16 Powering Up Your Design
Figure 2: BLDC and
PMSM motors diagram
(Source: Qorvo).
Power
Application
Controllers®
PAC5556 Power
Application
Controller
PAC5524 High
Pin-Count Motor
Controller and Driver
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Sensored and Sensorless BLDC and
PMSM motors
BLDC and PMSM motors can be sensored or sensorless.
Sensored motors (Figure 2) are used in applications
requiring the motor to start up under a load condition. They
use Hall sensors, which are embedded into the motor stator.
The sensor is essentially a switch with a digital output equal
to the sensed magnetic field polarity. The motor requires a
separate Hall sensor for each phase. A three-phase motor
requires three Hall sensors. Sensorless motors require
algorithms to operate using the motor as the sensor. They
rely on BEMF information. By sampling the BEMF, the rotor
position can be deduced, eliminating the need for hardware-
based sensors. Regardless of motor topology, controlling
these motors requires knowing the rotor position so the
motor can be efficiently commutated.
Motor Control Software Algorithms
Today, software algorithms (a set of instructions designed
to perform a specific task), such as computer programs, are
used to control BLDC and PMSM motors. These software
algorithms improve efficiency and reduce operating costs
An Explanation of Field-Oriented Control
To achieve the sinusoidal waveform that controls the PMSM
motor, a field-oriented control (FOC) algorithm is required.
FOC is typically used to maximize the efficiency of the PMSM
three-phase motor. The sinusoidal controller for the PMSM
is more complex and costlier than the BLDC trapezoidal
controller. However, this cost increase has advantages such
as lower noise and less harmonics in the current waveform.
The main advantage of the BLDC is it is easier to control.
Ultimately, the choice of which motor is best depends on its
application.
