The experiment that Stanley Milgram conducted in the 1960s provided Essay

The experiment that Stanley Milgram conducted in the 1960s provided empirical evidence in favour of what is now referred to as t - Essay Example The results of the experiment have been proved by many other researchers in later studies, which explored the small-world effect in various types of networks. It has been verified that the small-world effect can be seen in different extent in a number of the real-world networks. The small-world phenomenon has made a great contribution in the theory of networks as it helped to better understand the structure and dynamics of the complex networks. This paper intends to discuss the Milgram's experiment and to explore in what extent the small-world effect can be found in three main classes of networks – random graphs, scale-free networks and small-world networks. Keywords: networks, social networks, small-world, six degree, random graph, scale-free networks. Introduction It is widely acknowledged that networks are all around people; and people themselves as socio-biological systems are, for the most part, products of biochemical reactions and social relationships occurring in netwo rks. Networks are studied since 1736, at first in the domain of mathematical graph theory (Biggs et al., 1986), which has been gradually developed into the solid branch of knowledge that studies nature and properties of different networks, from very simple to large and complex networks that have irregular structure and complex dynamics. Examples of such networks can be found everywhere in nature and in society – food networks of biological species, communication networks and the Internet, social networks between individuals, transportation networks, metabolic and neural networks, and many others. Nowadays the study of networks got significant achievements in understanding of specific features, some of which have been investigated in depth only in the past few decades, with the advent of information and communications technologies and, particularly, the Internet. One of the fundamental features of networks was discovered in 1967, when a famous social psychologist Stanley Milgr am conducted a series of experiments, revealing that in spite of the enormous number of the global population, our world is actually rather small - any individual on the planet can reach any other individual through about six contacts in their social network. The phenomenon was called the small-world effect, while the modern popular scientific literature often mentions it as the â€Å"six degrees of separation† effect (Watts, 1999). The results of the Milgram’s experiments have been proved in a large number of experiments of other researchers. The phenomenon appears to be extremely useful for understanding the structure and dynamics of processes that takes place in different networks, for example the dynamics of spread of information across the network, or the dynamics of diffusions of epidemic diseases in a society. The small-world effect can be viewed in different networks; however, each of these networks has the distinctive characteristics, related to its structure and dynamics, so there are certain differences in the manifestations of the small-world effect in various networks. This essay intends to discuss the Milgram's experiment and to explore in what extent the small-world effect can be found in networks, namely, in three main kinds of networks – in classical random graphs; in scale-free networks, introduced by Barabasi and Albert (1999); and in small-world networks, invented by Watts and Strogatz (1998). The paper is aimed to show

Character analysis on young Goodman Brown Thesis

Character analysis on young Goodman Brown - Thesis Example In Young Goodman Brown, the character of Brown changes from faith and innocence to corruption and doubts as the devils distorts the way he thinks and perceives valuable people in his life. The faith and goodness of Brown are seen in the way he treats his father, grandfather, minister, and wife. He looks up to the goodness of his father and grandfather and the minister. Brown believes in the true Christina nature of the minister of Salem because he is a man of God. His wife Faith comes into his life a young immaculate and beautiful woman. He invests all his trust in the life of his wife, and life seems good in his belief that he has found a true partner to share his life happiness and glory. Faith is a staunch Christian, who is an epitome of good and purity but not until the devils come knocking on their doors. Brown’s innocence is lost when the devil visits his home and changes the way he views the valuable people in his life. Brown interjects, â€Å"what if the devil himself should be at my very elbow† (9). His wife Faith is no longer the pious and religious figure, and he hopes that the character would persist for the rest of her life. However, the arrival of the devil elicits doubts about the true nature of faith. He starts doubting her after seeing him in the evil ceremony in the forest. The devil also reveals the two followers, Deacon Gookin, and Goody Cloyse that Brown has known all along that they are staunch Christians (Hawthorne 16). The character of Brown here is seen to shaky because he is convinced to think otherwise about the community he has known his entire life. The arrival of the devil changes the faith and innocence of Brown to corruption. The evil nature of the people around him comes as a surprise, and that convinces him that the entire Puritan society is hypocritical. The revelations that come to him give him a different perspective of the society that he knows professes its Christian faith in

