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What Is An On-Board Charger For An Electric Vehicle?
Nimit Arora
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Published on 26th Nov 21
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What Is An On-Board Charger For An Electric Vehicle?

While safety, reliability and comfort are very important when choosing a vehicle, with electric vehicles there’s another critical factor to consider: the time taken to charge. While refuelling a conventional vehicle takes just a few minutes, the time needed to recharge the battery on EVs is significantly longer.

For EVs, charging can be either AC or DC. Most EVs come today with an onboard charger (OBC) equipped inside that converts the AC input from the grid to DC, which charges the battery. The primary role of an onboard charger is to manage the flow of electricity from the grid to the battery.

In the case of AC charging, conversion of the electrical current to DC happens inside the EV. All EVs come with onboard chargers capable of converting the current before supplying it to the car’s battery.

DC chargers enable the conversion of current from AC to DC outside the vehicle. DC is directly fed into the EV, surpassing the need for onboard conversion.

Here we will talk about AC Charging & On-Board Charger.

The on-board charger in electric vehicles consists of a unit that includes a variety of signal conditioning solutions, integrated high voltage isolation AC-DC converters, AC rectifiers, dual bridgeless power factor correction (PFC), gate drivers, error amplifiers and many other power electronic components.

Because the OBC is permanently mounted, its weight must be minimised to reduce its impact on the range of the vehicle.

For e-cars, the earliest OBCs only had 3.7 kW of charging power. Thus, some electric car batteries needed eight hours to replenish their energy sources.

Improvements in technology led to newer onboard charging systems offering from 6.6 to 22 kW. Those allowed fast charging capabilities for cars with AC charging setups. In the next few years, more than 98% of OBCs will be 6-11 kW types rather than 3-5 kW options. Charging infrastructure changes are the main drivers behind this transition. Some OBCs are being designed to provide the bidirectional capability, allowing both grid-to-vehicle and vehicle-to-grid power transfer.

For an electric vehicle, an onboard charger is one of the most important parts. Though it is much slower than the DC fast chargers, it provides great flexibility to charge an EV battery anywhere, anytime, using an AC power source.

In India, both Mahindra and Tata have launched electric cars with relatively small batteries (11–15 kWh) that are limited by their onboard AC charger at about 3 kW. Global EVs have onboard chargers with higher ratings between 7–20 kW AC.

Two-wheelers have relatively small batteries (2–3 kWh) which often are removable to enable home & office charging from a standard wall socket. Electric two-wheelers require a standard three-pin 15 amp connector and are limited in charging rate by the onboard AC charger in the range of 1–3 kW.

Internationally, EV charging can be categorized into different levels:

1. Level 1 AC charging has a nominal supply voltage of 120 V and a current up to 20 A. They are primarily used in residential settings, which use an onboard single-phase charger and have a power output of up to 2.4 kW. It is a plug-in technology and does not require any installation and hence is less expensive. The charging time is long, about 8 to 12 hours, due to the low charging power and is ideally suited for residential applications.

2. Level 2 AC charging has a nominal voltage of 240 V and a current up to 80 A. It uses an onboard charger and has a maximum power output of 19.2 kW. It requires installation work and hence is expensive as compared to level 1 AC charging. It is commonly installed in public parking areas, offices, malls, etc.

3. Level 3 charging, also known as DC fast charging, has an off-board 3-phase charger that supplies the DC power directly to the battery bypassing the onboard charger.

Conclusion

On-board charging is and will remain, an important aspect of all EVs for the foreseeable future as it allows greater flexibility to charge vehicles from commonly available power points, despite being slower than the rapid DC chargers. However, while the vehicle is in motion, the OBC has no function and if it’s excessively large or heavy, then all it does is reduce range.

Consequently, designers are being challenged to design OBCs that are not only highly efficient in operation but also small and lightweight. They must be able to cope with the challenges of the automotive environment (heat, voltage fluctuations, vibration, etc) as well as be able to be produced at a cost point that meets the demands of auto-makers.

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