Dynamic Operating Characteristics Research Articles

Dual-time scale optimal dispatch of the CSP-PV hybrid power plant considering dynamic operation

The concentrating solar power (CSP) plant, renowned for its flexibility, environmental friendliness, and energy storage capabilities, has become integral components of large-scale renewable energy projects in China. However, the grid connection methods for CSP plants, wind farms, and photovoltaic (PV) plants are independent. To enhance renewable energy consumption and improve the revenue of CSP and PV plants, this paper proposes a dual-time scale dispatch model for the dynamic operation of the CSP-PV hybrid plant. This model considers the actual startup conditions and dynamic switching models of the subsystems involved in the receiver, thermal storage subsystem, and power cycle. Based on the dynamic operation characteristics of the CSP-PV hybrid power plant, different time scales are used for prediction during day-ahead and intraday periods, improving the efficiency of the hybrid power plant and adapting to weather changes. The dispatch optimization outcomes of the CSP-PV hybrid plant serve as the reported curve for the day-ahead and intraday rolling optimal scheduling process, aiming to minimize the operating costs of the power system. A simulation is conducted to demonstrate the effectiveness of the proposed model, utilizing data from the Dunhuang area, Gansu Province, China.

Transient simulation and experimental analysis for the response of dual-cycle air-carrying energy radiant diffuse terminal

A novel air-carrying energy radiant diffuse terminal is proposed, and the response of the terminal is investigated by field experiment and numerical simulation. This paper explores the dynamic operation characteristics of the new system to guide the optimal operation of the system. A transient simulation method of three factors (conduction, convection, and radiation) with dual-circulation (air-carrying energy zone and occupied zone) is put forward for the radiant diffuse terminal with a fresh air system. This transient simulation sets up the porous baffle model coupling radiation model concurrently, revealing the dynamic thermal performance for the system's response accurately, quickly, and comprehensively. This method avoids the limits for the complexity of mini porous (Pore size of 1 mm–3mm) geometric models and the transient uncertainty in multiple combination models. The results show that the average error between the convective-conductive model and the convective-conductive-radiative model is about 8% at five different heights. This system has high response performance, which can quickly heat the room while maintaining the comfort requirements of vertical temperature. The radiated heat transfer between the radiant diffuse terminal and the occupied zone is greater than the convective heat transfer (Radiation accounts for 74%). This system has a short response time, high energy efficiency, uniform airflow, and eliminates draught rating. Moreover, the indoor non-uniform transient thermal and humid environments, the thermal comfort, and air quality for the response of the terminal with fresh air system under four different diffuser placements are compared using computational fluid dynamic simulation. The results indicate that introducing heating strategies featuring higher-positioned fresh air inlet and lower-positioned recirculation return air outlet for this system leads to a temperature efficiency increase by 5%, velocity uniformity by 8%, and age of air reduction by 16–50% in human-breathed zone and the response time by 25%, which shows substantial potential for energy savings. The transient simulation and experiments in the paper are beneficial to optimize design parameters and carry out energy-saving applications of operation energy consumption for the response of this terminal with a fresh air system in the future.

Optimal design of a renewable hydrogen production system by coordinating multiple PV arrays and multiple electrolyzers

In the design of a renewable hydrogen production system (RHPS), it is of great significance to coordinate the power generation and electrolyzers for efficient and stable hydrogen production. To investigate the coordination and complementary characteristics of multiple PV arrays and multiple electrolyzers in the optimal design of RHPS, a coordinated design approach based on mathematical optimization for the optimal RHPS with multiple PV arrays and multiple electrolyzers was proposed, which features comprehensive considerations of different characteristics of power generation and economy of different types of PV arrays, and the dynamic operating characteristics and economy of various types and capacity of electrolyzers to adapt to fluctuating hydrogen demand. The optimal configuration of the RHPS with minimal total cost can be obtained by combining multiple PV arrays with multiple electrolyzers. Furthermore, the impacts of power generation on the economy of the system are systematically explored, and electrolyzer types are optimally deployed. The influence of different PV array types on the economics of the system is analyzed. An example of the RHPS was employed to demonstrate the feasibility and effectiveness of the proposed method. Results show that for the RHPS, the selection of the type of electrolyzers is mainly affected by the characteristics of power generation. In the system with only PV arrays for power supply, the total cost of the system with proton exchange membrane electrolyzers (PEMEL) is 11.2% lower than that of the system with alkaline electrolyzers (AEL). In the system with simple wind turbines for power generation, the total cost of the system with AEL is lower than that of the system with PEMEL. The selections of type and capacity of the electrolyzers in the system are affected by the minimal power limit of the AEL. The total cost of the system can be effectively reduced by coordinating the power generation and electrolyzers and combining AEL and PEMEL in the system. The selection of PV types is related to the unit cost and the seasonal changes in the capacity factor of different PV arrays, which is also influenced by the hydrogen demand and the curtailment rate. When the variations of power generation align with hydrogen demands, the total cost can be reduced by lowering seasonal energy storage capacity.

