Decrease In System Efficiency Research Articles

Power loss minimization by optimal allocation and sizing of STATCOM via particle swarm optimization

The provision of electricity is problematic in remote and rural areas. The distribution system is insufficiently efficient to provide rural areas with electricity. Long distance between the power supply and rural areas is the reason why there is insufficient electricity. Static synchronous compensator (STATCOM) technology is one of the solutions that have more positive effects, such as reducing power losses, and can therefore increase the system’s efficacy. However, the non-optimal allocation and magnitude of STATCOM may increase losses and have a negative impact on power, resulting in a decrease in system efficiency. This paper introduces the Particle Swarm Optimization (PSO) algorithm as the proposed algorithm to optimize the location and capacity of STATCOM in order to reduce power losses in the distribution system. The proposed technique is implemented on a 15-bus IEEE system and simulated using the MATLAB program. The simulation results demonstrate that the optimal location and quantity of the STATCOM proposed by PSO effectively reduces power loss by 6.058% compared to without PSO implementation.

High-Misalignment Tolerance and Output Adjustable Wireless Charging System via Detuned Series–Series Compensated Reconfigurable Transmission Channels

This paper proposes a wireless charging system (WCS) with two reconfigurable transmission channels to achieve constant current/voltage (CC/CV) charging, anti-misalignment solid ability, and zero voltage switching (ZVS) operation. First, the structure design and working principle of the orthogonal magnetic coupler (OMC) are given. The OMC's parameters are optimized using the orthogonal experimental design. Then, the coupling performance of OMC is illustrated by Ansys simulations. Second, the topology and principle of the designed WCS are analyzed. The relationship between charging controllability, misalignment performance, and system parameters is presented. The design method and working principle of the magnetic flux controllable inductor (MFCI) used as the power adjustment circuit and auxiliary improvement of anti-misalignment ability are provided. Third, the schematic diagram and hardware of the closed-loop controller are given. The PLECS simulations verify the feasibility of using the MFCI to realize the above design goals. Finally, an experimental prototype of an unmanned aerial vehicle (UAV) is built to validate the method's feasibility. When the maximum charging power is 126 W, the maximum system efficiency is 91.6%. Besides, assuming system efficiency decreases by 5% from the maximum value, the maximum horizontal misalignment ratio is 42%, corresponding to a desired approximately circular charging region.

Experimental validation of passive and active fault-tolerant controls against sensor faults in a proton exchange membrane fuel cell system

A fuel-cell system is interconnected with subsystems such as the stack, thermal/water management systems, air/fuel supply systems, and inverter; if an abnormality occurs, operational efficiency and availability of the entire system can decrease. However, when faults occur in the system, terminating system operations or replacing faulty parts every time can be expensive and inefficient. Instead, appropriate decision-making is required, with fault-tolerant control considered an appropriate solution. This study presents methods and criteria for fault-tolerant control when a fault occurs in a proton exchange membrane fuel cell (PEMFC) system. By configuring a 1 kW residential PEMFC system, a fault occurring in either the thermocouple or mass flow meters – targets for the system control – is diagnosed, and real-time control change is performed instead of immediately repairing the sensor. This approach enables stable and continuous operation of the PEMFC system. The fault-tolerant control method consists of either the feed-back control method, using the real-time predicted value of each control sensor, or the feed-forward method, using the constant control-signal value learned in the normal state; the advantages and limitations of each method are compared. Futhermore, considering the system efficiency, stack durability, and operating control deterioration, a guideline is suggested for applying fault-tolerant control and improving its corresponding effectiveness. For example, fault-tolerant control can resolve a 4.6% decrease in system efficiency caused by a thermocouple fault. This study contributes to improving the system operation rate and reliability by applying fault-tolerant control, thus facilitating efficient decision-making following fault diagnosis.

