3 research outputs found
Transcritical bifurcation without parameters in memristive circuits
The transcritical bifurcation without parameters (TBWP) describes a stability
change along a line of equilibria, resulting from the loss of normal
hyperbolicity at a given point of such a line. Memristive circuits
systematically yield manifolds of non-isolated equilibria, and in this paper we
address a systematic characterization of the TBWP in circuits with a single
memristor. To achieve this we develop two mathematical results of independent
interest; the first one is an extension of the TBWP theorem to explicit
ordinary differential equations (ODEs) in arbitrary dimension; the second
result drives the characterization of this phenomenon to semiexplicit
differential-algebraic equations (DAEs), which provide the appropriate
framework for the analysis of circuit dynamics. In the circuit context the
analysis is performed in graph-theoretic terms: in this setting, our first
working scenario is restricted to passive problems (exception made of the
bifurcating memristor), and in a second step some results are presented for the
analysis of non-passive cases. The latter context is illustrated by means of a
memristive neural network model
Associate submersions and qualitative properties of nonlinear circuits with implicit characteristics
We introduce in this paper an equivalence notion for submersions ,
open in , which makes it possible to identify a smooth planar curve
with a unique class of submersions. This idea, which extends to the nonlinear
setting the construction of a dual projective space, provides a systematic way
to handle global implicit descriptions of smooth planar curves. We then apply
this framework to model nonlinear electrical devices as {\em classes of
equivalent functions}. In this setting, linearization naturally accommodates
incremental resistances (and other analogous notions) in homogeneous terms.
This approach, combined with a projectively-weighted version of the matrix-tree
theorem, makes it possible to formulate and address in great generality several
problems in nonlinear circuit theory. In particular, we tackle unique
solvability problems in resistive circuits, and discuss a general expression
for the characteristic polynomial of dynamic circuits at equilibria. Previously
known results, which were derived in the literature under unnecessarily
restrictive working assumptions, are simply obtained here by using
dehomogenization. Our results are shown to apply also to circuits with
memristors. We finally present a detailed, graph-theoretic study of certain
stationary bifurcations in nonlinear circuits using the formalism here
introduced
Homogeneous Models of Nonlinear Circuits
This paper develops a general approach to nonlinear circuit modelling aimed
at preserving the intrinsic symmetry of electrical circuits when formulating
reduced models. The goal is to provide a framework accommodating such
reductions in a global manner and without any loss of generality in the working
assumptions; that is, we avoid global hypotheses imposing the existence of a
classical circuit variable controlling each device. Classical (voltage/current
but also flux/charge) models are easily obtained as particular cases of a
general homogeneous model. Our approach extends the results introduced for
linear circuits in a previous paper, by means of a systematic use of global
parametrizations of smooth planar curves. This makes it possible to formulate
reduced models in terms of homogeneous variables also in the nonlinear context:
contrary to voltages and currents (and also to fluxes and charges), homogeneous
variables qualify as state variables in reduced models of uncoupled circuits
without any restriction in the characteristics of devices. The inherent
symmetry of this formalism makes it possible to address in broad generality
certain analytical problems in nonlinear circuit theory, such as the
state-space problem and related issues involving impasse phenomena, as well as
index analyses of differential-algebraic models. Our framework applies also to
circuits with memristors, and can be extended to include controlled sources and
coupling effects. Several examples illustrate the results.Comment: Updated versio