Vector control design for 3-phase drives using analog electronics - Page 1
Forum section: electronics / projects

author: MrWifiHifi
author_rank: Regular Contributor
timestamp: November 19, 2024, 07:48:31 am
content: HelloThis thought has been bothering me for a long time. That's why I did a little research to see if something like this would be possible and it looks like it is. This topic started to interest me since I had the opportunity to see an analog controllerr for PMSM, where there were only hybrid circuits and apparently some analog control was done there. I became very interested in how it could be done there.It's true that today it can be done with a microprocessor and it's much smaller and easier than analog, but for me analog still has its charm. Anyway, if I managed to put something like this together, it would only serve as an explanation of the principle of this control, with the fact that it would be possible to measure individual signals in the control, which is not very possible with a modern microprocessor.I have more or less solved the basic blocks, i.e. park clarke transformations, regulators, etc. What's still causing me a problem, I don't know how to measure the angle of rotation of the rotor, ideally from currents and back EMF, but I also don't know how to control the amplitude of the signal relatively easily. However, I have already considered one cirucit that would not require OTA amplifiers and it would be possible to do it with ordinary op amps, but it needs to be tested. If anyone is interested, I am willing to elaborate more on this topic.I will also be grateful for constructive criticism, or help in creating individual blocks for drive controlt.

author: uer166
author_rank: Super Contributor
timestamp: November 19, 2024, 08:50:26 am
content: Something like a senorseless observer is pretty complicated in code, I can't imagine doing it in analog domain.Easiest might be to use an analog output angle sensor (sensored mode BLDC), something like a resolver, convert to a rotating frame of reference, run the PI D/Q current loop, and convert back to fixed frame of reference and PWM modulators.It should all be quite doable as long as you test each system at a time and bring them up separately. Sensorless might be a black hole due to the discontinuous nature of the actual sensing.

author: johansen
author_rank: Super Contributor
timestamp: November 19, 2024, 05:16:09 pm
content: sensorless counting of the rotor position is done by measuring the inductance of the motor fast enough such that you can count the interference pattern of the typically 27 or 29 bar rotor against the 36 pole stator. (or 24)its not easy. but some people have done it and they aren't talking about it. i've only found one person on the internet who said that their company spent a lot of time making boge standard induction motors sing like servos, but ultimately it wasn't worth the effort due to the lower torque density of an induction motor, compared to a permanent magnet neodymium machine. but it is possible.I personaly wrote about a project here that no one has any interest in.https://endless-sphere.com/sphere/threads/attempt-to-achieve-torque-control-of-an-induction-motor-via-a-tachometer-and-off-the-shelf-vfd.119621/i did buy a good quality vfd that can handle forwards and reverse from a plus or minus 0-10 signal.. but.. my friend lent my 76 pound 5hp motor to a buddy and its gone now lol.I've had an interest in building an analog VFD for a while because off the shelf cheap vfds do not generate dc offset sine waves very nicely below about 20hz. they produce discontinuous blocks of current that are not handed off from one coil to the next smoothly. as such, its very hard to make an induction motor vfd reliably startup a permanent magnet motor. you have to pay extra for vfds that have that functionality built in, and they aren't particularly cheap.I have not yet found a vfd that can handle a torque command input.. which is what my tachometer wrap around loop would emulate in that endless sphere post.for induction motors there's a couple ways of changing the torque.. you can increase the voltage or you can increase the frequency, both will increase the current flowing. the slip can change between 1 and 6hz.. and at every output torque level there is an optimum amount of voltage and slip..most people use a lookup table rather than an algorithm that actually mathematically models the motor..and sensorless vector vfds.. i don't know what they do. but i know what they don't do: they don't drop the voltage at low loads to reduce wasted power consumption in the motor.

author: jbb
author_rank: Super Contributor
timestamp: November 19, 2024, 06:50:11 pm
content: I recall a 3rd hand story about this. Apparently, back in the days before good microcontrollers, someone made a prototype (by ?? Siemens ??) Field Oriented Control (FOC) drive using analog electronics as a proof of concept.According to my sources, it worked but was always subject to analog drifts. So it needed to be warmed up and then carefully offset nulled in many places before operation.

author: MrWifiHifi
author_rank: Regular Contributor
timestamp: November 20, 2024, 04:18:51 pm
content: Quote from: uer166 on November 19, 2024, 08:50:26 amI suspect that somehow the speed can be calculated from the slip and the angle of rotation can then be determined from that. I'll have to check it out.Anyway, I'm also thinking about the resolver. However, I don't have it at the moment, but if it came to me in the future I would definitely use it for that.Personally, I think that if the entire vector control fails, but at least individual blocks to begin with, it would be quite interesting anyway.Quote from: johansen on November 19, 2024, 05:16:09 pmI am in contact with one more guy from the Czech Republic and we managed to put together a 3F generation for simple scalar control, but the problem so far is some simple control of the amplitude of these signals using voltage. I would like to avoid OTA amps. So far, multiplication tables are the most suitable, but if there was a simpler solution, it would be much better.As for the scalar control of the asynchronous motor, I managed to get to the documentation of the converter, which was largely analog. It should be found under the name Minireg N, it was produced in Slovakia at the turn of the 80s and 90s. We originally wanted to use amplitude control as was used there. It's somehow done there using PWM and that's how the 4053 circuit is controlled. However, in the end we abandoned it because. Personally, I think that it is possible to build a relatively simple analog converter for scalar control of a 3-phase motor.Quote from: jbb on November 19, 2024, 06:50:11 pmI had a hunch that someone must have tried something like that. I would be interested in the main circuit solution and also the offset reset. It's quite complicated for analog, but it's not impossible to do it with it.

author: MrWifiHifi
author_rank: Regular Contributor
timestamp: November 20, 2024, 04:24:38 pm
content: Lest I forget to mention, we put together a sine generator with the guy from the Czech Republic, where it is possible to shift the phase. It is a fully analog connection. But I'm not publishing it yet, since it hasn't been tested and we don't have it finished. But what can I say, it is built only with op amps, no special ICs needed. it can be extended to three phases, a fixed angle can also be set and a sine cosine signal can be generated there. This connection has quite a lot of potential. When it's done, I'll be happy if we publish it together.

author: MrWifiHifi
author_rank: Regular Contributor
timestamp: July 09, 2025, 11:17:28 pm
content: I will revive it here a little after a long time.So as far as the vector motor control based on analog circuits is concerned, it looks like it's not entirely impossible.From my findings, the forward and inverse Park transformations are the biggest problem, since multipliers and sine and cosine functions are used there. Multipliers are not such a problem, rather the sine and cosine functions. If these could be done somehow easily, then analog vector control is possible.But what I could not find out is, for example, schematics of the AC Servo amplifiers of Fanuc, Heidenhain, etc. , which is quite a shame. I only found out that apparently the PMSM motor that was connected to the servo amplifiers was not vector controlled, but it was controlled as a BLDC motor.If anyone knows more info about it, I will be grateful if they share it. I will also appreciate any useful input.