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Consortium successfully runs silicon carbide multiport DC-DC converter in EV

11 July 2014

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Silicon Carbide multiport DC-DC converter fitted to the Tata Vista EV. Click to enlarge.

A consortium led by motorsport and technology company Prodrive has successfully run a silicon carbide-based multiport DC-DC converter in an electric car. The converter controls power flow between multiple energy sources and has been able to achieve efficiency of 98.7%, while increasing power density and reducing the size and weight of the converter when compared to silicon-based systems.

A key aspect of the converter is the use of silicon carbide devices. These operate at a much higher frequency than equivalent silicon components—at 75 kHz in the test vehicles—with a significant reduction in switching losses. This has resulted in a significant reduction in the size of the magnetic components and has enabled the converter to achieve an efficiency of 98.7%, a gravimetric power density of 10.5 kW/kg and a volumetric power density of 20 kW/liter.

The use of silicon carbide power modules could also allow much higher temperature operation than conventional silicon modules. This provides the potential to integrate the power electronics and IC engine cooling systems in hybrid applications.

The DC-DC converter acts as a hub that transfers energy between key components of the vehicle’s high voltage electrical system. It has four ports: two connect to the traction motor and high voltage battery; a third connects to a secondary energy source, which in this test car is a super capacitor bank; and the fourth powers the vehicle’s 12V systems.

The converter is able to match the voltages of these components and transfer energy between them in response to CAN commands from an external supervisory controller.

The test vehicle is a Tata Vista EV demonstrator vehicle, developed by the Tata Motors European Technical Centre in Warwick, which has a 220 V battery and 37 kW traction motor. The vehicle also has two 200 kJ super capacitor banks, which operate at 75-150 V.

In normal driving, the converter boosts the battery voltage to around 400 V to optimize motor performance and can supplement the battery supply with additional energy from the super-cap banks when the driving situation demands it. During re-generation, the converter transfers energy from the motor to the battery or super-capacitor banks as requested by the supervisory controller. Energy can also be transferred directly between the battery and super capacitor ports. The system can be configured to support other energy sources, such as fuel cells or could supply multiple traction motors.

—Mark Willows, Prodrive electrical systems and control specialist

The consortium is now working on a follow up project which increases the converter operating voltage to 750 V, further increases power density and demonstrates operation at increased coolant temperatures.

For this project we have developed a rolling test bed based on a light commercial vehicle chassis, which has a 75 kW traction motor. The energy storage consists of a 320 V Li-ion battery and two super capacitor banks, all of which were built by Prodrive specifically for this project.

—Mark Willows

The consortium of British companies is backed by the Technology Strategy Board and led by Prodrive, working in conjunction with The University of Manchester, Tata Motors European Technical Centre, IST Power Products, Raytheon Systems and SCISYS.

Prodrive has worked on hybrid and electric vehicle programs for more than a decade, starting with a prototype four-wheel drive parallel petrol/electric hybrid built in 2001. Subsequently it has worked on a number of hybrid and EV projects including: motorcycles, commuter vehicles, passenger cars and trucks covering prototype development through to homologation and diverse electrical technologies from HV batteries, super capacitors, fuel cells and high-speed electrical and mechanical flywheels.

July 11, 2014 in Electric (Battery), Power Electronics | Permalink | Comments (30) | TrackBack (0)

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Comments

Toyota may have produced a very similar unit. Which one is the best?

Advancements in rugged DC-DC and DC-AC high efficiency converters will soon make DC power grids a reality?

This is an incredibly important advancement. It's nearly as important as the batteries themselves as the inverters, converters, etc weigh as much as the electric motor and can increase the efficiency of the system so you NEED LESS BATTERIES, it takes up much less space, and it requires much less cooling so that again reduces complexity, weight and space.

In this case, it also allows you to get rid of the old 12V battery in a component that was already going to be there for other conversions anyway. It's a win, win, win, win, win.

What's not to love. :)

What's funny to me is how these types of announcements get almost no comments because people don't realize how important these things are to the EV industry. Next to the battery, this is the biggest area of improvement you can get in an EV right now.

It doesn't just need less cooling, it can use the engine coolant for cooling which in turn makes that heat available as cabin heat.  That isn't a huge amount at 1.3% losses, but every bit helps.

