Power Electronics: Introduction, Devices, and Applications, Slides of Power Electronics

Download Power Electronics: Introduction, Devices, and Applications and more Slides Power Electronics in PDF only on Docsity! Power Electronics HANY EBRAHIM TAHA ELBIALY Lecture-1 Introduction 1 Lecture Outline  Introduction to subject  Application Areas  Power Electronic Devices  Power Converters 2 What is power electronics? A more exact explanation: • The primary task of power electronics is to process and control the flow of electric energy by supplying voltages and currents in a form that is optimally suited for user loads. 5 Prerequisites • Power electronics incorporates concepts from the fields of – Analog circuits – Electronic devices – Control systems – Power systems – Magnetics – Electric machines – Numerical simulation 6 Scope • It is not possible to build practical computers, cell phones, personal data devices, cars, airplanes, industrial processes, and other everyday products without power electronics. • Alternative energy systems such as wind generators, solar power, fuel cells, and others require power electronics to function. • Technology advances such as electric and hybrid vehicles, laptop computers, microwave ovens, flat-panel displays, LED lighting, and hundreds of other innovations were not possible until advances in power electronics enabled their implementation. • Although no one can predict the future, it is certain that power electronics will be at the heart of fundamental energy innovations. 7 Applications: Variable-Speed Wind Turbine Systems • AC generator produces “wild ac”: frequency and amplitude change with wind speed. • Utility operates with constant frequency (60 Hz) constant voltage ac. • Power electronics changes the frequency and voltage, and also implements control functions • Cycloconverter, or • DC link system: rectifier, boost dc-dc, inverter 10 Applications: Photovoltaic Solar Power Systems DC Transformer 1:8 Zero-voltage switching Buck-boost converter (noninverting) + 48 V – PV input 12- 100 V + 400 V – Output to inverter Controller Grid-tied solar: inverter converts dc of solar panels to ac for grid. The grid-tied system will allow you to have more savings because it is efficient, it offers net metering, and it requires a low cost of equipment and installation Stand-alone solar: dc-dc converter interfaces solar panels to batteries A stand-alone solar system the solar panels are not connected to a grid but instead are used to charge a bank of batteries 11 A standalone photovoltaic power system The system constructed in ECEN 4517/5517 Power Electronics and Photovoltaic Systems Laboratory 12 Trends in Power Supplies • In the past, bulky "linear" power supplies with transformers and rectifiers were developed from the AC mains frequency to provide DC voltages for electronic circuits. • In a well-designed power electronic arrangement, now called a switching power supply, an AC source from a wall outlet is rectified without direct conversion. • The resulting high DC voltage is converted to the required 1, 3, 5, and 12 V or other values by a DC-DC converter. 15 Trends in Power Supplies • A personal computer commonly requires multiple 3.3- and 5-V supplies, 12-V supplies, additional levels, and a separate converter for 1-V delivery to the microprocessor. • Only a switch-mode supply can support such complex requirements with acceptable costs. 16 Key Characteristics of Power Converter • All power electronic circuits manage the flow of electrical energy between an electrical source and a load. • The parts of an electric circuit must conduct the electric currents and not stop them. • The function of the power converter in the middle is to control the energy flow between a source and a load. • A crucial point emerges for the construction of a power converter, we should consider only lossless components. • A realistic converter design must approach 100% efficiency. • In power electronics, rectification is the process of converting AC to DC, so a rectifier and an AC to DC converter mean the same thing. Rectifiers convert AC to DC, while converters convert AC to DC or DC to AC. Devices available to the circuit designer Power processing: avoid lossy elements 20 • Buck converters enable DC-DC conversion in power supplies to step down a high input voltage to a lower output voltage. • A boost converter (step-up converter) is a DC-to-DC power converter that steps up voltage (while stepping down current) from its input (supply) to its output (load). •  Switched-mode power supply (switching-mode power supply, switch-mode power supply, switched power supply, SMPS, or switcher) is an electronic  power supply that incorporates a switching regulator to convert electrical power efficiently . • In a linear power supply, the frequency input from an outlet or another source is input directly to the transformer, whereas in a switching power supply, the current after rectification is sent to the transformer as a high-frequency pulse • Switching semiconductor: Transistors and other semiconductor devices may also be used as switches. 21 Power loss in an ideal switch • Switch closed: v(t) = 0 • Switch open: i(t) = 0 • In either event: p(t) = v(t) i(t) = 0 • Ideal switch consumes zero power i v + – 1 0 22 Conversion Examples • Single-Switch Circuits – Consider the circuit shown in figure. – It contains an ac source, a switch, and a resistive load. – It is a simple but complete power electronic system. 25 • What if the switch is turned on whenever Vac >0, and turned off otherwise? 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