SENSORLESS FIELD ORIENTED CONTROL OF BRUSHLESS ...

egulators will be compared; in the second, the synchronous regulator will be developed further in
order to show how the decoupling of the motor circuits can be achieved.
To better visualize the synchronous regulator, Figure 5.14 can be “bent” into a linear form and
redrawn as Figure 5.24, where the loops and compensators are not shown. Previous diagrams
have been schematic-like (for example, the output of a motor is a wire and current must be sensed
with transducer). From now on they will be more transfer-function-like (where the output of a
load is the current thus a transducer is unnecessary).
Figure 5.24 – Model of motor load (ideal inverter) viewed from three perspectives.
It should be realized that the motor and power converter are always three-phase. The two-phase
stationary (αβ) and two-component synchronous (dq) voltages do not exist—they are only
commands representative of the three-phase voltages applied to the motor. Likewise the αβ and
dq currents do not exist—they are transformed versions of the physical measurement of the threephase
currents. However, it has been shown that three-phase quantities may be represented as a
SV in any arbitrary frame and that control can be carried out in that same frame. Since a
controller in a frame “sees” the motor model from the perspective of that frame, it is as if the
transformed voltages and currents existed and the motor can be modeled in the same frame, as
shown in Part III of Chapter 3. This assumes the transformations and the SVM inverter are ideal.
This assumption is not very practical because the SVM inverter has nonlinearities (dead-time
distortion, transistor voltage drop, bus voltage drop), but it is good enough to introduce the
concepts of three-phase current regulation and the synchronous regulator in particular.
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