The efficiency is based on a curve with a peak at 98.7@ efficiency. The harder you run this inverter, the lower the efficiency will get. It would be interesting to see at what power it drops below 80%.

The inverter could also be designed to run your house in a power outage. Either convert to the DC voltage of the house inerter or have a 120 volt ac inverter built into it.

@Jeffgreen54, true, but the real measure is the curve of this one against the curve of of traditional silicon.

Every bit of reseach I've seen with SiC has shown the curve to be higher across the board.

http://beaconnews.ca/blog/2014/07/new-battery-technology-developed-uofa-researchers/

You don't know which battery will make it to the market. If this is the future battery combined with an ultraefficient inverter, electric cars are just around the corner.

Upconverters have been successfull in automotive applications for quite a few years. Toyota happens to use them in 650Vdc circuits using just silicon devices.

The introduction of an upconverter from 2004 onwards in the Toyota HSD powertrain for the Prius was undoubtably a game changer in HEV performance. For one thing it allowed the previous battery voltage to be lowered from 273v to 201v which permitted the use of fewer cells in the battery pack and a useful cost reduction. You have to bear in mind that the original 273V battery held only a miniscule 1.3Kwhrs of energy yet required 38 sets of battery modules each consisting of six 1.2v NiMH cells.

However the major advantage of an upconverter in this application was that it enabled the inverter system bus to run at 500 Vdc even when the generator MG1 was forced to rotate well below its max rpm which would have otherwise crippled the operation of the traction motor MG2. The circuit which employed a dual mosfet upconverter performed both the role of raising the 201Vdc battery pack to 500Vdc while at other times returning power back to the battery pack when circumstances allowed or when the battery was needed as a 10Kw power sink during regenerative braking.

As regards HEVs, in a climate which finds increasing numbers of roadside superchargers being installed, I see less and less need for an ICE in the vehicle to be necessary either. The HEV is a bridge technology whose time is running out for passenger cars and delivery vans. Except for transport trucks where it may become the niche market.

I also don't have any enthusiasm for the installation of supercaps and flywheels also mentioned above. All I see is a complication with a questionable cost justification.

In the situation of a pure BEV I just don't see the need for modulating the main bus voltage in this way.
High current devices with low V/Hz motors are the way to go. I certainly would not advocate the implementation of an artificial 750Vdc bus just to permit the use of lower current devices in the traction inverter.

If the goal is seriously to improve effcy then maxing out top speeds in the vicinity of 65mph should be the goal, that way punitive aero losses can be prevented.

It seems that funding for SiC semiconductors is being used here for studying different powertrain architectures. May I suggest one useful research direction which I believe deserves investigating specifically is the use of multiple traction motors:

Given TWO motors is it better to have each of them installed on the same axle for individual wheel drive or is it better to have each of them installed on different axles for AWD ?

At least Tesla, for one, seems to be taking that latter approach with AWD for its Model X slated for limited production in 2015.

My preference in powertrain improvement is any move towards the elimination of the open differential.

Anyone agree it's time we abandonned this rube device of the nineteenth century together with its unpredictable tendency to lose traction in adverse conditions. So there it is, I am viewing individual wheel drive on the rear axle as preferable with the additional opportunity to provide torque vector steering and traction control.

Perhaps a motorsport company should be taking a look at this.

DaveD wrote
This is an incredibly important advancement. It's nearly as important as the batteries themselves as the inverters, converters, etc weigh as much as the electric motor

Nope, I beg to differ, today's inverters are good enough. And "good enough" is not the enemy of best.
Toyota has SiC technology as well but have said they won't be rolling it out until 2020 at the earliest.

Side view mirrors being replaced with cameras would be a significant advantage when motoring at speeds beyond 50 mph and I would expect them to net significant gains.

Public acceptance of slightly unusual aero dynamic body shapes would be helpful also. It is the rear of the car that needs fixing up with a boat tail. of course autonomous vehicles running in a close formation will mitigate aero losses as well. I would speculate that any 100 mile car @ 55mph would become at least 120 mile car @75 mph when travelling in a convoy.

Don't expect profound battery improvements anytime soon. Real world improvements in battery technology seem not to be following Moore's Law. More like 7% per year.

