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Variable Speed Drives

1.1    Scope

A variable speed drive is essentially an electronic power converter that generates a multi-phase, variable frequency output that can be used to drive a standard line operated ac motor, or permanent magnet synchronous or other converter-fed motor, and to modulate and control the motor’s speed, torque and mechanical power output.

Variable speed drives may be purchased either as a stand-alone product or purchased as part of another item of plant or machinery. They are included on the Energy Technology Product List because they can realise substantial energy savings when used to control the speed of machinery.

The Energy Technology List (ETL) Scheme covers two categories of products:

  1. Variable Speed Drives for line operated ac motors (as defined within the ETL category line operated ac motors)
  2. Variable Speed Drives for converter-fed motors (as defined within the ETL category converter-fed motors)

Products which are able to control both line operated ac motors and converter-fed motors are also covered, as long as all of the eligibility criteria are met for both forms of control.

To be eligible for inclusion on the ETL, products shall meet the requirements as set out below.

1.2    Definitions

A variable speed drive is specifically designed to drive a motor in a manner that rotates the motor’s drive shaft at a variable speed dictated by an external signal. 

1.3    Requirements 

1.3.1    Eligibility requirements  

Eligible products shall:

  • Incorporate an electronic VSD that generates a controlled variable frequency, variable voltage, 3 phase power output (with each phase displaced by approximately 120 degrees) that is suitable for operating a 3 phase motor.
  • Provide an adjustable variable-voltage, variable-frequency output that can be matched to the torque-speed characteristic of the load (being driven by the motor), including both loads with a quadratic torque-speed and linear torque-speed characteristics. The relationship between the voltage and frequency of the product's output shall either be:

a)    Predefined prior to sale to match a number of specific motor loads, which can be selected during commissioning; OR
b)    Programmed into the product during installation using a multi-point approximation or parametric motor model as part of a clearly defined commissioning procedure; OR
c)    Determined during commissioning by a self-tuning or automatic model identification algorithm that automatically minimises the energy consumption of the drive; OR
d)    Automatically adjusted during operation as part of a control algorithm in a manner that ensures the product's output matches the characteristics of the motor and its load and minimises energy consumption of the drive; OR
e)    Any combination of (a) to (d) above.

  • Be able to automatically vary, in response to an external control signal, the frequency of its output between 5% (or less) and 100% (or greater) of the frequency of its alternating current supply.
  • Be configured for direct connection to the UK public electricity supply system, or a private alternating current supply of nominally fixed frequency and voltage.
  • Be designed to make smooth controlled transitions between speed changes by the use of predefined, programmable, or automatically adjusted, acceleration and deceleration ramps.
  • Have an appropriate Conformity Assessment mark, or otherwise demonstrate conformity with the requirements of The Electromagnetic Compatibility Regulations 2016.
  • The Electromagnetic Compatibility Regulations 2016.
  • Not incorporate any type of mechanical apparatus that derives its motive force from the product’s variable frequency output, including any form of electric motor or fluid movement mechanism, except for fans or pumps incorporated solely for the purpose of product cooling.

Where the relationship between the voltage and frequency of the product's output is determined by a multi-point approximation, then flux optimisation shall be adjustable at a minimum of five points.

The criteria stated above shall be clearly presented in the product brochure, leaflet, technical specification sheet. It may also be supported by the relevant operation instruction document demonstrating the product’s functionality in accordance with the criteria listed above.

1.4    Verification for ETL Listing 

There are no testing requirements, however manufacturers shall provide sales and technical brochures to evidence the conformity of their products against the requirements from section 1.3.  

1.5    Conformity testing

Products listed on the ETL may be subject to the scheme’s conformity testing programme in order to ensure listed models continue to meet the ETL requirements.