Monthly Archives: December 2015

Numerical Determination of Inductance of a SMES Device Using the Response Surface Methodology Applied on FEM Modeling

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Abstract 

The paper proposes the determination of the inductance of a Superconducting Magnetic Energy Storage (SMES) device with modular toroid coil based on a new 2-D FEM modeling using the response surface methodology (RSM) applied on 3-D FEM modeling. An earlier 2-D FEM modeling of a SMES device created in FEMM software is based on the assumption of the equality between the inductances of the complete circular cross section toroid and of the rectangular cross section toroid, providing an approximationfor the depth of planar model which does not take into account the leakage magnetic flux. Therefore a 3-D model of real geometry was realized using ANSYS software to improve this approximation. Imposing the equality of the magnetic field energies in 2-D and 3-D simulations, a new value for depth of 2-D FEM planar modeling is derived as
polynomial regression of second order of the 3-D results, based on two factors characterizing the geometric torus shape: the coil inner diameter ratio and the coil thickness ratio. The application of analysis of variance (ANOVA) and the computation of some adjusting coefficients prove the descriptive and predictive power of this model. The inductances of different configurations of SMES device derived from the new 2-D FEM modeling are compared to those based on the earlier 2-D FEM modeling and on the 3-D
FEM modeling. The results indicate an underestimation of the depth of the earlier 2-D FEM planar modeling and consequently, of the magnetic field energy and of the inductance for SMES devices with large inner diameter, when the leakage magnetic flux increases. The proposed model can improve the results of optimizations of the SMES device performed in previous papers.		 images

The Online Temperature Control

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Abstract 

In this paper is presented the hardware and software design of a remote controlled system which can have multiple destinations. In particularly, this system is used to
create an online thermostat using a microcontroller with ARM Cortex M4 architecture and an application designed for Android operating system. The system was designed by
authors from the ground with the objective to create a framework for wide range of applications in electromechanical domain with network communication capabilities.
The main hardware element is the processing unit for which was chosen the STM32F407VGT6 microcontroller. This is based on a 32-bit architecture working at 168MHz frequency which allow very fast running several tasks: scanning of digital sensors and a touchscreen, achieve SPI communication with an Ethernet driver, run an algorithm for temperature control. All software routines for microcontroller were built to be easy to port in another applications being developed in C language and structured in reusable
functions. The application for mobile devices was written in Java language and was compiled with latest Android Studio. The system is functional and can be used in multiple applications offering the advantages provided by network connection. All presented stuff can be used to create a lot of network connected applications.		 images

Performance of an Active DC-Traction Substation with 12-Pulse Parallel Rectifier and Indirect Current Control

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Abstract 

The attention in this paper is directed to the transformation of an existing DC-traction substationsequipped with 12-pulse parallel uncontrolled rectifier into an active substation. In this manner, the traction substation gains the capability of redirecting the braking energy to the power supply and the power quality indicators during the
traction regime are greatly improved. The practical solution lies in adding a shunt active power filter, accompanied by appropriate circuits of connection on both the DC and AC
sides, between the DC-traction line and the primary of the traction transformer via a dedicated recovery transformer. To control the current provided by the shunt active filter in both traction/active filtering and regeneration regimes, the indirect method of handling the supply current has been adopted. The reference supply current during the operation in traction regime is calculated based on instantaneous powers provided by the concepts of the instantaneous reactive power theory. Two compensation strategies have been implemented for this operation mode, i.e. the total compensationof the current harmonics and reactive power and the partial compensation (only the current harmonics). In regeneration mode, the traction rectifier is blocked and the reference supply current is given by the voltage controller. Based on the conceived Matlab/Simulink models of the whole system, the proper operation is confirmed and the good performance of the system during both traction/filtering and regeneration regimes is shown. Indeed, the total harmonic distortion of the supply current is always below the limits and recommendations of the power quality standards and the operation in regeneration mode is allowed.		 images

Study of Low Power Alternating Current Motors by Functional and Energy Aspect

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Abstract 

The objectives followed in the frame of this paper are to approach comparatively the two types of motors, from the view point of operation performances and of exploitation
expenses obtained with them (asynchronous motor and permanent magnet synchronous motor), with the help of some specialized computation softwares. That is why the two motors are built in identical conditions, in order to analyze by comparison the load operation characteristics, the active and reactive electrical energy consumption. The
study lately developed regarding the optimization of alternating current electrical machine include especially the problem of efficiency and power factor increase. The utilization of permanent magnets having high specific energies for building low power synchronous motors influenced the machine performances, the machine cost and the exploitation cost. In case of drives using alternating current motors the exploitation costs can be reduced by choosing correctly the driving motor. In order to enlarge the sale market of the energetically efficient motors, the producers have aimed at proving that the motors having high efficiency might be an attractive alternative for customers. In the frame of the aided conception, the computer becomes a numerical laboratory for the prototypes construction, without costs and deadlines, specific to a real execution. The utilization of permanent magnet synchronous motor reduces the consumption of active electrical energy with 7.9%, reduces the consumption of reactive electrical power very much, resulting a total cost which is lower with 23.9%.		 images

Hardware Experiments for Simultaneous Control of Several Motors by a Microcontroller and a VHL Programming Language

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Abstract 

 

