Renewable Energy Conversion Systems Research Articles

Atomically dispersed cobalt-based species anchored on polythiophene as an efficient electrocatalyst for oxygen evolution reaction

For clean and renewable energy conversion systems, it is important to develop efficient, earth-abundant, low-cost and stable electrocatalysts for oxygen evolution reaction (OER). Herein, we prepared an atomically dispersed cobalt coordinated with oxygen and sulfur species on the conductive polymer polythiophene (PTh) via CoS bond as a stable noble-metal-free electrocatalyst for the OER. A novel cobalt-based catalytic site structure, CoxOyS4, is successfully fabricated. The resulting electrocatalyst, Co@PTh, exhibits an excellent OER performance with overpotential of 338 mV versus reversible hydrogen electrode (RHE) at a current density of 10 mA cm−2 and the Tafel slope of 52 mV dec−1 in alkaline electrolyte. This performance is better than that of the commercial RuO2 and even comparable with the state-of-the-art catalyst IrO2. Our work suggests that the atomically dispersed cobalt-based species decorated PTh may be a good alternative for precious-metal-based catalysts.

A Review on Ceo2‐Based Electrocatalyst and Photocatalyst in Energy Conversion

The activation and conversion of small molecules (H2, O2, H2O, CO2, N2, CH3OH, and C2H5OH) in energy‐related systems has attracted researchers’ attentions around the world. The conversion of these molecules plays a key role in renewable energy storage and conversion systems, and for that, the electrocatalysis and photocatalysis processes are considered as clean and efficient strategies. Numerous materials are designed to promote the conversion process to satisfy the different requirements for efficiency and selectivity. Due to the flexible switching between Ce3+ and Ce4+ with rich oxygen defects, CeO2‐based materials display excellent performance in all the related reaction processes. Herein, the CeO2‐based electro(photo)catalysts according to different reactions are summarized. Specifically, the influence of material compositions, morphologies, and structures on catalytic performance is discussed, and the significant role of CeO2 is emphasized. Finally, several approaches are advocated to promote the development of CeO2‐based electro(photo)catalysis and accelerate their industrial application.

Development of generalised and optimum structures of a multilevel inverter using switched capacitor technique for renewable energy conversion systems

A novel multilevel inverter topology is presented in this paper. The presented topology is based on the concept of switched capacitor technique. The important features of proposed topology are that it uses symmetrical DC power sources to generate different output voltage levels, it has self-voltage balancing capability to balance the capacitor voltages and it can boost the input voltages to desire voltage levels. Further, optimal structure of proposed topology is developed from general structure of presented topology. The proposed topology requires less components such as switching devices, DC power supplies, capacitors, diodes to generate specific number of output voltage levels in comparison with other topologies. Phase disposition pulse width modulation (PDPWM) scheme is employed for switching the proposed inverter. Extensive simulation and experimental studies of 17-level proposed inverter structure prove its merits and effectiveness. The proposed topology can be applied in renewable energy conversion systems such as photovoltaic systems to generate boosted multilevel output voltage from low voltage DC renewable sources.

High-performance electrocatalyst based on polyazine derived mesoporous nitrogen-doped carbon for oxygen reduction reaction.

Nitrogen-doped porous carbon materials have high potential in metal-free electrocatalysts, which is essential for several renewable energy conversion systems. Herein, we report a convenient and environment-friendly method to fabricate a nitrogen doped mesoporous carbon (NMC) using a nonionic surfactant of Pluronic F127 micelles as the template and a Schiff-base polymer (polyazine) as the precursor. The synthesized NMCs were of spheric morphology and mesoporous structures with surface area up to 1174 m2 g−1 and high level of nitrogen (2.9–19 at%) and oxygen (4.9–7.4 at%) simultaneously doped. The electrochemical data of NMCs were analyzed in the context of the BET and XPS information. A correlation between ORR activity and the pyridinic-N was found. The NMC-700 demonstrate the highest electrocatalytic activity for ORR among the studied materials, which can be ascribed to the reasonable surface area and mesoporous structure, as well as the most abundant touchable pyridinic-N, thus providing more effective active sites for the oxygen reduction. In comparsion to the control sample, the NMC-700 provides the ORR electrocatalytic activity approximate to that of commercial Pt/C catalyst with a highly long-term stability.

