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How Does Vehicle Electrification Work?

The fundamental and key objective of vehicle electrification is the replacement of a gasoline drive with an electric powertrain. In an electric powertrain, the traction battery pack uses the energy stored in it to drive the electric motor with help of a power electronics converter. During braking or when the speed of the vehicle is reduced, the electric energy is driven back to the battery using a regenerative braking system. Based on the type of electric motor used, the control technique and topology of the converter will vary. The various types of electric motors commonly used in an electric vehicle are the following:

• Brushless DC motor (BLDC motor). Used in most lightweight two-wheeler and three-wheeler EVs like electric scooters and electric motorcycles
• Permanent-magnet synchronous motor (PMSM). Used by many EV manufacturers for high-performance electric motorcycles, electric cars, and electric buses 
• AC induction motor (ACIM). Used by the manufacturer for two-wheeler and four-wheeler EVs
• Interior permanent magnet Motor (IPMM). Used by some manufacturers for high-performance, two-wheeler electric motorcycles
• Permanent-magnet switched reluctance motor (PMSRM). Used in four-wheeler EVs

For an EV, there are three levels of charging¡ªLevel 1, Level 2, and Level 3. In Level 1, the car is charged by plugging the vehicle into a 120-volt AC home outlet via an on-board charger. On average, this takes 17 hours to charge a car. In Level 2, the vehicle is plugged into a 240-volt power source at home or an outside charging station. This takes 3.5 to 7 hours. Level 3 involves a standalone DC fast-charging unit based on a 480-volt system. Charge times are faster, but these charging units are not geared for home installation. Instead, consumers must take the vehicle to a standalone charging station, much like taking a car to a gas station.

Vehicle electrification relies on collaboration from interdisciplinary teams responsible for areas such as: 

• Power electronics, motor drives, electric machines
• Advanced electro-mechanical powertrains, systems integration, and thermal management
• Vehicle controllers and electronic control units (ECUs)
• Batteries and energy storage systems
• Energy storage systems¡¯ electronic controls, management, and packaging
• Hybrid battery/ultra-capacitor energy storage systems
• Vehicle-to-grid (V2G), vehicle-to-infrastructure (V2I), and vehicle-to-home (V2H) integration

Types of Vehicle Electrification Technologies

It is challenging to completely replace a gasoline drivetrain with an electric drive with present battery technology and still meet all consumer demands. The main culprit is the limitation of maximum energy that can be stored in a battery cell. But hybrids, a combination of ICE and electric motor, can bridge this gap between the battery electric vehicle and conventional vehicle. Hybrids can also improve the efficiency of conventional gasoline vehicles. There are different types of technologies that exist for vehicle electrification, including:

• Hybrid Electric Vehicles (HEVs). HEVs have a combination of ICE with an electric propulsion system. ICE delivers most of the energy, and the electric powertrain system is used only to improve fuel efficiency.
• Plug-in Hybrid Electric Vehicles (PHEVs). PHEVs also have a combination of ICE and electric propulsion systems. A PHEV stores energy from the electric power grid or through regenerative braking. The PHEV runs on electric power until the battery is nearly depleted, and then the car automatically switches over to use the ICE. 

There are two main PHEV variants. Blended PHEVs use a mix of gasoline and electricity when the battery is charged and then switch entirely to gasoline when the battery is depleted. An advantage of blended operation is that because the electrical system does not need to satisfy peak power demands on its own, it can be smaller. Extended Range Electric Vehicles (EREVs) are PHEVs that use only electricity when the battery is charged and switch to gasoline when the battery is discharged. For trips shorter than the range of the battery, the vehicle operates as a BEV.

• Battery Electric Vehicles (BEVs). BEVs have larger battery packs to store more energy from the electric power grid for longer range. They have no backup gasoline engine. BEVs are also referred to by some as "pure-electric vehicles" or "all-electric vehicles" (AEVs).
• Fuel Cell Electric Vehicles (FCEVs). FCEVs refuel with hydrogen and use a fuel cell to produce electricity to propel the vehicle. FCEVs are also referred to as fuel-cell vehicles or FCVs.

