I have a converter whose output must be pulsed at anywhere from 1Hz to 100kHz at duty cycles of 5% to 95%. Using standard voltage mode control, I am able to regulate the output up to ~70% duty cycle for frequencies up to approximately 50kHz. 100kHz operation at low duty cycles such as 5% is also very good. However, when the duty cycle increases to levels such as 0.95D, (especially at high frequencies), the controller does not have sufficient time to recharge the capacitors before the next transient event occurs, and therefore the voltage will decay towards zero slowly. I believe this is due to the slow nature of the voltage loop.
Does anyone have suggestions for control schemes which can act upon transient behaviour such as the above. I have also tried implementing a peak current mode inner loop and voltage mode outer loop, to no avail. I have not yet tried average current mode but I doubt it is much better. I had seen a suggestion to use digital control, with a PI controller for the current inner loop and a "PR" controller for the voltage outer loop.
Any other suggestions?
Does anyone have suggestions for control schemes which can act upon transient behaviour such as the above. I have also tried implementing a peak current mode inner loop and voltage mode outer loop, to no avail. I have not yet tried average current mode but I doubt it is much better. I had seen a suggestion to use digital control, with a PI controller for the current inner loop and a "PR" controller for the voltage outer loop.
Any other suggestions?