SENSORLESS FIELD ORIENTED CONTROL OF BRUSHLESS ...

which polarity of current at what time (i.e., they are used with logic to “commutate the motor”).
Notice that the commutation scheme need only perform the traditional role of the commutator: to
reverse polarity and to interrupt current flow—the magnitude of the current is controlled
independently according to the torque demanded of the motor. A conceptual diagram of a
trapezoidal motor controller is shown in Figure 2.33, where the required current is given by
Equation (2.61) and KT is that for a trapezoidal motor. The commutation logic depends on the
placement of the Hall effect sensors but is always found in conjunction with Figure 2.31. For this
simple case the commanded current is a DC value given by Equation (2.62) and is equal to the
reference current since an ideal source is assumed.
ref
ref
KI T p Ip
(2.61)
K
*
i Ip
T
(2.62)
Figure 2.33 – Torque control of trapezoidal BPMS motor.
Though less fitting, electronic commutation is also used to describe current control in the
sinusoidal motor; sometimes it is called phasing. It is clear that the sine motor is capable of
producing ripple-free torque when driven with properly-phased sinusoidal currents. It is
sometimes called a Permanent Magnet Synchronous Motor (PMSM) since it is just like the
“classic” synchronous motor, with the wound-field rotor replaced by a PM rotor. The current
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