Energy Conversion Stages Research Articles

Parametric correction in the control system of the electric propulsion of autonomous underwater vehicles affected by random inputs

The paper deals with the problem of controlling a DC propulsion motor of an autonomous underwater vehicle using a bidirectional non-isolated DC-DC converter. An automatic speed control system with a parametric controller was developed in the Matlab / Simulink package. To reduce energy conversion stages, dc-dc converters are often used to control dc motors AUV. The result of the work is an adaptive control system for the speed of the AUV propeller, which would provide high accuracy for a wide range of speeds and at the same time limit the maximum current and voltage at the armature. The indicators of the quality of performance in various modes of operation were determined, maps of the controller settings were compiled, and parametric correction was introduced. The operation of the system is analyzed and drawbacks are eliminated, such as voltage surges when switching from one speed to another, a decrease in overshoot and settling time. The performance of the system is analyzed under the conditions of random inputs from the propeller. The description of the laboratory stand for the study of the control system is given. A description of the laboratory study of the operation of the "DC converter—engine" system under conditions of random fluctuations in the moments on the motor shaft is given. It is shown that the proposed system has shown itself well under laboratory conditions and the experimental results are consistent with modeling in Matlab / Simulink.

MODELING AND OPTIMIZATION OF A PCM-BASED OCEAN THERMAL ENERGY HARVESTER FOR POWERING UNCREWED UNDERWATER VEHICLES

Abstract As oceans cover over 70% of the planet's surface, they represent a large reservoir of resources that remained vastly untapped. Uncrewed Underwater Vehicles (UUVs) are becoming key technology for ocean exploration. Ocean thermal gradient is a permanent and reliable energy source that can be used to power UUVs using phase change material (PCM)-based thermal engines. When using PCM-based thermal engines to power UUVs, there are different energy conversion stages, thermal, hydraulic, kinetic, and electrical, dependent on a wide variety of parameters. Thus, optimization of the overall energy conversion is still a challenge for powering the increasing energy demanding UUVs for long missions. The goal of this study is to propose a PCM-based ocean thermal energy harvesting system for powering float type UUVs such as the Solo II float. This reduces the cost for battery replacement and expands the float's mission time. For this purpose, we developed a model consisting of hydraulic and electrical systems, designed to provide the electrical power needed by the UUV. The hydraulic and electrical systems are implemented using MATLAB-Simulink. The model developed can provide 13.66 kJ of electrical energy, which is more than 1.5 times the energy requirement per cycle for the SOLO II float.

Energy Harvesting from Water Flow by Using Piezoelectric Materials

As a promising energy‐harvesting technique, an increasing number of researchers seek to exploit the piezoelectric effect to power electronic devices by harvesting the energy associated with water flow. In this emerging field, a variety of research themes attract interest for investigation; these include selection of the excitation mechanism, oscillation structure, piezoelectric material, power management interface circuit, and application. Since there has been no comprehensive review to date with respect to the harvesting of water flow using piezoelectric materials, herein relevant work in the last 25 years is reviewed. To ensure that key aspects of the water‐flow energy harvester are overviewed, they are discussed in the context of energy‐flow theory, which includes the three stages of energy extraction, energy conversion, and energy transfer. The development of each energy‐flow process is reviewed in detail and combined with meta‐analysis of the published literature. Correlations between the harvesting processes and their contribution to the overall energy‐harvesting performance are illustrated, and directions for future research are also proposed. In this review, a comprehensive understanding of water‐flow piezoelectric energy harvesting is provided and it is aimed to guide future research and the development of piezoelectric harvesters for water‐flow‐powered devices is promoted.

Efficiency Optimization of the High-Power Isolated DC/DC Converters through THD and Losses Reduction in Isolation Transformers

This paper describes a method of improving efficiency of the high-power transformer-isolated DC/DC converters by means of proper selection of an inverter switch duty cycle. The paper revises old suggestions and recommendations for choosing the maximal duty cycle value on the basis of physical limits imposed by new solid-state devices. The resulting improved efficiency of the converter is described considering losses in separate energy conversion stages

Surface Engineered Single-atom Systems for Energy Conversion.

