Hi, do you guys have resources for induction AC motor control without using a VFD controller
So basically my application is
How can I slowly start and slowly stop the motor without using a VFD controller
jyu:
Hi, do you guys have resources for induction AC motor control without using a VFD controllerSo basically my application is
- arduino will control the on and off of the motor via sensor and relays
- when turning on and turning off the motor it would not jerk the motor, it would slowly start and slowly stop.
How can I slowly start and slowly stop the motor without using a VFD controller
You can't. And besides, a VFD will have a very small range of frequencies that will run the motor because it was designed to be run at your mains frequency.
Get a proper motor for your project.
Paul
It all depends upon how you define “slowly”. There are devices called “soft-starts” for AC induction motors. They vary the voltage using thyristors and can only operate over a very limited range of speed and time. They are used primarily for three phase motors as single phase motors generally don’t lend themselves to being soft-started without stalling and/or overheating.
To be able to run an AC motor at a specific or fully variable speed, you must change the applied voltage and frequency, in proportion, at the same time. For example, if you have a 230 volt 50 Hz motor, a VFD running the motor at half speed is outputting 115 volts at 25 Hz. A VFD achieves this with PWM but it is far more complex than the PWM coming out of an Arduino being used for DC motor control.
VFD’s are designed for 3 phase motors. The motor must also be designed to run at lower speeds and still dissipate the heat generated. It is difficult to vary the speed of a single phase AC motor and I know of only one company building single phase VFD’s, Invertek out of the UK.
A proper 3 phase AC motor and appropriately sized VFD is the proper approach for anything exceeding a few hundred watts. For a low power application, DC may be cheaper and easier.
Your requirements conflict - to control induction motor speed you need at least a V/f controller. Attempting to control the speed of some induction motors without frequency control may lead to stall and catch fire behaviour.
Depending on the rotor design you can arrange for a motor to handle stall conditions without massive current draw, or medium current draw or massive current draw - this is all to do with the rotor bar depth and profile, its not something you can compensate for externally without V/f control.
Put another way some motors are able to handle partial stall, others are not. If not they rapidly overheat
during stall (requiring rapid start up - an induction motor going slowly is in a stall condition and the windings may be dissipating over 100 times their design power - this is catch-fire levels)