Motor Control; V/F Control - Siemens SINAMICS G120 Operating Instructions Manual

9.6

Motor control

Decision-making criteria for the control mode that is suitable for your application is provided
in Section Factory setting of the inverter control (Page 55).
9.6.1

V/f control

V/f control sets the voltage at the motor terminals on the basis of the specified speed
setpoint. The relationship between the speed setpoint and stator voltage is calculated using
characteristic curves. The required output frequency is calculated on the basis of the speed
setpoint and the number of pole pairs of the motor (f = n * number of pole pairs / 60, in
particular: f
important characteristics (linear and square-law). User-defined characteristic curves are also
supported.
V/f control is not a high-precision method of controling the speed of the motor. The speed
setpoint and the speed of the motor shaft are always slightly different. The deviation
depends on the motor load. If the connected motor is loaded with the rated torque, the motor
speed is below the speed setpoint by the amount of the rated slip. If the load is driving the
motor (i.e. the motor is operating as a generator), the motor speed is above the speed
setpoint.
The characteristic is selected during commissioning, using p1300.
SINAMICS G120C frequency converter
Operating Instructions, 03/2012, FW V4.5, A5E02999804B AB
= p1082 * number of pole pairs / 60). The inverter provides the two most
max
Functions
9.6 Motor control
185