Explaining the decline of US wind output power density

US wind power generation has grown significantly over the last decades, in line with the number and average size of operating turbines. However, wind power density has declined, both measured in terms of wind power output per rotor swept area as well as per spacing area. To study this effect, we present a decomposition of US wind power generation data for the period 2001–2021 and examine how changes in input power density and system efficiency affected output power density. Here, input power density refers to the amount of wind available to turbines, system efficiency refers to the share of power in the wind flowing through rotor swept areas which is converted to electricity and output power density refers to the amount of wind power generated per rotor swept area. We show that, while power input available to turbines has increased in the period 2001–2021, system efficiency has decreased. In total, this has caused a decline in output power density in the last 10 years, explaining higher land-use requirements. The decrease in system efficiency is linked to the decrease in specific power, i.e. the ratio between the nameplate capacity of a turbine and its rotor swept area. Furthermore, we show that the wind available to turbines has increased substantially due to increases in the average hub height of turbines since 2001. However, site quality has slightly decreased in this period.

Design and Performance Analysis of a Novel Integrated Solar Combined Cycle (ISCC) with a Supercritical CO2 Bottom Cycle

The integrated solar combined cycle (ISCC) system is a proven solution for grid-connected power generation from solar energy. How to further improve the ISCC system efficiency and propose a more efficient system solution has become a research focus. A novel gas turbine combined cycle (GTCC) benchmark system is proposed by replacing the conventional steam Rankine bottom cycle with a supercritical CO2 Brayton cycle, whose output power and efficiency are increased by 9.07 MW and 1.3%, respectively, compared to those of the conventional GTCC system. Furthermore, the novel ISCC systems are established with the parabolic trough solar collector (PTC) and the solar tower (ST) collector coupled to the novel GTCC system. Thermal performance analysis, exergy performance analysis, and the sensitivity analysis of the ISCC systems have been performed, and the results show that the system efficiencies of both ISCC systems are lower than that of the GTCC system, at 57.1% and 57.5%, respectively, but the power generation of the ISCC system with PTC is greater than that of the benchmark system, while that of the ISCC system with ST is less than that of the benchmark system. The photoelectric efficiency of the ISCC system with PTC is 27.6%, which is 2.1% greater than that of ISCC system with ST. In the ISCC system with PTC, the components with the highest exergy destruction and the lowest exergy efficiency are the combustion chamber, and PTC, respectively. ST is the component with the highest exergy destruction and the lowest exergy efficiency in the ISCC system with ST. With the increase in direct normal irradiance (DNI), the total output power, solar energy output power, and photoelectric efficiency of the ISCC system with PTC increase, while the system efficiency decreases; the solar energy output power and photoelectric efficiency of the ISCC system with ST increase, while the total output power and system efficiency decrease. The photoelectric efficiency of the ISCC system with PTC is greater when the DNI is greater than 600 W/m2; conversely, the photoelectric efficiency of the ISCC system with ST is greater. After sensitivity analysis, the optimal intercooler pressure for the ISCC system is 11.3 MPa.

Performance analysis of a novel solar assisted ground source heat pump water heating system with graded thermal energy storage

The solar assisted ground source heat pump system (SAGSHP) is recognized as an efficient, clean and economical renewable energy technology for hot water supply. However, in SAGSHP systems with an all-day hot water supply, the solar collectors can only heat the water tank with intense solar radiation, which wastes moderate and weak solar resources. In addition, as the SAGSHP system draws heat from the soil for a long time, the soil temperature around the borehole decreases, causing the performance of the GSHP to deteriorate. To solve the above problems, a SAGSHP system with graded thermal energy storage (SAGSHP-GTES) was proposed. This paper investigated the performance and feasibility of the SAGSHP-GTES system, using a case study of hot water supply in a campus dormitory in Changsha, China. Firstly, the drawbacks of solar energy utilization in the conventional SAGSHP system were analyzed. Then, the SAGSHP-GTES system was modeled by TRNSYS, and its operational performance was evaluated and compared with the conventional SAGSHP system. Finally, the feasibility and performance of the SAGSHP-GTES system in different climate zones of China were analyzed. The results showed that the conventional SAGSHP system had a poor solar energy utilization efficiency, with an average thermal efficiency of the SC (ηSC) of only around 19.4%. The long period of operation caused the soil temperature to drop from 18.1 °C to 2.78 °C, which led to a decrease in system efficiency and an increase in electricity consumption. By controlling the heat collection of the SC and the graded utilization of solar energy in the SAGSHP-GTES system, a high ηSC of around 42.7% was obtained, which improved the system efficiency while eliminating the problem of soil temperature drop. After 15 years of operation, the soil temperature increased from 18.1 °C to 19.9 °C, which led to an increase in the coefficient of performance of the system (COPsys) from 3.77 kW/kW to 3.84 kW/kW and COPGSHP from 3.45 kW/kW to 3.5 kW/kW, and a reduction in electricity consumption from 51,746 kWh to 50,735 kWh. In addition, the conventional SAGSHP system was not feasible in severe cold zones (Harbin) and cold zones (Beijing) of China, where soil temperatures fell below 0 °C and freezing of the circulating fluid occurred, while the SAGSHP-GTES system showed excellent performance in all climatic zones of China and is a feasible and efficient technology for hot water supply.

