Capacitors

You need to read the Oak Ridge National Laboratory papers on the analysis of the Toyota Prius HSD System.

Google this phrase and it will get you started "oak ridge national" "prius"

Interesting piece of history on the ORNL papers and studies.. Back during the Clinton adminstration, challenge grants were setup by DOE through ORNL to motivate and provide research assistance to American auto manufacturers to develop more energy efficient cars... Toyota was not permitted to be a part of this study since they were a "foreign" manufacturer. None of the American manufacturers took this up in any serious manner; this was during the period that they were binging on the large sized SUV vehicles.

From the book written by one of the members of the Toyota Prius development team.....
Toyota's concern that this effort would produce a serious competitor to their small, fuel efficient market that they have dominated, and the fact that they took the original Kyoto Treaty on global warming seriously were the keystones in their all out effort to develop Prius that we know today.

Related to this were the advances made by the Japanese steel manufacturers to produce cost effective processes for mass production of UHS (Ultra High Strength) or boron steel, in response to one of Toyota's requirements that smaller cars can not be a compromise in safety. The Prius was the first mass produced car to make use of UHS steel.
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When the 97 1st generation Prius came on the market, ORNL did major tear down study to learn how Toyota had been able to achieve the efficiencies in the vehicle and what manufacturing technologies were involved. Again this research was done on the premise of helping American manufacturers. Still no interest by American big 3.. With the initial Prius on the market, a lot of FUD (fear, undercertainty, doubt) came out e.g. how long the batteries will last, expense, the Sudbury Canadian nickel mines, etc. ORNL continued to do a number of studies as the Prius HSD design evolved over several generations of the vehicle.

The ORNL papers are the most authoritative and substantive material I've been able to find for further engineering analysis and study.

I've love the one page chart by the then President of Toyota "Why Change" .....

 

Good summary of some of the Prius history. I would add that Ford did pay Toyota for rights to patents before they developed their hybrids. And you are the third to mention Oak Ridge in this thread.

 

Yes.. Ford did use Toyota technology in the first gen hybrids.. and I think of all the majors, Ford has really pushed the envelope.. with their EcoBoost engines, developing their own hybrid technology and of course the latest, mastering the production processes (and educating their dealer network) in the use of aluminum bodies in their new F-150s... and leveraging the work from the European design and production in building world class vehicles. Chrysler and even GM has some interesting efficient vehicles.

The willingness to invest in the R&D and push the envelope on fuel efficiency has greatly changed in the last decade.. Everybody is pretty much in the game.. The debates now are about the best means to accomplish... good situation!

 

Let's stretch things for the sake of having fun with numbers. The DC/DC converter, MG1, and MG2 duty cycles are not synchronized, so in the micro-second time frames that the power electronics live in, the capacitors may have to be the only source or sink of all the power that is being transferred at any instant.

MG2 can draw 60 kW of power, that's 100 amps at 600 volts. Let's assume the capacitors must supply the full 60 kW to MG2 for a full millisecond.

IIRC, a farad means the voltage will increase by 1 volt/second for each amp going into the capacitor. A 3300 uF cap is 3.3 millifarad, which means 3.3 amps will produce a 1 volt change in 1 millisecond, and 100 amps will produce a 30 volt change, or about 5% voltage change at 600 volts.

Given that the switching frequency is "thousands of times per second", the actual cycle time should be well under a millisecond, so the voltage on the caps is going to be quite steady (my educated guess here). The caps can supply full power for multiple cycles if needed, which makes them seem like a power source, at least in lay terms.

Or is my math totally wrong?

 

I hope you aren't a US electrical engineering student. I would be so embarrassed about your inability to ask a good EE question.

 

Hello All,
Since all of the labels are facing out so one can see them, I'd bet that these capacitors are wired in series, thus enabling them to withstand twice the voltage at 1/2 the capacitance. If this is set up to be a vfd to drive the pwm driven traction motors, then the voltage on these caps is rather high. Such as around 600 volts or so. If one uses the formula for charge which is C=1/2 CV (sq) then the energy that can be taken from these caps is very high, in this case 594 watt seconds (ws) per 2 capacitors x 3 = 1782 watt seconds. Since the voltage is fairly high, the current taken from these capacitors is relatively low.

Supercaps are nice but the voltage rating for the caps are very low. Say around 15 to 20 volts max without modification of the caps. By using the power laws; i.e. P=IE, and at these voltages, current would be extremely high plus the weight and cost of the copper to run the traction motors would be also very high. The power required for 1 horse power is 746 watts.

So, 746 watts / 600 volts is about 1.24 amps / horse power of the traction motor.

At 15 volts for a super cap, 746 / 15 = 49.7 amps / horse power of the traction motor.

Please correct me if I'm mistaken.

--Cougercat

 

i've been thinking along the same lines, but you explained it nicely.

 

Brakes have a backup capacitor bank next to the 12v battery

 

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The gen 2 Prius (2004–2009) has that capacitor-backed fallback power supply for the brake controls, but not any other generation of Prius.

That brake power supply is a 12-volt component, and isn't related to the capacitors in the high-voltage system asked about nine years ago by the OP.

 

I suspect the 38 year old op has either graduated and entered the real world or found another path nine years ago. He was somewhat off base on the role of capacitors in a Toyota hybrid system.