SENSORLESS FIELD ORIENTED CONTROL OF BRUSHLESS ...

Terminology
The terms field oriented control and vector control are in general used synonymously, although
some authors assign particular meaning to each. The first solid state three-phase induction motor
drives were simply variable-voltage, variable-frequency (VVVF) three-phase voltage sources
(also called a static inverter). The induction motor is asynchronous and the VVVF is all that is
required to deliver variable speed operation. However, such a drive provides poor transient
performance do to the induction motor dynamics. (The single phase equivalent model is only
valid for steady state. Further, they express torque in relation to a frequency/slip-dependent
circuit variable, not a spatial orientation [78, p.32].) Apparently one of the first successful
analyses of controlled induction motor dynamics was given by Hasse in his now-classic 1969
dissertation [19]. Since the work emphasized that torque production in the induction motor is a
spatial phenomenon (in contrast with the SPE tee circuit model) the name vector control was
eventually adopted. Blaschke is also credited as being an early pioneer of the concept via his
often-cited 1971 publication [20]. The title of his 1973 dissertation [21] contained the phrase
“principle of field orientation.” Since the original VVVFs only adjusted frequency and magnitude
there were retroactively renamed scalar drives. These are still manufactured and used in variable
speed applications that do not demand high dynamic performance, although at least one author
[61, p.6] believes they will eventually displace the scalar drives. There is quite a difference
between the approaches Hasse and Blaschke and hence, there are a large number of different
FOC/vector control schemes for induction motors; these are not mentioned further.
[78, p.32] gives a good perspective from a machine standpoint: field oriented control may be used
to describe distributed field quantities, whereas vector control may be used to describe the circuit
variables. Given the relationship between the two (discussed in Part II of Chapter 3), they are
essentially equivalent perspectives. However, the basic idea of controlling a vector quantity (e.g.,
a space vector) can be applied to stationary circuits as well, such as controlled rectifiers, inverters,
and active filters. In these cases it seems that term vector control is the most appropriate (and
most often used). On the contrary, vector control of a motor is called both that and FOC.
The ultimate objective in motor control is the control of torque. As hinted previously, FOC
achieves linear torque control by adjusting the current SV to lie entirely along the q axis. To the
extent that this instantaneous current control can be achieved, instantaneous torque control is
achieved. Thus, unlike the VVVF drive, vector drives allow direct control of the instantaneous
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