Operation Mode Changes Research Articles

Holistic Control Approach for the Grid-Connected Converter of a Battery Energy Storage System

This paper introduces a holistic control approach applied to a grid-connected converter of a Battery Energy Storage System (BESS). The BESS is mainly used for power peak shaving, frequency supporting, and islanded operation mode which implies multiple control transitions depending on the operation mode. One existing challenge is related to the multiple tuning controllers for the grid-connected converter required for each operation mode, including the rectifier operation. Moreover, when the rectifier operation is running the system is naturally nonlinear which motivates the use of nonlinear controllers. From this standpoint, a strong motivation for this research is the seeking of a holistic control to face all the operation-mode changes seamlessly. Hence, the merit of the proposed holistic control approach consists of using a unique tuning process based on the linear technique of state feedback with integral action for all operation modes, which are: 1) grid-connected mode as an inverter, 2) grid-connected mode as a rectifier, and 3) islanded mode. Of special attention is the grid-connected mode as rectifier since the proposal avoids the introduction of the PWM rectifier model which increases the model order and is inherently nonlinear. A thorough analysis of eigenvalues in open loop and closed loop with the same tuning gains is presented to demonstrate the stability and feasibility of the proposal. An affordable tuning methodology is proposed considering the physical restrictions of the grid-connected converter related to the LCL-filter bandwidth and the switching frequency. To demonstrate the merits of the holistic control approach, several simulations are presented using PSCAD/EMTDC on a 100 kW, 480 V rated BESS using a delta-connected LCL filter for interconnecting with the grid. Simulation results show that the seamless capability with steady-state and transient state operation runs smoothly.

Study on Harmonic Impedance Estimation and Harmonic Contribution Evaluation Index

Harmonic impedance estimation and suitable evaluation index selection are the key steps of harmonic contribution evaluation. Most of the traditional harmonic impedance estimation methods are only applicable to the scenario, where the background harmonic is stable and the utility impedance is constant. However, this scenario will change in many cases due to the fluctuation of harmonic, the change of system operation mode and so on. In order to improve the estimation accuracy for harmonic impedance, a harmonic impedance estimation method is proposed in this paper based on similarity measure and ordering points to identify the clustering structure (OPTICS). The total harmonic contribution index and harmonic comprehensive contribution index are proposed based on subjective analytic hierarchy process to simplify the evaluation results. Simulation analysis and their comparison with the traditional methods reveal that the proposed harmonic impedance estimation method can reduce the influence of background harmonic voltage fluctuation and utility impedance change, making the harmonic impedance estimation result more accurate. Besides, the proposed total harmonic contribution index and harmonic comprehensive contribution index can effectively simplify contribution evaluation results, which provide a new methodology for the evaluation of harmonic contribution.

Risk Assessment of Multi-area Interconnected Power System under Gas Station Network Attacked

Abstract This paper mainly investigates the risk assessment of multi-area interconnected power system with probabilistic optimal power flow (POPF) for charging load of plug-in hybrid electric vehicle (PHEV) under gas station network attacked. Firstly, the PHEV charging model is developed by analyzing the change of PHEV operation mode after running out of gasoline. Secondly, in a multi-region interconnected power system, a line overload risk index is established to evaluate the impact of PHEV charging on the tie-line powers with the gas station network unavailable, and POPF considering PHEVs, wind and photovoltaic generation is employed to reduce the risk of system operation. Finally, the method is tested on IEEE 118-bus system to analyze the impacts of PHEV charging on tie-line powers and the entire system under gas station network attacked, and the economy and safety of system operation are evaluated before and after optimization.

Adaptive Modeling and Operation Optimization for the Cold End System of Thermal Power Units based on Mechanism and Statistical Analysis

The operation optimization for the cold end system is an efficient means to improve the economy of steam turbine units. To compensate for the inadequacy of the traditional mechanism analysis utilized in obtaining actual operating characteristics of the cold end system, the prediction model of the exhaust pressure was established on the basis of mechanism analysis combined with data from the operation process. An online adaptive updating strategy was introduced to guarantee the modeling accuracy. A discrete model of the cooling tower outlet water temperature (CTOWT) was constructed based on the operation data partitioned into different groups according to the pump operating mode change (POMC). Combining the above two models, the coupled model of the cold end system was therefore obtained. A model-based operation optimization system was then implemented for the cold end system in a coal-fired power plant. Experimental trials authenticate that the optimization suggestions provided by the system can effectively enhance the benefit of power generation.

