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Hysteresis current control with TMS320F28335

BMJoshi
Prodigy 100 points
Other Parts Discussed in Thread: TMS320F28335

Hello,

 

I am writing an assembly language code for closed loop control of AC drives for TMS320F28335. I wanted to know how to implement hysteresis current control (controlling the current in a band by comparing the reference and actual currents and thus deciding upon the switching of the inverter).

 

Thanks!

 

  • 0
    Genius 5170 points

    I am not sure if it is possible to implement a true hysteresis control using these digital controllers but I am not sure if you really need to .... you can implement an excellent current loop using ADC/PWM module and close the loop at a very fast rate.  If you need to really implement a hysteresis control then please look at cycle-by-cyle trip function. One can use cycle-by-cycle to shut off PWM when the value reaches a ceratin high value. PWM will start working normally from the beginning of the next PWM cycle. I am curious to know the reasons behind selecting hysteresis control for this drive application - would you please share the insight?

  • 0 in reply to Arefeen
    Prodigy 100 points

    Hello,

    Well, I am doing the coding for field oriented control of induction motor, and it is in essence a current control strategy, so hysteresis band current control is mainly used there. Are there any sample codes for this available?

  • 0 in reply to BMJoshi
    Genius 5170 points

    Yes, there are example codes available from TI ... download and install their latest system examples available through Contol Suite. You will get system example code using "C" .

  • 0
    Intellectual 665 points

    I'm curious about why you'd want to use a hysteresis controller instead of fixed frequency PWM control...

    You have several options for hysteresis control. The most effective is probably to do the hysteresis part through analog circuitry, and just generate the reference from a DAC. If you want to implement hysteresis in software you'll have to ensure high ADC sampling frequency and keep comparing your feedback to your x phases current references.

    I'm not sure the DSP you picked has analog comparators (I think the piccolos have that), but if it does it could be something to look into.

    Good luck !

  • 0 in reply to SJU
    Prodigy 100 points

    When the closed loop system desires a current to be controlled, generally hysteresis current control is faster than controlling the current indirectly through voltage. Thats why.

  • 0 in reply to SJU
    Genius 5170 points

    It is true that hysteresis control offers faster response but note in hysteresis system the current is also controlled by voltage. Also, there are few inherent issues with hysteresis implementation - the most severe concern is the limit cycling - the switching frequency may become very high depending on the load situation and the resulting switching loss may become unacceptable. Anyway, please go through the exmaple systems and see if those can meet your performance requirement. The fixed frequency PWM should offers more than enough performance for most of the applications.

  • 0
    Prodigy 225 points

    Hello BMJoshi, I´m starting to program a hysteresis current control, i want to know if there is any code avaiable, or references to follow, saludos