Energy Storage Elements Research Articles

A simple and low-cost triboelectric nanogenerator based on two dimensional ZnO nanosheets and its application in portable electronics

The exploration of new triboelectric materials is considered a significant research area to reduce the cost and complexity of the triboelectric nanogenerator (TENG) device and improve its energy conversion efficiency. In this report, a new triboelectric material pair has been demonstrated to prepare an inexpensive and high-performance TENG. A low-cost hot plate-assisted hydrothermal process is used to prepare the ZnO nanosheets on an aluminum substrate. TENG is made using ZnO nanosheet film, PET/ITO, and operates in vertical contact separation mode. The proposed TENG generates electricity through contact electrification and electrostatic induction. The fabricated TENG is tested for the switching polarity test and confirmed the output voltage generated by TENG alone. The TENG can deliver an open-circuit voltage and short-circuit current of ~ 4.9 V and 10 µA, respectively, for repeated hand tapping.Further, the performance of the proposed TENG is tested under resistive loads, and the maximum power density of 1 µW/cm2 observed at a load resistance of 5 MΩ. Similarly, TENG is also tested under capacitive loads and found the maximum energy stored value of 16.9 μJ at the load capacitance of 47 μF. In addition, the effect of different frequencies of the applied force and device size on the TENG response is studied. The TENG can light up 3 LEDs instantaneously and power the digital watch and 24 LEDs using an energy storage element. The present TENG shows a low-cost and straightforward process and can harvest energy from low-frequency bio-mechanical vibrations. The proposed TENG has potential applications in self-powered electronic devices and systems.

Frequency Content Preservation in Fractional Multi-Frequency Oscillators Despite Reducing the Number of Energy Storage Elements

Frequency Content Preservation in Fractional Multi-Frequency Oscillators Despite Reducing the Number of Energy Storage Elements

New Family of Two-to-Three-Phase AC–AC Indirect Matrix Converters With Open-End Rectifier Stage

This article proposes a family of two-to-three-phase ac–ac indirect matrix converters with an open-end rectifier stage (IMCORS) which are direct ac–ac converters, having no energy storage element at their dc-link. The IMCORSs are the first indirect matrix converters (IMC) with an open-end rectifier stage, creating a new category of IMC. The IMCORS is a full-controlled and unidirectional power flow converter. By replacing four active/controlled switches of the rectifier stage of the IMCORS with four diodes, two new configurations are proposed with reduced active switch count, resulting in reduced costs and increased efficiency. Also, by adding an inverting link to the dc-link of the rectifier stage of the IMCORS (which enables the bidirectional power flow operation), another converter is proposed. The IMCORSs topologies are suitable for wind energy conversion systems. A new modulation scheme for the rectifier stage is proposed in this article, which is titled two-phase open-end modulation scheme. The zero dc-link current commutation and the space vector modulation applied to the proposed converters provide a unity power factor for the input system, reduction of power losses, and decrease the complexity of the commutation when compared with classical matrix converters. The proposed converters are verified by simulation and experimentally using a 1.7-kW/liter prototype operating at 1 kW.

Fractional Cascade LFC for Distributed Energy Sources via Advanced Optimization Technique Under High Renewable Shares

Unpredictable high renewable shares in standalone microgrid (MG) system with stochastic load demands introduces an unavoidable mismatch among loads and sources. This mismatch directly impacts the system frequency that can be mitigated via applying a suitable load frequency control (LFC) scheme. This brief proposes a maiden attempt of marine predator algorithm (MPA) assisted one plus proportional derivative with filter-fractional order proportional-integral ((1+PDF)-FOPI) controller to obtain the proper power flow management among loads and sources. The investigated MG system consists of a photovoltaic (PV) system, a wind turbine (WT) generator (WTG), and a diesel engine generator (DG) as the distributed energy sources, and an ultracapacitor (UC) and a flywheel are chosen as the energy storage elements (ESEs). Various system nonlinearities such as governor dead-band (GDB) and generation rate constraint (GRC) are also considered reflecting the practical scenario. Five state-of-the-art optimization techniques and three traditional controllers, PID, FOPID, and PI-PD, are vividly compared to assess the proposed scheme’s performance. The parametric uncertainties are considered to obtain the robust performance of the proposed control scheme. An eigenvalues-based stability evaluation of the considered plant employing the proposed LFC scheme is also included in this work. In the worst situation, the maximum frequency deviation is obtained as -0.016 Hz, which is entirely satisfactory and under the range of the IEEE standard. Finally, a modified New England IEEE-39 test bus system is chosen to perform the real-time validation.

