Steady-state Performance Analysis Research Articles

Rotor Configurations for Improved Starting and Synchronous Performance of Line Start Permanent-Magnet Synchronous Motor

This paper presents two new rotor configurations for the line start permanent-magnet synchronous motors (PMSMs). The first configuration proposed here uses inset consequent magnet pole arrangement with double cage, and results into improved starting performance when compared to the other rotor configurations previously used. The second configuration proposed uses a combination of circumferentially and radially magnetized magnets (hybrid rotor), with induced magnet poles, which results into improved synchronous performance. Two-dimensional finite-element analysis has been employed in the analysis of transient and steady-state performances. The experimental prototypes for the second configuration are built and tested extensively. To demonstrate the effectiveness of the hybrid rotor configuration, an additional prototype is made that employs the circumferentially magnetized magnets (spoke magnet type rotor), and performance of the proposed rotor is benchmarked with this. Analysis, simulation, and experimental results indicate that the proposed rotor configuration leads to improved steady-state performance, by utilizing 10% less magnet volume than the benchmarked spoke rotor. The proposed configurations are also suitable for inverter-fed brushless dc, and PMSMs.

Transient and steady state performance analysis of power flow control in a DFIG variable speed wind turbine

Abstract This paper presents transient and steady state performance analysis of power flow control in a 5.0 kW Doubly-Fed Induction Generator (DFIG) Variable Speed Wind Turbine (VSWT) under sub synchronous speed, super synchronous speed and synchronous speed modes of operation. Stator flux orientation is used for the control of the rotor-side converter (RSC) and DFIG whereas the grid (or stator) voltage orientation is the preferred choice for the control of the grid-side converter (GSC). In each of the three speeds modes, power is always supplied to the grid through the stator of the DFIG. The magnitude of net power (stator power plus rotor power) is less than stator power during the sub synchronous speed mode; it is greater than stator power during the super synchronous speed mode while it is equal to the stator power during the synchronous speed mode. In synchronous speed mode, the rotor power is zero indicating that power is neither supplied to the grid from the rotor nor supplied to the rotor from the grid; here the magnitude of net power is equal to stator power. The simulation results thus obtained in a MATLAB/SIMULINK environment laid credence to the controllability of power flow reversal in a DFIG-VSWT through back-to-back power electronic converter.

A Multi-Functional Fully Distributed Control Framework for AC Microgrids

This paper proposes a fully distributed control methodology for secondary control of ac microgrids. The control framework includes three modules: 1) voltage regulator; 2) reactive power regulator; and 3) active power/frequency regulator. The voltage regulator module maintains the average voltage of the microgrid distribution line at the rated value. The reactive power regulator compares the local normalized reactive power of an inverter with its neighbors’ powers on a communication graph and, accordingly, fine-tunes Q-V droop coefficients to mitigate any reactive power mismatch. Collectively, these two modules account for the effect of the distribution line impedance on the reactive power flow. The third module regulates all inverter frequencies at the nominal value while sharing the active power demand among them. Unlike most conventional methods, this controller does not utilize any explicit frequency measurement. The proposed controller is fully distributed; i.e., each controller requires information exchange with only its neighbors linked directly on the communication graph. Steady-state performance analysis assures the global voltage regulation, frequency synchronization, and proportional active/reactive power sharing. An ac microgrid is prototyped to experimentally validate the proposed control methodology against the load change, plug-and-play operation, and communication constraints such as delay, packet loss, and limited bandwidth.

A steady-state performance analysis of a non-circular cylindrical floating ring journal bearing

This paper analyses the steady-state performance behaviour of a new type of journal bearing, i.e. the non-circular cylindrical floating ring journal bearing. It consists of a floating ring in between the shaft and the upper and lower lobes of a two-lobe bearing. The journal and the inner surface of the ring are cylindrical while bearing surfaces are non-circular. The classical Navier–Stokes equations in the modified form together with the continuity equation are being solved by the finite element method. The cylindrical coordinates form of the Navier–Stokes equation and continuity equation are used in the present analysis to compute the important proposed bearing characteristics. In this analytical study, the finite bearing approximation ( L/ D=1) with a C2/ C1 value of 0.70 and 1.30 are being used to simulate the behaviour of non-circular cylindrical floating ring journal bearing. The Reynold’s boundary condition is used to enumerate the performance of the proposed bearing. In the present analysis, the steady-state parameters in terms of an inner and outer film eccentricity ratio, a speed ratio, attitude angle, load capacity, friction coefficient parameter, axial oil flow and rise in temperature variable are determined. The results reveal that the steady-state performance of the non-circular floating ring journal bearing is superior to a plain cylindrical floating ring journal bearing.