Single-atom catalysts (SACs) are demonstrated to show exceptional reactivity and selectivity in catalytic reactions by effectively utilizing metal species, making them a favorable choice among the different active materials for energy conversion. However, SACs are still in the early stages of energy conversion, and problems like agglomeration and low energy conversion efficiency are hampering their practical applications. Substantial research focus on support modifications, which are vital for SAC reactivity and stability due to the intimate relationship between metal atoms and support. In this review, a category of supports and a variety of surface engineering strategies employed in SA systems are summarized, including surface site engineering (heteroatom doping, vacancy introducing, surface groups grafting, and coordination tunning) and surface structure engineering (size/morphology control, cocatalyst deposition, facet engineering, and crystallinity control). Also, the merits of support surface engineering in single-atom systems are systematically introduced. Highlights are the comprehensive summary and discussions on the utilization of surface-engineered SACs in diversified energy conversion applications including photocatalysis, electrocatalysis, thermocatalysis, and energy conversion devices. At the end of this review, the potential and obstacles of using surface-engineered SACs in the field of energy conversion are discussed. This review aims to guide the rational design and manipulation of SACs for target-specific applications by capitalizing on the characteristic benefits of support surface engineering.

New Integrated Converter for Hydrogen Buffer Interfacing in Distributed Energy Systems

This paper presents a new integrated (multiport) DC/DC converter for hydrogen buffer interfacing in renewable energy systems. In comparison with traditional solutions based on individual converters for interfacing of electrolyser and fuel cell the proposed topology features the reduced energy conversion stages. The paper analyzes and discusses the operating principle of a new converter. Several guidelines are presented for the new converter design. Finally, theoretical background was verified by the simulations.

Distributed Integral Convex Optimization-Based Current Control for Power Loss Optimization in Direct Current Microgrids

Due to the advantages of fewer energy conversion stages and a simple structure, direct current (DC) microgrids are being increasingly studied and applied. To minimize distribution loss in DC microgrids, a systematic optimal control framework is proposed in this paper. By considering conduction loss, switching loss, reverse recovery loss, and ohmic loss, the general loss model of a DC microgrid is formulated as a multi-variable convex function. To solve the objective function, a top-layer distributed integral convex optimization algorithm (DICOA) is designed to optimize the current-sharing coefficients by exchanging the gradients of loss functions. Then, the injection currents of distributed energy resources (DERs) are allocated by the distributed adaptive control in the secondary control layer and local voltage–current control in the primary layer. Based on the DICOA, a three-layer control strategy is constructed to achieve loss minimization. By adopting a peer-to-peer data-exchange strategy, the robustness and scalability of the proposed systematic control are enhanced. Finally, the proposed distribution current dispatch control is implemented and verified by simulations and experimental results under different operating scenarios, including power limitation, communication failure, and plug-in-and-out of DERs.

DC-Bus Voltage Sensorless Control of an Active Rectifier with Modular Multilevel Converter

The modular multilevel converter (MMC) is recognized as one of the promising converters for the electrification of ships and railways. Among different energy conversion stages, the MMC-based rectifier should realize stable DC output voltage and accurate input current control. However, output DC-bus voltage sensors must be installed, which are costly and bulky. This paper presents a simple but effective control method for the MMC-based rectifier, removing the traditional output DC-bus voltage sensor. An accurate evaluation model of DC-bus voltage is developed as well as the implementing method. Meanwhile, a safe and fast pre-charging scheme is presented for the MMC-based rectifier without output voltage sensors. The fault-tolerant capability of the proposed method when the failure of the output DC-bus voltage sensor occurs is examined. Simulated and testing results demonstrate that the proposed method presents not only excellent steady-state and dynamic performance but also strong fault-tolerant capability. The proposed evaluation model for DC-bus voltage has a high accuracy with an error of less than 1%. Besides, the pre-charging time is less than 0.5 s using the proposed sensorless control.

Hybrid Renewable Energy System with High Gain Modified Z-Source Boost Converter for Grid-Tied Applications

In a hybrid renewable system, a conventional boost converter produces more losses at the time of the energy conversion process due to this, the performance of the hybrid system is reduced total harmonic distortion is increased, and the hybrid microgrid outcome is reduced. The main objective of the work enhancing the low DC voltage produced by the PV panel, a high gain Boost converter is utilized. The objectives of the work were achieved by a High Gain Modified Z-source Boost converter along with Modified Particle Swarm Optimized- Proportional Integral (MPSO-PI) controller employed in the energy conversion stage at Grid. It reduced power conversion stages and decreases the losses compared to existing Hybrid Grid-connected systems. A new 13-bus system is developed in this work for regulating the output voltage in distribution networks. The significance of our work lies in the design of an efficient microgrid system for grid-tied applications. High Gain Modified Z-source Boost converter along with Modified Particle Swarm Optimized- Proportional Integral (MPSO-PI) controller is employed to boost the voltage obtained from the PV system. A battery converter along with a bidirectional battery is connected to the DC link, to store energy generated by Hybrid Renewable Energy System (HRES) in excess amounts. The obtained DC link voltage is transferred to Three Phase VSI for the conversion of DC to AC voltage. Effective harmonic reduction is attained with the aid of an LC filter coupled to Three Phase grid, and the PI controller connected to Voltage Source Inverter(VSI) supports achieving effective grid synchronization. The proposed work was tested with 13 bus system through MATLAB Simulink.

