Optimisation, Optimal Control and Nonlinear Dynamics in Electrical Power, Energy Storage and Renewable Energy Systems

Dear Colleagues,

The electrical power system is undergoing a revolution that has been enabled by advances in telecommunications, computer hardware and software, measurement and metering systems, IoT, and power electronics. The increasing integration of intermittent renewable energy sources, energy storage devices, electric vehicles and the drive for energy efficiency have resulted in an evolution of the traditional power systems towards a smarter grid, which is characterised, in part, by a bi-directional flow of energy and information. The evolution of the power grid, as well as its interconnection with energy storage systems and renewable energy sources, has created new opportunities for optimising not only their techno-economic aspects at the planning stages but also their control and operation. However, new challenges are emerging in optimising these systems related to the complexity, the uncertainties involved, and the nonlinear dynamic behaviour that these systems exhibit.

We are pleased to invite prospective authors to submit original research submissions covering innovations associated with the optimisation and optimal control in electrical power, energy storage and renewable energy systems, and the challenges associated with their nonlinear, uncertain, and complex behaviour. Topics of interest include but are not limited to:

  • Novel approaches for the optimisation of techno-economic aspects of electrical power, energy storage or renewable energy systems at the planning stage;
  • Nonlinear dynamics in electrical power, energy storage or renewable energy systems;
  • Nonlinear and optimal control approaches for microgrids, energy storage, or the integration of renewable energy systems into the power grid;
  • Revenue maximisation of energy storage systems;
  • Nonlinear state estimation for electrical power, energy storage or renewable energy systems;
  • Optimal power flow with energy storage and/or renewable energy sources.

Deadline for abstract submissions: 15 December 2021.
Deadline for manuscript submissions: 15 April 2022.

Topic Board

Prof. Dr. Victor Becerra
E-Mail Website
Topic Editor-in-Chief
School of Engineering, University of Portsmouth, Anglesea Building, Anglesea Road, Portsmouth PO1 3DJ, UK
Interests: computational optimal control; nonlinear control; fault diagnosis; fault-tolerant control; autonomous control systems; state estimation; smart grids; solar energy; control of power systems; control of energy storage
Special Issues and Collections in MDPI journals
Prof. Dr. Ahmed Rachid
E-Mail Website
Topic Associate Editor-in-Chief
Laboratory of Innovative Technologies, Picardie Jules Verne University, 80025 Amiens, France
Interests: process and system modeling; simulation; control; diagnosis and observation with applications to electro-mechanical, thermal systems, and renewable energy
Special Issues and Collections in MDPI journals

Keywords

  • optimal control
  • nonlinear dynamics
  • optimization
  • nonlinear systems
  • nonlinear control
  • power systems
  • energy storage systems
  • renewable energy systems
  • renewable energy integration
  • smart grids
  • microgrids
  • electric vehicles
  • battery systems

Relevant Journals List

Journal Name Impact Factor CiteScore Launched Year First Decision (median) APC
Energies
energies
3.004 4.7 2008 15.92 Days 2000 CHF Submit
Electronics
electronics
2.397 2.7 2012 15.03 Days 1800 CHF Submit
Electricity
electricity
- - 2020 21.62 Days 1000 CHF Submit

Published Papers (16 papers)