Performance of Unified Power Quality Conditioner

Performance of Unified Power Quality Conditioner ABSTRACT Power electronics is playing an important role in transmission and utilization of electrical power due to its capability of processing electric power in most efficient and cost-effective way. However, the nonlinear characteristics of power electronic devices give rise to two important limitations; they generate harmonics and draw lagging current from the utility. In recent years unified power quality conditioner (UPQC) is being used as a universal active power conditioning device to compensate both harmonics as well as reactive power. UPQC is an advanced version of unified power flow controller (UPFC). The performance of UPQC mainly depends upon how quickly and accurately compensation signals are derived. The UPQC mitigates harmonics and provides reactive power to the power systems network so as to improve the power factor close to unity. The UPQC is a combination of shunt active and series active power filters connected through a dc bus. The shunt active filter of UPQC acts as a current source for injecting compensating current through a shunt transformer, whereas, the series active filter acts as a voltage source for feeding compensating voltage through a series transformer. The aim of the dissertation work is to study the control strategies of UPQC based on PI controller and fuzzy logic controller in detail. In the case of PI controller, the dc link voltage is sensed at regular intervals and is compared with a reference value. The error signal thus derived is processed in a PI controller. A limit is put on the output of the controller to ensure that the shunt active power filter supplies active power of the load through the series active power filter. The fuzzy logic controller is basically nonlinear and adaptive in nature. This gives a robust performance in the cases where the effects of parameter variation of controller are also taken into consideration. It is a well established fact that the fuzzy logic controller yields results that are superior to those obtained as compare to those obtained through conventional controllers such as PI and PID because of the fact that it is based on linguistic variable set theory and does not require a mathematical model. Generally, the input variables are error and rate of change of error. If the error if coarse, the fuzzy controller provide coarse tuning to the output variable and if the error is fine it provides fine tuning of the output variable. The present thesis investigates PI controller and fuzzy logic controller as concerned to UPQC application for power quality improvement. The UPQC is studied and its advantages over conventional APFs and UPFC are discussed in detail. The relevant mathematical models and equations to explain the working of UPFC are derived for both the cases (PI controller and fuzzy logic controller).The relevant simulations are carried out using MATLAB/Simulink. The result obtained reveals that the fuzzy logic controller gives better dynamic performance than the PI controller for power quality improvement. Chapter 1 INTRODUCTION 1.1 Theory The electrical power system consisting of generation, transmission and distribution system are based on alternative voltage and currents. When linear load consisting of inductances, capacitances and resistances are connected to the power system the sine wave is preserved and the system components are said to be linear. Traditionally, linear loads consume major part of electrical power. However situation has changed now as more and more electrical power are being developed using power electronic devices due to their energy efficiency and control. Power electronic devices possess inherent non linear characteristics. The nonlinear characteristics of this devices results in two important limitations, drawing of large reactive volt-amperes and injection of harmonics into the utility. Large reactive volt-amperes drawn from the utility leads to increase voltage drops at various buses. The harmonics increase the losses in transformers, generators, motors, capacitors, conductors, etc. some of the control devices interfaced with the utility starts malfunctioning due to excessive harmonic currents. As the non linear load consists of the major portion of the total load for the last two three decades, reactive power compensation and harmonic filtering have received a great deal of attention. To restrict the consumers against excessive loading VARs and harmonics, stricter standards has been laid down by the utilities. Most popular among them is standard 519-1992 [1]. Static VAR compensators using thyristor switched capacitors (TSC) and thyristor control inductors (TCI) [2], [3] have been traditionally used for reactive power compensation. As the VAR generated in these schemes are directly proportional to the energy storage capability of capacitors and inductors, there is considerable increase in the size of these elements when the VARs to be compensated are large. Moreover TSC and TCI produce additional current harmonics. Therefore shunt passive filters require filtering them out. Active power filter (APF) using voltage or current source inverter can be used for reactive power compensation and harmonic filtering together. The major advantage of using voltage source or current