Tech Briefs Magazine - March 2021 - ST-15

Practical Design Solutions to Improve Contactless Current Sensing in
Electric Vehicles
he automotive industry is moving beyond the small electric commuter car
and is now offering a variety of models to
meet an increasing range of needs, from
family transport to sports and recreation.
These vehicles are typically larger and, as
a result, heavier than earlier EV models.
These require larger electric motors
which, in turn, consume more power.
Whether the vehicle is full-electric, plugin hybrid, or mild hybrid, the voltage and
current levels involved are considerable.
In most cases, the batteries must supply
many hundreds of volts to achieve the
driving experience necessary to take electric vehicles to the next level of performance. Because of this, closely monitoring
the volume of current flowing to the
motor is becoming a critically important
function for automotive manufacturers.

The Challenge of Accurate Current
Measurements in EV Environments
The shift away from internal combustion toward electric drivetrains raises many
new challenges for engineers from multiple disciplines. For system engineers, the
challenge is balancing the power-to-weight
ratio, while electrical and electronic engineers need to focus on power management. Mor-e power means faster and more
responsive vehicles - but using too much
power, too quickly, leads to rapidly depleted power sources and reduced range. It is
therefore critical that every part of the
design must be optimized.
The key to power management is accurate measurement - the current sensor
is the EV equivalent to the fuel flow sensor in a conventional vehicle. Current
measurement can easily be achieved
using a shunt, or low-value resistor. The
higher the current, the larger the shunt,
so measuring currents of the magnitude
required for powerful electric motors
would demand physically large shunts
that are heavy and expensive.
Contactless current sensing provides an
attractive alternative to the shunt resistor.
Based on the magneto-resistive, or Hall
effect, it takes advantage of the electromagnetic fields generated as current passes through a conductor. Because of their
smaller size, non-intrusive nature, and
inherent galvanic isolation, contactless
current sensing is rapidly becoming the
preferred current measurement approach
for electric vehicle manufacturers.

Figure 1a. Core-based.

Figure 1b. U-shaped.

Figure 1c. Symmetrical.

Figure 1. The three main types of contactless current sensors used in automotive applications.
(Images courtesy of TDK-Micronas)

Contactless Sensor Types for
Automotive Applications
The size of the magnetic field surrounding the conductor is proportional to the current flowing, but even with
large currents, the field strength is still

Sensor Technology, March 2021

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relatively small. Although Hall sensing
elements can be very sensitive, this
sensitivity also makes them prone to
reading stray or background electromagnetic fields. Fortunately, this distortion can be reduced through shield15

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Tech Briefs Magazine - March 2021

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