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Article
Selection of Output Voltage Compensators Gains in Two Cascaded Boost Converters with Input Filters by Means of the \({\mathfrak{D}}\)-Decomposition Technique
Energies 2021, 14(18), 5883; https://0-doi-org.brum.beds.ac.uk/10.3390/en14185883 - 17 Sep 2021
Abstract
In this paper, the D-decomposition technique is investigated as an intuitive method for finding the non-linear trajectories of PI-compensator gains. The trajectories reflect the desired dynamic properties at a system level specified by the gain and the phase margin (GMPM) in the [...] Read more.
In this paper, the D-decomposition technique is investigated as an intuitive method for finding the non-linear trajectories of PI-compensator gains. The trajectories reflect the desired dynamic properties at a system level specified by the gain and the phase margin (GMPM) in the frequency domain. They are presented as parametric curves in the proportional and the integral gains coordinates in form of KI=f(KP) functions. The curves are inscribed into global stability boundaries (GSB). The corresponding Nyquist plots are included for comparison. The analysis is based on a system consisting of two serial-connected boost converters. Each converter has its input filter. The major parasitic components of the system are taken into account during the mathematical and simulation modelling. The control circuit time delays and non-linear semiconductors characteristics are also included. A complete set of practically useful system-level transfer functions in form of mathematical formulas is included. Selected aspects, such as the control-to-output voltage and the control-to-input current of one sub-system of the simulation model, have been verified experimentally. The presented results clearly indicate the need for interactions between the sub-systems of a system to be taken into account during controller gains selection. Full article
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Article
Air-Gap Flux Oriented Vector Control Based on Reduced-Order Flux Observer for EESM
Energies 2021, 14(18), 5874; https://0-doi-org.brum.beds.ac.uk/10.3390/en14185874 - 16 Sep 2021
Abstract
Electrically excited synchronous motor (EESM) has the characteristics of high order, nonlinear and strong coupling, so it is difficult to be controlled. However, it has the advantages of adjustable power factor, high efficiency, and high precision torque control, so it is widely used [...] Read more.
Electrically excited synchronous motor (EESM) has the characteristics of high order, nonlinear and strong coupling, so it is difficult to be controlled. However, it has the advantages of adjustable power factor, high efficiency, and high precision torque control, so it is widely used in high-power applications. The accuracy of a flux observer influences the speed control system of EESM. Based on state observer in modern control theory and electrical excitation synchronous machine state equation, a reduced-order flux observer is designed. Using the first-order difference method and forward bilinear transformation method, the reduced-order flux observer is discrete, and the stability of the motor system is analyzed. The analysis shows that the stability of the system using the bilinear transformation method is better than that using the first order forward difference method. In motor operation, motor parameters will be affected by the factors of temperature, magnetic saturation, and motor frequency. In this paper, the influence of parameter variation on the motor system is studied by using the variation of the pole distribution. Finally, the speed regulation system using the reduced-order observer is simulated, which verifies the accuracy of the reduced-order flux observer observation. Full article
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Article
The Potential of Variable Renewable Energy Sources in Mexico: A Temporally Evaluated and Geospatially Constrained Techno-Economical Assessment
Energies 2021, 14(18), 5779; https://0-doi-org.brum.beds.ac.uk/10.3390/en14185779 - 14 Sep 2021
Abstract
Due to the increasing global importance of decarbonizing human activities, especially the production of electricity, the optimal deployment of renewable energy technologies will play a crucial role in future energy systems. To accomplish this, particular attention must be accorded to the geospatial and [...] Read more.
Due to the increasing global importance of decarbonizing human activities, especially the production of electricity, the optimal deployment of renewable energy technologies will play a crucial role in future energy systems. To accomplish this, particular attention must be accorded to the geospatial and temporal distribution of variable renewable energy sources (VRES), such as wind and solar radiation, in order to match electricity supply and demand. This study presents a techno-economical assessment of four energy technologies in the hypothetical context of Mexico in 2050, namely: onshore and offshore wind turbines and open-field and rooftop photovoltaics. A land eligibility analysis incorporating physical, environmental, and sociopolitical eligibility constraints and individual turbine and photovoltaic park simulations, drawing on 39 years of climate data, is performed for individual sites across the country in an effort to determine the installable potential and the associated levelized costs of electricity. The results reveal that up to 54 PWh of renewable electricity can be produced at a levelized cost of electricity of less than 70 EUR·MWh−1. Around 91% (49 PWh) of this electricity would originate from 23 TW of open-field photovoltaic parks that could occupy up to 578,000 km2 of eligible land across the country. The remaining 9% (4.8 PWh) could be produced by 1.9 TW of onshore wind installations allocated to approximately 68,500 km2 of eligible land that is almost fully adjacent to three mountainous zones. The combination of rooftop photovoltaic and offshore wind turbines accounts for a very small share of less than 0.03% of the overall techno-economical potential. Full article
