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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
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