Partial Load Regime Research Articles

Test rig for stand-alone small power wind turbine emulation for variable wind and load

This paper presents futures from experimental investigation of an autonomous small power wind system. The envisaged wind system is based on a PMSG (Permanent Magnet Synchronous Generator) directly connected to the wind turbine shaft, while the DC output load is supplied by a rectifier and a chopper. The DC load is considered as a resistive load with wide values range. Experimental investigations are provided in partial load regime. The power optimization is performed through a power loop in two ways: by controlling the electrical power or by controlling the electromechanical power. For the above two situations it is shown how the optimization power loop reference and power loop feedbacks can be set, in order to obtain maximum electrical power, for each wind speed value corresponding to the partial load regime. It was also highlighted that for a wide range of DC load values the mechanical and electrical powers are not constant as it should be corresponding to the mathematical model of the optimal conversion. This is due to mechanic-electrical subsystem processes. The electrical power variation range with the load should be provided by the manufacturer in the low-power wind system data sheet.

Implementing the dynamic simulation approach for the design and optimization of ships energy systems: Methodology and applicability to modern cruise ships

To reduce the environmental impact of modern cruise ships, a crucial role is played by the recovery of waste heat from onboard diesel generators used to balance part of the onboard thermal energy demand. To maximize the recovered waste heat, this paper proposes a novel design methodology for ships energy systems based on the dynamic simulation approach, suitably enhanced to consider moving objects like ships. Through this approach, partial load regimes due to variable energy requirements and the relative response of innovative energy saving technologies are dynamically assessed by properly considering real cruising conditions as a function of the current ship position along its route. To this aim, 3-D ship envelope models, detailed energy ship-plant system layouts, and algorithms for deriving new customized hourly weather data files are suitably developed in MatLab and TRNSYS. To show the capability and potentials of the proposed methodology, a novel case study referred to an LNG-powered cruise ship traveling in the Norwegian fjords sea is presented. Different thermally and electrically activated technologies are coupled in 16 energy ship-plant system layouts, implementing novel controls strategies for optimizing the exploitation of the waste heat recoveries and cold-ironing. Encouraging results are achieved for the best layout, including primary energy savings of 18.1%, avoided pollutants emissions of 24.4 ktCO2/y, 40.0 tNOx/y, 90.0 tSOx/y, 84.0 tPM2.5/y, and a simple payback of 0.68 years. Finally, the proposed methodology represents a step forward toward the modern early design of onboard ship energy systems useful for ship designers, manufacturers, owners and operators.

Simulation of Optimizing the Partial Load Performance of a Gas Turbine Combined Cycle Using Exhaust Heat Recuperation and Inlet Bleed Heating

Abstract This paper proposes a novel method to extend the operating range and improve the partial load efficiency of the gas turbine combined cycle (GTCC). The combination of exhaust heat recuperation and inlet bleed heating (IBH) was evaluated through a cycle simulation. The degree of heat recuperation was modulated during partial load operation to enhance the cycle efficiency. The recuperation ratio was modulated before control of the variable inlet guide vane (VIGV) began. This means that the recuperation control covers the high partial load regime. The gas turbine power remained almost constant in this regime because the inlet flow rate and turbine inlet temperature (TIT) were kept constant. In contrast, the power of the bottoming cycle decreased with increasing recuperation ratio due to the decrease in exhaust gas energy. After the recuperation ratio reached a limit, the load control was the same, as in conventional plants: VIGV control followed by fuel only control. The purpose of using IBH was to reduce CO emissions in the low load regime. Some of the compressor discharge air was recirculated to the compressor inlet, and the combustion temperature was maintained at a high level. Both IBH and recuperation were effective in extending the operating range. The turndown ratio was predicted to decrease by approximately 10%p. The efficiency remained higher than the full load efficiency over a wide partial load range. The efficiency of the recuperated GTCC was 4.1%p higher at 50% power than that of the conventional GTCC.

Experimental Study of Transient Flow Regimes in a Model Hydroturbine Draft Tube

Swirling flow with the formation of a precessing vortex core (PVC) in the draft tube model of a hydroturbine was studied. Experiments were performed on an aerodynamic setup under transient operating conditions of the hydroturbine. The turbine operating conditions were varied by continuously changing the flow rate at a constant runner speed. The transition from the partial load regime, when a precessing vortex core is formed, to the best efficiency point without a core is considered. Applied to this task, a comparison of the windowed Fourier transform with wavelet analysis is given. The dependence of the PVC lifetime in the transient regime correlates with the transient time. It is shown that the velocity profiles and the spectrum of pressure pulsations in transient regimes change quasistatically between part-load operation and the best efficiency point of the turbine. The phase-averaged velocity distributions in the transient regimes show that a transient regime is a sequence of quasisteady regimes.

