Operation Mode Changes Research Articles

A new approach to instantaneous power based control of DFIG using active disturbance rejection control

This paper presents the design and control of a wind energy converter system that uses a doubly fed induction generator. It introduces a model that incorporates instantaneous active and reactive power as state variables to represent both the stator and rotor sides of the doubly fed induction generator. Subsequently, a linear active disturbance rejection-based control regulator is proposed for the control loops. The parameters of the linear active disturbance rejection controllers (ADRC) are adjusted by two methods: the single parameter tuning approach and the genetic algorithm (GA) method. The performance of the suggested controller is ultimately compared with a tuned proportional-integral (PI) control regulator in the MATLAB environment. In order to examine the performance of the system, various test scenarios are taken into account. These scenarios include different percentages of load change in both sub-synchronous and super-synchronous modes of operation, faults with different fault periods are considered in both modes of operation. The conventional PI controller-based approach requires 35 control cycles to reach steady state under load change conditions and 50 control cycles under symmetrical fault conditions, regardless of whether the system is operating in sub synchronous or super synchronous mode. The single parameter-based tuned ADRC approach only requires 15 control cycles for load change and 20 control cycles for symmetrical fault scenarios. In contrast, for both the load change and symmetrical fault scenarios, the ADRC with GA-based parameter tuning reaches steady state in just 5 control cycles. Furthermore, a case involving wind speed variation is presented to demonstrate the maximum power point tracking capability of the proposed control structure. Similarly, for the robustness test of the control regulator, variations in resistance and inductance are introduced to observe their impact on the response of the control regulators. Finally, a real-time hardware in loop setup is presented to validate the control strategy during the load change in the sub-synchronous mode of operation of the doubly fed induction generator.

КОНЦЕПЦІЯ ПОБУДОВИ ГІБРИДНОЇ СИСТЕМИ КЕРУВАННЯ МІКРОГІДРОЕЛЕКТРОСТАНЦІЄЮ

Methods of increasing the energy efficiency of micro-hydroelectric power plants are considered in the work. A new hy-brid concept of building a control system is proposed, which combines classical control laws and fuzzy logic. This makes it possible to improve the quality of the regulation of the parameters of the generated electricity regardless of changes in network operation modes and external conditions. It is shown that the use of hybrid filters will allow to in-crease the electromagnetic compatibility and, as a result, the energy efficiency of the system as a whole. References 12, figures 3.

Minimization of noise of the precision cooling system in the dynamic mode of the electronic apparatus

The design of a floor-standing telecommunication cabinet is considered. Air movement inside the cabinet is carried out in the vertical direction due to the simultaneous operation of supply and exhaust ventilation units. The reasons for the increased noise in the dynamic mode of operation are analyzed. The cabinet design is regarded as a mechanical and acoustic resonator with a heat-sensitive element that requires precision cooling. Constant airflow ensures constant element temperature. When the thermal power changes in a dynamic mode of operation, a change in the performance of ventilation units is required. This explains the occurrence of various resonances in the structure and, as a result, increased noise. Airflow consistency can be achieved using alternative operating modes of the supply and exhaust ventilation units. Analytically, families of isothermal supply voltage curves of ventilation units for laminar air movement have been constructed. The noise level's mathematical dependence on the fans' supply voltage is compiled, considering the resonances in the cabinet structure. Noise characteristics corresponding to isothermal voltage curves have characteristic minima. The transition between the isothermal supply voltage curves along the minimum noise trajectory controls the ventilation units. This method's possibility of minimizing noise has been confirmed analytically and experimentally. Keywords: electronic device, heat-sensitive element, ventilation unit, air flow, dynamic mode, isothermal stress curve, resonance, minimization, trajectory, noise.

