The Road Forward for Electric Vehicles
Addressing Technical Challenges on a Component LevelMustafa Dinc – Global Director for Automotive Business Development – Vishay Intertechnology
In today’s vehicles, the role of many new electronic systems is to save energy — whether it’s through direct injection, start-stop system or BLDC motor drives in body and chassis electronics. The push for greater fuel efficiency is increasing with carbon dioxide legislation, which in turn creates a demand for more vehicle electrification especially in urban areas where air quality depends on reducing particle emissions.
The following influential factors are responsible for the future trends and successes of electric vehicles (EV):
- Battery technology – energy density, size and price
- Driving range and efficiency
- Charging performance, time and infrastructure
- Price, incentives and taxes
- Reliability and maintenance cost
In a crash situation, the electronic system needs to disconnect from all existing energy storage elements, such as batteries, capacitors, and inductive components. Direct contact with high voltages can cause significant bodily harm to drivers, passengers, and first responders. To discharge the energy of such storage elements, resistive dummy loads need to be connected immediately.
Intelligent energy management is important in ensuring all safety-related applications — such as braking, steering, wiper, lighting, and passive safety systems — are available over long driving distances. In addition to safety electronics, which have the highest priority for power consumption, comfort electronics also have to be considered. Air conditioning during the summer and compartment heating and window defrosting during the winter are must-have features in a modern vehicle. In EV designs the big challenge is to reduce the electrical consumption of such high-power loads.
The next most important task is to provide enough charging stations for the area in which vehicles are moving and especially parking. Fast charging is of great importance for the end user, who usually does not like to wait more than two hours for a fully charged battery. During work hours, business visits or shopping times, the modern EV has to be fully charged. In addition, incentives are appreciated, such as rebates, alternative energies and reduced parking fees.
In EV designs the big challenge is to reduce the electrical consumption of such high-power loads.
An essential element of the EV is the on-board battery charger (OBC) system. Its main functions are to convert AC to DC, perform power factor correction (PFC) functions, and match the charging profile of the battery system. 3.7 kW OBC systems can’t accommodate faster charging, so new designs are now focusing on systems up to 7.2 kW.
There are two different major solutions and advantages for battery charging:
- On-board: 1-phase or 3-phase AC charging from the electric grid line
- Easy to connect to grid power
- No major charging infrastructure required
- Off-board: Electric Vehicle Supply Equipment (EVSE)
- Ultra-fast and high DC off-board charging
- Short time, high power, fast charging performance
- Charger infrastructure with universal high power DC chargers
A key part of an on-board charging system is the AC/DC inverter, which is fully integrated into the vehicle network. It connects the car to the AC electric grid and converts to DC power. Due to high voltage usage, safety is a concern and standards need to be applied. All electronics have to fulfill these automotive-grade quality standards.
Another option is to have an off-board DC/DC charger with high voltage DC input to the EV instead of AC input. This option offers very high power charging functionality and allows weight and space savings for the on-board charger function, which remains as the battery charging stage control and communicates with the off-board charger. It keeps AC voltage and its related safety concerns away from the vehicle and reduces the transient level for ECUs. Such industrial chargers with power up to 50 kW are available and will be part of infrastructure installations such as parking areas and bus stops as part of the automotive segment.
A third method is just on the horizon and concerns contactless inductive charging. It is aimed at providing a charging infrastructure almost everywhere to reduce the stop time for charging and offers almost instant charging possibilities.
The semiconductor and passive component industry has to design new components to reduce the cost of EV controllers and actuators. Mechatronic plus high voltage driver solutions are the key components in optimizing reliability and increasing efficiency.
Multi-phase converters and inverters are strong focuses for designs. All major component manufacturers are developing new cost-performance optimized components and new topologies for high power and high energy applications.
The semiconductor and passive component industry has to design new components to reduce the cost of EV controllers and actuators.
Major components for EVs are:
- IGBT modules for motor drives and inverters
- High-voltage MOSFETs
- High current filter inductors
- Planar transformers
- Solid state relays
- High voltage resistor dividers
- PTC current limiters
- High voltage diodes for power drives
- Rectification modules
Passive components need more space and have higher costs. Their design is also more critical than the design of semiconductor modules. New topologies work on higher switching frequencies to reduce the size of passive parts, such as transformers, filters, and energy storage components. These topologies include film capacitors for DC-linking or filtering, aluminum capacitors for DC-linking or buffering, and shunt resistors for high voltage and high current sensing. Planar transformers are unique solutions for high switching frequencies and offer the best efficiency in high voltage DC/DC converters.
The electronic drivers for EVs are split into two categories:
- High voltage applications (150 VDC to 550 VDC battery line)
- Low voltage applications (12 V loads)
The DC/DC buck converter, to generate the 12 V out of the high voltage Li-Ion battery, is responsible for low power loads up to 100 W. The efficiency for such converters has to be as high as possible.
One of the biggest challenges for EVs is in ensuring the efficiency of motor drives using high voltage semiconductor drivers. In addition, human safety is an important consideration. To avoid sparks in high voltage switches, it is necessary to discharge the energy stored in the battery and other elements by using dummy energy resistors, which quickly eliminate energy (Joules) to avoid a fire. The emergency battery disconnect is another area to be optimized by redesigning the existing big and heavy profiles.
As with conventional automobiles, system designers are trying to reduce the amount of parts. One example for achieving this goal is a new series of matched resistor dividers with exceptional accuracy for applications with voltages up to 3 kV. Such surface-mount, high voltage dividers can replace 20 to 40 single resistors. Those are currently used as floating dividers to detect voltage stability in the board system and support the voltage drop regulation for increased efficiency.
Various parts of the EV present their own particular challenges. For example, motor drives for air conditioning compressors require highly efficient galvanic isolated DC/DC converters. For this application, discrete components with extremely low profiles play a key role.
Voltages above 30 VAC and 60 VDC require enhanced protection against human body electric shock. Galvanic isolation between low voltage (12 V) digital/analog parts and the high voltage terminal is essential.
The following fields are affected by standardizations:
- Vehicle technology (power electronics and drive train)
- Product and operating safety (electrical and functional safety)
- Electromagnetic compatibility (EMC)
- Plug-in charger (on-board and off-board charging)
Electronic vehicles will be of interest for short-distance driving (average distance of 50 km/day and maximum of 100 km) and cannot yet satisfy long distance driving (> 150 km). Due to higher end user prices for EVs versus conventional cars, investment for charging infrastructure, and development towards alternative energies, mainly government regulations and incentives can enhance the quantitative development of battery electric vehicles (BEVs).
For information on Vishay’s automotive products, including electric vehicles, please visit our Automotive landing page.