Steady-state Operation Performance Research Articles

Experimental study on the effect of the gas reservoir on the performance of a nitrogen-charged cryogenic grooved heat pipe

Nitrogen-charged cryogenic grooved heat pipes require gas reservoirs to reduce their initial charging pressure. However, the effect of gas reservoir on the performance of the heat pipe has rarely been investigated. In this paper, experimental studies were conducted to analyze the effects of different gas reservoir connection positions (the evaporation section and the condensation section) and different gas reservoir volumes on the startup and steady-state operation performance of heat pipes. The results indicate that the connection position of the gas reservoir affects the pressure drop of vapor flow in the heat pipe. When the gas reservoir connected to the evaporator of the heat pipe, the vapor flow pressure drop is lower, which is more favorable for the steady-state performance of the heat pipe. Additionally, a smaller gas reservoir volume allows the heat pipe to startup at higher temperatures and pressures, which can accelerate the startup rate of the heat pipe. The selection criteria for the application of gas reservoir in cryogenic heat pipes were provided. These results can be useful for optimization design of cryogenic grooved heat pipe.

Transient and Steady-State Performance Improvement of IM Drives Based on Dual-Torque Model

Transient response performance and steady-state operation performance are the two most important performance indicators of a motor drive system. In order to solve these two problems, this study proposes a new induction motor (IM) model, and then designs a new simplified linearization controller method. First, the tangential force that determines the transient process of the motor is represented by electromagnetic torque, and the radial force is represented by reactive torque. Then, the dual-torque model of IM is derived, which not only accurately shows the rotating air-gap magnetic field through the amplitude and rotating angular frequency, but also visually demonstrates the physical essence of the transient process of IM. Then, this study proposes a simplified feedback linearization method without the analysis of zero dynamic. In addition, a time-scale hierarchical control system is designed to reduce the ripple caused by the coupling of different time-scale variables. The experimental results show that the steady-state torque ripple of the proposed method is 65% lower than that of RFOC, and the torque response speed is 10% higher than that of DTC.

Modified Analytical Approach for PV-DGs Integration into a Radial Distribution Network Considering Loss Sensitivity and Voltage Stability

Achieving the goals of distribution systems operation often involves taking vital decisions with adequate consideration for several but often contradictory technical and economic criteria. Hence, this paper presents a modified analytical approach for optimal location and sizing of solar PV-based DG units into radial distribution network (RDN) considering strategic combination of important power system planning criteria. The considered criteria are total planning cost, active power loss and voltage stability, under credible distribution network operation constraints. The optimal DG placement approach is derived from the modification of the analytical approach for DG placement using line-loss sensitivity factor and the multiobjective constriction factor-based particle swarm optimization is adopted for optimal sizing. The effectiveness of the proposed procedure is tested on the IEEE 33-bus system modeled using Matlab considering three scenarios. The results are compared with existing reports presented in the literature and the results obtained from the proposed approach shows credible improvement in the RDN steady-state operation performance for line-loss reduction, voltage profile improvement and voltage stability improvement.

The Influence of Second Air-Gap Length on the Performance of 10 kV, 1000 kW Permanent Magnet Synchronous Motor

Background: The influence of the second air-gap length on the performance of permanent magnet synchronous motor is usually ignored. A comparative analysis is made of line-start high-voltage permanent magnet synchronous motor in this paper. Objective: The purpose of this paper is to analyze the influence of the second air-gap length on the motor performance. Methods: A 10kV 1000kW permanent magnet synchronous motor is taken as an example and the model is established based on the finite element calculation method when the second air-gap length is different. The influence of the second air-gap length on the phasor diagram, no-load back electrodynamic force, starting performance and steady-state operation performance are studied. Based on the finite element calculation method, the torque angle, current, power factor, external power factor and d/q-axis current of the motor are analyzed, and the change of the motor phasor diagram is obtained. The influence of the second air-gap length on the no-load back electrodynamic force is studied. Results and Conclusion: The relationship between the no-load back electrodynamic force and the no-load air-gap fundamental magnetic field is determined, and the influence mechanism of the noload air-gap fundamental magnetic field on no-load back electrodynamic force is revealed. Furthermore, the influence of the no-load back electrodynamic force on the starting performance is studied. Finally, the influence of the second air-gap length on the 10kV 1000kW permanent magnet synchronous motor steady-state performance is obtained. Based on the above analysis, some references are given for the design of motor.

