Switched Reluctance Motor Driver - Page 1
Forum section: electronics / projects

author: njlroach
author_rank: Newbie
timestamp: May 23, 2020, 10:40:55 am
content: Hello. My friend has bought a sailboat which has an electric auxiliary motor. The control unit has got water in it and is damaged beyond all hope of repair. The motor and controller are designed to power a car and are very sophisticated and I think that a boat motor probably needs much less sophisticated control. To buy a new controller would cost several thousand dollars, and I want to try to build a new controller for him instead.This is the motor:https://www.evworks.com.au/hyper-9-isIt's a three phase permanent magnet assisted synchronous reluctance motor. I believe it needs to be driven by some type of three phase AC. It has encoder outputs, but I haven't been able to investigate exactly what sort of signal they put out.Could I drive this motor with a three phase square-wave voltage of the kind normally fed to BLDC motors? What would be the down-side of not feeding it a proper sine wave?I think that I should commutate the voltage to the windings according to the rotor position indicated by the encoders, keeping the angle constant at the position of maximum torque. Would I control the speed of the motor by varying the voltage applied using pulse width modulation?The batteries are currently rigged to produce 100V and the current that I will need to control might be up to 500A. I'm aware that I will need some sort of transistor switches (probably IGBTs) to control the voltage to the motor. I'm hoping to salvage them from the old controller or else buy them on eBay.What things do I need to consider in the design of my controller?Please be gentle, I don't have formal training in electronics. The controller doesn't have to be 100% efficient and it doesn't have to realize the maximum power that the motor and batteries are capable of, it just has to get the boat moving enough to move around in enclosed waters.Thanks so much. Any help would be greatly appreciated.

author: Slh
author_rank: Regular Contributor
timestamp: May 23, 2020, 12:06:14 pm
content: It should be possible to run with a trapezium/six step BLDC algorithm but it won't be very efficient, it will be rather noisy (aurally) and the torque ripple will be significant. If you want a controller that will run it smoothly at good efficiency then you'll probably be best off buying the recommended controller for it. Synchronous reluctance with permanent magnet motors get some of their torque from the magnets and some from the reluctance torque and there isn't a good easy relationship to work out what the phase should be for peak torque.To be honest, the boat control isn't going to be much less sophisticated than the car requirements. It won't have all of the same functional safety requirements but most of that is in the software rather than the hardware. Do you know if it runs in speed mode or torque mode?This is going to be a big project that's probably going to go wrong a few times if you're starting from scratch. You're talking about running a 100kW motor. Losses in a good controller will be >= 1kW so you' have to figure out how to get at least that much heat out of the MOSFETs. 120V probably won't kill you but you'll be launching MOSFETs all over the place if you have a problem.Do you know how much power it needs to push the boat around? Is it actually running at 100kW?If you really want to build your own then you'll want to be using MOSFETs for the voltage. IGBTs will work but aren't so good at lower voltages. Trapezium output is easier than a sine output but the electronics will be the same.It might be best to start with a little (<100W) brushed DC motor controller to get some practice in before you start looking into three phase.The encoder appears to be a sine/cosine output (page 8 of the manual linked). It's probably one sine per mechanical revolution. You'll have to figure out how many pole pairs the motor is (easy enough, give it a spin with an oscilloscope across two of the phases and on the sine output and count how many cycles you get on the motor for each mechanical revolution.Personally I'd buy an new controller and put it in a waterproof box. Then work up to building a replacement if that's really what you want to do.Hope that's somewhat helpful.

author: NiHaoMike
author_rank: Super Contributor
timestamp: May 23, 2020, 12:52:46 pm
content: Take a look athttps://openinverter.org

author: Dave
author_rank: Super Contributor
timestamp: May 23, 2020, 02:11:42 pm
content: I firmly believe that you're underestimating the complexity of the project you're thinking of taking on.Your friend will still have to buy another motor controller in the end, he just won't be able to use the boat for the time it takes you to realize you're in way over your head.Apologies if my statements might seem harsh, but I'd rather be honest and direct with you than give you false hope.Side note, I work in a company that produces electric motor drives (this seemed relevant to include).

author: MagicSmoker
author_rank: Super Contributor
timestamp: May 23, 2020, 10:55:39 pm
content: Quote from: njlroach on May 23, 2020, 10:40:55 amThat is almost certainly an interior permanent magnet synchronous AC motor, exhibiting a wide constant power speed range but which is notoriously difficult to drive (from a software standpoint - inverter hardware is the same for pretty much all 3-phase AC motors). It's also not an ideal choice of motor for a cubic-law load like a propeller, especially when regenerative or dynamic braking is unnecessary and/or impossible. I mean, it is possible to regen brake a sailboat, I just can't see why you'd want to do it - if the wind is up so much you are going too fast then you'd probably want to take down some sail area (reef?) first, right?Quote from: njlroach on May 23, 2020, 10:40:55 amIf you don't need lots of low end torque - and by definition, a cubic-law load like a fan, propeller, pump, etc., does not - then any old V/Hz (ie - scalar) inverter will work... it just needs a really oddball rating like 100V and 500A per phase... Maybe a Curtis 1238 or 1239 would be a good substitute?Quote from: njlroach on May 23, 2020, 10:40:55 amBuy an off the shelf drive / motor controller. There is a snowball's chance in hell of someone with limited electronics experience being able to roll their own EV drive, despite all the yahoos on sites like diyelectriccar.com claiming otherwise.

author: njlroach
author_rank: Newbie
timestamp: May 26, 2020, 12:25:27 am
content: Thanks everyone for the answers. Based on what you've all said, and on my research, I see that it will not be possible for me to make a controller that can run the motor at high power or good efficiency. However, I think that if I can get the motor to produce about 10kW, that would be worthwhile andrelativelyachievable just by building a simple controller on par with a BLDC motor controller but with some big mosfets. I recognize that there is still a significant chance of cost- and time blow-out and ultimate failure. I'll present that information to my friend and see what he says.