Maximum Efficiency Point Research Articles

High Efficiency Drive for Micro-Turbine Generator Based on Current Phase and Revolving Speed Optimizations

This paper presents a high efficiency drive strategy for micro-turbine generator (MTG) in which permanent magnet synchronous generator (PMSG) is used. PMSG operates at maximum efficiency point by optimizing the phase of armature current of PMSG; i.e., an optimum d-axis current in the rotor reference frame is analytically derived from mathematical model of PMSG taking iron loss into account. In addition, in order to use turbine output power effectively, compressor input power is minimized by optimizing revolving speed of PMSG. Simulation results confirm validity of the proposed method.

A comprehensive study on performance, emission, and combustion characteristics of a dual-fuel engine fuelled with orange oil and Jatropha oil

Performance of a single-cylinder, water-cooled, direct-injection diesel engine on dual-fuel operation with Jatropha oil (JO) as pilot fuel and orange oil as primary fuel was evaluated. Constant load test at different power outputs was conducted at the rated speed of 1500 r/min with varying orange oil quantities. The loads were fixed as 20 per cent, 40 per cent, 60 per cent, 80 per cent, and 100 per cent. In dual-fuel operation with orange oil induction, the thermal efficiency of JO was increased mainly at high power outputs. Maximum thermal efficiency with JO was found as 29 per cent at 31 per cent of orange oil induction at 100 per cent load. Smoke was reduced significantly with all orange oil induction rates at all power outputs in dual-fuel operation with JO. It was reduced from 4.4 to 3.3 BSU (Bosch Smoke Units) with JO at the maximum efficiency point at 100 per cent load. HC emissions were increased further at all power outputs in the dual-fuel mode with all rates of orange oil induction. Dual-fuel operation increased the ignition delay of JO. However, peak pressure and energy release rates were improved in the dual-fuel operation with orange oil induction. In general, dual-fuel operation with orange oil as inducted fuel with JO as pilot fuel showed inferior performance and emissions at part loads. It is concluded that the JO as pilots fuel and orange oil as the inducted fuel could be used in diesel engines with reduced smoke levels and improved thermal efficiencies with no major detoriation in performance.

Maximum Efficiency Point Tracking Algorithm Using Oxygen Access Ratio Control for Fuel Cell Systems

The air flow supplied to a fuel cell system is one of the most significant factors in determining fuel efficiency. The conventional method of controlling the air flow is to fix the oxygen supply at an estimated constant rate for optimal efficiency. However, the actual optimal point can deviated from the pre-set value due to temperature, load conditions and so on. In this paper, the maximum efficiency point tracking (MEPT) algorithm is proposed for finding the optimal air supply rate in real time to maximize the net-power generation of fuel cell systems. The fixed step MEPT algorithm has slow dynamics, thus it affects the overall efficiency. As a result, the variable step MEPT algorithm is proposed to compensate for this problem instead of a fixed one. The complete small signal model of a PEM Fuel cell system is developed to perform a stability analysis and to present a design guideline. For a design example, a 1kW PEM fuel cell system with a DSP 56F807 (Motorola Inc) was built and tested using the proposed MEPT algorithm. This control algorithm is very effective for a soft current change load like a grid connected system or a hybrid electric vehicle system with a secondary energy source.

Topological Overview of Powertrains for Battery-Powered Vehicles With Range Extenders

The paper presents a topological overview of hybrid powertrains for battery-powered vehicles reinforced by range extenders. First, tradeoffs of employing high energy versus high power battery are revealed. Then, different topologies of battery-ultracapacitor hybrids are discussed, highlighting pros and cons of each configuration. The superiority of fully active hybrids is indicated, obtained at the expense of increase of power electronic circuitry, control effort, and efficiency. The second part of the paper focuses on two types of range extenders: renewable energy and fuel-based units. The operation strategy is shown to be different for each range extender type. The renewable-energy-based range extender should be operated employing either passive or active maximum power point tracking strategy and hence not be involved in the powertrain energy balancing. It is shown that such a strategy allows the rest of system to perceive the renewable energy range extender (RERE) as a part of the load and act accordingly. Solar array is given as an example of a RERE and the possible connection topologies are discussed. On the other hand, the fuel-based range extender (FBRE) should be operated near the lowest specific fuel consumption point employing maximum efficiency point tracking strategy. Fuel cells and internal combustion engines are specified as examples of FBREs. The complete powertrain is shown to resemble a dc microgrid with source, storage, and load units connected through power management circuitry to a common dc link.

