New-Tech Magazine Europe | Dec 2015 Digital edition

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

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.

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