source inverter is that the size of the energy storing element is drastically reduced as compare to TSC or TCI. The shunt APF is the most commonly used APF. The power circuit of shunt APF is shown in Fig. 1.1. In shunt APF, a reactive volt ampere calculation estimates the real component of the load current, Ipland then determines the resistive component of the load current by subtracting Ipl from IL(Iql= IL-Ipl). If nonlinearity present in the load current, it is present in Iql as well. Since compensation current Icomp is made to follow Iql, load harmonics also get eliminated. Apart from shunt APF various other APF topologies such as series active filter, hybrid series active filter and power line conditioner have been proposed in the literature. The series active filter as shown in Fig. 1.2 is connected in series with supply mains using a matching transformer. Its limitation is that the presence of active impedance in series with source produces voltage harmonics. IL = Ipl +Iql Source Icomp = Iql Source Source side Series transformer Load side Shunt transformer DC Link Capacitor Converter 1 converter 2 Using combine series APF and shunt APF unified power flow controller (UPFC) realized, which performs active power compensation, reactive power compensation and phase angle regulation. UPFC believed to be the most complete power conditioning device. But as the time changes, problem also changes. Now days electrical engineers facing problem regarding harmonic compensation, voltage sag and voltage flickering and UPFC is not able to overcome these problems. So a new concept based on UPFC derived called unified power quality conditioner (UPQC) as shown in Fig. 1.3, which performs all the basic functions of UPFC in addition it also compensate for current /voltage harmonics with constant voltage maintenance at load terminals. 1.2 Unified Power Quality Conditioner The UPQC is the most versatile and complex of the FACTS devices, combining the features of the STATCOM and the SSSC. The UPQC can provide simultaneous control of all basic power system parameters, transmission voltage harmonic compensation, impedance and phase angle. It is recognized as the most sophisticated power flow controller currently, and probably the most expensive one. The basic components of the UPQC are two voltage source inverters (VSIs) sharing a common dc storage capacitor, and connected to the power system through coupling transformers. One VSI is connected to in shunt to the transmission system via a shunt transformer, while the other one is connected in series through a series transformer. A basic UPQC functional scheme is shown in Fig.1.3. The series inverter is controlled to inject a symmetrical three phase voltage system of controllable magnitude and phase angle in series with the line to control active and reactive power flows on the transmission line. So, this i nverter will exchange active and reactive power with the line. The reactive power is electronically provided by the series inverter, and the active power is transmitted to the dc terminals. The shunt inverter is operated in such a way as to demand this dc terminal power (positive or negative) from the line keeping the voltage across the storage capacitor Vdc constant. So, the net real power absorbed from the line by the UPQC is equal only to the losses of the inverters and their transformers. The remaining capacity of the shunt inverter can be used to exchange reactive power with the line so to provide a voltage regulation at the connection point [8]-[11]. A conventional UPQC topology is comprised of the integration of two active power filters connected back to back to a common dc link bus. A simple block diagram of a typical UPQC is shown in Fig. 1.4. The first active filter connected in series through an injection transformer is commonly termed as series filters (SF). It acts as a controlled voltage generator. It has capability of voltage imbalance compensation, voltage regulation and harmonic compensation at the utility-consumer PCC. In addition to this, it provides harmonic isolation between a sub-transmission system and a distribution system. A UPQC consists of combination of shunt active filter and series active filter with a common dc link as shown in Fig. 1.4. The dc link capacitor allows the active power generated by the shunt active filter and active power drawn by the series filter to be same. Further dc link capacitor increases or decreases with respect to rated voltage which depends upon power generated and absorbed by both active filter can be choosen independently which gives flexibility to the power outlet. The performance of these active filters is based on three basic design criteria. They are: Design of power inverter (semiconductor switches, inductances, capacitors, dc voltage); PWM control method (hysteresis, triangular carrier, periodical sampling); Method used to obtain the current reference or the control strategy used to generate the reference template. Both series voltage control and shunt current control involve use of voltage source converters. Both these inverters each consisting of six IGBTs with anti parallel diode connected with each IGBT are operated in current control mode employing PWM control technique. Capacitor is used as an interface between the two back to back connected inverters and the voltage across it acts as the dc voltage source driving the inverters The two VSIs can work independently of each other by separating the dc side. So in that case, the shunt inverter is operating