Micro Power Systems Research Articles

Flexural-Mode Piezoelectric Resonators: Structure, Performance, and Emerging Applications in Physical Sensing Technology, Micropower Systems, and Biomedicine.

Piezoelectric material-based devices have garnered considerable attention from scientists and engineers due to their unique physical characteristics, resulting in numerous intriguing and practical applications. Among these, flexural-mode piezoelectric resonators (FMPRs) are progressively gaining prominence due to their compact, precise, and efficient performance in diverse applications. FMPRs, resonators that utilize one- or two-dimensional piezoelectric materials as their resonant structure, vibrate in a flexural mode. The resonant properties of the resonator directly influence its performance, making in-depth research into the resonant characteristics of FMPRs practically significant for optimizing their design and enhancing their performance. With the swift advancement of micro-nano electronic technology, the application range of FMPRs continues to broaden. These resonators, representing a domain of piezoelectric material application in micro-nanoelectromechanical systems, have found extensive use in the field of physical sensing and are starting to be used in micropower systems and biomedicine. This paper reviews the structure, working principle, resonance characteristics, applications, and future prospects of FMPRs.

SECURITY OF PHOTOVOLTAIC SYSTEMS STANDARDS REVIEW

ABSTRACT: This document collects and summarizes the existing findings in the literature of regulations applicable to grid-connected and non-grid-connected photovoltaic systems at an international level. The documentary review synthesizes the content of each standard and shows the distribution of the actual regulations in Europe and America to find similarities and areas of opportunity with the aim of being a support and reference tool for those who regulate and monitor the deployment of technologies of generation of clean energy, in training courses for installers, users and anyone starting out in the photovoltaic energy business. Also, the IEC 60364 standard and NFPA 70 standard are compared, finding that the breakdown of elements is broader in NFPA 70, while the standards NEC do not cover installations photovoltaics that uses transport properties or utilities, only micropower systems with autonomous electronic equipment. In the case of off-grid photovoltaic installations the standardization focuses on promoting sustainable energies for electrification. Even though, PPP 59061A (2017) standard by TÜV SÜD covers functionality and affinity, taking the photovoltaic system as a whole, and showing the need for new standards that meet the demands of the current market. Keywords: Regulations, international standards, photovoltaic system, electrical safety, solar energy, renewable energy.

МЕТОДЫ УПРАВЛЕНИЯ И ОПТИМИЗАЦИЯ РАСПРЕДЕЛЕНИЯ ЭЛЕКТРИЧЕСКОЙ ЭНЕРГИИ В МИКРОЭНЕРГОСИСТЕМАХ

The article considers modern methods of control and optimization of electric energy distribution in micro-power systems (microgrids). The main attention is paid to various approaches, including centralized, decentralized and hierarchical control methods, as well as intelligent solutions based on artificial intelligence. The optimization methods aimed at increasing the efficiency and sustainability of micro-power systems are analyzed, taking into account the specifics of their operation and external conditions. A comparative analysis of the methods is given, their advantages and limitations in various scenarios of micro-power system operation are revealed.

Numerical identifications of T-shaped rod effect on thermal performance and exergy efficiency in methane/air combustion

To maximize the power output of micro-thermophotovoltaic systems, achieving a high and uniform wall temperature is desirable. Towards this goal, this work proposes a novel combustor with inserting a T-shaped rod and assesses the effectiveness of such a strategy in determining the thermal and exergy performances with a validated computational model. Results indicate that introducing such strategy results in a 50.4 K wall temperature elevation and a 30.5 % decrease in the temperature standard deviation at the inlet velocity of 0.6 m/s. The effectiveness of applying a T-shaped rod on wall temperature is also found to be dependent on the inlet velocity. In addition, the optimal equivalence ratio associated with the highest wall temperature is shown to be stoichiometric caused by the relatively larger volumetric thermal power density. Further analysis of the pressure loss and exergy energy is performed. While the presence of a T-shaped rod can lead to an increase in the pressure loss, these are negligible relative to the ambient pressure. Furthermore, in addition to the temperature enhancement, the T-shaped rod combustor is associated with a higher exergy and exergy efficiency, which is beneficial to improving the energy efficiency of combustion devices. This work provides valuable insight into enhancing the wall temperature and energy conversion efficiency for micro-power systems.

