A Variable Frequency Drive, abbreviated as VFD, is a power controlling device for AC motors, which utilizes frequency-changing technology and microelectronic technology to control the frequency of the power supply for the motors. Choosing VFDs can bring huge benefits, and using them is easier than it may seem. So what are vfd selection criteria for motors?
Environment: The operating environment for the motor and the power conversion equipment is the primary concern for vfd selection criteria for motors. When selecting the drive, its housing, and protection functions, ambient temperature, cooling air supply, as well as gas, humidity, and dust conditions should be taken into consideration.
Speed range: The minimum and maximum motor speeds applied will determine the base speed of the drive.
Speed regulation: The allowable speed variation should be considered. Will the application require a constant speed at all torque values, or can it tolerate changes?
Torque requirements: vfd selection criteria for motors should take into account startup torque, peak torque, and operating torque. The required startup torque can vary from a small fraction of full load to several times the full load torque. The peak torque will vary due to changes in load conditions or machine mechanical characteristics. The available motor torque of the driven machine must be greater than the torque required for starting up to full speed.
Acceleration: vfd selection criteria for motors should consider the necessary acceleration time. The acceleration time is directly proportional to the total inertia and inversely proportional to the available torque.
Duty cycle: Choosing the appropriate drive depends on whether the load is stable, variable, follows a repeating cycle of variations, or has pulsating torque. Duty cycle is defined as the ratio of ON time to cycle time of a fixed repeating load pattern over a given time period. Duty cycle becomes a factor in choosing the appropriate drive when the operating cycle causes the drive to run idle or at reduced load for more than 25% of the time.
Heating: The temperature of the motor or controller is a factor in ventilation and loss in vfd selection criteria for motors. Running a self-ventilated motor at reduced speed may cause the temperature to rise above normal. A ratings reduction or forced ventilation may be needed to achieve the motor's rated performance.
Drive type: Does the application require performance elements such as quick response or torque control? These may require the use of magnetic flux vector or closed-loop vector drives instead of volts/hertz drives.