Field Weakening Controller - Baumuller b maXX BM3000 Operating Manual

4.7
Controllers
4.7.4

Field weakening controller

At an asynchronous machine as well as at a synchronous machine regarding the operat-
ing range it is commonly distinguished between the basic speed range (typically below
the rated speed of the motor) and the field weakening range (typically above the rated
speed).
In the base speed range the flux remains constantly. In the field weakening range the flux
is reduced (ASM) or negative lsd current is applied to make greater speed possible at an
insufficient DC-link voltage
Field weakening factor
The field weakening at the voltage limit
accordant to the field weakening factor (see diagram in figure 125). The field weakening
factor represents the current level of the field weakening. The field weakening factor (pa-
rameter Z142.2–) is a factor without units, value range is between 0 ... 1.
ZFig. 162–
an open-loop controlled and the second channel is a closed-loop controlled field weaken-
ing.
Open-loop controlled field weakening
If the speed exceeds a specified speed threshold the flux is reduced after a characteristic
(see
rameter Speed threshold field weakening (Z142.9–) acts, if bit 1 was set by the field
weakening mode
of the open-loop controlled field weakening is the field weakening factor after the speed
Z142.12–.
Closed-loop controlled field weakening
The second channel contains a voltage controller that evaluates the difference between
the specified limit and the actual value of the motor voltage (parameter Z142.7–) and ac-
cordingly weakens the flux, so that the motor voltage doesn't increase anymore. The limit
is the lower one of two values of the voltage threshold specified via the parameter
Z142.8–
factor (Z142.15–). The maximum output voltage is continually calculated from the current
DC-link voltage provided that there is a full PWM control. The output of the closed-loop
controlled field weakening is the field weakening output Z142.13–.
Total field weakening factor
The a present degree of the field weakening (Field weakening factor Z142.2–) is given
by the lowest value of two channels (minimum value between
). This is additionally limited, so that it never falls below the specified limit of the parameter
Minimum field weak factor (Z142.5–).
494 Parameter manual b maXX BM3000
Document no.: 5.12001.07
of 820
shows that the field weakening is made via two channels. The first channel is
ZFig.
162–) inversely proportional to the speed. As a speed threshold either the pa-
Z142.1–
or the rated speed (Z142.7–) if this bit was not set. The output
and of the maximum output voltage (Z142.6–), which can be adjusted with a
(Z142.1– bit 0 = 1) at b maXX 5000 is structured
Z142.12–
Baumüller Nürnberg GmbH
Z142.13–
and