Output Power Variation Research Articles

Power Flow Analysis on the Dual Input Transmission Mechanism of Small Wind Turbine Systems

A parallel planetary gear train design is proposed to construct the wind turbine system that has double inputs and one output. The proposed system is flexible for the application, which may use a combination of two rotors, as used for horizontal axis or vertical axis wind turbines. The proposed transmission mechanism merges the dual time varied input wind powers to a synchronous generator. The effect of the gear train parameters on the dynamic power flow variation is modeled and simulated for the proposed wind turbine system. Results indicate the proposed planetary gear train system is a feasible and efficient design for its application to wind turbine systems. The dynamic torque equilibrium equations between meshed gear pairs are employed to analyze the dynamic power flow. The nonlinear behavior of a synchronous generator is also included in the modeling. The dynamic responses of the dual input transmission mechanism are simulated using the 4th order Runge–Kutta method. The study also investigates the effect of system parameters used in this wind turbine system (i.e., the wind speed, the magnetic flux synchronous generator, and the inertia of flywheels) on variations in electrical power output.

An Online Event-Based Grid Impedance Estimation Technique Using Grid-Connected Inverters

An increasing intake of grid-connected inverters could change the characteristics of low voltage networks including the equivalent grid impedance seen by each inverter at its point of common coupling. This can impact the overall performance of the inverters, and thus it becomes necessary for grid-connected inverters to estimate the grid impedance online. However, there are some challenges when it comes to grid impedance estimation using grid-connected inverters. These include the estimation accuracy and the associated power quality issues that are mainly related to the amplitude, frequency, and time period of the injected disturbance into the grid. To address these challenges, a novel online event-based grid impedance estimation technique for grid-connected inverters is proposed in this article. This technique combines an active grid impedance estimation technique, based on variations of the inverter's output power [active (P) and reactive (Q) power variations], and the continuous monitoring of the positive-sequence amplitude of the PCC voltage. The main advantage is that the estimation technique only performs a deliberate perturbation of P and Q if there is a certain change in voltage magnitude related to grid impedance change. This will significantly reduce the occurrence of required PQ variations, thus minimizing the power losses and the impact on power quality. Simulation and experimental results of a grid-connected inverter system validate the performance of the proposed technique.

Power Generation Optimization of the Combined Cycle Power-Plant System Comprising Turbo Expander Generator and Trigen in Conjunction with the Reinforcement Learning Technique

In this paper, a method that utilizes the reinforcement learning (RL) technique is proposed to establish an optimal operation plan to obtain maximum power output from a trigen generator. Trigen is a type of combined heat and power system (CHP) that provides chilling, heating, and power generation, and the turbo expander generator (TEG) is a generator that uses the decompression energy of gas to generate electricity. If the two are combined to form a power source, a power generation system with higher efficiency can be created. However, it is very difficult to control the heat and power generation amount of TEG and trigen according to the flow rate of natural gas that changes every moment. Accordingly, a method is proposed to utilize the RL technique to determine the operation process to attain an even higher efficiency. When the TEG and trigen are configured using the RL technique, the power output can be maximized, and the power output variability can be reduced to obtain high-quality power. When using the RL technique, it was confirmed that the overall efficiency was improved by an additional 3%.

Analysis on operation characteristic and output performance of free piston expander-linear generator based on displacement control strategy

In this paper, a free piston expander-linear generator (FPE-LG) test rig is established and the control strategy based on displacement is applied. The operation characteristic, output performance, and energy conversion efficiency of the FPE-LG are analyzed. The coefficient of equilibrium oscillation (C) is identified to evaluate the stability of the free piston assembly (FPA). Experimental results show that the FPA has best stability when fixed position point (FPP) is between 20 - 75 mm. The actual stroke and operation frequency increase with the intake pressure and load resistance. The variations of voltage and power output are in accordance with velocity. The average power output increases with intake pressure and FPP, but reduces with the advanced exhaust duration. The maximum average power output can be achieved when the load resistance is 20 Ω. The energy conversion efficiency first increases with intake pressure and then remains constant. The energy conversion efficiency reaches up to 17.5 % when intake pressure is 0.9 MPa, FPP is 40 - 55 mm, advanced exhaust duration is 0 ms, and load resistance is 20 Ω. The lower the coefficient of equilibrium oscillation is, the higher the average power output is.

