SENSORLESS FIELD ORIENTED CONTROL OF BRUSHLESS ...

variables to the stationary reference frame. 37 The stationary regulators are just as they were before
in the impressed-current (thus open-loop) case, but there is a problem: the α- and β- current
components do not exist. The simple answer is to use the Clarke transform to obtain them, as
shown in Figure 5.11. 38
Figure 5.11 – Torque control of sinusoidal motor; stationary reference frame.
It is clear that the current regulators are still handling the AC quantities. In the impressed-current
system, the next step was to generate the current reference in the rotor frame, thereby eliminating
the quadrature-phase sinusoidal commutator and replacing it with the inverse Park transform.
This is also the next step here. In addition, we will simultaneously move the current regulators to
the rotor frame, as shown in Figure 5.12.
37 The stationary reference frame is so called because it is fixed to the stator (it is also called the stator
reference frame). When drawing SV diagrams this is a clear interpretation, as the 0° reference never moves.
But in the control systems shown above, the control variables were “stationary” (unchanging DC
quantities) in the rotor frame and the signals oscillate in the stationary reference frame. One might use
caution in reading the popular literature, as sometimes the DC signals are referred to as “stationary signals”
but this does not mean they are in the stationary frame.
38 Notice that the problem mentioned in Footnote (36) is no longer of any concern because there are only
two commands generated and these dq or αβ components cannot contain a ZS component. Further, the
inverse Clarke transform is not capable of generating a ZS component!
217