Restructured LFC Scheme with Renewables and EV Penetration using Novel QOEA Optimized Parallel Fuzzy I-PID Controller

An effective controller configuration improves the action of the load frequency control (LFC) mechanism. In the present work, a novel parallel fuzzy integral - proportional-integral-derivative (FI-PID) controller is suggested for a two-area power system in the deregulated environment. The controller gains are optimized using novel quasi-oppositional equilibrium algorithm (QOEA). The proposed control scheme has been subjected to step and random load disturbances. Moreover, the suggested scheme is also compared with different prevalent controllers and optimizing techniques. EV and the distributed generation (DG) act as energy storing elements and improve system transients during peak demands. Hence, the integration of electric vehicle into the grid and its impact on frequency regulation is also studied. Simulation results establish the efficacy of the suggested controller over prevailing ones.

High‐Efficiency Power Generation Device of Magnetic Declination Thermoelectric Material and Multisource Coordination Optimization of Distribution Network

The first‐order phase transition compounds have attracted widespread attention from refrigeration enterprises and scientists due to their giant magnetocaloric effect and refrigeration temperature region spanning room temperature. Magnetic substances are crystal structures composed of magnetic ions or atoms with a certain thermal motion or vibration. This research mainly discusses the multisource coordination optimization of magnetic declination thermoelectric material efficient power generation device and distribution network. In this study, large doses of MnFe(P,Si) compounds with different ratios were prepared. The reason for choosing a large dose is that the properties and structures of the samples prepared in a large amount and a small amount will be more or less the same for the samples fired in the same proportion and in the same process. At the same time, mass production also prepares for future mass production. Thermomagnetic power generation described in this study is a form of power generation that converts thermal energy directly into electrical energy. The conversion of thermal energy to electric energy is realized by the change of magnetization in the closed coil by the thermomagnetic material in the magnetic field environment, and then, the change of the magnetic flux in the closed coil is realized. The distribution network refers to the power network that receives electrical energy from the transmission network or regional power plants and distributes it locally through distribution facilities or distributes it to various users step by step according to the voltage. It is composed of overhead lines, cables, towers, distribution transformers, isolating switches, reactive power compensators, and some ancillary facilities. A network that plays an important role in distributing electrical energy in the power grid. This research starts with the active distribution network scheduling priority and the distribution network scheduling coordination control framework. Combined with the scheduling and operation characteristics of each component in the distribution network, the coordinated optimization scheme of the distribution network and the source‐network load‐storage coordinated control framework are investigated and analyzed. The scheduling resources of the model include the power of the substation flowing into the distribution network, the output of the adjustable distributed power source, the output value of the energy storage element, the closing status of the tie switch, and the section switch. In the study, it was found that when the Fe content was 0.63, the Curie temperature of the compound could reach 273 K at the highest. Scientifically designing a thermomagnetic power generation demonstration device is an important part of the realization of thermomagnetic power generation. The magnetic declination thermoelectric materials designed in this study will help to improve the power generation efficiency.

Research on real-time control strategy of multi-power flow of dual-mode power-split hybrid electric vehicle

With the continuous development of hybrid vehicle control technology, great progress has been made in the research of multi-power flow collaborative control. Due to the internal delay link of each power component, the role of energy storage element, and the limitation of electric power in the whole system, the inevitable delay characteristic of state transfer is caused. Therefore, the speed of multi-power flow control torque coordinated response of hybrid vehicles needs to be improved. The dual-mode power-split hybrid electric vehicle (DMPS-HEV) overall structure and working modes are analyzed, by adopting the combination of theory and experiment method. In order to solve the problem that the power components of dual-mode power-split hybrid electric vehicle cannot follow the optimal control command of the upper energy management strategy quickly due to the engine response delay, thus affecting the control effect of the upper energy management strategy. The research on torque coordination control strategy is carried out, the reference model of electromechanical composite drive is established, and the model reference adaptive coordination control strategy based on Lyapunov stability theory is proposed. The results show that the proposed model reference adaptive torque coordinated control strategy significantly improves the effect of engine response delay on the optimization effect of energy management strategy, and can achieve the control effect of the optimal control strategy of 93.58%. The test platform of the dual-mode power-split hybrid electric vehicle was built. The control system was built based on the rapid control prototype, and the data acquisition system was built based on the NI data acquisition module. The coordinated control strategy of the dual-mode power-split hybrid electric vehicle power system proposed in this paper was verified through the bench test to significantly improve the vehicle fuel economy and the real-time performance of the control strategy, which has a good practical value

