State variable stability analysis of multi-loop PWM controlled dc/dc regulators in light and heavy mode

Stability analysis and transient response predictions of PWM controlled dc/dc regulators are now feasible in both continuous and discontinuous modes. A linear equivalent continuous model of the power stage is first established for the boost and the buck converter by means of state variable representation for each of the elementary structures occurring within one sampling period. This equivalent model turns out to be of first order for the discontinuous mode and of second order for the continuous mode. A general computer program has been implemented for the derivation of such a model and for the stability analysis and transient response of multiloop regulators. Special emphasis has been given to the boost converter in light conduction mode operation whether or not an ac feedback loop is included. The existence of the nonminimum phase effect associated with such a regulator for a heavy operation mode is shown to be dependent on the sampling frequency.