Monthly Archives: March 2015

Increasing Frequency Capability of PMSM Vector Controlled Drive for Pumped Storage

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Abstract 

The subject of this paper is a comparative study between two supply modes of a permanent magnet synchronous motor (PMSM). The goal is to obtain a better efficiency for a hydraulic pump drive system. The machine (PMSM) is operated in vector control mode. The inverter is controlled with a sinusoidal pulse-width modulation (SPWM) technique. The study will allow to increase the root mean square (RMS) of the voltage and hence speed, avoiding over-modulation. The comparison is also made between third harmonic injection and over-modulation.

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Numerical Models for Electric Train Energy-Efficient Operation

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Abstract 

The paper begins by presenting structure of the electric drives with traction induction motor used on locomotive fed from AC line. Are emphasized the main components of such a drive system: the main electric circuits, the mechanical part and the locomotive control.   For the traction induction motors, which it is included in both the main electrical circuits and in the mechanical part, it is proposed the fictitious split into an „electromagnetic part” and into a „mechanical part”. In order to modeling the mechanical part, they are established the equations of useful movement and it is built the structural diagram corresponding to a locomotive with „z” traction identical motors. The mathematical model and structural diagram of the mechanical part respects all the running conditions. On the structural diagram basis it is built the SIMULINK model associated of the useful movement. The implementation of the SIMULINK models is made easily (because their identical topology), starting from the adequate structural diagrams. The SIMULINK model is used to calculate the energy consumption for different running regimes and different route configurations and to identify energy efficient train control methods, avoiding utilization of complex mathematical methods. The numerical models presented can be used, with small modifications, for the study by simulation of useful movement of any type of electric vehicle. images

Simulation of Regenerative Braking at an Electrical Scooter

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Abstract 

The paper deals with MATLAB simulations of the regenerative braking for an electrical scooter. Various modern possibilities to achieve regenerative braking at light electric vehicles are approached firstly. Afterward one presents aspects of the original simulations related to a scooter equipped with a single-stage bidirectional DC/AC converter based on a general full-bridge inverter in order to implement regenerative braking. The simulator relies on a model from the SIMULINK library, which represents a synchronous motor with permanent magnet and trapezoidal excitation. Other major components of the simulator are: a model of converter with three-phase bridge, realized with MOSFET transistors and anti-parallel diodes; a logical model of the control circuits for the transistors placed on the bridge’s arms in order to make the motor to advance, respectively to cause its braking. Two modules were conceived to test the current drawn (or injected) from (or toward) the source during scooter’s advance (or brake), respectively to test the consumed (or recovered) energy. The paper includes the simulated waveforms corresponding to various quantities, at the beginning or ending of the braking process, considering a filling factor of 70%. Other simulations were performed with a variable filling factor, in order to evaluate the recovered energy when the speed was reduced from 45 km/h up to 20 km/h. Considering the variation of the recovered energy with the filling factor, the simulations revealed an increase of this energy up to a certain value when the factor is increased at the beginning of the variation range, followed by the recovered energy decrease for higher values of this factor. The phenomena responsible for these variations are discussed. For the studied scooter, the reducing of speed from 45 km/h up to 20 km/h is reflected in a maximum recovered energy   of 35% from the total energy stored as kinetic energy by the moving scooter with a maximum weight, respectively 43% from difference between the scooter’s initial and final kinetic energies respectively. images

Automation of a Sun Tracking System for Photo-voltaic Panel with Low Concentration of Solar Radiation

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Abstract 

Over the last decades, because of the pollution and awareness of limited resources of fossil fuels, the renewable sources of energy production gained increasing confidence as appropriate solution for humankind. Within the south region of Romania, due to the high solar potential there have been developed numerous photovoltaic stations. Still, one could note that these solar plants take a considerable part of agricultural land.  This paper is the starting work of a study that aims to address meaningfully the issues of increasing efficiency of the photovoltaic systems by utilization of solar radiation concentrator elements, as well as of reducing of costly photovoltaic surface. In the literature there are three types of solar concentrators: high, medium or low concentration (LCPV). To have a maximum efficiency the LCPV must include automatic sun tracking system. In practice there are two types of automatic tracking systems, those using solar sensors and those that follow a predetermined trajectory. This paper combines the two types of systems thus achieving low power consumption. It also allowed the monitoring and control of tracking system both locally and remotely using standard interfaces. Solutions and algorithms proposed in this paper are verified experimentally on a prototype developed by the authors. images

Extended Study Regarding Sustained Transfer Rate for 802.11 Wi-Fi Communications With Partially Overlapped Channels Interference

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Abstract 

This paper extends the pervious studies of the authors on the 802.11 Wi-Fi Communication regarding the influence on the sustained transfer rate caused by the existence of the Partially Overlapped Channels (POCs) interference. The main influence in this situation is the reducing of the sustain transfer rate caused by increasing number of the rejected cell, lost cells and delayed packets. The maximum channel throughput is dramatically reduced in the presence of the adjacent and eventually co-channels interference. The usual solution to this problem is the increasing of the distance between the wireless access points or increasing of the channel spacing. Our study proposes a better solution combining those two methods. For achieving the optimum solution first we make the necessary studies regarding the physical distance influence and the channel spacing influence to the interference. For this goal the test bed solution was redesigned in order of achieving the optimum measurements for sustained transfer rate.  Our contribution is related to the new perspective on the sustained transfer rate analysis and optimum parameter setup in the presence of the interference. The new data observations related to the maximum throughput, lost cells and average cell delays also could contribute to the optimum Wi-Fi coverage planning. Finally we made a personal interpretation of to the data measured in the laboratory. images