Effect of servers’ arrangement on the performance of a loop thermosyphon system used in data center

• A loop thermosyphon system was studied under four typical servers’ arrangements. • The servers’ arrangement had little influence on the steady-state operating performance. • Clumped the servers at the bottom of the rack can shorten the start-up time under low rack utilization. In applications, servers’ arrangements are often chaotic owing to a lack of regulation, which may affect the performance of loop thermosyphon systems. In this study, the optimal filling ratio, thermal resistance and operating performance of a loop thermosyphon system were experimentally investigated under four typical servers’ arrangements. Compared with other servers’ arrangements, the optimal filling ratio range changed from 30.3–37.3% to 28.0–35.0% when clumped the servers at the bottom of the rack. However, the system thermal resistances were approximately equal (0.0034–0.0036 °C/W) at optimal filling ratios under the four servers’ arrangements, indicating that a filling ratio within 30.3–35.0% was suitable for all servers’ arrangements. At 32.7% filling ratio, the operating performances under different servers’ arrangements and heating powers were compared and analyzed. Although the maximum difference in the evaporator inlet air temperatures exceeded 10 °C, the servers’ arrangement did not affect the steady-state operating performance. Moreover, the servers’ arrangement had little influence on start-up times under 4 kW and 6 kW heating powers but had a significant influence under 2 kW heating power. Clumped the servers at the bottom of the rack can shorten the start-up time under low rack utilization (2 kW heating power).

Steady-State Analysis Based on Space Vector Model of Self-Excited Induction Generators

In order to attain more optimization for the procedure of transient and steady-state operation performance analysis and evaluation of self-excited induction generators (SEIGs), the paper converts the state-space transient mathematic model with real domain into the space vector transient model with complex domain based on the same two-phase stationary reference frame, described by which the physical systems can apply extendedly the holistic analysis approach based on Lyapunov stability theory proposed in real domain. Through equivalent analysis, the extended form of the steady-state conditions and its mathematic description into the complex domain is obtained, that is, the extended quasi limit cycle and the steady-state operating points. The analytic calculation for the extended steady-state condition provides successively the analytic solutions of exciting capacitance, stator frequency, as well as the extended steady state conditions under given rotor speed and magnetizing inductance. The practical calculation example verifies correctness and effectiveness of the approach and the analytic solution of the extended steady-state condition, with engineering reference values.

Steady-State Performance Prediction for a Variable Speed Direct Expansion Air Conditioning System Using a White-Box Based Modeling Approach

When using a certain type of Heating, Ventilation & Air Conditioning (HVAC) systems, it is primary to obtain their steady-state operating behaviors for achieving a better indoor thermal environment. This paper reports a development of a white-box-based dynamic model for a direct expansion (DX) air conditioning (A/C) system to predict its steady-state operating performance under variable speed operation. The established model consists of five sub-models, i.e., a compressor, an electronic expansion valve, an evaporator, a condenser and a conditioned space. Each sub-model was developed based on partial lumped parameter approach. Using the available data generated from an experimental DX A/C system, both transient and steady-state behaviors predictions agreed well with the experimental ones. With the help of the validated white-box model, the inherent steady-state operating performance expressed in terms of the relationship among total cooling capacity (TCC), equipment sensible heat ratio (E SHR) and coefficient of performance (COP) under various speed combinations of compressor and supply fan were further examined. The results show that a higher COP could be achieved when the DX A/C system was operated at a higher fan speed or a lower compressor speed for dealing with a larger required E SHR. This model could be helpful for A/C system design and controller development.

