Although electric vehicles have become the prevailing development trend among current vehicles, the key factor that can really stimulate the rapid development of electric vehicles is the charging speed of batteries. This article will show you the current state of automotive charging technology and related solutions from onsemi.
Consumers are becoming more receptive to electric vehicles
In fact, electric vehicle, electric powertrains, and electronic technology for automobile functions have been knocking about for some years, with the first electric vehicle (EV) being launched in the late 19th century. However, it is only in the past three to five years that the adoption of electric vehicles has finally increased in the context of tighter government emissions standards, the deployment of more infrastructure to supply power to electric vehicles in tandem with the roll-out of more plug-in hybrid electric vehicles (PHEVs) and battery electric vehicles (BEVs).
On the consumer side, more and more consumers are being attracted to electric vehicles because governments have been offering subsidies and discounts of different natures to EV owners over the past few years to support the transition away from fuel vehicles, including tax exceptions, free parking and charging services, and high occupancy vehicle (HOV) lanes.
However, there are some potential hurdles that have held back the EV industry in the past, including most notably range anxiety, high EV prices, and longer charging time of batteries than refueling time of conventional vehicles, all of which have discouraged people from buying electric vehicles.
At present, the increased battery capacity and the optimized vehicle kwh/km ratio are solving the problem of range anxiety. The price of electric vehicles is declining steadily and is getting closer and closer to the price of internal combustion engine (ICE) vehicles. More and more vehicle manufacturers have invested in the development of electric vehicles, making more and more electric vehicle models available for consumers.
At present, the final hurdle to be overcome for electric vehicles is the slow charging time, making how to speed up the charging speed of electric vehicles the goal of vehicle manufacturers and solution suppliers.
Fast charging of electric vehicles improves charging efficiency
Currently available EV charging methods can be divided into slow charging (effective power of no more than 22 kW) and fast charging systems (22-400 kW and above). Slow charging systems have been widely used in households, public parking lots, and parking lots in workplaces, and fast charging systems are mainly used in public places, commercial areas, or charging stations/piles.
At the maximum rated power of slow charging, the system can provide about an additional 100 km range in 50-60 minutes. At the lower power end, 1.4-3.7 kW/h of power can be used for domestic and private purposes using dedicated cables connected to standard socket-outlet, with approximately 5 hours (3.7 kW) required for an additional 100 km range. A fast charging system, by contrast, offers a similar range in 10 minutes. The charging time will be cut at a higher power from the charging pile. As the battery capacity of electric vehicles continues to increase, combined with improvements in charging technology, higher peak power will be allowed to achieve faster charging rates.
High DC charging mode quickens the charging rate
AC charging and DC charging, as two charging methods of electric vehicles, were originally quite simple concepts, but they are also easily confused. Essentially speaking, the difference lies in the current mode used to transfer power to the vehicle's charging port (rather than into the battery).
In the AC charging mode, alternating current from the grid is delivered to the vehicle through an AC outlet or a charging stall, and the vehicle manages the AC-to-DC conversion through an on-board charger (OBC) and provides DC voltage and current to the battery. AC charging is commonly known as "slow charging" because of its power limitation (usually 22 kW at the top end) and the shortest necessary charging time.
On the other hand, AC-to-DC conversion is performed by an external charger in the DC charging mode. Given the more relaxed exterior space, weight, and thermal restrictions, DC charging ratings range widely, from less than 11 kW to up to 400 kW. However, not all vehicles can tolerate charging at high DC levels, and most vehicles available today typically support charging rates of at least 50 kW in DC mode.
A number of standards and IEC specifications have been developed to regulate and standardize AC and DC charging technologies and to promote and support the development of EV-compatible electric vehicle supply equipment (EVSE) ecosystems. These frameworks are set to be as global as possible to help associations and industries develop agreements and EVSE. Currently, there are three major DC charging implementation plans that are expanded globally, including CHAdeMO (short for "charge de move"), combined charging system (CCS), and Tesla Supercharger, while the unique and exclusive GB/T protocol standard is implemented in China.
Complete EV charging solutions are provided
Fast DC charging for electric vehicles is one of the drivers of innovation in power electronics and one of the fastest markets to adopt new power technologies such as silicon carbide (SiC). In high power and high voltage applications, EV fast charging can reap the benefits of SiC module technology, exhibiting higher breakdown voltage, lower RDSON and dynamic loss, and superior thermal performance.
The development of quick chargers for electric vehicles also needs to consider the stability of the use of SiC switches at high frequencies, where the gate driver system, as an important component, has a direct impact on the system performance. Another key consideration for the gate driver is on-chip integration (beyond galvanic−isolation) and protection. The NCD57XXX and NCD51XXX series of electrically isolated gate drivers from onsemi are available with 3.5 kV and 5 kV ratings, bringing design flexibility and system reliability to the development of fast chargers for electric vehicles. The gate drivers incorporate multiple functions and protections on chip and have demonstrated drive current capabilities of up to 9A. To meet different needs, onsemi offers a variety of product combinations, including single-channel drivers such as NCD57000/1, NCD5708x, NCD5709x and NCP51152/7, and dual-channel drivers such as NCP51561, NCP51563 and NCD57252/256, hoping to meet the needs of all usage cases.
In addition, a key point associated with gate drivers is the isolated power supply required to drive them, which needs to be compactness and ruggedness to ensure a stable voltage rail under all operating conditions. Power supplies around NCV3064 switching regulators such as LVDCDC3064-IGBT and LVDCDC3064-SIC will be conductive to meet these needs. Given the high power and high voltage required for fast DC chargers for electric vehicles, electrical isolation is also a must for high-side drivers. Isolated drivers enhance system ruggedness by maximizing their common-mode transient immunity (CMTI), which is especially important for driving at high dV/dt using fast- switched wide bandgap technology.
Another important consideration for the fast DC charging of electric vehicles is the necessary safety protection in the system, especially the safety protection stipulated by regulations. FAN4147 and NCS37014 Ground Fault Current (GFC) interrupters from onsemi, which meet various regulatory requirements, provide off-the-shelf solutions for developing EVSE in line with safety requirements.
Auxiliary power supply units (PSU) are ubiquitous in the power system, and fast DC charging of electric vehicles is no exception. The PSU developed around the NCP1362 quasi-resonant valley switching primary side or the NCP1252 and NCP12700 secondary side controllers can help address these needs. On the switching side, 1200V SiC MOSFET with high RDSON (160 mOhms) is rapidly being adopted because it offers excellent cost−to−performance ratio and is the optimal solution for 900V DC systems.
Conclusion
onsemi is a leading supplier of SiC technology and power integration modules and is recognized by its customers for its quality. onsemi, as one of the few suppliers with a complete SiC supply chain, has both 650V and 1200V solutions and can ensure the highest quality and reliability standards for discrete and modular SiC products, as well as excellent operation and flexibility, and will become the best partner for EV fast charging applications.