Program features 79
Motor control
Direct torque control (DTC)
The motor control of the ACS880 is based on direct torque control (DTC), the ABB
premium motor control platform. The switching of the output semiconductors is
controlled to achieve the required stator flux and motor torque. The switching
frequency is changed only if the actual torque and stator flux values differ from their
reference values by more than the allowed hysteresis. The reference value for the
torque controller comes from the speed controller or directly from an external torque
reference source.
Motor control requires measurement of the DC voltage and two motor phase
currents. Stator flux is calculated by integrating the motor voltage in vector space.
Motor torque is calculated as a cross product of the stator flux and the rotor current.
By utilizing the identified motor model, the stator flux estimate is improved. Actual
motor shaft speed is not needed for the motor control.
The main difference between traditional control and DTC is that torque control
operates on the same time level as the power switch control. There is no separate
voltage and frequency controlled PWM modulator; the output stage switching is
wholly based on the electromagnetic state of the motor.
The best motor control accuracy is achieved by activating a separate motor
identification run (ID run).
See also section Scalar motor control (page 95).
Settings
Parameters 99.04 Motor control mode (page 495) and 99.13 ID run requested (page
497).
Reference ramping
Acceleration and deceleration ramping times can be set individually for speed, torque
and frequency reference.
With a speed or frequency reference, the ramps are defined as the time it takes for
the drive to accelerate or decelerate between zero speed or frequency and the value
defined by parameter 46.01 Speed scaling or 46.02 Frequency scaling. The user can
switch between two preset ramp sets using a binary source such as a digital input.
For speed reference, also the shape of the ramp can be controlled.
With a torque reference, the ramps are defined as the time it takes for the reference
to change between zero and nominal motor torque (parameter 01.30 Nominal torque
scale).
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