Rockwell Automation 20D PowerFlex 700S with Phase I Control Reference Manual - Manual (Page 62)

62 Rockwell Automation Publication PFLEX-RM002D-EN-E - August 2013
Chapter 1 Detail Drive Configuration and Operation
Flying Start The Flying Start feature is used to start into a rotating motor, as quick as possible,
and resume normal operation with a minimal impact on load or speed.
When a drive is started in its normal mode it initially applies a frequency of 0 Hz
and ramps to the commanded speed. If the drive is started in this mode with the
motor already spinning, large currents will be generated. An overcurrent trip may
result if the current limiter cannot react quickly enough. The likelihood of an
overcurrent trip is further increased if there is residual voltage on the spinning
motor when the drive starts. Even if the current limiter is fast enough to prevent
an overcurrent trip, it may take an unacceptable amount of time for
synchronization to occur and for the motor to reach its desired frequency. In
addition, larger mechanical stress is placed on the application, increasing
downtime and repair costs while decreasing productivity.
The sensorless flying start function implements a frequency search algorithm that
searches for the rotor speed and when found provides flux up time for the motor
before transitioning to normal operation. The frequency search algorithm
searches for a motor voltage that corresponds with the excitation current applied
to the motor. This function is useful where very large inertia systems that would
take an extended period to come to a stop if a drive trip would occur or in cases
where an external source may be moving the motor before the drive would be
started.
The PowerFlex 700S Phase I must be version 1.017 or later to support flying start.
Sensorless Flying Start Operation
There two modes available for the frequency search: last known frequency and
preset frequency search.
Last Know Frequency
The last know frequency is the fastest method of flying start, with an initial
search frequency starting at the last known operating frequency. This mode will
search from the last known frequency toward zero frequency and, if the motor
speed is not found, perform a start from zero speed. If the motor speed could
reverse or increases to a larger speed a pull out or over voltage fault could occur. If
a reversal or increase in motor speed could occur the preset frequency search
should be used.
ATTENTION: The user must determine the safe frequency search configuration
at the system level. Incorrect selection(s) may result in personal injury due to
machine motion.
ATTENTION: The Flying Start function is only used for sensorless operation. In
all other cases the motor speed is known from the feedback device and a
normal start may be used even if the motor is rotating providing the user has
determined that the system is safe for re-starting while rotating.