Experimental analysis and multi-objective optimization of flame dynamics and combustion performance in methane-fueled slit-type combustors

Achieving a high wall temperature and wide flame stability limit is of extreme significance for the maximization of power generation in hydrocarbon fuel-driven micro-thermophotovoltaic and thermoelectric devices. For this, detailed experimental investigations are conducted on variable channel height combustors, with the emphasis on analyzing the flame dynamics and thermal performance. A preliminary understanding of the multiple flame morphologies in the combustors is developed by varying the input working conditions and wall materials. The basic types of unstable flames are clarified. The pinch-off phenomenon of a weak flame in a slit combustor is observed for the first time, and the cell tends to decrease and emerge with an increase in the flow rate. The combustible range is shown to be extended with increasing the channel height, while it exhibits a non-monotonic changing trend with the combustor thermal conductivity which highlights the importance of the balance between heat transfer due to the flame-wall coupling and heat losses. Furthermore, a Kriging-NSGA-II optimization model is also developed to obtain the optimal characteristics in terms of radiation efficiency, standard deviation and volume power density. A Pareto-optimal front solution is determined to identify three distinct regions of thermal conductivities, which is crucially useful in guiding the design of practical micro-power systems based on different working requirements.

Power Control and Optimization for Power Loss Reduction Using Deep Learning in Microgrid Systems

The effective management of microgrids, which incorporate DERs such as generators and batteries, is crucial for ensuring stability and efficiency in the power system. By evenly distributing the load across modules’ capabilities, frequencies, and voltages, a network of micropower systems can be created, capable of transitioning between various states such as islanding, leaving, and reentering the grid. Synchronizing controllers play a vital role in regulating these transitional phases and maintaining system stability, and we propose a Deep Learning approach for power regulation and optimization. By monitoring voltages, phases, and frequencies on both sides of the fixed switch, these controllers employ various control strategies to stabilize the system. Effective control mechanisms are necessary for achieving a sustainable energy economy as renewable energy sources become increasingly prevalent. Our analysis emphasizes the importance of such control methods in developing a reliable and efficient micropower system network.

Effect of hetero-/homogenous combustion on energy conversion performances and flame stability of methane/air-fueled micro-combustors with heat-recirculating structure and platinum-coated

In this work, the joint effect of applying Pt catalyst and heat-recirculating structure on the flame stability and thermal performance has been numerically investigated in methane-air-fueled micro-combustors by a detailed three-dimensional computational model. Numerical results indicate that such strategies contribute to improving outer wall temperature by 14.4% and extending the blowout limit by a factor of 0.6 compared to those in the straight non-catalytic combustor. Such enhancements are due to the intensified heat transfer, thus highlighting the contributions of heterogeneous combustion chemistry and heat-recirculating effect. Homogeneous chemistry in the presence of a Pt catalyst is shown to be self-sustained over wide-ranging conditions. Meanwhile, the effectiveness of heat recirculation structure on combustion performance is more significant as compared to that of the catalytic combustion effect, as evidenced by a 4% and 17.6% improvement in the wall mean temperature and blowout limit respectively. Further analysis of the heat recirculation catalytic combustors is conducted to obtain the optimal geometry. There exists a critical flow rate corresponding to the maximum outer wall temperature and radiation energy. In general, this work demonstrates the viability of applying a Pt catalyst and heat-recirculating structure to extend the flame stability limit and energy conversion performance in micro-power systems.