Research on solar-assisted ejector-enhanced air source heat pump cycle with dual-pressure condensation

ABSTRACT A novel solar-assisted ejector-enhanced air source heat pump cycle with dual-temperature condensation (SEASHP-DC) is proposed in this study. Two types of hot water with different temperatures can be supplied for heating. By using solar energy and ejector, the COP of the system can be improved in cold regions. The cycle can change operation mode according to the solar radiation intensity, which can turn into a conventional heat pump cycle with dual-pressure condensation (CHP-DC) when the solar radiation intensity is low or at night. The performance of the proposed cycle is simulated with different refrigerants (R134a, R1234yf, and R1234ze(E)). Results show that the R1234ze(E) is an ideal substitute for the R134a. The performance of the SEASHP-DC is investigated and compared with that of the CHP-DC under the given condition. Compared with the CHP-DC, a considerable improvement of 55.9% in COP at a heating capacity ratio equal to 1.5 is reached by the SEASHP-DC. The largest exergy destruction occurs at the solar collector due to the huge temperature difference between the solar collector and the environment. The feasibility of applying this system during the heating season is confirmed, with daily working hours ranging from 6 to 8 h.

Digital Operational Strategies in The Post-Pandemic Era for Travel Companies: A Case Study of Ctrip

The epidemic’s impact has caused the tourism industry to face major challenges and changes in the post-epidemic era, in which the digital operation model has become the key to driving recovery and innovation. Taking Ctrip as an example, this study provides an in-depth analysis of the changes in the digital operation mode of tourism enterprises in the post-epidemic era. Firstly, the context and situation of Ctrip’s activities have changed in the digital environment, expanding the online business space and strengthening the interaction between the company and consumers. Second, the digital environment has changed corporate and consumer behavior from competition to cooperative symbiosis while triggering the socialization and personalization of consumer behavior. In addition, Ctrip’s travel products have changed in the digital environment, with data analysis to tailor travel products for consumers. Practical applications of Ctrip’s digital operations, including user demand forecasting and product design optimization, are further discussed. It is concluded that digital operations are important in improving management efficiency, meeting consumer demand, pricing strategy, and risk control. However, digital operations face legal, protection, and risk issues that require further research and solutions. This study provides useful experiences and insights for developing digital operation modes in tourism enterprises.

ISOLATION OF HIGH PURITY PIPERYLENE

Piperylene is a valuable raw material component for petrochemical synthesis, perfumery and cosmetic products, and is used as a solvent for petroleum products in the production of synthetic rubbers and latexes, and in the paint and varnish industry. Piperylene in the form of a fraction is produced in the production of isoprene by the two-stage dehydrogenation of isopentane, where it is a secondary product of the main synthesis. Isolation of commercial piperylene of high purity will allow the production of a value-added product and expand the sales market. Currently, restrictions on the production of commercial piperylene are associated with the high content of an impurity – cyclopentadiene. Previous studies by the author showed the feasibility of extracting cyclopentadiene at the stage of obtaining the catalyzate of the second stage of isoprene dehydrogenation. Simulation of the technological scheme in the application program showed that, together, the extraction of cyclopentadiene by a chemical method and a change in the technological operating mode makes it possible to isolate piperylene with a content of 99.45 % wt and CPD equal to 0.0046 % wt.

Design and Application of Station Power Supply System for Lithium Iron Phosphate Battery Based on Power Exchange Operation

Based on the engineering application design and development of the power supply system of lithium iron phosphate battery pack in the operation and maintenance mode, this paper conducts the application research from four aspects of battery quantity selection, capacity calculation selection, battery management system design, battery pack modular design, etc. The design scheme of the lithium iron phosphate power supply system is formulated, and the matching battery management system is designed. A universal lithium iron phosphate battery module with an “N+1” redundant configuration is developed to improve the maintenance efficiency of the battery pack. It reliably supports the substation power changing operation and maintenance mode and ensures the reliability and operation safety of the substation power supply system.

Evaluation Method for Reverse Recovery Characteristics of Thyristors Based on Charge Measurement

The change of operation mode of the HVDC project causes a change of the external characteristic of the converter valve, and the reverse recovery characteristic of the thyristor inside the converter valve changes accordingly. Therefore, the reverse recovery charge measurement values of thyristors under different operating conditions cannot be directly compared, and the status of thyristors cannot be evaluated online. Therefore, a method of measuring the reverse recovery charge of series thyristor based on the turn-off voltage is presented in this paper. Then, the operation mode of the HVDC project is analyzed, and the external characteristics of the converter valve under different operation modes are discussed. Secondly, the external factors that affect the reverse recovery characteristics of thyristors are analyzed essentially, and the relationship between the external factors and the external characteristics of the converter valve is discussed. A reverse recovery charge model considering external factors is established, and a method to reduce the error is proposed. Finally, the reverse-recovery charge normalization coefficient is derived for the normalization of the measured values in different working conditions. Based on the charge online measurement method and the normalization method proposed in this paper, the reverse-recovery characteristic evaluation method of the thyristor is proposed, and the evaluation steps are introduced.

