Variable Frequency Drive

[Muhammad Daniyal 0]

Dear All, Hows going, i am here to ask something about the VFD's. i already have work on vfd's but the technology never stops. i want to know abt the diffrence between the Vector control Drives and general Drives. and the appliction of vector drives where it can be used. waiting for prompt reply.

[JMK 0]

A vector drive has more precision control of the application. Vector drives can also emulate the characteristics of DC drives, i.e. constant high torque at low speeds. For more info go HERE

[paulengr 44]

Vector drives just means a difference in algorithms. There are basically 3 algorithms for AC (you said VFD) drives out there: volts/hertz, sensorless flux-vector, and full vector control. Volts/hertz basically outputs a signal but doesn't monitor what the motor actually does with it. You get variable speed but really little control over torque. Speed control is usually about +/-10%. This is usually best for pumps and fans where speed control is noncritical. Full vector drives have an encoder for feedback. They can vary speed and torque pretty much independently. This is essentially a brushless AC servo drive application. They can operate at ANY speed with full torque, right down to 0 RPM (assuming the motor can handle the heat generated using it as a brake). Speed control is +/-0.1% or better. This design can not only control speed extremely well but can also control position, stopping the motor shaft at nearly any angle. Sensorless flux vector uses sensors to read the current draw from the motor to estimate the speed and torque. Control is about +/-1%. It can't control motor shaft angle but it has about 90% of the capabilities of the full vector configuration. These days almost all the better drives on the market offer this as a standard option along with volts/hertz. In addition, a drive may or may not have regeneration, or dynamic braking capability. The slowest way to stop a motor is by coasting to a stop. This generates some heat as the magnetic field is dissipated within the motor. The fastest way is to use a mechanical brake. Drives offer several options in between these extremes. Most drives can apply DC voltage, creating an AC flux which tends to slow down the drive, at the expense of adding heat to the drive. By changing from a simple diode rectifier to an SCR bank on the front end (which is a small cost increase), a drive can act in "regeneration" mode. The drive treats the motor as the power source and converts motor (now generator) energy back to line power and pumps the energy back into the supply system. This does not add heat to the drive but doesn't stop all that quickly either. Finally, you can add an external resistor bank to the drive (a "dynamic resistor"). The drive draws off current from the motor at it's maximum current handling capability. The DC bus is discharged through the resistor bank in the form of heat. Finally, if you are running a web tensioner application or something similar where one drive is trying to slow down while another is speeding up (or conversely, torque is shifting), you can run the drives with a common DC bus. In this configuration, energy can be simply transferred from one motor to another via the common DC bus. Most drives offer one or more of these braking options. You can use them together to slow down more quickly than any one technique alone can give you.

[Muhammad Daniyal 0]

Thanks Dear, i have understand all of the theorogram of Vector control VFD's. once again thanks so much. i hope u will cooporate in future