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Variable-Speed Drive (VSD)


1. What is Variable Speed Drive?
Variable Speed Drive (VSD) or Variable Frequency Drive (VFD) or inverter technologies are electro-mechanical drive systems that allow adjustable speed for AC electric motor speed and torque through frequency and voltage variations.
VSDs are solid-state devices that can change the speed of an AC electrical motor by converting frequency of the power fed into the machine.

2. How does a VSD work?
The revolution speed of AC electrical motor depends on the supplied current frequency as well as its number of electric poles.
A VSD can convert the 50Hz fixed-frequency and fixed-voltage AC power supply (from the grid) into a direct current (DC) supply, using an integrated rectifier. Integrated power electronics then convert the DC supply into a sinusoidal output with continuously variable frequency and voltage, which is used to drive the motor. In other words, a fixed sine wave in is converted into a variable sine wave out. (1)

3. What are the benefits of VSD?
Most of electric motors installed in buildings are AC (Alternative current) ones (centrifugal pumps, fans, compressors, etc…) and are fixed speed ones. VSDs can optimise operations by allowing speed and voltage control following the actual demand.
They allow to:
• Save energy and reduce costs for electrical motors operations
•  Provide lowest inrush motor starting – Ideal soft starter
•  Reduce mechanical wear and tear
•  Reduce overall maintenance costs
•  Reduce acoustic noise level as well as the draught from fan systems.

4. What are common applications of VSD?
All systems requiring flow or pressure control are most suited to the use of VSD. Such applications may include:
•  Fans and pumps: In applications where the flow of fluid is variable, considerable energy savings can be achieved by replacing existing throttling valves and dampers with VSDs
•  Conveyors: For conveyors with varying speed or with varying material flow, a VSD can adjust to the changing load requirements.
•  Air conditioning Compressors: similarly to fans and pumps, air conditionners’ compressors can be controlled by VSD to ensure an optimised flow to fulfill the actual cooling demand. In applications where the motor load remains more or less constant, a VSD is unlikely to achieve a significant saving, as the opportunity to reduce power is diminished.



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