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Article
Reinforcement Learning for Energy-Storage Systems in Grid-Connected Microgrids: An Investigation of Online vs. Offline Implementation
Energies 2021, 14(18), 5688; https://0-doi-org.brum.beds.ac.uk/10.3390/en14185688 - 09 Sep 2021
Abstract
Grid-connected microgrids consisting of renewable energy sources, battery storage, and load require an appropriate energy management system that controls the battery operation. Traditionally, the operation of the battery is optimised using 24 h of forecasted data of load demand and renewable energy sources [...] Read more.
Grid-connected microgrids consisting of renewable energy sources, battery storage, and load require an appropriate energy management system that controls the battery operation. Traditionally, the operation of the battery is optimised using 24 h of forecasted data of load demand and renewable energy sources (RES) generation using offline optimisation techniques, where the battery actions (charge/discharge/idle) are determined before the start of the day. Reinforcement Learning (RL) has recently been suggested as an alternative to these traditional techniques due to its ability to learn optimal policy online using real data. Two approaches of RL have been suggested in the literature viz. offline and online. In offline RL, the agent learns the optimum policy using predicted generation and load data. Once convergence is achieved, battery commands are dispatched in real time. This method is similar to traditional methods because it relies on forecasted data. In online RL, on the other hand, the agent learns the optimum policy by interacting with the system in real time using real data. This paper investigates the effectiveness of both the approaches. White Gaussian noise with different standard deviations was added to real data to create synthetic predicted data to validate the method. In the first approach, the predicted data were used by an offline RL algorithm. In the second approach, the online RL algorithm interacted with real streaming data in real time, and the agent was trained using real data. When the energy costs of the two approaches were compared, it was found that the online RL provides better results than the offline approach if the difference between real and predicted data is greater than 1.6%. Full article
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Article
Indonesia’s Vast Solar Energy Potential
Energies 2021, 14(17), 5424; https://0-doi-org.brum.beds.ac.uk/10.3390/en14175424 - 31 Aug 2021
Abstract
In this paper, we conclude that Indonesia has vast potential for generating and balancing solar photovoltaic (PV) energy to meet future energy needs at a competitive cost. We systematically analyse renewable energy potential in Indonesia. Solar PV is identified to be an energy [...] Read more.
In this paper, we conclude that Indonesia has vast potential for generating and balancing solar photovoltaic (PV) energy to meet future energy needs at a competitive cost. We systematically analyse renewable energy potential in Indonesia. Solar PV is identified to be an energy source whose technical, environmental and economic potential far exceeds Indonesia’s present and future energy requirements and is far larger than all other renewable energy resources combined. We estimate that electricity consumption in Indonesia could reach 9000 terawatt-hours per year by 2050, which is 30 times larger than at present. Indonesia has abundant space to deploy enough solar to meet this requirement, including on rooftops, inland reservoirs, mining wasteland, and in combination with agriculture. Importantly, Indonesia has a vast maritime area that almost never experiences strong winds or large waves that could host floating solar capable of generating >200,000 terawatt-hours per year. Indonesia also has far more off-river pumped hydro energy storage potential than required for balancing solar generation. Full article
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Article
VxG Pattern-Based Analysis and Battery Deterioration Diagnosis
Energies 2021, 14(17), 5422; https://0-doi-org.brum.beds.ac.uk/10.3390/en14175422 - 31 Aug 2021
Abstract
This paper presents the results of an analysis using the direct current internal resistance (DCIR) method on a nickel-cobalt-manganese oxide (NCM)-based battery with a nominal capacity of 55.6 Ah. The accelerated degradation test was performed on V0G, V1G, and V2G patterns, representing existing [...] Read more.
