SENSORLESS FIELD ORIENTED CONTROL OF BRUSHLESS ...

torque production; this is called direct torque control. However, there is a specific method of
motor control called “direct torque control” or DTC; this is not the FOC described here. DTC 33 is
somewhat of a merger between FOC and SVM, in which the motor torque and inverter control
scheme are integrated. Thus, the reader is alerted to the fact that many vector control schemes
yield “direct torque control” but that the same is also used to refer to a particular control structure.
An overview of the different types of DTC is given in [101].
Torque Control in the Rotor Reference Frame
In the literature one encounters the phrase “impressed stator currents;” this refers to the use of a
controlled current source to generate phase currents that exactly follow the commanded currents.
This assumption eliminates all disturbances to the current control loop and allows the underlying
torque control to be examined. Impressed stator currents will be used to demonstrate torque
control in the rotor frame and then the same will be demonstrated using practical CRPWM.
Using Impressed Stator Currents
When electronic commutation and phasing were introduced in Chapter 2, the concept was shown
for a sinusoidal motor as the control system in Figure 5.1, where the reference currents were
given by Equations (5.1) and (5.2). 34 The implementation of this concept will be developed first
in the phase-variable form, then in the stationary reference frame, and finally in the rotor
reference frame.
33 Although DTC is found throughout the literature as a control concept, DTC is (or at least at one time
was) a registered trademark of the Finnish company ABB Industry Oy.
34
In this chapter cosine waves will be plotted as a function of t , where t r /2.
This allows
the correct expressions (such as Equation 5.2) to be used while gaining the visual convenience of the
cosine.
209