Collocating offshore wind and wave generators to reduce power output variability: A Multi-site analysis

Offshore wind and wave power are renewable energy sources that share the marine environment. Collocating these systems can reduce power variability; however, the extent of this differs between sites. Regional differences in combined system variability are investigated. Potential power output of wind and wave systems is simulated for sites throughout the US East and West Coasts and UK North Sea using field observations of met-ocean conditions. The power production potential is approximated using an idealized power curve of the Siemens Gamesa SWT-6.0-154 6 MW wind turbine and the Pelamis 750 kW wave energy converter power matrix. The regional comparative approach provides novel insight into collocated system power variability on the US East Coast, and how it contrasts with the previously studied US West Coast and UK North Sea. Hourly and diurnal variability are found to decrease on the US West Coast and UK North Sea, with minimal effect on the US East Coast. The benefits for the West Coast extend to seasonal time scales (but as expected not to annual scales), but benefits for all regions depend on the specific wind-wave capacity mix. Reduced variability can benefit collocated wind and wave power, but these effects differ regionally and must be assessed locally.

Long-term power degradation testing of piezoelectric vibration energy harvesters for low-frequency applications

Piezoelectric energy harvesters represent a viable and well-proven solution to convert ambient vibrations into useful electric power within a number of modern life applications. Whilst a large amount of studies has focused on improving power output from these devices, relatively little research has been directed to investigate how these devices degrade over time and the effect this has on long-term power generation. This paper, therefore, aims to experimentally investigate how piezoelectric vibration energy harvesters degrade during long-term operation in realistic harvesting conditions. The harvesters tested are unimorph cantilevers based on three of the most commonly used piezoelectric options: polyvinylidene fluoride (PVDF), Macro Fiber Composite (MFC), and Quick Pack (QP). Testing was carried out under single-frequency excitation (10–40 Hz) of 1g amplitude for three million vibration cycles. Our results show that the natural frequency and the optimum load resistance of the harvesters may vary during prolonged operation. Importantly, a larger cumulative variation in natural frequency and optimum load resistance yields a larger variation in power output, thereby linking the variation in power to the variation of the mechanical and/or electrical properties of the harvesters. Comparing the average power values over the testing period we found that increasing the tip mass does not necessarily improve the average power output, suggesting that a larger tip mass may exacerbate the degradation of the mechanical and/or electrical properties of the harvester. This was particularly evident for the stiffest QP harvesters which showed the highest signs of power degradation; nevertheless, QP harvesters still managed to demonstrate the highest power density values. When cost consideration is taken into account in the assessment, PVDF harvesters managed to demonstrate the highest power density to cost ratio.

Wireless power transfer system design for electric vehicle dynamic charging application

This paper proposes and demonstrates a wireless power transfer system design for electric vehicle dynamic charging applications. The dynamic wireless charging (DWC) lane is designed for modularly. Each module has three shorttrack transmitter coils that are placed closely together and connected to a single inverter to reduce the number of inverters. The magnetic coupler design is analyzed and optimized by finite element analysis (FEA) to reduce the output power variation during dynamic charging. The LCC compensation circuit is designed according to the optimal load value to obtain maximum efficiency. The SIC devices are used to improve the efficiency of the high-frequency resonant inverter. A 1.5 kW dynamic charging system prototype is constructed. Experimental results show that the output power variation of 9.5% and the average efficiency of 89.5% are obtained in the moving condition.

