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TMS320F28069: Boost Converter light load regulation

Damith Pavithra
Expert 1125 points
Part Number: TMS320F28069


Hi

I built a boost converter to boost voltage from 200V dc to 400V dc. Power rating is 5kw, 
Problem is, converter voltage cannot regulated at light load. I added a PID to regulate the voltage. 
Its kp and Ki parameters are greatly varies with light load and larger load conditions. 
Therefore if i tuned the controller to work well with larger load, light load have larger swings. If the controller tuned for light loads, when a large load connoted,  response is too slow. it takes about 2 seconds to get the set point in this operating condition. . 
When its loaded, further load addition doesn't cause much trouble. For ex, if there is a 500w load already and if we added a 2kw load, Voltage swings is almost not visible. 
How can i successfully regulate and transform within these light load and loaded conditions of the boost converter. 

Thank you
Damith

  • 0
    TI__Genius 15935 points

    Hi Damith,

    You may try to use two or more groups of PID coefficients for light load and high load conditions. Also using non-linear PID could be another option.

    Regards,

    Chen  

  • 0 in reply to Chen Jiang ti
    Expert 1125 points

    Hi Chen

    Thank you.
    I think this is happening due to the boost converter going to continuous conduction mode from discontinuous conduction mode. Am i might?
    Is there any special way to deal with DCM. 
    I noticed that my PID controller causes voltage overshoot when transferring from the light load to large load. 
    Duty cycle difference between light load and large load is about 0.3. This larger duty cycle jump creates overshoot. If i slowed down the PID to compansate this, it become too much slow. 

    Regards
    Damith