Autonomous System for Energy Collection and Conversion Based on a Biofuel Cell

Functioning of a prototype of a micropower system (energy storage device) consisting of a biofuel cell (BFC) and converter–capacitor is demonstrated. The system allows conversion of a low input voltage from an unstable energy source to a standard working voltage used in radio equipment. For the series connection of two biofuel cells, the voltage is summed up and amounts to ~500 mV, and the output storage capacitor of 100 μF is charged in 13 min to a working voltage of 3.1 V upon a cold start of the converter. It is shown that energy storage substantially depends on the capacitance of the final storage unit and on the type of energy consumption. The proposed system can be used for different unstable energy sources.

Flow and transmission characteristics of the multistage hydrogen Knudsen pump in the micro-power system

The multistage hydrogen Knudsen pump based on the thermal transpiration effect has exciting application prospects for hydrogen transport in the micro-power system. The multistage hydrogen Knudsen pump with the silica microchannel is beneficial to its temperature control, which can accurately provide hydrogen transport and storage for the micro-power system. In this paper, the model of the multistage hydrogen Knudsen pump with the silica microchannel is established. The effects of the microchannel height, width and parallel number on the flow and transmission characteristics of the multistage hydrogen Knudsen pump are studied by using the method of N–S equations with the slip boundary. The temperature difference, Knudsen number, thermal transpiration effect, maximum mass flow rate, maximum pressure difference and performance curve under different microchannel parameters are analyzed in detail. The results show that the thermal transpiration effect increases with the microchannel height and decreases with the microchannel width. As the number of parallel microchannels increases, the microchannel is closer to the silicon cantilever, and the thermal transpiration effect becomes stronger. The pumping performance increases with the microchannel height, width and parallel number. The pressurization performance increases with the microchannel height and parallel number. The research results have important guiding significance for the application and design of the multistage hydrogen Knudsen pump in the micro-power system.

Micropower system optimization for the telecommunication towers based on various renewable energy sources

This study investigates the technical and cost-effective performance of options renewable energy sources to develop a green off-grid telecommunication tower to replace diesel generators in Malaysia. For this purpose, the solar, wind, pico-hydro energy, along with diesel generators, were examined to compare. In addition, the modeling of hybrid powering systems was conducted using hybrid optimization model for energy (HOMER) simulation based on techno-economic analysis to determine the optimal economically feasible system. The optimization findings showed that the hybrid high-efficiency fixed photovoltaic (PV) system with battery followed by 2 kW pico-hydropower and battery are the optimal configurations for powering off-grid telecommunication towers in Malaysia with the lowest net present cost (NPC) and cost of energy (COE). These costs of NPC and COE are more down than diesel generator costs with battery by 17.45%, 16.45%, 15.9%, and 15.5%, respectively. Furthermore, the economic evaluation of the high-efficiency solar fixed PV panels system annual cash flow compared to the diesel generator with the battery system indicated a ten-year payback period.

Flexible Bi2Te3-based thermoelectric generator with an ultra-high power density

• A flexible thermoelectric generator with newly structure design was fabricated. • The generator consists of rigid Bi 2 Te 3 legs sandwiched by two flexible substrates. • The upper substrate is diced into blocks to ensure the generator some flexibility. • A specific power density of 13.1 mW/cm 2 is achieved for the generator. • The output power of the generator remains almost unchanged after 7400 bends. Environmental energy harvesting based on flexible thermoelectric generator (f-TEG) provides an ideal micro-power source to drive the node sensors for the Internet of Things (IoT) and wearable electronics. However, the existing flexible thermoelectric devices have some disadvantages, such as low strength, large thermal resistance, complex manufacturing processes, and low reliability. Here, we report a high-performance f-TEG with a dimension of 2 × 16 × 0.6 mm 3 , encapsulating 18 pairs of thermoelectric legs with the size of 0.38 × 0.38 × 0.38 mm 3 . The flexible polyimide (PI) films with patterned electrodes act as the substrates, of which the upper one is cut into blocks to ensure the generator a minimum bending radius of 4.5 mm. The f-TEG can produce an open circuit voltage of 236 mV and output power of 4.19 mW under a temperature difference of 50 K, which remain almost unchanged even after 7400 times of bending tests. The power density reaches up to 13.1 mW/cm 2 at ΔT = 50 K, and the normalized output power density is 5.26 μW/cm 2 ·K 2 . These results are among the best performances reported for f-TEGs, which opens a new avenue for flexible micro-power system design and promotes the development of the next generation self-powered sensors and charge-free electronic devices.

