Direct Torque Control
Direct Torque Control (DTC) is an optimized motor control method for MV drives that allows direct control of all the core motor variables. This opens up AC drive capabilities never before realized and offers benefits for all applications.
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Typical torque (T) response of a DTC drive, compared with flux vector control and open loop pulse width modulation (PWM).
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What is Direct Torque Control?
Direct Torque Control (DTC) is a revolutionary motor control method for MV drives that allows accurate control of both motor speed and torque without pulse encoder feedback from the motor shaft.
In DTC, stator flux and torque are used as primary control variables. The motor state calculations are updated 40,000 times a second (i.e. every 25 µs) in the advanced motor software model by the high-speed digital signal processor. Due to the continuous updating of the motor state and the comparison of the actual values to the reference values, every single switching in the inverter is determined separately.
Maximized Starting Torque
Precise torque control provided by DTC allows the MV Drives to provide maximized starting torque that is both controllable and smooth.
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Fast Response to Mains Fluctuations and Process Side Changes
The exceptionally fast torque step response of the MV Drives means that it can respond
to process and mains changes extremely fast. This enables easy handling of power-loss situations and sudden load changes.
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Reduced Noise
Because of the separately determined switching, the MV Drives has no fixed switching frequency. This eliminates resonances that cause irritating noise associated with MV drives using conventional PWM technology.
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IGCT Technology
The Medium Voltage Challenge
Until now, the power switches for medium voltage drives have been either Gate Turn Off Thyristors (GTO) or Insulated Gate Bipolar Transistors (IGBT). For medium voltage app-lications, such devices force design trade-offs that increase the cost and complexity of power control systems. ABB is intimately familiar with these trade-offs. We have invested in and further developed these devices for many years.
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IGBT: Conventional Transistorized Approach
Both low voltage and high voltage IGBTs have been used in medium voltage drives. IGBTs are fast switching but conduction losses are high at medium voltage levels and complicated series connections of multiple IGBTs are required. High voltage IGBTs have fewer series-connected devices relative to low voltage IGBTs, but conduction losses are even higher. Overall parts count increases resulting in bigger drives. Costs go up. Reliability goes down.
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GTO: Thyristor Standard
GTO technology is reliable and conduction losses at medium voltage levels are tolerable. The problem is that non-homogeneous switching requires huge additional circuitry
for turn off. Again, parts count increases resulting in larger drives. Costs increase. Reliability decreases.
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IGCT: Specifically Designed for Medium Voltage
ABB is keenly aware of the need for a power-switching device that displays:
• High-speed switching like an IGBT
• Low-loss conduction like a GTO
• Reliability in a wide range of medium voltage applications |
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ABB has developed the simple solution based on proven technology: the Integrated Gate Commutated Thyristor (IGCT). This evolutionary technology consists of a redesigned GTO, which incorporates significant design breakthroughs. The new IGCT delivers fast, homogeneous switching and inherently low losses.
The IGCT is used with Voltage Source Inverter (VSI) topology which is intrinsically less complex and more efficient compared to other topologies. The IGCT-based drives meets the complex medium voltage drive challenge.
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Streamlined Technology Requires Fewer Parts
Depending on the voltage level, an IGCT-based medium voltage drive typically requires as little as one fifth the number of power semiconductor devices as existing low voltage IGBT solutions. IGCT’s lower losses mean less cooling equipment and higher inherent reliability. Fewer parts. Higher reliability. Simple solution.
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Operator Interface
 | Easy-to-use ACS family tools
The Medium Voltage AC Drives incorporates the same suite of user-friendly tools as other drives of the ACS product family. This makes it easier when working with many different ABB drives in one plant.
The PC-based tools include DriveWindow, DriveSupport and DriveOPC. They work
on-line and provide simple start-up, control, monitoring and maintenance features. |
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