Check Out This Medium-Voltage, Lightweight & Compact Fast Charger

OCT 24 2018 BY MARK KANE 20

Fast chargers of the future will be more efficient, smaller and lighter.

A research team at the North Carolina State University revealed a very interesting medium voltage fast charger (MVFC), which is over 60% more efficient, 10-times smaller and two times lighter than a typical fast charger.

The MVFC is rated for 50 kW and can recharge electric cars at an efficiency of 97.5%, compared to 93% in the case of an ordinary charger (transformer-and-charger stations). The big efficiency gain was achieved by designing the charger for medium-voltage power supply. In other words, it doesn’t require a distribution transformer that takes power from a utility medium-voltage line and steps down the voltage to 480 V for the charger.

Because of that, the entire system can be smaller and lighter (a transformer alone could be 1,000 kg). North Carolina State University says that the charger weighs just 100 kg, while the ordinary fast charger is 200-600 kg.

The concept of better fast chargers will have continuation as the team is now developing ultra-high power, multi-port fast chargers. One of the first examples could be 1 MW charger with five nodes and a split power feature (up to 350 kW per node).

The news already sparks high interest as North Carolina State University looks for industry partners.

Press release:

New Electric Car Charger Is More Efficient, 10 Times Smaller Than Current Tech

Researchers at North Carolina State University have built an electric vehicle fast charger that is at least 10 times smaller than existing systems and wastes 60 percent less power during the charging process, without sacrificing the charging time. The team is now building a version that is capable of charging vehicles more quickly, while also charging multiple vehicles at the same time.

The new technology is called a medium voltage fast charger (MVFC).

Conventional, 50 kilowatt (kW) state-of-the-art chargers include a distribution transformer, which weighs 1000 kilograms, and a separate fast charger unit, which weighs 200 to 600 kg. To support the weight, this transformer-and-charger system usually needs to be installed on a concrete slab.

The transformer takes power from a utility medium-voltage line line and steps down the voltage to 480 V so that it that can be used by the fast charger. The fast charger takes the AC voltage and converts it to DC voltage that is compatible with the electric vehicle’s battery.

“Our 50-kW MVFC weighs only around 100 kilograms and can be wall- or pole-mounted,” says Srdjan Lukic, an associate professor of electrical engineering at NC State and one of the researchers who developed the technology. “The MVFC does the work of both the transformer and the fast charger, taking power directly from a medium-voltage utility line and converting it for use in an electric vehicle battery.

“This new approach offers four times more power from the same system footprint, reducing the system installation costs at the same time,” says Srdjan Srdic, a research professor at NC State who also worked on developing the technology.

The researchers were able to make the technology so much smaller, in part, because they used wide bandgap semiconductor devices. This also made the technology more energy efficient.

At present, the best transformer-and-charger stations are reported as having an efficiency of up to 93 percent, meaning that at least 7 percent of the power is lost to heat during the charging process.

In testing, the prototype MVFC has an efficiency of at least 97.5 percent, meaning an additional 4.5 percent of the power is used to charge the vehicle, rather than being wasted as heat. This reduces operating costs, increasing revenue without increasing the cost to consumers.

“In other words, we were able to cut the wasted energy by more than 60 percent,” Srdic says.

Reporters can request a demonstration of the prototype MVFC.

The current version of the MVFC charges at the same speed as existing charging stations. That’s because this iteration of the MVFC was designed to operate at 50 kW, which is the power level of a typical fast charger.

However, the research team is in the process of building a next generation MVFC that handles much higher power, capable of charging more vehicles and charging them more quickly.

“We’ve had the more powerful, multi-vehicle MVFC in mind for some time, and recently received funding from the Department of Energy to build a next-generation prototype,” says Lukic, who is the deputy director of the FREEDM Engineering Research Center at NC State.

In the multi-port station design, a utility line is connected directly to a solid-state transformer, (SST), which is a power-electronics-based smart transformer. The SST then feeds a local DC microgrid, with battery storage systems and multiple charging nodes that vehicles can plug into.

“We are building five charging nodes into the prototype, but there could be twice as many or more,” Lukic says.

