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Unidrive M702 User Guide
Issue Number: 3
Pr 00.007 {05.014}
Open Loop Control Mode (cont)
Fixed boost
Neither the stator resistance nor the voltage offset are used in the control of the motor, instead a fixed characteristic with low frequency voltage
boost as defined by parameter Pr
00.008
, is used. Fixed boost mode should be used when the drive is controlling multiple motors. There are two
settings of fixed boost available:
(2)
Fixed
= This mode provides the motor with a linear voltage characteristic from 0 Hz to
Rated Frequency
(00.047), and then a constant voltage
above rated frequency.
(5)
Square
= This mode provides the motor with a square law voltage characteristic from 0 Hz to
Rated Frequency
(00.047), and then a constant
voltage above rated frequency. This mode is suitable for variable torque applications like fans and pumps where the load is proportional to the
square of the speed of the motor shaft. This mode should not be used if a high starting torque is required.
For both these modes, at low frequencies (from 0Hz to ½ x Pr
00.047
) a voltage boost is applied defined by Pr
00.008
as shown below:
Pr 05.027
Enable Slip Compensation
When a motor, being controlled in open loop mode, has load applied a characteristic of the motor is that the output speed droops in proportion to the
load applied as shown:
In order to prevent the speed droop shown above slip compensation should be enabled. To enable slip compensation Pr
05.027
must be set to a 1
(this is the default setting), and the motor rated speed must be entered in Pr
00.045
(Pr
05.008
).
The motor rated speed parameter should be set to the synchronous speed of the motor minus the slip speed. This is normally displayed on the
motor nameplate, i.e. for a typical 18.5 kW, 50 Hz, 4 pole motor, the motor rated speed would be approximately 1465 rpm. The synchronous speed
for a 50 Hz, 4 pole motor is 1500 rpm, so therefore the slip speed would be 35 rpm. If the synchronous speed is entered in Pr
00.045
, slip
compensation will be disabled. If too small a value is entered in Pr
00.045
, the motor will run faster than the demanded frequency. The synchronous
speeds for 50 Hz motors with different numbers of poles are as follows:
2 pole = 3000 rpm, 4 pole = 1500 rpm, 6pole =1000 rpm, 8 pole = 750 rpm
Output
voltage
Pr
/ 2
00.044
Pr
00.044
Pr
/
2
00.047
Pr
00.047
Output
frequency
Output voltage characteristic
(Fd)
Voltage boost
Pr
00.008
Pr
00.044
Pr
00.008
Pr
00.047
Shaft speed
Demanded speed
Load
Summary of Contents for Unidrive M702
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