as a STATCOM that generates or absorbs reactive power to regulate the voltage magnitude at the connection point. Instead, the series inverter is operating as SSSC that generates or absorbs reactive power to regulate the current flow, and hence the power flows on the transmission line. The UPQC has many possible operating modes. In particular, the shunt inverter is operating in such a way to inject a controllable current into the transmission line. The shunt inverter can be controlled in two different modes: (1) VAR Control Mode:The reference input is an inductive or capacitive VAR request. The shunt inverter control translates the VAR reference into a corresponding shunt current request and adjusts gating of the inverter to establish the desired current. For this mode of control a feedback signal representing the dc bus voltage, Vdc, is also required. (2)Automatic Voltage Control Mode:The shunt inverter reactive current is automatically regulated to maintain the transmission line voltage at the point of connection to a reference value.. The series inverter controls the magnitude and angle of the voltage injected in series with the line to influence the power flow on the line. The actual value of the injected voltage can be obtained in several ways: Direct Voltage Injection Mode:The reference inputs are directly the magnitude and phase angle of the series voltage. Phase Angle Shifter Emulation mode: The reference input is phase displacement between the sending end voltage and the receiving end voltage. Line Impedance Emulation mode: The reference input is an impedance value to insert in series with the line impedance. Automatic Power Flow Control Mode:The reference inputs are values of active and reactive power to maintain the transmission line despite system changes. A UPQC control strategy should preferably have following attributes: (1) Shunt converter Reactive power control by shunt current injection Real power regulation through dc link capacitor DC capacitor voltage regulation Harmonic compensation (2) Series converter Real reactive power control by series voltage injection Voltage control Phase angle regulation Power factor correction 1.3 Characteristics of UPQC Basic characteristics of UPQC are same as UPFC but UPQC in addition, performs active filtering. The operation of UPQC from the standpoint of conventional power transmission based on reactive shunt compensation, series compensation and phase angle regulation, the UPQC fulfill these functions there by meet multiple control objectives by adding injected voltage with appropriate magnitude and phase angle to the terminal voltage. Using phasor representation, basic UPQC control functions explained: (1)Terminal Voltage Regulation The change in voltage shown in Fig.1.5 is injected in phase or anti phase. UPQC with its series voltage control detects and calculates the required terminal voltage vo to be injected in series with the line to compensate both the dip and swell in the supply voltage. vo + vo vo (2) Series Capacitive Compensation Here, vpq = vc where vcis injected capacitive voltage in quadrature to the line current functionally it is similar to series capacitive and inductive line compensation attained by SSSC as shown in Fig. 1.6. Series inverter in combination with the insertion transformer produces the series injected voltage as calculated to mitigate the effects of the fluctuations of supply voltage by drawing the required power from the dc link. vc vo vo + vc Fig. 1.6 Series capacitive compensation (3) Transmission Angle Regulation Here, vpq = v (ÃŽ ´) is injected with an angular relationship with respect to the voltage that achieves desire phase shift without any change in the magnitude as shown in Fig. 1.7. At any given transmission angle ÃŽ ´, the transmitted real power demand P and reactive power demand at transmission line sending end Qs and receiving end Qr can be freely controlled by UPQC Vc vd ÃŽ ´ vo vo + vÃŽ ´ (4) Multifunction Power Flow Control This property is executed by simultaneous terminal voltage regulation, series capacitive line compensation and phase shifting as shown in Fig.1.8. This function makes UPQC unique device that performs all power quality improvement functions. vc ΔvvÃŽ ´ vpq vo + ÃŽ ´v + vc + vÃŽ ´ (e) Active Filtering The compensating shunt currents generated contain harmonic content of the load current but with opposite polarity such that when they are injected at the point of common coupling the harmonic content of supply current is effectively reduced. As discussed earlier in this chapter. 1.4 Aim of Work This work deals with UPQC, which aims at the integration of series-active and shunt-active power filters. Fig. 1.3 shows the basic system configuration of such a UPQC. In this system, the power supply is assumed to be a three-phase, three-wire system. The two active power filters are composed of two 3-leg voltage source (VSI). The main purpose of the series-APF is harmonic isolation between a sub transmission system and a distribution system. In addition, the series-APF has the capability of voltage imbalance compensation as well as voltage regulation and harmonic compensation at the utility-consumer point of common coupling (PCC). Atthe same time, the main purpose of the shunt- APF is to absorb current harmonics, compensate for active power and reactive power injected by the load. Also, the voltage of the DC link capacitor is controlled to a desired value by the shunt-APF. The aim of the dissertation is to design different control