M. Kassas

A PLC based power factor controller for a 3-phase induction motor

This paper proposes a power factor controller (PFC) for a three-phase induction motor (IM), utilizing the programmable logic controller (PLC). This work focuses on the implementation of a laboratory model for a PLC based PFC to improve the power factor of a three-phase induction motor. In addition to keep its voltage to frequency ratio constant in order to maintain a maximum torque over the whole control conditions. During the online process a set of capacitors sized in a binary ratio will be switched on or off with the help of zero voltage static switches according to a control strategy to obtain a pre-specified power factor. This control strategy relies on a look-up table and an expert system. The look-up table is prepared according to a measured value of the phase angle between the stator phase voltage and the stator phase current. Implementation of a software algorithm incorporates measuring the power factor angle, selecting the binary pattern according to the control strategy and sending command signals to switch the appropriate capacitors and protection switches. Zero voltage switching of static switches is also allocated in the control algorithm to prevent the occurrence of the transients, pseudo oscillation and harmonics. Experimental studies have been carried-out for verifying the operation performance of the proposed PFC under different operating conditions. Details of the experimental setup and test results in addition to the recommendations are also demonstrated.

Design and simulation of current regulators for induction motors using the error magnitude voltage vector correction (EMVVC)

An effective current controller algorithm is presented which achieves the elimination of voltage stress on the devices and complies with the pulse polarity consistency rule. The dynamic model of estimated electromotive force is developed to identify the fundamental line-line voltage zero crossing. This gives an optimal switching pattern of eight combinations 0-7 of states of the inverter devices. The voltage vector of the inverter output is determined from the desired voltage vector through the voltage vector selector in both EMVVC and EVVC (error voltage vector correction). As demonstrated by simulation results, the proposed EMVVC method outperforms the EVVC technique in four different data sets.<<ETX>>

Voltage stability control of a wind generation system

Voltage instability is the main cause of concern for the large scale integration of wind power into the power grid. For the induction generator based wind generation system, the fixed capacitor located at the generator terminal can not normally cater for the reactive power demand during the transient disturbances like wind gusts and faults on the system. This paper presents two schemes for enhancing voltage stability of grid connected wind generator system. These are: variable susceptance control thru SVC and reactive power compensation through static compensator system (STATCOM). Simulation results show that both schemes are well capable of providing voltage stability and damping transient arising from reasonable level of disturbances. The STATCOM, however, demonstrates superior performance because of its fast response capability as well as its ability to provide compensation independent of system voltage support.

Investigation into the Seebeck Coefficient in a Two-Layer Assembly during Laser Short-Pulse Heating

The Seebeck coefficient in a substrate varies with electron temperature such that it increases with increasing temperature. The Seebeck coefficient for different materials differs even though the materials have similar thermal properties. In this study, the Seebeck coefficient in a two-layer assembly exposed to laser short-pulse heating is considered. The assembly consists of gold and copper, and the gold layer is situated on top of the copper. In order to investigate the change in the Seebeck coefficient with layer thickness, three different thicknesses of gold layer are accommodated in the simulations. An abrupt change in the Seebeck coefficient occurs across the layers, despite the smooth decay of electron temperatures in this region due to the similar thermal properties of the layer materials. Consequently, the Seebeck coefficient variation across the layers can form the basis for measurement of layer thickness.

Modeling and Simulation of Residential HVAC Systems Energy Consumption

Abstract Saudi Arabia is characterized with high temperature, humidity, and dust storms. The air conditioning systems are an essential component in daily life. 60% of the energy consumed in the residential area is used by air conditioning systems. The aim of this paper is to build a residential thermal HVAC model, which could predict the amount of energy consumption required to get the comfort level using Matlab/Simulink. In this model the different physical properties of the building, weather, and heating gains are taken to account. The results of energy consumption obtained from Matlab/Simulink model are based on using the actual hourly outdoor temperature for a selected day of 2012 compared to the average outdoor temperature of the same selected day. The results of energy consumption for the actual and average temperatures are almost identical. For this reason, the results of total energy consumption are presented in this paper for every day of the annual year of 2012 based on the average hot and warm outdoor temperatures (7 1/2 months), and cool and cold temperatures (4 1/2 moths).