복수 실내기를 가지는 에어컨의 정상상태 성능해석

복수 실내기를 가지는 에어컨의 정상상태 성능해석

A Novel Distributed Secondary Coordination Control Approach for Islanded Microgrids

This paper develops a new distributed secondary cooperative control scheme to coordinate distributed generators (DGs) in islanded microgrids (MGs). A finite time frequency regulation strategy containing a consensus-based distributed active power regulator is presented, which can not only guarantee the active power sharing but also enable all DGs' frequencies to converge to the reference value within a finite time. This enables the frequency and voltage control designs to be separated. Then an observer-based distributed voltage regulator involving certain reactive power sharing constraints is proposed, which allows different set points for different DGs and, thus, accounts for the line impedance effects. The steady-state performance analysis shows that the voltage regulator can accurately address the issue of global voltage regulation and accurate reactive power sharing. Moreover, all the distributed controllers are equipped with bounded control inputs to suppress the transient overshoot, and they are implemented through sparse communication networks. The effectiveness of the control in case of load variation, plug-and-play capability, communication topology change, link failure, time delays, and data drop-out are verified by the simulation of an islanded MG in MATLAB/SimPowerSystems.

Determination of groove location of two-lobe hydrodynamic bearings for optimum performance using genetic algorithm

A steady-state performance analysis of two-lobe oil journal bearing has been carried out in this paper. A computer program has been prepared to calculate the steady-state hydrodynamic characteristics. To study the steady-state characteristics of two-lobe bearing, the nondimensional Reynolds’ equation is solved to obtain nondimensional values of load-carrying capacity, flow rate, attitude angle, and friction variable. Parameters of the design are studied for different groove configurations and an optimized groove location is obtained for two-lobe bearing is obtained using genetic algorithm. It has been found that placing the groove on different locations have greater influence on the design parameters such as the nondimensional oil flow rate, frictional variable, and nondimensional load-carrying capacity. From numerical simulation of two-lobe bearing, it has been found that in case of this bearing parameters shows optimum values when the grooves are arranged below the horizontal axis. There is an improvement in nondimensional values of friction variable, nondimensional flow rate, and nondimensional load-carrying capacity at optimum location of the groove. The analysis is carried out for an ellipticity ratio of 0.5 and the results obtained have been reported.

Complex vector modelling and sequence analysis of the integrated three‐phase rotating transformer for design of a symmetrical structure

In this paper, a complex vector model is provided for an integrated three-phase shell-type rotating transformer. The equivalent magnetic circuit is used to obtain the transformer parameters. Furthermore, using vector representation of the dq transformation, the voltage equations of the rotating transformer in double-reference synchronous frame are obtained. Thanks to the developed model, the transformer design parameters are selected such that the voltage equations in double-reference frames are decoupled. For the first time, the machine complex vector representation is exploited to design a symmetrical rotating three-phase transformer. For this purpose, two separated equivalent circuits in double-reference frames or two decoupled sequences networks are developed. The decoupled circuits simplify the analysis of the rotating transformer in the unbalanced conditions as well as balanced circuits. Being symmetrical is an important issue for the rotating transformer connected to the rotor winding of a doubly-fed induction generator. Moreover, the steady-state performance and sequence analysis of the rotating transformer are discussed. Finally, the validity of the obtained model and accuracy of the presented analysis are verified by finite element analysis and experimental tests.

Steady state performance analysis of OSR and serial OSR-WGS reactors

A lab scale fuel processor test prototype (FPP) was designed, constructed, and used in analyzing steady state performance of individual propane oxidative steam reforming (OSR) reactor and serially combined propane OSR and water gas shift (WGS) reactors. OSR and WGS reactions were performed over novel Pt‐Ni/δ-Al2O3 and Au‐Re/ZrO2 catalysts, respectively. During the steady state tests, concentrations of C3H8, O2, H2, CH4, CO and CO2 in the feed and product streams were measured on line-real time by a mass spectrometer. The tests have been conducted for different compositions of oxygen, propane and steam in the feed stream of OSR reactor in both individual and serial tests. The highest achieved H2/CO product ratio was ca. 32–33 for 723–623K and 673–573K OSR-WGS reactor temperature combinations in serial operation, with S/C feed ratio of 3 and O/C feed ratio of 0.74. In the performance tests, maximum conversions achieved were 100% C3H8 and 50% CO in the OSR and WGS reactors, respectively. In the tests, steady state, dry basis, inert free, H2 concentrations higher than 50% and CO concentrations as low as 1% in the WGS product stream were obtained. The performance stability of both catalysts were confirmed by the product concentration profiles obtained during 75h time-on-stream stability test performed on OSR-WGS system and by microstructural characterization of the OSR and WGS catalysts as well.