Check of Temperature-Rise Test of High Voltage Prefabricated Substations with Power up to 1600 kVA

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Abstract 

In the first part of this paper are presented the requirements of 62271-202/2014 – standard for temperature-rise tests of HV/LV prefabricated substations. Also is presented the new installation for temperature-rise test, according to IEC 62271-202/2014 of high voltage/low voltage prefabricated  substations with powers up to 1600 kVA and voltages up to 52 kV composed from a three-phase, low voltage AC supply with motor-generator group and a three-phase, high voltage AC supply realized within High Power Laboratory (HPL) of ICMET-Craiova with three single-phase groups autotransformers-transformers. The realized installation is an alternative to temperature-rise tests electrical equipment because it uses a supply different that motor-generator one. In second part there are presented experiments performed on a prefabricated substation. images

The Load Influence on the Diagnosis of the Three-Phase Rectifier by Using the Analytical Model Method

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Abstract 

For the operation of the static power converters, the experience of an expert is absolutely necessary for competitive operation. Minor faults or defects of the elements of the static power converters can lead to ravaging effects both for the other components as well as other equipment from their operating system. The paper proposes a diagnosis method based on the analytic model which investigates the output waveforms of a three-phase rectifier supplying two types of loads: a passive RLC load and a variable DC drive.  Two types of possible faults of the switches are considered: interrupted and short circuit. For identifying the defective components, the waveforms corresponding for different faults are stored in an information database in order to be compared with the ones corresponding to normal operation.. Another solved problem in this article refers to the influence’s analysis of the defect propagation in the driving system. There are analyzed the waveforms corresponding of the different faults for different types of loads including a passive RLC load and a variable DC drive. For the both types of faults, important oscillations of the output voltage of the static power converter are noticed which can damage the load, but also, determine the additional stress to other healthy switches. images

Smart Home Energy Management System for Peak Average Ratio Reduction

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Abstract 

High quality demand-side management has become indispensable in the smart grid infrastructure for enhanced energy reduction and system control. Most of the demand-side management systems that existed were focusing on the interaction between utility company and its customers. Naturally, each home would be interested in minimizing the utility bill. Given price information, an automated DR controller would manage those devices which are flexible to be controlled, to opportunistically take advantage of the times with lower prices. This may cause a “rebound” peak, due to appliances loads flooding to the times with low prices, a reason very different from the one for the day time peak typically caused by the devices which have to run at that time. Consequently, the Home Energy Management (HEM) systems plays a crucial role in realizing residential Demand Response (DR) programs in the smart environment. It provides a homeowner the ability to automatically perform smart load controls based on utility programs, customer’s preference and load priority. This paper presents the hardware demonstration of the proposed HEM system for managing the end-use appliances. The proposed algorithm manages the household loads according to their preset priority and fixed the total household power consumption under certain limit. This work achieves the purpose of reducing electricity expense and clipping the peak-to-average ratio (PAR).

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Design of Separately Windings Control System of Series/Compound DC Traction Motors

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Abstract 

This paper focuses on the problem of the control system of Series/Compound DC motor in both areas of speed adjustment. Traditional field weakening is achieved by means of resistances  and contactors wich  inserting  and/or shunting in  field circuits. It is characterized by shock currents, torque and speed as well as by increased energy consumption. To eliminate these disavantages  paper proposes separate control of  armature,  series and shunt windings  of Series/Compound DC motor and supply their own power converters. Keeping hyperbolic mechanical characteristic of these motors requires setting the series field  current equal to or less than armature current. Developed control system is equipped with a single loop for series field and two loops for armature with a  current and speed controllers. Imposing series excitation current required is achieved through a special computer based on actual values ​​of current and rotor speed. Control system design was made based on a mathematical model and   use  of default instrument of Matlab-Simulink for tuning of PID controllers. Simulation results demonstrate the system’s ability to control separate windings for continuous speed adjustment in both areas, strictly limiting the rotor current, reducing energy consumption and ensuring the imposed  performance indicators. The proposed control method is recommended for use in electric images

Transmission and Processing of the Measurement Signals Generated by a Transformer for the Current Measurement in Medium Voltage Networks

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Abstract 

The trends to improve the performances of the classic instrument transformers was oriented to introducing new materials, components and methods in its design, manufacturing and operation. This paper presents the technical solutions adopted to implement the measuring system at medium voltage based on this current instrument transformer. The transformer uses a fiber optic link to send the measuring signal from the medium voltage point to the monitoring point. The structural block diagram of this transformer is presented and the operation of the main blocks is described. On the monitoring side, the measuring signal is converted from the voltage signal at the current signal which flows through a current loop for remote control and telemetry. Also, analog to digital conversion and the sending of the result of measurement at master monitoring system is possible. A simple algorithm for remote control of the operation of  transformer is presented. If the transformer is integrated into a digital measurement system then it operates as a slave unit under the control of the master unit. The samples taken from the measurement signal are used for digital processing. It is analysed the possibility to realize a network of transformers using the communication bus RS 485 . Finally, the waveforms, recorded during the performed tests, are presented. images