The multi-port MVFC will have a rating capacity of one megawatt, with each charging node capable of providing up to 350 kW of power. The upgrade from 50 kW to 350 kW means that a vehicle can be charged up to seven times faster.

“We’re currently looking for industry partners to help us move from our fully functional prototypes to the marketplace,” Lukic says.

The development of the existing MVFC prototype was done with support from the PowerAmerica Institute, a public-private research initiative housed at NC State and funded by DOE’s Office of Energy Efficiency and Renewable Energy (EERE). The development of the multi-vehicle MVFC prototype is being funded by EERE. FREEDM was created with support from the National Science Foundation.

Source: North Carolina State University

Categories: Charging


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20 Comments on "Check Out This Medium-Voltage, Lightweight & Compact Fast Charger"

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Looks promising. I noticed that they are planning for built in storage too.

When they say medium voltage, is that 11kV?

Sounds like it. Essentially it is connecting straight to the distribution lines at whatever voltage that may be. In this case they can use a smaller transformer sized just enough for the charger versus the full size transformer needed for whatever else needs powered in the area.

I could see this being very useful in standalone locations such as proposed charging stations along highways. Could wire them in straight to distribution power lines where they may not need a beefier transformer for other equipment.

TLDR: They use solid-state instead of copper wound transformers.

The high-frequency transformer, being small, is probably copper wound as it is much less subject to work-hardening than aluminum.

“Mobile” 88kW DC charger with also ca. 100kg:
Half power -> half weight:
So where’s the news concerning this?
Ok, efficiency there is “only” >94%.


That “design werk” charger has a typical low-voltage input (400 VAC three phase). This article is about bypassing the low-voltage transformer and taking an input from “medium voltage” which means 6000 to 22,000 VAC in much of the US (technically medium voltage is defined as 601V-69,000V). That is a big difference and big cost savings. Medium voltage is typically what its up high on the top of the telephone poles running around a neighborhood. Medium voltage is never brought into houses, although it is brought into industrial facilities.

The trade off is that switch gear (circuit breakers and such) for medium voltage is big and expensive for safety reasons. So this device strikes me as a proof of concept.

I wouldn’t get too hung up on the efficiencies… 1000 kva eco transformers are typically over 99% efficient. The efficiency here is due to the latest solid-state devices.

As I say, they’ll have certification problems in the states, and probably Canada also, since there are currently attempts to harmonize regulations between the two countries.

You are missing the point. The chargers you linked will need a transformer.

This could really help make 50 kilowatt chargers as common as streetlights or parking meters.

I really could see parking meters upgraded in the future to have these on them.

Not to mention the much lower cost is what is impressive.

Ocean R don’t hold your breath. One thing all these guys – and everyone here – forgets, is that the trend is for distribution in the 50 – 500 kw range (in the past hundred years) to migrate from medium voltage to low voltage. Medium size commercial properties and large homes (mansions) may have 80 years ago been serviced with medium voltage facilities, yet Medium Voltage electrical equipment is no longer even available for replacement/refurbishment. Such installations that currently exist are retrofitted with brand new low-voltage equipment. Anything over 1500 volts that will comply with current safety standards, is very expensive. You used to see 30, 40 and 50 horsepower 2300 volt motors years ago. They are not even made anymore, not even by special order. Distribution transformers are cheap, can be made extremely efficient, and the protection devices for run of the mill equipment is very inexpensive since it is so commonplace. Schemes which in any way go against this will have an uphill battle that isn’t worth the trouble. Here’s the basic trouble. Say you have one of these ‘lunch box’ sized units. Tell the utility you want some 13.8 kv to run the thing. They’ll say FINE,… Read more »

This is true for a single charger. A MV charger would be very expensive when hooking up a LV charger to a pole pig could do the job. But consider a dozen 350 kW chargers in the same place. You’d have the engineering and metering cost no matter which solution you choose.

The current 350 kw chargers are all six phase units…..

Please show me the six 350 kw chargers you are talking about.