This paper presents the results of an analysis using the direct current internal resistance (DCIR) method on a nickel-cobalt-manganese oxide (NCM)-based battery with a nominal capacity of 55.6 Ah. The accelerated degradation test was performed on V0G, V1G, and V2G patterns, representing existing simple power supply, smart charging control, and bi-directional charge/discharge control, respectively. We assumed V0G, V1G, and V2G patterns and conducted charging and discharging experiments according to the set conditions. According to the pattern repetition, changes in the internal resistance of DCIR and AC-impedance were analyzed and battery deterioration was diagnosed. By comparing DCIR and AC-impedance, we confirmed that the changes in internal resistance has a similar trend. In particular, we propose a new DCIR analysis method in the “stop-operation” part rather than the traditional DCIR method. In the case of traditional DCIR method, time is required for the battery to stabilize. However, the newly proposed DCIR analysis method has the advantage of diagnosing the deterioration of the battery during system operation by analyzing the internal resistance without the stabilization time of the battery. Full article
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Article
Operation Method of a Load Test Device Using an Energy Storage System for Site Acceptance Test of a Fire-Fighting Emergency Generator
Energies 2021, 14(17), 5395; https://0-doi-org.brum.beds.ac.uk/10.3390/en14175395 - 30 Aug 2021
Abstract
Emergency generators are important facilities that supply emergency power to fire-fighting facilities in the event of a power outage. Accordingly, a load test of the emergency generator should be performed by cutting off the power source of the fire-fighting target in order to [...] Read more.
Emergency generators are important facilities that supply emergency power to fire-fighting facilities in the event of a power outage. Accordingly, a load test of the emergency generator should be performed by cutting off the power source of the fire-fighting target in order to accurately confirm the performance and condition of the emergency generator in normal circumstances. However, the test has usually been carried out without loads due to serious problems, which are caused by a shutdown of the power source for the load test of emergency generators, such as the shutdown of emergency load, etc. In order to overcome these problems, this paper proposes an operation method and algorithm of a load test device using ESS, which can conform to characteristics of emergency loads installed in fire-fighting targets by interconnecting it with the emergency generator. In addition, this paper performs a modeling of an emergency power system using PSCAD/EMTDC, and then this paper confirms the usefulness of the proposed method and operation algorithm of the load test device using ESS. Full article
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Review
Lithium-Ion Battery Operation, Degradation, and Aging Mechanism in Electric Vehicles: An Overview
Energies 2021, 14(17), 5220; https://0-doi-org.brum.beds.ac.uk/10.3390/en14175220 - 24 Aug 2021
Abstract
Understanding the aging mechanism for lithium-ion batteries (LiBs) is crucial for optimizing the battery operation in real-life applications. This article gives a systematic description of the LiBs aging in real-life electric vehicle (EV) applications. First, the characteristics of the common EVs and the [...] Read more.
Understanding the aging mechanism for lithium-ion batteries (LiBs) is crucial for optimizing the battery operation in real-life applications. This article gives a systematic description of the LiBs aging in real-life electric vehicle (EV) applications. First, the characteristics of the common EVs and the lithium-ion chemistries used in these applications are described. The battery operation in EVs is then classified into three modes: charging, standby, and driving, which are subsequently described. Finally, the aging behavior of LiBs in the actual charging, standby, and driving modes are reviewed, and the influence of different working conditions are considered. The degradation mechanisms of cathode, electrolyte, and anode during those processes are also discussed. Thus, a systematic analysis of the aging mechanisms of LiBs in real-life EV applications is achieved, providing practical guidance, methods to prolong the battery life for users, battery designers, vehicle manufacturers, and material recovery companies. Full article
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Article
Solar-Based DG Allocation Using Harris Hawks Optimization While Considering Practical Aspects
Energies 2021, 14(16), 5206; https://0-doi-org.brum.beds.ac.uk/10.3390/en14165206 - 23 Aug 2021
Abstract
The restructuring of power systems and the ever-increasing demand for electricity have given rise to congestion in power networks. The use of distributed generators (DGs) may play a significant role in tackling such issues. DGs may be integrated with electrical power networks to [...] Read more.
