M
OTOR
C
ONTROL
37
June 2014
The demand for electric motors is increasing
at a rate of 5-6 percent annually, and is pro-
jected to rise through 2017 to a total available
market of $14.4 billion in the US alone. The
growth rate is even higher in China and Asia,
as these countries modernize and improve in-
frastructure. Within these markets, the expan-
sion of mid-range horsepower motors outpaces
that of smaller fractional horsepower types.
Driving this demand are heating and cooling
equipment markets, along with electric vehicles,
which will provide the best growth opportuni-
ties. All systems, from industrial, avionic, mili-
tary and space are seeing demand to improve
efficiency and reduce weight. Along these lines,
European markets have issued a directive to
improve motor efficiency. Reductions in size
and improvements in operating and ownership
cost are also being driven in military and
avionic markets worldwide. To achieve these
goals, more reliable and efficient motors and
control techniques must be considered.
The BLDC motor provides clear advantage
over other motor types in terms of optimizing
efficiency and size in demanding motor appli-
cations. BLDC motors do not have brushes
and require less maintenance and system down
time. Yet these motors require electronic con-
trollers that range from simple to complex.
The motors typically have efficiency of over
80%, and the controllers in the 95% range.
Thus the enabling technology is the ever im-
proving evolution of the BLDCmotor controller.
The most efficient controllers use Pulse Width
Modulation (PWM) sampling to drive a motor
from DC power. There are other power condi-
tioning requirements that range from rectifica-
tion of an AC signal to electromagnetic inter-
ference (EMI) filtering that is required in most
applications. Defining and understanding the
motor application is essential to selecting the
optimum controller choice. The most common
motor control techniques and applications can
be broken down as follows:
Each of these systems utilizes specific motor
control techniques that require tuning of one
or more control loops – torque, speed and/or
position. Precision and efficiency is determined
on controlling voltage which sets the speed
and current that controls the torque. A designer
must consider the approaches of analog and
digital motor control solutions. Analog motor
controllers utilize resistors and capacitors for
loop tuning. This typically requires knowledge
of control loops and can be supported by data
sheets, technical staff and formulas that aid in
optimum component selection. Each loops’
design characteristics must be chosen carefully.
In the case of a speed and torque controller,
the loops must be tuned correctly. These de-
signs are application-specific and can require
additional optimization as the system is tested
to the full range of performance. Changes are
often required as motors and loads are changed
or added. The upside to the analog approach
is that these motor controllers come in a com-
pact form. The tuning is accomplished by
changing resistors and capacitors to set the
proportional and integral loop gains of each
loop. The compact size of analog controllers is
ideal for use in avionic applications due to the
size and the cost of certifying programmable
devices. Avionic specifications implemented
by the Federal Aviation Administration (FAA)
in 2005 to ensure the safety of civilian aircraft
electronic systems require rigorous design ap-
proach and certification. The specifications
that are used for design control are as follows.
DO254 sets development and compliance stan-
dards for complex electronic hardware such
as processors, field programmable gate arrays
(FPGAs), digital signal processors (DSP), pro-
grammable logic devices (PLD), and applica-
tion specific integrated circuits (ASICs). The
levels for this certification range fromA: Flight
BLDC motor controllers for simple
and complex systems
By Don Laskay,
Data Device Corporation
Modern Brushless DC (BLDC)
motor controllers housed in
compact assemblies are ideal
for integration into systems
that require precision control
and efficiency. This enabling
technology fulfils the require-
ments of both simple and
complex motor systems, while
offering significant advan-
tages and improving time to
market.
Complete enclosed motor con-
troller solution
Control Technique
Applications
Speed
Rotate at constant Pumps, Fans and or
multiple RPMs Compressors
Torque
Maintain force while Doors, Wing
changing direction Slats/Flaps, Fins
Position
Move to precise Robotics, Radar,
location
Satellite
Communications,
Turrets
