Transcript National Instruments Visit

CUER Electrical System
MPPTs
Solar Cell characteristics
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Photovoltaic Cells have a non-linear IV curve, like the one shown below
The curve shifts depending upon environmental conditions, eg: temperature,
incident light intensity.
The PV curve has a characteristic “Maximum power point (MPP)”.
P
MPP
V
Maximum Power Point Trackers
• Endeavour’s solar array is split into 4 discrete “modules”, each with an
output of roughly 40V. The battery system is over 100V, so the maximum
power point tracker (MPPT) acts as a boost converter to step up the
voltage.
MPPT
Solar Module
~40V
High voltage
battery
140V
Maximum Power Point Trackers
• But an MPPT must do more than simply boost the output of the solar
module.
• The module should always be operated at the MPP.
• The MPP varies depending on environmental conditions, so it must be
actively tracked
Maximum Power Point Trackers
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One common method of maximum power point tracking is “perturb and observe”.
The MPPT periodically perturbs the operating point, observes the output, and
decides which direction to perturb the voltage in next time.
This way the tracker is constantly hunting for the maximum power using a closedloop algorithm.
CUER’s MPPTs
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CUER uses Drivetek MPPTs. These originate from a Biel University project, and are
designed specifically for solar car use.
Efficiency is excellent, typically >95% under good sunlight (see below)
CUER’s MPPTs
• The switching circuit is a boost converter with “Active Snubber
Circuit”. This works to practically eliminate switching losses by
only switching the MOSFETs at zero current/zero voltage