strategies for (UPQC), which is one of the major custom power solutions capable of mitigating the effect of supply voltage sag, swell, flicker and spikes at the load end or at the Point of Common Coupling (PCC). It also prevents load current harmonics from entering the utility and corrects the input power factor of the load. Further, the main aim of the dissertation is to implement a control strategy for UPQC, modeling of UPQC using simulink and to analyze the control strategy to use the series voltage injection and shunt current injection for UPQC control The control strategies used here are based on PI controller, fuzzy controller. The relative performance of the two controls is also studied. The present work discusses the compensation principle and different control strategies (PI, Fuzzy) of the UPQC in detail [12]-[15]. The control strategies are modeled using MATLAB/Simulink. The performance of UPQC is examined by considering, a diode rectifier feeding an RL load (non linear load) that acts as a source of harmonics, to the system of concern. The performance is also observed by switching the extra RL load. The simulation results are listed in comparison of different control strategies and for the verification of result [16]-[18]. 1.5 Organization of the Report The report of the work done is organized as follows: Chapter 2 gives brief overview of control strategy of UPQC. In this chapter introduction to dq theory, compensation strategy, basic control function and modeling of UPQC using PI controller discussed with results. Chapter 3 discusses about fuzzy logic controller and implementation in UPQC. Membership functions, rule base table and surface viewer also discussed in this chapter. Chapter 4 gives comparison studied between fuzzy logic controller and PI controller. Simulation results of both are discussed in detail with the help of table and graphs. The last chapter 5 presents important conclusions and future work. Adequate references provided at the end of the chapter. Chapter 2 CONTROL STRATAGEY FOR UNIFIED POWER QUALITY CONDITIONER 2.1 Introduction Control strategy plays vital role in overall performance of power conditioner. Control strategy includes features like rapid detection of harmonic signals by maintaining higher accuracy, fast processing, and faster dynamic response of the controller. The control strategy can be realized using discrete analog and digital devices or advanced programmable devices, such as single chip micro computers, DSPs etc[10]. The control strategy determined by the appropriate switching pattern or signal obtained by compensating gate signal compared obtained by comparing with its reference value. Since derivation of reference signal plays an important role in control strategy, many theories and techniques were proposed in recent years. There are number of control strategies were proposed among them dq method is used in the present work and discussed below: 2.2 dq Transformation It is established that the active filter flows from leading voltage to lagging voltage and reactive power flows from higher voltage to lower voltage. Therefore both active and reactive power can be controlled by controlling the phase and the magnitude of the fundamental component of the converter voltage with respect to line voltage. dq theory provides an independent control of active reactive power by controlling phase and the magnitude of the fundamental component with respect to converter voltage According to the dq control theory three-phase line voltages and line currents are converted in to its equivalent two-phase system called stationary reference frame. These quantities further transformed into reference frame called synchronous reference frame. In synchronous reference frame, the components of current corresponding to active and reactive power are controlled in an independent manner. This three-phase dq transformation and dq to three-phase transformation are discussed in detail in this chapter. The outer loop controls the dc bus voltage and the inner loop controls the line currents. The instantaneous real power at any point on line can be defined by: p =vRIR + vBIb + vCIc (2.1) And we can define instantaneous reactive voltage conceptually as a part of three phase voltage set that could be eliminated at any instant without altering p. Reference frame theory based d-q model of shunt active filter is presented in this section. While dealing with instantaneous voltages and currents in three phase circuits mathematically, it is adequate to express their quantities as the instantaneous space vectors [10]. Vector representation of instantaneous three phase quantities R, Y and B which are displaced by an angle 2Ï€/3 from each other is shown in Fig.2.1 [17]. ÃŽ ² B 90o R ÃŽ ± 120o Y The instantaneous current and voltage space vectors are expressed in terms of instantaneous voltages and currents as: v= [vRvYvB] I = [IR IY IB] (2.2) Instantaneous voltages and currents on the RYB co ordinates can be transformed into the quadrature ÃŽ ±, ÃŽ ² coordinates by Clarke Transformation as follows: vÃŽ ±vÃŽ ²v0.=TvRvYvB. (2.3) IÃŽ ±IÃŽ ²I0.