Page 41 - Energize November 2022

TECHNICAL

Electronically commutated motors

Energy efficiency, whether mandated by the government or by the market itself, continues to

influence motor and drive technologies. Motors constitute a large percentage of the electric
energy load and there are continuous efforts to improve motor efficiency.

by Mike Rycroft, Energize

he use of advanced materials has improved motor brushless DC motor are the same.
efficiency but there is a limit to this, and other methods, Several types of ECM are available; single phase, two phase
Tsuch as the use of electronics in the motor design are being and three phase DC. The three-phase application appears to
pursued. The electronically commutated motor is one technology be the most common and will be described here. Figure 1
that has emerged from these efforts. shows the diagram of a typical three-phase double pole ECM.
The electronically commutated motor (ECM) or brushless DC The field windings of the three-phase ECM are connected in a
(BLDC) motor is popular in HVAC applications and is increasingly star arrangement. A typical ECM is shown diagrammatically in
used in the industrial sector as improved design offers more Figure 2.
functionality and extends the useful range of motor sizes.
The ECM does away with the mechanical commutator used in
traditional motors, replacing it with an electronic device that
improves the reliability and durability of the unit.
Electronic commutation allows a wide range of control over
motor operation, enabling accurate speed and torque control,
as well as ensuring the motor runs at peak efficiency. ECM
finds its main application in the HVAC field, but applications
are increasing, due both to declining costs and increasing
functionality. An advantage of the ECM is that it can be made
smaller and lighter than a brush type with the same power
output, making it suitable for applications where space is limited.
Although the BLDC requires an electronic control unit, such Figure 1: Typical ECM construction 1
devices are available as standard chipsets or modules from most
of the major electronics manufacturers. Programming and set up
of the controls are very simple. Mass production and wide market
penetration makes these devices economical.
The ECM is basically a DC motor and has a high starting torque
– significantly higher than in the case of an induction motor.
Another advantage of a DC motor is that it has linear speed torque
characteristics, which are well suited for speed, and position
control and high starting torque. The speed of the motor can be
varied linearly (i.e., proportionately) to the applied voltage.
The ECM is a permanent magnet DC motor that uses
electronic commutation. DC motors have a fixed magnetic field
which may be generated by DC energised field coils or permanent
magnets, and a rotating field which is generated by switching the
current to coils, which could either be in the stator or the rotor of
the motor. When current is applied to the field coils a magnetic
field is generated which causes the rotor to move relative to the
stator. As the rotor changes position the current will be switched
to change the polarity of the rotating field, causing the rotor to
rotate. The basic principles of the brushed DC motor and the Figure 2: A typical ECM diagram 1

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