Efficiency Performances of LVDC Supplies for Residential Building

The Low Voltage Direct Current (LVDC) architecture gives higher benefits over the classic low-voltage alternating current (LVAC) supply concept. LVDC has fewer energy conversion stages, is compatible with renewable energy sources, and is easier to integrate with accumulators. In this paper, an LVDC supply concept is proposed and compared with currently used conventional photovoltaic (PV) systems in terms of efficiency. The new LVDC photovoltaic system behavior is validated using LTspice modeling tool. The findings of this work prove that the concept of LVDC supply is highly attractive when the electricity produced by the photovoltaic is used onsite in the daytime. To carry out an efficient system, the PV power mounted in the houses should be precisely rated with respect to the magnitude of the load energy consumption. We proposed three house examples to verify the superiority of our proposed system in comparison with the traditional LVDC PV chain. An annual analysis of the energy saved by the studied systems was carried out. The main benefit of the suggested LVDC supply is the short way taken by the energy generated by the photovoltaic system to supply DC loads within daytime hours. The registered increase in system efficiency reached more than 20% for the proposed LVDC system.

Efficient bubble energy harvesting by promoting pressure potential energy release using helix flow channel

The bubble energy harvesting system can provide in-situ energy supply for the subsea observation equipment through two stages of energy conversion. However, the conversion efficiency of bubble potential energy to fluid energy in the first stage is much lower than that of fluid energy to electrical energy in the second stage, limiting the output capability of the bubble energy harvesting system. Here, a complete energy transfer and conversion model for the subsea bubble energy harvesting is established for the first time. Regardless of the type of transducer used in the system, increasing the released pressure potential energy can substantially improve the efficiency of bubble energy harvesting. Based on this mechanism, we proposed a method to improve the released pressure potential energy and verified the results using a bubble energy harvesting system with a 3D streamline. The flow velocity and fluid volume of the system can be controlled by adjusting the helix angle and cylindrical diameter. Compared with the original system, the fluid pressure potential energy released of a 3D-system with a helix angle of 50 degrees can increase by at least 26%. The output energy density of the 3D-system with a height of 1.6 m can reach 6.6 J/m3, which is 59 times higher than that of the existing technology. This technology can efficiently harvest energy from subsea gas sources, and has the potential to become a long-term in-situ power supply solution for subsea observation networks.

Concept Design of a Novel Superconducting PTO Actuator for Wave Energy Extraction

The role of the Power Take-Off (PTO) as part of modern Wave Energy Converters is becoming more and more relevant and many efforts have been done or are ongoing to improve its performance especially in terms of force density and efficiency. Electric Linear PTOs are inherently the most efficient category, since they are really direct drives with no intermediate stages of energy conversion. Nevertheless, conventional electric machines are usually limited in force while their efficiency is better than other type of drives but still does not allow an intense energy capture in a broad band of wave periods. In this regard, superconductivity may become a very helpful alternative that allows improving both: efficiency and force density in spite of the technological difficulties that are introduced in the Wave Energy Converter. This paper, after justifying the need for better PTO performances, presents a new concept of superconducting PTO in which both, the stator and the translator work at cold temperature, performing a reciprocating displacement inside a flexible cryostat. The concept is later applied to a Cylindrical Switched Reluctance machine whose global design is also presented in the paper. This activity has been performed as one of the work packages of the EU H2020 Sea Titan Project in which also a resistive PTO with a novel configuration has been developed.

Robust Optimization and Power Management of a Triple Junction Photovoltaic Electric Vehicle with Battery Storage.