Modelling and fault analysis of APROS-based moisture separation reheater

A modular modelling approach was adopted to build a dynamic simulation model of the moisture separation reheater on a high-precision APROS real-time platform to investigate the dynamic operating characteristics of the moisture separation reheater. The model was subjected to steady-state and step dynamic tests at different loads. The results show that the established model can correctly reflect the steam flow and heat transfer properties and can meet the requirements of the simulation. Using the one-dimensional distribution of the model, the effect of a small breakage failure in the heat exchanger bundle was further investigated. The results showed that the heat transfer tube bundle had leaks, reducing the heat transfer capacity and affecting the quality of the steam used to work in the low-pressure turbine. Simultaneously, the effect on steam outlet parameters increased with the degree of leakage in the heat exchanger.

Substations power quality improvement by flexible alternating current transmission system devices

<p>The increase in load demand has a negative impact on power system quality, reliability, and stability. Transporting reactive power from the generating side to the distribution side reduces the transmission line’s capacity to deliver active power to loads. In conventional power systems, during faults or sudden loads, the load flow changes and causes extra voltage drop. Reactive power compensation at the load side can improve voltage quality at distribution busbars, but the conventional compensation method doesn’t offer the required flexibility. With the development of the power electronics industry, flexible alternating current transmission system (FACTS) devices have been introduced. There are many categories for FACTS controllers, including series, shunt, and hybrid, which can exhibit dynamic operating characteristics. In this paper, two types of FACTS devices (STATCOM and fixed capacitor-thyristor-controlled reactors (FCTCR)) have been used to improve voltage profile in a part of Iraq’s high voltage power system during unusual operating conditions, such as sudden loads and the absence generation. Load flow calculations were conducted to determine the critical bus, and then the performance of the FACTS devices was investigated during heavy loading when the devices were connected separately to the critical bus. The voltage drop in the bus was 1.58%, which reduced to 0.78% with STATCOM and 0.96% with FCTCR.</p>

Study on optimal allocation of energy storage in multi-regional integrated energy system considering stepped carbon trading

Abstract In this study, an energy storage configuration optimization model of multi regional integrated energy system based on integrated scheduling and stepped Carbon emission trading is proposed. By analyzing the steady-state, dynamic, and variable operating characteristics of multi regional integrated energy systems, a distributed energy planning modeling method was adopted to construct energy storage configuration constraint objects and optimization models. The target scheme of energy storage configuration is optimized by using the results of integrated scheduling scheme and dynamic distribution analysis of ladder Carbon emission trading, and the parameters are optimally estimated by using Monte Carlo method and quadratic fitting algorithm. The simulation results show that this method has a strong scheduling capability in the context of stepped Carbon emission trading, can accurately assess the load demand and supply demand relationship, reduce carbon emissions, and improve energy efficiency, with an average of 0.9121.

