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3-Phase Power Solutions Vector-Variable Frequency Drives
The vector drive provides ultimate control of AC induction motors. With the use of a motor mounted encoder or similar feedback sensor, it precisely controls motor torque and speed. The Vector Drive Offers you Control on the Following:
The vector drive is easy to setup and operate by using a one-touch rotational or stationary auto tuner feature. The vector drive controls and adjusts the control loop while the motor is running. Vector Drives are available in horsepower from 3/4 to 125 Hp and voltage ranges from 180 to 660 volts. The vector drive allows for unity within the facility for both closed loop and open loop applications. How does a Vector Drive Work? The vector drive uses a powerful and fast microprocessor to maintain more precise control on an operating parameter. The microprocessor uses the feedback information it receives and calculates the exact vector of voltage and frequency to attain its goal. It tells the motor what to do and checks to see if it did it, and then changes its command to correct for any errors. Based upon the way they get their feedback information, vector drives come in two types - open loop and closed loop. |
Closed-Loop Vector Drives A closed loop uses a shaft encoder on the motor to give positive shaft position indication back to the microprocessor. An example is when the microprocessor says move x radians, the encoder says, "It only moved x-2radians." The microprocessor then alters the PWM signature on the fly to make up for the error. For torque control, the feedback allows the microprocessor to adjust the pattern to maintain constant level of torque regardless of speed. A true closed-loop vector drive can also make an AC motor develop continuous full torque at zero speed, something that previously only DC drives were capable of doing. That makes them suitable for crane and hoist applications. The motor must produce full torque before the brake is released or else the load begins dropping, and it can't be stopped. Open-Loop Vector Drives An open-loop vector drive is actually a closed-loop system, but the feedback comes from within the VFD instead of an external encoder. They are sometimes referred to as a sensorless-vector drive. With this system, the microprocessor creates a model of the motor operating parameters and keeps it in memory. As the motor operates, the microprocessor monitors the output current and determines what the different current effects mean on the motor performance and adjusts it accordingly. At zero speed, the open-loop vector drive is not reliable enough to use. There are also lots of great Internet sites that cover Variable Frequency Drives and offer them at excellent sales rates.
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