=TIRIYIB. (2.4) Where Transformation matrix T=2/31-1/2-1/203/2-3/21/21/21/2 (2.5) Since in a balanced three-phase three-wire system neutral current is zero, the zero sequence current does not exist and zero sequence current can also be eliminated using star delta transformer. These voltages in ÃŽ ±-ÃŽ ² reference frame can further be transformed into rotating d- q reference frame as Fig. 2.2. ÃŽ ² d Y R ÃŽ ± ω B q T1=cosωr-sinωrsinωrcosωr (2.7) Where ωr is the angular velocity of the d- q reference frame as shown in Fig. 2.2. The current components in the d- q reference frame can be similarly obtained using the ÃŽ ±-ÃŽ ² to d-q transformation matrix T1. The unit vector required for this transformation is generated using the grid voltage 2.3 Compensation Strategy vc iL ic VL vs As shown in Fig. 2.3,vs is the supply voltage. vc, Ic are the series compensation voltage, shunt compensation current and vL, iL are the load voltage and current respectively. The source voltage may contain negative, zero as well as harmonic components. The per phase voltage of the system can be expressed as: va=v1pm+sinωtsinÃŽ ¸+valn+k=2∞Vaksin kωt + ÃŽ ¸ka (2.8) Where v1pa is the fundamental frequency positive sequence components, v1naand v10a are negative and zero sequence components respectively. The last term of equation represents the harmonic content in the voltage. In order for the load voltage to be perfectly sinusoidal and balanced, the series filter should produce a voltage of: vah=v1an+v10a+ k=2∞vka sin kωt + ÃŽ ¸ka 2.9 In the latter section, it will be shown how the series-APF can be designed to operate as a controlled voltage source whose output voltage would be automatically controlled according to the above equation. The functions of the shunt active filter is to provide compensation of the load harmonic current, load reactive power demand and also to maintain dc link current constant. To provide load reactive power demand and compensation of the load harmonic and negative sequence currents, the shunt-APF acts as a controlled current source and its output components should include harmonic, reactive and negative-sequence components in order to compensate these quantities in the load current [6]. The per phase load current of shunt active filter is expressed as: Ial=I1pmcos ωt ÃŽ ¸1 + Taln+k=2∞Ialk (2.10) =I1pmcosωt cosÃŽ ¸1 + I1pmsin ωt sin ÃŽ ¸1 k=2∞Ialk (2.11) In order to compensate harmonic current and reactive power demand the shunt active filter should produce a current of: Iah=I1pm+sin ωt sin ÃŽ ¸1 +Ialn+k=2∞Iak (2.12) Then the harmonic, reactive and negative-sequence current will not flow into power source. Hence, the current from the source terminal will be: Ias=Ial-Iah=Ipmcos ωt ÃŽ ¸1 + Taln+k=2∞Ialk (2.13) This is a perfect harmonic free sinusoidal current in phase with voltage. 2.4 Basic Control Function It is evident from above discussion that UPQC should separate out the fundamental frequency positive sequence components first from the other components. Then it is required to control both series and shunt active filter to give output as shown in equations (2.9) and (2.18) respectively. The control strategy uses a PLL based unit vector template for extraction of reference signal from the distorted input supply. The block diagram of extraction of unit vector template is as given in Fig. 2.4. vm va,vb,vc vLa,vLb,vLc The input source voltage at point of common coupling contains fundamental and distorted component. To get unit vector templates of voltage, the input voltage is sensed and multiplied by gain equal to 1/vm, where vm is peak amplitude of fundamental input voltage. These unit vector templates are then passed through a PLL for synchronization of signals. The unit vector templates for different phases are obtained as follows: va=sin ωt vb=sin (ωt-1200) (2.14) vc=sin (ωt+1200) 2.5 Shunt Converter Control The unit vector template of voltage is used to generate the reference signal for shunt APF. The control block diagram of shunt active filter is given in Fig. 2.5. As indicated earlier, the shunt APF compensates current harmonics in addition to maintaining the dc link current at a constant level. To achieve this, dc link current of the UPQC is compared with a constant reference current of magnitude equal to peak of harmonic current [10.]. The error between measured dc link current and reference current is processed in a PI controller. Gatting Signals Ia Ib I vavbvc Iar Ibr Icr dc link Pdc Ploss Idc ref The output of PI controller is added to real power loss component to derive reference source current given as: vÃŽ ±vÃŽ ² = 1/2 -1/2-1/203/2 -3/2 vavbvc (2.15) IÃŽ ±IÃŽ ² =1/2 -1/2-1/203/2 -3/2IaIbIc (2.16) pt=vÃŽ ±tIÃŽ ±t+vÃŽ ²tIÃŽ ²t qt=-vÃŽ ²tIÃŽ ±t+vÃŽ ±tIÃŽ ²t (2.17) In matrix form it is given as: pq = vÃŽ ±vÃŽ ²-vÃŽ ²vÃŽ ± IÃŽ ±IÃŽ ² (2.18) From equation 2.18 the values of p and q can be expressed in terms of dc components plus the ac components as follows: p=p+p q=q+q (2.19) Where p is the dc component of the instantaneous power p, and is related to the fundamental active current. p is the ac component of the imaginary power p, and is related to the harmonic current caused by the ac component of the instantaneous real power q is the dc component of the imaginary instantaneous power q, and is related to the reactive power generated by the fundamental components of voltage and current qis the ac component of the instantaneous imaginary power q, and is related to the harmonic current caused by the ac component of instantaneous reactive power. To compute harmonic free unity power factor, three-phase currents, compensating powers pc and qc are selected as: pc = pldc + ploss (2.20) qc = 0 Where, plossis the instantaneous active power corresponding to the switching loss and resistive loss of UPQC. The total instantaneous active power is calculated by adding real power loss due to switching as shown in Fig.2.5. The orthogonal components of the fundamental current are obtained as follows: IÃŽ ±IÃŽ ² = vÃŽ ±vÃŽ ²-vÃŽ ²vÃŽ ± pcqc (2.21) The a-b-c components of fundamental reference current are obtained as follows: i*sai*sbi*sc =2/30-1/31/3-1/31/3IÃŽ ±IÃŽ ² (2.22) The reference currents are then; compared with actual source current in a hystresis controller band to derive the switching signals to shunt inverter. 