EE 261: DC & Asynchronous Machines - KNUST

• KNUST ranks number one globally for quality education (SDG 4).
• The course is EE 261, Asynchronous and DC Machines.
• The lecturer is Ing. Francis Boafo Effah, PhD, a senior lecturer in the Department of Electrical & Electronic Engineering, Faculty of Computer & Electrical Engineering, College of Engineering.
• Contact Email: [email protected]

Course Content Summary

• Covers the basic principles behind the operation of electrical machines.
• Details principles and structure of DC machines.
• Details principles and structure of Asynchronous (Induction) machines.

Learning Outcomes

• Covers basic concepts of electromagnetism and the underlying physical principles in electrical machines.
• Provides an understanding of the differences in construction and operation between DC and Asynchronous (Induction) machines.
• Covers how to select and employ techniques for analyzing electrical machines.
• Provides awareness of advancements in magnetic materials and power electronic converters.
• Provides awareness of technological breakthroughs in electrical machines for electrically driven mechanical loads in aerospace, automotive, and renewable energy generation.

Essential Knowledge

• Vector representation and calculus.
• Magnetic Fields.
• Steady-state DC circuit analysis, including DC power.
• Steady-state AC circuit analysis, including RLC loads, phase relationships, and power factor.
• Three-phase systems—star and delta connections, active and reactive power.

Recommended Books

• D. Stephen, A. E. Fitzgerald (2014): Electric machinery
• G. Turan, (2012): Electrical machines with MATLAB
• B. A. Theraja, A. K. Theraja (2005): A Textbook of Electrical Technology, S. Chand & Company Ltd, New Delhi
• Stephen D. Umans (2013): Fitzgerald & Kingsley's Electric machinery, 7th edition, McGraw-Hill Education
• T. Wildi (2013): Electrical Machines, Drives and Power System, 6th edition

Electrical Machines Overview

• Electrical machines act as converters of electrical energy to mechanical energy and vice versa.
• Traditional applications include industrial drives, pumps, and generators.
• Expanding application areas include:
• Embedded generation
• Electric and Hybrid vehicles
• All-Electric ships
• More Electric Aircraft
• Automation and manufacture

Enabling Technologies

• Enablers:
• Power Electronics
• Microprocessors
• New materials (permanent magnets)
• Drivers:
• Energy efficiency and reduced CO2 emissions
• Energy utilization
• More Electric Transport
• Renewable Energy

Electric and Hybrid Vehicles

• Improved efficiency of the traction drive system
• Increasing use of electrical machines for:
• Electrically assisted turbo-charging
• Electrical power steering
• Waste (exhaust) energy recovery

Pod Propulsion

• Increases usable space
• Decouples engine speed from propeller speed
• Faster dynamics
• Optimizes power use
• Several propellers supplied from one generator at low power
• No gearbox

More Electric Aircraft

• Reduced weight at aircraft level
• Higher efficiency
• Electrical machines are (or will be) used for:
• Generation (more electrical engine)
• Electrical actuation
• Environmental conditioning system (ECS)
• Fuel pumps, thrust reversers

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

Fundamental Questions

• 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 analyze the working method of a particular machine type?

Electrical Machine Components

• All electrical machines transfer energy between mechanical and electrical systems.
• Electrical power is expressed as Voltage times current (v × i).
• Mechanical power is expressed as either:
• Rotational form: Torque times angular velocity (Tm × Wm)
• Linear form: Force times linear velocity (Fm × Vm)
• Machines may be translational or rotational, involving mechanical movement.
• Machines have a fixed part (stator) and a moving part (rotor).

Conversion Types

• Electrical to mechanical conversion - Motor.
• Mechanical to electrical conversion - Generator.
• All machines can work in either mode.

Machine Form Factors

• Rotational machines look similar with a round or rectangular body and a shaft, electrical connections fastened to the top or side.
• Differences in forms are due to:
• Different electrical power inputs
• Different operation conditions
• Different operating requirements
• DC motors need to be operated from a DC supply or controller from the mains.
• AC motors can operate directly from the AC mains supply or with variable frequency from the mains.
• Induction motors produce torque at any speed, synchronous motors only produce torque at synchronous speed.
• DSP-based control via variable frequency AC power electronic supplies is common for AC motors.
• Some machines need a special power electronic controller
• Different motors have different characteristics like temperature, cost and efficiency.

Course Focus

• Analyze how machines work.
• Determine the size of a machine needed to deliver particular power.
• Discuss what is needed to know to use a certain machine type.
• Analyze the working method of a certain machine type.
• The remaining course will answer these questions for DC and Asynchronous machines.

Explore the principles and structure of DC and asynchronous machines in KNUST's EE 261 course. Understand electromagnetism and the differences in construction and operation. Learn techniques for analyzing electrical machines.