This paper highlights a robust optimization and power management algorithm that supervises the energy transfer flow to meet the photovoltaic (PV) electric vehicle demand, even when the traction system is in motion. The power stage of the studied system consists of a triple-junction PV generator as the main energy source, a lithium-ion battery as an auxiliary energy source, and an electric vehicle. The input–output signal adaptation is made by using a stage of energy conversion. A bidirectional DC-DC buck-boost connects the battery to the DC-link. Two unidirectional boost converters interface between the PV generator and the DC link. One is controlled with a maximum power point tracking (MPPT) algorithm to reach the maximum power points. The other is used to control the voltage across the DC-link. The converters are connected to the electric vehicle via a three-phase inverter via the same DC-link. By considering the nonlinear behavior of these elements, dynamic models are developed. A robust nonlinear MPPT algorithm has been developed owing to the nonlinear dynamics of the PV generator, metrological condition variations, and load changes. The high performance of the MPPT algorithm is effectively highlighted over a comparative study with two classical P & O and the fuzzy logic MPPT algorithms. A nonlinear control based on the Lyapunov function has been developed to simultaneously regulate the DC-link voltage and control battery charging and discharging operations. An energy management rule-based strategy is presented to effectively supervise the power flow. The conceived system, energy management, and control algorithms are implemented and verified in the Matlab/Simulink environment. Obtained results are presented and discussed under different operating conditions.

Intermittent series direct current arc fault detection in direct current more‐electric engine power systems based on wavelet energy spectra and artificial neural network

The move towards More-Electric Aircraft (MEA) and Engine (MEE) systems has resulted in system integrators exploring the use of Direct Current (DC) for primary power distribution to both reduce energy conversion stages and enable parallelling of non-synchronised engine off-take generation. A prevalent challenge of utilising DC systems is the safe management of arc faults. Arcing imposes a significant threat to aircraft and can result in critical system damage. Series intermittent arc faults in DC systems are particularly challenging to detect due to the lack of a zero current crossing coupled with the intermittency caused by in-flight vibrations. Additionally, several state-of-the-art arc fault detection methodologies fail to address the handling of aircraft system-specific conditions such as dynamic loading and stability requirements. This paper addresses these unique MEA/MEE issues through the proposal of a new generalised real-time arc fault detection methodology (WaSp) based on time–frequency domain-extracted features applied to a feed-forward Artificial Neural Network (ANN). The paper outlines the analysis of arc fault time–frequency domain features. Simulation-based case studies emulating a range of on-board EPS conditions are presented and show the proposed system has the potential for highly accurate and generalised detection performance with fast detection times.

Control Design of a 99% Efficiency Transformerless EV Charger Providing Standardized Grid Services

A nonisolated DC charger is proposed for electric vehicle (EV) battery system. The leakage current can be reduced by the novel charging system without bulky transformer. A zero sequence voltage control method is developed to stabilize the common-mode voltage, thus, reduce the leakage current. The proposed fast charger includes two energy conversion stages: DC–DC converter for battery side control; DC–AC converter for grid interface and common-mode voltage control. The parameters of the system with the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LCL</i> filter are analyzed and optimized for a better performance of grid interface. Grid service functions are designed for the EV charger to provide grid-voltage/frequency compensations. High power (22 kW) and high efficiency ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$&gt;$</tex-math></inline-formula> 99%) are achieved with low-leakage current ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$&lt;$</tex-math></inline-formula> 20 mA). The experiments are implemented to verify the proposed EV charger system.

Research on Constant Voltage/Current Output of LCC–S Envelope Modulation Wireless Power Transfer System

As a technology that makes power transfer more flexible, wireless power transfer (WPT) technology has become a hot research topic in recent years. However, most of the existing studies are based on a DC–DC WPT system. If applied to AC loads, the traditional system usually contains multiple energy conversion stages, which lead to a low transmission efficiency and therefore higher costs. Besides, the necessary large electrolytic capacitors make the system unreliable and bulky. The goal of this study is to design a reliable and efficient WPT system featuring constant current (CC) and constant voltage (CV) output for AC loads. In this work, an inductor–capacitor–capacitor series (LCC–S) enveloped modulation wireless power transfer (EM–WPT) system is proposed. The design of the proposed system is elaborated in this paper, including the working principle of the system’s power converters, the relationship between CC/CV output characteristics and the input current, and the control strategy of CC/CV output based on an AC–AC boost converter. Lastly, an experimental prototype is configured to verify the CC/CV characteristics. The measured overall efficiency of the system reaches 91% and the power factor of input power supply approaches 1.

