Program features 79Motor control Direct torque control (DTC)The motor control of the ACS880 is based on direct torque control (DTC), the ABBpremium motor control platform. The switching of the output semiconductors iscontrolled to achieve the required stator flux and motor torque. The switchingfrequency is changed only if the actual torque and stator flux values differ from theirreference values by more than the allowed hysteresis. The reference value for thetorque controller comes from the speed controller or directly from an external torquereference source.Motor control requires measurement of the DC voltage and two motor phasecurrents. 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. Actualmotor shaft speed is not needed for the motor control.The main difference between traditional control and DTC is that torque controloperates on the same time level as the power switch control. There is no separatevoltage and frequency controlled PWM modulator; the output stage switching iswholly based on the electromagnetic state of the motor.The best motor control accuracy is achieved by activating a separate motoridentification run (ID run).See also section Scalar motor control (page 95).SettingsParameters 99.04 Motor control mode (page 495) and 99.13 ID run requested (page497). Reference rampingAcceleration and deceleration ramping times can be set individually for speed, torqueand frequency reference.With a speed or frequency reference, the ramps are defined as the time it takes forthe drive to accelerate or decelerate between zero speed or frequency and the valuedefined by parameter 46.01 Speed scaling or 46.02 Frequency scaling. The user canswitch 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 referenceto change between zero and nominal motor torque (parameter 01.30 Nominal torquescale).