A novel control strategy for mode seamless switching of PV converter in DC microgrid based on double integral sliding mode control

With the photovoltaic (PV) penetration increases in dc microgrid, the traditional PV converters with maximum power point tracking (MPPT) control, which are equivalent to current sources, can hardly meet the needs of coordinated operation. The PV converter should operate in both MPPT and constant voltage control (CVC) modes. When the operation mode changes, the PV converter needs to switch between current and voltage sources. Inevitably, the bus voltage instability would be caused. This paper presents a novel switching strategy for the smooth and seamless operation of the PV converter between MPPT and CVC modes. The PV converter under these two modes is always controlled as a voltage source, and its control variables are both the output voltage of PV arrays. When its operation mode changes from MPPT to CVC, a small offset signal based on DC bus voltage would be introduced to the reference voltage of inner loop of the PV converter, so as to shift the maximum power point (MPP) voltage. Meanwhile in the voltage inner loop, a double integral sliding mode controller (DISMC) is used to improve the performance and anti-interference ability of the PV converter. This method unifies MPPT and bus voltage adjustment strategy without any communication and changing any hardware structure and control parameters. When mode switching occurs, only the reference value of voltage inner loop would be slightly adjusted near the maximum photovoltaic power point, so the seamless transition for PV converter between the two modes can be ensured. Finally, the effectiveness of the mode seamless switching control strategy is demonstrated by the simulation and experimental tests.

Changes in foreign operation modes: A review and research agenda

This paper addresses the growing but fragmented research area of changes in foreign operation modes. Previous research claims this field to be under-researched and at the same time more complex than hitherto assumed. Moreover, a majority of studies investigating mode change include the topic rather inexplicitly. In consequence, literature on mode change is fragmented across different research streams and is characterized by incoherent nomenclature, a variety of research foci as well as results that are hard to compare. By conducting a structured literature review we consolidate existing findings, provide a deeper understanding of firms’ foreign operation mode change, related theoretical perspectives, and its antecedents and consequences. Based on our findings we discuss relevant areas for future research in this research field.

Energy-efficient DAC switching scheme with operation-mode configurability for SAR ADCs

An energy-efficient digital-to-analogue converter switching scheme with operation-mode configurability is proposed for successive approximation register (SAR) analogue-to-digital converters (ADCs). The operation-mode configurability of the SAR ADC is realized by utilizing the single-side switching method, which can achieve operation-mode change between differential mode and single-ended mode. Compared to conventional scheme, the proposed switching scheme improves the energy-efficiency by 99.23% and 96.9% for differential mode and single-ended mode, respectively.

Optimization of the Heap Leaching Process through Changes in Modes of Operation and Discrete Event Simulation

The importance of mine planning is often underestimated. Nonetheless, it is essential in achieving high performance by identifying the potential value of mineral resources and providing an optimal, practical, and realistic strategy for extraction, which considers the greatest quantity of options, materials, and scenarios. Conventional mine planning is based on a mostly deterministic approach, ignoring part of the uncertainty presented in the input data, such as the mineralogical composition of the feed. This work develops a methodology to optimize the mineral recovery of the heap leaching phase by addressing the mineralogical variation of the feed, by alternating the mode of operation depending on the type of ore in the feed. The operational changes considered in the analysis include the leaching of oxide ores by adding only sulfuric acid (H2SO4) as reagent and adding chloride in the case of sulfide ores (secondary sulfides). The incorporation of uncertainty allows the creation of models that maximize the productivity, while confronting the geological uncertainty, as the extraction program progresses. The model seeks to increase the expected recovery from leaching, considering a set of equiprobable geological scenarios. The modeling and simulation of this productive phase is developed through a discrete event simulation (DES) framework. The results of the simulation indicate the potential to address the dynamics of feed variation through the implementation of alternating modes of operation.

