100 Powerdrive F300 Getting Started Guide
Issue Number: 5
8.4.2 Permanent magnet motor high speed operation
High speed servo mode is enabled by setting Pr 05.022 =1. Care must be taken when using this
mode with permanent magnet motor to avoid damaging the drive. The voltage produced by the
permanent magnet motor magnets is proportional to speed. For high speed operation the drive must
apply currents to the motor to counter-act the flux produced by the magnets. It is possible to operate
the motor at very high speeds that would give a very high motor terminal voltage, but this voltage is
prevented by the action of the drive.
If however, the drive is disabled (or tripped) when the motor voltages would be higher than the rating
of the drive without the currents to counter-act the flux from the magnets, it is possible to damage the
drive. If high speed mode is enabled the motor speed must be limited to the levels given in the table
below unless an additional hardware protection system is used to limit the voltages applied to the
drive output terminals to a safe level.
Ke is the ratio between r.m.s. line to line voltage produced by the motor and the speed in V/1000 rpm.
Care must also be taken not to de-magnetize the motor. The motor manufacturer should always be
consulted before using this mode.
By default, high speed operation is disabled (Pr 05.022 = 0).
It is also possible to enable high speed operation, and allow the drive to automatically limit the motor
speed to the levels specified in the tables and generate an Overspeed. 1 trip if the levels are
exceeded (Pr 05.022 = -1)
8.4.3 Maximum speed / frequency
In all operating modes (Open loop, RFC-A and RFC-S) the maximum output frequency is limited to
550 Hz. However, in RFC-S mode the speed is also limited by the voltage constant (Ke) of the motor.
Ke is a specific constant for the servo motor being used. It can normally be found on the motor data
sheet in V/k rpm (volts per 1,000 rpm).
8.4.4 Quasi-Square wave (open-loop only)
The maximum output voltage level of the drive is normally limited to an equivalent of the drive input
voltage minus voltage drops within the drive (the drive will also retain a few percent of the voltage in
order to maintain current control). If the motor rated voltage is set at the same level as the supply
voltage, some pulse deletion will occur as the drive output voltage approaches the rated voltage
level. If Pr 05.020 (Quasi-square wave enable) is set to 1 the modulator will allow over modulation,
so that as the output frequency increases beyond the rated frequency the voltage continues to
increase above the rated voltage. The modulation depth will increase beyond unity; first producing
trapezoidal and then quasi-square waveforms.
This can be used for example:
• To obtain high output frequencies with a low switching frequency which would not be possible
with space vector modulation limited to unity modulation depth,
or
• In order to maintain a higher output voltage with a low supply voltage.
The disadvantage is that the machine current will be distorted as the modulation depth increases
above unity, and will contain a significant amount of low order odd harmonics of the fundamental
output frequency. The additional low order harmonics cause increased losses and heating in the
motor.
Drive voltage
rating
Maximum motor speed
(rpm)
Maximum safe line to line voltage at the motor terminals
(V rms)
200 400 x 1000 / (Ke x √2) 400 / √2
400 800 x 1000 / (Ke x √2) 800 / √2
575 955 x 1000 / (Ke x √2) 955 / √2
690 1145 x 1000 / (Ke x √2) 1145 / √2
Powerdrive F300 Getting Started Guide English Iss2.book Page 100 Tuesday, July 28, 2015 3:23 PM
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