David D:
The reason posts like this attract few comments usually is that they are above the heads of us non-engineers.
Personally I think engineers are socially useful, in spite of everything, and should at all times be treated kindly, locked in an internet equipped room and fed coffee and pizza are required.
On no account should they be allowed to speak, as that normally spoils it all.

An engineer is a device for converting coffee into designs.

However, if you ever want to use what an engineer designs, you have to ask them.  Hilarity ensues.

'An engineer is a device for converting coffee into designs.'
:-0

That won't work without the pizza, any more than an anode without a cathode.

Sometimes you can almost imagine that they are human, but I discourage sentimentality and anthromorphism.

@T2,

Upping the voltage is important to reduce the size of the motor by running at higher rpm and in so doing, will reduce weight and cost. Copper and rare-earth magnet cost more than silicon used in the boost converter, and even more so for Si-C.

HEV's will remain very important long into the future. An HEV consumes far less battery capacity, less copper, magnet, and silicon than an equivalent BEV. A highly-efficient HEV can use synthetic fuel made from RE thus achieves independence from fossil fuel.

I share your idea regarding one motor per wheel hence eliminating the differential unit, while allowing vector control and assist with steering, traction and stability control, and lane control without requiring power steering servo. However, Henrik and Bernard did not agree with me on a previous discussion.

Davemart, I resemble that remark!

Davemart, LOL!!! Nice. As a former engineer who is now on the mgt side and one who has forgotten more than I now remember...I'll assume you're talking about E-P and not me

:)

Of course, I have two daughters in University as electrical engineers with both leaning towards power stuff (the older one is doing an intern at Oak Ridge National Lab this summer), I'm having to dig up the memory banks to keep up with them now. It's painful LOL

@T2,
I agree with you on the differential, but not too concerned about it as they're usually between 94-97% efficient. I'd like to see 4 motors with full on vectoring as Roger is suggesting, but I just don't know about the cost tradeoffs.

But I disagree with you on the "good enough" for silicon. As E-P points out, you can get rid of whole cooling systems AND combine and use the ones that are there for heating. That is a big savings for energy in cold weather. And when you can reduce the size and weight of inverters and converters by as much as 75%, that goes a long way towards saving weight and space which allows you to further reduce structural components. And the smaller size makes it easier to fix the aero which you mention as a big advantage.
Then you consider that in real world conditions, the SiC or possibly GaN can hit over 95% efficiency while silicon will really not be above 90%, that's a big win.

Throw in the fact that those efficiency numbers are even more important as you make round trips (to power the car, then back in again on regen braking, and from main battery to sub-systems like AC and wipers) these things really add up.

In addition, the Prius may have been taking advantage of SOME of these things, but I've yet to see a car that didn't have to deal with 12V systems in the car simply because that is what the auto supply chain has available. With the programmable nature of this converter, it can support 12V or future 48V systems.

No, I think these support systems for the EV cars are very important. Saying the existing stuff is good enough is like saying vacuum tubes were good enough, why go to LCD tech for televisions?

Prices are dropping for SiC already and by 2017, the ROI on them will be equal to traditional silicon.

Yes DaveD....another good side of multi output ports DC-DC converters is the possibility to supply 12 VDC (to replace current lead battery) + 48 VDC for future more efficient lights and ancillaries with smaller cables + variable VDC to match selected drive e-motors. All from the main on-board battery pack.

Of course, smaller volume, less weight and increased resistance to higher temperatures are valuable side benefits.

Advancements in AC to DC, DC to AC and DC to DC converters will also help people with domestic RE power generation and storage systems.

Eventually, we may see a return to more efficient HVDC networks and lower voltage DC distribution systems to better satisfy our fast growing DC loads including future PHEV, BEV and FCEV DC battery charging.

Too bad that batteries and vehicle body & parts are not evolving as fast. Future, much lighter, stronger materials will probably play an important role in post 2020 vehicles. An under 2,000 lbs extended range BEV wmay become a reality by 2025 or so.

750 VDC is very important for heavy EVs (class 8 in the US) and I expect it will go much higher when the technology can support it in a cost effective way.

There are many other projects using silicon carbide semiconductors though, this is far from unique. Nice that someone is bothering to publicize it for once.

Harvey,
Yes, every little bit helps. It all adds up and keeps building and we'll hit a turning point.