An Adaptive Energy Storage Technique for Efficiency Improvement of Single-Stage Three-Level Resonant AC/DC Converters

The use of single-stage power-factor-corrected (SSPFC) three-level resonant ac/dc converters solves many problems that present SSPFC converters face today, namely, high component stresses, high circulating currents, and low efficiency. This makes single-stage three-level resonant ac/dc converters a good candidate for high-power applications. These converters provide the flexibility of simultaneously using two control variables. They can operate with a combined variable-frequency and asymmetrical pulsewidth modulation or with a combined variable-frequency phase-shift modulation. This provides good regulation of the output voltage, dc-bus voltage, and input current. The drawback of these methods is that the efficiency of the converter drops as the load is reduced because the converter starts to drift away from its resonance frequency, thus leading to more circulating currents and conduction losses. Therefore, a load-adaptive energy storage technique is proposed in this paper to guarantee the converter operation near its maximum efficiency point for a wide range of loading. This leads to almost constant converter efficiency from full load to 40% load. The use of interleaved converters is also proposed to extend the constant efficiency range of operation to lighter loads (15%-20% of full load). Analytical simulation and experimental results are presented to verify the proposed methods.

Research on Switched Reluctance Generator for Off-Grid Variable-Speed Wind Energy Applications

This paper presents a theoretical analysis and experimental evaluation of the switched reluctance generator (SRG) for off-grid variable-speed wind energy applications. The detailed model, control parameters and operational characteristics of the SRG as well as variable-speed wind turbine are discussed. In order to drive the wind energy conversion system (WECS) to the point of maximum aerodynamic efficiency, a SRG power output feedback control strategy which optimized angle position-current chopping control cooperating PI regulator is proposed. The control strategy is also demonstrated by means of Matlab/Simulink. Moreover, an experimental test system is set up, which a cage induction machine is used to emulate the variable-speed wind turbine. The experimental results validate the proposed control strategy and confirm the SRG performance.

Concentration effects on the efficiency, thickness and J– V characteristics of the intermediate band solar cells

The J– V characteristics and efficiency as a function of active region thickness of the p-i-n intermediate band solar cells have been calculated. We compared the maximum efficiency point of three different cells made of well-known materials. Each cell includes a different size of quantum dot from other cells in the i-region which causes a different intermediate band position in the bandgap of the host semiconductor. In addition, it is illustrated that the maximum efficiency point increases with increasing the incident light concentration in the radiative limit. This article considered that using light concentrators can be useful to enhance the efficiency of the solar cell with respect to manufacturing and cost improvements.

Optimum criteria based on different pressure ratios of an irreversible intercooled-regenerative-reheat Brayton cycle

An irreversible model of a Brayton cycle, which includes a regenerator, an intercooler, and a reheater, is presented in this paper. The power output and the thermal efficiency are optimized with respect to different pressure ratios and cycle temperatures for a typical set of operating conditions. It is found that there are optimal values of the turbine outlet temperature, reheat, intercooling, and cycle pressure ratios at which the cycle attains the maximum power output and the maximum thermal efficiency. Also, the optimal values of the above-mentioned parameters are different for different parameters. The maximum power point and the maximum efficiency point exist but the power output corresponding to the maximum efficiency is found to be lower than that which can be attained. The optimum criteria for different pressure ratios and the turbine outlet temperature corresponding to maximum power output as well as corresponding to maximum thermal efficiency are obtained and discussed in detail.