An Efficiency Optimization Method Based on Double Side Impedance Angle Design for Wireless Power Transfer System

Wireless power transfer (WPT) system has already been applied to battery charging occasions, and the charging process can be roughly divided into two stages: constant current mode (CCM) and constant voltage mode (CVM). In CVM, researchers always focus on the effect of the primary phase angle (PPA) on the system efficiency but rarely pay attention to secondary phase angle (SPA). A large SPA will also lead to a decrease of system efficiency, which should be worth more attention and consideration when designing the system parameter. The double-sided <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LCC</i> compensation topology can not only achieve constant current or constant voltage output at different frequencies but also has the advantage of high parameter design freedom, so it is very suitable for battery charging scenarios. Considering the influence of the PPA and SPA on the system efficiency, a novel parameter design method based on double-sided <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LCC</i> compensation topology is proposed in this article. By changing the system operating frequency, the switching between CCM and quasi-constant voltage mode (QCVM) is realized. In order to verify the feasibility and practical effect of the parameter design method, an experimental prototype based on a planar square coil was established and three groups of comparative experiments were conducted. The experimental results show that the optimized WPT system efficiency is significantly improved under the same power level. The maximum output power of the system is 620 W. When the optimized system works in CCM and QCVM, the maximum efficiency is about 95%.

Performance analysis and optimization of combined heat and power system based on PEM fuel cell and [formula omitted] type Stirling engine

In this study, a new arrangement of a combined heat and power (CHP) system is proposed, which is designed based on a dual-prime mover of proton exchange membrane (PEM) fuel cell and β type Stirling engine. By using this CHP system based on Stirling engine and fuel cell in hybrid form, the potential of performance improbvement of the system can be analyzed and the appropriate operation condition compared to using the CHP system based on one prime mover can be achieved.Also, two suitable thermodynamic models have been used for modeling the fuel cell and Stirling engine from energy, environmental and economic issues. In addition, the effects of Stirling engine speed, temperature, and fuel cell current density on power, electrical efficiency, CHP efficiency, fuel cost savings, the amount of annual CO2 emission reduction (ACO2ER) and payback period have been investigated for the CHP system. Then, an optimization method has been performed with the help of a two-objective genetic algorithm and the TOPSIS methods, and several optimal cases from different viewpoints of the CHP system are presented. The modeling results showed that to increase the CHP system's efficiency, the engine speed should be in the range of 1500 rpm and to increase the system's capacity, a higher engine speed should be used. Also, based on the payback period analysis, the system has higher economic performance at a higher rotational speed.I addition, increasing the fuel cell's temperature increases the system's power and electrical efficiency. The system's capacity increases with the current density, but the system's efficiency decreases. The optimization results showed that the engine speed, the fuel cell temperature, and the current density are recommended to be 3000 rpm, 94.5 °C, and 0.67 A cm−2, respectively. Suppose the main goal is to maximize the CHP efficiency and ACO2ER simultaneously, the CHP system should be started with a slightly lower engine speed of around 2126 rpm, a lower temperature of around 70.11 °C and a higher current density of around 0.93 A cm−2.

