Steady-state Operating Conditions Research Articles

Experimental studies of the vibro-acoustic characteristics of an axial piston pump under run-up and steady-state operating conditions

The noise, vibration and harshness (NVH) behaviors of axial piston pumps are important performance criteria for their operation. A systematic investigation is required to study their vibro-acoustic characteristics. In this investigation, the vibro-acoustic characteristics of an axial piston pump were experimentally measured under run-up and steady-state operating conditions. The sound pressure level and vibration were measured, interpreted and analyzed under the run-up operating conditions. The sound quality of the pump, including its loudness, sharpness and roughness, was also evaluated. The effects of speed and pressure on loudness, sharpness and roughness were examined. The results showed that the proposed experimental methodology is effective for evaluating the overall vibro-acoustic characteristics of axial piston pumps. The most relevant noise components can be identified and extracted by a thorough analysis of the vibro-acoustic characteristics using the proposed analysis methodology. The study contributes to better understanding the vibro-acoustic characteristics of axial piston machines.

Dynamic performance simulation and control of gas turbines used for hybrid gas/wind energy applications

The exponential growth of renewable electricity generation has transformed significantly the operating environment of gas turbines. Nowadays, gas turbines operate under transient conditions to support their renewable partners. Gas turbine dynamic performance simulation provides the means for assessing the engine behavior and designing engine controllers that will enable them to fulfill their new operating role.This paper presents a novel gas turbine performance system for representing the nonlinear behavior of a two-shaft gas turbine engine. The developed gas turbine engine model in MATLAB/Simulink environment is capable of simulating both steady state and transient operating conditions, and to facilitate the design of controllers for stable engine operation. Validation of the developed engine model with a gas turbine simulation package confirmed the excellent agreement among all the simulated measurements at transient conditions. The simulated behavior of a hybrid gas/wind power plant enabled the development of an optimized controller for empowering the gas turbine to support the intermittent wind turbines. The time responses of the main parameters of the hybrid gas/wind power plant demonstrated the significant amount of transient conditions that a gas turbine experiences for fulfilling the energy gap imposed by the wind turbines. Finally, the performance comparison of the hybrid power plant to a twin gas turbine power plant highlighted the effective reduction in NOx emissions.

Analysis of half-wavelength transmission line under critical balanced faults: Voltage response and overvoltage mitigation procedure

This paper presents a detailed study of half-wavelength (HWL) transmission line system under critical fault conditions. This non-conventional ultra high voltage alternating current (UHVAC) transmission line has excellent properties in steady-state operation condition and economic advantage when compared to conventional UHVAC system and even high voltage direct current (HVDC) transmission systems for similar power capacity. This technology has been studied for many decades and its response under condition fault is an important topic. First, the point of fault and the type of fault conditions are evaluated to confirm that balanced faults in specific regions are critical. Then the main characteristics of voltage response of HWL transmission system under balanced fault are presented and critical regions that produce severe overvoltage are identified and main transient characteristics are described. Finally, a preliminary mitigation procedure is shown and its performance is evaluated.

Comparative studies on combustion, performance and emission characteristics of a two-wheeler with gasoline and 30% ethanol-gasoline blend using chassis dynamometer

Mid-level ethanol-gasoline blends such as E30 offers significant advantages in terms of higher octane number, desirable Reid vapor pressure and water tolerance characteristics compared to lower blends. An experimental study was undertaken on a motorcycle with commercial gasoline (E0) and 30% ethanol blended gasoline (E30) using a chassis dynamometer. Combustion, performance and emissions characteristics were investigated under steady state (wide-open throttle – WOT) and transient (Indian driving cycle – IDC) operating conditions. In the WOT test, carbon monoxide and hydrocarbon emissions decreased however oxides of nitrogen (NOx) increased with E30 compared to E0. The specific fuel consumption was higher with E30 but vehicle power decreased. Combustion analysis showed an increased combustion duration and delay in heat release rate with E30. The peak combustion pressure and maximum rate of pressure rise were also lower. Mass emission studies over IDC test show a decrease in CO and NOx emissions with E30 while hydrocarbon emission increased marginally. The notable point emerged from the study is that the operating conditions and change in air-fuel mixture regime impact the performance and emissions of two-wheeler significantly. The present work provides useful information for designing a dedicated spark ignition engine suitable for mid-level ethanol blends.