Time-Dependent Performance Analysis of IEEE 802.11p Vehicular Networks

The performance of vehicular ad hoc networks (VANETs) is subject to frequent changes due to node mobility so that nonstationary/transient network behavior always exists. In addition, safety applications in VANETs are very sensitive to the real-time performance of delay and packet delivery ratio (PDR). Although there are extensive studies on the steady-state (SS) performance analysis of vehicular networks, little work exists on evaluating their time-varying behavior. In this paper, we develop a performance model to efficiently estimate the dynamic behavior of VANETs. In this paper, vehicle's transmission queue is modeled using fluid-flow (FF)-based differential equations, which are solved using numerical methods, whereas the network hearing topology is modeled by a time-varying adjacency matrix that can be determined from stochastic models, measurements, or discrete event simulations. Numerical results illustrate that our performance model is able to promptly respond to the ongoing dynamic conditions of VANETs and provide reasonably accurate performance results.

Influence analysis of secondary O-ring seals in dynamic behavior of spiral groove gas face seals

The current research on secondary O-ring seals used in mechanical seals has begun to focus on their dynamic properties. However, detailed analysis of the dynamic properties of O-ring seals in spiral groove gas face seals is lacking. In particular a transient study and a difference analysis of steady-state and transient performance are imperative. In this paper, a case study is performed to gauge the effect of secondary O-ring seals on the dynamic behavior (steady-state performance and transient performance) of face seals. A numerical finite element method (FEM) model is developed for the dynamic analysis of spiral groove gas face seals with a flexibly mounted stator in the axial and angular modes. The rotor tilt angle, static stator tilt angle and O-ring damping are selected to investigate the effect of O-ring seals on face seals during stable running operation. The results show that the angular factor can be ignored to save time in the simulation under small damping or undamped conditions. However, large O-ring damping has an enormous effect on the angular phase difference of mated rings, affecting the steady-state performance of face seals and largely increasing the possibility of face contact that reduces the service life of face seals. A pressure drop fluctuation is carried out to analyze the effect of O-ring seals on the transient performance of face seals. The results show that face seals could remain stable without support stiffness and O-ring damping during normal stable operation but may enter a large-leakage state when confronting instantaneous fluctuations. The oscillation-amplitude shortening effect of O-ring damping on the axial mode is much greater than that on the angular modes and O-ring damping prefers to cater for axial motion at the cost of angular motion. This research proposes a detailed dynamic-property study of O-ring seals in spiral groove gas face seals, to assist in the design of face seals.

Diffusion minimum-Wilcoxon-norm over distributed adaptive networks: Formulation and performance analysis

This paper deals with the development of robust diffusion strategy for wireless sensor networks using minimum-Wilcoxon-norm. The Wilcoxon norm based robust estimation now-a-days has drawn the attention of the signal processing community for its scale equivariant property and simplicity. Exhaustive mathematical analysis has been presented to obtain the proposed diffusion minimum-Wilcoxon-norm (dMWN) algorithm. Steady state performance analysis of the algorithm has also been carried out to show the stability of the proposed method. Asymptotic linearity of rank test [1] is used for the convergence analysis of the proposed method. Extensive simulations have been given to demonstrate the efficacy of the proposed algorithm.

Coupling of an offshore wind-driven deep sea water pump to an air cycle machine for large-scale cooling applications

A system for using offshore wind energy to directly provide large-scale cooling through the exploitation of cold deep seawater below thermocline formations is proposed. The concept is based on an offshore wind-driven hydraulic pump supplying high pressure deep seawater to a land based plant. This pressurised seawater is used to power a hydraulic turbine which drives an inverse Brayton air cycle machine, and is then diverted to a heat exchanger to cool the pressurised air prior to flowing back to the sea.A mathematical model for steady-state performance analysis of the proposed system under specified ambient conditions is presented. It was found that the system coefficient of performance was highest at low wind speeds and improved with increasing ambient temperature and humidity. This makes the system ideal for hot and humid climates. The availability of a sufficiently cold deep seawater resource was also found to be crucial for the viability of the system.

