# Regenerative braking with an industrial vfd



## smoothflow (Oct 17, 2011)

Hello everyone. I am trying to build an electric motorcycle with a Fuji make industrial vfd. This vfd has a DC bus link. The DC link voltage is 600 V. I am planning to use a battery bank of 96 V and will be using a DC-DC converter to step up the voltage from 96 V to 600 V. My question is, if I use a uni directional DC-DC converter and a parallel circuit with a blocking diode for regenerative braking, do i need to step down the voltage from 600 V to the battery bank voltage of 96 V, or can i directly apply 600 V across the battery bank. Any help will be highly appreciated. Thanks in advance.


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## major (Apr 4, 2008)

smoothflow said:


> ....can i directly apply 600 V across the battery bank.


Nope, you need to step down to the normal charge voltage range for the battery.

Have you tried to source the 100 to 600V boost converter? I think you are making a big mistake. If you can even find such a thing, for a bike conversion, the mass and size will be prohibitive, not to mention the cost. But if you insist, take a look at the Prius system. Toyota uses a buck-boost converter, 200/600V, I think.


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## smoothflow (Oct 17, 2011)

Thanks Major. Actually I have not yet bought the converter. I am working in a company engaged in coating of carbon steel pipes and I do have a couple of industrial vfds which I am planning to use. Either I get a 96 V -600 V DC-DC converter or I have to use a battery bank of 600 V which i think would be quite impractical. I have come across a few bidirectional converters but not found exactly what i am looking for. Something similar to this <http://www.zemis.eu/en/products/bidirectional-converter-modules/data-sheet-350v-dc-module.html>


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## major (Apr 4, 2008)

smoothflow said:


> Something similar to this <http://www.zemis.eu/en/products/bidirectional-converter-modules/data-sheet-350v-dc-module.html>


Interesting  And idea of cost?


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## frodus (Apr 12, 2008)

That's a step down DC-DC converter, you'd need a Boost converter..... and 10A? you'll need something in the hundreds of amps on the 96V side.

Almost every time people look at this solution, they get the costs and decide it's too much money and it takes up way too much space on the vehicle. On a motorcycle, you're going to need a 20+kw peak DC-DC converter, plus a 20+kw peak inverter.... not that cheap. Buck converters tend to be small because they use the motor as the inductor. Boost converters before a controller have no such luxury.

You'd be better off using something that is made for a lower voltage DC pack already, or find something that runs off 120/208V, and make a 250+V or so pack (which is the type of solution that people use with VFD's).

Lets say you want a 30hp peak motorcycle (typical for a small conversion), that's ~22kw at 600V. That'd be another 10% needed before the VFD, or ~24kw. Then you need to convert that again through a DC-DC, there's 10-15%, or ~28kw and at 96V, that's almost 300A. 96V to 600V 30kw Boost converter.....those wont' be easy to find, nor will they be cheap.


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## major (Apr 4, 2008)

frodus said:


> That's a step down DC-DC converter, you'd need a Boost converter..... and 10A?


Hey frod,

That's what I thought at first glance. Then further reading, this: 


> variable voltage – side of the module on which the components were connected. The term „output“ can be used, but is not correct due to the bidirectional mode of action.


 From http://www.zemis.eu/en/products/bidirectional-converter-modules.html 

What that spec calls output current (10A) is really the variable side of the buck-boost unit. And a 1.3 kg package, it looks pretty sweet. That's why I was interested in the cost.

But as you point out, 10A at 100V is 1 kW and even for a really low power, low speed MC, he'd need like 10 of these, and they're half the voltage he needs for the inverter. And I think it said they were not isolated, so he can't use 2 in series like the Vicors. I was able to use 2 Vicor boost converters rated at 95V out, 12V in to get 190V in an application. I think that was about 200W. And someone else's budget 

major


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## smoothflow (Oct 17, 2011)

Hi everyone,

Since I am finding it hard to source a 96 V to 600 V boost converter for my electric motorcycle project, I am planning to use 600 V battery pack. The batteries planned are sealed lead acid 9 Ah. This will give me a total energy of 5400 wh. The battery pack weight will be 125 kg approx.The current draw from the batteries can be up to 3C which should not be a problem since the motor controller will take a maximum of 10 A at 600 V. My question is, are there any 600 V battery chargers available in the market which will be able to charge from a domestic 220 V supply. If not than can it be designed economically. Also kindly let me know of any problems I might face if I go ahead with such a conversion. Thanks in advance.


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## dougingraham (Jul 26, 2011)

smoothflow said:


> Hi everyone,
> 
> Since I am finding it hard to source a 96 V to 600 V boost converter for my electric motorcycle project, I am planning to use 600 V battery pack. The batteries planned are sealed lead acid 9 Ah. This will give me a total energy of 5400 wh. The battery pack weight will be 125 kg approx.The current draw from the batteries can be up to 3C which should not be a problem since the motor controller will take a maximum of 10 A at 600 V. My question is, are there any 600 V battery chargers available in the market which will be able to charge from a domestic 220 V supply. If not than can it be designed economically. Also kindly let me know of any problems I might face if I go ahead with such a conversion. Thanks in advance.


