Direct Torque Control - History

History

DTC was patented by Manfred Depenbrock in the US and in Germany, the latter patent having been filed on October 20, 1984, both patents having been termed direct self-control (DSC). However, Isao Takahashi and Toshihiko Noguchi described a similar control technique termed DTC in an IEEJ paper presented in September 1984 and in an IEEE paper published in late 1986. The DTC innovation is thus usually credited to all three individuals.

The only difference between DTC and DSC is the shape of the path along which the flux vector is controlled, the former path being quasi-circular whereas the latter is hexagonal such that the switching frequency of DTC is higher than DSC. DTC is accordingly aimed at low-to-mid power drives whereas DSC is usually used for higher power drives. (For simplicity, the rest of the article only uses the term DTC.)

Since its mid-1980s introduction applications, DTC have been used to advantage because of its simplicity and very fast torque and flux control response for high performance induction motor (IM) drive applications.

DTC was also studied in Baader's 1989 thesis, which provides a very good treatment of the subject.

The first major successful commercial DTC products, developed by ABB, involved traction applications late in the 1980s for German DE502 and DE10023 diesel-electric locomotives and the 1995 launch of the ACS600 drives family. ACS600 drives has since been replaced by ACS800 drives. Vas, Nash and Tiitinen provide a good treatment of ACS600 and DTC.

DTC has also been applied to three-phase grid side converter control. Grid side converter is identical in structure to the transistor inverter controlling the machine. Thus it can in addition to rectifying AC to DC also feed back energy from the DC to the AC grid. Further, the waveform of the phase currents is very sinusoidal and power factor can be adjusted as desired. In the grid side converter DTC version the grid is considered to be a big electric machine.

DTC techniques for the interior permanent magnet synchronous machine (IPMSM) were introduced in the late 1990s.

DTC was applied to doubly fed machine control in the early 2000s, doubly-fed generators now commonly being used in wind turbine applications.

Given DTC's outstanding torque control performance, it was surprising that ABB's first servo drive family, the ACSM1, was only introduced in 2007.

During the 2000s several papers have been published about DTC including in terms of space vector modulation, which offers constant switching frequency, and DTC drive compatibility of synchronous reluctance motors (SynRM) in addition to induction machines (IM) and permanent magnet machines (PMM).

In light of the mid-2000s expiration of Depenbrock's key DTC patents, it is to be expected that companies other than ABB will develop DTC-controlled drives.