IDENTIFICATION OF REAR MODEL OF TV3-117 AIRCRAFT ENGINE BASED ON THE BASIS OF NEURO-MULTI-FUNCTIONAL TECHNOLOGIES

The subject matter in the article is TV3-117 aircraft engine and methods of identification of its technical condition. The goal of the work is to develop methods for identifying the technical state of the aircraft engine TV3-117 on the basis of real-time neural network technologies. The following tasks were solved in the article: the task of identifying the reverse multi-mode model of the aircraft engine TV3-117 using neural networks. The following methods used are – methods of probability theory and mathematical statistics, methods of neuroinformatics, methods of the theory of information systems and data processing. The following results were obtained – The application of the neural network apparatus is effective in solving a large range of tasks: identifying the mathematical model of the aircraft engine TV3-117, diagnosing the condition, analyzing the trends, forecasting the parameters, etc., despite the fact that these tasks usually relate to the class difficultly formalized (poorly structured), neural networks are adequate and effective in the process of their solution. In the process of solving the task of identifying the mathematical model of the aircraft engine TV3-117 on the basis of neural networks, it was established that neural networks solve the problem of identification more precisely classical methods. Conclusions: It was established that the error of identification of the aircraft engine TV3-117 with the help of a neural network of type perceptron did not exceed 1.8 %; For the neural network of radial-basic function (RBF) – 4.6 %, whereas for the classical method (LSM) it makes about 5.7 % in the considered range of changes in engine operation modes. It was found that neural network methods are more robust to external perturbations: for noise level σ = 0.01, the error of identification of aircraft engine TV3-117 with the use of perceptron has increased from 1.8 to 3.8 %; for the neural network RBF – from 4.6 to 5.7 %, and for the least squares method – from 5.7 to 13.93 %. In the process of solving the task of identifying the inverse multi-mode model of the aviation engine TV3-117 on its parameters on the basis of neural networks (perceptron and RBF) it was shown that their use allows for indirect measurement of the parameters of the flowing part of the engine at different modes of its operation: in the absence of noise – with an error of not more than 1,8 and 4,6 % respectively; in the presence of noise (σ = 0,01) – with an error of not more than 3,8 and 5,7 % respectively. Application in these conditions of the least squares method (polynomial regression model of the 8th order) allows us to obtain the error value: in the absence of noise – no more than 5,7 %; in the presence of noise – no more than 13,93 %.

Experimental investigation of heat transfer by unsteady natural convection at a vertical flat plate

The present study considers the influence of unsteady flow structures in natural convection on the heat transfer from a vertical flat plate to air. The mean and momentary intensity of convective heat transfer were determined experimentally for specific variations of the boundary conditions. For cyclic and step-like changing operation modes of a direct-electrically heated, 2 m-high copper plate, laminar, transitional and turbulent flow regimes were considered. Compared to a quasi-stationary approach, mean deviations of up to 22.0% for cyclic variations and up to 30.2% for step-like changes occur during an unsteady phase. The extent of the deviations shows a dependence on the mean Grashof number, as well as further influencing factors. Phenomenological observations of the unsteady convection flow in the form of visualizations show a temporarily increased mixing of the boundary layer, which also deviates distinctly from a quasi-stationary development. In particular, a temporary occurrence of Kelvin-Helmholtz vortices can be observed.

Pressure pulsations during a fast transition from pump to turbine mode of operation in laboratory and field experiment

The reversible pump turbine (RPT) is a suitable machine to meet fluctuations in the energy market. The usage of RPTs for this purpose will increase the number of operational mode changes of the machine. In order to reduce the response time of the machine, fast transitions in the mode of operation are desired. Therefore, increased knowledge of how the machine operates during these fast transitions is needed. This paper presents measurements done both at the NTNU Waterpower Laboratory and Tevla Pump Power Plant. The two machines are not geometrically similar, and part of the result focus on the similarities in the measurements despite the differences in the two RPTs. Tevla is owned by the Norwegian company Nord-Trøndelag Energi (NTE) and consists of two reversible pump turbines. The installed capacity is 50 MW. The focus is on the pressure pulsations during the fast transition from pump to turbine mode of operation. Results from both the laboratory and field measurements show few but high pressure amplitudes during the fast transition.

