Valentin Navrapescu

Single-Phase Unified Power Quality Conditioner with Optimum Voltage Angle Injection for Minimum VA requirement

The paper deals with an optimized Unified Power Quality Conditioner (UPQC), which aims at the integration of series and shunt active power filters with minimum VA loading of the UPQC. The series active filter is a Dynamic Voltage Restorer (DVR), that operates in two functioning modes. During the unbalanced voltage sag/swell at the input side, the DVR maintains the rated voltage at the load side. It regulates the load voltage with minimum VA loading of the overall UPQC by an optimum voltage angle injection. A technique of achieving both input current distortion compensation, power factor correction and also mitigating the supply-voltage variation (sag/swell) at the load side, is presented as well. To reduce the total cost, but to increase the performance, the system is fully digital-controlled using the fixed-point TMS320F240 digital signal processor. The present paper discusses the VA requirement issues of the proposed UPQC. The performances of the optimum UPQC have been verified on an experimental prototype.

Dynamic Simulation of the Transverse Flux Machine using Linear Model and Finite Element Method

Basically, there are two developments in the field of transverse flux machines, without or with permanent magnets as excitation. Since the main feature of transverse flux machine is the high thrust force density, the linear motor topology including also permanent magnets as excitation is the most promising one. Because the transverse flux machine flux pattern is complicate due to the nonlinearities introduced by the iron core saturation and permanent magnet operating point, the system analysis is not possible by using exact analytical relation. Therefore, the flux linkage and thrust force must be computed via 3D-nonlinear Finite Element Method-FEM, including the obtained results into the linear motor base model using SIMULINK. To have a more realistic approach of the overall drive system, this way is proposed in the paper for dynamic simulation. The dynamic simulation of the two kind of linear motors is presented, in order to demonstrate the advantage of the proposed transverse flux linear motor including permanent magnets over the electrically excited one, as well. The compared results of dynamic simulation are very useful for studying and analyzing different control methods that can be approached for linear motors. The simulation results show the good dynamics and high accuracy of the system model.

On the model of a Hybrid Step Motor

The paper presents numerical simulation results and experimental data used for modeling a hybrid step motor (HSM). Two different HSM models have been developed starting from available technical data of a HSM (2-phase, bipolar, frame size 56.4 mm). One of the models is adequate for analyzing the HSM response to different control strategies, while the second one can be used for performing an electromagnetic field analysis.

Modelling of iron losses in salient pole permanent magnet synchronous motors

Today, for the same rated power and speed electrical drives we have a strong competitor to the induction motors. This one it is represented by permanent magnet synchronous motors (PMSM) with salient pole rotors. In this paper are presented dedicated analytical and numerical models for the iron loss effect over the motor performance. It is presented a comprehensive comparison between no-load and loaded conditions test data for all the models presented.

Magnetic materials in design and construction of electrical motors

Electromechanical steels, currently used in the manufacture of electrical machines possess high induction of magnetic saturation (Bs/spl sim/2T), low coercive force (Hc<100 A/m), and they are characterised by low total losses P (1,5/50)=1-3 W/kg. The soft magnetic composite materials are characterised by their high losses (7-10 W/kg), due to the vortex flow, stimulated by the absence of interfaces between the magnetic circuit components. In the case of polymeric bound materials, the losses due to mixing are of the order 5-8 W/kg. To gain maximum benefit from the manufacturing of small electrical machines by using soft magnetic material, it is important to choose the suitable material for every application. Excellent high frequency performance, a similar average performance for several types of electrical machines, and an important cut in the manufacturing expense (material loss, simple technology) are the main characteristics for a soft magnetic material core made electrical motor. The paper presents the comparison between two single-phase motors, with a magnetic core manufactured with laminated steels, and soft magnetic composite materials respectively. The geometrical dimensions are identical.

A new five-level voltage-source-inverter using unidirectional switching cells and a coupled-inductor

Recently, a new five-level (5L) inverter has been developed. It is named 5L-USC1 and was based on the use of four 2L unidirectional switching cells (USC) and a coupled-inductor (CI) for each phase. This topology was derived from three-level Neutral-Point-Clamped (3L-NPC) inverter. In the paper a new 5L inverter based on basic USC is presented. It is named 5L-USC3 and is based on the use of six 2L unidirectional switching cells and a coupled-inductor for each phase. The proposed topology is derived from 3L-Active-NPC inverter by separation the bidirectional switching cells into two USC groups. The new 5L topology has more degrees of freedom in comparison with the recent 5L-USC1 inverter. As a result, the apparent switching frequency of the output voltage is four times the switching frequency of power devices and so, the current ripple is reduced by half. The apparent switching frequency in each inductor winding is twice the switching frequency of the power devices and thus, the magnetically coupled-inductor windings are considerably reduced.

Thermal study of induction machine using Motor-CAD

The paper presents thermal studies of three-phase induction motor during steady-state and transient regimes using Motor-CAD environment. The graphical interfaces for data input (motor geometry, materials properties) are also shown. The supposed duty cycles are S1, S2, and S3 (continuous, short-time and intermittent periodic duty respectively). As output data the temperatures for various motor parts (housing, stator windings, squirrel-cage rotor windings) are obtained.

CAD for three phase ONAN cooling system transformers

This paper presents a Computer-Aided Design method for a three phase power transformer using MATLAB programming environment. The considered transformer is Oil Natural Air Natural cooling system type. During the designing by changing the value of just one single variable implies to recalculate everything. Such operation is time consuming but this drawback can be overcome by fully automating the design procedure, for example using MATLAB. The developed program is written in script format so that it can be easily modified to fit the imposed parameters of the transformer. The designing algorithm of the transformer has been optimized. Thus, it has ten steps with nine validation checkpoints. It may also be used as an educational model. The validations are implemented into the code and are required because there is no sure-fire method for designing a transformer from the first attempt. During the design it is necessary to change various values. Thus, only when all nine verifications are satisfied one may conclude that the transformer is well designed.

Method for estimating the lifetime of electric motors insulation

In this paper we present the results of a study over the aging and the estimating lifetime of a new insulation system for a DC motor. In order to achieve the lifetime experiments, a group of 7 motorettes (made under IEC 60216-1) have been subjected to accelerated thermal aging at T = 260 ° C (for 1000 hours), followed by their requests to vibrations (1 hour) and humidity (48 hours). At every 200 hours were measured the insulation resistance, the losses factor and the electric capacity of motorettes, then these were tested in the AC withstand test voltage (600 V). The activation energy of oxidation of the enamel used as insulator of the conductors has been determinated by Differential Scanning Calorimetry (DSC). Considering as a diagnostic factor the insulation resistance and using the activation energy value determined by DSC the lifetime line to constant stress and then, the lifetime values for different temperatures were determined.

Educational platform for working with programmable logic controllers

The restructuring and the reorganization of the educational teaching system has comprehended not only the academic teaching curriculum and management system but also the teaching methods. Educational platforms and virtual laboratories are increasingly becoming a key component during the teaching process especially for technical teaching. Although the existence of virtual laboratories and e-learning platforms can be very useful tools for electrical engineering in particular they will never replace real laboratories. The main reason is that using real educational platforms the students have the opportunity to become familiar with the basic principles and real elements of a particular area. Moreover, they can develop various complex applications and test their behavior. In the end, the main objective is that the present students - future engineers should be able to both operate real world systems and implement designed solutions that are likewise the teaching platforms. In this vein it is proposed a platform based on the programmable logic controllers (PLC) technology that has not been done so far. It is designed to be open enabling to add new modules and features. While the considered platform is based on a specific brand of PLC it can be very easily adapted without major technical issues to other brands.