Application of cascade and fuzzy logic based control in a model of a fuel-cell hybrid tramway

This paper presents a model for a fuel cell (FC)–battery powered hybrid system for the Metro-Centro tramway (400 kW) from Seville, Spain. Modeling of each component, implemented in MATLAB/SIMULINK environment, is briefly presented. Polymer Electrolyte Membrane (PEM) FC and Ni-MH battery models are designed from commercial available components. Two control strategies are presented and tested for the energy management of the hybrid system: cascade and fuzzy logic. The objective of both strategies is to manage the primary (PEM FC) and secondary (battery) energy source to supply the power requirements of the tramway forcing the FC to work around its maximum efficiency point and maintaining the battery state of charge (SOC) in a desired level.

Organic Solar Cell Efficiencies Under the Aspect of Reduced Surface Recombination Velocities

The charge carrier mobility is a key parameter for the organic bulk heterojunction solar cell efficiency. It was recently shown that the interplay charge carrier transport and recombination, both depending on electron and hole mobilities, leads to a point of maximum power conversion efficiency at a finite mobility. Changes of bulk and surface recombination rate, however, can strongly influence this behavior. These processes were previously not considered adequately, as surface recombination velocities of infinity were implicitly assumed or bulk recombination parameters not discussed in detail. In this manuscript, using a macroscopic effective medium simulation, we consider how a reduced bulk recombination process in combination with finite surface recombination velocities affect the power conversion efficiency. Instead of a maximum efficiency at a specific charge carrier mobility, we show that with realistic assumptions and passivated surfaces the efficiency is increased further, saturating only at higher mobilities. Thus, a mobility optimisation is more important for the solar cell performance then previously shown.

Adaptive Digital Controller and Design Considerations for a Variable Switching Frequency Voltage Regulator

An auto-tuning adaptive digital controller with maximum efficiency point tracking to optimize dc-dc converter switching frequency is presented in this paper. The adaptive-frequency-optimization (AFO) controller adjusts the dc-dc converter switching frequency while tracking the converter minimum input power (maximum efficiency) point under variable operation conditions of the power converter. The AFO digital controller continuously finds the optimum switching frequency that will result in minimum total power loss while converter parameters and conditions vary. Moreover, the presented controller addresses the issues that are associated with implementing variable switching frequency in digital controllers, including limit cycle oscillation and possible performance degradation, by using a dynamic algorithm to maintain converter system stability under variable switching frequency operation. In this paper, the proposed controller is discussed, analyzed, and its digital control algorithms and experimental results are presented.

Experimental Investigations to Improve the Performance of Rubber Seed Oil–Fueled Diesel Engine by Dual Fueling with Hydrogen

In this experimental work, base data were generated with diesel and neat high free fatty acid (FFA) rubber seed oil (RSO) using a single-cylinder air-cooled diesel engine with a rated output of 4.4 kW at 1500 rpm. Neat RSO results in reduced thermal efficiency of 26.6% compared with diesel efficiency of 29.9% and high smoke emissions compared to diesel. This is mainly due to low volatility, higher viscosity, and density of RSO. In order to improve the performance of the RSO-fueled diesel engine, experiments were conducted with hydrogen as the inducted fuel and RSO as the main fuel in dual-fuel operation. Experimental results indicate that the brake thermal efficiency increases from 75% load to full load in the dual-fuel operation. At full load, the maximum brake thermal efficiency is 28.1% with RSO-hydrogen dual-fuel mode at hydrogen energy share of 8.39%. The smoke level is reduced at all loads with RSO-hydrogen dual-fuel mode. The smoke level is reduced from 6.1 to 3.8 BSU in dual-fuel operation at the maximum efficiency point at full load. Hydrogen induction reduces HC and CO at all loads, but NOx increases at 75% and full load, but there is no appreciable change at lower loads. The combustion duration decreases with hydrogen addition. This will also contribute to higher heat release rate in the premixed combustion phase. The cylinder peak pressure and maximum rate of pressure rise increases mainly at higher outputs. On the whole it is concluded that hydrogen can be inducted along with air in order to reduce smoke levels and improve thermal efficiency of rubber seed oil–fueled diesel engines for loads above part load.

