A normalized digital compensator for variable frequency PWM

Implementing variable frequency modulation using low-cost digital signal processors introduces two main design issues: variability in the converter response due to the modulator delay, and a widely varying controller response due to the changing sampling period. While the first issue has been modeled several times in literature, the second has been largely ignored, and becomes an even greater issue as the frequency range is increased. As a solution, a digital compensator with adaptive gains that is normalized against frequency variations is proposed. A method for calculating the coefficients is also provided, along with a theoretical analysis of the converter frequency response. The frequency-normalized compensator is then implemented on a 180W prototype dc-dc converter, and the improvements in converter stability and system bandwidth are verified experimentally using a frequency response analyzer. For a frequency range of 25–75kHz, bandwidth improvements of up to 300% are shown for the prototype system.