What Is Power Electronics Engineering Essay

What Is Power Electronics Engineering EssayPower electronics involves the study of electronic lots intended to control the unraveling of electrical efficiency. These circuits handle actor flow at levels much eminenter than the individual device ratings.It has been said that people do non use electricity, alone rather they use communication, light, mechanical work, entertainment, and all the tangible benefits of both energy and electronics. In this sense, electrical engineering is a discipline very much concern in energy changeover and information. In the prevalent world of electronics engineering, the circuits engineers design and use are intended to convert information, with energy merely a unessential checkation in most cases. This is true of both analog and digital circuit design. In radio frequency applications, energy and information are sometimes on a more equal footing, but the main function of any circuit is that of information transfer.What about the conversion and control of electrical energy itself? electricalal energy commencements are varied and of many types. It is natural, then, to consider how electronic circuits and systems can be applied to the challenges of energy conversion and management. This is the framework of originator electronics, a discipline that is defined in terms of electrical energy conversion, applications, and electronic devices. More specifically, Rectifiers are probably the most familiar example of circuits that meet this definition. Inverters (a general term for dc-ac converters) and dc-dc converters for world-beater supplies are also greens applications. As shown in Fig. 1.1, tycoon electronics represents a median point at which the topics of energy systems, electronics, and control adjoin and combine 1.Any useful circuit design for the control of power must address issues of both devices and control, as well as of the energy itself. Among the odd aspects of power electronics are its emphasis on large semiconductor devices, the application of magnetic devices for energy storage, and surplus control methods that must be applied to nonlinear systems. In any study of electrical engineering, power electronics must be placed on a level with digital, analog, and radio-frequency electronics if we are to reflect its distinctive design methods and unique challenges.FIGURE 1.1 Control, energy, and power electronics are interrelated.All power electronic circuits manage the flow of electrical energy between some sort of source and a load. The parts in a circuit must direct electrical flows, non impede them. A general power conversion system is shown in Fig. 1.2. The function of the power converter positioned at the middle is that of controlling energy flow between a presumption electrical source and a given load. For our purposes, the power converter forget be implemented with a power electronic circuit. As a power converter appears between a source and a load, any energy used inwardly the converter is lost to the overall system. A crucial point emergesto build a power converter, we should consider only lossless components. A realistic converter design must approach 100% efficiency. A power converter connected between a source and a load also affects system reliability.FIGURE 1.2 General systems for electric power conversionA circuit built from ideal switches will be lossless. As a result, switches are the main components of power converters, and many people equate power electronics with the study of switching power converters. Magnetic transformers and lossless storage elements such as capacitors and inductors are also valid candidates for use in power converters. The complete concept, shown in Fig. 1.3, illustrates a power electronic system. much(prenominal) a system consists of an energy source, an electrical load, a power electronic circuit, and control functions. The power electronic circuit contains switches, lossless energy storage elements, and magnetic transformers. The controls take information from the source, load, and designer and then determine how the switches operate to achieve the desired conversion. The controls are usually built up with conventional low-power analog and digital electronics.FIGURE 1.3 a basic power electronic systemTrends in Power Supplies As speak tos of electronics decline, the power supply becomes a larger dissever of system cost and design effort. One major manufacturer estimates that power supply cost will soon reach 50% of the total cost of a typical electronic product such as a cordless telephone or personal computing device. Thus, new technology developments in power supplies are critically important.In the past, bulky linear power supplies were designed with transformers and rectifiers from the ac line frequency to provide low-level dc voltages for electronic circuits. novel in the 1960s, use of dc sources in aerospace applications led to the development of power electronic dc-dc conversion ci rcuits for power supplies. In a typical power electronics battle array today, an ac source from a wall outlet is rectified without any transformation the resulting high dc voltage is converted through a dc-dc circuit to the 5V, 12 V, or some other level required. These switched-mode power supplies are rapidly supplanting linear supplies across the full spectrum of circuit applications. A personal computer commonly requires three different 5V supplies, two .12 V supplies, a 12 V supply, a 24 V supply, and perhaps a few more.This does not include supplies for 1 Introduction 3 video display or peripheral devices. Only a switched-mode supply can support such analyzable requirements without high costs. The bulk and weight of linear supplies make them infeasible for hand-held communication devices, calculators, notebook computers, and similar equipment. Switched-mode supplies often take advantage of MOSfield-effect transistor semiconductor technology. Trends toward high reliability, lo w cost, and miniaturization have reached the point at which a 5 V power supply sold today might last 1,000,000 hr (more than 100 yr), provide 100Wof output in a