Experimental study on a cross-flow regenerative indirect evaporative cooling system

The evaporative cooling is an energy-saving and environmentally-friendly air-conditioning method. A cross-flow regenerative indirect evaporative heat exchanger (IEHX) has been designed and fabricated. In the proposed IEHX, the working air is gradually diverted into the wet channels through the holes distributed along dry channels. This arrangement allows the working air to be pre-cooled before entering the wet channel. The experimental study was carried out to investigate the performance of the IEHX under specific inlet conditions. Measurements have been conducted during steady-state operating conditions. Experimental results have demonstrated that the product air can be gradually cooled along its flow direction by transferring its heat to the working air. In addition, the proposed cross-flow IEHX is able to reduce the air temperature below wet-bulb temperature.

Power alternator simulation models for diagnostic purposes

Park models, also known as dq-models, are a simple and very efficient way to obtain a faithful image of the behaviour of a machine in transient and steady-state operating conditions to deal with control issues. Their precision is based on the use of saturated direct and quadrature reactances that truly represent the dynamics and the magnitude of the electrical signals at nominal operating point. However, these constant parameters are not sufficient to accurately take into account the saliency of the machine and, therefore, to precisely simulate the harmonic contents of these signals: the latter point can be very problematic for diagnostic purposes. This paper uses simulation results and experimental measurements on a Leroy-Somer 27kVA alternator to clearly show the lack of coherence between the simulated spectra from a dq-model and the experimental data retrieved from a real power alternator. For that reason, a new methodology of machine modelling consisting of a co-simulation process between Flux2D and Matlab software is presented. The use of finite elements enables a fine identification of the inductances of the system. These take into account the geometrical specificities of both the exciter and the main generator and are then used in an analytical model developed in the Matlab environment. Spectral comparisons with experimental data demonstrate the improved accuracy of this new modelling method compared to dq-models in terms of harmonic contents.

DTC strategies for three-switch three-phase inverter-fed induction motor drives

PurposeThis paper aims to investigate the performance of two novel direct torque control (DTC) schemes dedicated to three-switch three-phase inverter (B3-VSI), also called delta inverter, fed induction motor (IM) drives.Design/methodology/approachThe principle of operation of the B3-VSI-fed IM drive is recalled in a first step. Then, the basis of both proposed DTC strategies is presented. The first DTC scheme considers a subdivision of the stationary plane into three sectors and the application of the intrinsic as well as virtual voltage vectors to achieve the control combinations. While, the second DTC scheme considers a subdivision of the stationary plane into six sectors and a limitation of the voltage vectors incorporated in the look-up table to the three intrinsic ones.FindingsSimulation and experimental results have revealed that, under steady-state operation and transient conditions, the harmonic content of the IM stator phase currents is lower in the case of the DTC2 strategy, resulting in a lower ripple of electromagnetic torque. Furthermore, it has led to a quasi-circular shape of the locus described by the stator flux vector in the stationary plane.Research limitations/implicationsThis work should be extended to the synthesis and performance analysis of a new DTC strategy for B3-VSI-fed IM drive, which emulates the operation of the conventional six-switch three-phase inverter-fed IM drive.Originality/valueThe limitation associated with the reduced number of the intrinsic voltage vectors generated by the B3-VSI has been eradicated, thanks to the suitable synthesis of the look-up table incorporated in the DTC scheme.

Physical Parameters of a Reactor-Stellarator with Small Ripples of the Helical Magnetic Field

The paper describes the calculation data on the physical parameters of a reactor-stellarator, where the nonuniformities of the helical field are smaller than the toroidal magnetic field nonuniformities: eh et case, in the present calculations, these coefficients were assumed to be in proportion to the first power of the collision frequency, Di ∝ ν for νeff < 2ωE, and to Di ∝ ν−1 for the inverse inequality. Here, ωE is the rotation frequency of plasma in the radial electric field. As before, the plasma electrons corresponded to the mode of De ∝ ν−1. As initial parameters for numerical calculations, a reactor with R = 8 m, rp = 2 m, and B0 = 5 Т was taken. A numerical code was used to solve the set of equations that describes the plasma space−time behavior in the reactor-stellarator under the conditions of equal diffusion fluxes. The start of reactor operation in the mode of thermonuclear burning was provided by heating sources with a power of several tens of megawatts. Steady-state operating conditions of a self-sustained thermonuclear reaction were attained by maintaining the plasma density through DT fuel pellet injection into the plasma.

