Menu 5
Parameter
structure
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Parameter
x.00
Parameter
description format
Advanced parameter
descriptions
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protocol
Electronic
nameplate
Performance RFC mode
116
Unidrive SP Advanced User Guide
www.controltechniques.com Issue Number: 10
When the drive operates between rated frequency/4 and rated frequency/2 the Rs compensation is gradually reduced to zero as the frequency
increases. For the vector modes to operate correctly the stator resistance (Pr
5.17
), motor rated power factor (Pr
5.10
) and voltage offset (Pr
5.23
) are
all required to be set up accurately.
Fixed boost mode: Fd
A linear characteristic is used from 0Hz to rated frequency, and then constant voltage above rated frequency. Low frequency voltage boost as defined
by Pr
5.15
is applied as shown below.
Square law mode: SrE
A square law characteristic is used from 0Hz to rated frequency, and then constant voltage above rated frequency. Low frequency voltage boost
raises the start point of the square law characteristic as shown below.
Closed loop vector
The rated voltage is used by the field controller to limit the voltage applied to the motor. Normally this is set to the nameplate value. So that current
control can be maintained it is necessary for the drive to leave some 'headroom' between the machine terminal voltage and the maximum available
drive output voltage. The drive allows over-modulation of the PWM inverter which can produce a fundamental voltage that is higher than the drive
input voltage, but would cause substantial odd harmonic distortion if used in steady state operation. Therefore the drive uses a headroom limit which
allows the inverter to give a steady state output voltage equivalent to the input voltage minus voltage drops inside the drive. This gives enough
headroom for the current controllers to operate satisfactorily. However, for good transient performance at high speed the rated voltage should be set
below 95% of the minimum supply voltage to the drive.
The rated voltage is also used in conjunction with the motor rated frequency (Pr
5.06
) during the rotating auto-tune test (see Pr
on page 117) and
in the calculations required for automatic optimization of the rated motor slip. It is important, therefore that the correct rated voltage for the motor is
used. In some applications it may be necessary to restrict the voltage applied to the motor to a level lower than the nameplate rated voltage of the
motor. In this case the rated frequency (Pr
5.06
) must be adjusted to maintain the ratio of rated voltage and frequency given on the motor nameplate.
The rated frequency will then be different to the nameplate value, and so the rated speed must be changed from the nameplate value to give the
correct rated slip.
Servo
The rated voltage is used by the field controller to limit the voltage applied to the motor if high speed operation is required. As in closed-loop vector
mode some headroom must be left for the current controllers to operate, and so the drive will use the voltage level set by this parameter or the
headroom limit whichever is the lower.
Voltage
boost Pr
5.15
Output
voltage
Pr
5.09
Pr
/ 2
5.09
Pr
/ 2
5.06
Pr
5.06
Output
frequency
Output voltage characteristic
Pr
5.09
Pr
5.15
Pr
5.06
Pr
+
[(freq/Pr )
x
(Pr
-
Pr )]
5.15
5.06
5.09
5.15
2
Summary of Contents for unidrive sp
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