Electrical Vehicle Charging Applications

Posted:
Jul. 20 2018
Category:
General News

Electric Vehicles (EV) are still a small percentage of the overall number of vehicles used in North America (NA), but this is forecasted to change quickly in the next few years. The U.S. expects 1,000,000 EV’s will be on the road by 2020, with about half used in California. While Canada expects an additional 80,000 vehicles by 2020. As a result, EV charging infrastructure must be developed rapidly. In fact, many NA building codes define a minimum level of EV charging support for new commercial and multi-tenant construction.

Currently, there are four levels of EV charging:

  • Level 1
    • Uses onboard car charger at 120V
    • 2-5 miles per hour of charging
  • Level 2:
    • Uses onboard car charger at 240V or 208V, up to 80A but typically at 30A
    • 10-11 miles per hour of charging
  • Level 3:
    • Creates DC from 240 or 480 single of three phase sources
    • 50-100 miles per hour of charging
  • Level 4:
    • Creates DC from 240 or 480 single of three phase sources
    • 170+ miles per hour of charging
    • 350 kW units can charge for 200 miles in 15 minutes

Level 1 and 2 are typically used for home, public and fleet charging, with level 2 being the most common. Eight hours of level 2 charging will cover over 95% of the average person’s commuting distance. Levels 3 and 4 charging stations, often referred to as “Fast DC Chargers”, are typically seen in public installations. Due to the high costs of installation, approximately US$40k-$85k per unit, these may only be found in groupings of 1-2 charging units. Levels 3 and 4 charging provides a quick means to top off low battery levels – vehicles typically spend less than one hour charging. Currently only Tesla and a few other suppliers (ABB & Schneider Electric) offer Level 4 charging but this is expected to be widely common among vehicles in the early 2020s.

Typically, there are few concerns for single or double point installations, usually found in residential customers or as small service charging areas in parking lots. Utilities are concerned about the long term effects that a higher concentration of electrical vehicles will cause, as residential and commercial grids will have increased charging loads in the future. These concerns include overall power quality issues caused by DC chargers, transformer losses caused by harmonics, brownouts and being able to supply the overall increased loads.

There are increasing concerns caused by the large loads of multiple class 1 and 2 chargers in facilities such a public garages and EV fleets. A single Level 3 or 4 charger can have an equivalent load of a dozen or more level 1 or 2 chargers and cause similar concerns.

The major issues are:

  • Power Quality: Numerous studies have shown large EV charging loads can create THDi levels in excess of the IEEE 519 8% levels, in some cases over twice. This can result in issues typical of poor power quality and may result in additional charges from the utility or involve additional requirements for the utility to operate effectively
  • Current Surges: Depending on the number of EV’s, level of charger, vehicle type and individual level of battery charge, large current surges can be created. These surges can cause brownouts, stress electrical components and result in higher utility demand charges. In addition, a combination of site installation issues can provide further challenges
  • Public Installation: Most ventilated magnetics are not recommended to be installed in areas accessible to the general public
    • Aesthetics may be a consideration
  • Exterior Installation: Magnetics must be able to handle local environmental conditions

 

The following recommendations are made for the magnetics used in EV charging:

  • High Harmonics: At a minimum, three phase units should be specified at a minimum of K=4 but it is preferred to specify at K=9
  • Power Quality: K-rated units will have a 200% rated neutral to deal with harmonics caused by Level 1 and 2 chargers
    • Utilizing Harmonic Mitigating Transformers (HMT’s) can provide significant power quality improvement if multiple Level 1-4 charging stations are installed
  • Local Environmental Conditions: If installed in a non-temperature controlled area, 130°C or 115°C temperature rise units can contend with high ambient temperatures
    • Enhanced type 3R enclosures can be used if horizontally blowing rain or snow are a concern
  • Safety: Units should be installed in areas that are not accessible to the general public. If that is not possible, additional options can be considered including tamper resistant hardware, hinged and lockable enclosures or non-ventilated enclosures
    • Local Electrical codes may require bollards or other installation requirements to protect transformers from vehicle damage. Transformers also should not be installed under water lines, water drains, etc., which could direct water onto the enclosure if broken
  • Low Site Voltage: Use integral taps or buck-boost transformers to adjust voltage
  • Aesthetics: Custom enclosure colors or stainless steel is available. In some cases smaller autotransformers instead of isolation transformers may be used

The concerns with EV charging will be a growing issue in the future. Care should be taken when specifying systems today since issues such as power quality can affect all components of the local grid, not just those devices directly supplying the EV charging points.

For further information on how HPS can help you with your EV application, please contact Mike Van Gheem, U.S. Marketing Manager – mvan@hammondpowersolutions.com.

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