I also should have said I disagree with T2 on one other item: I think supercaps could be a big winner combined with a battery system. Providing as little as 200Wh of supercaps that could handle acceleration and regen braking would allow the battery packs to be run at a nice, low C/2 or even less which increases their energy density and reduces wear and tear on the battery pack.
It does add some complexity, but I think that will be minor in the long run.

Yes, a few ultra caps could compensate for current batteries short comings. The extra control system required may not be a major challenge.

However, in the post 2020 era, many improved EV batteries may have enough quick charge capabilities to recover a much higher percentage of braking/deceleration energy and may also last 15+ years instead of current 10+ years.

Who knows where ultra caps technology and improved EV batteries will be in the middle of the next decade?

I'm with Jim McLaughlin on this one too...I'm just happy to see someone reporting on developments in this area.

Thanks GCC!


Hi, Roger, I was trying to make the point that you should not be needing a dedicated upconverter to supply high voltage to run 3-phase motors in a BEV.

But you still wrote Upping the voltage is important to reduce the size of the motor by running at higher rpm and in so doing, will reduce weight and cost.

The fact that Toyota was using an upconverter inside its HSD is an entirely different application in which it was necessary to stabilise an otherwise wildly fluctuating bus voltage by augmenting the bus voltage to 500Vdc from a 201V battery source. In retrospect I now regret I even brought it up.

On the other hand when used in a BEV, the use of upconverters would force a more complicated two stage process. It is obvious to me that the root of the problem could be solved by having the motor wound with the correct V/Hz in the first place. Such low V/Hz motors have been around in aircraft usage for decades. Mostly rated at 100Vac @ 400Hz meaning V/Hz = 0.25 and with direct online starting capability. Much different from the industrial machines of 480Vac/60Hz which have a V/Hz of 8.0.

-DaveD wrote about the promise of supercaps ability to harvest regen energy and perhaps be pre-charged with enough energy (560Kj) to permit rapid acceleration from rest without caning the small battery in a HEV. Well, last year I might have even agreed with you on that, Dave, but today I see HEVs as bridge technology to keep us tied to the oil companies. Same reasoning to have us transition over to Hydrogen based FCEVs.

Roger and DaveD it's time you came over to the Dark Side and joined me where passenger cars are concerned. In a future where you always charge at home and leave the house with a "full tank" every morning. And perhaps twice a year for those longer trips you'll be using one of them there superchargers somewhere out on the major hi-ways.

At the moment you guys are thinking like my father once did. You were probably not around sixty years ago when most cars had a hole cut into the radiator at the front of the car where you could poke a starting handle whenever a flat battery required the engine to be hand cranked. Eventually the point was reached where manufacturers could abandon that convenience feature. Clearly that point was reached a little too early for my father. I remember his consternation about having to buy a newer vehicle with that radiator hole missing.

"Starting handle anxiety" they would have called it.

@T2,
Hmmm, no, I think you misunderstood where I was going with that. I agree with you wholeheartedly that pure BEVs are the way to go. Charging at home and only using fast chargers for the occasional "top off" is the way to go.

What I was alluding to is the energy density and cycle life curves for current lithium chemistry batteries. They all do better if you keep them at low C rates, preferably C/2 or even lower. You'll see batteries that are over 1,000mAh/g at c/4 and around 700mAh/g at C or C2.

So what i was saying is that until battery tech improves more, we could use Supercaps to do regen braking and then to accelerate again and take the high C rates off the main batteries. Otherwise, you have to have larger batteries to distribute the load.

It wouldn't take many supercaps as only about 200Wh can handle most accelerating and regen braking on light duty passenger vehicles. Slightly more complex in the electronics, but we're better at those than we are on batteries :)

But I'm totally with you on the "dark side"...it's BEVs for me all the way.

@DaveD,
I agree that a low c rate will prolong battery longevity and supercaps can help this by suppressing load peaks but that would appear to go against other determined efforts to encourage the use of even more trips to the Supercharger.

I wonder if you are aware that Tesla has a design team investigating the use of supercooling the battery enclosure when the driver has indicated that the vehicle is to be stopping at the next supercharger site. The intention is to have the pack prepped such that it is less vulnerable to the effects of internal heating during high current recharging.

I am concerned that the 10% degradation per year measured for continuous usage of a supercharger will make resale of Tesla vehicles or any EV, for that matter, a difficult process unless a verification of remaining battery life can be assured to the buyer.

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