Diverse technologies enable electric vehicle fast charging systems
The number of electric vehicles (EVs) and plug-in hybrid electric vehicles (HEVs) is, at present, low compared to internal combustion engine vehicles. However, the switch to HEVs and EVs is accelerating. Forecasts are looking at about 40% growth by 2020, to 30.3 million vehicles from about 4.2 million vehicles in 2017. Numbers vary among reports, but all predict that in the next years we will see incredible growth in HEVs and EVs. The switch to electric is a quiet country lane today that will become a six-lane highway tomorrow.
The speed of that transformation depends on many factors. Currently, two of the biggest limitations are a lack of vehicle charging infrastructure and the time it takes drivers to charge their cars. That’s why developing a network of DC fast charging stations is so important.
Surprisingly, the growth in DC fast charging stations is modest because hybrid-electric cars do not use DC charging and because not all completely electric cars are able to use fast charging. By 2023, experts predict there will be 2,000 DC fast charging stations, of which very few will be truly fast, having more than 50 kW of charging power.
Nevertheless, these charging stations will have an outsized impact on the electronics industry. The number of power semiconductors in a DC fast charging stations is so large that, even with low numbers of units, the total market for power semiconductor devices could reach more than 120 million devices by 2030. The growth rate for charging systems is expected to explode around 2030, and so the market for power semiconductor devices and associated components is expected to grow exponentially.
Figure 1 DC charging systems use a variety of circuit protection and power semiconductor technologies.
Governmental regulation and legislation are driving this growth, as leaders in the United States, China and Europe push the switch to HEVs and EVs to meet the goals of CO2reduction and higher fuel efficiency standards.
Consumers seem ready. The limited driving range on a single charge has been a challenge to consumer adoption. But battery technology has been improving in the past several years. Battery charging capacity and power density are increasing at the same time battery cost is falling. With batteries becoming lighter and more powerful, we are seeing new electric cars with a driving range of 300 miles and even more, very close to the range of combustion engine cars. That’s sparking adoption.
Another enabling technology has been the emergence of silicon carbide and gallium nitride power semiconductor devices and modules. EV charging stations at 50 kW and higher need high efficiency power conversion. Every percentage of power loss creates an engineering challenge in how to deal with the heat dissipation.
Imagine that a consumer wants to charge his or her car at a DC fast charging station capable of delivering more than 50 kW. This involves extremely high levels of current and therefore losses in the charging cable overheating it. This means that designs will need cooling for the cable, a complexity that is not required for the older generation of charging stations.
The physics are driving the industry to seek new technologies that offer higher power efficiency during power conversion. Design engineers are embracing Wide Band Gap (WBG) power semiconductor devices because those technologies lower power loss. SiC devices in particular have become very reliable and more affordable, and that is helping to enable the switch to electric vehicles.
Figure 2 SiC MOSFETs and Schottky diodes, like these from Littelfuse, are designed for EV charging applications by offering low power switching loss.
>> Continue reading the next section, "On-board versus off-board charging", on page two of this article originally published on our sister site, EDN:"Electric Vehicle charging: How technology and smart engineering will make our electric future possible."