Thermal Performance Modeling of Foil Conductor Concentrated Windings in Electric Machines

While the use of foil windings in transformers and air core inductors is not uncommon, their use in electric machines is just emerging. Although prototype realizations have been reported in the literature, a definitive analysis of their thermal performance is necessary to evaluate their potential for broad applications. This paper is devoted to presenting a comprehensive model for evaluating their thermal performance including loss modeling and temperature rise prediction in realistic designs. An overview of foil windings in electric machines and their advantages in improved fill factor is presented, along with experimental results that compare the ac losses and temperature distribution under identical steady-state operating conditions with a prototype round conductor coil and foil conductor coil. A lumped parameter thermal model that predicts the heat transfer behavior of the foil conductor coil is presented along with supporting experimental results.

Periodic Steady State Assessment of Microgrids with Photovoltaic Generation Using Limit Cycle Extrapolation and Cubic Splines

This paper proposes a fast and accurate time domain (TD) methodology for the assessment of the dynamic and periodic steady state operation of microgrids with photovoltaic (PV) energy sources. The proposed methodology uses the trapezoidal rule (TR) technique to integrate the set of first-order differential algebraic equations (DAE), generated by the entire electrical system. The Numerical Differentiation (ND) method is used to significantly speed-up the process of convergence of the state variables to the limit cycle with the fewest number of possible time steps per cycle. After that, the cubic spline interpolation (CSI) algorithm is used to reconstruct the steady state waveform obtained from the ND method and to increase the efficiency of the conventional TR method. This curve-fitting algorithm is used only once at the end part of the algorithm. The ND-CSI can be used to assess stability, power quality, dynamic and periodic steady state operation, fault and transient conditions, among other issues, of microgrids with PV sources. The results are successfully validated through direct comparison against those obtained with the PSCAD/EMTDC simulator, widely accepted by the power industry.

Influence of the initial sludge characteristics and acclimation on the long-term performance of double-compartment acetate-fed microbial fuel cells

In this work, three double-compartment MFCs (DC-MFC) were operated for 1 month in order to compare their performances in terms of wastewater treatment capacity and electricity production and to get information about how this performance is influenced by the start-up procedure. To do this, they underwent different start-up procedures. One of them (aerobic-starved MFC) was inoculated with 100% fresh aerobic sludge, another (anaerobic-starved MFC) using 100% fresh anaerobic sludge, and finally a third one (aerobic-fed MFC) was inoculated using a mixture 10% fresh aerobic sludge and 90% synthetic wastewater (based on acetate). Then, from this start-up, the cells were operated exactly under the same feeding and operation conditions and they underwent the same tests. Results demonstrate that after one month of operation, in DC-MFCs, there are no significant differences in the steady state operation conditions reached because the three cells lead to a very similar treatment capacity, quantified in terms of the COD consumption rate, and to a quite similar value of the current produced. A comprehensive electrochemical characterization informed that the small differences cannot be explained in terms of the different start-up period. This means that the DC-MFC technology is robust enough regarding the inoculation and within systems undergoing the same disturbances, outputs obtained are quite the same, which becomes a very important observation for future works.

Mixed stochastic-deterministic tube MPC for offset-free tracking in the presence of plant-model mismatch

This paper presents a stochastic-tube model predictive control (MPC) strategy that systematically handles plant-model mismatch, guarantees stability in the presence of changing operating conditions, and ensures offset-free tracking for all reachable operating conditions. The key notion of this work is to separate the system uncertainty into two distinct sources of additive bounded state error. The first source is a non-random uncertainty that represents mismatch between the linear model of the controller and the true plant (as well as other types of persistent disturbances). The second source represents random fluctuations due to either the intrinsic stochastic variability of the system, or exogenous disturbances. Recursive feasibility and stability of the stochastic-tube MPC strategy is guaranteed by defining the terminal invariant set to include the effect of changes in the steady-state operating conditions. Offset-free tracking is achieved with a disturbance estimator that can be tuned independently of the controller. To reduce the conservatism inherent to robust control performance, a new filter model for deterministic disturbances is proposed that predicts uncertainty in the future evolution of the disturbances based on a bound on how quickly the plant-model mismatch can vary. The stochastic-tube MPC strategy is demonstrated on two simulation case studies—a benchmark DC-DC converter and an industrially-motivated fluidized-bed catalytic cracking unit.

