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total wind resistance is the equivalent of a
conventional car’s wing mirror. The driver must then
race as fast as possible but not so fast that the car’s
battery runs out of power when it is not in bright
sunlight.
There are four important electrical systems in a
solar race car, the array of solar panels, the battery
and its management system, the inverter (motor
drive), which converts the solar panels’ direct
current output to a three-phase alternating current
supplied to the motor, and the motor itself. The
team was aiming for better than 99% efficiency for
the electrical power conversion circuits.
“We were looking for that extra 1% efficiency to
give us an edge over other race cars.” says Rob
Kräwinkel, team electrical engineer, “When you are
already at better than 95% efficiency, eliminating
any remaining losses is really hard to do. You have
to be able to look at a detailed level at tiny
deviations in voltage or current. That means you
need a really accurate and sensitive power
measurement system.”
To achieve the accuracy and precision required,
the team chose the Yokogawa WT5000 for two
crucial tasks. Firstly, to validate the accuracy of the
‘fuel gauge’, the car’s on-board sensor measuring
the battery’s state of charge. This system measures
current flowing into the battery (from the solar
panels) and flowing out of the battery (to the
motor). By subtracting output from input, it can
calculate the residual charge in the battery. This
required extremely accurate continuous
measurement of current flows. Secondly, to
measure the power output of the motor system, gauge circuit had an offset, which were making the
including the inverter and the motor itself, at a car’s state-of-charge measurements inherently
range of power input values, to enable the team to inaccurate. By compensating for the offset, we
refine the design and incrementally improve its could confidently provide the driver with a vital
efficiency. This called for extremely accurate power extra 1 or 2 km of range from the battery at a given
analysis at a high sampling frequency. speed.”
Rob confesses, “With the WT5000, we also The modular and extensible WT5000 is the
discovered that that the current sensors in the fuel- world’s most accurate precision power analyzer

June 2020 • INDUSTRIAL TECHNOLOGY EXTRA! • p11