Lucian Mandache

Aspects Concerning the Simulation of Active Filters Used in Urban Transportation Substations Using SPICE

The paper presents some of the active filters topologies used for the improving of power quality. One presents some recordings and numerical simulations made over the electric signals from a substation used for the supplying of a d.c. line of 600 V. Based on the obtained results one proposes solutions for active compensations with the consideration of a number of filtering components. In order to verify the compensation efficiency, through SPICE simulation one estimates the effects of compensation. One can also notice a power factor correction effect through the displacement of the filtered current waveform in advance relative to the initial current.

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.

Practical aspects on the improved DC driving system used in electric urban traction

The paper presents some practical considerations and experimental results obtained by the exploitation of a tram that has an electric driving system with an improved technological solution. One presents the technological solution using chopper that substitutes the initial accelerators of the tram. Some aspects concerning the operation in running and respectively in braking regimes in the new configuration (including the regenerative braking regime) are discussed. Some considerations with respect to the electromagnetic compatibility problems and modalities to improve it are made. The recordings of the current and voltage waveforms, during the normal running stage, when the tram climbs a ramp and respectively goes down on a slope are presented and explained. The experimental determinations revealed that the system was designed correctly, in order to support all the operational conditions that could appear in its exploitation.

An Accurate Design Tool for Filter Inductors

The paper is focused on a new and accurate design tool which uses a high precision model for nonlinear lossy ferromagnetic cores. It can be easily included in a time-domain circuit simulator, like SPICE, being suitable to simulate any saturable inductor operating in any distorting regime at low or medium frequencies such cases are found in power electronics applications. The model uses as entry data the geometric dimensions of the magnetic core including air-gaps, the magnetic material properties given by the manufacturer data sheet and the winding constructive parameters. Therefore, the correspondence with the real device is realistic and undoubted. The proposed modeling technique takes its mathematical root from the Maxwells theory. The simulation results give time-domain flux distribution in the magnetic core, the total core losses, as well as any working parameter of the circuit which includes the magnetic device. Experimental results obtained on a single phase inductor are compared with the obtained simulation results. Excellent concordance between both results is demonstrated in this paper.

High Precision Modeling of Nonlinear Lossy Magnetic Devices

The paper proposes a high efficiency and totally feasible tool that permits a rigorous study of magnetic devices, being intended firstly to the research and design activity. The method uses the most modern tools in circuit analysis, being a result of a long-time experience of authors. It deals with an accurate modeling that permits to find the distribution of magnetic fluxes everywhere in the core, at any time. The modeling is made through an equivalent electric circuit described by the same differential-algebraic equation system as the studied device in transient regime. Therefore, this circuit is analyzed using dedicated software, like SPICE. Such software has special capabilities to prevent convergence problems that usually occur in nonlinear DAE solving, as well as performing optimizations of certain parameters. The method permits not only the rigorous study of the magnetic device, but additionally a high precision analysis of complex equipments that contain magnetic devices

New high precision harmonic analysis method for power quality assessment

The power quality is one of actual major problems in electrical engineering. Generally, power electronics equipments damage power quality parameters, disturbing radio communications or the functionality of other equipments. A rigorous design of most appropriate filters for power quality improvement is possible only through a high precision analysis that allows estimating power quality parameters and the influence of each harmonic component on the network-drive system. Actual industrial equipments intended to perform spectral analysis are not appropriate for strongly deformed signals, with frequent discontinuities, as in power electronics. Our paper presents a new and accurate method of harmonic analysis that permits to mitigate most of power quality related problems. The principle is to estimate intermediate points between the initial samples given by the available data acquisition system; therefore, the Fourier coefficients are estimated more precisely using the fast Fourier transform. As interpolation technique we chose the reconstruction of the analog signal using an ideal lowpass filter. The excellent results are validated on a pair of synthesized signals having known harmonic spectrum

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.

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.