88 Powerdrive F300 Getting Started Guide
Issue Number: 5
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 0 Hz 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
Powerdrive F300 Getting Started Guide English Iss2.book Page 88 Tuesday, July 28, 2015 3:23 PM
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