Digital contol of single supply AC Induction motors

[vsmGuy]

I want to control my overhead AC Induction Fans remotely.

That means I have to control the speed of the fans electronically.

As far as I have understood, the fans we have in our houses are Permanent split-capacitor motors.

The speed of these fans can be controlled using a TRIAC using a tuning circuit to change the firing angle.

We can also control the speed by changing the frequency of the input voltage to the fans.

What method would you recommend ? Specifically I am looking forward to a working implementatiion.

If possible, I would like to remove the capacitor (which produces an extra phase from the single phase input supply) and wire the three terminals of my fans directly to my interfacing circuit.

I am willing to use ATMEL 8051 or PIC Microcontrollers for the interfacing - I just need to know how to achieve speed control of these fans.

 

[vsmGuy]

No leads anyone ?

 

[budhy]

The speed of these fans can be controlled using a TRIAC using a tuning circuit to change the firing angle.

This method named AC phase control, can be implemented with 8051 like this:

   ORG $0
   LJMP Start          ; Main program
   ORG $3
   LJMP ZeroCrossing   ; Zero crossing detector
   ORG $B
   LJMP TriggerTRIAC   ; Trigger TRIAC
;
Start:
   MOV  TMOD,#1        ; Timer0 mode
   SETB EX0            ; enable INT0 interrupt
   SETB IT0            ;  ‘1’ ke ‘0’ transition
   SETB EA             ; enable system interrupt
   MOV  B,#5           ; P/Pmax = 0,5
   SJMP *              ; program utama
;
ZeroCrossing:
   MOV  DPTR,#DelayTime
   MOV  A,B            ; P/Pmax value
   MOVC A,@A+DPTR      ; get delay constant
   MOV  TL0,A          ; save to Timer0
   MOV  A,B            ; P/Pmax value
   INC  A              ; 2nd byte
   MOVC A,@A+DPTR      ; get delay constant
   MOV  TH0,A          ; save to Timer0
   SETB TR0            ; start Timer0
   SETB ET0            ; enable Timer0 interrupt
   RETI
;
*** Delay constant table
DelayTime:
   DW $FFFF-10000,$FFFF-7440,$FFFF-6550
   DW $FFFF-5940,$FFFF-5400,$FFFF-5000
   DW $FFFF-4550,$FFFF-4050,$FFFF-3380
   DW $FFFF-2710 
;
TriggerTRIAC:
   CLR  TR0            ; stop Timer0 
   CLR  ET0            ; stop Timer0 interrupt
   CLR P1.7            ; turn on MOC3021 LED 
   NOP                 ; wait a moment
   SETB P1.7           ; turn off LED MOC3021 LED 
   RETI

Change the register B value to control the power

 

[vsmGuy]

@budhy : The circuit seems ok.. have you tested it ?

Can you explain the code to me.. just a running commentary will do...

 

[budhy]

It is a fully interrupt driven code.

Every zero crossing of line voltage, µC is interrupted thru P3.2/INT0, this event is handled with ZeroCrossing: Interrupt Service Routine (ISR) as follow :
:arrow:get the delay constant from DelayTime:, this value is a time constant to control Timer0 and store at TH0 and TL0
:arrow:after that start the Timer0 and set Timer0 Interrupt

Timer0 Overflow Interrupt (TriggerTRIAC: ISR) handling :
:arrow: Clear Timer0 Interrupt
:arrow: Trigger the TRIAC thru P1.7

Illustration of the whole process

 

[vsmGuy]

No no... I did not mean for you to translate the ASM code to english.... I can read ASM perfectly well

I am interested in knowing things like :

1. Where/how did you get the delay values ?
2. Why not calculate the pulse width of zero crossings and calculate time delay accordingly using percentage ?

These answers I am interested in

 

[budhy]

1. Where/how did you get the delay values ?

I derivate the delay value from this graph

2. Why not calculate the pulse width of zero crossings and calculate time delay accordingly using percentage ?

Because the P/Pmax vs time delay variation isn't linear

 

[vsmGuy]

@budhy : I will read your posts thoroughly and get back to you

Can we talk via email ?

 

[Prabakaran]

Hi VSM GUY
i too interested in this topic can i join with u . Cos i m currently working to control the Speed control of the fan. But i dont have any idea about the Triac circuit . i know the opeartion of the triac family . hope u both have communication with me too about this.

prabaece@gmail.com is my id

 

[vsmGuy]

@budhy

Di you get my latest messages ?

BTW - I had a look the the MOC3021 datasheet and I see it requires atleast 15mA to turn on.

I think the 2051 supplies only a good 5ma... don't you think it's better to use a transistor to boost the current ?

Added after 5 minutes:

I see you are sinking in current onto the 2051 pin from the LED.. how much current can the 2051 sink.. where is it in the datasheet ?

Added after 14 minutes:

Read the 2051 DS more..

The 2051 can actually drive 20mA through port1.

So why not source current from the port ?

 

[bagusdj]

I derivate the delay value from this graph

Because the P/Pmax vs time delay variation isn't linear

mas budhy, i have phase firing angle circuit that would give 110vac if i applied 5ms delay. but from the graph, i will get 155vac. which one is true? is it suppose to be half power or half voltage?

 

[Medtronic]

nice work budhy

please can you help me to control the power to the load and change the relation to linear ? i need to changing the load power linearly as say 20 step

Many thanks

MedTronic