SENSORLESS FIELD ORIENTED CONTROL OF BRUSHLESS ...

vector theory to model a machine, which was formalized in 1959 by Kovács and Rácz in Hungary
[15]. (Transient phenomena in AC machines had already been documented [16], [17]—it seems
that it was the space vector’s complex-valued notation and ability to combine electrical and
mechanical quantities that made it of value.)
Regardless of any gains in theoretical understanding of the induction motor, it seems that the
motor continued to be controlled as described earlier, until the late 1960s when Germans
Blaschke and Hasse made some key innovations [19], [20], [21]. It seems that their efforts led to
the first control systems that attempted to control the induction motor based on its transient model
instead of the steady-state equivalent circuit—they were the first form of “vector control.” Instead
of simply generating three-phase voltages of varying frequency and amplitude in order to achieve
variable speed operation, the vector control also controlled the phase of the output waveforms.
This was the beginning of a revolution that would allow the induction motor to be used in speed
control applications requiring dynamic performance, eliminating the need to oversize motors to
achieve satisfactory transient performance. Vector control is also known as field oriented control
(FOC). FOC can be applied to other AC machines as well and there is benefit in doing this.
However, the benefits obtained in applying FOC to a synchronous machine are not the same as
those obtained with the induction motor. At the simplest level, vector control of a synchronous
machine provides a control structure that makes decoupling control and arbitrary control schemes
easier to implement. Due to the fact that the structure performs inherent synchronous frame
current regulation, it also affords better steady-steady control at high speeds where traditional
“stationary frame” regulators begin to lose gain and phase. In contrast, FOC control tames the
dynamics of the induction motor (which are more sluggish than those of the synchronous
machine). It seems as if the drastic benefits provided by FOC of an induction motor have been
ascribed to the synchronous machine as well, causing some general misunderstanding as to the
benefits of FOC. It is interesting to note that according to [100] most major servo drive
manufacturers use FOC for sinusoidal drives (as opposed to non-FOC sinusoidal commutation),
yet very few advertise this fact. In this case, the servo manufacturers are not contributing to the
confusion between FOC of a BPMS motor and FOC and induction motor; it seems that most of
the confusion has been caused by the other articles in the popular literature. Additional
information on AC motor drives can be found in [64], [75], [81], [92], [93], [94], [95], [96], [97],
[99].
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