Commissioning
5.2 Preparing for commissioning
Inverter with CU230P-2 Control Units
78 Operating Instructions, 11/2013, FW V4.6.6, A5E02430659B AG
V/f control or vector control (speed/torque)?
For induction motors, there are two different open-loop control or closed-loop control
techniques:
● V/f control (calculation of the motor voltage using a characteristic curve)
● Closed-loop speed control (also: field-oriented control or vector control)
Criteria for selecting either V/f control or vector control
In many applications, the V/f control suffices to change the speed of induction motors.
Examples of typical applications for V/f control include:
● Pumps
● Fans
● Compressors
● Horizontal conveyors
When compared to V/f control, vector control offers the following advantages:
● The speed is more stable for motor load changes
● Shorter accelerating times when the setpoint changes.
● Acceleration and braking are possible with an adjustable maximum torque
● Improved protection of the motor and the driven machine as a result of the adjustable
torque limiting
● Full torque is possible at standstill
Examples of typical applications in which speed control is used:
● Hoisting gear and vertical conveyors
● Winders
● Extruders
We also always recommend the use of speed control for Power Modules with powers above
160 kW.
It is not permissible to use vector control in the following cases:
● If the motor is too small in comparison to the inverter (the rated motor power must not be
less than one quarter of the rated inverter power)
● When you operate several motors on one inverter
● If a power contactor is used between the inverter and motor, and is opened while the
motor is powered up
● When the maximum motor speed exceeds the following values:
Maximum motor speed [rpm]
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