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5.5.3 Sensor-less Vector Control
This sensor-less vector control performs the vector control of the induction motor without use of the speed
sensor. Conventionally, there has been the V/f control without the speed sensor. However, this sensor-less
vector control provides the simple control feature of the V/f control and the high performance of the vector
control. The following describes the features of the sensor-less vector control.
(1) Sensor installation and wiring construction are not required.
(2) This control is applicable to motors, in which the sensor cannot be installed, such as two-axis motors or
super high-speed motors, and other motors, which require special sensors, such as explosion-proof
motors.
(3) This vector control technology is used for parallel drive of multiple motors, which is difficult to control by the
conventional vector control.
(4) This sensor-less vector control provides excellent stability and large start-up torque when compared to the
V/f control.
(5) The torque can be limited, ensuring stable rapid acceleration and deceleration.
5.5.4 V/f Control
The restrictions described in Section 3.3.3 are imposed to the multiple motor parallel drive method by
sensorless vector control. Especially pay attention to the following restrictions:
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The change in the number of motor units can be allowed up to 50%.
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Motors can be added during operation only when the operation speed is 30% or slower and the
number of units to be added does not exceed 50% of the connected units.
With these restrictions, in sensorless control, since “voltage is output, as a result of controlling current”,
excessive change in the number of units may cause a transient instability, which can result in equipment stop.
Whereas, V/f control is less affected by external disturbance such as a change in the number of units, since
“voltage is output according to frequency.”
Consequently, it is recommended to use V/f control for purposes where fast response is not critical and the
change in the number of motor units exceeds the restriction described above.
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