Characteristics of SACI combustion in a diesel rotary engine based on combined 1D and 3D comprehensive transient simulations

Wankel rotary engines (WREs) are widely used in aviation equipment, vehicles, micropower systems, etc. Diesel WREs are well suited for military and aerospace applications due to great safety features of the diesel fuel. In this paper, the transient in-chamber flow and combustion processes of a spark-assisted compression-ignition (SACI) direct injection diesel WRE were numerically simulated. Firstly, an effective method of using two rotating vectors is proposed to calculate the crank-angle-based instantaneous position of each location on the rotor surface in the rotor housing, which defines the law of dynamic boundary changes, to realize transient simulation. Secondly, the one-dimensional (1D) simulation results were used as the initial boundary conditions of the three-dimensional (3D) simulation, which improves the accuracy of the simulation and reduces the number of computational cycles during the validation of the 3D simulation model. Thirdly, model reduction and dynamic mesh control were used in the numerical simulation. The time of one calculation cycle was reduced from 223 h to 125 h, which is a 43.95% reduction. Finally, the 1D simulation revealed that ignoring the leakage between two adjacent combustion chambers was one of the main reasons for the error between the 3D simulated in-cylinder pressure and the experimental result. Based on the simulation methodology developed in this paper, the SACI combustion characteristics of a direct-injection diesel WRE were revealed. This paper provides an efficient simulation method for optimizing the design of novel WREs.

Investigation of thermal performance and energy conversion in a novel planar micro-combustor with four-corner entrances for thermo-photovoltaic power generators

A novel planar micro-combustor with four-corner entrances is proposed by considering high and uniform outer wall temperature distribution used in micro thermo-photovoltaic generator. For this, a three-dimensional numerical model with detailed chemical mechanism, transport, and heat transfer and a thermo-photovoltaic energy conversion model are developed to examine its performance. Results show that the proposed micro-combustor has excellent wall temperature uniformity because a uniform distribution of high-temperature zones of four individual flames is formed in the combustion chamber. Thermal performance and energy efficiency of the proposed micro-combustor are better than conventional micro-combustor at a low flow rate ( m ) and large equivalence ratio ( φ ). Additionally, the implemented plate-insertion strategy effectively overcome the deterioration of combustor performance under higher m or lower φ . Proposed micro-combustor with plates insertion has the largest wall temperature and energy efficiency, no matter what φ and m are adopted. Plates extend the fluid ravel path and produce some recirculation zones, which promotes heat transfer, preferential diffusion, and flame anchoring, while its pressure loss is larger. Of all the tested cases, the system efficiency reaches a maximum of 6.39%, corresponding to 12.1 W electricity output. This work provides effective combustor design and research insights to develop high-efficiency micro-power system. • A novel micro-combustor with four entrances is proposed for micro-TPV system. • Excellent performance of wall temperature uniformity is obtained. • Inserting plates boosts thermal performance and energy conversion efficiency. • A maximum system efficiency of 6.39% is achieved with 12.1 W electric output.