Mathematical modeling and analysis of steady state performance of a heat pipe network

In the current study, the thermal-fluid phenomenon inside a heat pipe network is simulated numerically. The heat pipe is specially configured to be implemented in thermal energy storage units for a concentrating solar power system. It composed of a main heat pipe and an array of secondary heat pipes. The applied thermal energy to the disc-shaped evaporator is transferred to the heat engine by the primary heat pipe. The extra heat is delivered to the phase change material through the concentric secondary heat pipes. The vapor flow leaving the adiabatic pipe section of the primary heat pipe to the disc-shaped condenser behaves similarly to the confined jet impingement. Therefore, the condensation is not uniform over the main condenser. In order to model the physical phenomenon inside the heat pipe network, a new numerical procedure was developed. The feature that makes the procedure distinguished from other available techniques is its ability to simulate non-uniform condensation of the working fluid in the condenser section. The vapor jet impingement on the condenser surface along with condensation was modeled by attaching a porous layer adjacent to the condenser wall. This porous layer acts as a wall and let the vapor flow to split out radially while it allows mass transfer through it. The effects on the pressure and temperature distributions from the heat input, portion of heat transferred to the phase change material, main condenser geometry and secondary heat pipe configurations have been investigated. The result showed that the temperature distributions of main and secondary heat pipes are greatly affected by the geometrical features. The formed recirculation zones in the main condenser region, which depend on geometrical parameters, make the performance of heat pipes convoluted. For the case with one secondary heat pipe, placing it away from the primary heat pipe provides higher temperatures at the primary and the secondary heat pipes. It also yields more uniform temperature at the main condenser. For cases with two and three secondary heat pipes, the temperature of the secondary heat pipes highly depends on the secondary heat pipes position and the ratio of heat transfer to the PCM.

Droop-Free Distributed Control for AC Microgrids

A cooperative distributed secondary/primary control paradigm for AC microgrids is proposed. This solution replaces the centralized secondary control and the primary-level droop mechanism of each inverter with three separate regulators: voltage, reactive power, and active power regulators. A sparse communication network is spanned across the microgrid to facilitate limited data exchange among inverter controllers. Each controller processes its local and neighbors' information to update its voltage magnitude and frequency (or, equivalently, phase angle) set points. A voltage estimator finds the average voltage across the microgrid, which is then compared to the rated voltage to produce the first-voltage correction term. The reactive power regulator at each inverter compares its normalized reactive power with those of its neighbors, and the difference is fed to a subsequent PI controller that generates the second-voltage correction term. The controller adds the voltage correction terms to the microgrid rated voltage (provided by the tertiary control) to generate the local voltage magnitude set point. The voltage regulators collectively adjust the average voltage of the microgrid at the rated voltage. The voltage regulators allow different set points for different bus voltages and, thus, account for the line impedance effects. Moreover, the reactive power regulators adjust the voltage to achieve proportional reactive load sharing. The third module, the active power regulator, compares the local normalized active power of each inverter with its neighbors' and uses the difference to update the frequency and, accordingly, the phase angle of that inverter. The global dynamic model of the microgrid, including distribution grid, regulator modules, and the communication network, is derived, and controller design guidelines are provided. Steady-state performance analysis shows that the proposed controller can accurately handle the global voltage regulation and proportional load sharing. An AC microgrid prototype is set up, where the controller performance, plug-and-play capability, and resiliency to the failure in the communication links are successfully verified.

Steady-state off-design thermodynamic performance analysis of a SCCP system

A steady-state model of a small combined cooling and power (SCCP) system, which includes a micro gas turbine (MGT) and a LiBr–H2O single-effect absorption chiller with a cooling tower, is built to investigate the off-design performance of the system. The off-design performance of the compressor and expander of the MGT is described by characteristic maps. Holman correlation is applied to the calculation of heat transfer coefficients of the recuperator, evaporator, condenser, solution heat exchanger, and generator. The heat and mass transfer in the absorber are described according to a physical model based on Nusselt's film theory. The F-LMED method is applied in the cooling tower model. The system is evaluated under different MGT output power and ambient temperature. The effect of the different operation modes of cooling tower is studied. Simulation results show that the performance deterioration of the system is mainly caused by the poor performance of the MGT. The COP and cooling capacity vary smoothly under off-design condition in which the outlet water temperature of the cooling tower remains constant. The effects of the two operation modes of the cooling tower on the cooling capacity of the system do not differ greatly when energy quality is considered.

