Congratulations, it's a VSD

Paul Boughton

Jonathan Wilkins discusses the milestones in the history of the variable speed drive

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. Although often overlooked, the VSD is the apple of our energy efficiency eye.

Not content with simply reducing the energy consumption of motors by as much as 50%, VSDs also ensure compliance with regulations and reduce monthly electricity bills. For example, retrofitting a used VSD to a 90kW motor in continuous duty can mean savings of over £9,000 per year. Take a bow.

From humble beginnings, VSDs have cemented their place in the hearts of many plant managers - or should I say proud parents. However, lack of market penetration still highlights significant energy efficiency improvement opportunities.

As a testament to the secret golden child, here's our look back at milestones in the VSDs development; an inverter 'best bits' if you will.

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 ascendency 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.

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 in other fields.

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 around the globe, businesses are subject to ever increasing energy efficiency regulations. 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 since they were solely used in heavy industry. A new generation of devices, like Yaskawa's matrix drive, have many additional features and benefits other than simple speed control. 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 so as 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. Think how much that could save on your electricity bill every year.

Despite this ode to the wonder child that is the VSD, it's still a greatly underappreciated device in industry. Even if you don't want to go for a top of the line drive with harmonic filtering and regenerative energy conversion, retrofitting a used VSD to a motor will cut down on your carbon footprint and save you money come the end of the month. Almost brings a tear to your eye doesn't it? They grow up so fast.

Jonathan Wilkins is with industrial automation parts supplier European Automation.