Where can i get a basic vfd circuit

eddycheong · Mar 5, 2008

as far as i know the VFD can vary the frequency thus vary the speed of an induction motor(1 Ph). im trying to search the circuit of the operation and if it is simple im gonna make a simple vfd of my own if possible..but can someone help me find it on the web?the major components that i know:
Rectifier
DC Bus
Inverter
Controller

tragically1969 · Mar 5, 2008

eddycheong said:
im gonna make a simple vfd of my own if possible

Why ?

eddycheong · Mar 5, 2008

because the VFD in the market too expensive..and im only using it for a small project.

tragically1969 · Mar 5, 2008

Just realised you said 1Ph motor, its cheaper to buy a 3Ph motor and single to 3 phase VFD for this sort of thing, a .75KW VFD is less than £100 in the UK !!

eddycheong · Mar 5, 2008

tragically1969 said:
Just realised you said 1Ph motor, its cheaper to buy a 3Ph motor and single to 3 phase VFD for this sort of thing, a .75KW VFD is less than £100 in the UK !!

a 1 ph motor i already have. just need to vary the frequency for speed control. so planning to construct a simple circuit to vary the frequency. if there is any simple circuit on the web pls reply here

tragically1969 · Mar 5, 2008

I suggest you search this site, it has been discussed many times on here before, each post essentially has the same outcome:

There is no easy way to control the speed of a single phase motor

rdrast · Mar 5, 2008

You 'CAN' do a simple 555 timer circuit, driving a push-pull output stage, to a center tapped transformer, BUT you still will not be able to control a single phase AC motor speed very well, and you will have very high losses at frequencies less than 20Hz or so.

Single phase AC Motors are simply not designed for variable speed control. That is why variable speed consumer grade power tools invariably use universal motors.

Paulus · Mar 5, 2008

I do remember (almost too long ago), being involved with a job where they were using a 'Fan Speed Controller' on a single phase motor.

http://www.europeanthermodynamics.com/fan_control/Nimbus%20Data%20Page.pdf

Seem to recall that there were quite a few problems with torque however!

eddycheong · Mar 5, 2008

Paulus said:
I do remember (almost too long ago), being involved with a job where they were using a 'Fan Speed Controller' on a single phase motor.

http://www.europeanthermodynamics.com/fan_control/Nimbus%20Data%20Page.pdf

Seem to recall that there were quite a few problems with torque however!

thanks but torque doesnt matters to me..is there any component can be used to change the frequency?for example a dc motor we can limit the current to reduce the motor speed. either rheostat or resistor can be used. planning to make 2 diff speed if possible. im a degree student and doing a mini project for my FYP preparation

Lancie1 · Mar 5, 2008

... planning to make 2 different speeds, if possible.

If you only need 2 discrete speeds, then it would be much easier (and cheaper) to trade your 1-phase AC motor for a 2-speed, 2-winding motor. (Sell your motor and buy one that will work without a VFD).

Or, if it is continuously variable speed that you need, trade for a DC (or "universal" type) motor with speed rheostat.

eddycheong · Mar 5, 2008

Lancie1 said:
If you only need 2 discrete speeds, then it would be much easier (and cheaper) to trade your 1-phase AC motor for a 2-speed, 2-winding motor. (Sell your motor and buy one that will work without a VFD).

Or, if it is continuously variable speed that you need, trade for a DC (or "universal" type) motor with speed rheostat.

so there is no other way to do a simple frequency control of the induction motor?

tragically1969 · Mar 5, 2008

eddycheong said:
so there is no other way to do a simple frequency control of the induction motor?

No !!!!

there was a thread on here a few months back that ran to six or seven pages on exactly the same project as yours by another student, read that !!

rdrast · Mar 5, 2008

eddycheong said:
so there is no other way to do a simple frequency control of the

Single Phase

induction motor?

As stated above, No. Single phase AC motors have no inherent method of starting to rotate in any direction. In order to actually develop rotation, many design tricks are used; things like off-balancing the power supplied to the windings (Starting caps, Shaded pole motors, Starting Windings, etc), mechanical starting, or other tricks.

Three phase motors inherently start and run in one direction due to the rotating field presented.

The tricks used in order to get a single phase motor started preclude it from being a viable application for a variable frequency drive.

Lancie1 · Mar 5, 2008

So there is no other way to do a simple frequency control of the induction motor?

There are some ways to control the SPEED of a 1-phase AC motor, depending on what TYPE of motor you have. Read these old threads:

http://www.plctalk.net/qanda/showthread.php?t=29961&highlight=phase+AC+motor+control

http://www.plctalk.net/qanda/showthread.php?t=33433&page=7&pp=5&highlight=phase+motor+speed+control

http://www.plctalk.net/qanda/showthread.php?t=29961&highlight=phase+AC+motor+control

Where can i get a basic vfd circuit

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