I have a fuzzy logic controller for motor speed in air-conditioning unit application. The manufacturer claimed that their unit controls speed by varying the voltage. However, when I test the unit, while the speed reduces, the electrical frequency (Hz) increases. This puzzles me. I expect the frequency to remain constant.

Anyone has experience or knowledge on this subject?

 

Its probably just a run of the mill AC motor that varies frequency with an inverter drive to vary the motor speed.

~Ken

 

the speed of an ac motor can be controlled

1)by varying voltage really inefficient not practical for industries
2)by varying frequency again inefficient
3)by maintaining v/f almost constant means varying the frequency(speed= 120*frequency/poles) and voltage so that v/f remains constant

there are other methods like vector control etc but v/f is the least basic solution that one can use in industries. for more help feel free

[email protected]

 

Well speed of the motor can be controlled in many ways.

r.p.m speed= voltage/frequency

therefore obviously frequency has to rise to keep speed low...
It is not so easy to vary the voltage except by multiples... so the easiest way is to vary the frequency....

frequency is varied by first varying current which in turn varies frequency via in pulse width modulation and pulse position modulation.

current control or current variation is used to vary frequency.

 

Karl,

When the OEM states they vary voltage they most likly mean the control signal to the drive, 2-10vdc or 0-10vdc. Voltage and Frequency need to be changed together at a set v/hz setting in the drive.

Mike

 

Karl,
How are you measuring frequency?