PI controller for refrigerator

Discussion in 'The Projects Forum' started by velile, Oct 3, 2009.

  1. velile

    Thread Starter New Member

    Oct 3, 2009
    hi all

    i have to implement an analog PI controller (with op amp,resistors and capacitor) to control a small bar frigde.my feedback is from a temperature sensor(which is a DC voltage) and my reference is set manually.i only have to monitor the output of the controller as it goes to a DSP from which i determine the duty cycle and hence the voltage applied to the refrigerator compressor. the higher the voltage,the faster higher the speed.the faster is cools and reaches the set point.

    i have designed the PI controller,however, the output of the controller is just the saturation voltage of the op amp(12V) even when the error signal(differnce between set temperature and the sensor temperature) is changing.i am expecting it to be in the range of 0V-12V with a change in the error.what am i missing.please HELP????
  2. KMoffett

    AAC Fanatic!

    Dec 19, 2007
    I've never heard of controlling refrigeration by controlling the compressor voltage. Every one I've ever seen (but then, I haven't seen everything ;) ) control the compressor's run-time. Do you have a link to this concept...or to the fridge.

  3. DrNick

    Active Member

    Dec 13, 2006
    If you have a DSP and an ADC (for reading the error), Why not just input the sensor output to the ADC and implement the PI control in the DSP?

    If you really want to use the op-amp circuit, post it. It either has an error or is broken...neither can be determined without the schematic.
  4. velile

    Thread Starter New Member

    Oct 3, 2009

    At KMoffett,im controlling the speed of the compressor (which is proportional to the applied voltage). so the faster it spins,the faster it cools.

    at DrNick..i must use the op amps but if you have stuff on how to implement it on the dsp please send them to me...however, i have attached the schematics.please help,im running out of time.

    thanks all!!!
  5. velile

    Thread Starter New Member

    Oct 3, 2009
    Anybody please help with the PI controller....i think im missing something with the op amp...HEEEEELP!!!