The restructuring of power systems and the ever-increasing demand for electricity have given rise to congestion in power networks. The use of distributed generators (DGs) may play a significant role in tackling such issues. DGs may be integrated with electrical power networks to regulate the drift of power in the transmission lines, thereby increasing the power transfer capabilities of lines and improving the overall performance of electrical networks. In this article, an effective method based on the Harris hawks optimization (HHO) algorithm is used to select the optimum capacity, number, and site of solar-based DGs to reduce real power losses and voltage deviation. The proposed HHO has been tested with a complex benchmark function then applied to the IEEE 33 and IEEE 69 bus radial distribution systems. The single and multiple solar-based DGs are optimized for the optimum size and site with a unity power factor. It is observed that the overall performance of the systems is enhanced when additional DGs are installed. Moreover, considering the stochastic and sporadic nature of solar irradiance, the practical size of DG has been suggested based on analysis that may be adopted while designing the actual photovoltaic (PV) plant for usage. The obtained simulation outcomes are compared with the latest state-of-the-art literature and suggest that the proposed HHO is capable of processing complex high dimensional benchmark functions and has capability to handle problems pertaining to electrical distribution in an effective manner. Full article
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Article
Comprehensive Modeling and Control of Grid-Connected Hybrid Energy Sources Using MPPT Controller
Energies 2021, 14(16), 5142; https://0-doi-org.brum.beds.ac.uk/10.3390/en14165142 - 20 Aug 2021
Abstract
Nuclear and renewables energies are the two variants for low-carbon energy and the evolving grid suggests possible synergies between them. Nuclear energy introduces supple operations based on power demand, while renewables such as PV and wind hybrid systems depend on the presence and [...] Read more.
Nuclear and renewables energies are the two variants for low-carbon energy and the evolving grid suggests possible synergies between them. Nuclear energy introduces supple operations based on power demand, while renewables such as PV and wind hybrid systems depend on the presence and strength of sunlight or wind. For grid stability, there is need to improve their performance in order to overcome the impact of this disadvantage. The paper is a step in this direction as it addresses a detailed comprehensive dynamic modeling and an efficient control of grid-connected energy sources such as PV or wind system to increase system reliability and to ensure the power quality and safe operation of critical demands. The behavior of the suggested hybrid system is tested at different climate circumstances such as variation of sun radiation and wind speed. The PV is equipped with a boost converter and a three-phase pulse width modulation (PWM) inverter. The wind energy comprises a doubly fed generator (DFIG) based on a variable-speed wind turbine. The two controllers’ rotor-side and grid-side converters of DFIG have the ability to generate and observe reactive power, to keep constant speed of the rotor and control the DC-link voltage. The proposed scheme was investigated using MATLAB software. The maximum power point tracking (MPPT) was used for two systems, PV and wind, in varying weather conditions. The simulation results prove that the voltage at the point of common coupling was constant. Furthermore, the injected current of the grid side was in sinusoidal form and was synchronized with grid side voltage. In addition, the injected power-to-utility grid was around power delivered by the hybrid PV and wind system. Full article
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Article
Heat and Mass Transfer Analysis in Chemically Reacting Flow of Non-Newtonian Liquid with Local Thermal Non-Equilibrium Conditions: A Comparative Study
Energies 2021, 14(16), 5019; https://0-doi-org.brum.beds.ac.uk/10.3390/en14165019 - 16 Aug 2021
Abstract
In the current paper, we endeavour to execute a numerical analysis in connection with the boundary layer flow induced in a non-Newtonian liquid by a stretching sheet with heat and mass transfer. The effects of chemical reactions and local thermal non-equilibrium (LTNE) conditions [...] Read more.
In the current paper, we endeavour to execute a numerical analysis in connection with the boundary layer flow induced in a non-Newtonian liquid by a stretching sheet with heat and mass transfer. The effects of chemical reactions and local thermal non-equilibrium (LTNE) conditions are considered in the modelling. The LTNE model is based on energy equations, and provides unique heat transfer for both liquid phases. As a result, different temperature profiles for both the fluid and solid phases are used in this work. The model equation system is reduced by means of appropriate similarity transformations, which are then numerically solved by employing the classical Runge–Kutta (RK) scheme along with the shooting method. The resultant findings are graphed to show the effects of various physical factors on the involved distributions. Outcomes reveal that Jeffrey fluid shows improved velocity for lower values of porosity when compared to Oldroyd-B fluid. However, for higher values of porosity, the velocity of the Jeffery fluid declines faster than that of the Oldroyd-B fluid. Jeffery liquid shows improved fluid phase mass transfer, and decays more slowly than Oldroyd-B liquid for higher values of chemical reaction rate parameter. Full article
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Article
Design of Dual Ultra–Wideband Band–Pass Filter Using Stepped Impedance Resonator λg/4 Short Stubs and T–Shaped Band-Stop Filter
Electronics 2021, 10(16), 1951; https://0-doi-org.brum.beds.ac.uk/10.3390/electronics10161951 - 13 Aug 2021
Abstract