ANALYSIS OF PERFORMANCE COEFFICIENTS IN MAXIMUM ELECTRICAL POWER EXTRACTION FROM STAND-ALONE WIND ENERGY CONVERSION SYSTEM

Increasing performance and improving efficiency in maximum power extraction from Wind Energy Conversion Systems (WECS) is a quite important research topic. Today, in the large-scale WECS, it is widely aimed to extract the maximum mechanical power from the wind turbine using the Maximum Power Point Tracking (MPPT) unit. Similarly, it can also be targeted to achieve maximum mechanical power in small-scale WECS applications. However, losses occur in structural subsystems and electrical subunits located in WECS. Due to these losses, the overall system efficiency decreases and the characteristic of the system is also affected. The operation of these systems can also be performed via maximum electrical output power extraction, which is one of the most up-to-date ideas. Thus, the overall WECS rather than the wind turbine can be optimally controlled. Eventually, maximum electrical power tracking (MEPT) based designs can provide higher power extraction with higher efficiency than MPPT-based ones. In this paper, considering the system operating concepts with MPPT and MEPT for a stand-alone Permanent Magnet Synchronous Generator (PMSG) based WECS, the changes in performance coefficients at defined focus points in terms of system efficiency are evaluated. Technical and theoretical comparative analyzes are also made for each specific wind speed between 8m/s and 12m/s.

Automatic Placement of Visual Sensors in a Smart Space to Ensure Required PPM Level in Specified Regions of Interest.

This work is devoted to a cost-effective method for the automatic placement of visual sensors within a smart room to ensure the requirements for its design. Various unique conditions make the process of manually placing sensors time consuming and can also lead to a decrease in system efficiency. To automate the design process, we solve a multi-objective optimization problem known as the art gallery problem in 3D, modified as follows. For the specified regions of interest within a smart room, the required pixels per meter level (PPM) should be ensured. The optimization criteria are visibility of the room and the cost of equipment. To meet these criteria, we describe a room model with doors, windows, and obstacles represented in such a way as to consider their impact on the field of view of the sensors. To model sensor placement, a genetic algorithm is used. The optimal solution is selected from the Pareto front by means of the technique for order of preference by similarity to ideal solution (TOPSIS). The developed method’s effectiveness has been tested on modeling real premises of various types. The method is flexible because of the assignment of weights to certain aspects when placing sensors. Further, it can be scalable to other types of sensors.

Heat to Hydrogen by Reverse Electrodialysis—Using a Non-Equilibrium Thermodynamics Model to Evaluate Hydrogen Production Concepts Utilising Waste Heat

The reverse electrodialysis heat engine (REDHE) is a promising salinity gradient energy technology, capable of producing hydrogen with an input of waste heat at temperatures below 100 °C. A salinity gradient drives water electrolysis in the reverse electrodialysis (RED) cell, and spent solutions are regenerated using waste heat in a precipitation or evaporation unit. This work presents a non-equilibrium thermodynamics model for the RED cell, and the hydrogen production is investigated for KCl/water solutions. The results show that the evaporation concept requires 40 times less waste heat and produces three times more hydrogen than the precipitation concept. With commercial evaporation technology, a system efficiency of 2% is obtained, with a hydrogen production rate of 0.38 gH2 m−2h−1 and a waste heat requirement of 1.7 kWh gH2−1. The water transference coefficient and the salt diffusion coefficient are identified as membrane properties with a large negative impact on hydrogen production and system efficiency. Each unit of the water transference coefficient in the range tw=[0–10] causes a −7 mV decrease in unit cell electric potential, and a −0.3% decrease in system efficiency. Increasing the membrane salt diffusion coefficient from 10−12 to 10−11 leads to the system efficiency decreasing from 2% to 0.6%.

Off-design modeling and performance analysis of supercritical compressed air energy storage systems with packed bed cold storage

Supercritical compressed air energy storage (SC-CAES) systems have particular merits of both high efficiency and high energy density. In SC-CAES systems, the use of packed bed cold storage has plentiful advantages of simple structure, safety and reliability. However, the previous studies of packed bed models traditionally adopted the assumption of uniform flow which is not applicable in cold storage actually. Meanwhile, the coupling relationship between the dynamic behavior of packed bed and the operation performance of other system parts is not clear. Aiming at the above issues, a detailed revised packed bed model is developed, and the calculation model of off-design characteristics of SC-CAES system is established. Besides, the evaluation indexes of system efficiency considering the changes of mass and energy in the packed bed are established. With the above models, the temperature distribution in the packed bed is deeply analyzed, and the off-design characteristics of SC-CAES system are revealed comprehensively on the conditions that the thermocline is steep and flat, respectively. Results show that the temperature difference under flat thermocline condition is much smaller than that under the steep thermocline condition, which makes the system efficiency corresponding to the flat thermocline achieve 13.4 percentage points higher than the other one. Due to the uneven mass distribution in the packed bed, the mass flow rate of liquid expander/cryopump is greater than that of compressor/expander. When the ambient temperature increases by 10 K, the system efficiency decreases by 0.5–0.75 percentage points on average. The fluctuating load has slight impact on the system efficiency.

