Fuzzy logic MPPT to improve PV system performance


Researchers from Comsats University Islamabad in Pakistan and China’s Hohai University have demonstrated a new maximum power point tracking (MTTP) technique that's based on a fuzzy logic algorithm and is said to provide faster results than conventional methods such as incremental conduction.

“It tracks the maximum power in 0.03 seconds as shown in simulation results,” the scientists said.

Fuzzy logic is known to provide clear solutions to complex problems, as it reflects human thinking and decision-making. While conventional logic works on precise inputs and produces definite outputs such as “true” or “false” and “yes” or “no”, fuzzy logic tends to include the range of possibilities between “yes” or “no” – like “certainly yes” or “possibly not,” for example. It is an approach to computing that is based on “degrees of truth” rather than the usual “true or false” dichotomy.

The researchers presented their findings in “Design and analysis of robust fuzzy logic maximum power point tracking based isolated photovoltaic energy system,” which was recently published in Engineering Reports. The proposed technique was simulated through MATLAB-based Simulink software. The scientists used a 250 W Canadian Solar panel with an open circuit voltage of 59.9 V and a short circuit current of 5.49 A, at standard conditions of 25 C and 1,000 W/m2 irradiance.

They also used a fuzzy logic controller (FLC) in a simulated offgrid PV system and boosted it through a push‐pull DC‐DC converter, which consists of a transformer to provide the isolation and a proper boost in voltage.

“The boosted DC energy is inverted into AC using a sine wave inverter and LCL filter,” the scientists said. The LCL filter is commonly used to attenuate the switching frequency harmonics produced by grid-connected inverters.

“The proposed fuzzy logic voltage source inverter is capable of producing different types of output such as square wave, modified square wave, and pure sine wave depending on the requirements of application,” the scientists explained.

The transformer boosts the DC output voltage of the PV system to 330 V DC, which is in turn converted into root mean square (RMS) 220 V AC through the fuzzy logic power inverter and an H‐Bridge inverter. The H-bridge inverter is an inverter topology that enables voltage to be applied across a load in either direction. “This inverter is designed at 10 kHz switching frequency and the fuzzy logic controller is used to remove the lower order harmonics,” the scientists said.

The proposed converter technology has a significant impact on PV system efficiency, while also providing isolation between the load and the PV array, the scientists concluded. The fuzzy logic MPPT algorithm at the core of their technique can help them to sense the voltage and current at each time step and then calculate the power.

“This power is compared with the previous instant power for obtaining the change in power as well as the current is also compared with the previous current for obtaining the change in current,” the scientists wrote. “This change in power is divided by the change in current for obtaining the error. Then this error is compared with the previous error, for obtaining the change in error.”

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