Breaking the myth: Wide-bandgap semiconductors not always the best for betavoltaic batteries

Betavoltaic batteries are appealing power sources for micro-power systems and applications in extreme environments due to their superlong lifetimes, high energy densities, and impressive environmental adaptability. However, little work has been done on building a comprehensive device model with the consideration of all the physical processes. In this work, we proposed one device model integrating models of both radioactive sources and semiconductor units, aiming to guide the design of high-performance devices under specific application requirements. A systematical investigation was conducted on the determining factors on energy losses in planar betavoltaic batteries consisting of typical β sources, such as 147Pm2O3, Ti3H2, 63Ni, and 14C(PMMA), and semiconductors, including Si, GaAs, GaP, SiC, and GaN. Our results show that the output power and the emitting β particle energy of radioactive sources will cause the difference in the major energy loss mechanisms, leading to the different selection rules for semiconductor units. The well-accepted conclusion that efficiency of betavoltaic batteries increases with the width of bandgap no longer holds any more, especially considering high-output power sources and the reality of semiconductor technology. The device model developed in this work provides a powerful tool for the design of high-performance betavoltaic batteries applied in various occasions and will effectively guide the fabrication of high-performance devices.

Photopatternable hydroxide ion electrolyte for solid-state micro-supercapacitors

<h2>Summary</h2> Electrochemical energy storage (EES) devices that provide high power and energy for micropower systems are considered to be essential for developing micro/nano electronics such as nanorobotics, environmental sensors, and connected smart electronics. One promising research direction in this field has been to develop on-chip EES devices whose length scales integrate with those of miniaturized electronic devices. In the work described here, we provide the first report of a hydroxide-ion-conducting solid electrolyte that can be patterned using standard lithography. By combining a negative photoresist with a polymerizable ionic liquid, we obtain a thermally and dimensionally stable, hydroxide-ion-conducting solid electrolyte with a conductivity of 10 mS cm⁻¹. Patterning the solid electrolyte directly on interdigitated vanadium nitride (VN) electrodes enables a scalable fabrication approach for producing high-resolution, solid-state VN micro-supercapacitors (MSC) in both single and multiple devices.

Microgrid Model on Homer Software

A new concept in power generation is a microgrid. The Microgrid concept assumes a cluster of loads and microsources operating as a single controllable system that provides power to its local area. This concept provides a new paradigm for defining the operation of distributed generation. The microsources of special interest for MGs are small (&lt;100-kW) units with power electronic interfaces. These sources are placed at customers sites. They are low cost, low voltage and have a high reliability with few emissions. Power electronics provide the control and flexibility required by the MG concept. A properly designed power electronics and controllers insure that the MG can meet the needs of its customers as well as the utilities. The goal of this project is to build a complete model of Microgrid including the power sources, their power electronics, and a load and mains model in THE HOMER. The HOMER Micropower Optimization Model is a computer model developed by the U.S. National Renewable Energy Laboratory (NREL) to assist in the design of micropower systems and to facilitate the comparison of power generation technologies across a wide range of applications. HOMER models a power system’s physical behavior and its life-cycle cost, which is the total cost of installing and operating the system over its life span. HOMER allows the modeler to compare many different design options based on their technical and economic merits. It also assists in understanding and quantifying the effects of uncertainty or changes in the inputs.

Evaluation of NOx emissions characteristics in a CO2-Free micro-power system by implementing a perforated plate

Ammonia (NH3), as a carbon-free fuel with a high hydrogen content, has been considered as a promising candidate to be applied for transportation, propulsion, and power generation sectors. However, due to the presence of nitrogen atoms, direct combustion of NH3 features a high NOx emission, which could hinder its wide application. Thus it is important to mitigate or minimize these emissions. For this, a three-dimensional (3D) computational model is developed by considering a detailed chemical-kinetic mechanism. The effects of 1) the perforated plate porosity σ, 2) the perforated plate thickness t1, 3) the perforated orifice off-z axis distance d, and 4) inlet thermodynamic pressure Pin are evaluated. Numerical results indicate that σ plays an important role in determining the NO formation. This is the combined effect of the strong species preferential diffusion and low flame temperature within the recirculation zone. Furthermore, varying t1 is shown to affect the NO generation rate due to the varied recirculation zone. Although the flow field is affected by d to some degree, it has a negligible effect on the NO generation. Finally, the emission behavior is found to have a strong dependence on Pin. Approximately 50% reduction of NO emission is achieved as the inlet pressure is varied from 1 to 3 atm. The present work opens up an applicable way to enable low-NOx ammonia-fueled power systems, and some of the findings could be applied for hydrocarbon systems design.