Evolution of a swirling flow in a draft tube model at transient operation regimes

This work deals with the experimental study of transient flow regimes occurring in the laboratory model of a hydraulic turbine draft tube at a change in the control parameters of setup. The transition from the partial load regime, when a precessing vortex core is formed, to the best efficiency point without a core is considered. To set accurately the speed of runner rotation and the flow rate of the working medium, the setup was controlled by special software. To ensure accurate multiple reproduction of a given transition cycle between two regimes, the control program has been upgraded. Using a specially developed procedure of phase averaging of a laser Doppler anemometer (LDA) signal recorded during multiple repetitions of transient regimes, the velocity profiles were obtained for different phases of changing the setup operating conditions.

Mitigation of flow-induced pressure fluctuations in a Francis turbine operating at the design and partial load regimes—LES simulations

High-fidelity large eddy simulations (LES) were conducted to characterize the spatial and temporal structure of turbulent flows in an industrial-sized Francis turbine while the unit operated at the design point and partial load. A pressure surge with an amplitude of 8% of the turbine head was observed at partial load while the amplitude was <1% at the design point. The vortex rope precession observed in the draft tube correlated to the amplitude and frequency of the pressure surge. Central and peripheral water injections at various volumetric rates were considered to control the flow-induced pressure fluctuations. Central injection at the 4% and 6% flow rates attenuated high amplitude pressure fluctuations by 40% and 75% respectively at partial load. At the same operating conditions, peripheral injections did not have the same desired effect. Although power generation was not changed with water injection at the design point, it was reduced by about 2.5% by central injection and 0.5% by peripheral injection at partial load, showing a water injection mitigation strategy could be applied without any penalty.

Влияние переходных режимов на нестационарные вихревые явления в модели отсасывающей трубы гидротурбины

This article is devoted to study the swirling flow with the formation of the precessing vortex core (PVC) in the cone of the model of the draft tube of the hydraulic turbine. The experiments were carried out on the aerodynamic set-up both in stationary and in transient regimes of operation of the hydraulic turbine. The hydraulic turbine operating conditions were varied by continuously changing the flow rate at a constant rotor speed. The formation of the PVC in the flow and the maximum level of pressure pulsations in the regime modeling the partial load regime of a turbine are revealed. The boundaries of the occurrence of the PVC effect are determined with varying rotor speed and air flow rate. It was found that the dependence of the PVC lifetime in transition regimes correlate with the transition time. It was shown that the velocity profiles in transient conditions change quasistatically between the operation regime with partial loading of the turbine and the regime of the highest efficiency of the turbine.

Does heat pumps perform energy efficiently as we expected: Field tests and evaluations on various kinds of heat pump systems for space heating

This paper introduces continuously field test results on operational energy performance of 32 heat pump systems for space heating with various heat sources in cold region of China. Therefore, normalized energy performance index for the holistic heat pump based space heating system including compressor electricity use, circulating pumps energy use for both heat source and heat sink, were introduced to evaluate and compare between different systems or different control strategies. Results showed that over-sized heat pump capacity design and install declined heat pumps efficiency during whole heating season especially in partial load regime, and solo heat pump station with large heating distribution networks led to dramatic heat loss and hydraulic unbalance problems. In addition, complicated control strategy for both heat pumps and circulating pumps did not performed properly according to building heat demand fluctuating and heat source temperature variation during whole winter. The paper disclosed clearly that optimized design and operation of the holistic heat pump based space heating systems during the heating season are essential to ensure the actual energy performance for any kinds of heat pumps rather than believing in theoretical assumption.

Wind Turbine Torque Oscillation Reduction Using Soft Switching Multiple Model Predictive Control Based on the Gap Metric and Kalman Filter Estimator

A new multiple model predictive control (MMPC) is reported to regulate the output power of the National Renewable Energy Laboratory (NREL) 1.5 MW baseline wind turbine (WT). The maximum power point tracking in the wide range of the partial load regime without losing any control performance is the goal of the proposed algorithm. To do this, the whole area of the partial load regime is divided into adequate linear models using a mathematical tool called gap metric. Next, we set different MPCs (controller bank) to each model. The controller selection is conducted based on wind speed value estimated using a neural network estimator. The sudden change between controllers applies a hazardous chattering to control signal. To tackle this problem and reduce the chattering, a new soft switching MMPC (SSMMPC) is introduced. Furthermore, the stability of the closed-loop system is guaranteed using Lyapunov theory creating novelty in this work. Moreover, to validate the proposed algorithm, SSMMPC and classical MMPC are implemented on the NREL 1.5 MW baseline WT using fatigue aerodynamic structure and turbulence simulator. Finally, the simulation results and comparisons demonstrate the effectiveness of the proposed controller in the tracking error, oscillation in control signal, and mechanical power.

