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12 Unidrive M100 User Guide
Issue Number: 1
2.2.1 Typical short term overload limits
The maximum percentage overload limit changes depending on the selected motor. Variations in motor rated current, motor power factor and motor
leakage inductance all result in changes in the maximum possible overload. The exact value for a specific motor can be calculated using the
equations detailed in Menu 4 in the Parameter Reference Guide.
Typical values are shown in the table below for open loop (OL) modes:
Table 2-4 Typical overload limits
Generally the drive rated current is higher than the matching motor rated current allowing a higher level of overload than the default setting.
The time allowed in the overload region is proportionally reduced at very low output frequency on some drive ratings.
The maximum overload level which can be attained is independent of the speed.
2.3 Operating modes
The drive is designed to operate in any of the following modes:
1. Open loop mode
Open loop vector mode
Fixed V/F mode (V/Hz)
Square V/F mode (V/Hz)
2.3.1 Open loop mode
The drive applies power to the motor at frequencies varied by the user. The motor speed is a result of the output frequency of the drive and slip due
to the mechanical load. The drive can improve the speed control of the motor by applying slip compensation. The performance at low speed depends
on whether V/F mode or open loop vector mode is selected.
Open loop vector mode
The voltage applied to the motor is directly proportional to the frequency except at low speed where the drive uses motor parameters to apply the
correct voltage to keep the flux constant under varying load conditions.
Typically 100 % torque is available down to 1 Hz for a 50 Hz motor.
Fixed V/F mode
The voltage applied to the motor is directly proportional to the frequency except at low speed where a voltage boost is provided which is set by the
user. This mode can be used for multi-motor applications.
Typically 100 % torque is available down to 4 Hz for a 50 Hz motor.
Square V/F mode
The voltage applied to the motor is directly proportional to the square of the frequency except at low speed where a voltage boost is provided which is
set by the user. This mode can be used for running fan or pump applications with quadratic load characteristics or for multi-motor applications. This
mode is not suitable for applications requiring a high starting torque.
Operating mode Open loop from cold Open loop from 100 %
Heavy Duty overload with motor rated current = drive rated current 150 % for 60 s 150 % for 8 s
NOTE