controling a brush less motor

Hello
It is my first real go with this forum. I hope to get answers to some of my questions, since electric and electronic control is not my main area. I mean, I have a fair idea of what is going on in most control circuits. I know what PWM is, current and voltage and watts.
Now, imagine you have a brushless dc motor which you want to control the speed and acceleration of in one direction. The reason for the brushless dc motor is, that this motor exist. The alternative, a 3 phase induction motor with permanent magnets, in the design I like, yet have to be invented. Besides, I have learned that vfd is a heavy mustard that needs a lot of cooling, so why not stick with the dc?
Ogre say this motor is rated at “x” kW, at 3600 rpm at 48 volts. If one takes a PWM amplifier and starts playing with the 48 volts, that would be big news, right. I assume that’s exactly how most modern forklifts work. So, is this the most efficient way to control speed and torque of a dc motor?
What will happen if I gave this motor 100 volts or even 300 volts for a limited time?
Would it be possible to create a controler that controls current as well as voltage? Thinking that volts multiplied with current equals force.
I have to admit I know too little. I’m thinking to use this electric motor for a vehicle. So far a motor of 17kW is available and that’s a bit less than what I would like to see. On the other hand, the outside dimensions suit me very fine, so why not try and chock the life out of it, since its not for an industrial application and reliability is not defined at the moment.
Give me any input you may think I need. I really need to learn of the possibilities of electricity.

Regards, smedsgenbo

Hello smedsgenbo,

This isn’t really the best forum for these questions. We handle the control side, and your questions are about the power side of motion. I’ll try to give you a little bit of information to get you going in the right direction.

A brushless DC motor is actually a 3-phase AC motor, usually with permanent magnet rotor, that is driven by a special amplifier (drive) that makes it behave much like a DC motor.

Induction motors don’t have permanent magnets. Current is induced in the rotor windings (hence the name) in order to generate the rotor’s magnetic field.

The voltage value in a motor’s specifications is just a single operating point. Motors can be (and usually are) operated at other voltages.

With a brushless DC motor (or a standard DC motor) the torque generated is proportional to the current. (Voltage times current = power, not force) Most amplifiers (drives) actually control the current to the motor. The current in the motor is a function of the voltage applied, the motor characteristics and the motor speed. Drives usually will sense the current and apply the correct voltage to maintain the desired current. They use PWM to generate the correct voltage.

The motor’s life is going to be determined by how hot and fast you run it and how good the bearings are. It is possible to demagnetize the permanent magnets if you run too much current through the motor, but with modern motors I don’t think this is generally a problem.

It sounds like you need to get in touch with a company that makes amplifiers (drives) so they can help you select the correct drive for your motor. The drive will likely cost a few thousand dollars. The drive may have enough intelligence to do whatever control you need, or you may also need to get a controller.

Good luck with your project.

Thank you for the prompt reply. I have to apologise for my own late response. I will try to address my question elsewhere. Any good forums you can recommend?

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