A Flexible Maximum Power Point Tracking Control Strategy Considering Both Conversion Efficiency and Power Fluctuation for Large-inertia Wind Turbines

In wind turbine control, maximum power point tracking (MPPT) control is the main control mode for partial-load regimes. Efficiency potentiation of energy conversion and power smoothing are both two important control objectives in partial-load regime. However, on the one hand, low power fluctuation signifies inefficiency of energy conversion. On the other hand, enhancing efficiency may increase output power fluctuation as well. Thus the two objectives are contradictory and difficult to balance. This paper proposes a flexible MPPT control framework to improve the performance of both conversion efficiency and power smoothing, by adaptively compensating the torque reference value. The compensation was determined by a proposed model predictive control (MPC) method with dynamic weights in the cost function, which improved control performance. The computational burden of the MPC solver was reduced by transforming the cost function representation. Theoretical analysis proved the good stability and robustness. Simulation results showed that the proposed method not only kept efficiency at a high level, but also reduced power fluctuations as much as possible. Therefore, the proposed method could improve wind farm profits and power grid reliability.

Effect of LOS/NLOS propagation on 5G ultra-dense networks

The combined presence of Line-of-Sight (LOS) and Non-Line-of-Sight (NLOS) components in the radio propagation environment can severely degrade the Ultra-Dense Networks (UDNs) performance. Backed by a stochastic geometry model, we show that when the LOS/NLOS propagation components are taken into account, and as the cell density increases, UDNs suffer from low coverage and the Area Spectral Efficiency (ASE) grows sub-linearly. However, we show that this performance drop can be compensated by increasing the frequency reuse factor or by steering the network into the partial load regime, which occurs when the base stations outnumber the users. In the former, it emerges that frequency reuse improves the ASE vs coverage trade-off of cell densification with respect to a traditional full frequency reuse, provided there is a degree of freedom on the density of cells; in addition, this trade-off improves with the frequency reuse factor N. Finally, we investigate the energy efficiency of UDNs for which we show that, as a combined result of LOS/NLOS propagation and partial load regime, up to two optimal base station densities exist. As a whole, our work provides novel insights on how to overcome the limitations and to take advantage of extreme cell densification in the upcoming 5G wireless networks.

Intelligent Control of a Distributed Energy Generation System Based on Renewable Sources

The control of low power systems, which include renewable energy sources, a local network, an electrochemical storage subsystem and a grid connection, is inherently hierarchical. The lower level consists of the wind energy sources (power limitation at rated value in full load regime and energy optimization in partial load regime) and photovoltaic (energy conversion optimization) control systems. The present paper deals with control problem at the higher level and aims at generating the control solution for the energetic transfer between the system components, given that the powers of the renewable energy sources and the power in the local network have random characteristics. For the higher level, the paper proposes a mixed performance criterion, which includes an energy sub-criterion concerning the costs of electricity supplied to local consumers, and a sub-criterion related to the lifetime of the battery. Three variants were defined for the control algorithm implemented by using fuzzy logic techniques, in order to control the energy transfer in the system. Particular attention was given to developing the models used for the simulation of the distributed energy system components and to the whole control system, given that the objective is not the real-time optimization of the criterion, but to establish by numerical simulation in the design stage the “proper” parameters of the control system. This is done by taking into account the multi-criteria performance objective when the power of renewable energy sources and the load have random characteristics.

Modelling Inlet Flow In Draft Tube For Different Regimes Of Hydroturbine Operation

One of the main sources of powerful pressure pulsations in the fluid flow parts of the hydroturbine at partial load or overload operation regimes is the precessing vortex rope forming due to high residual swirl of the flow downstream the hydroturbine wheel. Numerical simulation and experiments have been performed in order to study the influence of inlet flow conditions in the draft tube on level of the flow pulsations. Numerical calculations have shown that it is possible to reproduce velocity distributions at the draft tube inlet corresponding to different operation regimes of the real hydroturbines using a combination of two blade grids – rotor and stator. Experimental verification of numerical calculations was performed using an aerodynamic test rig and method of 3-d printing for fabrication of the blade grids and draft tube model. Velocity field measurements at entrance of the draft tube conical part making use of an laser-Doppler anemometer and level of the pressure pulsations using acoustic probes have allowed to define correlation between the velocity distribution type and amplitude-frequency characteristics of the flow pulsations which generated by the precessing rope.

