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What is a VSD and why is it important to consider for your Renewable Energy installation?

In a previous article we spoke about the importance of an Energy Management System (EMS) and why it is required when installing a renewable energy system. This is applicable to Residential systems as well as Commercial and Industrial systems. Energy Management and the improvement thereof is gathered by data generated by the EMS for you to review and allows you see where you can make improvements for maximum performance and efficiency of your system.


One of the factors that will be visible on your EMS is the installation of a VSD or Variable Speed Drive. This equipment’s main function is to control the frequency of energy from your main load supply, which is Alternating Current, for the starting current of a rotating motor. It reduces peak energy demand as well as power when it’s not required.


An example of this is the start and stop function of an elevator in a building. The elevator would start elevating slowly(energy) and increase its speed(power) only to reduce it gradually once again when it reaches the selected floor.


It would also be for applications where a pump or fans have been installed and would require a VSD. The pump would have a high inrush current with operating current requiring less power. The power provided to the VSD remains the same but the supply to the pump/fans will be variable to control the rotational speed of the motor with frequency. Power flows into a rectifier which converts AC to DC power and then to a DC bus, generally a capacitor, to smooth out the voltage into a clean, smooth and constant DC voltage. It then enters into an inverter(AC) made up of a number of IGBTs in pairs which open and close rapidly to control the flow of electricity.


The initial cost of a VSD is outweighed by the energy savings as well as operational costs once the VSD has been installed. Mechanical strain on equipment is reduced which enhances the lifetime of the equipment. The efficiency of a VSD and the gains of using one is not only applicable to Commercial use but also visible on a Residential scale.


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