Variable speed drives (VSDs), also known as variable frequency drives (VFDs) or adjustable frequency drives (AFDs), are electronic devices that control the speed and torque of electric motors. They achieve this by converting fixed frequency and voltage input to a variable frequency and voltage output, which is then supplied to the motor. This allows for precise control of motor speed, enabling energy savings, improved process control, and extended motor life. 
Key Aspects of Variable Speed Drives:

• Function:
  VSDs regulate the speed of electric motors, which are used to power pumps, fans, compressors, and other mechanical components in various industrial applications. 
• Mechanism:
  They adjust the frequency and voltage supplied to the motor, which in turn affects its rotational speed. 
• Energy Savings:
  VSDs can significantly reduce energy consumption, especially in applications where motors don't need to run at full speed constantly, such as pumps and fans. 
• Types:
  Common types include VFDs for AC motors and other VSDs for DC motors. 
• Applications:
  VSDs are widely used in industries like manufacturing, oil and gas, water and wastewater, and HVAC systems. 
• Benefits:
  In addition to energy savings, VSDs offer benefits like improved process control, reduced mechanical stress on motors and driven equipment, and extended motor lifespan. 
• Cost:
  The cost of a VSD can vary significantly depending on the size and complexity of the drive, with smaller drives being less expensive than those used to control larger motors. 
• Potential Issues:
  VSDs can introduce harmonics and electromagnetic interference, which may require mitigation measures such as filtering components. 
• Configuration:
  Tools like the Altivar Process Configurator from Schneider Electric can help users configure and customize their VSDs for specific applications.