Trade-Offs in Current PI Controllers Design for Switching Power Converters

Proportional-Integrative (PI) controllers are probably the simplest yet most commonly-employed current control loop regulators in switching power conversion systems. Usually, crossover frequency of the current loop (and hence the controller gain) is maximized under tolerated phase margin constraint, yielding tracking step response with the shortest possible rise time. Controller zero location is then typically placed a decade below the crossover frequency to reduce the influence of controller phase on the phase margin. On the other hand, infinite amount of PI controller coefficient sets satisfying a given phase margin requirement exist in general. Consequently, the paper explores the whole feasible controller design space, revealing that current loop crossover frequency maximization does not necessarily yield the best disturbance rejection in terms of the commonly adopted Integral Time Absolute Error (ITAE) criteria. Methodology for obtaining the set of PI controller coefficients yielding ITAE-optimal disturbance rejection is proposed and accurately validated by time-domain simulations.