Failure probabilities of SiC clad fuel during a LOCA in public acceptable simple SMR (PASS)

Structural integrity of SiC clad fuels in reference Small Modular Reactors (SMRs) (NuScale, SMART, IRIS) and a commercial pressurized water reactor (PWR) are assessed with a multi-layered SiC cladding structural analysis code. Featured with low fuel pin power and temperature, SMRs demonstrate markedly reduced incore-residence fracture probabilities below ∼10−7, compared to those of commercial PWRs ∼10−6–10−1. This demonstrates that SMRs can serve as a near-term deployment fit to SiC cladding with a sound management of its statistical brittle fracture. We proposed a novel SMR named Public Acceptable Simple SMR (PASS), which is featured with 14×14 assemblies of SiC clad fuels arranged in a square ring layout. PASS aims to rely on radiative cooling of fuel rods during a loss of coolant accident (LOCA) by fully leveraging high temperature tolerance of SiC cladding. An overarching assessment of SiC clad fuel performance in PASS was conducted with a combined methodology—(1) FRAPCON-SiC for steady-state performance analysis of PASS fuel rods, (2) computational fluid dynamics code FLUENT for radiative cooling rate of fuel rods during a LOCA, and (3) multi-layered SiC cladding structural analysis code with previously developed SiC recession correlations under steam environments for both steady-state and LOCA. The results show that PASS simultaneously maintains desirable fuel cooling rate with the sole radiation and sound structural integrity of fuel rods for over 36 days of a LOCA without water supply. The stress level of PASS fuel rods during LOCA is predominantly governed by the initial cold gap pressure; a decrease of the cold gas gap pressure is a handy design direction to assure structural safety margin for SiC cladding.

Mathematical Modelling and Steady State Performance Analysis of a Markovian Queue with Heterogeneous Servers and Working Vacation

In the present paper, mathematical modeling for analyzing a Markovian queueing system with two heterogeneous servers and working vacation has been demonstrated. Keeping in view queueing situations in real life problems, here we consider service policy that initially both the heterogeneous servers take vacation when there are no customers waiting for service in the queue; however, after this server 1 is always available but the other goes on vacation whenever server 2 is idle. The vacationing server however, returns to serve at a low rate as an arrival finds the other server busy. Busy period analysis for the working vacation model with heterogeneous servers has been worked out. Performance measures of the Markovian queueing system with varying parameters have been explored under steady state using matrix geometric method. Finally, based on sensitivity analysis of the performance measures, conclusive observations have been focused.

An Active Clamp High Step-Up Boost Converter with a Coupled Inductor

An active clamp high step-up boost converter with a coupled inductor is proposed in this paper. In the proposed strategy, a coupled inductor is adopted to achieve a high voltage gain. The clamp circuit is included to achieve the zero-voltage-switching (ZVS) condition for both the main and clamp switches. A rectifier composed of a capacitor and a diode is added to reduce the voltage stress of the output rectifier diode. As a result, diodes with a low reverse-recovery time and forward voltage-drop can be utilized. Since the voltage stresses of the main and clamp switches are far below the output voltage, low-voltage-rated MOSFETs can be adopted to reduce conduction losses. Moreover, the reverse-recovery losses of the diodes are reduced due to the inherent leakage inductance of the coupled inductor. Therefore, high efficiency can be expected. Firstly, the derivation of the proposed converter is given and the operation analysis is described. Then, a steady-state performance analysis of the proposed converter is analyzed in detail. Finally, a 250 W prototype is built to verify the analysis. The measured maximum efficiency of the prototype is 95%.

Steady state performance analysis of multi-phase induction motor with non-sinusoidal supply

Electromagnetic performance analysis is the very foundation for electric machine design optimization. Thus, the research on performance evaluation methods for multi-phase induction machines with non-sinusoidal supply is of great theoretical value and practical importance, as such process is much more complicated than traditional methods developed for three-phase induction machines. The fundamental and third harmonic equivalent circuits are employed as design tools for induction machines supplied by non-sinusoidal voltages with third harmonic injection. Considering that the air-gap flux density is asymmetrical, extended distributed magnetic circuit approach(EDMCA) is used to calculate the fundamental and third harmonic EMFs. The performance of the induction machine is finally determined by calculating quantities such as the fundamental and third harmonic currents in steady state through 3 layers of iterations. Particularly, the inner-layer iteration that calculates the air-gap magnetic flux and the middle-layer iteration that determines the magnetizing current is quite different from the traditional performance analysis approach for three-phase induction machines. The proposed method is applied to a prototype fifteen-phase induction machine with non-sinusoidal supply. Close agreement between the calculated and experimental results at various working conditions indicates the high accuracy of the proposed method.