Variable frequency motor drives are also known as motor drives, variable frequency drives, VFD’s, variable speed drives, adjustable frequency drives, AFD’s, adjustable speed drives and ASD’s. Motor drives are solid state motor control systems used to regulate the speed of alternating (AC) electric motors. Motor drives are mainly used to reduce energy consumption on electric motors for industrial manufacturers.

Motor drives operate as load controls within applications that may accomplish up to 50% reduction in energy costs by speed reduction on applications where the full speed (RPM) of the electric motor is not required. Motor drives are used in AC Servo Systems, Air Compressors, Conveyor Systems, Lathes, Mills, Plastic Extrusion, Slitter Lines, Food Processing, Waste Water Treatment Systems, Submersible Pumps, HVAC Fans and Blowers, and many more AC motor applications.

Many manufacturers apply motor drives with rotating equipment to reduce amperage spikes upon start up of large electric motors. Choosing the right motor drive for an application will benefit rotating equipment by providing less wear on the electric motor where applied. This is accomplished by adjusting the acceleration and deceleration time of electric motors. Adjusting the acceleration and deceleration time of an electric motor will greatly increase the lifespan of an electric motor. Motor drives provide the ability to control the frequency of starting and stopping of an AC electric motor. This ability provides a means by which an AC electric motor is only operating when needed for the equipment it’s rotating, and electric motors have a longer lifespan if they are not continuously operating when they don’t need to be.

Approximately one third of the world’s electrical energy is supplied by electric motors in fixed-speed centrifugal pump, fan, and air compressor applications. These fixed-speed applications hardly ever require the full load speed (RPM) of the electric motor they’re operating. By integrating motor drives to these applications, the motor speeds are reduced, and power costs can be reduced by 50% or more. Technology has reduced cost and physical size of motor drives, and has improved performance through advances in semiconductor switching devices, simulation, control techniques, and control hardware and software.

Power Savings With Motor Drives

The majority of motor drives in the market today contain electronic circuitry that converts 60 Hertz Line power into direct current. The motor drive converts this line power into a pulsed output voltage that duplicates varying alternating current to a desired frequency (speed). A properly applied motor drive when paired with an AC electric motor, will significantly reduce operating costs. This is particularly true for variable torque loads such as Fans, Blowers, and Pumps. Blowers, for example, are often used with dampers to control air flow. These dampers may operate either manually or automatically. When dampers are closed, 50% of the electric motor current will drop to approximately 60% of Full Load nameplate current. By utilizing a motor drive in this application, current draw in the motor will be reduced 30% for every 10% drop in speed. The same electric motor operating from a motor drive at 50% speed, will draw approximately 20% of the full load current.

Types Of Motor Drives

Volts Per Hertz motor drives are the most common type of drive and are known as a V/Hz drives, or volts by hertz drives. V/Hz motor drives are used in applications such as fans, pumps, air compressors, and other related applications where high starting torque is not required. V/Hz drive applications typically do not require full torque when the AC motor is operating at less than the base speed (RPM) of the electric motor. V/Hz drives are the most inexpensive type of motor drive. V/Hz drives do not provide full motor torque at low RPM.

Open-Loop vector motor drives are also known as “sensorless vector” drives. Open loop vector drives adapted the name “sensorless vector” because they do not use an external encoder for speed feedback to the motor. Open loop vector drives are used in applications where high starting torque and full torque at low speed (RPM) is required. Open-Loop vector drives operating a motor a zero RPM should not be used on crane or hoist applications. Most open-loop vector drives are used on CNC machines, mixers, mills, lathes, and other applications where high starting torque or full torque at low RPM is needed. Open loop vector drives are usually more expensive than V/Hz inverter drives.

Closed-Loop vector motor drives are used in applications where precise speed control (0.01%) is needed, or in applications where extensive programming is needed. Closed-Loop vector drives use an encoder on the motor to provide constant shaft position indication to the drive’s microprocessor. The encoder feedback allows the drive microprocessor to constantly control torque no matter how many RPM the motor is operating at. Closed-Loop vector motor drives are used to provide the motor to operate at full torque even at zero RPM. Closed-Loop vector drives are commonly used on hoist and crane applications because crane and hoist motors must produce full torque prior to it’s brake being released, or the load will drop and it will not be able to stop.

To learn more about motor drives or for motor drive repairs and replacement quotes, contact Precision Electric, Inc.