2.6 Series Converter Control In order for the load voltage to be perfectly sinusoidal and balanced, the series filter should produce a voltage equal to equation (2.9). The reference load voltages are obtained by multiplying the unit vector templates with a constant equal to peak amplitude of fundamental input voltage. The compensation signals for series filter are thus obtained by comparing these reference load voltages with actual source voltage using equation (2.23). v*fa=vsa-vmva v*fa=vsb-vmvb v*fa=vsc-vmvc (2.23) The control of the series-active power filter is given in Fig. 2.6. The series-APF should behave as a controlled voltage source and its output should follow the pattern of voltage given in equation (2.9). This compensating voltage signal can be obtained by comparing the actual load terminal voltage with the desired value. These compensation signals are compared with actual signals at the terminals of series filter and the error is taken to hystresis controller to generate the required gating signal for series filter as shown in Fig. 2.6. vla v v*fa Gatting va signal v*fb vb v*fa vlb vfa vfb vfc Fig. 2.6 Control block diagram of series-APF 2.7 Modeling of UPQC The three-phase system shown in Fig. 2.7 is considered for verifying the performance of UPQC. Three-phase source feeding this system at one end. For the best performance, UPQC is placed at the midpoint of the system as shown in Fig. 2.7. UPQC is placed between two sections B1and B2 of the transmission line. The complete system parameters are given in Table 2.1. The STATCOM model in UPQC is connected in shunt with transmission line using step down transformer. the voltage can be regulated to improve the voltage stability of the power system. Thus the main function of the STATCOM is to regulate key bus voltage magnitude by dynamically absorbing or generating power to the ac transmission line. The SSSC which is connected by series transformer with transmission line generates three-phase voltage of controllable magnitude and phase angle. This voltage injection in series with the transmission line is almost in quadrature with the line current and hence emulates an equivalent inductive or capacitive reactance in series with the transmission line. A small part of this injected voltage is in phase with the transmission line current supplying the required losses in the Inverter Bridge and transformer. Three-phase AC source Rated voltage 11 kV Frequency 50 Hz SC level 200 MVA Base voltage 11 KV X/R 8 Transmission line parameters Resistance of the line 0.01273 ÃŽ ©/km

Vince Lombardi - Winning is the Only Thing That Matters :: essays research papers fc

Vince Lombardi’s statement that â€Å"winning is the only thing that matters in sport†, is one of the truths that are inherent in the world of sports. Athletes are willing to cheat to guarantee success, either through the use of performance-enhancing drugs, or through the act of injuring others. Lombardi’s statement not only applies to athletes, but it also applies to countries that athletes are representing. Events such as the Olympics and the World Cup of Hockey are a source of national pride and some countries are willing to try anything to bring a little prestige back, while other athletes, who are representing their country will resort to unethical tactics. Judges and officials are bribed in order to win events. Lombardi’s statement also affects coaches, owners, and managers. They too place winning as their number one concern. Fair play generally takes a back seat to the desire for winning that some will bend rules, while others will outright cheat. The corruptness of sports today has lead to many methods of unethical behaviour. Winning is a very important thing not only to athletes, but winning is very important to countries as well. In the early 1960s drugs were used more frequently among the communist nations who wanted to enhance their national prestige through sports. Countries such as China and East Germany have been guilty of using such practices as doping their athletes. The glory of winning a gold medal and what will follow after that is more important than anything else. It one of the major influences behind drug use in sports. The main concern now for athletes who are representing their countries is not just about the satisfaction of winning but the rewards for success. The rewards are staggering, as the dollar volume being showered on winners is second to none. The figures have become so mind-boggling that the interests of people involved in this lucrative business is no longer centred around ethical and health-related concerns. Athletes are willing to give up all that they have worked for their entire lives in order to win a gold medal. Athletes use performance-enhancing drugs to help break records or win gold medals. Blood doping is another example in which athletes attempt to improve performance. Drug related scandals are some of the major concerns with the Olympics. Drug testing was introduced at the Olympics in 1967, when at the 1960 Olympics in Rome, Swedish cyclist Knut Jensen took compound drugs to compete in the road race during which he collapsed and died.