Review on Single-DC-Source Multilevel Inverters: Topologies, Challenges, Industrial Applications, and Recommendations

Having a reduced number of switches and isolated DC sources yet generating a higher number of voltage levels has been always the challenge when selecting the appropriate Multilevel Inverter (MLI) topology. Nowadays, Single-DC-Source Multilevel Inverter (SDCS-MLI) topologies are being considered as more suitable for many power system applications such as Renewable Energy (RE) conversion systems and electrified transportations compared to the Multiple-DC-Source MLIs (MDCS-MLIs). Moreover, increasing the power rating and minimizing the switching frequency while maintaining reasonable power quality using a SDCS-MLI is an important requirement and a persistent challenge for the industry. Thus, this paper presents a general review on the available SDCS-MLI topologies and future trends. Existing solutions are discussed and analyzed based on their topologies, number of output voltage levels, number of active/passive components, advantages/limitations, maturity, and industrial applications. Furthermore, recommendations for future research and development are suggested in this paper.

Development of generalised and optimum structures of a multilevel inverter using switched capacitor technique for renewable energy conversion systems

Development of generalised and optimum structures of a multilevel inverter using switched capacitor technique for renewable energy conversion systems

Interface engineering triggered by carbon nanotube-supported multiple sulfides for boosting oxygen evolution.

Finding an efficient, stable and cheap oxygen evolution reaction (OER) catalyst is very important for renewable energy conversion systems. There are relatively few related research reports due to the thermodynamic instability of transition metal sulfides (TMSs) at the oxidation potential and these are usually focused on single metal sulfides or bimetal sulfides. Metal sulfide mixture systems are rarely studied. The fabrication of a TMS/TMS interface is a feasible method to improve the kinetics of the OER. Here, we constructed TMS hybrid electrocatalysts with multiple phase interfaces for the oxygen evolution reaction, named S-CoFe/CNTs. The results show that the S-CoFe/CNT catalyst exhibits a low overpotential of 258 mV to achieve a current density of 10 mA cm-2, and has high activity in the OER process. Meanwhile, the catalyst also shows a low Tafel slope (69 mV dec-1) and good stability. This can be attributed to the synergistic catalysis of the multiphase interface in the catalyst and the rapid electron transfer pathway brought by CNTs. The new strategy for the synthesis of catalysts containing the TMS/TMS interface provides a new idea and method for the development of efficient and practical water splitting catalysts.

ANALIZA NUMERICA 3D A UNEI TURBINE EOLIENE DE PUTERE MICA CU AX ORIZONTAL IN VEDEREA IMPLEMENTARII IN FERMELE AGRICOLE

The purpose of this paper is the numerical study of the effects of the fluid interaction with the blades of the working bodies of the renewable energy conversion systems. The paper presents the results of numerical research regarding the influence of the blade shape (straight), the number of blades (2, 3, 4) or the wind speed in the area on the output power of the small capacity wind turbines. The validation of the simulation data was performed by comparison with the experimental data obtained on a Windtrainer Junior laboratory wind energy system. Computed power coefficients are in good agreement with the experimental results. Increasing the efficiency of energy conversion for small wind turbines for their implementation in green farms represents a significant step in the concept of sustainable rural development.

Manipulating Interfaces of Electrocatalysts Down to Atomic Scales: Fundamentals, Strategies, and Electrocatalytic Applications.

Raising electrocatalysis by rationally devising catalysts plays a core role in almost all renewable energy conversion and storage systems. The principal catalytic properties can be controlled and improved well by manipulation of interfaces, ascribed to the interactions among different components/players at the interfaces. In particular, manipulating interfaces down to atomic scales is becoming increasingly attractive, not only because those atoms at around the interface are the key players during electrocatalysis, but also, understandings on the atomic level electrocatalysis allow one to gain deep insights into the reaction mechanism. With the feature down-sizing to atomic scales, there is a timely need to redefine the interfaces, as some of them have gone beyond the conventionally perceived interfacial concept. In this overview, the key active players participating in the interfacial manipulation of electrocatalysts are examined, from a new angle of "atomic interface," including those individual atoms, defects, and their interactions, together with the essential characterization techniques for them. The specific approaches and pathways to engineer better atomic interfaces are investigated, and thus to enable the unique electrocatalysis for targeted applications. Looking beyond recent progress, the challenges and prospects of the atomic level interfacial engineering are also briefly visited.