Analysis of output power change of polycrystalline silicon solar power generation system considering temperature factor

In order to improve the quality of polysilicon solar power generation system, the output power variation of polysilicon solar power generation system with temperature factor is analyzed in the present paper. The functions of photoelectric current, series resistance, parallel resistance, and temperature are obtained through the current and voltage display equations of solar cells, and the mathematical model of photovoltaic connection circuit in the series/parallel solar power generation system is established. The quadratic interpolation method is used to track the maximum output power of the series/parallel solar power generation system. The influence of temperature on the key parameters such as the maximum output power, the maximum photoelectric efficiency mode output power, and the constant voltage mode output power of the PV/T system composed of polysilicon photovoltaic cells is analyzed. The results show that when the temperature is different, the series circuit decreases by 58.08, 58.12, and 50.51%. The maximum output power, maximum photoelectric efficiency mode output power, and constant voltage mode output power of the polysilicon solar power generation system decreased by 2.05, 2.05, and 4.76%, respectively, with the increase of local temperature, and the parallel circuit decreased by 5.31, 8.73, and 50.51%, respectively, in order to improve the power generation quality of the polysilicon solar power generation system.

Maximum expected ramp rates using cloud speed sensor measurements

Large ramps and ramp rates in photovoltaic (PV) power output are of concern and sometimes even explicitly restricted by grid operators. Battery energy storage systems can smooth the power output and maintain ramp rates within permissible limits. To enable PV plant and energy storage system design and planning, a method to estimate the largest expected ramps for a given location is proposed. Because clouds are the dominant source of PV power output variability, an analytical relationship between the worst expected ramp rate, cloud motion vector, and the geometrical layout of the PV plant is developed. The ability of the proposed method to bracket actual ramp rates is assessed over 10 months under different meteorological conditions, demonstrating an average compliance rate of 98.9% for a 2 min evaluation time window. The largest observed ramp of 29.7% s−1 is contained with the worst case estimate of 34.3% s−1. This method provides a convenient yet economical approach to worst-case PV ramp rate modeling and is compatible with solar irradiance measured at coarse temporal resolution.

Effects of Different Inertial Load Settings on Power Output using a Flywheel Leg Curl Exercise and its Inter-Session Reliability.

This study aimed to analyze the influence of the inertial load on both concentric and eccentric power output production during the flywheel leg curl exercise, and to assess the reliability of power output variables. Sixteen participants (8 males, 8 females) attended 4 testing sessions. During testing, participants performed one set of eight repetitions using a specific inertial load (0.083, 0.132, 0.182, 0.266 and 0.350 kg·m2) with a flywheel leg curl exercise. Concentric (CON) power, eccentric (ECC) power and the ECC/CON ratio were analyzed. The reliability analysis between sessions was performed. A significant interaction of inertia load x gender was found in CON power (p < 0.001) and in ECC power (p = 0.004), but not in the ECC/CON ratio (p = 0.731). A significant with-in (inertia loads) effect was found in CON power (p < 0.001) and in ECC power (p < 0.001), but not in the ECC/CON ratio (p = 0.096). CON power showed very high reliability scores, ECC power showed high to very high reliability scores, while the ECC/CON ratio ranged from poor to moderate. A significant between gender effect was found in CON power (p < 0.001) and in ECC power (p < 0.001), but not in the ECC/CON ratio (p = 0.752). This study is the first to report that power output in the flywheel leg curl exercise is altered by the inertia load used, as well as power output is different according to gender. CON and ECC power output presents high to very high reliability scores, and the ECC/CON ratio should not be used instead. These results can have important practical implications for testing and training prescription in sports.

Physiological Response to Cycling With Variable Versus Constant Power Output.

Introduction: Variable power output (VP) is one of the main characteristics of a road cycling mass-start. Tolerating VP during outdoor road cycling highly influences performance. There is a lack of continuous and comprehensive measurements during this power condition. Accordingly, the aim of the present study was to investigate physiological response to VP vs. constant power output (CP) as well as the perceived exertion of these two power conditions, and to investigate if variations in power output which span above lactate threshold (LT), differ from variations below LT.Methods: 15 elite competitive cyclists completed three test days, including 1 day of baseline testing and 2 days of main testing, consisting of four bouts of 28 min at two different intensities, “low” at 70% of LT and “high” at 95% of LT, with VP and CP. VP was performed with a 15% fluctuation of the average power output every second minute. Maximal oxygen uptake (VO2), respiratory exchange ratio (RER), heart rate (HR), blood lactate (LA), rating of perceived exertion (RPE), cadence (RPM) and power output (W) were measured.Results: At both low and high intensity, the VP condition induced a significantly higher VO2, HR and LA than the CP condition. Whole-bout RPE was similar between power conditions at high intensity. Additionally, at the high intensity, cycling with VP led to a greater increase in LA and lesser increase in RPE compared to cycling with CP.Discussion: The results of this study show that, despite considerable differences in the demand during the VP and CP bouts, there are minor differences in the perceptual and physiological response directly following these two power conditions in a cohort of elite competitive cyclists. A practical implication of these findings is that training with VP seems to be a viable alternative to training with CP, at least at high intensity.

