Electronic speed control of standard 3-phase Induction motors by Variable Speed Drives (VSD’s) has become a reliable and accepted industrial solution since the late 1980’s. With the digital revolution came higher power, faster-switching, lower loss power devices such as the now widely used Insulated Gate Bipolar Transistor (IGBT) which not only vastly improved the efficiency but also the robustness of variable frequency drives. As the voltage ratings and current switching capacity of these devices increased so their use became more widespread in higher power drives. Large scale integration technology also enabled the design of powerful microprocessors, application specific integrated circuits and huge advances in memory technology, all of which meant VSD’s could have high functionality and could be used for many more applications than previously possible.
Now the use of fast switching power semiconductors in VSD’s have become the norm, the risk of unwanted interference with other sensitive equipment has increased so it is common to see modern digital drives fitted with devices such as harmonic reducing chokes and radio frequency interference (RFI/EMC) filters to improve power quality and reduce the chance of disturbance to other devices.
Innovative control methods such as Field Orientation and closed-loop vector control using encoder feedback now meant that more demanding applications such as winding, lifting and plastic extrusion where full rated torque could be required at the motor shaft at zero speed, and that were only possible using DC motors, could now be easily adapted to standard lower cost AC motors using VSD control.
Seven segment LED and multi-language LCD displays on push-button operator panels simplified the setup of drives compared to traditional trimmer pots found on early-design analogue VSD’s. Parameterisation of functions with application macros and ‘quick start’ menus have become the industry standard making for a much more user-friendly experience for the non-expert. Another big advantage in this kind of operator interface is that diagnostics of alarm conditions and real-time information can be accessed by maintenance engineers for monitoring and fault finding purposes.
High-speed communication links between PLC’s or BMS systems and drives and other devices soon became a reality as factories and buildings became fully automated which have resulted in ever-increasing manufacturing and building efficiency and operating performance.
The fundamental requirements of different applications vary widely beginning with matching the drive’s rated input voltage to the site supply voltage and depending on where it will be installed choosing an appropriate drive construction for the installation, for example up to IP20 for installing inside an enclosure or IP54 or IP66 for direct wall fixing or mounting on the side of an air handler.
Apart from potentially significant energy savings, using a VSD for controlling the speed of a fan or centrifugal pump has many advantages, namely soft starting and soft stopping to remove damaging pressure surges and water hammer for example. Another useful advantage can be seen by utilising the on-board PID function for controlling flow, pressure or level in a pumping system. A further advanced feature embedded in many pump and HVAC specific drives is a real time clock (RTC) with calendar function for programmed stop/starting over a time period removing the need for external timers etc. Many pumping specific drives are also able to control multiple pump motors for duty-assist, duty-standby, cascade and similar applications.
Enhanced designed-in safety has also become mandatory for machine builders and OEM’s alike and the use of safety relays in machine control circuits to monitor E-stops, light curtains and other safety critical devices found on a factory floor is common practice. With this in mind many modern drives have integrated dual-channel safety inputs to give a safe torque off (STO) condition at the motor in the event of the safety relay operating.
LS Industrial Systems – formerly LG Industrial Systems design and manufacture a Variable Speed Drive for almost every common application.
| Model Name | Typical Applications | Input Voltage | Power Range | Standard Features |
| M100 | Conveyors, small fans & pumps | 230V/1-ph | 0.2 to 2.2kW |
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| Model Name | Typical Applications | Input Voltage | Power Range | Standard Features |
| S100 | General purpose | 400V/3-ph | 0.4 to 90kW |
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| Model Name | Typical Applications | Input Voltage | Power Range | Standard Features |
| H100 | Supply and Extract Fans & Pumping systems | 400V/3-ph | 0.4 to 90kW |
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| Model Name | Typical Applications | Input Voltage | Power Range | Standard Features |
| iS7 | High power fans & Pumps, large conveyors, extruders, lifts, hoists, winches, machine tools, crushers, mixers, | 400V/3-ph | 0.75 to 450kW |
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VSD Range