Entropy generation due flow passing over the porous block in the cavity

Flow over porous structures finds applications in heat transferring devices due to attainment of high heat transfer rates. Thermodynamic irreversibility can be used as a measure of quality of the porous body in the thermal system. In the present study, flow over a porous block situated in a square open–ends cavity and rate of entropy generation due to heat transfer and fluid friction are considered. The effects of the block aspect ratio and porosity on volumetric entropy generation rate are examined numerically. In the simulations, four aspect ratios and three porosities of the block are accommodated. The total area of the block is kept constant for all the aspect ratios considered in the simulations. A uniform heat generation (105 W/m²) is considered in the block resembling the heat generating device, such as encapsulated electronic device, and air is used as working fluid in the cavity. It is found that volumetric entropy generation rate in the cavity reduces with increasing aspect ratio and porosity of the block. Entropy generation rate due to heat transfer is considerably higher than its counter part due to fluid friction because of low Reynolds number flow at cavity inlet and small natural convection current generated in the cavity.

LabVIEW Based PV Panel Online Characteristics and Parameters Estimation

Abstract This paper focuses and presents the online performance, characteristics evaluation and parameters estimations for stand-alone Photovoltaic (PV) panel. The PV panel is subjected to very harsh working surrounding conditions characterized by very high air temperature, very high humidity fluctuations. The local area experience heavy and seasonal dust storms. The area is rarely cloudy and the irradiation level is on the high side in most period of the year. This experimental work is centralized around Laboratory Virtual Instrument Engineering Workbench (LabVIEW) environment. Three LabVIEW graphical programming blocks are developed to acquire data, to present numerical display and to store environment and electrical parameters. The Fourth block is dedicated to execute graphical online display of environment data. The Fifth module follows and display the electrical variables under clean and dusty condition. The sixth block is designed to acquire the I-V and P-V characteristics simultaneously. The seventh module estimates series and shunt resistance of PV panel under changing condition. The developed environment was fast and accurate in collecting and storing the data. It was very satisfactory to monitor the weather parameters and its impact on the electrical PV performance. The developed system was successful to reach I-V and P-V characteristics accurately. The series and shunt resistance were estimated and found to very close to the simulation results.

PV generator performance using Cassy System

This paper presents an experimental investigation for the performance of a PV generator using Cassy System environment. Two PV panels were exposed to severe environmental conditions such as high temperature, high humidity, relatively high irradiation and frequently high levels of dust deposition. Each PV panel of 150 W rating was feeding a variable resistive load. The measurement was taken through a conditioning amplifier and Profi-Cassy analog to a digital converter. Cassy System displayed the voltage, the current, the delivered power and the irradiation on-line with the desired frequency of measurement and storage rate. I-V and P-V characteristics were accurately displayed and stored. Cassy environment allows appending the characteristics for the sake of comparison, investigation and research purposes. The obtained results were validated against simulation to show a very good degree of accuracy. Cassy System environment has shown high degree of simplicity and flexibility in programming, to record and display a large number of variables manually and automatically. The measurement system has shown clearly the impact of dust, of high temperature and of the irradiation changes on the PV panel efficiency certifying his candidacy for research and educational purposes.

A programmable SCR-based AC voltage regulator

This paper describes the design, simulation and implementation of a self adjustment programmable AC voltage regulator. The regulator hardware consists of thyristors, a signal conditioner and, an 8-bit microcontroller. The regulator monitors the voltage across a load. The firing angles of the thyristors are automatically adjusted to keep the voltage within the prescribed level independent of the load fluctuations. The regulator was tested for resistive and inductive loads. The results indicate acceptable accuracy levels depending on the control range specified by the user. The regulation range can be from 0-220 V AC.

Inverter switching patterns using a neural network

The authors present a method of switching mode selection for a digital current controller using a neural network. The neural network was trained to act as a vector selector for the inverter. The desired voltage vector was calculated from parameters of the induction motor, stator currents, and electromotive force. The backpropagation technique for training neural networks was used based on input/output data obtained from previous simulation studies. The results show excellent correlation between the output of the neural vector selector and the vector selection based on analytical methods. The neural network approach was faster than the previously used analytical methods, making it possible to increase the switching frequency.<<ETX>>