How the speed of AC motor & DC motor is controlled by Drives (inverters) ?

[phatcreators]

How the speed of AC motor & DC motor is controlled by Drives (inverters) ?

Do we only control the frequency of the motors & hence by controlling the frequency we control the voltage of the motor (because frequency of motor & voltage has a relationship) ? Is it right ?

Is it right for both AC & DC motors ?

thanks$

 

[tpetar]

Best to see that in practice is Inverter Air Conditioner (split system).

Must be special designed motor for that purposes.

 

[kak111]

DC-motor and 1-phase AC-motor speed is controlled by controlling voltage and current of motor power supply.
1-phase synchronous AC-motor speed is controlled by controlling frequency of motor power supply.

3-phase AC-motor , BLDC-motor and stepper motor speed is controlled by controlling frequency of motor power supply.
3-phase AC-motor and BLDC-motor principle can be synchronous or asynchronous.
BLDC-motor = Brushless DC-motor , it has same working principle as 3-phase AC-motor.
Multiphase Stepper-motor is synchronous motor.

3-phase AC-motor and BLDC-motor is controlled with Variable Frequency Drive (VFD)
Due to the electronic structure of the motor, when frequency adjustment range is large
motor drive unit must adjust the motor supply voltage in proportion to the frequency change.

 

[FvM]

DC motors are supplied by DC which has no frequency. You would need to refer to the specific DC motor type to discuss the available control methods, but controlling the DC voltage basically works.

AC induction motors are primarly controlled by frequency as you said, the voltage will be linked to frequency according to a specific characteristic. Linear voltage versus frequency is used for many general pupose drives. Centrifugal pumps and fans can save energy using a quadratic characteristic. Refer to VFD application literature for practical suggestions. Modern inverters can be usually programmed with an individual voltage characteristics.

 

[munzir]

what about 1 phase & 3 phase asynchronous motor's controlling principle ?

thanks esp KAK

 

[kak111]

Most common 3-phase induction motor is
asynchronous induction motor with a short-circuit rotor,
more commonly defined squirrelcage rotor.
These motors are usually is driven by VDF.

Single-phase induction motors are brushless motors
designed either with a single coil plus a shaded pole coil,
or two stator coils and a phase-shift capacitor.

Three Ways to Control a Single-Phase Induction Motor
**broken link removed**

Phase-Control Alternatives for Single-Phase AC Motors
Offer Smart, Low-Cost, Solutions
https://aircareautomation.com/data/article1.pdf

 

[FvM]

Interestingsly, in "Three Ways to Control a Single-Phase Induction Motor" all three methods are VFD, two of them are assuming a two-phase (capacitor) motor and are supplying a rotating field to it. In other words, they are pretty similar to standard 3-phase induction motor VFD.

Triac control of single phase motors gives acceptable speed control quality for drives with speed proportional torque, e.g. fans.

 

[munzir]

what about servo motors ? What's their controlling principle ?

 

[kak111]

A servomotor is a motor which forms part of a servomechanism.
The servomotor is paired with some type of encoder to provide position/speed feedback.
https://en.wikipedia.org/wiki/Servo_motor

A servomechanism, sometimes shortened to servo, is an automatic device
that uses error-sensing negative feedback to correct the performance of a mechanism.

The term correctly applies only to systems where the feedback or error-correction signals help control mechanical position,
speed or other parameters.
For example, an automotive power window control is not a servomechanism,
as there is no automatic feedback that controls position—the operator does this by observation.
By contrast the car's cruise control uses closed loop feedback, which classifies it as a servomechanism.

A common type of servo provides position control.
Servos are commonly electrical or partially electronic in nature, using an electric motor as the primary means of creating mechanical force.
Other types of servos use hydraulics, pneumatics, or magnetic principles.
Servos operate on the principle of negative feedback, where the control input is compared to the actual position
of the mechanical system as measured by some sort of transducer at the output.
Any difference between the actual and wanted values (an "error signal") is amplified (and converted) and used to drive
the system in the direction necessary to reduce or eliminate the error.
This procedure is one widely used application of control theory.