Role of hydrogen addition in propane/air flame characteristic and stability in a micro-planar combustor

For combustion occurring under micro-scale conditions, how to enhance the flame stability is of significance. For this, a micro-planar quartz combustor with transparent main walls is designed to experimentally shed lights on the flame stabilization mechanism of premixed propane flame with hydrogen added in terms of flame dynamics. Experimental results show that as far as the pure propane combustion is concerned, there are six types of flame structures with varying the gaseous inlet velocity, i.e., flame repetitive extinction and ignition (FREI flame), cellular flame, planar flame, U-shaped flame, inclined flame and spinning flame. Furthermore, blending hydrogen is found to significantly extend the flame stability. This is due to the fact that the addition of hydrogen can overcome the inlet velocity inertia and restrain flame instability caused by hysteresis. For the inlet velocity considered in this work, hydrogen addition can inhibit transformation of flame type from U-shaped flame to inclined flame. Finally, the flame position, thickness and curvature of U-shaped flame are shown to be significantly affected by hydrogen addition ratio. Specifically, the larger the hydrogen addition ratio, the smaller the flame thickness, indicating that hydrogen addition is conducive to maintaining symmetry of the flame back and forth. In general, this work has an implication of designing a high stability micro-power system by reasonably considering the inlet parameter.

A Novel Structure of a Power System Stabilizer for Microgrids

This paper proposes a novel structure of a power system stabilizer (PSS) to improve the stability of synchronous generators (SGs) in microgrids. Microgrids are relatively vulnerable in terms of stability due to their small size and low inertia. The rotational inertia and voltage support of SGs are highly suitable for getting over the vulnerabilities of microgrids, but there exist weaknesses in low-frequency oscillations (LFOs) and limitations of synchronization due to electromagnetic characteristics. Therefore, we study how to accommodate the features of microgrids in the PSS of SGs and further enhance present advantages. The PSS proposed in this paper not only damps out LFOs by conventional lead-lag compensation but also provides additional damping torque according to the magnitude of the perturbation using a synchronous impedance characteristic (SIC). The proposed Lyapunov energy-function-based control strategy can also increase the synchronizing power of the SG to improve transient stability. For performance verification, we use parameters obtained by the particle swarm optimization (PSO) algorithm to compare the existing PSS with the proposed one and analyze them. The effect of the proposed micro-power system stabilizer (μPSS) is analyzed through frequency response analysis, and finally, small-signal stability analysis and the performance of transient stability are verified by time-domain simulation (TDS) on MATLAB/Simulink.

Mitigating NOx emissions from an ammonia-fueled micro-power system with a perforated plate implemented

In this work, three-dimensional numerical simulations with a simplified reaction mechanism are conducted to investigate the effect of implementing a perforated plate in an ammonia-fueled micro-power systems on the NOx emission behavior. Detailed analyses on 1) the perforated plate hole dimensionless width w, dimensionless location l as well as the material property are performed. Results show that with an optimized perforated plate implemented, the NO emission is reduced by up to 73.3 % compared to those in the absence of perforated plates. The decrease is mainly due to the formation of a recirculation zone with a low flame temperature. Increasing w is shown to play a positive role in minimizing the NO generation, while l leads to a reverse trend resulting from the size variation of the recirculation zone. In contrast, the plate material has a negligible effect on NOx emissions. It is also shown that the pressure loss Ploss is varied non-monotonically with l, but monotonically with w and the NH3 volumetric flow rate. Furthermore, the conjugate heat transfer between the plate and combustion products has a certain impact on Ploss. The present work shed lights on reducing NOx emissions by implementing a well-designed perforated plate for practical micro-power systems.