A ripple theorem for PWM DC-to-DC converters operating in continuous conduction mode

It is well known that the switching ripple information is lost in a linearized average model of a PWM converter. In this work it is shown that the switching ripple component of any state in a PWM DC-to-DC converter operating in continuous conduction mode can be recovered with remarkable accuracy from the linearized, average, small-signal model of the converter by replacing the duty-ratio control signal, D_s, with the AC component of the switching PWM drive signal, D_s(t)-D, in the control-to-state transfer function. The theorem is very useful for estimating the peak-to-peak ripple in any state of a converter and is used here to determine, for the first time, the actual ripple in the zero-ripple, coupled Cuk converter as a function of the load.