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SENSORLESS FIELD ORIENTED CONTROL OF BRUSHLESS ...

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CHAPTER 2 - Fundamentals of Electric Motors<br />

This chapter presents some fundamentals of electric motors and their models, eventually<br />

narrowing the focus to the brushless permanent magnet synchronous (BPMS) motor that is the<br />

subject of this report.<br />

To begin, the general physical structure of some common motors is presented. The major types of<br />

motors are organized using various classification schemes in order to provide some perspective<br />

on the types of motors discussed in this report. A basic definition of saliency is used to extend<br />

these classifications and this is followed by the introduction of concept of the armature and field.<br />

The bulk of the chapter is concerned with establishing a generalized electrical and mechanical<br />

model for an individual winding in a brushless permanent magnet motor (the “per-phase model”).<br />

The two most fundamental aspects of an electric machine (the induction of voltage and the<br />

production of force) are a recurrent theme. The second section develops these using an<br />

elementary physics-based approach (the laws of Faraday and Lorentz). The basic magnetic<br />

structure of the brushless permanent magnet motor is shown and is used to develop notions of<br />

inductance and flux linkage. Together with the two laws, this understanding allows the<br />

development of the per-phase (scalar) electrical model.<br />

In the third section, the per-phase back-EMF generation and torque production are examined for<br />

each of two simple conceptual machines (sinusoidal and trapezoidal). This will show the<br />

equivalence between back-EMF generation and torque production on a per-phase basis. Equally<br />

importantly, it is shown that that their equivalence is innately related to the rotor-to-stator flux<br />

linkage that will be important in later chapters.<br />

In section four, the general per-phase electromechanical model is given and is extended to form<br />

the “phase-variable” time-domain model of a three-phase brushless permanent magnet<br />

synchronous (BPMS) motor.<br />

Finally, the fifth section examines the similarities and differences between three-phase sinusoidal<br />

and trapezoidal motors. The phase-variable model is used to examine torque production in the<br />

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