Energy harvesting performance of an inerter-based electromagnetic damper with application to stay cables

Energy harvested from vibrating cables can serve as a sustainable and green power source for low-power sensing systems and vibration control systems. However, the energy-harvesting performance of inerter-based dampers installed at stay cables has rarely been reported so far. This paper investigates the energy-harvesting performance of a novel inerter-based electromagnetic damper, termed tuned inertial mass electromagnetic damper (TIMED), which is capable of converting cable vibration energy into electric energy to be harvested. Based on energy balance principles, a power flow model is established for the TIMED, considering major and minor power terms, which account for different power losses occurring during the energy conversion stages. This model is capable of predicting the output power and energy-harvesting efficiency under harmonic displacement or harmonic force inputs. A series of MTS dynamic tests were performed in a TIMED prototype to validate the theoretical model. Under a harmonic force excitation of 1.6kN near the damper’s resonance, the TIMED achieved a maximum output power of 69.54 W. To evaluate the actual performance of the TIMED, we conducted a full-scale experiment on a 135 m-long stay cable with the TIMED prototype. Full-scale experimental results illustrate that the maximum average output power of the TIMED attached to the tested cable in the free vibration case is up to 13.6 W, which is 48.3% larger than the counterpart of an electromagnetic damper (EMD). In addition, an optimal design strategy is proposed and validated for the cable-TIMED system. Numerical results demonstrated that, in theory, the output power of the TIMED can be 81.7% larger than that of an EMD. The performance enhancement of the TIMED over conventional EMD attributes to its displacement and energy amplification near resonance. This study may help to put forward the development of self-powered dampers or self-powered sensing systems in the years to come.

Comparative analysis of Si, SiC and GaN based quasi impedance source inverter

The impedance source inverter reduces the number of stages of energy conversion due to its ability to increase the output voltage. Silicon based semiconductor power devices are commonly used for inverters, but as the voltage and current rating of the inverter increases with demand for high efficiency, the Silicon Carbide and Gallium Nitride power devices are most preferred. These wide bandgap devices enable the switches to be operated at high switching frequencies and with the increase in switching frequency, the size of the impedance network elements present in the inverter can be reduced. Thus, obtaining a compact and highly efficient inverter module. This paper presents a comparative analysis of Silicon, Silicon – Carbide and Gallium Nitride based quasi – impedance source inverters through simulation study. The performance of the inverters is analysed based on its efficiency, voltage stress and current stress across the switches and the results are validated.

콘크리트 양생용 거푸집의 온도분포 최적화를 위한 유도가열 코일 배열 및 배치 비교평가

This paper proposes coil design conditions of a concrete curing system based on induction heating method for efficient concrete curing. The concrete curing method using an induction heating coil has the advantage of low energy consumption by using a high-efficiency system compared to the existing methods that undergoes several stages of energy conversion. When the induction heating coil is used, it is important to obtain uniform temperature surface on the formwork temperature. When a temperature difference occurs in the vertical section of a concrete form due to an uneven temperature distribution during concrete curing, it may cause a decrease in concrete strength. In this paper, in order to efficiently heat the concrete formwork surface, the temperature distribution according to the arrangement of the induction heating coil was analyzed and the current strength flowing through the coil was studied. The design conditions and results of the induction heating coil were presented using FEM simulation to obtain a uniform temperature distribution. Based on the proposed two-turn induction coil, the temperature distribution inside the formwork was analyzed using the distance between the formwork and the coil and the distance between the coil turns as design parameters. In addition, the simulation results were verified through an induction heating experiment using an experimental formwork.

Current Control Strategies for a Star Connected Cascaded H-Bridge Converter Operating as MV-AC to MV-DC Stage of a Solid State Transformer

Nowadays, the increasing number of nonlinear loads and renewable energy resources pose new challenges for the standard electrical grid. Conventional solutions cannot handle most of them. The weakest component in the whole system is a conventional distribution (converting medium to low AC voltage) transformer. It should not operate with unbalanced, heavily distorted voltage and cannot control power flow or compensate current harmonics. One of the promising solutions to replace the conventional transformer and thus minimize power flow and grid distortions is a power electronics device called a solid state transformer (SST). Depending on the SST topology, it can have different functionalities, and, with the proper control algorithm, it is able to compensate any power imbalances in both low voltage (LV) and medium voltage (MV) grid sides. In the case of a three energy conversion stage SST, the LV and the MV stages can be treated separately. This paper focuses on the MV-AC to the MV-DC stage only based on a star-connected cascaded H-bridge converter. In this paper, a simple control solution for such a converter enabling different current control strategies to distribute power among the phases in an MV grid in the case of voltage imbalances is proposed. Simulation and experimental results proved good performance and verified the validity of the proposed control algorithm.