Citation
Tan, Fang Dong (1994) Modeling and control of switching converters : I. Unified modeling and measurement of currentprogrammed converters. II. A generic averaged model for switches in dctodc converters. Dissertation (Ph.D.), California Institute of Technology. http://resolver.caltech.edu/CaltechETD:etd12072007113216
Abstract
NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document. Part I A unified model is established for a currentprogrammed converter, which unifies and extends previous models. A lowfrequency modification leads to a unified dutyratio control law for the buck, the boost, and the buck/boost converters, which results in improved predictions for several essential quantities of the currentloop gain. Inclusion of the sampling effect allows the presence of an additional pole [...] in the currentloop gain to be derived. The resulting final doubleslope asymptote is fixed in position, and the crossover frequency cannot exceed half the switching frequency. Two parameters are found to be central quantities of interest. A parameter [...] represents the minimum value of D', the complementary duty ratio, to maintain stability of the current loop, and shows explicitly the stabilizing effect of a compensating ramp. A "stability parameter" [...] determines the additional pole [...] and describes the degree of peaking in the closedloop transfer functions. Experimental verification employs an analog signal injection technique, which is easier to use, and contains more information about highfrequency dynamics than a conventional digital signal injection technique. Part II A generic averaged model for switches in dctodc converters is established for the first time by using, in addition to averaging, voltsecond and ampsecond balance equations. The generic model inherits advantages of previous models and extend then to a new height: switches in dctodc converters can now be handled as lineartimeinvariant twoterminal circuit elements for their lowfrequency characterizations. It is shown that the generic model is equivalent to the canonical circuit model from statespace averaging when it is substituted into a particular converter. It is also shown that the model for PWM switches is a special case of the generic model. A theoretical discussion about the equivalent duty ratio [...] reveals that averaging can retain lowfrequency information contained in the original quantity regardless of its ripple content. The conditions are that the dc value of the original quantity is not vanishingly small, and the perturbation frequency is limited to half the switching frequency for amplitude perturbation or to a quarter of the switching frequency for frequency perturbation. Extensions of the generic model to converters with isolations, in discontinuous conduction mode, in current programming, and in other modes of operation are obtained. The concept of equivalent duty ratio is found useful. One salient feature of the extended generic model, which distinguishes it from similar previous models, is that different versions of the model have exactly the same form. The invariance of the form of the model is extremely useful for computer simulations of the averaged large and smallsignal dynamics in dctodc converters under various modes of operation. One important feature of the approach, which separates it from all previous modeling approaches, is that its application is not limited by the number of switches in a converter. A threeswitch converter is analyzed to show key steps in the derivation of a generic model for converters with multiple switches. Experimental results support the predictions from the generic model for the threeswitch converter.
Item Type:  Thesis (Dissertation (Ph.D.)) 

Subject Keywords:  switching converters, electrical engineering, unified model, current programmed converters, currentmode control, sampling effect, current loop gain 
Degree Grantor:  California Institute of Technology 
Division:  Engineering and Applied Science 
Major Option:  Electrical Engineering 
Thesis Availability:  Public (worldwide access) 
Research Advisor(s): 

Thesis Committee: 

Defense Date:  10 November 1993 
Record Number:  CaltechETD:etd12072007113216 
Persistent URL:  http://resolver.caltech.edu/CaltechETD:etd12072007113216 
Default Usage Policy:  No commercial reproduction, distribution, display or performance rights in this work are provided. 
ID Code:  4848 
Collection:  CaltechTHESIS 
Deposited By:  Imported from ETDdb 
Deposited On:  14 Dec 2007 
Last Modified:  26 Dec 2012 03:12 
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