Publication Date

2011

Document Type

Thesis

Committee Members

Marian Kazimierczuk (Advisor), Marian Kazimierczuk (Committee Chair), Saiyu Ren (Committee Member), Zhang Xiaodang (Committee Member)

Degree Name

Master of Science in Engineering (MSEgr)

Abstract

Current-mode control is the most popular scheme used for the operation of SMPS (Switch Mode Power Supplies). Current-mode control, also known as current-programmed mode or current-injected control is a multi-loop control scheme that has an inner loop and an outer voltage loop. The current loop controls the inductor peak current while the voltage loop controls the output voltage. The inner loop follows a set program by the outer loop. Some of the most popular small-signal models that predict the small-signal characteristics of current-mode control scheme have been analyzed and compared in this thesis. A PWM dc-dc buck converter in CCM(Continuous Conduction Mode) has been chosen to explain the phenomenon of current-mode control in all these models. Small-signal characteristics are generated in MATLAB using the simplified analytical transfer functions. Some of the important small-signal characteristics include the current loop gain, control-to-output gain with the current-loop closed and outer loop open, audio susceptibility, and output impedance. The two most important models in consideration are: 1) Continuous-Time Model and 2) Peak Current-Mode control Model. Despite the fact that both these models predict the instability of current-mode control at a duty ratio of 0.5, these models differ significantly in deriving the expression for the sampling gain. As a result, their small-signal characteristics differ over a wide frequency range. Also, a very less explored average current mode control is compared with the peak-current mode control based on the similar small-signal characteristics.

Page Count

96

Department or Program

Department of Electrical Engineering

Year Degree Awarded

2011

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