If you pull 10 amps from those 9AH sealed batteries you will only get about 5AH out of them when they are new. A better solution would be the 8AH Headways. You would need approximately 166 in series. That way the full charge voltage would not exceed your 600V controller rating. 176 cells in series would give you a little cushion if you let the pack rest a few minutes after charging. With 166 cells the pack would be an honest 4.25kwh and weigh a little over 55kg. Your lead pack would weigh more than twice as much and the effective rating will be closer to 2.7kwh. You could get the 5.4kwh only if you limit your current to around a half an amp.

The problems are great when you start to use very high pack voltages. I don't know of any chargers that will do 600V off the shelf. Since your charge currents are going to be reasonably low it would not be terrible to build if you have the skills to do so. Likewise if you need 12V for the regular systems on the vehicle you may be hard pressed to find a DC-DC converter from 600V down.

There is also the shock hazard. 600V of batteries is bad news. Touching full pack voltage would, lets say no good would come from it. It won't be just a tingle. It won't just be painful. The best I can say is it will be bad. I am not saying not to do this, just be extremely careful.


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## frodus (Apr 12, 2008)

Everything gets harder when you start going up in voltage..... harder to wire all those batteries together in a huge series string, higher shock hazard, harder to find a suitable charger, contactors, fuses, cable (600V is the max of some of the wiring you'd find easily), DC-DC converters are much harder to find. Isolation of the pack becomes more important than ever.

You'd spend less time and money finding a suitable controller in the 400V and below range than you would with 600V.


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## smoothflow (Oct 17, 2011)

The last option is to use a high frequency inverter circuit i.e. mosfets / scr switches, high frequency transformer and then bridge rectifier to convert 96 V DC to 600 V DC. Then use a similar circuit in reverse for regen. Is it possible? Because here in India I can get high frequency inverter circuits for about 100-150 USD.


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## dougingraham (Jul 26, 2011)

smoothflow said:


> The last option is to use a high frequency inverter circuit i.e. mosfets / scr switches, high frequency transformer and then bridge rectifier to convert 96 V DC to 600 V DC. Then use a similar circuit in reverse for regen. Is it possible? Because here in India I can get high frequency inverter circuits for about 100-150 USD.


You mentioned 10A at 600V which even at 100% efficiency is 6000 watts (8hp). So you need a step up converter that can do 6kw for motor drive. This is 62.5A on the 96V side. That is not a lot of power in the EV world but it is a pretty good amount of power for a portable switching supply. This is the kind of thing you need for a battery charger so if you can get stuff that handles 6kw power levels for 100 to 150 dollars you should be packaging it up and selling it as battery chargers. Chargers with that kind of power level sell for $2000 and up and would be a really decent profit margin.

At the power levels you are hinting at this must be for a motor cycle. It just isn't enough power to operate a car at reasonable speeds. You have a 96 battery. A device to boost that battery voltage to 600V at 6000w power levels. A 6000w motor controller which can do the motor drive and produce the power during regen. You need a device that can take the regen energy during braking and step it down and put it back into the battery. And if you want to be able to charge when out driving around there will need to be a device that can charge the battery when plugged into an AC outlet. Some of these components could be designed to do a couple of the functions in one device. The step down converter could be configured as the battery charger. That is what it does when it is regenning anyway. But to combine the boost converter and buck converter in the same device along with the charger is a whole huge project all by itself and not something you can just buy off the shelf. And it is going to be pretty bulky to place on a motorcycle even if combined into one black box. Three separate devices will be even worse.

Can it be done? Sure. Is it practical? Not in my opinion. The extra cost, complexity, weight and space considerations all work against it.


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## frodus (Apr 12, 2008)

smoothflow said:


> The last option is to use a high frequency inverter circuit i.e. mosfets / scr switches, high frequency transformer and then bridge rectifier to convert 96 V DC to 600 V DC. Then use a similar circuit in reverse for regen. Is it possible? Because here in India I can get high frequency inverter circuits for about 100-150 USD.


That's a type of boost converter, but a lossy one because you have to first convert DC to AC, go through a transformer, then rectifier then to the VFD.

A DC boost converter that boosts DC would be easier, and no huge transformer (but a huge inductor). The problem is, with any converter of any decent power, it's large and heavy.


I'm sure he wants a motorcycle that can put out over 10kw and isn't 600lbs.




I think he should ditch the 600V inverter idea and just use a normal motor and controller. 96-600V isn't practical whether he does that or 600V battery pack, it's going to be dangerous to work on.


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