Combing dynamic parameter identification and singular value decomposition adaptive unscented Kalman filter for predictive state of charge of lithium-ion batteries

The development of a secure battery management system (BMS) for electric vehicles depends heavily on the correct assessment of the online state-of-charge (SOC) of Li-ion batteries. The ternary lithium battery is used as the research object in this paper, and a second-order RC equivalent circuit model is developed to characterize the dynamic operating characteristics of the battery. In order to solve the problem that the adaptive unscented Kalman filter (AUKF) algorithm is easy to fail SOC estimation because the error covariance matrix is not positively definite due to the incomplete accuracy of the equivalent circuit model, a corresponding solution is proposed. Considering the poor real-time battery SOC estimate caused by the battery model’s fixed parameters, therefore we propose the Variable Forgetting Factor Recursive Least Squares (VFFRLS) algorithm for joint estimation of Li-battery SOC and the Singular Value Decomposition-AUKF (SVD-AUKF) algorithm. The SVD-AUKF algorithm can accurately estimate the SOC of the battery when the error covariance is negative. The algorithm can be adaptively adjusted in both the parameter identification and SOC estimation stages, which can effectively solve the problem of poor estimation accuracy caused by fixed parameters. According to experiments, under two separate dynamic operating situations, the joint estimation algorithm’s error is less than 2%, and its stability has also been greatly enhanced. At the same time, when the initial SOC value is set incorrectly, the convergence time of the algorithm proposed in this paper can reach within 2.1 seconds for BBDST and DST conditions, which can be well adapted to complex working conditions.

A knowledge transfer-based method for risk analysis and procedure optimization of emergency schemes

Due to insufficient knowledge of rare accidents, it is essential to transfer knowledge from source domain with sufficient cases (e.g., onshore blowouts) into target domain with limited cases (e.g., deepwater blowouts). In this paper, a knowledge transfer-based method is proposed to evaluate the performance of emergency schemes in presence of limited accident cases. By considering dynamic evolution and operational characteristics of the accident, to evaluate emergency schemes from the perspectives of emergency risk and timeliness, a hybrid model integrating dynamic Bayesian networks (DBN) and program evaluation and review technique (PERT) is applied. In the integrated model, we transferred graph structures and parameters to obtain emergency schemes based on the similarities between the source systems and target systems. On the one hand, to evaluate and control emergency risk, DBN is utilized for dynamic risk analysis of emergency operations. On the other hand, to judge the response-time requirement, an optimized PERT is applied to enhance the completion probabilities of the emergency procedures. A case study on the installation of onshore blowout preventer and offshore capping stack is applied to illustrate the applicability of the proposed methodology. The results show that equipment failure and human error are crucial risk-influencing factors leading to emergency failure. Activities duration and completion probability of emergency schemes are optimized by emergency timeliness analysis.

Experimental study on a concentrating solar photovoltaic/thermal system using different fluid spectral beam filters

Spectral splitting photovoltaic/thermal technology is the leading field in the area of extremely efficient utilization of solar energy. Due to its complexity, experimental research on spectral splitting photovoltaic/thermal devices is relatively limited, mainly focusing on the laboratory scale energy efficiency test or calculation process verification. These studies do not provide intuitionistic guidance for the actual operation of engineering systems. In this paper, a fluid filter-based compound parabolic concentrator solar photovoltaic/thermal system with engineering application dimensions is designed and experimentally studied under actual outdoor environments. Different fluid filters are prepared and used to regulate the spectral splitting characteristics of the proposed system, including the deionized water, silver/water nanofluids and silver-cobalt sulfate/water nanofluids. When the environmental parameters are relatively stable, the method of adjusting the composition of the fluid filter is used to obtain the dynamic operating characteristics of the system. The results show that silver nanoparticles and cobalt sulfate can improve the spectral absorptivity of the deionized water. Compared with the deionized water, when the silver/water nanofluids is used as the fluid filter, the thermal efficiency of the system increases, the electric efficiency and overall exergy efficiency of the system both decrease, and the three efficiencies are 56.0%, 8.5% and 19.6%, while for the silver-cobalt sulfate/water nanofluids, the efficiencies are 58.0% 8.0% and 20.0%. Moreover, the results reveal that for the photovoltaic/thermal system with a low solar concentration ratio, by enhancing the absorptivity of the fluid filter, the fill factor of the photovoltaic module can increase, but the output electric power will decrease. When the silver-cobalt sulfate/water nanofluids is used, the fill factor and maximum output power of the proposed system are 0.633 and 69.2 W. For a unit consisting of four sets of the proposed photovoltaic/thermal systems, the emission reductions of CO2, NOx, SO2 and dust for the whole lifetime are approximately 7794.19 kg, 181.48 kg, 191.95 kg and 111.68 kg, respectively.

