Web handling is a small player (<10% of the market) for Variable Speed Drives. Most of our drives are used in fractional or low-power applications. High-power drives (0.4 to 200 MVA) are used in mission-critical applications in industries such as fans, magnetic levitation traction, wind energy, pumps, compressors, mining, petrochemical, and metals.
There is a lot of design work being done with drives to improve on some of the known deficiencies with the Pulse Width Modulation (PWM) drives and induction motors commonly used in web handling. The most common drive topology is called a Two-Level Variable Speed Control (2L-VSD) The known problems or weaknesses of commonly available low voltage drives (<690V) include:
- Voltage limitations
- Low voltage requires high current and heavier gauge cabling
- Full Regenerative applications
- Need for a Load Filter once cable length reaches a limit
- Heat Dissipation and losses
- Uses squirrel cage induction motors. Synchronous motors and permanent magnet motors require different invertors and controls.
- There are many new semiconductor switches besides the thyristors and Insulated Gate Bipolar Transistors (IGBT’s) in common use.
- Power Quality (power factor and harmonics)
- Single Point of Failure
An article in IEEE Industry Applications Magazine July-August 2012 entitled “Powering the Future of Industry: High-Power Adjustable Speed Drive Topologies” by Kouro, S. discusses the various new and old drive topologies and their characteristics. Also in this issue of the same magazine is a two-part article “System Design of Adjustable Speed Drives” by Skibinski, G.L.Tallam, R.M.; Pande, M.; Kerkman, R.J.; Schlegel, D.W.
Some of these topologies produce near sinusoidal voltage signals to the drives by switching up to 17 voltage levels. Some of the topologies can reduce Total Harmonic Distortion at the power grid as low as 2.3%. Many of these High Power drives use redundant power semiconductors to provide fault tolerance and improved reliability.