package with volume This type of supply brings an interesting dilemma the ac line cord to plenty it in actually takes up more space than the power supply itself. Innovative concepts such as integrating a power supply within a connection cable will be used in the future.Device technology for power supplies is being driven by expanding needs in the automotive and telecommunications industries as well as in markets for portable equipment. The automotive industry is making a transition to 42 V systems to handle change magnitude electric power needs. Power conversion for this industry must be cost effective, yet rugged enough to survive the high vibration and panoptic temperature range to which a passenger car is exposed. Global communication is possible only when sophisticated equipment can be used almost anywhere.This brings a special challenge, because electrical supplies are neither reliable nor consistent throughout much of the world. While in North America voltage swings in the domestic ac supply are often Given the enormous size of worldwide markets for telephones and consumer electronics, there is a clear need for flexible-source equipment. Designers are challenged to obtain maximum death penalty from small batteries, and to create equipment with minimal energy requirements.DEVICE TYPE CHARACTERISTICS OF POWER DEVICESDiode Current ratings from 5000 A. Voltage ratings from 10V to 10 kV or more. The fastest power devices switch in BJT (Bipolar Junction Transistor) Conducts collector current (in one direction) when sufficient base current is applied. Power device current ratings from 0.5 to 500 A or more voltages from 30 to 1200V. Switching times from 0.5 to 100 ms. The function applies to dc-dc circuits combinations with crystal rectifiers are used in inverters. Power BJTs are being supplanted b y FETs and IGBTs.FET (Field outlet Transistor) Conducts drain current when sufficient gate voltage is applied. Power FETs (nearly always enhancement mode MOSFETs) have a parallel connected reverse diode by virtue of their construction. Ratings from _1 to _100 A and 30 up to 1000V. Switching times are fast, from 50 or less up to 200 ns. The function applies to dc-dc conversion, where the FET is in wide use, and to inverters.IGBT (Insulated Gate Bipolar Transistor) A special type of power FET that has the function of a BJT with its base driven by a FET. Faster than a BJT of similar ratings, and easy to use. Ratings from 10 to 600 A, with voltages of 600 to 1700V. The IGBT is popular in inverters from _1 to 100kW or more. It is found almost exclusively in power electronics applications.SCR (Silicon Controlled Rectifier) A thyristor that conducts give care a diode after a gate pulse is applied. Turns off only when current becomes zero. Prevents current flow until a pulse appears. Rati ngs from 10 up to more than 5000 A, and from 200V up to 6 kV. Switching requires 1 to 200 ms. widely used for controlled rectifiers. The SCR is found almost exclusively in power electronics applications, and is the most common member of the thyristor family.GTO (Gate Turn-Off Thyristor) an SCR that can be turned off by sending a negative pulse to its gate terminal. Can substitute for BJTs in applications where power ratings must be very high. The ratings approach those of SCRs, and the speeds are similar as well. Used in inverters rated 100 kW.TRIAC A semiconductor constructed to resemble two SCRs connected in reverse parallel. Ratings from 2 to 50 A and 200 to 800V. Used in lamp dimmers, home appliances, and hand tools. Not as rugged as many other device types, but very convenient for many ac applications.MCT (MOSFET Controlled Thyristor) A special type of SCR that has the function of a GTO with its gate driven from a FET. oftentimes faster than conventional GTOs, and easier to us e. These devices are supplanting GTOs in some application areas.POWER CONVERTERSThe power processors usually consist of more than one power conversion stage where the operation of these stages is decoupled on an instantaneous basis by means of energy storage elements such as capacitors and inductors. Therefore, the instantaneous power input does not have to equal the instantaneous power output.We will refer to each power conversion stage as a converter. Thus, a converter is a basic module (building block) of power electronic systems. It utilizes power semiconductor devices controlled by signal electronics (integrated circuits) and possibly energy storage elements such as inductors and capacitors. Based on the form (frequency) on the two sides, converters can be divided into the following broad categories1. AC to DC2. DC to AC3. DC to DC4. AC to ACWe will use converter as a generic tenn to refer to a single power conversion stage that may coif any of the functions listed above. To b e more specific, in ac-to-dc and dc-to-ac conversion, rectifier refers to a converter when the average power flow is from the ac to the dc side. Inverter refers to the converter when the average power flow is from the dc to the ac side. In fact, the power flow through the converter may be reversible.Power Electronic Applications(a) ResidentialRefrigeration and freezersSpace thawingAir conditioningCookingLightingElectronics (personal computers,other entertainment equipment)(b) CommercialHeating. ventilating, and airconditioningCentral refrigerationLightingComputers and office equipmentUninterruptible power supplies(UPSs)Elevators(c) industrialPumpsCompressorsBlowers and fansMachine tools (robots)Arc furnaces, induction furnacesLightingIndustrial lasersInduction heatingWelding(d) TransportationTraction control of electric vehiclesBattery chargers for electric vehiclesElectric locomotivesStreet cars, trolley busesSubwaysAutomotive electronics including enginecontrols(e) Utility system sHigh-voltage dc transmission (HVOC)Static var compensation (SVC)Supplemental energy sources (wind,photovoltaic), fuel cells faculty storage systemsInduced-draft fans and boilerfeed water pumps(f) AerospaceSpace shuttle power supply systemsSatellite power systemsAircraft power systems(g) TelecommunicationsBattery chargersPower supplies (dc and UPS)