An Efficient Asymmetric Direct Current (DC) Source Configured Switched Capacitor Multi-level Inverter

This paper is dealing about Switched Capacitor Multi-Level Inverter (SCMLI) circuit which is controlled by triangular multicarrier Sinewave Pulse Width Modulation (SPWM) technique. The proposed SCMLI is powered from asymmetric DC source configuration to obtain multi-level output voltage by applying switching pulse to the main circuit from control circuit for switching operation. Fourteen switches and four capacitors are employing to do the proposed inversion operation in an effective way. Switching capacitors can perform boost operation to enhance voltage from the source level to the required level. Input DC from the asymmetric sources is converted to AC voltage for the application of consumers. This proposed conversion system is applicable for mainly in industrial and renewable energy-based energy conversion system because it can carry high output voltages. This proposed method gives about more efficiency. Also reduces switching losses in lower value, low conduction losses and capacitor ripple losses. The simulation model is analyzed in MATLAB/SIMULINK platform and the same validated in hardware results. The developed SCMLI structure is witness over other topologies for the power inversion process in the multi-level.

Wind turbine doubly-fed induction generator defects diagnosis using rotor currents lissajous curves

Nowadays, inverters are power electronics devices used in the renewable energy conversion systems. Therefore, the continuity of service of power converter has been a major concern. In this paper, a technique for diagnosing multiple open switch faults in three phase voltage inverters feeding Doubly Fed Induction Generator DFIG is presented. It is based on the so-called the Lissajous curves of DFIG rotor currents. For this purpose, the modeling of a non-defected wind conversion system based on mathematic model created in Matlab Simulink is firstly presented, after that, an indirect stator field vector-oriented control is applied to obtain the wind system performance. Finally, rotor currents Lissajous curves are analyzed in case of a non-defected and defected inverter. Simulation results show the effectiveness of the proposed method

Bioengineering technologies used for the development and equipment of complex installations to obtain energy from three renewable sources. Complex installations for coastal areas

Considering that the production of energy from fossil sources causes environmental pollution, increasing health hazards or climate change, the research for new alternative energy sources and the development of high-performance renewable energy conversion systems are a basic concern nowadays. Thus, the development and the use of renewable energy sources can increase diversity in energy supply markets, help to ensure long-term sustainable energy resources, to reduce local and global air emissions, and provide commercial attractive options to meet the specific needs of energy services. This paper aims to improve the efficiency of a patented complex installation which was developed vertically to ensure high-energy efficiency in relation to the occupied area, that integrates three renewable energy sources (wind, solar and hydro), by applying bioengineering solutions. Improvements to the original installation consisted in modifying the initial characteristics of the off-shore system (number of slots, deflectors angle, width of slots and width of deflectors), modification of aerial module blades according to the bioengineering model of the thistle seed (Carduus nutans), and modification of the submerged module paddies according to the bioengineering model of a fish species swimmers. Following the tests performed on the modified complex installation, a major improvement of the energy efficiency compared to the (initial) control installation was observed.

Intermetallic Co-Pt/C Nanoparticles Synthesized Via Sonochemical Method As Enhanced Electrocatalysts for Cathode of PEMFC

For fuel cell stack of 80 kW, platinum for electrocatalyst requires around 10 g per fuel cell electric vehicle (FCEV). A large-scale synthesis method for the low-platinum catalyst is necessary for this field to reduce man-power. Ultrasound-assisted polyol synthesis (UPS) is a method for the preparation of small and uniform size transition metal core-platinum shell nanoparticles evenly distributed on the support. Platinum(Ⅱ) acetylacetonate, Cobalt(Ⅱ) acetylacetonate, and carbon support were dispersed in ethylene glycol which is reducing agent and irradiated by ultrasound for 3 h to reduce the precursor to metal nanoparticles, followed by washing and drying to obtain a powder. The characterization was observed by solution color visualization, X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), inductively coupled plasma atomic emission spectroscopy (ICP-AES) and electrocatalytic performance. Also, the synthesized samples were calcined at various temperatures to cause the atomic rearrangement to the most stable arrangement, and atomic accumulation of boundary between each atom and compression of platinum lattice that affects activity or durability of electrocatalyst has changed. Synthesized sample with optimized synthesis and treatment condition shows improved electrochemically active surface area (ECSA) and Oxygen reduction reaction (ORR) catalytic activity in the half-cell test and durable catalytic activity in the performance evaluation of membrane-electrode assembly (MEA) compared to existing Platinum catalyst. As renewable energy conversion and storage system is one of the main challenges, FCEV is developed to solve pollution from CO2 emission and oil depletion issues. Our low-platinum nanoparticle with uniform distribution synthesized using a sonochemical method will replace precious metal catalysts used in fuel cells instead of platinum catalysts.

