Electric vehicles are an important wave of the future, offering motorists a cleaner and more efficient way to travel. But when it comes to charging their batteries, electric vehicles have a particular challenge: converting electricity from an alternating current to a direct current.
Fortunately, new innovations in semiconductor devices can help. Enabling electric vehicles to convert AC to DC is key in ensuring they can be charged easily in the average home without succumbing to the drawbacks of using inverters, the current prevailing method of converting AC to DC for electric vehicle charging.
What is AC and DC?
AC and DC are simply the abbreviations of alternating current (AC) and direct current (DC), used in reference to electrical systems and the way electricity travels throughout the circuit. While the voltage in an AC keeps alternating between positive and negative, the voltage in a DC is the same or constant.
How does AC and DC affect electric vehicles?
So, what does an electric car have to do with this? Electric vehicle (EV) manufacturers understand that most drivers will charge their vehicles at home, where their houses use alternating current for their power supply.. As a result, EVs are designed to support household charging through a single-phase alternating current supply present in households. This allows EV owners to charge their vehicles overnight.
However, electric vehicle batteries require a direct current supply for charging. Every EV, therefore, is outfitted with an inverter to convert AC to DC, which can in turn charge the EV’s battery.
The shortcomings of inverters in electric vehicles
There are a few key challenges that arise from the need for EVs to convert the electrical current used to charge them into the direct current needed to operate them.
Slower charging times
Inverters slow down the time it takes for an electric vehicle to fully charge. AC chargers often deliver limited power, usually less about 22kW, and that limited supply is further diminished by the need for an inverter. Generally, it will take about 12 hours to charge a standard EV battery depending on the battery characteristics and the power level of the charger. This is the first AC/DC problem in EVs.
To solve this problem, there has always been the need to develop universal off-board DC chargers that operate within the normal constraints of cooling, efficiency, and weight factors, which often limit both the charging speed and the charging power.
DC charging limitations
The second AC/DC problem in EVs lies in DC charging. Well, there is no doubt that DC charging significantly reduces the charging time since it is capable of generating high voltage (300V to 700V) that is directly fed into the battery management system (BMS) of the vehicle.
DC charging generates high voltage and is often limited by the Grid Peak Power. Whenever multiple high-power entities such as EVs are fed directly into the electric grid, the power churn by the grid is often increased to unwanted levels. For instance, when charging five typical electric vehicles at once, it is a matter of minutes before the peak power delivered by the grid is increased by more than 1MW.
Grid capacity and peak power
Remember, the grid is only designed to deliver so much power for 15 minutes. Therefore, most city planners have resorted to improving the capacity of the grid to enable it to have a much higher Grid Peak Power. The use of locally generated power from renewable sources such as wind and solar is part of improving the grid infrastructure. But this is also limited by the fact that energy generated from renewable sources is intermittent.
The solution here would be to establish large energy storage systems which would basically serve as large batteries that would store the locally generated energy, which would later be used to charge EVs as needed.
High voltage-related temperature increases
Still, when it comes to DC charging there are issues around managing the heat generated by such high levels of electricity. For instance, a 350kW charger has a 1% loss inefficiency. To put it into perspective, this is the same as 3.3kW of power dissipation. The system's temperature is likely to be increased since power is dissipated in the form of heat. Therefore, highly efficient components have been used to design these systems. For instance, they use Silicon MOSFETs rather than silicon IGBTs.
SiC MOSFETs are better semiconductors than silicon IGBTs. This is because SiC MOSFETs have high electric-field breakdown capability, high-temperature operation capability, and higher thermal conductivity due to their wide electronic bandgap. Alternatively, an improved version of the IGBT can be included. For example, the new 650V IGBTs from Infineon Technologies can deliver the highest efficiency in the supercharge industry.
With these two technologies, power losses can be reduced during charging, improving the reliability of both hybrid electric vehicles and electric vehicles. Also, the two technologies can reduce the saturation voltage, reduce the switching losses by half, and lower the gate charge minimizing the need for cooling.
Overall, the use of SiC MOSFETs, improved IGBTs, and semiconductor devices like Ideal Power’s Bi-Direction, Bi-Polar Junction Transistor (B-TRANTM) will enable EV manufacturers to develop vehicles with high efficiency and extended cruising ranges using smaller batteries.
References
Carriero, C. Battery Stack Monitor Maximizes Performance of Li-Ion Batteries in Hybrid and Electric Vehicles.
Cloudflare. https://www.allaboutcircuits.com/news/challenges-ac-dc-charging-slowing-electric-vehicle-adoption/
Chatterjee, P., & Hermwille, M. (2020). Tackling the challenges of electric vehicle fast charging. ATZelectronics worldwide, 15(10), 18-22.
650 V IGBTs offer fast switching in electric and hybrid vehicles. (2015, April 9). Power Electronics. https://www.powerelectronics.com/technologies/discrete-power-semis/article/21862443/650-v-igbts-offer-fast-switching-in-electric-and-hybrid-vehicles
The views and opinions expressed herein are the views and opinions of the author and do not necessarily reflect those of Nasdaq, Inc.
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Dan Brdar
Dan Brdar is the President, CEO and a Director of Ideal Power. He has over 30 years of experience in the power systems and energy industries and has held a variety of leadership positions during his career. In addition to his role at Ideal Power, Dan previously served as President and CEO of FuelCell Energy Inc., a Nasdaq-listed company with a market cap of over $250 million.
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