Clarification on controller basics
Admitted I am very new to this game, but I wanted to make sure that what I have gathered so far is correct. Please correct me if I am wrong in how controllers work. A microcontroller creates a variable pulse width modulation signal, that is then fed to the inputs of a simple amplifier circuit. Now if I have this correct, one could theoretically use any microcontroller and simply adjust the power handling abilities of the amplifier for their power needs correct?
Hi Tinkerer,
It's a little more complicated than that. The usual way is for the microcontroller (MCU) to generate the PWM. This is then fed to "driver" circuits (an IC) - these are called FET drivers, or gate drivers (they feed the gate input on the FETS). The FETs (MOSFET actually) perform the power switching. FETs are used for low voltage (<100 V, usually 48-60 V) applications, whilst higher voltage applications use IGBTs. Because the motor is a large inductor, there is an inductive kick generated when the FET turns off. This kick will blow out the FET if left unchecked. To absorb the kick, a reverse biased diode is placed across the output of the FET - these are called freewheel diodes.
A drive circuit can employ just one FET. In this case, all the controller is capable of is spinning the motor in one direction, and there is no braking (regen). Reverse direction is handled by heavy duty relays, called contactors. In more advanced controllers, four FETs are employed in what is called an H-bridge. This gives a four quadrant controller; the four quadrants are: forward motion, forward braking, reverse motion, reverse braking. Here the direction and braking are all controlled electronically and no contactors (except one that connects battery to the controller) are required. A single MCU can support all these modes, and the designer can choose what type of power stage (number of FETs) to use.
There is an excellent book that explains all this (and quite a bit more!) very clearly. The title is "Motor Control Electronics Handbook", the author is Richard Valentine and the publisher McGraw Hill. You can get it on Amazon. A bit pricey, but it really covers everything in deatil (700 pages). It also covers synchronous and induction motors, which a more complex than simple brushed motors.
Patrick
thank you very much for your informative reply, Thats some good knowlege for me to do a little more studying off of.
Looking for " Controllers For Dummies " Any thoughts ?
Still working through (EV Tech. Larminie/Lowery) 2-3 more reads and I'll get it ?
Understanding controllers is next.
Thanks any and all
Also, reading up on the subject I came across this:
The 12V "kicks" may be audible if the motor is not well-mounted, especially at low revs. A clicking or growling vibration at PWM frequency can be amplified by case panels. A way of overcoming this by "blunting" the square-wave pulse is described in Application Note #58 from Telcom.
(a 58k pdf file, right-click to download). I've tried this, it works, but some of advantage is lost.
Some authorities claim the pulsed power puts more stress on the fan bearings and windings, shortening its life.
I could see this being true for brushed dc motors, but would this affect induction or brushless?
Wont catch me ridin dirty