Maximum power point tracking | EPFL Graph Search

Maximum power point tracking (MPPT), or sometimes just power point tracking (PPT), is a technique used with variable power sources to maximize energy extraction as conditions vary. The technique is most commonly used with photovoltaic (PV) solar systems, but can also be used with wind turbines, optical power transmission and thermophotovoltaics. PV solar systems have varying relationships to inverter systems, external grids, battery banks, and other electrical loads. The central problem addressed by MPPT is that the efficiency of power transfer from the solar cell depends on the amount of available sunlight, shading, solar panel temperature and the load's electrical characteristics. As these conditions vary, the load characteristic (impedance) that gives the highest power transfer changes. The system is optimized when the load characteristic changes to keep power transfer at highest efficiency. This optimal load characteristic is called the maximum power point (MPP). MPPT is the proc

27.2 An Adiabatic Sense and Set Rectifier for Improved Maximum-Power-Point Tracking in Piezoelectric Harvesting with 541% Energy Extraction Gain

Yimai Peng

Piezoelectric energy harvesters (PEHs) convert mechanical energy from vibrations into electrical energy. They have become popular in energy-autonomous IoT systems. However, the total energy extracted by a PEH is highly sensitive to matching between the PEH impedance and the energy extraction circuit. Prior solutions include the use of a full-bridge rectifier (FBR) and a so-called synchronous electric-charge extraction (SECE) [1], and are suitable for non-periodic vibrations. However, their extraction efficiency is low since the large internal capacitance C p (usually 10's of nF) of the PEH (Fig. 27.2.1) prevents the output voltage from reaching its maximum power point (MPP) under a typical sinusoidal and transient excitation (V MPP = 1/2·I p R p ). A recently proposed technique [2,3,4], called bias-flip, achieves a higher extraction efficiency by forcing a predetermined constant voltage at the PEH output, V p , which is then flipped every half-period of the assumed sinusoidal excitation (Fig. 27.2.1, top left). To flip V p , the energy in capacitor C p is extracted using either a large external inductor [2,3] or capacitor arrays [4]. It is then restored with the opposite polarity (Fig. 27.2.1, top). However, V MPP of the PEH varies with sinusoidal current I p ; hence, the two fixed values of V p in the flip-bias technique either over or underestimate V MPP for much of the oscillation cycle (pattern filled regions in Fig. 27.2.1, top right). In addition, none of the prior approaches compensate for V MPP -waveform amplitude changes, due to input intensity variations or decaying oscillations after an impulse, further degrading efficiency.

IEEE2019

Composition and Interface Engineering of High Performing Perovskite Solar Cells

Mousa Abdulla M E Abuhelaiqa

Perovskite solar cells have been established as a disruptive technology in the domain of photo-voltaics. Their facile, low-temperature processing and high-power conversion efficiency make them stand-out among other mature solar technologies. The performance of perovskite solar cells is pro-foundly tied to an interplay of material properties of singular thin films that are assembled to form the photovoltaic device stack. An understanding of optoelectronic, morphological, and other key charac-teristics of each layer and its interfaces is instrumental in advancing the science of perovskite solar cells. Since their inception after just over a decade, much work on perovskite solar cell has been stag-nant to bring the technology to the market. The long-term stability remains foremostly the main hin-drance to facilitating technology transfer. Therefore, the work presented in this thesis explores multi-ple interface and compositional approaches to promote stability and other photovoltaic parameters of perovskite solar cells.In the second chapter of the thesis, a light-soaking exploration was done on perovskite sam-ples that utilize single (TiO2 and SnO2) and bilayered (TiO2/SnO2) electron transporting materials. The work aims to expand consensus on the optoelectronic and morphological features of light-soaked samples and link them with long-term stability. Upon preliminary testing, maximum power point tracking on each sample reveals efficiency preservation of SnO2 and TiO2/SnO2 samples over the course of 1000 hours while prominent degradation was revealed for the TiO2 sample. On a secondary investigation, light-soaking characterizations were performed where fresh and light-soaked samples were characterized to obtain photoluminescence, microscopic, and crystallographic features. The work reveals the added benefit of employing TiO2/SnO2 transporting bilayers to improve both the stability and power conversion efficiency of a perovskite solar cell. Building on an effort to understand TiO2/SnO2 bilayer behaviors, the third chapter investigates the role of halide passivating elements in SnO2 on the performance of perovskite solar cells. The study utilizes three metalorganic precursors based on acetylacetone complexes with chloride and bromide groups to fabricate SnO2 layers at different annealing temperatures. Upon thermal and elemental in-vestigations, the study clearly links the presence of amorphous halide elements in SnO2 to the power conversion efficiency of perovskite solar cells. More-in-depth, the optimal SnO2 annealing tempera-ture for bromide containing samples 250 ï°C compared with 220 ï°C for chloride containing samples. The higher temperature tolerance tendency was correlated to bromideâs lower sublimation sensitivity. Overall, the study highlights the importance of amorphous passivating elements in SnO2 for high per-forming planar perovskite solar cells. Finally, the fourth chapter involves a novel cation mixing approach for 2D perovskites at the interface of the 3D perovskite and the hole transporting layer. Alkyl ammonium halides have been widely used to form light-stable 2D perovskite films upon interaction with excess PbI2. In this study, different alkyl chain cations (propylammonium iodide and octylammonium iodide) were mixed in one solution to form a novel 2D perovskite crystal lattice. Photoluminescence and x-ray diffraction spec-troscopy investigations reveal a unique crystal lattice and a uniform quasi-2

EPFL2022

An Efficient Piezoelectric Energy Harvesting Interface Circuit Using a Sense-and-Set Rectifier

Yimai Peng

Piezoelectric energy harvesters (PEHs) are widely deployed in many self-sustaining systems, and proper rectifier circuits can significantly improve the energy conversion efficiency and, thus, increase the harvested energy. Various active rectifiers have been proposed in the past decade, such as synchronized switch harvesting on inductor (SSHI) and synchronous electric charge extraction (SECE). This article presents a sense-andset (SaS) rectifier that achieves maximum-power-point-tracking (MPPT) of PEHs and maintains optimal energy extraction for different input excitation levels and output voltages. The proposed circuit is fabricated in the 0.18-μm CMOS process with a 0.47-mm 2 core area, a 230-nW active power, and a 7-nW leakage power. Measured with a commercial PEH device (Mide PPA-1022) at 85and 60-Hz vibration frequency, the proposed circuit shows 512% and 541% power extraction improvement [figure of merit (FoM)] compared with an ideal full-bridge rectifier (FBR) for ON-resonance and OFF-resonance vibrations, respectively, while maintaining high efficiency across different input levels and PEH parameters.

IEEE2019

Composition and Interface Engineering of High Performing Perovskite Solar Cells

Mousa Abdulla M E Abuhelaiqa

EPFL2022