Chemically durable polymer electrolytes for solid-state alkaline water electrolysis

Generation of high purity hydrogen using electrochemical splitting of water is one of the most promising methods for sustainable fuel production. The materials to be used as solid-state electrolytes for alkaline water electrolyzer require high thermochemical stability against hydroxide ion attack in alkaline environment during the operation of electrolysis. In this study, two quaternary ammonium-tethered aromatic polymers were synthesized and investigated for anion exchange membrane (AEM)-based alkaline water electrolyzer. The membranes properties including ion exchange capacity (IEC), water uptake, swelling degree, and anion conductivity were studied. The membranes composed of all C–C bond polymer backbones and flexible side chain terminated by cation head groups exhibited remarkably good chemical stability by maintaining structural integrity in 1 M NaOH solution at 95 °C for 60 days. Initial electrochemical performance and steady-state operation performance were evaluated, and both membranes showed a good stabilization of the cell voltage during the steady-state operation at the constant current density at 200 mA/cm2. Although both membranes in current form require improvement in mechanical stability to afford better durability in electrolysis operation, the next generation AEMs based on this report could lead to potentially viable AEM candidates which can provide high electrolysis performance under alkaline operating condition.

A Digital Method of Power-Sharing and Cross-Regulation Suppression for Single-Inductor Multiple-Input Multiple-Output DC–DC Converter

This paper presents a digital method to regulate the single-inductor multiple-input multiple-output (SI-MIMO) dc–dc converter, which can integrate renewable sources and loads as the hybrid renewable energy system with less components. The digital method is able to achieve power-sharing and cross-regulation suppression, and it is named as PS-CRS. PS-CRS is based on model predictive control, power sharing, and time multiplexing. A power-sharing controller is developed to regulate the power from multiple power sources. A cross-regulation-suppression controller is designed to control the output voltages independently with reduced cross regulation, which is the critical issue of the single-inductor multiple-output dc–dc converter. Experimental prototype of a single-inductor dual-input dual-output buck converter is built for verification. The steady-state operation and dynamic performance cases are studied. The results demonstrate that PS-CRS is able to regulate the SI-MIMO dc–dc converter effectively and robustly.

Feed-Forward-based Control in a DC–DC Converter of Asymmetric Multistage-Stacked Boost Architecture

A new feed-forward control technique for a dc–dc step-up converter based on the asymmetric multistage stacked boost architecture (MSBA) is proposed. The developed feed-forward controller directly handles the load current and the perturbations that may be caused by the dynamic operation of the converter. Thus, there is no time delay for estimating the error in a control process, and therefore, both robust steady-state operation and high dynamic performance can be achieved. The asymmetric MSBA dc–dc converter is a single-output high-voltage topology that embodies several in-series active voltage-balancing circuits. Thus, there is a need for an improved balancing control method. This can be accomplished by replacing the conventional proportional-integral controllers with feed-forward type and therefore improved balancing between the stages can be attained, because the steady-state errors are suppressed and the dynamic response can be enhanced. A thorough theoretical analysis is conducted for verifying the stability of the suggested feed-forward control technique in an asymmetric MSBA converter, and selective simulation and experimental results are demonstrated in order to validate the effectiveness and feasibility of the proposed control scheme.

Build‐up steady‐state analysis of wind‐driven self‐excited induction generators

For the contradiction between the increasing importance of the application of induction generator in the new energy power generation such as wind energy and the relative laggard of research on its comprehensive performance, the build-up steady-state analysis is performed for the wind-driven self-excited induction generator (SEIG) system based on the unloaded transient equivalent circuits and its mathematic model of SEIG in the two-phase stationary reference frame. Thus, it obtains the build-up steady-state conditions represented by the unloaded transient mathematic model. On the basis of the result obtained for the build-up steady-state limit cycle condition, the analytic solution for the build-up steady-state operating point condition and the analytic formulas for the limit magnetising induction are further obtained. Example analysis is to test out the only set of analytic solution for the build-up steady-state condition. Thus, the analytic solution for the build-up steady-state condition produces the formulas of the torture and the power factor, which can be applicable to further analysis for the system dynamics and build-up steady-state operating performance, showing practicability and referenced value in engineering.