Optimal multi-energy portfolio towards zero carbon data center buildings in the presence of proactive demand response programs

Multiple geographically dispersed data center buildings have been increasingly positioned in renewable-rich areas due to their high energy consumption. This paper proposes an optimal multi-energy portfolio for zero carbon data center buildings in the presence of proactive demand response programs. In the data center buildings, the complementarities of hydro-solar-wind hybrid renewable energy sources (RESs) are fully exploited via multi-energy conversion and storage devices, which are modeled as 100% renewable energy hubs for zero carbon multi-energy supplies. In order to exploit the hub-internal operational dispatchability and flexibility, a comprehensive energy consumption model of data center buildings is proposed to facilitate the demand response in terms of available serves, while the variable speed pumped storage (VSPS) is modeled to capture its dynamic operational characteristics. The energy‑carbon production, conversion, storage, and consumption are formulated as an energy‑carbon matrix, which are solved via a two-stage method to obtain the optimal portfolio. Case studies on southwest China data center buildings are implemented to demonstrate the effectiveness and superiority of the proposed methodology on cost-effective accommodation of RESs. Simulations results show that the system portfolio cost can be reduced by at most 17.8% with a higher operational flexibility.

Dynamic characteristics and energy efficiency evaluation of a novel solar seasonal thermal storage - heating system

This paper proposes solar seasonal thermal energy storage system compounded with long-term and short-term energy storage tanks for a single-family dwelling, which using assisted water source heat pump to further improve the systems stability. With the objective of improving the solar energy utilization efficiency and reducing the primary energy consumption, the dynamic simulation model of the “heat collection-heat storage-heat supply” system under the non-stationary boundary conditions throughout the year is established. The energy transfer and conversion law of each subsystem and the dynamic operation characteristics are analyzed through simulation method. The system cooperative control strategy is proposed and parameter optimization is carried out. Results indicate that the annual heat collection efficiency of the water source heat pump composite system has been improved by 2.2 % compared with the electric auxiliary heating system. Meanwhile, the heat storage efficiency and the solar energy guarantee rate increased by 5.8 % and 8.3 %, respectively. Moreover, the optimal water source heat pump composite system not only improves energy efficiency and achieves the cost savings compared with the electric auxiliary heating system, but also reduces carbon dioxide emission by 10.3 %, which have great advantages for energy saving and emission reduction.

A step towards dynamic: An investigation on a carbon dioxide binary mixtures based compressed gas energy storage system using energy and exergy analysis

A dynamic model of a compressed gas energy storage system is constructed in this paper to discover the system's non-equilibrium nature. Meanwhile, the dynamic characteristics of the CO2 binary mixture (i.e., CO2/propane, CO2/propylene, CO2/R161, CO2/R32, and CO2/DME) based system are first studied through energy and exergy analyses. Performance indicators are considered, including round trip efficiency, exergy efficiency, energy density, discharge time, and average power output. The effects of tank volume and ambient temperature on the system performance are analyzed. According to the results, although the round trip efficiency of the CO2 mixture system is reduced by about 0.68%–11.97% compared to pure CO2, the compressor performance and the system pressure stability are improved. When the tank volume increases from 10,000 m3 to 15,000 m3, the system round trip efficiency increases by 0.16%–0.33%. A further improvement of round trip efficiency for the CO2 mixture is found compared to pure CO2 at higher ambient temperature. This paper demonstrates the dynamic operational characteristics of the compressed gas energy storage system when using different CO2 binary mixtures, providing a reference for optimizing related systems. Potential scenarios and applications for the CO2 binary mixture are discussed for future research.

