BEE208S

Unit Description and General Aims

The objective of this unit is for students to obtain detailed knowledge of the fundamental principles of power electronics; the devices used in power electronics; common circuits, such as converters, inverters, and switched mode power supplies; and, the controls applicable to these circuits. Information covered in this unit will also include variable speed drives for DC and AC motors, their protection, control, and applications in industry. Students will also undertake a project involving AC variable speed drive selection for typical applications, including their required settings and energy savings estimates.

Learning Outcomes

On successful completion of this Unit, students are expected to be able to:

1. Discuss the principles behind different power electronic devices, typical circuits based on the devices, and their applications.
   Bloom’s Level 4
2. Design the basic parameters of a switched mode power supply (SMPS), including the selection of the components used.
   Bloom’s Level 6
3. Explain the principles of controlling the output of rectifiers and their application in DC drives.
   Bloom’s Level 4
4. Explain the different types of inverters and compare their relative advantages and disadvantages.
   Bloom’s Level 4
5. Discuss the typical control methods of a pulse width modulated (PWM) AC drive focussing on their energy saving feature.
   Bloom’s Level 4
6. Select an appropriate AC drive for a given application and work out its settings.
   Bloom’s Level 6

Student assessment

-

Prescribed and Recommended Readings

Required textbook(s)

• Barnes, M. (2003). Practical Variable Speed Drives and Power Electronics, 1st Edition, Newnes – ISBN: 978-0750658089

Reference Materials

• Rashid, M. H. (2017). Power Electronics Handbook, 4th Edition, Butterworth-Heinemann – ISBN: 978-0128114070
• EIT reference book on Variable Speed Drives (Course code VSD)
• The number of peer-reviewed journals and websites (advised during lectures).
• An example of such webpage is: http://en.wikipedia.org/wiki/Vector_control_(motor)

Unit Content

Topics 1 and 2

Power electronic devices, typical applications, and circuits

1. Power diodes, their types and working principles
2. Power transistors, their types and working principles
3. Thyristors, their types and working principles
4. Gate turn off thyristors, their types and working principles
5. IGBT and IGCT, their construction and working principles
6. Uncontrolled and controlled rectifiers, their output waveforms and output voltage calculation
7. Inverters: Devices used and output waveforms; effect of load inductance

Topics 3 and 4

Switched mode power supply circuits, design, and component ratings

1. Need for switched mode power supply
2. Working principle of a switched mode power supply
3. Typical circuit of a switched mode power supply
4. Output wave form of a switched mode power supply
5. Effect of a filter on the output waveform
6. Design aspects of a switched mode power supply
7. Component selection
8. Control of switched mode power supply
9. Stability issues

Topics 5 and 6

Rectifiers, their types, control methods, and DC drives in the industry

1. Common devices used for power rectifier circuits
2. Uncontrolled rectifier; single and 3 phase circuits of different configurations
3. Output voltage and waveforms of an uncontrolled rectifier
4. Controlled rectifier and control methods
5. The output waveform of differently controlled rectifiers
6. Comparison of different devices used as controlled rectifiers
7. DC drives: principles of speed control by armature voltage and by field weakening
8. Applying controlled rectifiers for variable speed DC drives
9. Common industrial applications of DC drives, their advantages and shortcomings

Topic 7

Inverter basic principle, voltage and current source inverters, and line-commutated inverters

1. Basic principle of an inverter using switching as the basis of getting an AC output from DC input
2. Voltage source and current source inverters
3. Line commutated inverters
4. Comparison of different types and their applications
5. Waveforms obtainable with different types of inverters

Topics 8 and 9

Pulse width modulated AC drives, open loop drives, vector control drives, and sensor-less vector control drives

1. Pulse width modulation principle
2. Importance of carrier frequency in a PWM inverter
3. Simple circuit applying PWM such as UPS with fixed output frequency/voltage
4. Importance of DC bus and choice of DC bus voltage
5. The advantage of a PWM circuit and limitations
6. PWM application to AC motors using VVVF principle
7. Problems when applying PWM AC drives with a high carrier frequency
8. Control strategies to obtain coordinated V/F control in open loop drives
9. Performance improvement using feedback methods
10. Vector control principles/applications
11. Sensorless vector control principles/applications

Topics 10 and 11

Typical applications of AC drives, drive selection for different applications, energy saving calculations, and drive settings

1. Typical applications of different forms of inverters for control of LV and HV AC motors
2. Need for variable speed AC drives and benefits (when compared to DC drives)
3. AC drives with induction and synchronous motors – the main differences
4. Torque-speed characteristics of different mechanical equipment
5. Energy saving calculations when using variable speed drives
6. Selection of a PWM AC drive for a given application by comparing motor and load torque
7. Selection of a suitable motor for use with an AC drive
8. Special requirements of motors when driven by AC PWM drives
9. Bearing problems and need to use insulated bearings
10. Retrofitting a VSD in an existing installation and interfacing with C&I systems
11. Harmonic problems and EMI
12. Typical setting options available and how to determine the settings in a given application

Topic 12

Unit Review

In the final week, students will have an opportunity to review the contents covered so far. Opportunity will be provided for a review of student work and to clarify any outstanding issues. Instructors/facilitators may choose to cover a specialized topic if applicable to that cohort.

Software/Hardware Used

Software

• Software: MATLAB/SIMULINK; PSCAD

• Version: PSCAD Version 5

• Instructions:  N/A

• Additional resources or files: N/A

Hardware

• N/A