An experimental study of leaning blades on the half-cone rotor of a squirrel cage fan

This article presents an improvement for the blade configuration of a squirrel cage fan. Numerical simulations have shown that a-2° lean angle applied to a half-cone rotor of+10° produces a higher efficiency. This is expected to be a result of blade alignment with the inlet stream. Performance curves in this article compare this new rotor with both a simple half cone of the same cone angle and a corresponding cylindrical rotor. The half-cone rotor with leaning blades had improved head coefficient and efficiency in the normal operating range, which is to the right of maximum head or efficiency points. The simple half-cone rotor had almost constant efficiency for all flow ranges, which is a very demanding feature for any fan. A study of velocity profiles inside the volute showed that maximum flow exited the rotor close to the cut-off. A leaning blade had negligible effect on radial and tangential components at this location but it changed the axial component. This was due to a movement of the vortex behind the inlet and a larger active region of the rotor blades.

Plasma free metanephrines are superior to urine and plasma catecholamines and urine catecholamine metabolites for the investigation of phaeochromocytoma

To compare the relative diagnostic efficacy of several different tests used to establish a diagnosis of phaeochromocytoma, in patients with a proven diagnosis of phaeochromocytoma, and in hospital patients with significant disease of other types. We prospectively compared biochemical markers of catecholamine output and metabolism in plasma and urine in 22 patients with histologically proven phaeochromocytoma, 15 intensive care unit (ICU) patients, 30 patients on chronic haemodialysis and both hypertensive (n = 10) and normotensive (n = 16) controls. Receiver operating characteristic curves were plotted. At the point of maximum efficiency, plasma free metanephrines showed 100% sensitivity and 97.6% specificity, compared with plasma catecholamines (78.6% and 70.7%), urine catecholamines (78.6% and 87.8%), urine metanephrines (85.7% and 95.1%), and urine hydroxymethoxymandelic acid (HMMA or VMA) (93.0% and 75.8%). All patients with phaeochromocytoma had plasma free metanephrine concentrations at least 27% above the upper limit of the reference range. Only three other patients (two on haemodialysis and one in ICU) had PFM concentrations more than 50% above the upper limit of the reference range. In patients with phaeochromocytoma, plasma free metanephrines displayed superior diagnostic sensitivity and specificity compared with other biochemical markers of catecholamine output and metabolism.

ケーシング幅が二重反転多翼ファンの性能に及ぼす影響(流体工学,流体機械)

A sirocco fan using contra-rotating rotors in which an inner rotor was settled inside the sirocco fan rotor and each rotor rotated in an opposite direction was proposed for the purpose of getting the higher pressure and making the structure of a sirocco fan compact more. If the high discharge pressure is obtained with the adoption of the contra-rotating rotors, it could be used for various purposes. Pressure coefficient of the sirocco fan with contra-rotating rotors was 2.4 times as high as the conventional sirocco fan and the maximum efficiency point of contra-rotating rotors shifted larger flow rate than the conventional sirocco fan. On the other hand, it was clarified from the flow measurement results that the larger back flow region than conventional one occurred at the shroud of the casing in the case of contra-rotating type and this would induce decrease of the efficiecy. In the present paper, the performance of the conventional sirocco fan and the sirocco fan with contra-rotating rotors are shown and the internal flow field at the outlet of the outer rotor of both cases is clarified Then, the effect of casing width on the performance and the internal flow field is investigated and the casing width which would be suitable for the contra-rotating type would be discussed.

Studies on dual fuel operation of rubber seed oil and its bio-diesel with hydrogen as the inducted fuel

The main problems with the use of neat vegetable oils in diesel engines are higher smoke levels and lower thermal efficiency as compared to diesel. The problem can be tackled by inducting a gaseous fuel in the intake manifold along with air. In this investigation, hydrogen is used as the inducted fuel and rubber seed oil (RSO), rubber seed oil methyl ester (RSOME) and diesel are used as main fuels in a dual fuel engine. A single cylinder diesel engine with rated output of 4.4 kW at 1500 rpm was converted to operate in the dual fuel mode. Dual fuel operation of varying hydrogen quantity with RSO and RSOME results in higher brake thermal efficiency and significant reduction in smoke levels at high outputs. The maximum brake thermal efficiency is 28.12%, 29.26% and 31.62% with RSO, RSOME and diesel at hydrogen energy share of 8.39%, 8.73% and 10.1%, respectively. Smoke is reduced from 5.5 to 3.5 BSU with RSOME and for RSO it is from 6.1 to 3.8 BSU at the maximum efficiency point. The peak pressure and maximum rate of pressure rise increase with hydrogen induction. Heat release rate indicates an increase in the combustion rate with hydrogen induction. On the whole it is concluded that hydrogen can be inducted along with air in order to reduce smoke levels and improve thermal efficiency of RSO and its bio-diesel fuelled diesel engines.