Design of a Partially Grid-Connected Photovoltaic Microgrid Using IoT Technology

This study describes the design and control algorithms of an IoT-connected photovoltaic microgrid operating in a partially grid-connected mode. The proposed architecture and control design aim to connect or disconnect non-critical loads between the microgrid and utility grid. Different components of the microgrid, such as photovoltaic arrays, energy storage elements, inverters, solid-state transfer switches, smart-meters, and communication networks were modeled and simulated. The communication between smart meters and the microgrid controller is designed using LoRa communication protocol for the control and monitoring of loads in residential buildings. An IoT-enabled smart meter has been designed using ZigBee communication protocol to evaluate data transmission requirements in the microgrid. The loads were managed by a proposed under-voltage load-shedding algorithm that selects suitable loads to be disconnected from the microgrid and transferred to the utility grid. The simulation results showed that the duty cycle of LoRa and its bit rate can handle the communication requirements in the proposed PV microgrid architecture.

An Overview of Voltage Boosting Techniques and Step-Up DC-DC Converters Topologies for PV Applications

The development of technologies to improve the performance of photovoltaic (PV) module integrated converters (MICs) is fundamental to increase the use of distributed generation systems with photovoltaic power source in large urban centers, mainly for complex residential roofs. For two-stage PV MICs, high step-up DC-DC converters are required to boost the low PV module voltage to a higher voltage, in order to suit the DC bus voltage requirements of grid-tied inverters. Thus, to support researchers interested in developing DC-DC power conversion for PV microinverters, this paper classifies the DC-DC converters according to their operational and constructive characteristics and presents some elementary voltage-boosting techniques to aid in analyzing and understanding more complex topologies. Finally, high step-up DC-DC converters based on magnetic coupling and switched capacitor widely cited by important works related to PV applications are presented, with their principles of operation analysed in a simple and objective way, but sufficient to understand their capability to provide high voltage gain. The approach presented by this paper leads to insight into how to place the energy storage elements to create new topologies of DC-DC converters, so that high voltage gain is achieved, and how to analise the high voltage gain capability of complex topologies

A Method to Find the Differential Equations from the Bond Graph Containing Inertial Elements in Derivative Causality

Abstract The bond-graph method is used for finding the equations which describe the systems dynamics, by analysing the way of power transmission from the source to the working elements. When the energy storage elements I and C are in integral causality, the number of state equations equals the number of these elements. If there are also energy storage elements in derivative causality, the system contains a number of differential equations equal to the number of energy storage elements in integral causality and a number of algebraic equations equal to the number of energy storage elements in derivative causality. The work presents a new method for finding the system of differential equations for mechanical systems with one degree of freedom, starting from the original system which contains both algebraic and differential equations.

Inside Front Cover: An optimal design approach on energy storage elements of DC/DC converters via matching principles

The cover image is based on the Original Article An optimal design approach on energy storage elements of DC/DC converters via matching principles by Guangyu Liu et al., https://doi.org/10.1049/rpg2.12308.

Muti-level voltage synthetic voltage direct power flow controller

Aiming at the defects of DC energy storage elements, complex structure and large volume of unified power flow controller (UPFC), the paper combines flying capacitor multilevel technology and voltage vector synthesis technology with unified direct power flow controller. A three-level direct power flow controller (3L-DPFC) and a new control strategy are proposed. By obtaining the power parameters of the receiving end and substituting them into the derived calculation formula, the compensation voltage can be deduced to adjust the phase and amplitude, and the change relationship between the compensation voltage and the power parameters of the receiving end can be calculated through multiple groups of data, so as to adjust the active power flow and reactive power flow in the power grid. Compared with the unified direct power flow controller, it has the advantages of no DC energy storage element, small volume, simple structure, and the voltage stress of each switch is reduced by half, which reduces the failure rate and economic cost of the controller. In the paper, the topology and control strategy of three-level synthetic DPFC are described in detail, and its buck AC conversion theoretical analysis is verified by simulation.

