Motors and Drives
A motor control technique for all seasons
Ere Jääskeläinen outlines the benefits of direct torque control (DTC) technology.
requirements. Most VSDs in the market rely on a modulator stage
V
that conditions voltage and frequency inputs to the motor, but causes inherent time delay in processing control signals. In contrast, premium ABB drives employ innovative
direct torque control (DTC) - greatly increasing motor torque response. DTC technology also provides other benefits ranging up to system-level features. High-performance AC drives from ABB offer an
innovative technology called direct torque control (DTC). As the name suggests, the method controls motor flux and torque directly, instead of trying to control motor currents indirectly like AC vector drives and DC drives. This means better accuracy in matching the driven system’s load requirements. Originated by one of the founding companies of ABB and patented in the mid-1980s, DTC eliminates the need for an extra modulator stage thus achieving control dynamics close to the theoretical maximum.
ariable-speed drives (VSDs) have enabled unprecedented performance in electric motors and delivered dramatic energy savings by matching motor speed and torque to the driven load
When ABB introduced its first direct torque control AC drive to the market in 1995, DTC was already a leading technology. Subsequent improvements in processor computational power, application programming, and communication interfaces have continually enabled higher DTC performance, providing premium motor control for a broad range of applications. DTC’s operation and other technology details are shown in Fig. 1.
Why use DTC?
Besides superior torque response, DTC offers other customer benefits, including:
● No need for motor speed or position feedback in 95 per cent of applications. Thus, installation of costly encoders or other feedback devices can be avoided.
● DTC control available for different types of motors, including permanent magnet and the new synchronous reluctance motors.
● Accurate torque and speed control down to low speeds, as well as full startup torque down to zero speed.
● Excellent torque linearity.
Fig. 1. Direct Torque Control’s (DTC) operation principle.
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