Variable speed drives are highly versatile assets, and universally used across a wide range of sectors. One of the main reasons for that is because they’re closely tied with electric motors. Electric motors play a crucial role in countless aspects of modern industry; moving conveyor belts, pumping fluids, running compressors, and more. However, not all applications require motors to constantly run at full speed. And that’s where variable speed drives (VSDs) come in.

Basically, a variable speed drives allows precise control over the speed and torque of an electric motor by adjusting the power supply. That makes it incredibly useful for reducing energy consumption, improving operational efficiency, and extending the lifespan of equipment.

We have an excellent range of Variable Speed Drives to choose from ourselves here at LED Controls – and with more than 20 years of experience to our name, that puts us in the perfect position to give you the essentials of what you need to know.

What is a variable speed drive?

Sometimes known as a variable-frequency drive, a variable speed drive (VSD) is a type of AC motor drive that regulates the flow of energy from the mains to the motor, and optimises it according to shifting system requirements.

To give you a little bit more detail, from its position between the electrical supply and the motor, it regulates power delivery by converting the incoming electricity into a form that can be adjusted based on demand. This flexibility allows motors to operate at varying speeds rather than simply switching between “on” and “off” states, as is the case with traditional fixed-speed systems.

How does a variable speed drive work?

As with many examples of this type of equipment, the internal workings of VSDs are relatively complex to the layman – but the principles of how they function are surprisingly simple.

In a nutshell

The core function of a VSD is to control the voltage and frequency supplied to an electric motor. It does this in several key steps:

  • Convert incoming AC to DC

The VSD receives three-phase AC power from the mains and converts it into direct current (DC) using a rectifier circuit.

  • Smooth the DC wave

The DC power is then processed through capacitors to smooth out fluctuations, creating a stable DC supply.

  • Convert DC to variable AC

The drive calculates the exact voltage and frequency required by the motor. Using an inverter, the DC power is then converted back into AC at a precise frequency and voltage level.

  • Calculate and repeat

The VSD continuously monitors and adjusts the power output, ensuring that the motor only receives what it needs. This ongoing calculation is what allows the motor to operate efficiently and reduces energy wastage.

To explain in more detail

The VSD first converts three-phase AC power into DC using a rectifier. This DC power is then smoothed by capacitors, ensuring a stable and consistent supply. The stabilised DC power then moves to an inverter, which converts it back into AC, but with an adjustable frequency and voltage.

This precise control allows the motor to run only as fast or as powerfully as needed, reducing energy waste and mechanical wear. Instead of using dampers or valves to regulate output, the motor itself adjusts dynamically to match demand. As well as improving efficiency, this also reduces strain on mechanical components, lowering maintenance costs over time.

A VSD also ensures a smoother start-up by gradually increasing power instead of delivering a sudden surge. This minimises mechanical stress, prevents overheating, and extends the lifespan of both the motor and connected equipment. Maintaining optimal motor performance ensures that VSDs also contribute to improved process stability, reducing fluctuations that could impact production quality or operational reliability.

Why are variable speed drives so useful for so many businesses?

As we’ve touched on above, electric motors are responsible for nearly 70% of all industrial electricity consumption, making their efficiency a critical concern for businesses. In many industrial settings, motors are traditionally run at a constant speed, with adjustments to flow or pressure made manually through valves and dampers. It’s not always the most efficient approach – and it can also be labour-intensive, requiring frequent manual interventions to regulate performance.

A VSD on the other hand can be useful for automating and improving these processes. Rather than running motors at full power and then restricting output mechanically, a VSD allows motors to operate only at the speed and torque required – so you benefit from immediate energy savings and long-term reductions in operational costs.

So, to quickly recap a full list of these benefits in a bit more detail, variable speed drives can give you:

  • Improved operational efficiency

Automating motor control reduces the need for manual intervention, cutting down on labour costs and increasing productivity.
Smoother and more precise control over processes helps reduce inefficiencies and waste.

  • Savings on the electricity bill

Adjusting motor speed to match real-time demand reduces energy consumption significantly – sometimes by up to 50%.
Many industrial processes involve running motors at partial load, where VSDs excel in reducing unnecessary power usage.

  • Savings in capital expenditure

The energy reductions provided by VSDs ensure a fast return on investment. In some cases, especially for pump and fan applications, businesses can see payback within months.

  • Savings in maintenance and spare part costs
  1. Reducing mechanical stress on motors and connected equipment ensures a longer operational lifespan.
  2. Lower stress during start-up reduces wear and tear, cutting maintenance and replacement expenses.

That’s all the essentials covered! You can explore our own range of variable speed drives over on our dedicated page – and of course if you can’t find something you’re looking for, or you need any help or advice, don’t hesitate to ask one of our team. You can get in touch by giving us a call on 01706 242 050, or drop us a line on website@ledcontrols.co.uk. We’re always happy to help!