Table of Contents
Safety information
Introduction
3.2
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)
Quadratic V/F mode (V/Hz)
2. RFC - A mode
With position feedback sensor
Without position feedback sensor (Sensorless)
3. RFC - S mode
With position feedback sensor
Without position feedback sensor (Sensorless)
4. Regen mode
3.2.1
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.
Quadratic 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.
3.2.2
RFC-A mode
Rotor Flux Control for Asynchronous (induction) motors (RFC-A) encompasses closed loop vector control with a position feedback device
With position feedback
For use with induction motors with a feedback device installed. The drive directly controls the speed of the motor using the feedback device to ensure
the rotor speed exactly as demanded. Motor flux is accurately controlled at all times to provide full torque all the way down to zero speed.
Without position feedback (Sensorless)
Sensorless mode provides closed loop control without the need for position feedback by using current, voltages and key motor parameters to
estimate the motor speed. It can eliminate instability traditionally associated with open loop control such as operating large motors with light loads at
low frequencies.
3.2.3
RFC-S mode
Rotor Flux Control for Synchronous (permanent magnet brushless) motors (RFC-S) provides closed loop control with position feedback device.
With position feedback
For use with permanent magnet brushless motors with a feedback device installed.
The drive directly controls the speed of the motor using the feedback device to ensure the rotor speed is exactly as demanded. Flux control is not
required because the motor is self excited by the permanent magnets which form part of the rotor.
Absolute position information is required from the feedback device to ensure the output voltage is accurately matched to the back EMF of the motor.
Full torque is available all the way down to zero speed.
3.2.4
Regen mode
For use as a regenerative front end for four quadrant operation.
Regen operation allows bi-directional power flow to and from the AC supply. This provides far greater efficiency levels in applications which would
otherwise dissipate large amounts of energy in the form of heat in a braking resistor.
The harmonic content of the input current is negligible due to the sinusoidal nature of the waveform when compared to a conventional bridge rectifier
or SCR/thyristor front end.
Unidrive M / Unidrive HS Modular Installation Guide
Issue Number: 5
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