Daily Archives: 16 December 2015

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

16 December 2015Fără categoriecburada

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%.

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

16 December 2015Fără categoriecburada

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.

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

16 December 2015Fără categoriecburada

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.

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

16 December 2015Fără categoriecburada

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.

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

16 December 2015Fără categoriecburada

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.

Optimal Heating Time for Cylindrical Items Removal from the Shaft

16 December 2015Fără categoriecburada

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.

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

16 December 2015Fără categoriecburada

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.

Predictive versus Classic Control of the Induction Motor Drives

16 December 2015Fără categoriecburada

Abstract 

The paper deals with techniques which use the predictive concepts in order to obtain both the pulse width modulation strategy of a voltage fed inverter and the predictive control of the induction motor drive. Concerning the PWM technique, it is applied for the case when the inverter supplies an induction motor, the reference values of the currents being obtained from a classical vector control scheme. The described technique is then simulated and the waveforms are compared with ones obtained with preset currents (bang-bang) pulse width modulation, as the behavior of the two strategies is similar. The results are also compared with the ones resulted when a classical DTC controls the induction motor, as the both determine, during each sampling period, the next stator voltage phasor, but considering different criteria. Concerning the control of the drive, the vector control and the predictive control of the induction motor are compared. For the vector control, the rotor flux oriented one is pointed out, with highlight on the voltage source inverter type. A simple (and practical) method for avoiding the influences of the stator resistance variations when a voltage source inverter is used is presented, based on proper simulation models. For the predictive control of the induction motor, a sensorless diagram is considered. Finally, further actions are proposed for the work continuation.

Control circuit of an Electronically Controlled Capacitor for the Optimization of the Single Phase Induction Motor

16 December 2015Fără categoriecburada

Abstract

The control circuit of an Electronically Controlled Capacitor (ECC) for the optimization of the Single Phase Induction Motor (SPIM) with auxiliary winding is presented. The control circuit is based on a fixed value AC capacitor within a full bidirectional switches bridge PWM controlled at much higher than line frequency (in kHz range). The power bridge circuit and its embedded pulse driver circuit are presented within the theoretical sections of the paper. In the experimental section, using a small electric motors test bench and a two speed SPIM with auxiliary winding, are analyzed the main influences of the pulse drive circuit over the ECC. Firstly, being considered that the optimum is reached at the maximum motor torque, the optimal pulses frequency has been established around 4 kHz. Secondly, the switches over-voltages at the ommutations moments being a serious drawback of the ECC, are analyzed the influence of the fixed capacitor value and the dead time of the pulse shape over the MOS-FET power transistors of the bidirectional switches over-voltages. The overvoltages diminish as both the capacitor value and the dead time diminish. More than that, in contrast with some authors, there are no disadvantages as dead time became zero. These issues are the main contributions of this paper.

Modelling of Transformer Windings and Computation of Very Fast Transient Over-Voltages

16 December 2015Fără categoriecburada

Abstract

The main objective of this paper is represented by analysis and modeling of the transformer windings stressed by over-voltage with direct impact on voltage distribution across the winding. The authors considered both approaches in modeling the winding: windings with distributed electrical parameters respectively composed from disk coils with concentrated parameters. Both types of voltages applied across the transformer winding will generate free oscillations which are analyzed further on. According to the model, the transformer’s windings are divided in several disk coils with concentrated known parameters. This results in a complete electrical network used for simulations. All simulations have been performed using the software package SYSEG (SYmbolic State Equation Generation).