Model Predictive Voltage Control for Single-Inductor Multiple-Output DC–DC Converter With Reduced Cross Regulation

This paper presents a model predictive voltage control (MPVC) method for the single-inductor multiple-output (SIMO) dc-dc converter. The proposed MPVC method is able to solve the cross-regulation problem, which is a critical issue in SIMO dc-dc converters. The design of the proposed method including augmented state-space model, cost function, enumerated algorithm, and constraints for the SIMO dc-dc converter is discussed. Simulation for the influences of predict horizon N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">P</sub> , control horizon N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">C</sub> , and Lagrange multiplier λ on the voltage ripple is conducted to guide the control parameters' setting for hardware implementation. Steady-state operation and dynamic performance of the proposed MPVC method are conducted in simulation and experiment based on the single-inductor dual-output (SIDO) buck converter to verify the proposed MPVC method. In addition, the comparison between the proposed method and state-of-art methods for the SIMO dc-dc converters is presented. Simulation and experimental results demonstrate that the MPVC method guarantees low cross regulation for the SIMO dc-dc converter in continuous-conduction mode (CCM) and has a fast response speed to variations in load and reference.

Induction Motor with Adjustable Windings for High Efficiency Drive in Light Load Operation

Heavy load start but light load operation is a common case in practical drive applications. When an induction motor is employed for such applications, its rated power is usually chosen according to the heavy load start. Then, during light load operation, its efficiency and power factor are low. To solve this problem, it is proposed to adjust the motor windings from the startup to the normal operation conditions. In this paper, arrangement of the adjustable windings is introduced, air gap field with different windings is investigated, and steady state operation performance under various loads is examined. It can be seen that by using proper winding arrangement both startup and operation performances are satisfactory.

Design research on the conductor of 10 kA class HTS DC power cable

High temperature superconducting (HTS) DC power cable shows a wide application prospect in the field of power transmission for its nearly lossless and rather high capacity. A 360m/10kA HTS DC power cable system, which connects the rectifier output of a substation with the bus bar of an electrolytic aluminium cell, will be put into operation at Henan Zhongfu Industrial Co., Ltd. As one of the items in this project, a 5m/10kA HTS DC power cable was developed, which is used to investigate the conductor design, fabrication, current-carrying capacity and stability of the 360m/10kA HTS power cable.The HTS DC power cable core consists of five conductor layers wound with spliced Bi-2223 wires with the length of 600m. The cable core has five layers and 23 conductors in each layer with the outer diameter of 45.42mm. The superconducting power cable is fabricated and tested. The critical current is about 14.3kA at 77K. The superconducting power cable is charged to 10kA with rate of 10A/s and operates at steady-state for 30min.In this paper, the 10kA HTS DC power cable design, fabrication and test are presented. The experimental research of the performance of spliced superconducting wire and charging, steady-state operating performance of the cable was carried out.

Wake effect in wind farm performance: Steady-state and dynamic behavior

The aim of this paper is to evaluate the impact of the wake effect on both the steady-state operation and dynamic performance of a wind farm and provide conclusions that can be used as thumb rules in generic assessments where the full details of the wind farms are unknown. A simplified explicit model of the wake effect is presented, which includes: the cumulative impact of multiple shadowing, the effects of wind direction and the wind speed time delay. The model is implemented in MATLAB ® and then integrated into a power system simulation package to describe the wake effect and its impact on a wind farm, particularly in terms of the wake coefficient and overall active power losses. Results for two wind farm layouts are presented to illustrate the importance of wind turbine spacing and the directionality of wind speeds when assessing the wake effect during steady-state operation and dynamic behavior.

