Viewpoint: don’t underestimate the VSD

If we were to personify the variable speed drive (VSD), it would have to be the underrated middle child in the family.

Motors would be the problematic first born – the result of parenting inexperience – and PLCs represent the youngest child, the know-it-all.

VSDs also ensure compliance with regulations, reduce monthly electricity bills and can lower the energy consumption of motors by as much as 50%.For example, retrofitting a used VSD to a 90kW motor in continuous duty can mean savings of over $9000 per year.

As a testament to the secret golden child, here’s our look back at the milestones of VSD development.

VSDs also ensure compliance with regulations, reduce monthly electricity bills and can lower the energy consumption of motors by as much as 50%

When legendary inventor Nikola Tesla was granted patents for the first three phase alternating current (AC) induction motor in 1888, he knew his invention was more efficient and reliable than Thomas Edison’s direct current (DC) motor.

However, varying AC motor speed control isn’t a simple process and even decades after widespread implementation of AC induction motors, controlling their speed remained a difficult task. Consequently, DC motors were still necessary in applications that required accurate control and significant power output.

Cue the ascendancy of the latchkey kid. Before the 1980s, VSDs were in their infancy – only used in heavy industry for large motors. Still, they plugged away and did a fastidious job regulating frequency, lowering motor wear and reducing electricity bills.

Wider appeal

However, advances in AC motor control technology in the 1980s and 90s meant the VSD graduated from only serving heavy industry to become more widely used.

Advancements in semiconductor switching, drive topologies, simulation and control techniques, control hardware and software, made VSDs more reliable and inexpensive enough to compete with the more traditional DC motor control.

This propelled them into the big wide world, but uptake still wasn’t anything to write home about.

Fast forward to today. When reducing industry’s carbon footprint became a priority, it didn’t take long for engineers to point fingers at the inefficiency of the problematic first child – motors – and suggest possible solutions. One of which is the widespread implementation of the old reliable VSD.

Modern day VSDs have come a long way. A new generation of devices have many additional features and benefits other than simple speed control.

When reducing industry’s carbon footprint became a priority, it didn’t take long for engineers to point fingers at the inefficiency of the problematic first child – motors – and suggest possible solutions

The very nature of converting devices, like VSDs, causes harmonic distortion in a system. Harmonics can cause the malfunction of precision instruments, overheating of generators and have an adverse affect on the grid.

Traditionally, other instruments were added to the system to mitigate harmonics, but the matrix drive has been specially designed to negate the need for subsequent harmonic filtering devices.

This feature cuts footfall and reduces costs by making a dedicated harmonic filter redundant. Furthermore, some modern VSDs not only save energy through precise motor control, they also deliver energy that would have otherwise been wasted as heat, back to the power source to be redistributed.

They grow up so fast, don’t they?

• Jonathan Wilkins is marketing director of industrial automation parts supplier European Automation.