EE 261 Asynchronous and DC Machines PDF

EE 261 ASYNCHRONOUS AND DC MACHINES Ing. Francis Boafo Effah, PhD Senior Lecturer Department of Electrical & Electronic Eng. Faculty of Computer & Electrical Eng. College of Engineering 1 Room BKB 13, Bamfo Kwakye Building Email: [email protected]...

EE 261 ASYNCHRONOUS AND DC MACHINES Ing. Francis Boafo Effah, PhD Senior Lecturer Department of Electrical & Electronic Eng. Faculty of Computer & Electrical Eng. College of Engineering 1 Room BKB 13, Bamfo Kwakye Building Email: [email protected] INTRODUCTION 2 Summary of content Basic principles behind the operation of electrical machines Principles and structure of DC machines Principles and structure of Asynchronous (Induction) machines 3 Learning outcomes Basic concepts of electromagnetism and the underlying physical principles of operation of electrical machines. Understand the differences in construction and operation between DC and Asynchronous (Induction) machines. Select and employ techniques for analysing electrical machines. Be aware of the advancements in magnetic materials and power electronic converters that drive forward electrical machine technology. Be aware of the technological breakthroughs in electrical machines that are driving forward electrically driven mechanical loads in aerospace, automotive, and renewable energy generation. 4 Things you should know well Vector representation and calculus. Magnetic Fields. Steady-state DC circuit analysis – DC power. Steady-state AC circuit analysis – RLC loads, phase relationships, power factor. Three-phase systems – star and delta connections, active and reactive power. You should revise this material to ensure you have a good grounding in the basics, which will be essential in completing this course. 5 Recommended books 1. D. Stephen, A. E. Fitzgerald (2014): Electric machinery 2. G. Turan, (2012): Electrical machines with MATLAB 3. B. A. Theraja, A. K. Theraja (2005): A Textbook of Electrical Technology, S. Chand & Company Ltd, New Delhi 4. Stephen D. Umans (2013): Fitzgerald & Kingsley’s Electric machinery, 7th edition, McGraw-Hill Education 5. T. Wildi (2013): Electrical Machines, Drives and Power System, 6th edition 6 A Glimpse of Electrical Machines Converter of electrical energy to mechanical energy and vice versa. Traditional Applications - Industrial drives, pumps, generators. Expanding application areas: Embedded generation, Electric and Hybrid vehicles, The All-Electric ship, The More Electric Aircraft, Automation and manufacture. 7 Enabling Technologies Enablers Power Electronics Microprocessors New materials (permanent magnets) Drivers Energy efficiency and reduced CO 2 emissions Energy utilisation More Electric Transport Renewable Energy 8 Electric and Hybrid Vehicles Improved efficiency of the traction drive system. Electrical machines are also increasingly being used for: Electrically assisted turbo- charging, Electrical power steering and Waste (exhaust) energy recovery. 9 Pod propulsion Increases usable space Decouples engine speed from propeller speed Faster dynamics Optimised power use: Several propellers supplied from one generator at low power No gearbox 10 More Electric Aircraft Reduced weight at aircraft level and thus higher efficiency Electrical machines are (or will be) used for: Generation (more electrical engine) Electrical actuation Environmental conditioning system (ECS) Fuel pumps, thrust reversers. 11 Renewable Energy Rapidly expanding application area. Different types of machines can be used, for example: Doubly-fed induction machines Wound synchronous machines Permanent magnet machines Reliability and maintainability are essential properties, especially for machines used in off-shore generation. 12 Fundamental matters What constitutes an electrical machine? Why are there different forms? How do they work? How big will a machine have to be to deliver a particular power? What do I need to know to use a particular machine type? How can I analyse the working method of a particular machine type? 13 What constitutes an electrical machine? All electrical machines are used to transfer energy between mechanical and electrical systems. Electrical power is expressed as: Voltage times current (𝑣 × 𝑖) Mechanical power can be expressed either as: Rotational form: Torque times angular velocity (𝑇𝑚 × 𝜔𝑚 ) Linear form: Force times linear velocity (𝐹𝑚 × 𝑉𝑚 ) 14 What constitutes an electrical machine? Thus, machines may be either translational or rotational, but they all involve mechanical movement at some time. Thus, all machines have two parts, one fixed (stator) and the other moving relative to it (rotor). Conversion Electrical to mechanical is a Motor. Mechanical to electrical is a Generator. All machines can work in either mode. 15 Why are there different forms? The rotational ones all look very similar from the outside: A round or rectangular body with a shaft sticking out of one end—usually some box to make the electrical connections fastened to the top or side. Differences may be due to the fact: The electrical power input is different The operation conditions are different The operating requirements are different 16 Why are there different forms? Differences may be due to the fact: The electrical power input is different. DC motor must be operated from a DC supply or via a power electronic controller from the mains. AC motor can operate directly from the AC mains supply or a power electronic variable frequency AC source from the mains or a DC source. The operation conditions are different. Induction motors can produce torque at any speed other than synchronous, whilst synchronous motors only produce torque at synchronous speed. 17 Why are there different forms? Differences may be due to the fact: The operating requirements are different DC machines were favourites for speed control up until some time ago. DSP-based control via variable frequency AC power electronic supplies is now common primarily for AC motors. Some machines can’t operate without a special power electronic controller, e.g. switched reluctance machines. Different motors have different characteristics: temperature, cost, efficiency,… 18 What’s next? How do they work? How big will a machine have to be to deliver a particular power? What do I need to know to use a particular machine type? How can I analyse the working method of a particular machine type? The remaining part of the course will answer these questions for DC and Asynchronous machines. 19 THANK YOU ANY QUESTIONS?