PWM in motor control

not bad, it decrease switcher device's on off power dissipate.

but the inrush current and heat dissipate in motor has nothing to do with the pwm,

these items relay on the control circuits.

hoever I vote you as a good answer.

We control the inrush current of our motors by implementing a soft start.

Heating is reduced at lower speeds since less current is required to generate torque at full voltage than at lower voltage.

bhankii,

I hvnt said you are wrong.

soft start can restrain inrush current. but soft start can implemented by either pwn or pfm or others power modulator like in SCR circuit.

promote efficiency is main aim of all inverters to decrease unneccesory heat. how ever, the one way of pwm is that we often used at present.

Look at bottom, I vote your answer as a good. not a bad.

Both bhankiii and cn power gave valid answers but they left out one feature that can be a real advantage under certain conditions. If you use the motor to move something to a particular position, and then stop, PWM drive with position feedback gives you a much faster responding and accurate control system.

emc,

how does that work?

This is actually how we use PWM in linear actuators in spacecraft docking. We have a resolver that gives us position data which is fed to a processor, along with force info from load cells, and it cranks through a fancy algorithm to produce an effect something like a shock absorber.

Sorry, folks, I was the "Guest" that posted number 5. I forgot to log in, so I didn't get joined up till after I'd already edited, and posted, it.

Mike

Correct me if I'm wrong, but I don't think PWM changes the voltage applied, rather it varies the amount of on/off time that the voltage is applied.

Absolutely correct. And it is THAT which makes PWM such a useful tool. Since the voltage is ALWAYS at the rated value, stall torque is kept high, stall current is limited to near zero, and heating is minimized. PWM does add cost, due to the necessity for building and installing the PWM control circuit, along with, usually, at least a 1/2 H-bridge, which would allow for reversible control of a single motor. If differential control of two motors is required, a full H-Bridge serves, which both allows reversing either or both motors, and also provides a guarantee against applying both forward and reverse current to a single motor at one time, which causes a direct short through the motor AND the controller boards, and usually fries them and the PWM controlling device. More cost, more complexity, but the added functionality, when it is needed, more than makes up for the downsides.

Mike