Unit 68 Applications of Power Electronics

 

Unit 68:

Applications of Power Electronics


Unit code:
D/601/1391

QCF level:
4


Credit value:
15






Aim

This unit will develop a technical understanding of power electronics and their application to variable speed drives.

Unit abstract

Power electronics involves the use of semiconductor devices to control a range of applications in rectification, DC and AC motor control and controlled power supplies. To meet the challenges expected of a modern ‘heavy current’ engineer the unit carries an emphasis on the application of power electronics to variable speed controllers. The focus is on the power aspects rather than the associated detail of the electronic control and firing circuitry.

In every aspect of engineering variability exists and therefore acceptable tolerances are specified to define close limits of output. Testing and measurement must make use of safe techniques and in this case are conducted via the use of isolating probes and transducers in systems operating from earthed power systems.

The unit involves practical investigations of common configurations of controlled rectifier and inverter systems, as applied to alternating and direct current motor control. The use of commercial/industrial variable speed drives provides a relevant and convenient method of investigation. To broaden the scope of the subject, non-drive applications of power electronics are investigated and developed to meet local industrial requirements.

No matter in which sector he/she is involved, the modern engineer needs to be energy conscious and therefore must seek and implement ways of conserving valuable resources.
 Learning outcomes

On successful completion of this unit a learner will:

1     Understand common configurations for controlled and uncontrolled rectification

2     Understand the methods used for AC motor control

3     Understand the methods used for DC motor control

4       Understand other applications of power electronics.



Unit content

1      Understand common configurations for controlled and uncontrolled rectification

Standard configurations: half wave and full wave bridge circuits; resistive and inductive loads, flywheel diodes

Signal parameters: amplitude; peak-to-peak; waveforms; full and half wave forms; ripple; average and root-mean-square (RMS) values; pulse number; harmonics; resonance calculations of signal parameters of rectified waveforms eg average and root-mean-square (RMS) values, pulse number, waveforms, harmonics

Device protection: protection methods for power semiconductors eg over-voltage, over-current, transients

Measurement techniques: safety considerations in a heavy current power environment eg in systems where voltages exceed 50V; use of isolated differential voltage attenuator probes; Hall effect current probes; power oscilloscope


2      Understand the methods used for AC motor control

Frequency conversion methods: inverter switching strategies eg quasi-square-wave, pulse width modulation, cycloconverter, waveforms, harmonics, filters

AC motor control: soft starter; speed; torque; reversal; braking; voltage; frequency; voltage/frequency (V/Hz); vector control

Investigation of an industrial AC motor controller: preparation and interpretation of circuit and block diagrams; setting of parameters eg min/max speed, ramp up/down time, current/torque limits; applications eg process control, mills, fans, conveyor systems; specification and selection


3      Understand the methods used for DC motor control

Speed control of DC motor: armature voltage; field weakening; DC choppers; controlled rectifiers; closed loop; tacho-generator; reversal; braking; waveforms

Torque control of DC motor: armature current control loops; speed reversal; braking; single quadrant; four quadrant operation; regeneration

Investigation of an industrial DC motor controller: preparation and interpretation of circuit and block diagrams; setting of parameters eg min/max speed, ramp up/down time, current/torque limits; applications eg process control, mills, pumps, CNC machinery; specification and selection


4      Understand other applications of power electronics

Principles: comparison of the principles of operation; control techniques; protection methods; use of block and circuit diagrams

Other applications: applications eg uninterruptible power supplies, high voltage DC links, inductive heating, welding machines, compact fluorescent lighting


Learning outcomes and assessment criteria


Learning outcomes
Assessment criteria for pass


On successful completion of
The learner can:


this unit a learner will:










LO1 Understand common

1.1
compare standard configurations used in single and


configurations for controlled


three-phase systems


and uncontrolled

1.2
calculate signal parameters of a rectified waveform


rectification










1.3
explain methods of device protection




1.4
use safe measurement techniques when measuring





current and voltage in earthed systems








LO2 Understand the methods

2.1
explain methods of frequency conversion


used for AC motor control

2.2
explain methods of control for an AC motor








2.3
investigate an industrial AC motor controller







LO3 Understand the methods

3.1
explain methods of speed control for a DC motor


used for DC motor control

3.2
explain methods of torque control for a DC motor








3.3
examine an industrial DC motor controller







LO4 Understand other

4.1
compare the principles of three other applications of


applications of power


power electronics


electronics

4.2
investigate an area of application for each of the three









applications.







Guidance



Links

This unit may be linked with Unit 1: Analytical Methods for Engineers, Unit 5: Electrical and Electronic Principles, Unit 63: Electrical Power and Unit 67: Further Electrical Power.

Essential requirements

Centres will need to provide access to sufficient laboratory and test equipment to support a range of practical investigations (eg differential isolated voltage probes, Hall effect current probes, power analyser, DC and AC motors, industrial motor controllers, etc).

Employer engagement and vocational contexts

The delivery of this unit will benefit from centres establishing strong links with employers willing to contribute to the delivery of teaching, work-based placements and/or detailed case study materials.



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