NOx emissions prediction for MSWI process based on dynamic modular neural network

Accurate prediction of nitrogen oxides (NOx) is crucial for improving the efficiency of denitrification systems in municipal solid waste incineration (MSWI) process. Due to the change of feed composition and operation mode, it is difficult to predict NOx emissions with complex dynamics. For this reason, a dynamic modular neural network (DMNN) is proposed for NOx emissions prediction in MSWI process. First, a principal component analysis (PCA)-based dynamic task decomposition method is proposed, and then the original task with time varying characteristic is divided into several sub-tasks for effectual handing. Next, an adaptive long short-term memory (ALSTM) network is designed driven by the corresponding sub-task. Then, the nonlinearity between dominant variables and NOx value is learned to guarantee the prediction accuracy. Finally, the merits of proposed DMNN are confirmed on a benchmark and real industrial data of a MSWI process. The experimental results further demonstrate the superiority and potential of DMNN for industrial applications.

Emulation of Integrated Starter/Generator Using Power Electronic Devices

Integrated starter/generator (ISG) is an important facility in transportation power systems. Using power electronics based motor emulator (ME) to test the motor controller is an emerging technique to optimize the design process of the motor drive system. In this paper, an ME is designed to test the control system of ISG in the full operation process. Facing the challenge of dual-mode emulation, a voltage-in-voltage-out interface is proposed to handle the causality problem caused by operation mode change during the starting/generating process. The LCL interface with predictive voltage closed-loop control is proposed to ensure emulation accuracy. A prototype of ME has been developed. The experiment has been done to validate the performance of the emulator, showing that the proposed method can be used to test the ISG controller in full operational mode with accuracy and fast dynamics.

Clinical effects of robot-assisted esophageal hiatal hernia repair and laparoscopic esophageal hiatal hernia repair: a retrospective comparative study

Objective: To analyze the short-term clinical effects of robot-assisted and laparoscopic repair of the hiatal hernia. Methods: The clinical data of 56 patients underwent minimally invasive hiatal hernia repair from January 2021 to January 2022 in the Department of Minimally Invasive Surgery, Hernias and Abdominal Wall Surgery, People's Hospital of Xinjiang Uygur Autonomous Region were retrospectively analyzed. There were 32 males and 24 females, aging (59.7±10.7) years (range: 28 to 75 years). All patients were divided into laparoscopy group (n=27) and robot group (n=29) according to surgical procedures. Perioperative conditions, hospital stay, and improvement in symptoms before and after surgery were compared between the two groups by the t test, Wilcoxon rank-sum test and χ2 test. Results: All surgical procedures were successfully completed, without conversion to laparotomy or change in operation mode. There were no serious complications related to the operation. The intraoperative blood loss of the robot group was less than that of the laparoscopic group (M (IQR)): (20 (110) ml vs. 40 (80) ml, Z=-4.098, P<0.01). The operation time ((111.7±33.6) minutes vs. (120.4±35.0) minutes, t=-0.943, P=0.350) and hospitalization time ((3.9±1.4) days vs. (4.7±1.9) days, t=-1.980, P=0.053) of the robot group and the laparoscopic group were similar. Follow-up for 12 months after the operation showed no postoperative complications and recurrence. The score of the health-related quality of life questionnaire for gastroesophageal reflux disease in the robot group decreased from 10.8±2.8 before the operation to 6.5±0.6 after the operation, and that in the laparoscopic group decreased from 10.6±2.1 before the operation to 6.3±0.6 after the operation. There was no difference in the influence of different surgical methods on the change in score (t=0.030,P=0.976). Conclusion: Compared with laparoscopic repair of the hiatal hernia, robot-assisted hiatal hernia repair has the advantages of less bleeding, rapid postoperative recovery and good short-term effect.