Dynamic operating characteristics of a compressed CO2 energy storage system

For the first time, the study investigated the dynamic performances of a compressed CO2 energy storage (CCES) system based on a dynamic model, which was validated using experimental data. The dynamic round-trip efficiency (RTE) of a scaled-up CCES system in two typical operation modes was studied, including Mode 1: the basic operation mode, where the inlet pressure of the compressor or the expander is not controlled, and Mode 2: the controlled operation mode, where the capacity for compression or expansion is regulated to remain constant. Dynamic RTE varies in the range 16.7%-56.7% in various operation modes. A new key performance indicator, utilization of tank (UOT), was defined to reflect how much working gas is used in a charging or a discharging process. In general, high charging and high discharging capacities lead to low UOTs and low RTEs. Moreover, the comparison between the dynamic model and its equivalent steady-state model showed a significant difference in system performances. The RTE of the steady-state model reaches 68.5%, which is much higher than the corresponding dynamic RTE of 55.3%.

The dynamic performance of a compact LN2 depressurization cryocooling system

Liquid nitrogen (LN2) has been widely used as a cooling medium. A compact LN2 depressurization cryocooling system can be used as a portable cooling unit to satisfy flexible cooling requirements. A prototype of this cryocooling system which was mainly composed of a LN2 tank, a LN2 pump, a heat exchanger and a vacuum pump was built and tested. In the test, the lowest cooling temperature could reach below 65 K, and the average temperature of 0.95 m3 LN2 dropped from 73.5 K to 68.1 K after 6814 s of running. The average refrigeration power reached 1326 W at 65 K. Meanwhile, the system operation process was simulated through theoretical analysis and modeling. Simulation results were nearly consistent with experimental results and the dynamic operating characteristics were well captured. For the experimental apparatus, the LN2 supplement and shutdown of the liquid-ring pump affect the system cooling performance, and modeling results show that the cooling efficiency decreases with the LN2 volume flow rate V̇LN2 increasing whenV̇LN2 > 0.9 m3/h.

Analysis of Dynamic Operation Characteristics of the Integrated Energy System

Gas turbines make the coupling between the natural gas system(NGS) and the power system tighter. So Natural gas systems and power systems are interdependent in security and stability, and only paying attention to the security of the power system itself can not guarantee the security and stability of the system. To meet the problem and challenge, in this paper, a technical route based on the method of characteristic (MOC) is proposed to analyze the interaction of integrated energy systems (IES). It can calculate the transient process of the active and reactive power output of GT after the fluctuation of the NGS. Then, according to the dynamic math model of the natural gas in the pipeline(line-pack), the dynamic change of the line-pack is calculated, and the maximum interruption time of the gas source can be calculated according to the line-pack calculation result. Because of the intrinsic mechanism advantages of the MOC, the time step in the simulation calculation can be very small, which does not affect the calculation efficiency. It can calculate the dynamic change of GT output power, identify weak links in the operation of the system, and provide an important decision-making basis for taking safety control measures. Finally, based on an IES case, it is verified that the method proposed in this paper is of great value to analyze the security and stability of the IES.

A Study of Digital Measurement and Analysis Technology for Transformer Excitation Magnetizing Curve

Transformer excitation magnetizing curves (TEMC) reflect the dynamic operation characteristics of iron-core materials. Using numerical analysis and the waveform recording function of digital oscilloscopes, we developed a cost-effective method for determining the TEMC. This approach eliminates the need for conventional analog integrator circuits. To address the potential obstacles to the digital generation of TEMC—namely, curve offsets and curve transients—we proposed solutions involving Fourier filtering and determining the initial point of integration. The results indicate that the proposed approach yields results consistent with those of conventional analog integrator circuits and highlight its promise for applications in data processing.

Critical Percolation on Temporal High-Speed Railway Networks

Deeply understanding the dynamic operating characteristics of high-speed railway (HSR) systems is of essential significance in theory and practice for the planning, construction, and operational management of HSR systems. In this paper, the HSR system is described as a temporal network, and the evolution of connected clusters in the system is considered as a percolation process. The critical integration time Tc of the percolation process can determine the formation of a globally connected cluster and measure the transport performance of the HSR system. The appearance time of critical edges identified at Tc can significantly affect the reliability of the transport performance of an HSR system. Compared to random percolation in the static HSR network, it can be found that the critical fraction pc of the percolation process in a temporal HSR network is almost always larger. This indicates that the global connectivity and the transport performance of HSR systems is overestimated by the static network abstraction. This paper provides a promising way of understanding the dynamic characteristics of HSR systems, evaluating their transport performance, and improving their reliability.

