1、毕业设计（论文） - 1 - 附录 A：英文参考文献及其翻译 Direct torque control Direct torque control (DTC) is one method used in variable frequency drives to control the torque (and thus finally the speed) of three-phaseAC electric motors. This involves calculating an estimate of the motors magnetic flux and torque based on
2、the measured voltage and current of the motor. Method Statorflux linkage is estimated by integrating the stator voltages. Torque is estimated as a cross product of estimated stator flux linkagevector and measured motor currentvector. The estimated flux magnitude and torque are then compared with the
3、ir reference values. If either the estimated flux or torque deviates from the reference more than allowed tolerance, the transistors of the variable frequency drive are turned off and on in such a way that the flux and torque will return in their tolerance bands as fast as possible. Thus direct torq
4、ue control is one form of the hysteresis or bang-bang control. This control method implies the following properties of the control: Torque and flux can be changed very fast by changing the references High efficiency & low losses - switching losses are minimized because the transistors are switched o
5、nly when it is needed to keep torque and flux within their hysteresis bands The step response has no overshoot No coordinate transforms are needed, all calculations are done in stationary coordinate system No separate modulator is needed, the hysteresis control defines the switch control signals dir
6、ectly There are no PI current controllers. Thus no tuning of the control is required The switching frequency of the transistors is not constant. However, by controlling the width of the tolerance bands the average switching frequency can be kept roughly at its reference value. This also keeps the cu
7、rrent and torque ripple small. Thus the torque and current ripple are of the same magnitude than with vector controlled drives with the same switching frequency. Due to the hysteresis control the switching process is random by nature. Thus there are no peaks in the current spectrum. This further mea
8、ns that the audible noise of the machine is low The intermediate DC circuits voltage variation is automatically taken into account in the algorithm (in voltage integration). Thus no problems exist due to dc voltage ripple (aliasing) or dc voltage transients Synchronization to rotating machine is str
9、aightforward due to the fast control； Just make the torque reference zero and start the inverter. The flux will be identified by the first current pulse 毕业设计（论文） - 2 - Digital control equipment has to be very fast in order to be able to prevent the flux and torque from deviating far from the toleran
10、ce bands. Typically the control algorithm has to be performed with 10 - 30 microseconds or shorter intervals. However, the amount of calculations required is small due to the simplicity of the algorithm The current and voltage measuring devices have to be high quality ones without noise and low-pass
11、 filtering, because noise and slow response ruins the hysteresis control In higher speeds the method is not sensitive to any motor parameters. However, at low speeds the error in stator resistance used in stator flux estimation becomes critical The direct torque method performs very well even withou
12、t speed sensors. However, the flux estimation is usually based on the integration of the motor phase voltages. Due to the inevitable errors in the voltage measurement and stator resistance estimate the integrals tend to become erroneous at low speed. Thus it is not possible to control the motor if t
13、he output frequency of the variable frequency drive is zero. However, by careful design of the control system it is possible to have the minimum frequency in the range 0.5 Hz to 1 Hz that is enough to make possible to start an induction motor with full torque from a standstill situation. A reversal
14、of the rotation direction is possible too if the speed is passing through the zero range rapidly enough to prevent excessive flux estimate deviation. If continuous operation at low speeds including zero frequency operation is required, a speed or position sensor can be added to the DTC system. With
15、the sensor, high accuracy of the torque and speed control can be maintained in the whole speed range. History Direct torque control was patented by Manfred Depenbrock in U.S. Patent 4,678,248 filed originally on October 20, 1984 in Germany. He called it Direct Self-Control (DSC). However, Isao Takah
16、ashi and Toshihiko Noguchi presented a similar idea only few months later in a Japanese journal. Thus direct torque control is usually credited to all three gentlemen. The only difference between DTC and DSC is the shape of the path along which the flux vector is controlled to follow. In DTC the pat
17、h is a circle and in DSC it was a hexagon. Today DTC uses hexagon flux path only when full voltage is required at high speeds. Since Depenbrock, Takahashi and Noguchi had proposed direct torque control (DTC) for induction machines in the mid 1980s, this new torque control scheme has gained much mome
18、ntum. From its introduction, the Direct Torque control or Direct Self Control (DSC) principle has been used for Induction Motor (IM) drives with fast dynamics. Despite its simplicity, DTC is able to produce very fast torque and flux control, if the torque and flux are correctly estimated. Among the
19、others, DTC/DSC was further studied in Ruhr-University in Bochum, Germany at the end of 80s. A very good treatment of the subject 。 DTC has also been applied to three-phasegrid side converter control (U.S. Patent 5,940,286). Grid side converter is identical in structure to the transistorinverter con
20、trolling 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 毕业设计（论文） - 3 - adjusted as desired. In the grid side converter DTC version the grid is conside
21、red to be a big electric machine (which, actually, there are many in the grid!). In the late 1990s DTC techniques for the Interior Permanent MagnetSynchronous Machine (IPMSM) appeared. Further, in the beginning of 2000s DTC was applied to doubly fed machine control (U.S. Patent 6,448,735). Doubly fed generators are today commonly used in wind turbine applications. During 2000s several papers have been published about DTC. Also several modifications such as space vector modulated DTC that has constant switching frequency, has been presented.
