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Unidrive User Guide

www.controltechniques.com Issue Number: 9

2.4.2 Unidrive LFT

...for lift applications
Overloads and operating modes as Unidrive standard industrial, in
addition:

low acoustic noise
9kHz default switching frequency
S4/S5 duty cycle only

Figure 2-3 Standard S4/S5 duty cycle (Unidrive LFT)

2.4.3 Unidrive VTC

...for quadratic load (variable torque) applications (fans and pumps)
Open loop fixed boost mode only

120% overload for 60s

Figure 2-4 Variable torque mode

2.4.4 Unidrive REGEN

All sizes of Unidrive can be used in regen mode. However, Unidrive
sizes 3 and 4 require an internal modification before being used in a
regen system.
This modification is already completed if the drive has been ordered as a
Unidrive REGEN.

2.5 Operating modes

All variants of Unidrive (except VTC) are designed to operate in any of
the following modes:
1. Open loop mode

V/f mode (V/ Hz)
Open loop vector

2. Closed loop vector
3. Servo
4. Regen
Unidrive VTC can only operate in open loop quadratic V/f mode.

2.5.1 Open Loop mode (OL)

For use with standard AC induction motors.
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 performance 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.

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 should used for multi-motor applications.
Typically 100% torque at 4Hz.

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 at 1Hz.

2.5.2 Closed loop vector mode (VT)

For use with induction motors with a speed feedback device fitted.
The drive directly controls the speed of the motor using the feedback
device to ensure the rotor speed is exactly as demanded. Motor flux is
accurately controlled at all times to provide full torque all the way down
to zero speed.
Typically 175% torque at 0rpm.

2.5.3 Servo (SV)

For use with permanent magnet brushless motors with a speed and
position feedback device fitted.
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.
Typically 175% torque at 0rpm

2.5.4 Regen

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 thyristor front end.
See the

Regen Installation Guide

for more information on this operating

mode.

2.5.5 Key to operating mode abbreviations

Abbreviations are throughout this User Guide to define the operating
mode for which the information applies as follows:

OL>

Open loop

CL>

Closed loop (which incorporates closed loop vector and
servo mode)

VT>

Closed loop vector mode

SV>