Suppression Method of DC-offset in Transformer Current for Flying Capacitor Dual Active Bridge Converter at Changing Operation Mode

Suppression Method of DC-offset in Transformer Current for Flying Capacitor Dual Active Bridge Converter at Changing Operation Mode

Transient Processes in Air Separation Plants

A modern air separation plant control system must solve a host of problems, including variation in conditions of plant operation with full guarantee of its automatic flow. The procedure of gearing the plant from one operation mode to another is based on gradual change of control action and collection of desired products without impairment of their quality below the allowable level. To accomplish this task, it is essential to determine the values of the key process parameters for various air separation plant operation conditions and the maximally allowable control action variation rate. Based on the investigation results and comparative analysis of the values of the key process parameters of optimized static-state regimes in UniSim Design environment and actual indicators with a real plant, we found insignificant deviation of the calculated parameters from the actual values during the plant operation. It was concluded that the results of air separation process modeling in UniSim Design environment or the magnitudes of control actions derived by equations of material and heat balances of the plant can be used, in a first approximation, in plant operation mode change algorithm.

Integrated control strategy for smooth switching of the PV and battery‐storage micro‐grid based on operation state tracking

Micro-grid which connects with the main grid can operate under the grid-connected mode or the islands mode. During the switching process between the two operation modes, if the control strategy is not complete, there will be problems such as the AC bus voltage oscillation and current surge, which will result in the switchover failure. An improved energy storage inverter control method based on operation states tracking is adopted for the optical storage micro-grid using master–slave control, which solves the problem of control variables mutation. Secondly, an improved software phase-locked method based on grid phase state tracking is proposed in an energy storage inverter. The problem of instantaneous mutation of the phase angle is solved by cooperating with the micro-grid operation state control signal during operation mode changes. Through the improvement of the two control strategies above, the transient shock phenomena of the micro-grid voltage and current during the switching process is obviously improved, and the harmonic content of the AC voltage and current is obviously reduced. Finally, a detailed model of optical storage micro-grid is established in MATLAB/Simulink, and the correctness and practicability of the improved control strategy are verified by simulation.

Iterative ADP Optimal Control for GGBS Production Based on Dynamic Target Optimization

In this paper, a novel optimal control scheme for ground-granulated blast-furnace slag (GGBS) production process is proposed by using the iterative adaptive dynamic programming (ADP) method and dynamic optimization of desired values. To handle the characteristic of changing operation modes and to obtain a practical optimal control result, this paper formulates the GGBS optimal control problem based on an intensive study of the production technique, and constructs the optimal control scheme based on the repetitive optimization strategy - “target optimization” and “process optimization”. To obtain the optimal targets matching with changing operation modes, SVM modeling and multi-objective optimization method are utilized to solve the multi-objective optimization problem. In order to minimize the performance index function further and faster, iterative tuning technology is adopted to design the ADP based optimal control method. Finally, simulation is conducted to verify the effectiveness of the proposed approach.

