Basics of Variable-Speed Drives (VSD) and Power Electronics--Article Index

The rapid adoption of automation techniques in industry has increased the requirement for better process control. This has resulted in many new applications for AC variable speed drives (VSDs) to control the speed and torque of driven machinery. Variable speed drives (VSDs) are also used to meet particular starting and stopping requirements.

The variable speed drives guide promotes a sound understanding of how VSDs work and how to correctly select, install, commission and maintain them. There is also detailed coverage of many typical applications in process control and materials handling such as those for pumping, ventilation, conveyers and hoists.

Our guide benefits anyone associated with the use of VSDs in the industrial or automation environment. Our guide also helps those working in system design as well as site commissioning, maintenance and troubleshooting.

Although a basic understanding of electrical/electronics engineering principles is fundamental, even those with a superficial knowledge of VSDs will substantially benefit from our guide.

In particular, if you work in any of the following areas, you’ll benefit from our guide:

1. Consulting electrical engineers
2. Plant engineers and instrument technicians
3. Operations technicians
4. Electrical maintenance technicians and supervisors
5. Instrumentation and control system engineers
6. Process control engineers
7. Mechanical engineers

Goals of this guide -- learn the following:

1. The principles of AC variable speed drives for industrial speed control
2. The essentials of squirrel cage induction motors
3. The latest developments in power electronic converters used for VSDs
4. How to select the correct AC variable speed drive for industrial applications
5. How to identify faults on VSDs and how to rectify them
6. The key issues about flux vector control and how it can be used in drive applications
7. The main concepts in interfacing the control circuits of VSDs with PLCs/DCSs using serial data communications

Guide outline:

1. Introduction. A review of the fundamentals in variable speed drives including motion concepts, torque speed curves, types of variable speed drives, mechanical variable speed drive methods and electrical variable speed drive methods.
2. 3-phase AC induction motors. These versatile and robust devices are the prime movers for the vast majority of machines. This Section covers the basic construction, electrical and mechanical performance, motor acceleration, AC induction generator performance, efficiency of electric motors, rating of AC induction motors, duty cycles, cooling and ventilation, degree of protection of motor enclosures, methods of starting and motor selection.
3. Power electronic converters. This section deals with the active components (e.g. diodes, thyristors, transistors) and passive components (e.g. resistors, chokes, capacitors) used in power electronic circuits and converters.
4. Electromagnetic compatibility (EMC). Interference in circuits refers to the presence of unwanted voltages or currents in electrical equipment, which can damage the equipment or degrade its performance. The impact of variable speed drives can be severe and this Section examines what causes interference and how to minimize its impact.
5. Protection of AC converters and motors. The protection of AC variable speed drives includes the protection of the AC converter and the electric motor. The main methods of protection are examined.
6. Control systems for AC variable speed drives. The overall control system can be divided into four main areas of the inverter control system, speed feedback and control system, current feedback and control system and the external interface.
7. Selecting VSDs and AC motor converters. Although manufacturers' catalogs try to make it as easy as possible, there are many variables associated with the selection and rating of the optimum electric motor and AC converter for a VSD application. This Section covers many of the principles for the correct selection for AC variable speed drives, which use pwm-type variable voltage variable frequency (VVVF) converters to control the speed of standard AC squirrel cage induction motors.
8. VSD and Power Electronics Installation. The main issues here of general installation and environmental requirements, power supply and earthing requirements, start/stop of AC drives, installing AC converters into metal enclosures, control wiring and commissioning variable speed drives.
9. Special topics and new developments. Typical topics of soft-switching and the matrix converter are examined here.

[2] 3-Phase AC induction motor:

1. Intro to 3-Phase AC induction motors
2. Basic construction
3. Principles of operation
4. Equivalent circuit
5. Electrical and mechanical performance
6. Motor acceleration
7. AC induction generator performance
8. Efficiency of electric motors
9. Rating of AC induction motors
10. Electric motor duty cycles
11. Cooling and ventilation of electric motors
12. Degree of protection of motor enclosures
13. Construction and mounting of AC induction motors
14. Anti-condensation heaters
15. Methods of starting AC induction motors
16. Motor selection

[3] Power electronic converters:

1. Intro
2. Definitions
3. Power diodes
4. Power thyristors
5. Commutation
6. Power electronic rectifiers (AC/DC converters)
7. Gate-commutated inverters (DC/AC converters)
8. Gate-controlled power electronic devices
9. Other power converter circuit components

[4] VSD motors and Electromagnetic compatibility (EMC)

[5] Protecting AC converters and motors

[6] Control systems for AC Motor VSDs (part 1, part 2, part 3)

[7] Selecting VSDs and AC motor converters (part 1, part 2, part 3, part 4)

[8] Installing VSDs and related Power Electronics

[9] VSD and Power Electronics--Special topics, new developments

[Extra] Motor Protection -- via direct temperature sensing