Motor Control; Direct Torque Control (Dtc); Reference Ramping - ABB ACS880 Firmware Manual

28 Program features

Motor control



Direct torque control (DTC)

The motor control of the ACS880 is based on direct torque control (DTC). 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 has
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
Settings
Parameters 99.04 Motor ctrl mode
(page 222).


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
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
scale).
(page 33).
(page 220) and
46.01 Speed scaling
99.13 Identification run request
or 46.02 Frequency scaling. The user can
01.30 Nominal torque