Automatic Voltage Regulator(AVR) for standalone single phase alternators(230V,50Hz)

Discussion in 'The Projects Forum' started by vks_foe, Feb 15, 2009.

  1. vks_foe

    Thread Starter Active Member

    Jan 11, 2009
    55
    5
    Hi,
    this is my project and i need some help.
    I have decided to use pulse width modulation of field voltage in order to change the field current and hence regulate the terminal voltage. Further, i've selected TL494 for this.
    My difficulties:

    1) I have to couple TL494 with a power mosfet. I've decided the switching frequency of TL 494 to be 20 KHz. The drain of mosfet would be connected to the voltage obtained by rectifying (half wave) the terminal voltage of that alternator. The source will be connected to one end of the field winding.
    I require 5 A continuous current and in short duration, 6 A for 10 sec.
    Kindly suggest a Power Mosfet which is easily available and cheap.
    Also a proper optocoupler/pulse transformer for coupling.


    2) the AVR circuitry will also be fed form the rectified terminal voltage. So i need to design a zener regulator .Kindly suggest a BJT so that the O/P of zener regulator is 15Volts, 25Watts max.(fig attatched)

    I'll post the schematic soon..

    PS: The AVR ahould be such that it can be used with alternators of different rating. (Max limit 5 KVA). Also, i need the cost to be low. Current AVRs available in India cost Rs. 2000 approx.
     
  2. bertus

    Administrator

    Apr 5, 2008
    15,647
    2,346
    Hello,

    You say the input is 104 Volts. The output must be 15 Volts. That is a difference of about 90 Volts.
    The power in the resistor Rs will be very high.
    The current must be higher than 25 / 15 = 1.6666 A.
    The power dissipated in resistor Rs can be upto 90 * 1.6666 = 150 Watts (witch will be transformed in heat).
    Better think of someting else like a DC/DC converter.

    Greetings,
    Bertus
     
  3. blhoward

    New Member

    Feb 4, 2009
    5
    0

    Most AC generators use a voltage to the fields of about 12VDC at no load to 65VDC at
    full load. Some are over 100VDC at full load. I think the Indian "ST" generators run at about 63VDC at full load. The needed output also depends on different field resistances of different alternators. If you want this to be a generic, fits-all regulator, the output will have to be adjustable over a very wide range. I am VERY interested in this idea.
     
  4. vks_foe

    Thread Starter Active Member

    Jan 11, 2009
    55
    5
    Please suggest some ckt for DC - Dc conversion.

    I know abt DC Chopper. It also requires switching of a transistor which is done using 555 in astable mode. But 555 also requires a supply voltage. so problem remains the same...

    Actually, i'm unable to decide the supply voltage too. I have a constraint of 22 V at higher end and 8 V at lower end by NJM 4151 (freq to voltage converter). I thought 15 volts would be suitable.
     
  5. bertus

    Administrator

    Apr 5, 2008
    15,647
    2,346
    Hello,

    Take a look at the LM5035 from national.
    See datasheet.

    Greetings,
    Bertus
     
  6. vks_foe

    Thread Starter Active Member

    Jan 11, 2009
    55
    5
    Hi,
    I have already decided much of my ckt. Using Lm5035 to replace only the zener regulator will be quite expensive. Replacing the whole of TL 494 ckt with LM 3035 is tedious and time taking. I have hardly 2-3 months to finish this(including board develoment and other things).

    Isn't there any other solution???

    thanks.
     
  7. vks_foe

    Thread Starter Active Member

    Jan 11, 2009
    55
    5
    thanks for your responses.. I've modified the zener regulator circuit posted above.. Also there was some error in my calculations.. I don't require a power output of 25 Watts any more.
     
    Last edited: Feb 19, 2009
  8. vks_foe

    Thread Starter Active Member

    Jan 11, 2009
    55
    5
    Further, i have to sense the terminal voltage and then compare it with a reference and then feed into tl494. I i simply rectify the terminal voltage and then filter to measure it, i require a large filtering capacitor (>50mf @ V > 325 volts). This doesn't appear feasible.

    Pls suggest a proper and simple method of measuring the terminal voltage (230 V rms, 50 Hz) and getting a voltage in proportion to the rms or peak.
     
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