Caren Tischendorf

Structural analysis of electric circuits and consequences for MNA

The development of integrated circuits requires powerful numerical simulation programs. Naturally, there is no method that treats all the different kinds of circuits successfully. The numerical simulation tools provide reliable results only if the circuit model meets the assumptions that guarantee a successful application of the integration software. Owing to the large dimension of many circuits (about 107 circuit elements) it is often difficult to find the circuit configurations that lead to numerical difficulties. In this paper, we analyse electric circuits with respect to their structural properties in order to give circuit designers some help for fixing modelling problems if the numerical simulation fails. We consider one of the most frequently used modelling techniques, the modified nodal analysis (MNA), and discuss the index of the differential algebraic equations (DAEs) obtained by this kind of modelling. Copyright

Differential-algebraic equations : a projector based analysis

Notations.- Introduction.- Part I. Projector based approach.- 1 Linear constant coefficient DAEs.-.2 Linear DAEs with variable coefficients.- 3 Nonlinear DAEs.- Part II. Index-1 DAEs: Analysis and numerical treatment.- 4 Analysis.- 5 Numerical integration.- 6 Stability issues.- Part III. Computational aspects.- 7 Computational linear algebra aspects.- 8 Aspects of the numerical treatment of higher index DAEs.- Part IV. Advanced topics.- 9 Quasi-regular DAEs.- 10 Nonregular DAEs.- 11 Minimization with constraints described by DAEs.- 12 Abstract differential algebraic equations.- A. Linear Algebra - Basics.-.B. Technical Computations.- C Analysis.- References.- Index.

Elliptic Partial Differential-Algebraic Multiphysics Models in Electrical Network Design

In refined network analysis, a compact network model is combined with distributed models for semiconductor devices in a multiphysics approach. For linear RLC networks containing diodes as distributed devices, we construct a mathematical model that combines the differential-algebraic network equations of the circuit with elliptic boundary value problems modeling the diodes. For this mixed initial-boundary value problem of partial differential-algebraic equations a first existence result is given.

Stability preserving integration of index-1 DAEs

For index-1 DAEs with properly stated leading term, we characterize dissipative and contractive flows and study how the qualitative properties of the DAE solutions are reflected by numerical approximations. The best situation occurs when the discretization and the decoupling procedure commute. It turns out that this is the case if the relevant part of the inherent regular ODE has a constant state space. Different kinds of reformulations are studied to obtain this property. Those reformulations might be expensive, hence, in order to avoid them, criteria ensuring the given DAE to be numerically equivalent to a numerically qualified representation are proved.

On the stability of solutions of autonomous index-1 tractable and quasilinear index-2 tractable DAEs

ConclusionWe have seen that the stationary solutions of the regularized equations are asymptotically stable if the stationary solution of the original quasilinear index-2 tractable DAE is so. In other words, the given regularizations supply a solution sharing the stability properties of the solution of the unperturbed equation.

Recent Results in Solving Index-2 Differential-Algebraic Equations in Circuit Simulation

In electric circuit simulation the charge-oriented modified nodal analysis may lead to highly nonlinear DAEs with low smoothness properties. They may have index 2 but they do not belong to the class of Hessenberg form systems that are well understood. In the present paper, on the background of a detailed analysis of the resulting structure, it is shown that charge-oriented modified nodal analysis yields the same index as does the classical modified nodal analysis. Moreover, for index 2 DAEs in the charge-oriented case, a further careful analysis with respect to solvability, linearization, and numerical integration is given.

Finding Beneficial DAE Structures in Circuit Simulation

Circuit simulation is a standard task for the computer-aided design of electronic circuits. The transient analysis is well understood and realized in powerful simulation packages for conventional circuits. But further developments in the production engineering lead to new classes of circuits which may cause difficulties for the numerical integration. The dimension of circuit models can be quite large (105 equations). The complexity of the models demands a higher abstraction level. In this paper, we analyze electric circuits with respect to their structural properties. We discuss the relevant subspaces of the resulting differential algebraic equations (DAEs) and present algorithms for calculating the index as well as consistent initial values.

PDAE models of integrated circuits and index analysis

A coupled system modelling an electric circuit containing semiconductors is presented. The modified nodal analysis leads to a differential algebraic equation (DAE) describing the electric network. The nonlinear behaviour of the semiconductors is modelled by the drift diffusion equations. Coupling relations are defined and a generalization of the tractability index to systems of infinite dimensions is presented and applied to the resulting partial differential algebraic equation (PDAE). The PDAE turns out to have the same index as the electrical network equations.

Steady-State Behavior of Large Water Distribution Systems: Algebraic Multigrid Method for the Fast Solution of the Linear Step

AbstractThe Newton-based global gradient algorithm (GGA) (also known as the Todini and Pilati method) is a widely used method for computing the steady-state solution of the hydraulic variables within a water distribution system (WDS). The Newton-based computation involves solving a linear system of equations arising from the Jacobian of the WDS equations. This step is the most computationally expensive process within the GGA, particularly for large networks involving up to O(105) variables. An increasingly popular solver for large linear systems of the M-matrix class is the algebraic multigrid (AMG) method, a hierarchical-based method that uses a sequence of smaller dimensional systems to approximate the original system. This paper studies the application of AMG to the steady-state solution of WDSs through its incorporation as the linear solver within the GGA. The form of the Jacobian within the GGA is proved to be an M-matrix (under specific criteria on the pipe resistance functions), and thus able to be...

Model Order Reduction of Differential Algebraic Equations Arising from the Simulation of Gas Transport Networks

We explore the Tractability Index of Differential Algebraic Equations (DAEs) that emerge in the simulation of gas transport networks. Depending on the complexity of the network, systems of index 1 or index 2 can arise. It is then shown that these systems can be rewritten as Ordinary Differential Equations (ODEs). We furthermore apply Model Order Reduction (MOR) techniques such as Proper Orthogonal Decomposition (POD) to a network of moderate size and complexity and show that one can reduce the system size significantly.