Magnetek HPV 900 Series 2, Техническое руководство

Страница: 95 / 230

Power Convert A4 Submenu
73
FLUX WEAKENING
ii
AT VOLTAGE LIMITS
Flux Weakening Parameters
The following HPV 900 S2 PM parameters
affect flux weakening:

Flux Weakening Slew (FLUX WEAKEN
RATE (A4))

Flux Weakening Level (FLUX WEAKEN
LEV (A4))
Permanent magnets are used to generate a
constant flux linkage in PM synchronous
motors. Under normal operating conditions,
the PM drive only controls torque production
as the machine is permanently excited.
Rarely, is there a need to reduce the flux level
in a PM motor.
However, with an elevator application, the
need may arise to reduce the flux level if the
input voltage to the drive is relatively low in
comparison to the maximum motor voltage.
The drive is capable of supplying more current
with the same terminal voltage as the counter
electromotive force (CEMF) is lower at a given
speed.
In order to weaken the flux in a PM motor, an
additional current component is injected and
the current required to produce certain torque
will increase. This increased current demand
will reduce the efficiency of the system and
increase thermal stress on the drive and the
motor. For these reasons, flux weakening
should be used if only absolutely necessary.
This feature is disabled by default (FLUX
WEAKEN RATE (A4) = 0).
The parameter Flux Weakening Rate (FLUX
WEAKEN RATE, A4) is used to set how fast
flux weakening occurs when the output voltage
reaches the limit. Set this to a minimum value
that ensures successful acceleration of the
fully loaded car for more gradual flux
weakening.
With flux weakening enabled, the HPV 900 S2
PM will automatically adjust the current to keep
the output voltage from reaching the voltage
limits. The HPV 900 S2 PM can begin flux
weakening before the motor reaches the
voltage limit or at the very limit. The limit
depends upon the setting of FLUX WEAKEN
LEV (A4). The sooner the flux weakening
begins, the more voltage margin is available to
compensate transient disturbances. However,
the set point must be set higher than rated
motor voltage such that the full flux (NO flux
weakening) is available for cruising speed.
The flux weakening can also lead to an abrupt
reduction of torque producing capability of the
motor. Different motors have different flux
weakening capabilities. In some cases the
maximum torque increase cannot be achieved.
Even then, it may be worth using flux
weakening as it allows the drive to accelerate
to full speed on a compromised curve without
declaring current regulator fault.
When the drive is flux weakening, the monitor
function D-CURR REFERENCE (D2) will be
negative. It is advisable to verify the reference
is zero when the car is running fully loaded at
constant speed.