Unidrive SP Low Voltage DC Installation Guide 7
Issue Number: 1 www.controltechniques.com
Safety Information
Introduction
Product information System design Component data Index
change-over from AC to DC or DC to AC is not possible. See Chapter 4.7 Power circuit
control logic and sequencing on page 24.
For Low Voltage DC operation, as well as the main Low Voltage DC supply the following
external supplies are required.
• For Unidrive SP sizes 1 to 6, a 24Vdc supply must be connected to the +24V
external input on the green control terminal block of the drive (see Chapter
4 System design ). This supplies the control circuitry and may be connected
permanently.
• For Unidrive SP4 SP5 SP6 a 24V external supply needs to be connected to the
24V Low Voltage DC mode enable terminal of the drive. This supply should only be
connected when in Low Voltage DC operation (this supply is in addition to the +24V
external input).(see Chapter 4 System design )
2.3 Operating modes
Low Voltage DC operation can be used in any of the following modes:
1. Open loop mode
• Open loop vector
• Fixed V/F mode (V/Hz)
• Quadratic V/F mode (V/Hz)
2. RFC mode
3. Closed loop vector
4. Servo
2.4 Low Voltage DC speed limitation
When set up for Low Voltage DC operation, the drive can provide rated torque to the motor
at low speeds. The maximum speed that can be achieved whilst operating from this supply
is dependent on the type of motor connected to the drive as described below.
2.4.1 Operation with an induction motor
When operating with an induction motor the drive will effectively start to field weaken at
the point that the output voltage requirement (based on the programmed V/F) reaches
the maximum that the DC bus voltage of the drive can support (about 34V based on a
DC bus of 48V). e.g. The drive would begin to field weaken the motor at around 4Hz for
a 50Hz 400V motor.
The drive may continue to rotate the motor up to base speed. However, even with no
external load (just a bare motor shaft) the motor could stall due to the reduced torque
available whilst so far into field weakening.
Be aware that reduced torque may be experienced in instances where the motor
requires significant volts to magnetise; the reasons for this are listed below.
• The external Low Voltage DC power supply has reached it's maximum supply
voltage to the drive.
• The drive has reached the maximum allowable output voltage available in this mode
of operation.
Low Voltage DC operation CANNOT be used to limit the speed of an induction motor.
The drive can only provide rated torque at low speeds as described above. It is very
important to consider this when operating with an overhauling load such as lift
applications, even with the correct braking resistor selection, the drive may not be able
to maintain control of the load if the drive goes into field weakening.
WARNING
WARNING
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