69 / 84
for solar cells provide code-optimized
building blocks to implement a variety
of power topologies and algorithms
such as maximum power point tracking
(MPPT) and Software Phase Locked
Loops (PLL) to help design optimized
solar inverters to power equipment.
There are three basic MPPT algorithms
that can be easily tested out in a
microcontroller. The most popular
is the perturbation and observation
(P&O) algorithm, also called the
‘hill climbing method’, where the
controller moves, or perturbs, the
voltage coming from the array by a
small amount and measures power.
If the power increases, the voltage
is changed a little more in the same
direction until
A third MPPT approach is the fractional
open-circuit voltage: This algorithm
is based on the principle that the
maximum power point voltage is
always a constant fraction of the
open circuit voltage. The open circuit
voltage of the cells in the solar cell is
measured and used as an input to the
controller.
These power management algorithms
can be tested out on the Solar
Micro Inverter development kit
from Texas Instruments, which is
based on the Piccolo TMS320F28035
microcontroller and serves as a
complete grid-tied solar micro inverter.
The topology of the micro inverter
consists of an active clamp fly-back
DC/DC converter with secondary
voltage multiplier, maximum power
point tracking (MPPT), and a grid-
tied DC/AC inverter. The single Piccolo
controller handles both power stages
and the execution of the MPPT
algorithms.
Other evaluation boards, such as
the MAX17710, allow the different
topologies and algorithms to be
tested, varying the energy storage
elements and the control algorithms.
Operating at the ultralow power levels
of an energy harvesting source brings
a number of challenges to the power
systems developer. Keeping a close
eye on the lower and upper limits of
the energy source make the system
design significantly easier. Developers
can also evaluate the different control
algorithms and tweak them to provide
the most
Conclusion
efficient power conversion for the
chosen energy source, whether that is
an array of solar cells, a piezoelectric
vibration transducer, or a thermal
energy source. These can be easily
tested out, alongside the right choice
of a battery cell or a capacitor, with a
choice of evaluation boards.
Contributed By Publitek
Marketing
Communications
Figure 4: The Solar Micro Inverter development kit
from Texas Instruments allows digital libraries of
MPPT algorithms to be evaluated.
Figure 5: The MAX17710 evaluation board allows
developers to charge a protected lithium battery cell
from an energy source such as a solar cell
69 l New-Tech Magazine Europe