Mihai Iordache

Modeling and Characterization of Oscillator Circuits by Van der Pol Model using Parameter Estimation

In this paper, we present a new method for the modeling and characterization of oscillator circuit with a Van Der Pol (VDP) model using parameter identification. We also discussed and investigated the problem of estimation in nonlinear system based on time domain data. The approach is based on an appropriate state space representation of Van der Pol oscillator that allows an optimal parameter estimation. Using sampled output voltage signal, model parameters are obtained by an iterative identification algorithm based on Output Error method. Normalization issues are fixed by an appropriate transformation allowing a quickly global minimum search. Finally, the proposed estimation method is tested and validated using simulation data from a 1 GHz oscillator circuit in GaAs technology.

Circuit analysis of frequency splitting phenomena in wireless power transfer systems

The paper treats the wireless power transfer systems with series-series resonators from the point of view of the frequency splitting and bifurcation phenomena. We develop an exact mathematical model of the splitting phenomena (splitting equation) based on the algebraic equation theory, which allows finding exact values of the splitting frequencies. This is extremely useful to setup the magnetic coupling for any connection of the wireless power transfer systems. It is also investigated the variation of the splitting frequencies and the transferred power peaks in function of the magnetic coupling. The exact analysis of the frequency bifurcation phenomena is also studied and the relationship between frequency bifurcation and splitting is elucidated. It is also found an exact mathematical procedure, based on the algebraic equation theory, which allows finding exact values of the bifurcation coupling and the bifurcations frequencies. The theoretical results are validated by numerical simulations based on frequency analysis with different values of the system parameters and by a 10-W prototype with planar spiral coils [10].

On wireless power transfer

The paper is a general survey on power transfer by induction. The physical principle is pointed out and the constraints for an optimal operation applied both to the emitter and receiver are specified. Couple mode theory is used to study the wireless power transfer and a comparison with the circuit theory results is made. The analysis is focused on the power transfer efficiency in connection with the mutual inductance. An accurate method for mutual inductance computation is presented and the power transfer optimization is performed for different geometrical configurations which involve different mutual inductances.

SPICE model for effective and accurate time domain simulation of power transformers

The paper proposes an effective time-domain modeling and simulation strategy of power transformers, using the SPICE circuit simulator. The nonlinear phenomena of the iron core are carefully considered, including saturation, static hysteresis and eddy currents. The principle of magnetic circuit modeling is based on analog lumped equivalent circuits and the SPICE implementation uses the principle of modularity. Such a module includes a transformer winding and its core leg together with the ferromagnetic phenomena. The method allows simulating normal operation modes, as well as critical transients and faulty conditions, the simulation result containing all electromagnetic quantities as time-domain functions. The method is remarkable through its extremely short computation time and reasonable accuracy, it being conceived firstly as useful tool for design purposes.

TIME DOMAIN DIAKOPTIC ANALYSIS BASED ON REDUCED-ORDER STATE EQUATIONS

In this paper we present some new tearing techniques to systematically formulate the state equations in symbolic normal-form for linear and/or nonlinear time-invariant large-scale analog circuits. The excess elements of the first and of the second kind are unitarily treated in order to allow a symbolic representation of the circuit with a minimum number of state variables. A procedure to reduce the state equation number of each subcircuit is also presented. The reduced-order is based on an implicit integration algorithm and on the successive elimination of the selected state variables. Examples are given to illustrate the decomposition procedure, the assignment of the connection sources and the reduced-order technique.

On the time-domain analysis of analog circuits containing nonlinear inductors

The paper proposes effective solutions to include nonlinear inductors with soft ferromagnetic core in the time-domain circuit analyses. Three inductor models are developed, tested and compared. They are conceived for different degrees of accuracy related to the real devices. The models are robust and reliable due to the modeling concept that avoids numerical instabilities. An enhanced inductor model can serve to numerical analyses aiming the optimization of some constructive parameters (as the airgap length or number of turns). A SPICE implementation was performed and exemplified for different operation conditions.

A new approach to the computation of reduced order models for one-port and two-port RC circuits

A method for the computation of a reduced order circuit model, based on the approximation of |Y(jomega)| with a set of assymptotes corresponding to a simple RC admittance is presented. The circuit passivity is preserved unlike the majority of other approaches. A 1033 node RC circuit is reduced to admittance with one pole and two zeros for a frequency range of three decades

On exact circuit analysis of frequency splitting and bifurcation phenomena in wireless power transfer systems

The paper is focused on the exact analysis of the frequency splitting and bifurcation phenomena in the wireless power transfer (WPT) systems with series-parallel, parallel-series and parallel-parallel resonators. Starting from the analysis in sinusoidal behavior of a WPT system we build, using the algebraic equation theory, the exact splitting mathematical model for any connection of the WPT systems and whether this phenomenon exists or not. It is also investigated the exact analysis of the frequency bifurcation phenomena and the relationship between frequency bifurcation and splitting for all connections named before. In this way it is possible to find exactly the splitting and bifurcation couplings. The splitting and bifurcation frequencies and the load power peak curves are computed with respect to the constructive parameters of the system. Finally, the theoretical results are validated by numerical simulations.

SPICE Model for Fast Time Domain Simulation of Power Transformers, Exploiting the Ferromagnetic Hysteresis and Eddy-Currents

The paper proposes an effective time-domain modeling and simulation strategy of power transformers, using the SPICE circuit simulator. The nonlinear phenomena involved by the iron core are carefully considered, including the nonlinearity with saturation, static hysteresis and eddy currents. The principle of magnetic circuit modeling is based on analog lumped equivalent circuits and the SPICE implementation uses the principle of modularity. Such a module includes one transformer winding (either primary or secondary) and its core leg, implemented as a subcircuit with user-defined parameters. The method allows simulating normal operation modes, as well as critical transients and faulty conditions, the simulation result containing all electromagnetic quantities as time-domain functions. It is remarkable through its extremely short computation time and reasonable accuracy, it being conceived firstly as useful tool for design purposes, especially for repeated simulations required by optimization algorithms. A case study is presented to prove the feasibility, usefulness and accuracy of the proposed modeling and simulation approach, where the SPICE results are validated by experimental ones.

On analog circuit parameter estimation

Our paper presents a new method to estimate the analog circuit parameters based on some measurements performed on the real circuit, the parameters of interest being those which are difficult or impossible to be measured directly. Starting from the equivalent scheme of an analog circuit in sinusoidal behavior, we generate the network function in full symbolic form, obtaining an appropriate frequency space representation based on the complex or Laplace modified nodal equations. The magnitude and the phase of the complex transfer function can be measured by supplying the circuit with a variable frequency sinusoidal voltage. Using the measured parameters as reference and the symbolic transfer function computed before, the model parameters of interest are obtained by an iterative identification algorithm based on Output Error method. In this paper are defined two new objective functions which can be minimized using one of the fminimax or fminunc functions from the Matlab toolbox. Both algorithms are based on iterative computation starting from certain initial values, being efficient for less than four estimated parameters. The algorithms are suitable for linear circuits, as well as for small-signal nonlinear circuits. Finally, the proposed estimation techniques were tested and validated on simulation data on an illustrative example.