Bench Talk

The Road to eMobility: From EV Charging to Zero Emissions and More

(Source: phonlamaiphoto / stock.adobe.com)

Safe EV Charging via Circuit Protection

Fast EV chargers aim to close the gap between the time required to charge an EV and the time required to fuel a combustion vehicle. Level 1 home chargers providing 1–2kW of power take 40–50 hours to charge a battery, but DC fast chargers produce up to 350kW of power and can charge a battery to 80 percent in about 20 minutes. Circuit protection must scale with voltage and power levels to keep users and equipment safe in fast charging applications.

DC fast chargers must be able to withstand overvoltage, transients, and surges from the grid, lightning, or ESD. Circuits should also be designed to detect potential ground faults, while the chargers must be ruggedized against moisture and dust to ensure safety and longevity in outdoor environments.

Littelfuse offers a wide variety of circuit protection and switchingfor high-power applications like DC fast chargers. Littelfuse DCNHS 1000VDC Max Contactor Relays provide rugged and reliable performance in high-power applications and enable charger cabinet control circuits to toggle high-voltage lines safely.

A robust charger design includes TVS diodes and ESD suppressors for fast voltage spikes, fuses for overvoltages, and temperature sensors to protect high-voltage circuits, as well as low-voltage user interface components. With such a design, the entire DC charger will have circuit protection throughout (Figure 1).

Figure 1: DC fast charging station overview. (Source: Littelfuse)

Commercial Vehicles Driving Toward Zero Emissions

While most electric vehicles (EVs) on the road are two- and four-door passenger vehicles, improvements in charging and energy storage technologies enable the electrification of large commercial vehicles. Long-haul trucks, city and interstate buses, and delivery vans have more uptime than personal vehicles and require larger batteries and robust charging infrastructure.

Most commercial EVs use the same lithium-ion (Li-ion) battery technology as passenger EVs, but on a larger scale. The cost of raw materials for Li-ion batteries, particularly nickel and cobalt, becomes a constraint for larger batteries as global Li-ion demand drives up prices. Lithium iron phosphate (LFP) is an established battery chemistry that does not have the energy density of Li-ion but contains more readily available materials and offers excellent longevity over repeated charge cycles. Select models of commercial and passenger EVs have adopted LFP batteries as an easy-to-source and long-lasting alternative to Li-ion.

Charging infrastructure also requires upgrades to meet the demands of commercial EVs. Opportunity charging enables charging along vehicle routes, such as pantographs charging buses at stops (Figure 2). For traditional wired charging, higher charging power levels reduce charging time. 4MW chargers provide a 500kWh charge in less than 15 minutes. Littelfuse SiC MOSFETs provide extremely low on-resistance and fast switching speeds, improving efficiency at high power levels. The high thermal conductivity of SiC dissipates heat without bulky cooling systems, providing high performance in compact and demanding EV environments.

Figure 2: An electric bus charging by pantograph. (Source: scharfsinn86/stock.adobe.com))

Electrifying Small Vehicles

In addition to commercial vehicles, small two- and three-wheeled passenger vehicles also comprise a significant portion of the eMobility market. In many cities, motorcycles, scooters, and mopeds are the most popular form of transportation. Many of these small vehicles are powered by two-stroke engines, which emit a disproportionate amount of pollutants for their small size. Electrifying small vehicles has the potential to make big improvements in air quality and help reach reduced-emissions goals.

For small vehicles where users are sitting directly on top of batteries or even swapping batteries themselves (Figure 3), circuit protection mitigates voltage spikes and transients that could lead to injury or dangerous battery fires. These small vehicles may contain batteries up to 72V on high-performance models, requiring protection to low-voltage ICs and microcontrollers.

Figure 3: A rendering of batteries for electric scooters that can be removed, placed in a charging wall, and then replaced by a fully changed battery. (Source: Generated by AI).

Transient voltage suppression (TVS) diodes protect circuit components from voltage surges like electrical fast transient (EFT) and electrostatic discharge (ESD) by safely passing large currents to ground. TVS diodes respond quickly to voltage surges but are not well-suited for prolonged overvoltage situations such as shorts. As such, circuit protection should include both TVS diodes and fuses to account for short and sustained overvoltages. Fuses protect downstream components in sustained overvoltages by opening the circuit. Littelfuse 437A Surface Mount Fuses are AECQ-compliant for use in automotive applications and provide protection for automotive components such as displays, battery management systems, and lighting.

EV Component Protection

As higher voltage batteries and DC fast charging become more common, designers must take additional care to protect valuable EV components from damage. In addition to the battery packs, EVs contain control, infotainment, and ADAS components that a power surge could damage.

EV battery packs contain cells packed into tight configurations with total capacities generally ranging from 35 to 100kWh. Protection from shorts is critical with so many cells and so much power. Littelfuse 881 AEC-Q200 High-Current Subminiature SMD Fuses provide protection at the module level and should be used with cell-level fuses and large fuses for the entire battery pack in order to protect the battery at every level.

Infotainment systems include low-voltage audio, video, display, and connectivity circuits. Infotainment components should include TVS diodes such as the Littelfuse AQ24COM and AQ27COM TVS Diode Arrays to protect against ESD and other voltage spikes. Moreover, ADAS circuits involve a variety of sensitive instruments and carry critical data. When it comes to protecting ADAS components, Littelfuse AXGD Xtreme-Guard Automotive Suppressors provide ultra-low capacitance to protect high-speed lines like automotive Ethernet.

Thyristors for Megawatt EV Charging

While 350kW chargers provide fast charging for passenger vehicles, larger commercial vehicles require even higher power levels to charge larger batteries and minimize downtime. The current standards for High-Power Charging for Commercial Vehicles (HPCCV) allow for a maximum of 1500V to 3000A, making for a maximum charging power rate of 2.2MW. In the future, the maximum power level may be extended to 4.5MW to further reduce downtime.

Today, high-power fast chargers contain rectifiers and converters that convert each phase of a three-phase AC input into DC outputs. These circuits contain SiC MOSFETs that provide efficiencies of 97 to 98 percent. Scaling the 350kW topology up to a megawatt charger would involve many SiC MOSFETs generating a large amount of heat, resulting in a bulky and expensive solution.

Meanwhile, thyristors excel in very high power applications due to their strong blocking ability when not in their conducting state and their ability to be controlled by relatively small power levels. Thyristors operate at line frequencies, providing highly efficient AC to DC conversion with less resistive losses than MOSFETs at high power levels. IXYS N1718NC200 Capsule Type Phase Control Thyristors could form the foundation of a megawatt charger with their ability to handle 2000V and 1718A.

For a deeper dive into next-generation eMobility, read the Electrifying the Future of eMobility eBook by Littelfuse.

Author

Alex Pluemer is a senior technical writer for Wavefront Marketing specializing in advanced electronics, emerging technologies and responsible technology development.