The paper presents a hardware solution for the digital control of a multi-motor drive system using a very high level programming language and a single microcontroller.
It follows a previous one for developing the software design. These two papers are related because each side (hardware / software) is interrelated and linked to each other. The hardware platform as well as the results recorded during on-line tests by means of a logic analyzer are presented and analyzed. The purpose of the research is the simultaneous control of several motor units with their own motion parameters using a fast design cycle for the software support and a minimal hardware configuration. The main contribution refers to a software / hardware solution for obtaining independent / parallel control of the time delays for several channels. The programming environment is Flowcode 5. As hardware, a modular platform based on a PIC microcontroller is used. The application implements a simultaneous control of 2 different steppers and 2 different DC motors, each of them with different adjustable speed and its own motion direction. Another contribution is apractical tool for revealing the entire on-line timing by recording
all real-time tasks. The obtained results are useful both for a qualitative check as well as for precise quantitative evaluations, inserted examples being illustrative.		 images

Designing a Simultaneous Control of Several Motors with a VHL Programming Language for a Single Microcontroller

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Abstract 

The paper is focused, mainly, on the timing design for the simultaneous digital control of several electrical motors using a very high level programming language (under an Integrated Development Environment – IDE) and a single microcontroller. The initial problem that had led to this work was the control of a tool trajectory in a multi-axis system with minimal control equipment and by means of a very friendly software support. The results are included in two papers. This first one contains the software support. The main contribution refers to a programming solution for obtaining independent / parallel control of the time delays for several channels. The author gives also original formulas for the timing calibration. The application implements a simultaneous control of two different steppers and two different DC motors, each of them with different adjustable speed and its own motion direction. The program is designed in a modular manner using several user macros. The paper presents also the simulation results by the graphical interface. The validity of the solution is proved by some experimental results, included in the paper. The application fields concern both the academic area and the industry, the best known examples being robotics, machine-tools, electrical vehicles, drones and many others. images

Analysis of a Step-Down DC-DC Converter: Linear Versus Nonlinear Circuit

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Abstract 

This paper aims to investigate the step-down dc-dc converters from circuit analysis viewpoint. These converters have a lot of utilizations, including different applications in power energy conversion domain, being mentioned also in electromagnetic compatibility studies.That is why the study and the analysis of such devices were and continue to be of a real interest for the scientific community. For this purpose this paper aims to bring a contribution in the domain, by offering equivalent schemes of different accuracies and alternative methods of analysis in time-varying regimes for step-down dc-dc converters used in electromagnetic compatibility investigations. Various time analysis methods are used here in order to analyze the step-down dc-dc converter circuit. Each method is well explained, starting from the basic equations of the circuit, continuing with the particularities of the approaches and finalizing with the presentation of the equations sets in the final form. For each method a program was created where the obtained equations were implemented. The most important results are presented in each case; they correspond both to the steady state and to the initial variable regime. The final part focuses on the differences between the results obtained using the real nonlinear
characteristics of some elements and those resulted using their linearized model. The resulted waveforms are discussed comparatively not only using different methods of
analysis and linear and nonlinear schemes of the converter, but also using results offered by commercial software specialized in electric and electronic circuit analysis. Finally
the advantages and the disadvantages of each method are underlined and some conclusions are depicted.		 images

Analytical Algorithms for Synthesis of Modal Controllers by the Maximum Stability Degree Criterion

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Abstract 

The practice of synthesis the controllers demonstrates,
that for the determination of the dynamic tuning
parameters of the controller is more convenient to operate
with the analytical expressions with a low volume of calculations
that dependent on the known parameters of control
object. The analytical synthesis expressions, on the one hand
have the advantage of decreasing the volume of calculation
of tuning parameters (compared with the synthesis methods
and algorithms that include a number of steps) and, by the
other hand, using of the analytical expressions is a good alternative in case of the controllers with auto-tuning and adaptive control, where the controller retuning is done in function of the parameters variation of the control object during operation of the control system. Based on this consideration, in this paper it is proposed the analytical algorithms of synthesis the modal controllers, in form of algebraic expressions, for control objects with arbitrary order inertia and astatism by the maximum stability
degree criterion. This criterion offers to the designed control systems an aperiodic step response, high performance
and better robustness. The elaborated algorithms represent
simple analytical procedures with reduced volume of
calculation and without any imposing conditions to the
complexity of the control object. They allow also to impose
or to optimize the settling time of the designed automatic
control system.		 images

Optimal Heating Time for Cylindrical Items Removal from the Shaft

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Abstract 

For easy removal of cylindrical items from the shaft, they are heated on their external cylindrical surface for thermal dilatation. The best result is obtained if the temperatures gradient inside the item is highest on the separation surface. In the paper, considering a suddenly occurring constant high temperature on the external cylindrical surface of the homogeneous item, the shaft with the same thermal diffusivity and neglecting the contact thermal resistance, the transitory thermal field is analyzed and optimal time for item removal is determined. Example is given. images

Analytical-Numerical Method for Design of a Single-Phase AC Inductors with Ferromagnetic Core

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Abstract 

This paper proposes a more accurate design of a single-phase AC current inductors with ferromagnetic core, for given values of inductance, of peak value of current and of magnetic flux density. The procedure combines an analytical computation design method (analytical model) with a numerical analysis by FEM (numerical model) using
QuickField or FEMM software. The analytical model has two components, one considering the ideal coil (without iron losses) and another component considering real coil (with iron losses). The numerical model also has two components, one magnetic (AC Magnetic Problem) which determines the value of inductance and another component consisting of a thermal model (Steady-State Heat Transfer Problem) which determines the temperature distribution in the electromagnetic device. In the magnetic model was
considered a constant permeability, but both software allow a nonlinear computation. The method presented in this paper has been indirectly experimentally validated.		 images