Centralized Airflow Control to Reduce Output Power Variation in a Complex OWC Ocean Energy Network

A centralized airflow control scheme for a complex ocean energy network (OEN) is proposed in this paper to reduce the output power variation (OPV). The OEN is an integrated network of multiple oscillating water columns (OWCs) that are located at different geographical sites connected to a common electrical grid. The complexity of the OWC-OEN increases manifolds due to the integration of several OWCs and design of controllers become very challenging task. So, the centralized airflow control scheme is designed in two stages. In control stage-1, a proportional-integral- (PI-) type controller is designed to provide a common reference command to control stage-2. In control stage-2, the antiwindup PID controllers are implemented for the airflow control of all the OWCs simultaneously. In order to tune the large number of control parameters of this complex system, a fitness function based on integral squared error (ISE) is minimized using the widely adopted particle swarm optimization (PSO) technique. Next, the simulation results were obtained with random wave profiles created using the Joint North Sea Wave Project (JONSWAP) irregular wave model. The OPV of the proposed OWC-OEN was reduced significantly as compared to the individual OWC. It was further observed that the OPV of the proposed scheme was lower than that achieved with uncontrolled and MPPT controlled OWC-OEN. The effect of communication delay on the OPV of the proposed OWC-OEN scheme was also investigated with the proposed controller, which was found to be robust for a delay up to 100 ms.

A Probabilistic Approach to Analyze Wind Energy Curtailment in Non-Interconnected Greek Islands Based on Typical Wind Year Meteorological Data

Wind energy and photovoltaic solar energy (PV) are the most mature renewable energy technologies and are widely used to increase renewable energy penetration in non-interconnected Greek islands. However, their penetration is restricted due to technical issues related to the safe operation of autonomous power systems, the current conventional power infrastructure and their variable power output. In this framework, renewable energy curtailment is sometimes a necessity to ensure the balance between demand and supply. The ability of autonomous power systems to absorb wind and PV power is related to the load demand profile, the type and the flexibility of conventional power plants, the size of power system and the spatial dispersion of wind farms. In this connection, a probabilistic approach for estimating wind energy curtailment is thoroughly applied in most of the autonomous power systems in Greece, using detailed information about load demand and conventional power supply. In parallel, high resolution mesoscale model-based hourly wind data for typical meteorological wind year are used to represent the wind features in all the sites of interest. Technical constraints imposed by the local power system operator, related to the commitment of conventional power plants and the load dispatch strategies are taken into account to maximize renewable energy penetration levels. Finally, application for wide ranges of wind and PV capacity and the thorough analysis of the parameters leads to the presentation of comparable results and conclusions, which could be widely used to predict wind energy curtailment in non-interconnected power systems.

Integration of gas switching combustion and membrane reactors for exceeding 50% efficiency in flexible IGCC plants with near-zero CO2 emissions

