SENSORLESS FIELD ORIENTED CONTROL OF BRUSHLESS ...

From the summary above, it can be understood that the history of motor control spans more than
a century and is very multifaceted. To understand where the material in this report fits into the
overall picture, some points should be summarized. The realization of AC motor control via the
generation of variable voltage and frequency current (using solid-state devices) was a landmark
achievement. This was followed by the development of power devices that could be turned off at
will, which allowed PWM to become a reality. In the beginning this was used to create VVVF
induction motor drives. At some time, a line-start permanent magnet synchronous motor was
introduced but it was not used in variable-frequency applications. In addition, an electronicallycommutated
(thus brushless) permanent magnet machine was devised. Eventually the concept of
a sinusoidal permanent magnet synchronous machine was combined with an inverter to yield an
adjustable-speed AC drive without brushes, capable of servo-like performance. The electronically
commutated motor also served in this capacity, with the distinct advantages of using less
expensive shaft position sensors and power electronics; due to the lower cost and simplicity of the
system, the technique is still used today. Separate from all of this, vector control allowed linear
control over the torque produced by an induction motor; this eventually allowed the induction
motor to be used in servo-like applications as well where it was previously not possible. The
vector control scheme can be applied to other motors and it provides distinct benefits, but these
benefits are not the same as those achieved with the induction motor. All methods of synchronous
machine control and all methods of vector control (of any machine) require knowledge of the
rotor flux, which can be obtained directly or indirectly from a shaft sensor. There are many
benefits to eliminating the shaft sensor, yielding so-called sensorless control.
The original purpose of the research that led to this report was to investigate the advantages and
disadvantages of the sensorless FOC of a BPMS motor. This involved learning the fundamentals
of brushless motor operation; since this is not taught in most curricula the initial sources of
information were application notes written by servo motor and servo drive manufacturers, and by
manufacturers of silicon devices (ASICs, MCUs, DSPs) involved in motor control. The motor
drive literature was naturally lacking on the details of how the controls were implemented
internally, and the silicon device literature was geared toward the implementation in a particular
device and was lacking in theory. All of that literature would be useful for practical applications
of the manufacturer’s product, but it is not useful to learn theory. In addition, this literature is
very lacking in performance data. Manufacturers are quick to list benefits of using their products,
but often these claims are misleading at best. This literature (as well as all articles in trade
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