A novel continuous control set model predictive control to guarantee stability and robustness for buck power converter in DC microgrids

In this paper, an adaptive continuous control set model predictive control (CCS-MPC) is proposed to eliminate the instability problem caused by the constant power load (CPL) in DC–DC​ buck converter applied in DC microgrids. Based on the dynamic model of energy storage elements(inductor and capacitor) in circuit, a parallel feedforward algorithm (PFA) is designed to estimate the variation of the load and input voltage. By supplying the information of the variation to the CCS-MPC controller, the large signal stability and fast recovery performance can be ensured under the existence of disturbances. To verify the control robustness of the adaptive CCS-MPC controller, the MATLAB simulations, hardware-in-loop (HIL) experiments and rapid-control-prototype (RCP) experimental results are conducted. Moreover, the comparative simulations and HIL experiments towards other nonlinear controller are conducted to investigates its dynamic performance.

An optimal design approach on energy storage elements of DC/DC converters via matching principles

DC/DC converters are ubiquitous in renewable energies such as photovoltaic power systems. A novel and general approach is proposed that consists of three matching principles, which enables one to assign a best set of energy storage elements to a DC/DC converter to meet both desirable transients and small ripples, facilitating the design of a controlled DC/DC system. First, the principle of specification matching introduces a ‘virtual’ lower order model to meet the prescribed specifications. Second, the rule of order matching augments the ‘virtual’ model to a higher order, the same as that of the actual DC/DC circuit if necessary. Third, the principle of parameter matching helps derive desirable element parameters through solving an optimization nonlinear function with constraints. These principles are realized through a specific design method for boost DC/DC converters of a photovoltaic power system. Given some specifications, a numerical optimal design is executed to verify the effectiveness of the specific design tool as well as the proposed theory. A photovoltaic power system with the designed boost DC/DC converter is implemented in both the simulated environment and the physical environment.The experimental results show that both transient responses and steady state responses (or ripples) meet the given specifications. The proposed theory can either work alone in simple designs or assist in advanced control designs for a better performance.

Modeling and Maximum Power Tracking of a Solar-Wind Microgeneration System

Abstract The global energy scenario is changing, and clean generation is leading the way. As new ways of producing energy becomes more popular, microgeneration takes a greater share of the market, supplying both isolated and grid connected systems. In such context, hybrid systems that combine two or more different types of sources are a promising approach, although their valuable application depends on many intrinsic and ambient factors and should be thoroughly evaluated. To assess system performance in advance, not only to better predict its operation but also to well design it for specific applications without the need to install it on site, accurate computational models that reflect its real behavior should be developed. Aiming to contribute on this matter, this work presents a dynamic model for a solar-wind microgeneration system, which allows the evaluation of the system’s behavior under different demand scenarios, as well as to implement different energy management strategies. In addition to the base model comprised a photovoltaic panel, a wind turbine, an inverter, and an energy storage element, this work presents the implementation and performance comparison of two different maximum power point tracking algorithms based on soft computing techniques and on real data collected at a meteorological station. Results validate the hybrid microgeneration model and provides insight on the specification of maximum power point tracking algorithms for specific applications.

Performance analysis of unpowered lower limb exoskeleton during sit down and stand up

ABSTRACTConventional unpowered lower limb exoskeleton paid little attention to the metabolic cost of body during sit down (SD)/stand up (SU). The SD motion model and the motion characteristics of lower extremity are analyzed; then, a novel unpowered lower limb exoskeleton is proposed, and the contribution degree of muscles and stiffness of joints are used for determining the location and stiffness of energy storage element. The metabolic cost of relevant muscles in joints of the left leg is obtained based on Opensim software. The results show that metabolic cost of the gracilis, rectus femoris (RF), and long head of the biceps femoris decreased about 13%, 9%, and 68%, respectively. The total metabolic cost of body decreased about 14% during SD. However, the metabolic cost of the gracilis, RF, and long/short head of the biceps femoris increased about 22%, 33%, 208%, and 46%, respectively. And the metabolic cost of sartorius reduces about 39%, the total metabolic cost of body increased about 25.6% during SU, under the exoskeleton conditions. The results of this study can provide a theoretical basis for the optimal design of unpowered lower limb exoskeleton.