• Gas switching combustion and membrane reactors are integrated in an IGCC plant. • The proposed plants produce flexible electricity/H 2 with CCS to balance renewables. • IGCC benchmarks with/without CCS incorporate hot gas clean-up and H-class turbines. • Electric/H 2 LHV efficiencies up to 50.3%/62.4% with >98% CO 2 capture are achieved. • The energy penalty is less than 2%-points relative to the unabated IGCC plant. Thermal power plants face substantial challenges to remain competitive in energy systems with high shares of variable renewables, especially inflexible integrated gasification combined cycles (IGCC). This study addresses this challenge through the integration of Gas Switching Combustion (GSC) and Membrane Assisted Water Gas Shift (MAWGS) reactors in an IGCC plant for flexible electricity and/or H 2 production with inherent CO 2 capture. When electricity prices are high, H 2 from the MAWGS reactor is used for added firing after the GSC reactors to reach the high turbine inlet temperature of the H-class gas turbine. In periods of low electricity prices, the turbine operates at 10% of its rated power to satisfy the internal electricity demand, while a large portion of the syngas heating value is extracted as H 2 in the MAWGS reactor and sold to the market. This product flexibility allows the inflexible process units such as gasification, gas treating, air separation unit and CO 2 compression, transport, and storage to operate continuously, while the plant supplies variable power output. Two configurations of the GSC-MAWGS plant are presented. The base configuration achieves 47.2% electric efficiency and 56.6% equivalent hydrogen production efficiency with 94.8–95.6% CO 2 capture. An advanced scheme using the GSC reduction gases for coal-water slurry preheating and pre-gasification reached an electric efficiency of 50.3%, hydrogen efficiency of 62.4%, and CO 2 capture ratio of 98.1–99.5%. The efficiency is 8.4%-points higher than the pre-combustion CO 2 capture benchmark and only 1.9%-points below the unabated IGCC benchmark.

Study on the effects of runner geometries on the performance of inline cross-flow turbine used in water pipelines

To supply continuous and reliable power to the water monitoring systems and motorized control valves in urban water supply networks, the inline cross-flow turbine has been developed. This study aims to investigate the effects of different runner geometries on the performance of inline cross-flow turbines and to determine the optimal runner geometrical parameters. In this paper, a theoretical analysis of the working mechanism of a cross-flow runner is first performed to study the impacts of the runner geometry on turbine performance. Thereafter, several turbine models with different runner geometries are built and simulated to analyse the output power, water head reduction and torque generation at each runner stage. The results indicate that a good match between the flow inlet angle and blade outer angle notably enhances the turbine performance. Based on the results, the recommended optimal blade outer angle in this research is 30°. In addition, the results also show that the runner diameter ratio has a major impact on torque generation at the runner first stage. A lower runner diameter ratio leads to a higher output power, but the water head reduction is also higher. Based on the results, the suggested runner diameter ratio is 0.68. A numerical study on the number of blades indicates that when the number of blades increases from 20 to 24, the turbine output power considerably rises, and the maximum output power reaches 2285 W. However, if the blade number is further increased, the variation in output power is very slight. Thus, the proposed optimal blade number is 24. Based on the research results, the maximum turbine efficiency can reach 50.9% after runner optimization.

An Ultra-Low-Power Low-Voltage WuTx With Built-In Analog Sensing for Self-Powered WSN

This paper presents an ultra-low-power, low-voltage wake-up transmitter (WuTx) capable of transmitting two sensors’ analog output simultaneously using short pulses that their LOW and HIGH time are modulated with the analog inputs. A subthreshold relaxation oscillator along with an ultra-low-power comparator and voltage reference creates a baseband signal modulated based on two input analog signals, a ring oscillator upconverts the baseband signal to the desired transmission channel frequency (915 MHz or 2.4 GHz), and finally, an efficient Class E power amplifier with variable output power drives the antenna. The minimalist design of the proposed transmitter avoiding power-hungry data converters for sensor readout circuitry and modulation, short pulses at the output that enable the power amplifier for a short time during transmission along with the operation in the subthreshold region significantly reduces the overall power consumption. The proposed low-power and low-voltage transmitter is ideal for the long-term deployment of self-powered wireless sensors when the voltage gain and efficiency of harvesters are limited. Fabricated in a 65nm standard TSMC CMOS process, the proposed transmitter consumes a minimum of $5.41~\mu W$ average power when it is on while delivering the output power of −1dBm and $7nW$ when it is completely off.

Gamma Radiation-Induced Effects over an Optical Fiber Laser: Towards New Sensing Applications.

In the present work, the effect of gamma radiation on the performance of different types of erbium-doped fibers (EDFs) when they are used in a fiber ring cavity (FRC) configuration is studied. Several pieces of commercial EDF are gamma-ray irradiated with different doses to evaluate the output power variations over time. The influence of different doses, from 150 Gy to 1000 Gy, over the output power level measurement and their amplified spontaneous emission (ASE) are experimentally evaluated both in the C and L bands. By using an FRC configuration we can detect the presence of gamma radiation. We can also estimate the irradiation doses applied to EDFs by measuring the slope of the short-term emission power.