Work attitude in Vietnam

Work attitudes have become the most critical point for managers In the context that there Is a shift from a planned to market economy In developing countries. This raised a question for managers about whether or not this change may affect employee attitudes about work, commitment to a company, satisfaction and willingness to work hard. In a research conducted in Vietnam, three researchers, namely, El NCO Hung, Stephen Apollo and Earn Eagleburger explored and clarified the issues of organizational commitment, Job satisfaction and reasons affecting work attitudes in Vietnam.To begin with, the critical reason for this survey conducted in Vietnam was that Vietnam was one of the most suitable countries for this research where employees have traditionally worked for state-owned enterprises (Goes) but now are starting to work In economic market. Moreover, Vietnam had a potential labor workforce and nearly 80 million people were born after 1975. Thus, If the government can utilize this advan tage by effective Investment or attracting foreign Investors, It will be a considerable competitive force.Otherwise, It might trigger to various social problems. As the research revealed, generally speaking, Vietnamese employees expressed positive work value. In specific, older employees were more committed to their organizations and more satisfied with their jobs, while employees with more education had lower commitment and Job satisfaction. They also reported more committed when they held a Job that was complicated, required more teamwork or they considered their Job as a central life interest.Employees who sought more independent or high income were less satisfied with their Jobs. However, there are some distinctions in attitude of employees between working in Goes and private companies as well as in regions. There was a trend that employees working In private firms were more satisfied and committed than their counterparts In Goes. Relating to regional differences, the attitudes of older workers In the south of Vietnam were more positive than the north and SEE employees In the north had such more negative attitudes than their counterparts in the south.The main purpose of this research was better understand employees as well as find the best way to treat them in order to enhance their organizational commitment and job satisfaction. This research also indicated economic restructuring was the core leading to negative attitudes in the north because nearly all of their Job were in Goes. With the change in this structure, a great deal of downsizing and Job changing may be more extensive in the north, triggering to uncertainty in their minds.

Comparison and Contrast of Main Characters Essay

Nora and Tom are the main characters of two plays, the Doll House and the Glass Menagerie respectively. In comparing and contrasting these two characters, it is vital to analyze the plays and to gain and understanding of their personalities and relationships with other people. Nora is the wife of Torvald, and their marriage is characterized by the domination of Tovarld over Nora and her complacent passivity. As a wife during the late 1800s, it was typical of women to have been treated like children with little to no independence. However, it is the failure of Nora to remain stuck in her gender role as the immature ornament. Tom is the son of Amanda and the brother of Laura, and his position in the family is marked by the absence of his own father. Tom is expected to fully maintain the family, yet his youth and inexperience, coupled by his mother’s demanding exasperation, do not equip him to be a successful head of the household. In analyzing these two characters, it is interesting to note the ways in which Nora and Tom are similar and different in regard to gender roles and passivity. Gender Roles & Passivity In regard to gender roles and passivity, it is clear that Nora and Tom are caught up in the expectations of other people and playing out stereotypical functions to an extreme degree. Nora herself describes her situation as a wife with no ambitions and blames her husband, saying, â€Å"I lived by performing tricks for you†¦ you and father have done me a great wrong†¦ it’s your fault that my life has been wasted† (Ibsen, 1890, 117). In this comment, one can see the full frustration of Nora in regard to her plight as a fully dependent wife. However, one could dispute her allegation that all of the culpability rests on the shoulders of her husband and not at all on herself. As far as Tom is concerned, he is stuck taking care of his mother and sister, when he would truly rather be making more of a life for himself, stating â€Å"I tried to leave you behind me, but I am more faithful than I intended to be† (Williams, 1999, 97). Tom expresses his irritation with the situation of him being expected to perform all of the duties as the head of the household, a role which he increasingly rejects. Similar to Nora, he finds himself playing a part which he does not want to be playing. However, a vital difference is that Tom takes responsibility for remaining passively in a role which does not suit him and does not try to place the full blame on other people. Conclusion Nora and Tom are both characters who find themselves doing the bidding of other people in response to social expectations, rather than following their instincts in living their lives more for themselves. While Nora finds herself shaming her husband for her life mistakes, Tom is more apt to shame himself. However, in the end, both characters are able to break free of the gender roles and passivity which have bound them all too closely and dependently to other people. Nora ends up leaving her husband, just as Tom ends up leaving his wife and mother. While Nora ends the play on a note of anger and full finger pointing, Tome ends the play with a sense of regret that he must leave his family. Nora and Tom are able to escape the oppressive forces in their lives, yet they have markedly different approaches to assigning fault. Works Cited Ibsen, H. (1890). A Doll’s House. W. H. Baker. Williams, T. (1999). The Glass Menagerie. New Directions Publishing.