Effect of the engine calibration parameters on gasoline partially premixed combustion performance and emissions compared to conventional diesel combustion in a light-duty Euro 6 engine

A design of experiments analysis was performed to investigate the effects of pilot quantity, combustion phasing and exhaust gas recirculation on performance and emissions in a gasoline partially premixed combustion to find out the optimal combination of the all varied parameters.The experimental activities were performed on a light-duty Volvo Euro 6 diesel engine. The test was performed under steady-state operating conditions, nine test points were chosen inside the operating area of the New European Driving Cycle and the Worldwide Harmonized Light vehicles Test Cycles. A fractional factorial analysis in partially premixed combustion on the single and combined effect of the main engine calibration parameters and a global comparison between partially premixed combustion and conventional diesel combustion on the engine performance and emissions adopting the optimal calibration parameters obtained from design of experiments analysis for both combustion modes analysed were presented. The purpose was to obtain the calibration parameters setting that permits to achieve high efficiency and low emissions as well.The partially premixed combustion results show the highest efficiency and lowest NOx emissions adopting a high exhaust gas recirculation rate combined with advanced combustion phasing and lower pilot quantity. Higher efficiency, up to 2.0% units, was obtained in partially premixed combustion with respect to the conventional diesel combustion due to the lower heat transfer loss. Lower soot (about two times) and NOx (about −0.5 g/kWh) levels with partially premixed combustion were obtained and compared to conventional diesel combustion at the same exhaust gas recirculation level.A reduction of about 5% of CO2 and fuel consumption with a 50% of reduction on NOx and soot simultaneously were obtained for partially premixed combustion on the New European Driving Cycle estimation results with respect to the diesel combustion. The information derived from this work are useful to develop and calibrate a light-duty engine that operate in gasoline partially premixed combustion mode achieving NOx close to the Euro 6 limit without adopting any after treatment system.

Investigating Factors That Influence Conditioning Time of PEFCs

The conditioning time required for PEFCs to reach either peak performance or system power requirement will have a definite impact on overall system cost. During the past decade, FC research and development has focused its efforts on overcoming several technical barriers (targets) that could compromise the viability of the technology. Performance, cost, and durability are three of the barriers in which a large portion of the efforts were placed. Consequently, this attention led to substantial improvements in the FC materials and components helping meet and or surpass technical targets. While these scientific advances were instrumental in the emergence of pilot Fuel Cell Electric Vehicles; it becomes critical that the conditioning time be minimal in order to produce affordable Fuel Cell systems for large scale production. We will present results on factors that influence the PEFC conditioning time. The various aspects that can affect the conditioning time include: MEA manufacturing processing conditions (pressing / drying conditions)Electrode Morphology/Engineering (Ionomer/carbon ratio, catalyst and catalyst support materials, membrane (composition, thickness, radical scavenger additives),Conditioning methodology (potential cycling versus steady state)Operating conditions (Temp, relative humidity)

Analytical modelling and numerical experiment for simultaneous identification of unbalance and rolling-bearing coefficients of the continuous single-disc and single-span rotor-bearing system with Rayleigh beam model

Abstract This study proposes an algorithm for the simultaneous identification of residual unbalance and bearing dynamic coefficients of a single-disc and single-span rotor based on the unbalance response. The rotor is modelled as a homogeneous and continuous Rayleigh beam. A fourth-order non-homogeneous partial differential equation set with a homogeneous boundary condition is solved to obtain the analytical solution, which expresses the unbalance response as a function of position, rotor unbalance, and bearing stiffness and damping coefficients. Accordingly, the inverse problem is studied. A novel algorithm that can be applied to both a rolling-bearing rotor and an oil journal bearing rotor is proposed to identify the rotor unbalance during operation. Another novel algorithm is developed to identify the bearing stiffness and damping coefficients for a rolling-bearing rotor. Only four measured unbalance responses are required in the two above-mentioned algorithms. Thus, a simultaneous identification of the rotor unbalance and the roll-bearing dynamic coefficients can be achieved. Furthermore, only a measured response registered for the disc, the two bearings and any other selected cross-section of the rotor shaft under steady-state operating conditions is required. Numerical simulation shows that the proposed identification algorithms have excellent detection capabilities. In summary, the proposed algorithms provide an efficient means for rotor parameter identification without test runs or external excitations.

