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Power Electronics
- 3. Course Outline 3 Power Electronic Devices • Diodes • Power Transistors • IGBTs • etc. Power Converters • Uncontrolled Rectifiers • Controlled rectifiers • Inverters • Converters
- 4. What is power electronics? 1) Definition • Power Electronics: is the electronics applied to conversion and control of electric power. Electric Power Converter Power output Power input Control input 4
- 5. 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
- 6. Prerequisites • Power electronics incorporates concepts from the fields of – Analog circuits – Electronic devices – Control systems – Power systems – Magnetics – Electric machines – Numerical simulation 6
- 7. 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
- 8. Applications: Electric Vehicle Tesla Model S Functions of the power electronics: 1. Convert the DC battery voltage to the variable AC required to drive the AC motor • 240 V battery • Variable-frequency, variable- voltage AC drives the motor • AC motor propels the rear axle • Up to 330 kW (acceleration) • Up to 60 kW regenerative braking 2. Control charging of the battery • Interface to 240 V 60 Hz 1φ 100 A circuit in garage. • Control AC current waveform to be sinusoidal, unity power factor. • Control charging of battery to maximize life. 8
- 9. Applications: Hybrid Vehicles Prius Power Electronics Module: • Convert the DC battery voltage to the variable AC required to drive the AC motor. • Includes dc-dc boost converter and dc-3φ ac inverter • Control system can operate in all- electric mode or in hybrid gas+electric mode • Partial-power electronics Under the hood: Gas engine Power electronics module 9
- 10. Applications: Variable-Speed Wind Turbine Systems • AC generator produces “wild ac”: frequency and amplitude change with wind speed. • Utility operates with constant frequency (60Hz/50Hz) 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
- 11. 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. Stand-alone solar: dc-dc converter interfaces solar panels to batteries 11
- 12. A standalone photovoltaic power system 12
- 13. Applications: Computer power supply systems vac(t) iac(t) Charger PWM Rectifier Lithium battery ac line input 85–265 Vrms Inverter Buck converter Boost converter Display backlighting Microprocessor Power management Disk drive Laptop power system iPhone power system and charger 13
- 14. Trends in Power Supplies • Two distinct trends drive electronic power supplies, one of the major classes of power electronic circuits. – At one end, microprocessors, memory chips, and other advanced digital circuits require increasing power levels and increasing performance at very low voltage. – At the other end, the explosive growth of portable devices with rechargeable batteries. The power supplies for these devices and for other consumer products must be cheap and efficient. 14
- 15. Trends in Power Supplies • In the past, bulky “linear” power supplies were designed with transformers and rectifiers from the ac line frequency to provide dc voltages for electronic circuits. • In a well-designed power electronics arrangement today, called a switch-mode power supply, an ac source from a wall outlet is rectified without direct transformation. • The resulting high dc voltage is converted through a dc– dc converter to the 1, 3, 5, and 12V, or other levels required. 15
- 16. 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
- 17. Key Characteristics of Power Converter • All power electronic circuits manage the flow of electrical energy between an electrical source and a load. • The parts in a circuit must direct electrical flows, not impede 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: to build a power converter, we should consider only lossless components. • A realistic converter design must approach 100% efficiency. 17
- 18. Devices Available to the circuit designer 18
- 19. Devices available to the circuit designer Signal processing: avoid magnetics 19
- 20. Devices available to the circuit designer Power processing: avoid lossy elements 20
- 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 21
- 22. Power Electronic Devices • The power Electronic devices provides the utility of switching. • The flow of power through these devices can be controlled via small currents. • Power electronics devices differ from ordinary electronics devices in terms of their characteristics. 22
- 23. Power Electronic Devices • Power Semiconductor Devices can be classified into three groups according to their degree of controllability. – Diodes (on and off controlled by power circuit) – Thyristors (latched on by control signal but must be turned off by power circuit) – Controllable Switches (turned on and off by control signal) 23
- 24. 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. 24 • What if the switch is turned on whenever Vac >0, and turned off otherwise?