A statistics-based review on island detection methods in microgrids: Overall investigation and state-of-the-art

AbstractIn this paper, a comprehensive statistics-based review of islanding detection methods (IDMs) in microgrids (MGs) is presented. Islanding detection is the situation of isolating the MG from the main grid whether programmed as a result of load managing purposes or un-programmed due to the occurrence of faults. Islanding detection is a vital issue in MG's analyses due to the prevention of subsequent protection problems in the power system. In other words, when the MG's operation mode changes, the current passing through the protective devices changes subsequently and the protection system should be able to adapt the new settings to the protective devices. So, IDMs are vital for electrical engineers to overcome the abovementioned protection issue. This review paper surveys the existing literature in IDMs by concentration on total publications, type of publications (journal, conference paper, or book), five authors with the highest number of publications (including the affiliations), and five most published sources. Also, the five most cited publications and state-of-the-art IDMs are investigated in detail, utilizing some known and novel categorizations. This paper will be useful for the MG's researchers to know the most desirable IDMs, especially in recent years, and provides an insightful overview for future studies.

Adaptive additional current-based line differential protection in the presence of converter- interfaced sources with four quadrant operation capability

As typical representatives of converter-interfaced sources with four quadrant operation capability, battery energy storage station (BESS) and VSC-HVDC station behave differently with synchronous generator. This leads to the high risk of incorrect operation of current differential protection (CDP), seriously threatening the security of transmission network. Motivated by this issue, this paper presents adaptive additional current-based differential protection (AAC-DP). Adaptive additional current is introduced to modify the criterion of current differential protection. Ulteriorly, the unified expression of adaptive additional current for internal and external faults is designed. Adaptive additional current can increase the sensitivity during internal fault, whereas it improves the security during external fault. The sensitivity and dependability of AAC-DP was widely evaluated by changing operation mode, fault condition, and type of power source using PSCAD and RTDS-based experimental platform. Also, the adverse factors, such as saturation and error of current transformer(CT), and noise, were taken into account; thereof, the excellent security of AAC-DP was confirmed. The results confirm that AAC-DP exhibits excellent performance in operating speed, sensitivity, the adaptation to fault behaviors of BESS and VSC-HVDC, and robustness against saturation and error of CT, and noise.

Taking the long view of the multinational

PurposeThis paper argues for the benefits to international business (IB) of taking a much longer view at the engagement by multinational enterprises (MNEs) with host locations.Design/methodology/approachThe authors showcase a project tracking the engagement by MNEs with Australia over the past two centuries. Extensive archival work has been undertaken to identify and document modes of entry, home countries, industries, operational modes and company types among the MNEs operating in Australia. The authors also describe the shifting nature of Australia as a host location.FindingsThe authors demonstrate the historical and ongoing diversity of ways in which MNEs interact with a host. They show that different organisational forms have prevailed over time, and that considerable operational mode changes can best be observed when a long lens is adopted. The authors show how these mode changes interact with host country dynamics, and also the broader context of the MNE and its altering strategies.Research limitations/implicationsThe authors urge IB scholars to embrace longer timeframes to capture the complexity of MNEs’ growth and adaptation more meaningfully.Originality/valueBy taking such a long-run perspective, the authors shed new light on the importance of moving beyond simple snapshots to analyse key IB constructs and phenomenon.

Effects of the host-country institutional environment on the operation mode change of international construction enterprises

PurposeThe operation mode of enterprises will affect its resource commitment in the host country, involving different costs and time, as well as risks. Yet, the current state of knowledge about how the institutional environment affects the operation mode change of international construction enterprises is equivocal. This study aims to explore the impact of a host country's institutional environment on the operation mode change of international construction enterprises.Design/methodology/approachFirst, this study proposes a model on the impact of the institutional environment on the operation mode change of international construction enterprises. Second, this study used the Worldwide Governance Indicators (WGI) published by the World Bank and a questionnaire survey to collect data. Finally, the study employs a multiple regression methodology to test the hypothesis and discusses the results.FindingsResults highlight that the important impact of the institutional environment on the operation mode change of international construction enterprises. The results showed that enterprises are more willing to increase resource commitments under the condition of stable institutional environment. In addition, enterprises' market-specific experience and general international experience, as moderating variables, weaken the impact of the institutional environment on the operation mode change. However, general international experience has no significant moderating effect.Practical implicationsThe findings of this study provide practical implications for the investment risk assessment of international construction enterprises. Enterprises need to consider the change in institutional quality and institutional instability of the host country, as well as their own international experience when changing operation mode.Originality/valueThis study extends internationalization theory to the international construction field and provided theoretical guidance for the mechanism of operation mode change of international construction enterprises.

