PRODUCTS & SERVICES
Perfomance IPM motors
As the EV industry trends toward the use of interior permanent magnet motors, specialist
solutions have been designed to overcome the challenge of their optimal control and testing
As production shifts from
traditional ICE-powered cars
to electric vehicles, manufacturers
and OEMs face many challenges.
One of these is how to test,
characterize and optimize the
approach 30,000rpm.
including induction,
e iciency, and
to properly control.
Id and Iq). In a typical SMPM motor,
the inductance seen along the
d-axis is essentially the same as the
inductance seen along the q-axis.
However, the topology of the IPM
motor creates saliency, meaning the
inductance along the d-axis is not
the same as the q-axis. Additionally,
this inductance will change
depending on load, as the iron core
of the motor rotor saturates. This
saturation tends to a ect both
d-and q-axis inductance equally,
but this is not the case in an IPM
motor. Because of this saliency,
an IPM motor is able to produce
both magnetic torque and
reluctance torque while an SMPM
motor has only magnetic torque.
To properly and optimally control
an IPM motor, the inverter must be
able to account for the varying
d-axis and q-axis inductance as
a function of both speed and torque,
and it must be able to adjust the
phase angle of its current in order
to make optimal use of both
magnetic and reluctance torque.
Most general purpose inverters
are not able to do this.
Vehicle based inverters are
purpose-built and matched to
specific IPM motors. However,
Unico o ers specialist test stand
inverters with multiple features
designed to allow them to control a
wide range of IPM motors from any
manufacturer. It o ers the ability to
178 // July 2019 // www.electrichybridvehicletechnology.com
A typical eAxle used for electric vehicle application
Unico has also built tables into
the drive that can be used to store
the mapped characteristics of an
IPM motor. Once the map data has
been entered, the Unico inverter is
able to control the IPM motor like
any other motor, regulating torque,
speed, or position as required by the
specific application. The inverter will
be able to take advantage of both
magnetic and reluctance torque and
produce the optimal torque per amp.
It has automated setup routines that
can be used to characterize an
unknown IPM motor and generate
the map data.
Aside from the challenges
inherent in controlling IPM motors,
speed can be a big challenge when
it comes to testing EV motors. As
speed increases, so too does the
electrical frequency of the motors.
Modern inverters use transistors
to create a PWM voltage and
current to the motor.
In order to produce the sinusoidal
current required by the motor, the
switching frequency of the inverter
needs to be more than an order of
magnitude faster than the electrical
frequency of the motor. In the case
of a six-pole motor rotating at
30,000rpm, it will have an electrical
frequency of 1500Hz. For proper
control of such a motor, a switching
frequency of 18-24kHz would be
recommended. Unico’s inverters
have switching frequencies as high
as 30kHz, which can be fine-tuned
based on the application and the
specific motor being used.
The 2400 is
an all-digital
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pulse-widthmodulated
(PWM) inverter
electric motors used in the vehicles.
This is particularly challenging in
motorsport applications,
where motor speeds can
There are many types
of motors used in EVs,
SMPM (surface-mounted
permanent magnet), and
IPM (interior permanent
magnet), but the trend is
toward the latter. The IPM
design is attractive due to
high power density, high
mechanical robustness,
compared to the other
motor types. However,
they are more challenging
Modern inverters for
electric motors use vector
control and regulate the
motor current along two vectors
that are 90 apart (generally called
operate in direct current control,
where the inverter will follow
commands from an external
controller. These external
commands can be in the form of
either id and iq current vectors, or
current magnitude and phase angle.
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