Speed control via a governor is another type of servomechanism.

https://en.wikipedia.org/wiki/Servomechanism

As explained above any type of motor can be called as servomotor
in the case that there is built in some components of the servo mechanism. ( usually positioning sensor )
This motor acts as a source of operating power or an active part of a servo mechanism.

So servomotor can be any electric- , hydraulic- or pneumatic motor.

 

[kak111]

What's their controlling principle ?

Learn more .... about motor drives and controllers.
( videos , applications.... )


Industrial PLC and Automation
Learning : Motor Drive and Control

 

[danishdeshmuk]

How to differentiate between synchronous & asynchronous motor ?
What about the controlling techniques of the other types of DC motors (series, compound, shunt etc.)?
How about the controlling methods of other types of stepper motors other than multiphase which you told me in your post ?

thankx

 

[manishanand14]

You have to be very specific about the type of motor whose speed you want to control because there are various types of AC and DC Motors.

Speed of a DC Motor can be controlled by PWM[Pulse width modulation] Technique.In this technique by changing the duty cycle we are varying the average voltage appearing across the motor terminals and hence changing the motor speed.

Single phase AC Motors can be controlled by AC Voltage controller[Fan speed controller]

 

[munzir]

How about the controlling of series dc motor ?

 

[kak111]

Basic control principles for ac- and dc-series motors....

 

[BradtheRad]

I can state a method that will not work. I once tried to reduce speed of an AC motor by installing power resistors inline.

With low ohm values, the motor continued to operate close to its original speed (upwards of 1800 rpm). Even when the voltage was dropped quite a bit, the motor speed did not drop hardly at all.

I installed greater resistance until motor speed dropped noticeably. However by that point there was hardly any torque. I had reduced power through the motor so much that it would barely start up from a dead stop.

I concluded that the AC supply frequency is what determines motor speed. At least for that type of motor.

On the other hand my triac-based speed control worked to reduce motor speed.

 

[FvM]

On the other hand my triac-based speed control worked to reduce motor speed.

Do you mean for the same motor and same load situation that failed with series resistor speed control?

According to my experience, I would claim, that a simple triac control doesn't behave much better than a variable series resistor.It can only work, if the motor is loaded with a strongly speed dependent torque, e.g. a fan or centrifugal pump.

Special designed triac controls can achieve a better behaviour, either by implementing speed feedback or by generating a sub-harmonic drive frequency.

 

[danishdeshmuk]

What is the procedure of controlling the compound dc motor ? Can any kind of drive system be used with it ?

 

[kak111]

What is the procedure of controlling the compound dc motor ?

NI Developer Zone
Compound Motors
**broken link removed**

DC Compound Motors
https://www.industrial-electronics.com/elecy4_3.html

 

[BradtheRad]

Do you mean for the same motor and same load situation that failed with series resistor speed control?

According to my experience, I would claim, that a simple triac control doesn't behave much better than a variable series resistor.It can only work, if the motor is loaded with a strongly speed dependent torque, e.g. a fan or centrifugal pump.

Special designed triac controls can achieve a better behaviour, either by implementing speed feedback or by generating a sub-harmonic drive frequency.

I must believe you're correct. My triac dimmer was not substantially different from using inline resistors. Both methods only reduce power.

There were two AC motors I once experimented with. One was in a reel-to-reel tape deck.

The other was a fan attached to a wood stove. (This was 25 years ago. At the time I thought maybe a motor was called a 'squirrel cage' motor because it drove a fan which was shaped like a squirrel cage.)

I definitely remember my experiments were not successful when I tried to slow down the tape deck motor by adding resistance inline.

By the time I got it to go slower, it was too underpowered to maintain smooth tape travel.

It indicated that the motor's speed depended more on supply frequency than supply voltage.

The fan motor operated successfully with my homebrew triac dimmer. Its speed did not depend on supply voltage.

So now I guess the tape deck motor was not successful with the dimmer after all. Because if it had been, then I would have played at speeding up and slowing down music with it.

 

[danishdeshmuk]

any vfd can work with it ? or what design should be used for the better controlling of compound dc motors ?