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Egyptian researchers have developed a multi-string photovoltaic system with a converter control strategy, achieving an efficiency of 99.81% with a direct duty cycle for maximum power point tracking (MPPT).
Researchers from Egypts South Valley University have developed a novel control strategy to address partial shading in photovoltaic systems. The new approach uses a multi-string PV system with a converter control strategy that uses a direct duty cycle to track the maximum power point (MPP) under shade.
“This study proposes a reconfiguration of the PV system to suppress the negative impact of partial shading on the performance of the PV system by dividing it into multiple parallel strings,” the scientists explain. “In this work, the proposed system consists of four chains, and each chain comprises three subchains in parallel.”
The proposed multiple maximum power point tracking (MMPPT) method consists of connecting each string to a DC-DC converter, optimizing the energy extraction from the individual strings of photovoltaic solar panels. This differs from the proven maximum power point tracking (SMPPT) arrangement in a PV system, where a single converter is connected to parallel strings of solar panels.
The MMPPT approach uses a direct duty cycle control strategy to find the desired converter duty cycles. Then, through direct duty cycle control (DDCC), it adapts the duty cycle of the DC-DC converter to the calculated results, regulating the power produced.
To calculate the desired duty cycle, the existing sensors in the photovoltaic system are used to estimate the radiation, derived from changes in the current and voltage of the photovoltaic cells.
“The proposed technique minimizes the total cost of the system by reducing the number of sensors required through a radiation estimation strategy,” the researchers explain. “The DDCC technique increases overall system efficiency through the elimination of steady-state oscillations, hardware simplification, and ease of implementation. Additionally, the DDCC has a fast tracking speed for global maximum power point tracking (GMPPT) extraction under partial shading conditions.”
The researchers presented the results of the comparison between the MMPPT system and the SMPPT in “ Investigation of single and multiple MPPT structures of solar PV-system under partial shading conditions considering direct duty-cycle controller ” solar photovoltaic in partial shade conditions considering a direct duty cycle controller), recently published in Scientific Reports . The systems were simulated with MATLAB/SIMULINK software under three shading conditions.
The four photovoltaic strings were subjected to a uniform irradiance of 1,000 W/m2 in the first shading pattern. In the second pattern, however, the first two chains had a constant irradiation profile of 1,000 W/m2, while the other two had a uniform irradiation profile of 1,000 W/m2 for half a second, and then dropped to 500 W /m2 for another half second.
In the third pattern, the first two chains were again under a uniform irradiance profile of 1,000 W/m2, while the remaining two started with 1,000 W/m2 for 0.3 seconds, changed to 500 W/m2 for another 0. .3 seconds and dropped to 250 W/m2 for 0.4 seconds.
“Under these conditions, the average efficiency of the SMPPT system is 98.98%, while the MMPPT system reaches an efficiency of 99.81%. These results validate the proposed approach,” the researchers conclude. “The MMPPT setup uses a real radiation data set from Benban, a town in southern Egypt. “The results demonstrate that the proposed control system improves overall system effectiveness while reducing installation costs.” |