Portable wireless communication systems are increasingly in demand in small sizes for human convenience. In wireless communication systems, the performance, size, and unit cost are very important. A band−pass filter is important to sharp cut–off frequency characteristics, size, and frequency selectivity in wireless [...] Read more.
Portable wireless communication systems are increasingly in demand in small sizes for human convenience. In wireless communication systems, the performance, size, and unit cost are very important. A band−pass filter is important to sharp cut–off frequency characteristics, size, and frequency selectivity in wireless communication systems. The band−pass filter has three types of techniques in the transmission−zero method, stub−loaded resonator, and stepped impedance resonator for the sharp cut−off frequency characteristic, adjustable bandwidth, and excellent frequency response characteristics. To obtain these characteristics, the impedance ratio and length of a stub are mainly adjusted. It also utilizes a multi–mode technique to increase bandwidth. However, it is analyzed that the problem of reducing the size of the device still remains. To solve these problems, the paper is applied to a stub−loaded resonator and a stepped impedance resonator to control the impedance ratio and the length of the stub to obtain the results of the transmission−zero method, bandwidth control, and size reduction through the folded structure. Dual−band bandwidth was secured by integrating a T−shaped band−stop filter. The designed band–pass filter has center frequencies of 243 GHz and 7.49 GHz, and the insertion loss of a proposed band−pass filter is 0.102 dB and 0.103 dB. Additionally, the return loss of a proposed band−pass filter is 19.13 dB and 19.96 dB, respectively. The bandwidth of a filter is 120% and 105%, respectively. The size of the filter is 0.0708 λg × 0.0533 λg. The designed filter has a good skirt phenomenon, small size, low insertion loss, and dual−band characteristics. Full article
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Article
Complementary Optimization of Hydropower with Pumped Hydro Storage–Photovoltaic Plant for All-Day Peak Electricity Demand in Malawi
Energies 2021, 14(16), 4948; https://0-doi-org.brum.beds.ac.uk/10.3390/en14164948 - 12 Aug 2021
Abstract
Solar energy is currently dispatched ahead of other renewable energy sources. For the first time, this study presents a concept of exploiting temporary–periodical runoff discharge in the Shire River. Pumped hydro storage–photovoltaic plant (PHS–PV) was optimized to satisfy the all-day peak electricity demand [...] Read more.
Solar energy is currently dispatched ahead of other renewable energy sources. For the first time, this study presents a concept of exploiting temporary–periodical runoff discharge in the Shire River. Pumped hydro storage–photovoltaic plant (PHS–PV) was optimized to satisfy the all-day peak electricity demand in Malawi. The effect of varying the net head on the PHS system in both the generation and pumping operation modes was investigated. The bi-objective optimization evaluated the system reliability for day-time and night-time operation together with implied costs of investment for the whole system. The optimized system generated above 53% of added power as contrasted to single-source power generation from the existing hydropower plants. The estimated optimal capacities were 182 MWp (solar PV) and 86 MW (PHS plant). These additional optimal capacities achieved a 99.8% maximum system reliability (Loss of Power Supply Probability—LPSP—of 0.2%) and Levelized Cost of Energy—LCOE—of 0.13 USD/kWh. The overall investment cost of the PHS–PV system was estimated at 671.23 USD for an LPSP of 0.20%. The net head varies from 15.5 to 17.8 m with an impact on electricity generation of the PHS–PV system. More notably, the PHS–PV production matches with daily day-time and night-time peak loads and functions as a peaking plant. Full article
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Article
Energy Management of Hybrid UAV Based on Reinforcement Learning
Electronics 2021, 10(16), 1929; https://0-doi-org.brum.beds.ac.uk/10.3390/electronics10161929 - 11 Aug 2021
Abstract
In order to solve the flight time problem of Unmanned Aerial Vehicles (UAV), this paper proposes a set of energy management strategies based on reinforcement learning for hybrid agricultural UAV. The battery is used to optimize the working point of internal combustion engines [...] Read more.
In order to solve the flight time problem of Unmanned Aerial Vehicles (UAV), this paper proposes a set of energy management strategies based on reinforcement learning for hybrid agricultural UAV. The battery is used to optimize the working point of internal combustion engines to the greatest extent while solving the high power demand issues of UAV and the response problem of internal combustion engines. Firstly, the decision-making oriented hybrid model and UAV dynamic model are established. Owing to the characteristics of the energy management strategy (EMS) based on reinforcement learning (RL), which is an intelligent optimization algorithm that has emerged in recent years, the complex theoretical formula derivation is avoided in the modeling process. In terms of the EMS, a double Q learning algorithm with strong convergence is adopted. The algorithm separates the state action value function database used in derivation decisions and the state action value function-updated database brought by the decision, so as to avoid delay and shock within the convergence