Ioana-Gabriela Sirbu

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.

A novel model of DC series motor based on electrical equivalent circuit

This paper proposes a novel model of dc series motors. The dependency between the field flux and current was replaced by the magnetic circuit of the motor. The magnetic circuit is modeled by electrical equivalent circuit which has nonlinear elements depending on the saturation and hysteresis phenomena. The nonlinear model of the dc motor considers also the nonlinear dependency of the load torque on the speed. The proposed model can be adapted easily to the constructive specific features of any dc motor. The results of the simulations realized in SPICE proved to be in very good agreement with the previous theoretical and experimental results.

About the experimental results of an electric driving system based on asynchronous motor and PWM converter

The paper deals with special features related to the a.c. electric driving system of a trolley-bus. One presents the driving system consisting of an asynchronous motor and inverter and some aspects regarding the PWM inverter control. The tests over the manufactured asynchronous motor were performed at a frequency equal to 50 Hz (for the rated speed) and a frequency equal to 106.6 Hz corresponding to a synchronous speed equal to 3200 rpm. The inverter was separately tested, before its inclusion in the driving system and some of the tests results presented (heating tests for the main components, the behavior at the discontinuous variation of line voltage, a.o.). Some tests concerning the behavior of the entire system at forward and backward running regimes are also presented.

On electric vehicle wireless chargers with tight coupling

Recently the information from industry shows that inductive power transfer electric vehicle chargers that use tight coupling between the inductive coupler coils were achieved. This paper includes a theoretical and experimental study on the possibilities that tight coupling offers versus loose coupling - widely used so far - in what concerns the ratio between the output transmitted power and the efficiency of the input-output transfer. The obtained results allowed defining a preferred domain for the coupling factor that provides a transfer efficiency of about 90% at load powers adequate for the electric vehicle chargers.

Comparative study of the frequency splitting and bifurcation phenomena for equivalent circuits of the wireless power transfer system

This paper presents a study of the frequency splitting and bifurcation phenomena in the wireless power transfer systems. Using electric circuit model methods and mathematical calculus, the two phenomena are analyzed for all the possible configurations of the coupled circuits, i.e. seriesseries, series-parallel, parallel-series and parallel-parallel. For a specific case including two identical printed coils, for each configuration some characteristics are represented graphically and the appearance of each phenomenon is commented. The analytical results and the numerical simulations are correlated and commented comparatively, in order to obtain useful conclusions.

On the electric field simulation in the electrostatic precipitators

This paper analyses the distribution of the electric field in an electrostatic precipitator through simulation techniques. For this reason the finite volume method is used. The computational program, created in MATLAB, considers the nonuniform distribution of the electrical charge density. The technique used to estimate the charge density in every point of the computational domain is similar to that used for the determination of electrostatic potential. This analogy was possible based on the observations made by analyzing the computational and experimental results obtained by other scientists and published in their previous works. So our computational model calculates both charge density and electrical field distributions using almost the same numerical techniques. The results are presented in a comparative manner. Both constant and variable charge density distributions were considered in the electrical potential and the electric field strength calculations. Also they were compared with results obtained by using a commercial program, QuickField Professional, that uses finite element method to calculate the electric field, but only for a constant value of the electrical charge density. Finally the error calculation was done. Its maximum value proved to be less than 1 %; this remark permits to formulate some conclusions. The results obtained by using our program are in good agreement with those obtained and published by other researchers.

Comparative analysis of different topologies for wireless power transfer systems

In the last years the use of the wireless power transfer systems has experienced a significant increase. In this context the study of the behavior of these systems has been the subject of debate for many researchers, in order to understand and improve their performances. This paper aims to bring a contribution in this regard. Based on previous studies, the paper makes a comparative analysis of three possible topologies met in wireless power transfer systems with inductive coupling, namely: series-series, series-parallel and parallel-parallel. Input and output quantities of the system are mainly represented here, for highlighting the conditions in which high performances are achieved. Finally important conclusions for practice are formulated.

On the power transfer in series-series magnetically coupled circuits with non-matched natural frequencies

The paper proposes to analyze series-series magnetically coupled circuits that include circuits with different natural frequencies. An analytical-numerical calculation on this configuration of coupled circuits was realized. The work was centered on obtaining those frequencies that characterize the extreme points of the load active power - frequency characteristic. The mathematical calculus was correlated with the calculation based on the electrical circuit theory, thereby underlining its usefulness and its accuracy. This study may prove to be extremely useful in practice, finding an especial utility in designing and in the optimization of the wireless power transfer systems.

Aspects on a transportation system operating in normal and short circuit regimes

This paper relies on the development of a model for an urban electric transportation system. This model is used to simulate the system operation both in normal and abnormal (short circuit) regimes. The simulation results are compared with the results of some theoretical studies presented in the technical literature and also with some experimental results. Unlike the theoretical idealized studies our model offers more realistic results that are comparable with those offered by the system under real operating conditions.

The circuit analysis of a step-down DC-DC converter under ideal and real passive components assumption

This paper focuses on the differences between an ideal and a real electrical circuit diagram of a step-down dc-dc converter and their influences on the converter operation. For each diagram the circuit equations are obtained, processed accordingly and implemented in new created programs. The resulted waveforms are discussed and some conclusions are depicted.