The Challenges of Vehicle Electrification

Challenges related to BEVs include limited driving range, high costs, battery issues, long charging time, and inadequate charging infrastructure. Also, with vehicle electrification there are issues with various power semiconductors and other devices.

Limited driving range and battery issues. Charging is a crucial topic for the success of vehicle electrification. The top technical challenge is that the energy density of lithium-ion batteries can provide a limited driving range of 400 to 500 km (249 to 311 miles), while consumers prefer a driving range of 700 km (435 miles) or more. Also, the design of a battery pack is limited by the size and mass of the pack. More battery cells mean more mass for the vehicle. Increased mass requires more energy for vehicle movement, and also affects vehicle maneuverability such as handling, acceleration, and braking. The greater the mass, the harder it is to achieve good results on those performance metrics. Also, all BEV batteries degrade (become less efficient). Most car manufacturers warrant EV batteries to not degrade below a certain level for around eight years. So, it may become necessary to replace a battery in an EV while the driver owns the vehicle.

Long charging time and inadequate charging infrastructure. With the right mix of infrastructure and charging comfort, EVs could become competitive with vehicles powered by ICE. The big issue is long-distance travel, where charging stations are not always available. Installing more fast-charging stations takes massive investments. However, daily re-charging at home or work or at public or commercial parking areas (retail locations, motorway rest areas, etc.) would mean that drivers never have to stop at filling stations in the future. Charging comfort, in general, would strongly benefit PHEV use by ensuring that they are operated in electric mode in urban areas as much as possible, while minimizing range anxiety during longer trips where the availability of (and access to) suitable charging facilities are uncertain.

Power semiconductors. Power conversion systems are essential and important to modern EVs. A DC-AC inverter system is used to convert DC from the battery and run an AC induction motor. A combination of AC-DC converter and DC-DC converter along with power factor corrector (PFC) is used in charging systems. Other DC-DC converters power other auxiliary electrical systems in a vehicle. A power converter system uses power semiconductor switches such as power MOSFETs and the insulated-gate bipolar transistor (IGBT) to boost the efficiencies and minimize the energy losses in systems. The dominant power semiconductor types are based on silicon. But silicon power MOSFETs are limited in operating voltage up to 250 volts. IGBTs are powerlifters as they can handle operating voltage from 400 volts to 1600 volts. However, IGBTs are not used in high-frequency operation (>30 kHz) due to poor switching performance. Power MOSFETs with better switching performance are used in frequency >200 kHz. To overcome these limitations, wide-bandgap devices such as SiC and GaN must be used. Wide-bandgap devices can operate in high voltage (> 1200 volts) and high frequency (> 200 kHz) due to the wide energy bandgap. They also operate with less on-state resistance and high thermal conductivity. This improves the efficiency by 2%, which is a great deal in EVs. Since the power density and thermal conductivity are higher for the same power rating, the size of the device and thermal management system (heat sink) is also smaller. With the higher operating frequency, the size of the passive components is also smaller. Size and weight are huge considerations in EVs. SiC diodes are also sometimes recommended for the PFC to make the charger more efficient and reduce the size of the components. But wide-bandgap devices are expensive and not many manufacturers commercially produce them. Therefore, not many EV manufacturers opt for wide-bandgap devices as it is a premium solution. 

Other devices. Robustness and reliability of the integrated power devices are key challenges for automotive power IC designs and manufacturing. One of the biggest challenges for EVs and hybrids is how the microcontroller can optimize the power efficiency for different components inside the EV, from high- to low-end designs to ensure long-term design flexibility. Also, on-chip memory solutions need to comply with the AEC-Q100 standard to satisfy the stringent operating temperature specifications. The use of 7nm and 10nm parts create lots of systematic defects and integration challenges that haven¡¯t been debugged yet. These processes still have a lot of maturing to do.