ther at home or a commercial charging station. The only thing keeping EVs from completely dominating auto sales is the constant need for battery charging, the dearth of commercial charging stations, and the limited range of the vehicles themselves. Fast, reliable battery charging is the key to EV eventual success.
So, let’s take a look at onboard chargers, how they work, and why they’re used. Also discussed are charging stations and how they interact with onboard charger and EV battery-management systems (BMS).
All EVs and HEVs have an onboard charger for the main HV drive battery. It takes the ac from a home or commercial charging station and conditions it into dc to charge the battery. The charging station hardware is typically referred to as the electric-vehicle service equipment (EVSE). The other form of external charger is a dc source that connects directly to the HV battery and provides a rapid recharge.
Three classes or levels of vehicle charging have been defined by the Society of Automotive Engineers (SAE) (see table). Level 1 and 2 chargers are built into the vehicle itself. Level 3 chargers are defined primarily for public charging stations.
Other organizations also define charging-related standards. The International Electrotechnical Commission (IEC) defines four charging modes. In addition, four charger connection plugs have been specified. Added to all that are the many governmental safety codes/standards and regulations related to EMC, efficiency, and safety.
Figure 4 shows a generalized EVSE powering an onboard charger. The EVSE equipment conditions and controls the AC while communicating with the vehicle a CAN bus connection (COMMS). The onboard charger first performs power factor correction (PFC) on the ac to keep the input current in phase with the ac mains voltage to meet the power-factor requirements of the regulations. A DC-DC converter then develops the output to charge the battery.
4. The generic content of an EVSE Level 2 charger that supplies ac to the vehicle.
Figure 5 shows a Level 3 charger. The three-phase ac input undergoes PFC to produce an acceptable power factor. That ac then goes to an ac-dc converter to generate the high voltage (HV) that charges the HV battery directly. Output voltage is in the 300- to 800-V range. A separate low-voltage supply powers the remaining circuitry, including the MCU and COMMS.
5. An EVSE Level 3 HV dc charger is used for faster charging.
All of these chargers are controlled by an MCU, and the power-conversion circuits are of the switch-mode variety to ensure maximum efficiency.