Steady-state operating performance modelling and prediction for a direct expansion air conditioning system using artificial neural network

A two-in two-out steady-state artificial neural network (ANN)-based model for an experimental variable speed direct expansion (DX) air conditioning (A/C) system has been developed for simulating its total output cooling capacity and equipment sensible heat ratio under different combinations of compressor and supply fan speeds. Experiments were carried out, and totally 169 sets of experimental data were obtained for ANN training and testing. An ANN-based model having the configuration of 2 neurons in the input layer, 2 neurons in the output layer and 6 neurons in each of the 2 hidden layers, i.e. 2-6-6-2 configuration, was thus developed. The ANN-based model developed can be used to predict the operating performance of the DX A/C system with a higher accuracy. It is expected that the model developed can help design a multivariable-input multivariable-output strategy to simultaneously control indoor air temperature and humidity. Practical applications: The work reported in this paper demonstrates that the operating performance of a DX A/C system under different compressor and supply fan speeds can well be represented using ANN model technique, as an alternative to traditional physical-based modelling techniques, with a higher predicting accuracy and less computational effort. The ANN-based model for the DX A/C system is expected to be very useful in developing an efficient control algorithm for simultaneous indoor temperature and humidity using the ANN technique.

SPEED AND PARAMETER IDENTIFICATION FOR SENSORLESS VECTOR CONTROL OF INDUCTION MOTORS AT VERY LOW SPEED

A novel sensorless vector controlled induction motor drive system is presented in this paper. In this system, compensation of the drift components of the stator voltage vector is done by offset voltage vector estimation to improve the low-speed drive characteristics. The motor speed is estimated from the difference between the estimated synchronous and slip speed. An effective on-line method for estimating both stator and rotor resistances is introduced in this system to achieve high-precision control at low-speed. The estimation method for rotor resistance is based on the error signal between the command value of reactive power and its actual value being based on stator voltage and current measurements. On the other hand, the error between the magnitude of the stator current command and its measured value is used to estimate the stator resistance variations from its set value. This paper clarifies that the low-speed estimation is possible with stator and rotor resistance estimation and the zero-speed control is achieved under load condition. Simulation results are provided to demonstrate smooth steady-state operation and high dynamic performance of the drive system at very low-speed and at zero-speed.

Sensorless vector control of induction motors at very low speed using a nonlinear inverter model and parameter identification

The performance of vector-controlled induction motor drives without a speed sensor is generally poor at very low speed. The reasons are offset and drift components in the acquired feedback signals, voltage distortions caused by the nonlinear behavior of the switching converter, and the increased sensitivity against model parameter mismatch. New modeling and identification techniques are proposed to overcome these problems. A pure integrator is employed for stator flux estimation which permits high-estimation bandwidth. Compensation of the drift components is done by offset identification. The nonlinear voltage distortions are corrected by a self-adjusting inverter model. A further improvement is a novel method for online adaptation of the stator resistance. Experiments demonstrate smooth steady-state operation and high dynamic performance at extremely low speed.

Testing of the US Solar Pilot Plant Receiver

The US Department of Energy (DOE) is actively engaged in the design and construction of America’s first Solar Thermal Electric Pilot Plant at Barstow, California. Preconstruction tests of the external, single-pass-to-superheat, water/steam receiver under actual solar operating conditions were conducted to validate the design at the earliest possible date to assure the achievement of Pilot Plant operating goals. Receiver steady-state and transient operating characteristics and performance were investigated during clear day, intermittent cloud, and simulated emergency situations. Testing concluded with limited testing of the receiver at flux and power levels above the maximum expected Pilot Plant conditions. The test program successfully achieved the overall objective of confirming the design of the Pilot Plant solar receiver.

Overlapping commutation-mode analysis of a high-frequency inverter

This paper describes the steady-state operating analysis and performance evaluation of a high-frequency inverter for high-intensity ultrasonic power supply. The high-frequency inverter using reverse-conducting thyristors (abbreviated RTh type inverter) is analysed with an R–C load model of the ultrasonic transducer System. The steady-state characteristics and circuit operation, in which the overlapping commutcation-mode is considered, are quantitatively discussed and compared with those of a basic series-capacitor-commutated inverter (abbreviated basic type inverter). The necessary data for circuit design of the power supply are also presented.