Charged EVs | Designing DC quick charging stations for next-gen EVs

Charged EVs | Designing DC quick charging stations for next-gen EVs


Sponsored by Littelfuse

Supercharged options that present for quick charging reliability, effectivity, and security

The adoption of EVs will cut back air pollution and assist sluggish the consequences of local weather change. A big obstacle to broader EV adoption is each a public charging infrastructure that may assist long-distance journey and chargers that may recharge an EV battery in a time that drivers will settle for.

At the moment, 300 kW chargers can recharge a battery in underneath quarter-hour. Whereas the time is appropriate, the first problem for design engineers is defending customers from 300 kW. 

Secondarily, designers should maximize effectivity to reduce energy consumption and temperature rise. As well as, designs should carry out reliably regardless of publicity to a variety of environmental situations. 

Determine 1 reveals a number of varieties of charging stations. North America classifies charging stations into “Ranges,” whereas the European Union differentiates charging stations utilizing “Modes.”. Organizations such because the Society of Automotive Engineers, the European Union automotive requirements group, and Asian international locations like Japan and China are working to standardize charging stations.

Determine 1: EV charging station sorts and their present capability

A DC Quick Charger (Determine 2) can cost an EV battery to 80% capability in underneath quarter-hour. These chargers have energy scores as much as 350 kW and may provide as much as 500 A to a battery. To develop these chargers, designers should overcome the challenges of security, effectivity, and reliability.

Determine 2: DC charging station and the really useful safety, management, and sensing elements


Methodologies for charger and consumer safety

Figures 3, 4, and 5 illustrate the circuits and elements of a DC charger. A 350 kW charger requires a excessive voltage, high-current capability AC enter. To guard in opposition to overloads, use fast-acting, high-current fuses. Make sure the fuses have a present interrupting ranking massive sufficient to exceed the vitality accessible from the AC line. Fuses can have scores as much as 200 kA. 

Think about using a surge protector to soak up voltage transients. Surge protectors can take up as a lot as 50 kA of transient present. They clamp the voltage transient to a secure stage stopping vitality from propagating into the circuit and damaging elements. Additionally, contemplate including a surge safety fuse to guard the surge protector.

With excessive AC line energy, designers ought to defend in opposition to floor present faults. Use a present transformer sensor that may detect floor currents underneath 30 mA. A ground-fault safety relay can measure the present from the sensor and disconnect energy if detecting a excessive floor present.

The DC charger energy converter circuits additionally interface with the AC energy line and require enter fuse safety and transient overload suppression. Use fast-acting semiconductor fuses to guard the downstream semiconductor elements. Think about both metallic oxide varistors (MOVs) and gasoline discharge tubes or MOVs and safety thyristors to protect in opposition to transients. Decrease energy charger subunits want solely MOVs or a MOSFET for secondary stage transient safety.  

Defend the Communication, Person Interface, and Entry Panel Sensor circuits from electrostatic discharge (ESD) harm. Examine transient voltage suppressor (TVS) diode arrays.

Defend the DC output circuitry from load present shorts with a fast-responding, high-current, high-voltage-rated fuse. The CHAdeMO (CHArge de MOve) Affiliation promotes a fast-charging infrastructure for DC charging that requires a reverse-flow safety diode within the secondary rectifier. This diode serves as redundant safety in opposition to a brief situation. 

For the consumer interfaces with the charging gun, use temperature sensors to stop extreme temperatures and use proximity sensors to make sure the gun is accurately engaged earlier than energy is utilized.

Circuit topologies and element choice to maximise effectivity 

With chargers that may ship as much as 350 kW, minimizing energy losses can considerably influence diminished energy consumption. Think about the next suggestions for maximizing effectivity:

  • Use of a Vienna rectifier stage, a bridgeless energy issue correction circuit, which each minimizes present draw from the facility line and makes use of a minimal variety of transistors and diodes
  • Use of Schottky diodes with low ahead voltage drop and low leakage present in rectifying circuits
  • Use SiC MOSFETs within the DC-DC converter circuits for quick switching charges to allow a extra environment friendly, switch-mode DC-DC converter. SiC MOSFETs even have low RDS(On), lowering on-state energy losses and low RthJC, permitting a simplified thermal design. 
  • Use environment friendly gate driver chips to simplify management of the MOSFETs and reduce energy consumption.

Growing a bi-directional design to return energy to the grid can considerably save energy prices. See the MOSFET-based design illustrated in Determine 5.

Required requirements

Since DC charging stations devour and ship a excessive energy, they need to meet a number of security certifications. See Desk 1.

Desk 1: Security requirements for EV Charging Stations

Meet security and effectivity objectives with a producer’s steerage

Designers should be sure that battery charging circuits are protected against environmental hazards and secure for consumer interplay. Producers of safety merchandise may also help designers save growth time by providing design suggestions. Utility engineers can present useful recommendation on the tradeoffs between energy, house, effectivity, and element value. Some producers will even help with requirements compliance and may supply pre-compliance testing companies. Producers can cost-effectively assist designers obtain charger security and effectivity objectives.


Sponsored by Littelfuse


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September 2022