A Feedback Linearization Based Nonlinear Control Approach for Variable Speed Wind Turbines

This paper describes the design and implementation of a nonlinear control strategy for the control of the shaft speed of wind turbine systems. The proposed approach is based on input-output linearization techniques. Because wind turbine systems are highly nonlinear, feedback linearization constitutes a suitable optimal control design for those systems. Further, Electromechanical systems in general are good candidates for nonlinear control applications because the nonlinearities, being modeled on the basis of physical principles, are often significant and exactly known. The underlying design objective is to endow the wind turbine with high performance dynamics while maximizing power extraction when the wind turbine operates in the partial load regime. In addition to fulfilling the aforementioned control objectives, our control design aims to reduce the complexity of the control scheme, saving thereby the computation time of the control algorithm, which is an improvement over previous work found in the technical literature. Application of the proposed approach to an induction generator based variable speed wind turbine has led to optimum operations and maximization of power extraction when the wind turbine operates in the partial load regime.

A sensorless control method for variable-speed small wind turbines

This paper describes an integrated sensorless control method for small variable-speed, fixed-pitch wind turbines with direct-drive permanent magnet synchronous generator (PMSG), which covers both partial- and full-load operation modes. In partial-load regime, the control system aims to maximize the wind energy conversion by keeping the wind turbine on its optimal power-speed characteristic, while in the full-load regime, when the generator reaches the rated power, the control acts over the rotor speed to create the condition of aerodynamic stall, and thus the output power is substantially reduced. Two PI controllers act on the generator speed and output power by measuring only two DC electrical quantities, i.e. voltage and current. The simulations accomplished with a reduced model and the experiments on a 2.2 kW laboratory test bench assess the effectiveness of the proposed control system. The results emphasize the performance of the proposed solution while also showing its limitations.

Multiple Model Predictive Control for Wind Turbines With Doubly Fed Induction Generators

A multivariable control strategy based on model predictive control techniques for the control of variable-speed variable-pitch wind turbines is proposed. The proposed control strategy is described for the whole operating region of the wind turbine, i.e., both partial and full load regimes. Pitch angle and generator torque are controlled simultaneously to maximize energy capture, mitigate drive train transient loads, and smooth the power generated while reducing the pitch actuator activity. This has the effect of improving the efficiency and the power quality of the electrical power generated, and increasing the life expectancy of the installation. Furthermore, safe and acceptable operation of the system is guaranteed by incorporating most of the constraints on the physical variables of the wind energy conversion system (WECS) in the controller design. In order to cope with nonlinearities in the WECS and continuous variations in the operating point, a multiple model predictive controller is suggested which provides acceptable performance throughout the whole operating region.

Eulerian and Lagrangian spray simulations of an aeronautical multipoint injector

Lean-burn combustors developed for low NO X aero-engines include staged fuel injectors, characterized by a complex geometry and often by the introduction of multipoint injection systems where fuel is injected by a series of liquid jets oriented perpendicularly to the airflow. Large Eddy simulations (LES) combined with methods to simulate liquid fuel sprays are well-adapted to the simulation of such flows. The present work compares Eulerian and Lagrangian methods for the simulation of the dispersed phase. The evaluation is carried out on a single injector mounted in an experimental rig installed at ONERA. The non-reactive operating condition corresponds to a partial load regime at 4.37 bar and 473 K in the chamber inlet. This allows to study droplet dynamics and evaporation under realistic conditions. The simulation cases include a purely gaseous flow, an Eulerian spray simulation as well as a monodisperse and a polydisperse Lagrangian simulation, all using the same grid. The analysis focuses on the comparison of gaseous and liquid phase velocities and fluctuations. Equivalence ratio fields are also visualized, allowing to identify regions suitable for ignition.

Numerical investigation of GTE-45 gas turbine unit operation at partial-load regimes

Results from numerical investigation of GTE-45 gas turbine unit operation under partial electric load regimes are presented. Analysis of the efficiency of the gas turbine unit operation with the use of turning guide vanes in the compressor is performed.