Synthesis of MgNiO2/CoNC-Based Ternary Metallic Dual-Active Interfacial Porous Hollow Nanocages as Efficient Oxygen Reduction Reaction and Oxygen Evolution Reaction Bi-Functional Electrocatalysts

Combining the catalytic activities of the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) into one electrocatalyst is of great significance in simultaneously prompting the charge-discharge cycles of various renewable energy storage and conversion systems such as metal-air batteries. Herein we report a ternary metallic based MgNiO2/CoNC porous hollow nanocage composite, which assembled with intimate contacted MgNiO2 and Co species to form the ultrathin nanocage shells and serve as the ORR and OER active components respectively to reveal a highly bi-functional catalytic performance. The possible synergy of each seamlessly connected metallic sites renders the hybrid material with excellent ORR and OER activities, which outperform than the corresponding benchmarks. Particularly, we speculate such efficient catalytic activity might arise from the synergistic chemical coupling effects within MgNiO2/CoNC and therefore, these results reveals promising prospects in developing multi-metallic composites toward efficient electrochemical energy devices.

Oscillation Damping for Wind Energy Conversion System with Doubly Fed Induction Generator Association with Synchronous Generator

The main purpose of this paper is to enhance the operation of renewable wind energy conversion (WEC) systems connected to power systems. To achieve this, we consider a linear quadratic Gaussian (LQG) control approach for regulating the effects of a WEC system with doubly fed induction generator (DFIG) on the synchronous generator (SG) rotor speed of the interconnected power system. First, we present the mathematical formulation of the interconnected power system comprises a single synchronous generator and a wind turbine with DFIG connected to an infinite bus bar system through a transmission line. We consider that the system is operated under various loading conditions and parameters variation. Second, a frequency damping oscillation observer is designed via Kalman filtering together with an optimal linear quadratic regulator to mitigate the impacts of the WEC system on the SG rotor speed. The performance of the developed interconnected power system is simulated using a MATLAB/SIMULINK environment to verify the effectiveness of the developed controller. In comparison with previously reported results, the proposed approach can stabilize the interconnected power system within 1.28 s compared to 1.3 s without the DFIG.

Ultrafine Ru nanoparticles confined in 3D nitrogen-doped porous carbon nanosheet networks for alkali-acid Zn-H2 hybrid battery

The rational design of a highly active, stable and Pt-free electrocatalyst for hydrogen evolution reaction (HER) is critical to the development of renewable energy conversion systems but extremely challenging. Herein, a facile top-down strategy is presented to synthesize ultrafine Ru nanoparticles confined in three-dimensional (3D) porous nitrogen-doped carbon nanosheets (Ru/3DNCN). Compared with the state-of-the-art Pt/C catalyst, the Ru/3DNCN exhibits significantly boosted HER activity and stability over a wide pH range, which only requires the overpotential as low as 37 mV, 66 mV, and 17 mV to achieve a current density of 10 mA cm−2 in 0.5 M H2SO4, 1.0 M PBS, and 1.0 M KOH, respectively. Moreover, an alkali-acid Zn-H2 battery is assembled by using the Ru/3DNCN as acid cathode and Zn plate as alkaline anode. Such hybrid battery can fulfill simultaneously hydrogen evolution and electricity generation, thanks to harvesting energy from both neutralization and Zn oxidation.

