How to brake a three phase brushless motor?

Thread Starter

mtcs

Joined Jan 21, 2019
10
Hello! I'm trying to smoothly brake a three phase brushless motor, by short circuiting the phases. At this moment an overvoltage occurs damaging the power circuit. Is this the right way to do it? Thanks
 

MaxHeadRoom

Joined Jul 18, 2013
20,081
One method is DC braking for a induction motor.
If BLDC, then short circuit the winding's should work, but the motor has to be disconnected completely from the supply.
Max.
 

larrydd

Joined Nov 4, 2015
3
Hello! I'm trying to smoothly brake a three phase brushless motor, by short circuiting the phases. At this moment an overvoltage occurs damaging the power circuit. Is this the right way to do it? Thanks
I'm going to assume you are referring to an AC Brushless Induction Motor, in other words a 3 phase motor with a permanent magnet rotor (armature), not a standard AC 3 phase induction motor. If so, the back EMF from the rotating armature is very substantial and shorting the motor phases at rated speed could damage the motor. If you want to decelerate the motor without using the VFD (variable frequency drive) you need to first disconnect the VFD T-leads from the motor, then connect an appropriately sized resistor bank across the motor T-leads. Without knowing a lot more (i.e. motor rating, deceleration delta-t, etc.) I can't estimate the resistor values.
Also, opening the T-leads while the VFD transistors are conducting could cause transistor failure, so the VFD output should be interlocked with the contactor used to isolate the motor from the VFD output so they are not conducting at that instant. That will also minimize the contact wear.
 
Last edited:

MaxHeadRoom

Joined Jul 18, 2013
20,081
One method used is a very low value resistor between the low side motor control devices and GND, the volt drop across this resistor is then fed into a op amp and then to the controller for controlled braking.
i.e. switching on/controlling Both low devices of a H-bridge for example.
Picmicro app sheets have examples.
Max.
 

Janis59

Joined Aug 21, 2017
1,063
Ultra-hard beaking is short circuiting. Mild breaking is giving the co-supplement of DC along with decreased voltage on bobbins or no AC at all but mild DC (current stabilized regime) on it.
 
Top