К оценке состояния гидротехнических сооружений гидроузлов в современных условиях

The effect the limitations imposed on the water storage reservoir’s headrace level (HRL) variation rate have on the hydroelectric power plant (HPP) power performance indicators is studied taking the cascade of Yenisei HPPs as an example. For quantitatively determining the effect the limitations imposed on the Sayano-Shushenskaya HPP’s HRL variation rate (depending on the air temperature in the preceding period) have on the HPP power performance indicators, water energy calculations were carried out for the following Yenisei cascade operation scenarios: operation of the Sayano-Shushenskaya HPP with variable limitations imposed on the HRL variation rate depending on the air temperature in the previous period; operation of the Sayano-Shushenskaya and Krasnoyarsk HPPs with variable limitations imposed on the HRL variation rate depending on the air temperature in the previous period. The mean energy capability (E0) and the guaranteed power output in winter (Nguar) were taken as the HPP performance indicators from which the effect of limitations was estimated. As a result of the accomplished computations, the guaranteed winter power output in the Sayano-Shushenskaya hydropower system decreased by 17.37%, and its mean energy capability decreased by 3.29%. Based on the accomplished water-energy calculations, a new (corrected) operating mode of the Sayano-Shushenskaya HPP was obtained, in which the regime of levels did not escape beyond the temperature-related limitations. The changes in the Sayano-Shushenskaya HPP operation mode led to a change in the HPP tail race flows. As a result, the Krashoyarsk HPP operation mode was also changed due to the new inflow regime to its site. The study results show very clearly that application of environment temperature-related limitations on the Sayano-Shushenskaya HPP hydraulic structures directly affects the power performance indicators of the Krasnoyarsk HPP. The strongest effect on the Krasnoyarsk HPP parameters takes place at the average temperature in the Karlov site from –17 °С to –11.8 °С in winter and from +8.5 °С to +11 °С in summer. This is connected with the Sayano-Shushenskaya HPP HRL variation rate limitation curve pattern, which in its turn entails a decrease in the HPP tail race flow and, as a consequence, a decrease in the total inflow to the Krasnoyarsk HPP site. As regards the temperature range at the Krasnoyarskaya HPP site, it is from –20 °C to –11 °C for the winter period and from +5 °C to +8 °C for the summer period. The difference in the mean energy capability and guaranteed power output of the Krasnoyarsk HPP during operation under the above-mentioned conditions is 12.9% for mean energy capability and 13.7% for guaranteed winter power output. Key words: limitation of water level variation rate in a water storage reservoir, change of power performance parameters, cascade of Yenisei HPPs.

К оценке состояния гидротехнических сооружений гидроузлов в современных условиях

The effect the limitations imposed on the water storage reservoir’s headrace level (HRL) variation rate have on the hydroelectric power plant (HPP) power performance indicators is studied taking the cascade of Yenisei HPPs as an example. For quantitatively determining the effect the limitations imposed on the Sayano-Shushenskaya HPP’s HRL variation rate (depending on the air temperature in the preceding period) have on the HPP power performance indicators, water energy calculations were carried out for the following Yenisei cascade operation scenarios: operation of the Sayano-Shushenskaya HPP with variable limitations imposed on the HRL variation rate depending on the air temperature in the previous period; operation of the Sayano-Shushenskaya and Krasnoyarsk HPPs with variable limitations imposed on the HRL variation rate depending on the air temperature in the previous period. The mean energy capability (E0) and the guaranteed power output in winter (Nguar) were taken as the HPP performance indicators from which the effect of limitations was estimated. As a result of the accomplished computations, the guaranteed winter power output in the Sayano-Shushenskaya hydropower system decreased by 17.37%, and its mean energy capability decreased by 3.29%. Based on the accomplished water-energy calculations, a new (corrected) operating mode of the Sayano-Shushenskaya HPP was obtained, in which the regime of levels did not escape beyond the temperature-related limitations. The changes in the Sayano-Shushenskaya HPP operation mode led to a change in the HPP tail race flows. As a result, the Krashoyarsk HPP operation mode was also changed due to the new inflow regime to its site. The study results show very clearly that application of environment temperature-related limitations on the Sayano-Shushenskaya HPP hydraulic structures directly affects the power performance indicators of the Krasnoyarsk HPP. The strongest effect on the Krasnoyarsk HPP parameters takes place at the average temperature in the Karlov site from –17 °С to –11.8 °С in winter and from +8.5 °С to +11 °С in summer. This is connected with the Sayano-Shushenskaya HPP HRL variation rate limitation curve pattern, which in its turn entails a decrease in the HPP tail race flow and, as a consequence, a decrease in the total inflow to the Krasnoyarsk HPP site. As regards the temperature range at the Krasnoyarskaya HPP site, it is from –20 °C to –11 °C for the winter period and from +5 °C to +8 °C for the summer period. The difference in the mean energy capability and guaranteed power output of the Krasnoyarsk HPP during operation under the above-mentioned conditions is 12.9% for mean energy capability and 13.7% for guaranteed winter power output. Key words: limitation of water level variation rate in a water storage reservoir, change of power performance parameters, cascade of Yenisei HPPs.