Power ramp-rates of utility-scale PV systems under passing clouds: Module-level emulation with cloud shadow modeling

The short-term power output variability of solar photovoltaic (PV) systems caused by passing clouds is becoming a major concern for grid operators. As the penetration of utility-scale PV systems boosts, the rapid power fluctuations greatly challenge the grid transient stability. In this regard, the concept of power ramp-rate (RR) has been recently imposed to quantify the PV fluctuations, and a series of ramp regulations are implemented by utilities. However, due to the limitations in terms of high-resolution simulation of utility-scale PV systems and reproducing cloud shadow natures, current studies still show deficiencies in comprehensively investigating the RRs rising from both endogenous and exogenous factors during cloud shadow transitions.With the objective of producing high-resolution and high-accuracy emulations of utility-scale PV systems under passing clouds, thus providing a clearer understanding on the cloud-induced RRs, this paper first sets forth a partial shading emulator that is capable of efficiently mimicking the behaviors of an arbitrary partially shaded PV system, in accuracy of the PV module level. Then a fully customizable shadow model that can reproduce the natures of a real cloud shadow is introduced. Based on the developed emulation tools, the effects of two endogenous factors i.e., PV array arrangement and system orientation, and three exogenous factors i.e., shadow intensity, shadow velocity, and shadow size on RRs are explored for a range of utility-scale PV systems from 1 MW to 60 MW. Furthermore, in order to assess the RRs in reality, a total of 3747 cloud shadow transitions exploited from real measurements have been applied for emulations. The results reveal that the RRs caused by passing clouds are critical problems for system operations, and a larger system can suffer more from ramp violations, indicating that the advanced ramp control strategies should be essential for contemporary utility-scale PV systems.

The Design and Analysis of Large Solar PV Farm Configurations With DC-Connected Battery Systems

Typically, solar inverters curtail or “clip” the available power from the photovoltaic (PV) system when it exceeds the maximum ac capacity. This article discusses a battery system connected to the dc link of an inverter to recuperate this PV energy. Contrary to conventional approaches, which employ two dc–dc converters, one each for the battery and solar PV system, the proposed configuration utilizes a single dc–dc converter capable of simultaneously operating as a charge controller and a maximum power point tracking (MPPT) device. In addition to improving the overall system capacity factor, increasing the conversion efficiencies, and ensuring MPPT stability, the proposed configuration offers a simple solution for adding energy storage to existing PV installations. With this configuration, the excess power that will otherwise be curtailed due to inverter rating limitations is stored in the battery and supplied to the grid during periods of reduced irradiance. Moreover, a systematic methodology for sizing a dc-bus connected battery to minimize total PV energy curtailed was developed using an annual PV generation profile at the Louisville Gas and Electric and Kentucky Utilities E. W. Brown solar facility at Kentucky. The detailed behavior of the proposed system and its power electronics controls and operations were validated with case studies developed in PSCAD/EMTDC software for variable power generation and PV output power smoothing.

Effects of critical temperature, critical pressure and dryness of working fluids on the performance of the transcritical organic rankine cycle

Thermodynamic properties of working fluids have significant effects on the system performance of the transcritical organic Rankine cycle, and the optimal working fluid is related to the heat source temperature. In this paper, both separate and combined effects of the critical temperature (Tcri), critical pressure (Pcri) and dryness (ξ) of working fluids on the performance of TORCs were investigated under different heat source temperatures. The trends in variation of maximum net power output (Wmax) based on the increase of the critical temperatures of working fluids were also investigated. The results indicated that a lower Tcri of working fluids would lead to an increase in the expander’s outlet temperature and a worse thermal match in the condenser. However, a higher Tcri would result an increase in the heat source outlet temperature and a worse thermal match in the vapor generator. In addition, a higher Pcri would lead to an uneven temperature curve for the working fluid and a worse thermal match in the vapor generator. A larger ξ would result in high superheat at the condensation pressure and a worse thermal match in the condenser. Working fluids with suitable Tcri, lower Pcri and lower ξ could achieve better net power output performance.