Is the US really that complicated? In Europe the trend for PV is to go directly into the Medium Voltage 3 Phase grid (can be 10kV, 20kV or 30kV depending on where exactly) for large arrays and skip any low voltage except for auxiliary devices.

It is just so simple to do it with semi conductors. The railway system of the Deutsche Bahn uses 15kV 3P @16.7Hz. They started a few years ago to interconnect their grid with the regular Medium Voltage grid 10,20,30kV 3P @50Hz using inverters at lots of railway stations instead of the big installations and power plants they used to use. This allows them to sell their transmission capacity of which they have a lot to spare. The train stations very often are directly in highly build up areas where you otherwise would have trouble increasing capacity. No footprints for transformers involved.

You’d have to show me pictures….. All those pictures of the ABB “Substation at each bus stop” ridiculous things they were trying to use, instead of a decently sized battery for their electric busses proves to me that the same physics controlling construction in North America is at work across the pond also.

HAHAHA!!! This article is a lot of fun. They took juice already at LOW VOLTAGE, and with the wood skid mounted polyphase transformer, up’d the voltage to whatever the unspecified voltage (4800 volts or whatever) to run the unit. In real life there would be absolutely HUGE switch gear sections, and it is questionable whether the unit can be certified to provide “Per Phase” overcurrent protection such that only One extremely expensive switchgear cabinet provided the “SHORT CIRCUIT CURRENT” protection , and thereby would feed several ‘low cost, medium voltage chargers since they’d all have their own overcurrent protection. Now one thing that COULD be done cost effectively, is – say you have 10 of these 50 kw MV chargers in a location, – and one of the units sensed a ‘problem’. There could be a Shunt Trip on the REQUIRED SINGLE switchgear cabinet such that it killed all the power everywhere until the problem was resolved, which would also be pressed into service for the requisite emergency shut down facility. So, a tentative thumbs up from me. I say tentative since the thing just looks way too small to meet any kind of NEMA standards for use in North… Read more »

If engineers can design HVDC links that cross seas, I’m sure they can solve the problem of MV AC in a parking lot. Make one big housing for all the power conversion equipment and just take the EV charging voltage out to the “customer interface”. Monitoring and protection can be at the LV side but still within the common housing.

Oh hell – hehehehe, do you know how much ANY HVDC link costs? Gimme a break.

Sure – reinvent the wheel. Why would anyone in their right mind want to use standardized, low-cost equipment?

Ok you guys…. You can see all you need to know from the one photograph provided.

If they are going to demonstrate a “Medium Voltage Charging Station”, they COULD have come in with something at medium voltage (typically either 15 kv class , or 35 kv class), and run the charger off that – since that is the point they are trying to make, in other words – no low voltage necessary.

They did not do that in the demonstration photo. They used a Schneider Electric (Square – D) QED2 LOW VOLTAGE power distribution switchboard, then put it through a skid- mounted (wood) Dry Polyphase transformer, and ran a small flex cable to their unit.

So the point is this – if you are trying to DEMONSTRATE something – go ahead and demonstrate it. They didn’t do so here since having the LOW VOLTAGE link was so much easier and cheaper!

Pardon my ignorance, and please explain.

If there are expensive, strict interconnection safety standards and equipment necessary from MV AV to the direct-to-DC charging unit, why are these similarly expensive things not needed for the MV to low voltage AC transformer which feeds to a DC inverter/charger?

I don’t understand why it’s cheaper to have an intermediate transformer in the path.

Is there a safety improvement by having a transformer in the middle? Suppose it were a 12kv to 12kv transformer? Would that help save on other necessary gear?

In Europe a fully equipped MV (24kV) to LV (400V) substation with power output of 630kW cost about 40 000$.
If you want to built a supercharger-like facility with say eight or more charging bays its better to have you own substation.
But if you want just one or two and there is not enough power in low voltage network, this is a great solution.
The problem in reality is, that the semiconductor parts used in SST can work with around 1500V max. so for a 12kV middle voltage network you have to stack eight in series and the costs run up.
There is no one size fits all solution for DC fast chargers, each location and size of the station is best fit with different systems.