SENSORLESS FIELD ORIENTED CONTROL OF BRUSHLESS ...

control scheme must keep sinusoidal currents aligned in time with the rotor position. In its most
basic form, this requires a continuous position sensor (resolver) or near-continuous sensor
(absolute encoder). While the rotor is rotating the required instantaneous value of phase current
changes continuously, even when the commanded torque is constant. Thus for the sinusoidal
motor, current control cannot be separated from the commutation or phasing as it can for the
electronically switched motor. A conceptual diagram of a sinusoidal motor controller is shown in
Figure 2.34, where the peak reference current is again given by Equation (2.61) and the
commanded currents of each phase are given by Equation (2.63), where KT is that for a sinusoidal
motor.
sin( )
* ref
iA Ip
r
* ref
iB Ip
sin( r
120
)
* ref
iC Ip
sin( r
120
)
Figure 2.34 – Torque control of sinusoidal BPMS motor.
(2.63)
The actual circuitry to accomplish the conceptual torque control presented here will be discussed
in Chapter 4 (for the case of sinusoidal motors).
Types of Brushless Permanent Magnet Motors
A ridiculous number of acronyms are found in the literature to describe BPMS motors, such as
the following:
BACM brushless AC motor
BDCM brush/brushless DC motor
BLDC brushless DC
BLSM brushless servo/synchronous motor
59