The global inverter drive market is expected to experience healthy growth over the next few years. These drives are becoming an integral part of several small and large machine markets around the world. They are used in a variety of applications from small equipment to large compressors. Variable frequency drives are power conversion devices that can be used as AC drives, DC drives, and servo drives. So what are the advantages of variable frequency drive ?
Unlike traditional stop-and-go motors, one of the advantages of variable frequency drives is that with variable frequency drives, changes can be made to the process to optimize the process. This allows starting at a reduced speed and allows the speed to be adjusted remotely via a programmable controller or process controller. Control, in an industrial sense, is always a big plus for production!
One of the advantages of variable frequency drives is that using a variable frequency drive protects the machine from damage and protects the process or product (as the amount of torque applied can be precisely controlled). An example is a clogged conveyor belt. If only one AC motor is connected, the motor will continue to try to spin until the motor's overload device opens. In turn, the VFD can be set to limit the amount of torque (AMP/CURRENT), so the AC motor will never exceed this limit.
Variable torque loads, such as centrifugal fans and pumps running with variable frequency drives, will reduce energy consumption. Centrifugal fans and pumps follow a variable torque load with horsepower proportional to the cube of speed and torque proportional to the square of speed, also known as the "law of affinity". If you halve the speed of the fan, the horsepower required to run the fan under load is eight times less (1/2)3 = 1/8. When trying to replicate this advantage with a standard induction motor, some type of mechanical throttling is required, such as vanes or dampers; but the motor will still run at full load and full speed (full power).
Example: Variable frequency drive control of a pump motor that is typically running at less than full speed can significantly reduce the energy consumption of the motor running at a constant speed for the same amount of time. For a 25 hp motor running 23 hours a day (2 hours at 100% speed; 8 hours at 75%; 8 hours at 67%; 5 hours at 50%), a variable frequency drive can reduce energy usage by 45%. At $0.10 per kWh, the annual savings is $5,374. Because this variable frequency drive benefit varies with system variables such as pump size, load curve, static head amount, and friction, it is important to calculate the benefit for each application before specifying a variable frequency drive. With this variable frequency drive advantage, the savings may be enough to shorten the payback period.