Development of dimensionally stable structures of multilayer pipelines and cylindrical pressure vessels from carbon fiber reinforced plastic

In the framework of the momentless theory of cylindrical thin shells, the elastic deformation of multilayer pipes and pressure vessels is investigated. It is assumed that the pipes and pressure vessels are made by two-way spiral winding of carbon fiber reinforced plastic tape on a metal mandrel. The analysis of the dependences of elastic deformations on the reinforcement angles is performed. The relations for axial and circumferential deformations of the wall, depending on the structure of the layer package, reinforcement angles under static loading are obtained. The separate and combined effect of internal pressure and temperature is considered. For the separate effect of loads, the graphs of deformations against the winding angle are plotted. Composite pipes made of KMU-4L carbon fiber reinforced plastic, as well as composite metal-composite pipes, are investigated. The results obtained for thermal loads are in good agreement with the data of the known experiment and solution. Depending on the load parameters, composite and metal-composite structures with dimensionally stable properties are determined. It is shown that dimensionally stable structures can be used to solve the problem of compensation of elastic deformations of pipelines. For this purpose, using the ASCP software package, the variant analysis of model structures is performed. By the comparative analysis of the three versions of the structure, layer package structures and reinforcement schemes, ensuring a significant reduction of loads on the supporting elements are obtained. On the example of a pipeline with a flowing fluid, it is shown that the use of dimensionally stable multilayer pipes makes it possible to eliminate bending deformations and significantly reduce the level of working forces and stresses. Dimensionally stable composite multilayer pipes open up new approaches to the design of pipelines and pressure vessels. It is possible to create structures with predetermined (not necessarily zero) displacement fields, consistent with the fields of the initial technological displacements, as well as with the displacements of conjugate elastic elements and equipment when the operating mode changes. The scope of such structures is not limited to hot pipes. The results can be used in cryogenic engineering

Dynamic behavior and control strategy study of CO2/H2O co-electrolysis in solid oxide electrolysis cells

The co-electrolysis of CO2 and H2O in high temperature solid oxide electrolysis cells (SOECs) is a promising energy storage method for intermittent renewable energy sources. In this paper, a three-dimensional (3D) continuum model of a 3-kW 40-cell planar SOEC stack is employed to study the dynamic behavior and control strategy under variable working conditions. The dynamic responses of stack power, current density, output H2/CO ratio and stack temperature are evaluated for a scaled real-time wind power input over a whole day. The fluctuation of the wind power input leads to SOEC stack temperature fluctuation, which illustrates the need for temperature control. Two representative cases with voltage step changes in both endothermic and exothermic operation modes are studied to predict the temperature control by the variation of excess air ratio. The effects of excess air ratio on both the steady-state temperature gradient and the transient temperature variation rate are analyzed in both cases. The temperature fluctuation is successfully controlled by applying an excess air ratio profile that changes with the wind power input.

УДОСКОНАЛЕННЯ ПЕРЕТВОРЮВАЛЬНОГО АГРЕГАТУ СИСТЕМИ ЕЛЕКТРОЖИВЛЕННЯ З ФОТОЕЛЕКТРИЧНОЮ СОНЯЧНОЮ БАТАРЕЄЮ

Improving of the converter unit for the power supply system with a photovoltaic solar battery by reducing power losses and eliminating transient components of the current when the operating mode changes. Synthesis of structure of the converter control system based on the analysis of processes in electrical circuits taking into account voltage changes, energy losses in semiconductor switches and using computer simulation. The possibility of reducing energy losses in the keys of the converter unit and improving the harmonic composition of the output current of the grid inverter has been substantiated; the structure of the converter control system has been developed with voltage regulation at the input of the grid inverter and switching from work in parallel with the grid to the autonomous mode and vice versa; a computer model of the system “converter unit with solar battery, grid and load” with a unit for determining energy losses in keys of circuit was developed. Improved: the structure of the control system of the converter unit with voltage regulation in the DC link; the structure of the generator with the combination of the function of phase-locked loop. The dependence of the voltage value at the input of the grid inverter is obtained according to the grid voltage, provided that the current quality is maintained at the grid connection point.