Analysis of Dynamic Operating Characteristics of a Pulse Detonation Turbine Engine

In order to obtain the dynamic operating characteristics of a pulse detonation turbine engine (PDTE), a transient model is established considering the shaft dynamics and the volumetric effect of the components in the PDTE. The accuracy of the model is verified with the experimental data from a pulse detonation prototype engine. The deviations between the calculated data and the experimental results are no more than 7.61%. The numerical results show that the operating state of the PDTE will change gradually with the increase of the fuel flow rate or the firing frequency. The quasi-steady state calculations show that there are maximum values for the rotor speed, thrust, and specific thrust when the fuel flow rate is increased from 0.0056 kg/s to 0.0129 kg/s at firing frequency of 10 Hz. The rotor speed, thrust, and specific thrust will suddenly decrease due to the over rich of fuel in the PDC with the increasing of the fuel flow rate. The specific fuel consumption has a minimize value during this process. When the firing frequency is increased from 7 Hz to 18 Hz at a fixed fuel flow rate, the performance parameters such as the thrust, specific thrust, and specific fuel consumption have a similar variation trend. The extremum values of the performance parameters are obtained at firing frequency of 12 Hz. For the dynamic operating process of the PDTE, parameters such as the rotor speed or pressure ratio of the compressor are increased in a cyclic oscillation way when the fuel flow rate or the firing frequency is changed.

Simulation and Experimental Verification of Dynamic Characteristics on Gas Foil Thrust Bearings Based on Multi-Physics Three-Dimensional Computer Aided Engineering Methods

This paper presents a method to simulate the dynamic operating characteristics of a gas foil thrust bearing based on linear elastic support and constant ambient temperature to mimic the transient structure–fluid interactions. In the physical model, the top and bump foils are simply represented by an infinite number of Hookean springs attached to a solid wall with a small amount of deformation, whereas the gas film in the bearing is under quasi-steady lubrication flow conditions with hydrodynamic pressure distributed on the little-deformed top foil. A three-dimensional multi-physics model in a cylindrical coordinate system is established via a commercial computer-aided engineering software package to predict the nominal dynamic characteristics of the gas foil thrust bearing. To verify the multi-physics model, an experimental bench was built in-house to measure the thrust force on the support of the bearing. With the pertinent bearing parameters being entered into the package, the simulations agree well with the experimental thrust forces. As a further step, a simulation model of a clamped-rotor gas foil thrust bearing design was thoroughly investigated under nominal operating conditions, resulting in predictions of underdamped oscillations in rotor motions. The phenomenon could be described using a linear mass–spring–damper model that is dependent on the gas film thickness. The stiffness and damping coefficients could serve as a base reference for rotor dynamics analysis. This concludes the potential development of a digital twin for gas foil thrust bearing systems.

Dynamic Modeling and Comparison Study of Control Strategies of a Small-Scale Organic Rankine Cycle

The control strategy is crucial for the effective and safe operation of the ORC system. A transient model of the ORC system was developed in the present work and validated by the experimental data of a 4 kW ORC prototype. Then, the effect of heat source temperature on the dynamic response and operation characteristics of the ORC system were analyzed. Five control strategies were compared: the constant working fluid mass flow rate mode, constant vapor superheat mode, constant vapor temperature mode, constant evaporation pressure mode and constant output power load mode. Under the constraint that the working fluid at the expander inlet should be superheated, we found that the constant vapor superheat mode enabled the safe operation with the largest range of heat source temperature, while the other four modes were only available for a certain temperature range. Apart from the constant output power mode, the constant evaporation pressure mode can also provide a relatively stable performance for the ORC unit. The variation of the thermal efficiency was limited when the heat source temperature was higher than 125 °C, except for the constant vapor temperature mode. Considering the high performance and stable operation of the ORC system, it is necessary to have different operation modes combined in the control strategy according to the specific working scenarios.