Control art of switching converters

Citation

Smedley, Keyue Ma (1991) Control art of switching converters. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/TQG2-GK48. https://resolver.caltech.edu/CaltechETD:etd-06062005-152649

Abstract

Switching Flow-Graph Model:

The Switching Flow-Graph is a unified graphical model of large-signal, small-signal and steady-state behavior of pulse-width-modulated (PWM) switching converters. Switching branches are introduced into the flow-graph to represent the switches of the PWM switching converters. The Switching Flow-Graph model is easy to derive, and it provides a visual physical understanding of switching converter systems. The small-signal Switching Flow-Graph generates analytical transfer functions and the large-signal Switching Flow-Graph is compatible with the TUTSIM simulation program. The Switching Flow-Graphs of PWM switching converters reveal a regular pattern, and they predict right-half-plane (RHP) zeros, caused by the imbalanced effects of the duty-ratio control signal on the output of the switching converters. Criteria are found for the design of damping circuits that are capable of eliminating RHP zeros. General models are derived for current-mode controlled switching converters. In addition, the large-signal model and the small-signal model are verified by experiments.

One-Cycle Control Technique:

The One-Cycle Control technique is conceived to control the duty-ratio d of the switch in real time such that in each cycle the average of the chopped waveform at the switch output is exactly equal to the control reference. Implementation circuits are found for any type of switch, constant frequency, constant ON-time, constant OFF-time, and variable. One-Cycle Control fully rejects the input signal, and linearly all passes the control signal. This technique turns a nonlinear switch into a linear one. Experiments were conducted using the One-Cycle Control technique on the buck converter and the Cuk converter. One-Cycle Control was found to reject input perturbations and input filter dynamics. The diode voltage of One-Cycle Controlled converters follows the control reference instantaneously in one cycle. One-Cycle Control takes advantage of the pulsed and nonlinear nature of switching converters to achieve instantaneous control of the average value of the diode voltage. This technique is suitable for large-signal control of PWM switching converters and quasi-resonant converters.

Thesis Files