Effect of seawater temperature rising to the performance of Northern Gorontalo small scale power plant

The change of seawater temperature is suspected to affect the power plant condenser’s overall performance. In this paper, we present a gate cycle model of the Northern Gorontalo steam power plant system to investigate the effect of the seawater temperature variation used as the condenser cooling medium on the performance of the steam power plant. The model shows that the power plant can still achieve the required power output even when a significant change in the temperature occurs. Based on the gate cycle model, higher seawater temperatures result in smaller values of the generated power and efficiency of the steam power plant and an increased condenser’s load. This finding is consistent with the reported increased production cost of electrical energy. We have found that an increase in seawater temperature of 2.5 °C results in a 0.33% decrease in system efficiency compared to the reference value.

Study on the coupling properties of hydrogen PEMFC and air source heat pump

Abstract A steady-state model for the coupling of a proton exchange membrane fuel cell and an air source heat pump (PEMFC–ASHP) is established in this paper. The influence of reaction pressure and relative humidity on the polarization curve and operating characteristics of PEMFC, as well as the influence of ambient temperature and compressor speed on the system performance are investigated. The results show that the increase of reaction pressure and relative humidity is conducive to the improvement of fuel cell output voltage and efficiency, and the influence of reactant gas relative humidity is more obvious. As the increase of ambient temperature and compressor speed, the heat pump efficiency and system efficiency decrease. The research results can provide theoretical guidance for the design and operation of the PEMFC–ASHP system.

Coupling impacts of SOFC operating temperature and fuel utilization on system net efficiency in natural gas hybrid SOFC/GT system

The major design parameters of SOFC have great impacts on the net electrical efficiency of SOFC/GT hybrid systems. The influence of the SOFC operating temperature and fuel utilization on the net efficiency of a pressurized solid oxide fuel cell gas turbine hybrid system was studied in this paper. The system model was combined a 1D SOFC model, which included a lumped equilibrium steam methane reformer model in the Simulink, with a gas turbine recuperated cycle model in Ebsilon®. A system design point study was established to observe the coupling impacts of SOFC operating temperature and fuel utilization on the system performance. Thirty design cases of SOFC operating temperatures (635 °C–835 °C) over a range of SOFC fuel utilization(45%–90%) were evaluated. The optimal SOFC fuel utilization shifted from 65% to 55% when the SOFC operating temperature decreased from 835 °C to 635 °C. The maximal(minimal) system efficiency was 74%(49%) at 65%(90%) SOFC fuel utilization with operating SOFC at 835 °C(635 °C). The results show that high operating temperature leads to the high efficiency of the entire hybrid system, but high fuel utilization might cause a decrease in system efficiency.

Unsteady characteristics of compressed air energy storage systems with thermal storage from thermodynamic perspective

Unsteady characteristics of compressed air energy storage (CAES) systems are critical for optimal system design and operation control. In this paper, a comprehensive unsteady model concerning thermal inertia and volume effect for CAES systems with thermal storage (TS-CAES) is established, in which exergy efficiencies of key processes at each time are focused on to follow performance trajectories, and the control for sliding-pressure and constant-pressure operations is introduced. Meanwhile, a revised system efficiency model is proposed with energy transfer involved in joint chamber between components. Based on the model, the unsteady characteristics of charging process and discharging process of TS-CAES are first studied in depth. The difference between system performance under unsteady and steady operation is discovered, and the influence of unsteady factors, such as volume effect, thermal inertia, air reservoir size and pressure variation range on the system efficiency of TS-CAES system is studied for the first time. Results show that the unsteady effect has evident impact on the variation of operating parameters. For the whole system, the stronger the unsteady effect is, the less system efficiency and energy density are, while the thermal inertia having slight effect on system efficiency. The large air storage reservoir is beneficial to weaken volume effect's influence on system efficiency. The study of pressure-range effect indicates that the system efficiency decreases by an average of 0.95% with the maximum relative storage pressure increasing by 0.1, while the system efficiency decreases about 0.35% with the minimum relative storage pressure decreasing by 0.2.

