Application and Operation
6.2 The Control Modes
Product User Manual
110 Operating Instructions, Version AE 12/2009, A5E01454341C
6.2.1 Open Loop Vector Control (OLVC)
This control mode should be used for most applications with single induction motors. In this
method, the control estimates motor slip as a function of load torque, and provides a
performance that matches a vector controlled drive (with speed sensor/transducer) above a
certain minimum speed. With the correct motor parameters, the control can provide good
performance even at 1% of rated speed.
Speed feedback is synthesized from the stator frequency and the estimated motor slip, as
shown in Figure "Block Diagram of Vector Control Algorithms for Induction and Synchronous
Motor Control". With this control method, slip compensation is automatic.
In this control mode, if Spinning Load is selected, the drive begins by scanning the frequency
range to detect the speed of the rotating motor (please refer to Section "Spinning Load") for
a description of Spinning Load Operation). Once the drive has completed the scan or if the
feature is disabled, the drive goes into Magnetizing State. During this state, the drive ramps
the motor flux to its commanded value at the specified Flux Ramp Rate. Only when the flux
feedback is within 90% of the commanded flux, the drive changes to the Run State. Once in
Run State, the drive increases the speed to the desired value. All motor and drive
parameters as described in the NXG Control Manual (19001588) are required for this mode
of operation. Default values for the control loop gains are sufficient for most applications.
6.2.2 Open Loop Test Mode (OLTM)
In this control method, the motor current feeback signals are ignored. This control mode
should be used drive set-up, when the modulation on the cells is to be verified, or when
testing the drive without a load. I can also be used when the motor is first connected to the
drive to make sure that the Hall Effect Transducers are working correctly and are providing
the correct feedback signals. This method should not be used to adjust scale factors for input
and output, voltage and currents.
In this mode, the drive goes trough the Magnetizing State to the Run State without looking at
the motor flux. Only motor nameplate values and some drive related parameters are required
for this mode. Special attention should be given to the following parameters:
1. Spinning Load and Fast Bypass should be disabled.
2. Acceleration and deceleration times (in the Speed Ramp Menu) should be increased.
3. Flux Demand should be reduced.
6.2.3 Synchronous Motor Control (SMC)
For synchronous motor control (SMC), the drive is equipped with a field exciter that usually
consists of a SCR based current regulator. The field exciter operates to maintain a field
current level that is commanded by the flux regulator. An example application for a brushless
synchronous motor is shown in Figure "Harmony Drive Arrangement for Brushless
Synchronous Motor". For brushless motors, the diagram assumes that the exciter stator is
wound for 3 phase AC in the range of 350 to 400 volts. If that is not the case, a transformer
will be necessary between the auxiliary power and the field exciter. The circuit wheel needs
only a rectifier. For the brushless case without bypass, the motor does not require any
protection other than that included in the drive. Next Gen Control will trip the drive on a loss
of field fault if the motor draws excessive reactive current, which will occur when the exciter
fails full on or off.
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