electronica Nov 2014
31
M
ICROCONTROLLERS
Optimised MCUs enable
a new spin on motor control
By Danny Basler,
Freescale
This article discusses
the new Kinetis V series MCUs,
the supporting Kinetis motor suite
tool and the benefits they offer
for leveraging modern
motor technologies.
Motor control has an impact. Although
not as fashionable as the current hot trends
of IoT and smart mobile devices, it remains
an expansive feature of the embedded control
landscape and a huge area of opportunity for
microcontroller (MCU) development. While
the adoption of new motor technologies is
increasing, many motors still achieve rela-
tively low levels of efficiency – 50% in many
cases. Multiply that by the billions of home
appliances, HVAC units, elevators, genera-
tors, etc and it accounts for a staggering 45%
of global electricity demand. That’s worthy of
considerable attention.
Thankfully, help is at hand in the form of
sophisticated MCUs that can help improve
motor efficiency up to around 80% and
beyond. The environmental benefits are obvi-
ous, and improved torque, speed and position
control (vs. the basic ‘off/full speed’ approach),
can promote the motor to centre stage in the
application. But while adopting an MCU is
clearly an easy decision, using it to its full
potential can present significant challenges to
the less seasoned motor control system devel-
oper. New Freescale Kinetis V series MCUs
based on ARM Cortex-M cores and the
accompanying Kinetis motor suite tool pro-
vide a fresh-looking solution. Scalable MCU
families that blend potent processing power,
precision analog and cutting-edge timers, and
an intuitive, all-encompassing development
tool that makes light work of algorithm tun-
ing and trims weeks off development cycles.
The Kinetis V series is the latest product fam-
ily in rich motor control legacy from Freescale
that includes 8-, 16- and 32-bit MCUs, digi-
tal signal controllers and now ARM-based
MCUs with mass market appeal. The V series
benefits from several decades worth of motor
control R&D innovation captured in state-of-
the-art hardware building blocks that support
all motor control use cases. Like other Kinetis
series, these blocks are woven through mul-
tiple MCU families that offer scalable per-
formance, memory and feature integration
to support a broad spectrum of end product
functionality and price requirements.
The Kinetis KV1x family is the entry point
but developers should dismiss any notion of
it being a low-end MCU – it’s a very capa-
ble performer and can easily tackle BLDC
and low-dynamic control PMSM applica-
tions. Processing power comes from a 75
MHz ARM Cortex-M0+ MCU core and a
memory-mapped integer divide and square
root co-processor (MMDIVSQ). ARM cores
in the Cortex-M family implementing the
ARMv6-M ISA do not include hardware sup-
port for integer divide or square root opera-
tions, two calculations commonly executed in
motor control algorithms. With software emu-
lated divides typically requiring 100s of CPU
cycles, this can amount to a significant drain
on precious CPU bandwidth. Designers also
benefit from a bit manipulation engine (BME)
which improves cycle time and code size by
an average of 40 percent when performing
bit-oriented math operations on peripherals
such as OR, AND, XOR, bit field insert and
bit field extract. On processing power alone,
similar MCUs will struggle to keep pace with
the Kinetis KV1x family at managing the rig-
orous demands of modern control algorithms.
However, such horsepower is only useful if
it can be harnessed appropriately and that
calls for tightly coupled, high speed/reso-
lution ADCs and PWMs to facilitate quick
and accurate signal capture, processing and
response. Dual 16-bit ADCs achieve 1.2
Msps (833 ns) when configured in 12-bit
mode, adhering to the sub-1μs conversion
time threshold that most modern motor
technologies require. Single or continuous
conversion, sample time and conversion
speed are also user configurable.
The latest generation of Freescale motor con-
trol FlexTimers (FTMs) – refined over many
years in response to customer feedback – gen-
erate multi-channel, high-resolution PWM
waveforms and support dead-time insertion,
