Motor Applications for Small Appliances0 pages

Beyond Bits

Motor Control Edition

Motor Applications for
Small Appliances
Using BLDC motors in small home appliances
Introduction
Brushless motors are more efficient at
converting electricity into mechanical
power than brushed motors. Lack
of a commutator allows for reduced
complexity and maintenance, as well
as lower electromagnetic interference.
Brushless motors can develop high
torque with a good speed response
and can be easily controlled by an
MCU. They can also operate in a
very wide speed range to enable
fine motion control and hold torque
when stationary.
Brushless motors have come to
dominate many applications, namely
hard drives, CD/DVD players, pumps,
fans, robotic vacuum cleaners, coffee
machines, mixers, hairdryers, bread
cutters and spindle drives in adjustable
or variable speed applications. They
are also a popular motor choice for
helping to increase battery life for
model aircraft, remote control (RC)
cars and portable power tools.

Application Requirements
Each application has very specific
requirements. Though it’s not easy to
cover all solutions through a single
example, Freescale offers many

Figure 1: BLDC Motor
Cross Section

Figure 2: Freescale Kinetis BLDC Sensorless Reference
Design Block Diagram
BLDC Sensorless
Motor Control for K60

Three-Phase Inverter
Overcurrent
Flag

MC33927
MOS-FET
driver

Browser

Input Voltage
Three-Phase
Low-Voltage
Power
Stage

BEMF
Voltage

DC Bus U,I

Input

Kinetis K60

App.
State
Machine

Ethernet
Buttons

ThreePhase
BLDC
Motor

PBD

PWM
FlexTimer0

Commutation

ADC
BE/MF Sense

API
PI Controller
Speed Ramp

SCI

Speed
Computing
and Scaling

FlexTimer1

Fault
Protection

Input

FreeMASTER

Kinetis Peripheral

Input

Software

application reference designs and/or
demo software which can be easily
reconfigured according to applicationspecific needs.

High Efficiency
Brushless motors are used in place
of various types of AC motors. The
most significant reason to switch to
a brushless motor is the dramatic
reduction in power required to operate
them versus a typical AC motor. Some
devices use brushless motors in order
to increase overall system efficiency
and achieve a higher efficiency class
according to the European Union
energy label. In small, battery-powered
devices, improving drive efficiency also
helps to lengthen battery life.

Speed Variability and
Speed Control
In addition to the brushless motor’s
higher efficiency, certain home
appliance devices use brushless
motors because the built-in MCU
allows for programmability, variablespeed and/or load modulation with
enough precision. A robotic vacuum

Motor Parts

Device on Three-Phase Inverter

cleaner is a typical example of when
MCU speed control is needed. It
enables bi-directional operation with
fast torque response and low noise.
RC toys and vacuum cleaners also
utilize very high-speed operation.

Low Price, High Quality
Small appliances are usually produced
in very large volumes, therefore one
of the most important requirements
is cost effectiveness. Cost-effective
control topology with BLDC motors
allows for lower device prices while
maintaining the quality of the product.
Additional price reduction can be
achieved by removing the position
sensor. For more information on this
option, see the related small appliance
articles in this edition of Beyond Bits.

High Reliability
Reliability is an important aspect of
brushless motors, as they contain
a minimal number of mechanical
parts: no commutator, no slip rings,
and no winding on rotary parts. The
most important parts of the drive are