Question about Controller and VFD

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attz
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Question about Controller and VFD

Post by attz » Sat, 26 Oct 2019, 18:23

Hi guys,

I'm very new for an EV here. I come from Thailand where EV is not getting started at the moment. I have some question about the controller, VFD not too sure someone can helps me enlighten my knowledge :D

I inspired by this thread http://forums.aeva.asn.au/viewtopic.php?f=41&t=3333 "AC electric motor rewinding for EV use". So, my first EV project would be modified Industrial AC Induction Motor. However, I am confuse between this two device Controller and VFD is it the same?

Most of the EV forums discussed about Curtis Controller. but I search around internet (including YouTube) it said that controller AC motor must use VFD (something like this https://th.aliexpress.com/item/32794013 ... b201603_52)

What should I use? are these two different?

Thank you very much for any answer

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coulomb
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Re: Question about Controller and VFD

Post by coulomb » Sat, 26 Oct 2019, 21:03

attz wrote:
Sat, 26 Oct 2019, 18:23
I'm very new for an EV here.
Welcome to the forum.
What should I use? are these two different?
I would say it's a matter of definitions. An EV's motor controller is a sort of Variable Frequency Drive (VFD), sometimes also called a Variable Speed Drive (VSD).

Usually, the terms VFD and VSD are reserved for those pieces of equipment that drive a three phase motor, and accept power from the utility (usually also three phase, but for smaller devices, it can be single phase). Many VFDs have DC bus terminals, so that multiple motors can share power with each other (e.g. while one is regenerating, it can be supplying power to the other one(s) that are using power. A battery can in fact be connected to these terminals, making it usable in an Electric Vehicle (see below).

A "motor controller" is more something you'd find in an Electric Vehicle, and is designed to run from a DC source such as a battery or a fuel cell.

I was involved with a certain MX-5 starting ten years ago. It used and still uses an industrial 3-phase motor, albeit a slightly unusual one wound for 230 V phase to phase, and one that is unusually compact for its power. It's something like a 22 kW nominal motor (26 kW @ 60 Hz), and it regularly dishes out about 100 kW for short periods of time, through the magic of "overclocking" (giving a motor more voltage and frequency than it was designed for). Initially, the idea was to use an industrial VFD to power this industrial motor. Unfortunately, the size of a 100 kW peak VFD is such that it could not be fitted into the smallish sports car that is an MX-5, if there was any hope of fitting batteries and the motor as well. So it was ultimately sold off and replaced by a purpose-built motor controller (a Tritium Wavesculptor). Things have moved on, and Tritium are now known mainly for their DC fast chargers, ironically some of which (I believe) still use electronics that can be traced back to the Wavesculptor motor controller. After all, a VFD and a motor controller are essentially power converters (a VFD also has a rectifier, which would not be used in an EV application).

Being water cooled, the Wavesculptor was vastly more compact than the industrial VFD, and even with the need for a small radiator and pump, fitted much better into the MX-5.

To answer the first part of your question, however, you could use either, but be aware that VFDs are typically not designed with compact size as any sort of goal. The kind that you linked to are very small, and would only be suitable for the tiniest electric vehicles, perhaps an electric bicycle. So almost certainly, you will be better off with a motor controller designed for electric vehicles. If you happen to be converting a truck, it might be possible to use an industrial controller, and you might be able to get your hands on one cheaper than a similarly powerful motor controller.

The MX-5 topic is quite large at some 68 pages (of 25 posts each), but I suspect you could learn a lot by skimming important parts. Use the index to find the parts of interest.

Good luck.
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attz
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Re: Question about Controller and VFD

Post by attz » Sat, 26 Oct 2019, 22:06

Hi coulomb,

Thank You for your information, get better understanding now. Will read your suggested post to speed up the knowledge!

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