On thermodynamic optimisation of solar collector model under maximum ecological conditions

AbstractIn this work, within a finite time thermodynamics context, the authors calculate the optimum operation temperature of a solar collector coupled to an endoreversible heat engine (the Curzon-Ahlborn model). This calculation is made under several regimes of performance: maximum efficiency, maximum power output, and maximum ecological function. The authors assume the collector has heat losses given by different heat transfer laws: Newtonian, Dulong-Petit and Stefan-Boltzmann laws. The resulting optimum temperature under ecological conditions is between the maximum power output and the maximum efficiency points. The system's efficiency is calculated in terms of the optimum collector temperature under the three operation regimes mentioned.

Performance and internal flow of sirocco fan using contra-rotating rotors

A sirocco fan using contra-rotating rotors in which an inner rotor is settled inside the sirocco fan rotor and each rotor rotates in an opposite direction was proposed for the purpose of getting the higher pressure and making the structure of a sirocco fan more compact. If the high discharge pressure is obtained with the adoption of the contra-rotating rotors, it could be used for various purposes. Pressure coefficient of a sirocco fan with contra-rotating rotors is 2.5 times as high as the conventional sirocco fan and the maximum efficiency point of contra-rotating rotors shifts to larger flow rate than a conventional sirocco fan. On the other hand, it was clarified from the flow measurement results that circumferential velocity component at the outlet of the outer rotor of contra-rotating rotors becomes larger than a conventional one. In the present paper, the performance of a conventional sirocco fan and a sirocco fan with contra-rotating rotors are shown and the internal flow field at the outlet of outer rotor of both cases is clarified. Then, the effect of different kind of contra-rotating rotors on the performance and internal flow field is investigated and the rotor design with higher performance would be discussed.

Leaf phenology and carbon dynamics in six leguminous trees

AbstractI documented photosynthetic rates and seasonal stem total nonstructural carbohydrates (TNC) in six leguminous tree species Burkea africana, Baikiaea plurijuga, Erythrophleum africanum, Guibourtia coleosperma, Julbernardia globiflora and Pterocarpus angolensis exhibiting a range of leaf phenological patterns. My goal was to (i) measure photosynthetic characteristics and levels of stored stem carbohydrates in species with varying patterns of leaf phenology and (ii) determine seasonal patterns of stem carbohydrate storage.Despite significant differences in the timing of bud break and leaf cover between the six species, there were no significant differences in maximum photosynthetic rate, quantum efficiency or light saturation point between species. Similarly, there was no significant difference in seasonal mean stem TNC levels despite significant differences in the timing of bud break and leaf cover both between species and within a single species. However, while the average amount of TNC does not seem to be related to leaf phenology, the patterns of carbohydrate use and storage do seem to be related to leaf phenology.

A suitable model plant for control of the set fuel cell−DC/DC converter

In this work a state and transfer function model of the set made up of a proton exchange membrane (PEM) fuel cell and a DC/DC converter is developed. The set is modelled as a plant controlled by the converter duty cycle. In addition to allow setting the plant operating point at any point of its characteristic curve (two interesting points are maximum efficiency and maximum power points), this approach also allows the connection of the fuel cell to other energy generation and storage devices, given that, as they all usually share a single DC bus, a thorough control of the interconnected devices is required. First, the state and transfer function models of the fuel cell and the converter are obtained. Then, both models are related in order to achieve the fuel cell+DC/DC converter set (plant) model. The results of the theoretical developments are validated by simulation on a real fuel cell model.