Justification of the parameters and operating modes of the rotary treated for layer-by-layer processing of seeds

Purpose. Increasing the efficiency of the use of pesticides thanks to the substantiation of the parameters of the working bodies and modes of the technological process of layer-by-layer seed treatment, which will ensure an increase in the quality of seed treatment and ecological safety of the environment. Methods. The study used an experimental method Microsoft Office using software environments. Results. The experimental dependences of the height of the seed intensifiers on the angular speed of the rotor and the mass of the seed portion and the dependences of the completeness of seed processing on the mixing time and the mass of the seed portion were obtained. The ranges of changes in rational parameters and modes of operation of working bodies, which ensure the implementation of the technological process of applying protective- stimulating-nutritive preparations to seeds with the required quality of seed processing, is determined. Conclusions. Experimental dependences of the height of the seed intensifiers on the angular speed of the rotor and the mass of the seed portion were obtained and it was established that to ensure the work process of applying preparations to the seeds in the range of angular velocities of the rotor from 15 rad/s to 40 rad/s and the mass of the seed portion from 2.5 kg up to 12.5 kg, the height of the intensifiers should be from 40 mm to 185 mm. Experimental dependences of the completeness of seed treatment on the time of mixing and the weight of the seed portion were obtained and it was established that the completeness of the layer-by-layer treatment of the seeds increases intensively in the first 20 s of mixing, reaching the required value of 80%, and decreases with the increase in the weight of the seed portion. The range of changes in rational parameters and modes of operation of working bodies, which ensure the implementation of the technological process of applying protective-stimulating-nutritive preparations to seeds with the required quality of seed treatment, is determined: the angular speed of the rotor – from 20 rad/s to 40 rad/s, the weight of a portion of seed – from 2.5 kg to 7 kg, supply of working liquid – 4 ml/kg of seeds, temperature of drying agent – up to 100 ºС, supply of drying agent – 0.45 m /min, mixing time – up to 20 s, drying time – up to 30 s/. Keywords: portion of seeds, seed treater, layer-by-layer processing, protective-stimulating- nutritious preparations.

Analysis of Additional Damping Control Strategy and Parameter Optimization for Improving Small Signal Stability of VSC-HVDC System

The voltage source converter based high voltage direct current (VSC-HVDC) system is based on voltage source converter, and its control system is more complex. Also affected by the fast control of power electronics, oscillation phenomenon in wide frequency domain may occur. To address the problem of small signal stability of the VSC-HVDC system, a converter control strategy is designed to improve its small signal stability, and the risk of system oscillation is reduced by attaching a damping controller and optimizing the control parameters. Based on the modeling of the VSC-HVDC system, the general architecture of the inner and outer loop control of the VSC-HVDC converter is established; and the damping controllers for DC control and AC control are designed in the phase-locked loop and the inner and outer loop control parts respectively; the state-space state model of the control system is established to analyze its performance. And the electromagnetic transient simulation model is built on the PSCAD/EMTDC simulation platform to verify the accuracy of the small signal model. The influence of the parameters of each control part on the stability of the system is summarized. The main control parts affecting stability are optimized for the phenomenon of oscillation due to changes in operation mode occurring on the AC side due to faults and other reasons, which effectively eliminates system oscillation and improves system small signal stability, providing a certain reference for engineering design.

A Model-Free Capacitor Voltage Balancing Method for Multilevel DAB Converters

Capacitor voltage balancing is of importance in the neutral-point-clamped based dual-active-bridge converters. Most of traditional voltage balancing methods adopt the transformer current models in the balancing process, as the direction of the neutral-point current is affected by the transformer current polarity. However, this approach requires heavy and repetitive offline precalculation for the transformer current polarity under various operating modes, and thus, leading to complicated implementation. To overcome this, a model-free voltage balancing scheme based on a fixed-switching-state method is proposed in this letter. Two switching states are employed during the voltage balancing process in the proposed method, where the direction of the neutral-point current is independent on the transformer current polarity. Hence, the implementation can be simplified without the precalculation of transformer current polarity. Furthermore, the model-free feature of the proposed method is more robust against parameter variations or operating mode changes. Experimental tests are performed, which verify that the proposed method can achieve voltage balancing in terms of easy implementation and fast dynamics.