Evolution in diagnosis and detection of brain tumor – review

Diagnosis of Brain tumor at an early stage has became an important topic of research in recent time. Detection of tumor at an early stage for primary treatment increases the patient’s survival rate. Processing of Magnetic resonance image (MRI) for an early tumor detection face the challenge of high processing overhead due to large volume of image input to the processing system. This result to large delay and decrease in system efficiency. Hence, the need of an enhanced detection system for accurate segmentation and representation for a faster and accurate processing has evolved in recent past. Development of new approaches based on improved learning and processing for brain tumor detection has been proposed in recent literatures. This paper outlines a brief review on the developments made in the area of MRI processing for an early diagnosis and detection of brain tumor for segmentation, representation and applying new machine learning (ML) methods in decision making. The learning ability and fine processing of Machine learning algorithms has shown an improvement in the current automation systems for faster and more accurate processing for brain tumor detection. The current trends in the automation of brain tumor detection, advantages, limitations and the future perspective of existing methods for computer aided diagnosis in brain tumor detection is outlined.

Dynamic Task Allocation Method of Swarm Robots Based on Optimal Mass Transport Theory

It is difficult for swarm robots to allocate tasks efficiently by self-organization in a dynamic unknown environment. The computational cost of swarm robots will be significantly increased for large-scale tasks, and the unbalanced task allocation of robots will also lead to a decrease in system efficiency. To address these issues, we propose a dynamic task allocation method of swarm robots based on optimal mass transport theory. The problem of large-scale tasks is solved by grouping swarm robots to complete regional tasks. The task reallocation mechanism realizes the balanced task allocation of individual robots. This paper solves the symmetric assignment between robot and task and between the robot groups and the regional tasks. Our simulation and experimental results demonstrate that the proposed method can make the swarm robots self-organize to allocate large-scale dynamic tasks effectively. The tasks can also be balanced allocated to each robot in the swarm of robots.

Simultaneous Identification and Control for Hybrid Energy Storage System Using Model Predictive Control and Active Signal Injection

A battery/supercapacitor hybrid energy storage system (HESS) is overactuated in the sense that there are two power sources providing a single power output. This feature of HESS is exploited in this article to simultaneously achieve accurate identification of the battery states/parameters and high system efficiency. By actively injecting current signals, the state of charge and state of health, together with other battery parameters, can be identified sequentially. Sufficient richness in the input (i.e., battery current) is necessary to ensure identification accuracy. Since signal richness for identification can be in conflict with efficient operation, a novel model predictive control (MPC) strategy is used to simultaneously consider both objectives to determine the optimal power distribution between supercapacitor and battery. The tradeoff between identification accuracy and system efficiency is investigated. Simulation results show that the proposed MPC can significantly improve identification accuracy at the expense of a slight decrease in system efficiency when compared to the baseline MPC, which does not consider the signal richness. Therefore, it is validated that the proposed MPC can effectively achieve simultaneous identification and efficient operation.

Techno-economic analysis of methanol and electricity poly-generation system based on coal partial gasification

The methanol and electricity poly-generation system based on coal partial gasification is proposed. Techno-economic analysis of the system is conducted by using Aspen Plus and the effects of methanol synthesis temperature and cyclic gas reflux ratio on the system performance are studied. The detailed economic data are obtained. The IGCC system is established simultaneously and compared with the poly-generation system. The results show that both methanol production and system efficiency decrease with the increase of methanol synthesis temperature. Methanol production increases while system efficiency decreases with increase of the recycle gas ratio. System efficiency would reach as high as 56.8%, while the system efficiency of IGCC is 53.11%. By the calculation of the economic data, the IRR and the payback period of the poly-generation system are 24.1% and 4.14 years, respectively. While IRR and payback period of IGCC system are 3.4% and 18.06 years, respectively. The results show that methanol and electricity poly-generation system based on coal partial gasification has a promising prospect.