A balancing control method by considering lithium batteries state of charge

In order to quickly and accurately reduce the inconsistency of charge between lithium battery and prolong the service life of lithium battery, a balancing control method for lithium batteries state of charge (SOC) is proposed in this paper. The difference of each adjacent battery pack in the series lithium batteries and the difference of each adjacent battery pack in each monomer lithium battery are used as the equalization criteria, a bi-directional energy flow topology circuit is constructed using inductor as energy storage element. The magnitude and direction of the equalization current are controlled, and the balancing control of the whole lithium batteries is finally realized by controlling the on-off time of the Mosfet tube. Compared with the traditional extreme difference control method, the simulation results show that the two-level layered balancing control method proposed in this paper increases the rapidity of static and random currents by 23% and 17.1% respectively, and the accuracy increases by 13.3%. The proposed control approach can be provided with equalization efficiency highly, and give some advice for servicing lithium battery application.

Power decoupling capability with PR controller for Micro-Inverter applications

Micro-inverters have been known as promising structures for small-scale PV systems. However, these structures need energy storage elements to balance the instantaneous output and input power. Demanding a large size capacitor forces using an electrolytic type at the dc-link that affects the micro-inverter lifetime. This paper presents a new Active Power Decoupling (APD) circuit for the micro-inverters to reduce the capacitor size at the dc-link and utilize film capacitors instead of electrolytic types. The proposed APD circuit is based on a single-phase flyback converter. This structure is controlled based on the PQ theory and a Proportional Resonant (PR) controller for delivering the PV panel energy to the grid and eliminating the pulsation power through the switching pattern control. Simulations and experimental results of a 180 W single-phase micro-inverter prototype were performed to evaluate the performance of the proposed structure and the control scheme. It was found that this controller can accurately regulate the switching pattern to remove the ripples of input current and voltage. Furthermore, the robustness and fast dynamic performance of the proposed configuration have been confirmed during input power variation. In conclusion, this single-phase micro-inverter structure has an efficiency of ∼ 91%, THDi of 3.6%, and a long lifetime.

Sustainability Analysis of a ZnO-NaCl-Based Capacitor Using Accelerated Life Testing and an Intelligent Modeling Approach

From small toys to satellites, capacitors play a vital role as an energy storage element, filtering or controlling other critical tasks. This research paper focuses on estimating the remaining useful life of a nanocomposite-based fabricated capacitor using various experimental and artificial intelligence techniques. Accelerated life testing is used to explore the sustainability and remaining useful life of the fabricated capacitor. The acceleration factors affecting the health of capacitors are investigated, and experiments are designed using Taguchi’s approach. The remaining useful lifetime of the fabricated capacitor is calculated using a statistical technique, i.e., regression analysis using Minitab 18.1 software. An expert model is designed using artificial neural networks (ANN), which warns the user of any upcoming faults and failures. The average remaining useful life of the fabricated capacitor, using accelerated life testing, regression, and artificial neural network, is reported as 13,724.3 h, 14,515.9 h, and 14,247.1 h, respectively. A comparison analysis is conducted, and performance metrics are analyzed to opt for the most efficient technique for the prediction of the remaining useful life of the fabricated capacitor, which confirms 93.83% accuracy using the statistical method and 95.82% accuracy using artificial neural networks. The root mean square error (RMSE) of regression and artificial neural networks is found to be 0.102 and 0.167, respectively, which validates the consistency of the reliability methods.

Power Distribution Strategy for an Electric Bus with a Hybrid Energy Storage System

To address the power distribution problem that occurs in hybrid energy storage systems (HESSs) in electric vehicles, a fuzzy control distribution method is proposed in this paper, taking the vehicle demand power; supercapacitor power, PSC;; and lithium battery power, Pbat, as the inputs and the power distribution factor of the supercapacitor as the output to control the power distribution of the composite energy storage system, in addition to dividing the whole working condition into three time scales, namely, long, medium and short. In this study, we conducted a comprehensive analysis and comparison with typical control methods regarding the energy storage element output power, battery state of charge (SOC) change, energy flow diagram and power frequency. The simulation experiment results show that the proposed strategy is more effective in reducing the peak output power of the power battery, improving the effective power utilization rate of HESS and the effective energy utilization rate. In order to further verify the effectiveness of the control strategy, a pure electric bus power system test bench was built based on similar principles, and a representative time period under the driving conditions of the China city bus (CHTC-B) was selected, involving an acceleration process from 30 to 48 s (process 1), a uniform speed process from 636 to 671 s (process 2) and a regenerative braking process from 1290 to 1304 s (process 3), further verifying the effectiveness and feasibility of the proposed control strategy.