Siemens MICROMASTER 411 - Manual (Page 120)

10 Engineering Information Issue 03/01
MICROMASTER 411 & COMBIMASTER 411 Operating Instructions
120 6SE6400-5CA00-0BP0
10.2 Control and Operating Modes
10.2.1 Boost
Boost is used to increase the output voltage in order to overcome losses and non-
linearity at low frequencies. If the correct amount of boost is applied, the current
and torque will be increased at low frequencies. However, if too much boost is
applied, the motor may overheat if run at low frequencies for a long time and
excessive boost may also saturate the motor, leading to loss of torque.
The I
2 t function helps protect the motor under these circumstances. Boost is
calculated such that 100% boost is the voltage given by:
Stator resistance (P0350) multiplied by rated motor current (P0305).
Which means that changing the value of these parameters will affect the boost
level.
Frequency
Boost increases
voltage here
Voltage
Figure 10-3 Boost-Level
P1310 This parameter sets the % boost applied at 0 Hz. The boost level is then
reduced with increasing frequency to a minimum value, set by P1316,
typically around about 10 Hz.
P1311 This parameter sets a boost voltage, as P1310, except that the boost is
applied only during acceleration, either following a start command or from
set point changes.
P1312 This parameter allows a constant linear boost, again as P1310, to be
applied following a start command only to improve ‘first time’ starting.
Maximum values of P1310, 1311,and 1312 are 250%, but the overall maximum
boost is limited by P0640, the motor overload setting. The boost voltage will also
be limited by the operation of the I
2 t function, so boost may be reduced further if
the motor is in danger of overheating. The progress of the I 2 t function can be
monitored by parameter r0034.
The default settings (P1310 = 50, P1311 and P1312 = 0) allow satisfactory
operation with most loads. Increasing the boost up to say 200% (note that P0640
setting will limit) on smaller motors and 100% on larger motors will often give
improved torque at low frequencies. Use P1311 and P1312 to limit this to
accelerating boost only (e.g. P1310 = 100, P1312 = 100), to reduce the possibility
of overheating.