Optimal Feedback Linearization Control of Interior PM Synchronous Motors Subject to Time-Varying Operation Conditions Minimizing Power Loss

This paper presents development of an optimal feedback linearization control for interior permanent magnet synchronous machines operating in a nonsteady-state operating point, i.e., varying torque and speed, to achieve precision tracking performance and energy saving by minimizing the copper loss. An isomorphism mapping between the dq axes phase voltages and two auxiliary control inputs over full ranges of torque and speed is established by the linearization controller using the notion of orthogonal projection. The auxiliary control inputs are defined to be exclusively responsible for torque generation and power consumption. Subsequently, an analytical solution for the optimal-linearization control is derived in a closed form by applying the Hamiltonian of optimal control theory in conjunction with the Pontryagin's minimum principle. The optimal controller takes the maximum voltage limit and torque tracking constraint into account while maximizing machine efficiency for nonconstant operational load torque and speed. Unlike the convectional quadratic regulator-based control of electric motors, the proposed control approach does not rely on steady-state operation conditions and hence, it is suitable for such applications as electric vehicles and robotics. Experimental results demonstrate torque-tracking and energy-efficiency performance of a motor operating with nonconstant torque.

Advanced Active Power Filter Performance for Grid Integrated Hybrid Renewable Power Generation Systems

An active power filter implemented with a four leg voltage-source inverter using a predictive control scheme is presented. The use of a four leg voltage-source inverter allows the compensation of current harmonic components, as well as unbalanced current generated by single-phase nonlinear loads. A detailed yet simple mathematical model of the active power filter, including the effect of the equivalent power system impedance, is derived and used to design the predictive control algorithm. The compensation performance of the proposed active power filter and the associated control scheme under steady state and transient operating conditions is demonstrated through simulations and experimental results.

A novel intelligent modeling framework integrating convolutional neural network with an adaptive time-series window and its application to industrial process operational optimization

With the increasing complexity of industrial processes, it becomes more and more difficult to set up process operational optimization models. Recently, the convolutional neural network (CNN) has been widely and successfully applied to extracting useful information due to its deep learning capability. Aiming at extracting useful information concerning operational optimization from complex industrial process data, this paper proposes a novel framework integrating CNN with an adaptive time-series window (ATSW-CNN). The proposed ATSW-CNN method is composed of four kinds of network layers, i.e. the proposed adaptive layer, convolutional layers, pooling layers and fully connected layers. The proposed adaptive layer provides CNN paradigms with a capability of adaptively selecting appropriate time-series windows for different steady-state operational optimization data. As a result, the proposed ATSW-CNN method can effectively extract steady-state optimal operating conditions from process time-series data. In order to validate the performance of the proposed ATSW-CNN, simulations on an industrial furnace are carried out. Simulation results verify the effectiveness of the proposed method, which demonstrates the proposed ATSW-CNN method is applicable for searching steady state operating strategies.

Fuel performance of chromium-coated zirconium alloy and silicon carbide accident tolerant fuel claddings

The U.S. Department of Energy’s Accident Tolerant Fuel program is focused on extending the time for fuel failure during postulated severe accidents compared to the standard UO2-Zr alloy fuel system. This paper investigates the feasibility of two different chromium-coated cladding concepts, one of which is zirconium-alloy based and the other is composite-SiC based. Both claddings had 50 µm coatings, deducted from the base layer thicknesses. The claddings were studied, using the multi-physics fuel performance tool BISON, under steady-state PWR operating conditions as well as under two transients: a power ramp and a loss-of-coolant accident (LOCA). The chromium-coated claddings showed comparable thermo-mechanical performance to the reference Zircaloy-4 cladding. As chromium is reported to provide an order of magnitude improvement in oxidation resistance, it is expected to be a better alternative in accident scenarios. Simulation results for both concepts show that further experimental investigation as well as modeling of beyond design-basis accidents is warranted.

Fault detection and classification of permanent magnet synchronous motor in variable load and speed conditions using order tracking and machine learning

Permanent magnet synchronous machines have gained popularity in wind turbines due to their merits of high efficiency, power density, and reliability. The wind turbines normally work in a wide range of operations, and harsh environments, so unexpected faults may occur and result in productivity losses. The common faults in the permanent magnet machines occur in the bearing and stator winding, being mainly detected in steady-state operating conditions under constant loads and speeds. However, variable loads and speeds are typical operations in wind turbines and powertrain applications. Therefore, it is important to detect bearing and stator winding faults in variable speed and load conditions. This paper proposes an algorithm to diagnose multiple faults in variable speed and load conditions. The algorithm is based on tracking the frequency orders associated with faults from the normalised order spectrum. The normalised order spectrum is generated by resampling the measured vibration signal via estimated motor speeds. The fault features are then generated from the tracking orders in addition to the estimated torque and speed features. Finally, support vector machine algorithm is used to classify the faults. The proposed method is validated using experimental data, and the validated results confirm its usefulness for practical applications.