CSF-PC based grid tied improved hybrid three quasi Z source converter

Purpose A new control method is proposed for grid integration of improved hybrid three quasi z source converter (IHTQZSC). The proposed controller provides a constant switching frequency with an improved dynamic response with fewer computations. The proposed constant switching frequency predictive controller (CSF-PC) does not need weighting factors and reduces the complexity of the control circuit. Design/methodology/approach A single PI controller is intended to control voltage across dc-link by generating the necessary shoot-through duty ratio. The predictive controller produces the modulating signals required to inject the desired grid current. The performance of the proposed controller is validated with MATLAB/Simulink software. Findings The discrete-time instantaneous model on the grid side in the proposed controller influences the inductor current with minimum ripples. Dynamic response and computational complexity of the converter with the PI controller, finite set model predictive controller (FS-MPC) and the proposed controller are discussed. Practical implications The converter belongs to impedance source converters (ISC) family, delivers higher voltage gain in a single-stage power conversion process, extract the energy from the intermittent nature of renewable energy conversion systems. Implementing CSF-PC for ISC is simple, as it has a single PI controller. Originality/value Grid integration of high voltage gain IHTQZSC is accomplished with PI, FS-MPC and CSF-PC. Though the FS-MPC exhibits superior dynamic response under input voltage disturbance and grid current variation, total harmonic distortion (THD) in the grid current is high. CSF-PC provides better THD with a good dynamic response with reduced inductor current ripples.

Earth-abundant coal-derived carbon nanotube/carbon composites as efficient bifunctional oxygen electrocatalysts for rechargeable zinc-air batteries

The exploration of active and robust electrocatalysts for both the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is the bottleneck to realize the commercialization of rechargeable metal-air batteries and regenerative fuel cells. Here we report facile synthesis of three-dimensional (3D) carbon nanotube (CNT)/carbon composites using earth-abundant coal as the carbon source, hydrogen reductant and heteroatom dopant to grow CNTs. The prepared composite featuring 3D structural merits and multiple active sites can efficiently catalyze both ORR and OER, affording high activity, fast kinetics, and long-term stability. With the additional incorporation of manganese, the developed catalyst afforded a potential difference of 0.80 V between ORR at the half wave potential and OER at a current density of 10 mA cm−2. The optimized sample has presented excellent OER performance within a constructed solar-powered water splitting system with continuously generating oxygen bubbles at anode. Notably, it can be further used as a durable air-electrode catalyst in constructed Zn-air battery, delivering an initial discharge/charge voltage gap of 0.73 V, a remained voltaic efficiency of 61.2% after 160 cycles and capability to power LED light for at least 80 h. This study provides an efficient approach for converting traditional energy resource i.e. coal to value-added alternative oxygen electrocatalysts in renewable energy conversion systems.

Three-Port High Step-Up and High Step-Down DC-DC Converter With Zero Input Current Ripple

In this article, a nonisolated three-port dc-dc converter with high voltage conversion ratio is proposed. In the proposed converter, by changing the place of input voltage source between each of the three ports, three different single-input two-output operation modes are achieved. The input current ripple of the proposed converter is eliminated at the low voltage side for the whole range of duty cycles. The voltage conversion ratios of the proposed converter can be increased by increasing the turns ratio of second winding of coupled inductors. Moreover, the proposed converter has achieved proper output voltage regulations for all output ports, simultaneously. The proposed converter can be utilized in the renewable energy conversion systems such as in photovoltaic and fuel cells. In this article, the voltage conversion ratios of the output ports, the voltage stress on switches, the average currents of switches and inductors, and the required condition for cancelling input current ripple at low voltage side are calculated theoretically. The theoretical results are verified and experimental results for 24 V input voltage and 304 V, 240 V output voltages with 400 W power are extracted for two different operation modes.

Surface engineered NiO–Co3O4 nanostructures as high-performance electrocatalysts for oxygen reduction reaction

The development of low-cost and high-performance oxygen reduction reaction (ORR) catalysts is important for renewable energy storage and conversion systems, such as fuel cell. Herein, we report a simple and facile surface engineering strategy for nickel and cobalt based (NiO–Co3O4) hybrid as efficient and robust ORR electrocatalyst. The surface nanostructure of NiO–Co3O4 nanohybrids can be easily tuned by controlling the precursor amounts of nickel and cobalt during a wet-chemical synthesis. With an optimal composition, an intriguing surface structure consisted of one dimensional (1D) nanorod with two dimensional (2D) nanosheet can be obtained for NiO–Co3O4 nanohybrids, which significantly boosts ORR electrocatalytic activity as well as stability. A facile charge or mass transfer within 1D and 2D open surface nanostructures is mainly responsible for an excellent catalytic performance of NiO–Co3O4 nanohybrids.