Nonlinear feedback regulator design for the Cuk converter

The method of extended linearization is used to design stabilizing nonlinear proportional-integral feedback controllers which regulate to a constant set-point value the average output inductor current, the average input inductor current, or the average transfer capacitor voltage of a PWM (pulse width modulation) controlled Cuk converter. The design is carried out on the basis of the frequency domain Ziegler-Nichols method applied to a family of linearized transfer function models of the converter, parametrized by constant operating equilibrium points of the average PWM controlled circuit. Some simulation examples highlighting the nonlinear P-I controller performance are presented. The nonlinear controller scheme, as applied to the actual discontinuous PWM regulated Cuk converter, is shown to comply with the same qualitative stabilization features that are imposed on the average model design, provided the output feedback signal is properly processed through a low pass filter with a small cut-off frequency and a sufficiently high sampling frequency is used in the PWM actuator