ІНТЕГРАЛЬНА ІНФОРМАЦІЙНО-ОБЧИСЛЮВАЛЬНА СИСТЕМА, ЩО ЗАБЕЗПЕЧУЄ ТЕХНІЧНЕ ОБСЛУГОВУВАННЯ ЗА СТАНОМ СИЛОВИХ ГАЗОТУРБІННИХ УСТАНОВОК

The effectiveness of the chosen maintenance strategy is determined by the completeness of information about the current technical condition of the facility. The real current state of a dynamic object should specify the list and scope of preventive and remedial work for each specific maintenance object. Existing strategies and programs according to the technical condition of dynamic objects are conditionally divided into three groups: with control over the level of reliability of the operating object; with control of the parameters of the object of operation; hybrid. Power gas turbine plants are objects of operation with high functional significance. They have an insufficient degree of redundancy, as well as a low level of operational manufacturability. Therefore, it is advisable for them to apply a maintenance strategy as per the parameter control. The article proposes general principles on the basis of which an integral information-computing system for processing parameters can be built. This system is the main element of the automated control system for the technical condition of the gas turbine power plant. Synthesized adaptive system for dynamic control of parameters characterizing the current technical state of a gas turbine power plant. Closing the control loop of the technical condition of the object with negative feedback allows you to switch from the strategy of its maintenance according to the operating time to the maintenance strategy according to the state with the control of parameters. The integrated information-computing system should solve two main tasks: a reliable assessment of the current technical state of a dynamic object and prediction of a pre-failure state in the medium and long term. The main condition for organizing the maintenance of dynamic objects according to the state with the control of parameters is the possibility of continuous monitoring of the parameters characterizing the current technical state. The choice of such parameters is ambiguous, which is due to both the specific features of dynamic object and diverse nature of relationship between faults and controlled parameters. The requirements for the determining parameters are of a general nature: the parameters must have acceptable accuracy and stability of readings over time; have the greatest diagnostic value among other parameters; not depend on changes in external operating conditions and modes of operation; based on standard measurements. The system of continuous monitoring of parameters characterizing technical state of a dynamic object must be adaptive. It should change in accordance with the change in technical condition of the gas turbine power plant. The use of a set of parameters of its dynamic linear model as characteristic of the current technical state of an object is justified for a wide class of objects. The control system of such objects operates in the stabilization mode, therefore, the adaptive system of continuous monitoring synthesized on the basis of this model provides the possibility of assessing the current technical state of the gas turbine power plant and makes it possible to predict its technical state. At the same time, the adaptation of the parameters of the linear dynamic model of the object to the new technical condition of the gas turbine plant should be carried out with the least interference in the normal operation of the plant.

Numerical Investigations on Operation Modes and Transients of IPM Machines with Dual Windings

This paper investigates the flux-weakening characteristics and transient response of a dual winding interior permanent magnet (DWIPM) machine designed using the 2010 Toyota Prius IPM Machine specifications. In order to thoroughly adjust the main flux, dual windings are fed by separate identical inverters. Thus, significantly high-torque for high-speed requirements can be simply achieved by making one of the inverters open-circuited. Transient response of the DWIPM machine, including torque and current pulsations, occurring during normal drive or deactivation of one of the inverters has also been investigated for different operation modes. The flux-weakening performance characteristics of the proposed DWIPM machine have been compared with those of its single-fed counterpart in order to highlight the benefits and drawbacks of the dual-winding topology. The steady-state performance characteristics, torque/speed and power/speed curves, efficiency maps, machine transient response, different machine design options with various numbers of turns per phase and current amplitudes, and the importance of the electromagnetic coupling between dual windings have all been addressed. For transient and steady-state analyses, 2D, nonlinear, time-stepping finite element method (FEM) has been employed. It has been revealed that the proposed DWIPM machine exhibit significantly improved flux-weakening characteristics, particularly high-power at constant power region and high efficiency at constant torque region, and quite low current and torque pulsations occurring during operation mode change.