Siemens Simovert Masterdrives Compendium page 275

Functions
7.3.8 "Field weakening for synchronous motor" function
(function diagram 389)
NOTE
Commissioning the
field weakening
function
IMPORTANT
7-66
The magnetic flux is constant in the base speed range of the
permanent-field synchronous motor. The voltage requirement increases
in proportion to speed until it exceeds the maximum converter output
voltage.
In the field weakening range, the magnetic flux must be reduced in
proportion to speed through application of a magnetic field which
opposes the permanent magnet field.
In the field weakening range, an internal counter-voltage proportional to
speed must be generated to weaken the effect of the permanent
magnetic field on the terminal voltage (EMF).
If the closed-loop control or power section of the synchronous motor
fails at high speed, the motor regenerates power to the DC link at high
voltage. To prevent damage to the converter caused by overvoltage
under fault conditions, the VPM (Voltage Protection Module) can be
used as an overvoltage protection mechanism. The VPM detects an
excessive motor terminal voltage and shorts the three motor cables.
The regeneration voltage of the synchronous motor can be defined by
the voltage constant (k
n
⋅ ⋅ <
max
If k 2 800
E
1000
protection.
The motor and encoder data must first be entered in the "Drive Setting"
menu (see Section 6.2.3 "Drive Setting"). The "Field weakening for
synchronous motor" function is activated in parameter P300
SelectFieldWeak. A useful assignment of the field weakening activation
speed P299 and the motor short-circuit current P105 MotPwrFactor
can be obtained through the automatic parameterization run (P115 =
1). Both parameters define the flux setpoint control in the field
weakening range. If the exact setting values of parameters P299 and
P105 are known, they can, of course, be set manually.
The motor short-circuit is significantly higher than the rated motor
current. Adjust parameter P128 Max Current accordingly.
Adjust the reference variables P350 ... P354 for field weakening
operation.
) specified in the Engineering Information.
E
V , there is no need to provide overvoltage
6SE7087-6QX70 (Version AK)
Compendium Motion Control
09.2008
Siemens AG
SIMOVERT MASTERDRIVES