brake of a permanent magnet syncronous motor
brake of a permanent magnet syncronous motor
(OP)
I´ll use a propeller with permanent magnet syncronous motor.. and i´ll like to brake with short circuit resistence...how could i define the value of the resistence? I think the value must be determined by the inertia of the load and the magnetism of the rotor...but i´ll like to know if it´s posible to have a easy rule to define it or other way for braking?
thanks
thanks





RE: brake of a permanent magnet syncronous motor
R = Peak Phase BEMF at RPM / Maximum Peak Current
For maximum breaking.
Peak phase voltage = Peak Phase-Phase voltage / SQRT 3
RE: brake of a permanent magnet syncronous motor
RE: brake of a permanent magnet syncronous motor
BEMF is Back Electro-Motoric Force. That is the voltage you get from the motor when you turn it.
There is a slight ambiguity in the Peak Voltage and Peak Current terms. It shall not be interpreted as peak of the sinewave, but peak permissible short time current. That is usually (safely) around twice the motor rated current. If you have the motor data available, it can easily be more than the thermal rating of the motor.The limit is when the current gets so high that you risk demagnetizing the rotor. But two times rated thermal current is safe.
You can either connect the resistors between phases (Delta) or in Wye. If you go for Delta, then calculate the resistors according to R = (U/(2xIrated))xsqrt(3). Example: motor rated voltage is 400 V and rated line current is 10 A. Then three resistors with R = (400/(2x10))x1.732 = 35 ohms are needed. The closest standard value is 33 ohms, which you can use without too much concern.
Resistor power will be U^2/R, but this will be at the beginning of the braking so something like a fourth of that value - probably less - can be used if your load does not have a large flywheel attached.
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: brake of a permanent magnet syncronous motor
RE: brake of a permanent magnet syncronous motor
I'll agree with Gunner except we have used 3 times rated motor current in the past to brake large synchronous motors. So, try a resistor bank that would produce 2 to 3 times rated motor current when rated motor voltage is applied. Get resistors with adjustable taps if you want to be safe.
Shorting could work but remember that the motor becomes a generator when braking this way. Supplying a resistor that will dump power (and therefore use the kinetic energy from the motor) will likely brake quicker than shorting. Also, with a short, almost all of the rotational energy in the motor has to be dissipated as heat in the motor windings.
RE: brake of a permanent magnet syncronous motor
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: brake of a permanent magnet syncronous motor
if i use inductive resistors, maybe i could get a higher brake in the rotor? how to calculate?
RE: brake of a permanent magnet syncronous motor
The RL idea is not bad. Keep the impedance fairly constant by selecting wL so that you get, say three times rated load at rated frequency. Then add R to reduce current to two times rated load. At these rather high levels, I would not risk demagnetization by going above double rated current. The motor manufacturer should have some idea where the limit is.
As motor brakes, voltage and frequency goes down, wL follows frequency down, so current would stay constant if no R in circuit. With R in circuit, the current drops, of course.
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: brake of a permanent magnet syncronous motor
RE: brake of a permanent magnet syncronous motor
thanks all of you
RE: brake of a permanent magnet syncronous motor
Not really. Search the internet. They are what you will find in a Toaster Oven that sits on you counter top at home. You just need bigger, industrial heating versions.
RE: brake of a permanent magnet syncronous motor
Feeding DC into the motor will not brake it. You would essentially be slipping poles which would cause large current and torque transients that could be damaging.
Maybe you really want to know how much energy needs to be dissipated in the resistors? Calculate the rotational energy in the system. Reduce it a certain percentage to account for the losses that brake the system. If it's a flywheel type load then there won't a lot of losses. You could calculate that around 10% would be lost to the system. So, the remaining 90% of the rotational energy is the energy that must be dumped into the resistors.
RE: brake of a permanent magnet syncronous motor
RE: brake of a permanent magnet syncronous motor
http://www.infrared-dryers.com/series-f.html
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: brake of a permanent magnet syncronous motor
thanks a lot.