process caused by maximum deviation. After the improvement, the off-line training is carried out with a large number of flight data generated in the past. The simulation results demonstrate that the improved algorithm can show better performance with less learning cost than before by virtue of the search function strategy proposed in this paper. In the state space, time-based and residual fuel-based selection are carried out successively, and the convergence rate and application effect are compared and analyzed. The results show that the learning algorithm has stronger robustness and convergence speed due to the appropriate selection of state space under different types of operating cycles. After 120,000 cycles of training, the fuel economy of the improved algorithm in this paper can reach more than 90% of that of the optimal solution, and can perform stably in actual flight. Full article
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Article
Dissociation and Combustion of a Layer of Methane Hydrate Powder: Ways to Increase the Efficiency of Combustion and Degassing
Energies 2021, 14(16), 4855; https://0-doi-org.brum.beds.ac.uk/10.3390/en14164855 - 09 Aug 2021
Abstract
The interest in natural gas hydrates is due both to huge natural reserves and to the strengthened role of environmentally friendly energy sources conditioned by the deterioration of the global environmental situation. The combustion efficiency increase is associated with the development of understanding [...] Read more.
The interest in natural gas hydrates is due both to huge natural reserves and to the strengthened role of environmentally friendly energy sources conditioned by the deterioration of the global environmental situation. The combustion efficiency increase is associated with the development of understanding of both the processes of dissociation and combustion of gas hydrates. To date, the problems of dissociation and combustion have, as a rule, been considered separately, despite their close interrelation. Usually, during combustion, there is a predetermined methane flow from the powder surface. In the present paper, the combustion of methane hydrate is simulated taking into account the non-stationary dissociation process in the powder layer. Experimental studies on the methane hydrate dissociation at negative temperatures have been carried out. It is shown that due to the increase in the layer temperature and changes in the porosity of the layer over time, i.e., coalescence of particles, the thermal conductivity of the layer can change significantly, which affects the heat flux and the dissociation rate. The flame front velocity was measured at different external air velocities. The air velocity and the vapor concentration in the combustion zone are shown to strongly affect the combustion temperature, flame stability and the flame front velocity. The obtained results may be applied to increase the efficiency of burning of a layer of methane hydrate powder, as well as for technologies of degassing the combustible gases and their application in the energy sector. Full article
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Article
The Network Topology Metrics Contributing to Local-Area Frequency Stability in Power System Networks
Energies 2021, 14(15), 4643; https://0-doi-org.brum.beds.ac.uk/10.3390/en14154643 - 30 Jul 2021
Cited by 1
Abstract
The power system network topology influences the system frequency response to power imbalance disturbances. Here, the objective is to find the network metric(s) contributing to frequency transient stability. The graph Laplacians of six 4-node network topologies are analysed using Spectral Graph Theory. For [...] Read more.
The power system network topology influences the system frequency response to power imbalance disturbances. Here, the objective is to find the network metric(s) contributing to frequency transient stability. The graph Laplacians of six 4-node network topologies are analysed using Spectral Graph Theory. For homogeneous network connections, we show that the node degree measure indicates node robustness. Based on these analytical results, the investigation expands to a 10-node network topology consisting of two clusters, which provide further insight into the spectral results. The research then involves a simulation of a power imbalance disturbance on three 20-node networks with different topologies based on node degree, where we link the node degree measure to imbalance disturbance propagation through Wave Theory. The results provide an intuitive understanding of the impact of network topology on power system frequency stability. The analytical and simulation results indicate that a node’s sensitivity to disturbances is partially due to its node degree, reactance from disturbance location, and the link it has to other higher degree nodes (hierarchical position in network topology). Testing of the analytical and simulation results takes place on the nonhomogeneous IEEE-14 bus and IEEE-39 bus networks. These results provide insights into optimal inertia placement to improve the frequency robustness of low-inertia power systems. The network topology, considering node degrees, influences the speed at which the disturbance impact propagates from the disturbance location and how fast-standing waves form. The topology thus contributes to how fast the energy in a disturbance dissipates to zero. Full article
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