and digital isolators with integrated DC/DC power converters, including Si86xx and Si88xx.