Functions
5.7 Closed-loop control
Frequency inverter
Operating Instructions, 08.10. 2008, t.b.d.
109
5.7.1.2
V/f control with linear characteristic
V/f control with a linear characteristic is mainly used in applications in
which the motor torque must be independent of the motor speed.
Examples of such applications include horizontal conveyors or
compressors.
9
Q
I
9
3
Table 5- 20 Setting the control type
Parameter Description
P0003 = 2
Extended access to the inverter functions
P1300 = 0
Control type: V/f control with linear characteristic
Optimizing the linear characteristic for special applications
The linear characteristic of the V/f control assumes an ideal motor without resistive losses.
The resistive losses in the motor stator resistance and in the motor cable reduce the
available torque and must not be neglected in all applications. These losses play a more
significant role the smaller the motor and the lower the motor speed.
The losses can be compensated by the V/f control by increasing the voltage at low speeds.
Examples of applications where this is necessary, include:
●
Holding a load
●
Driven machines with a high breakaway torque
●
Utilizing the brief overload capability of the motor when accelerating
Table 5- 21 Optimizing the linear characteristic
Parameter Description
P0003 = 2
Extended access to the frequency inverter functions
P1310 = … Voltage boost to compensate resistive losses
The voltage boost is effective for all speeds below the rated speed and continually
decreases as the speed increases.
The maximum voltage boost is effective at zero speed and is in V:
Rated motor current (P305) × stator resistance (P350) × P1310 /100
P1311 = … Voltage boost when accelerating
The voltage boost is effective from standstill up to the rated speed. The voltage boost
is independent of the speed.
The voltage boost in V is:
Rated motor current (P305) × stator resistance (P350) × P1311 /100