With the rapid development of renewable energy, the demand for grid-scale energy storage solutions is increasing to address the challenges posed by intermittent and variable power generation. As an integration of various mature electrothermal conversion and storage technologies, Carnot battery is gaining increasing attentions due to its scalability and independence from geographical constraints. The fundamental principles, key technologies, application prospects and current research status of Carnot battery are reviewed. The definition of high-temperature Carnot battery technology and the operational characteristics and technical challenges of related key equipment such as compressors and expanders are discussed. Additionally, practical application cases and technological prospects of Carnot battery systems based on electric heating and bidirectional cycles (such as Brayton and Rankine cycles) are analyzed, providing a reference for future research and technological development.

The proton exchange membrane (PEM) electrolyzer can convert green electricity into hydrogen energy, but the conversion efficiency of PEM electrolyzer is low, the thermal energy in the electrolyzer outlet water is not fully utilized. To fully use the waste heat in the PEM electrolyzer hydrogen production system, integrated systems incorporating a 660 MW coal-fired unit and PEM electrolyzer are proposed in both power generation (PG) and combined heat and power (CHP) scenarios. EBSILON and MATLAB Simulink softwares are applied for modelling, and thermodynamic and economic analysis is conducted. In PG scenario, the electrolyzer outlet water is used to heat the feedwater of coal-fired unit. While for CHP scenario, the electrolyzer outlet water is used to heat the return water from heating supply network along with the extraction steam. The produced oxygen is sent into the boiler for combustion. The results show that, compared with the reference coal-fired unit, in PG scenario, the power output is enhanced by 2.55 MW with an power supply efficiency rise of 0.17%, and the boiler efficiency increases by 0.04%. While in CHP scenario, the power output can be enhanced by 5.83 MW with an efficiency rise of 0.40%. After attributing the net power output increment to the PEM hydrogen production system, the exergy efficiency of the PEM hydrogen production system is 69.74% in PG mode with an increase of 3.44%, and 75.41% in CHP mode with an increase of 9.11%. For these two scenarios, the system exergy efficiencies reach up to 40.20% and 40.18%. Economic analysis shows that, the annual income growth by selling electricity for PG and CHP scenarios are 5 460 000 yuan and 12 460 000 yuan, with the increments of net present value of 61 320 000 yuan and 140 140 000 yuan, respectively. The levelized cost of hydrogen production in the reference system is 42.72 yuan/kg. The levelized cost of hydrogen production in PG and CHP modes in the integrated system is 42.55 yuan/kg and 40.79 yuan/kg, respectively.

Aiming at the characteristics of complex and variable load and strong coupling of integrated energy system, a combined forecasting model based on variational mode decomposition (VMD), Prophet model, long- and short-term memory network (LSTM) and autoregressive integrated moving average (ARIMA) model is proposed for short-term electrical load prediction. Firstly, the electric load eigen mode functions with different center frequencies and relatively stable ones are obtained by VMD. Then, after calculating the value of zero cross rate, the modal components of each group are superimposed respectively to form the high-frequency and low-frequency timing components, and the Prophet model is used to extract the high-frequency components for timing features. Finally, the ARIMA prediction model is used to predict the low frequency component, and the LSTM neural network model is applied to predict the high frequency component. The final predicted electric load is obtained by superimposing the respective prediction results. The proposed method is applied to the actual integrated energy system, and the example analysis shows that the combined forecasting method presented above has good forecasting performance for the integrated energy system

With the increase of wind power penetration in power systems, the inertia of the power system decreases and the frequency regulation resources are insufficient. The frequency response margin approaches the critical value, which results in great challenges to frequency security. To solve the problem, from the perspective of regulation mechanism, a wind-thermal cooperative frequency control model based on virtual inertia control of wind power is constructed. The kinetic energy of rotor is used for fast frequency regulation. Then, a load frequency controller of wind-thermal cooperative power system based on a novel active disturbance rejection control (ADRC) method is proposed and designed. This improves the anti-disturbance capability to uncertain wind power and load disturbances. The designed cascade extended state observer also solves the contradiction between high frequency noise suppression and fast response performance of conventional ADRC. The excessive regulation of wind power and thermal power units caused by frequency measurement noise can be avoided and the quality of wind-thermal coordination regulation can be improved. Finally, genetic algorithm based particle swarm optimization is used to optimize the parameters of the proposed load frequency controller. The simulation results show that, compared with the conventional ADRC and other conventional control methods, the proposed strategy can effectively improve the frequency response characteristics, and suppress the effect of measurement noise on the amplitude of system frequency response and control signal.

Enhancing peak shaving capability of supercritical carbon dioxide (S-CO₂) boiler is the key to realize flexible operation of S-CO₂ coal-fired power plants. Research on dynamic characteristics of S-CO₂ boiler is beneficial to optimize the boiler operation control strategies. A dynamic simulation model of S-CO₂ boiler is established by the principles of thermodynamics and heat transfer based on the boiler of a 5 MW S-CO₂ cycle power unit designed and built by Xi’an Thermal Power Research Institute, and the reliability of the model is validated with operational data from unit. Based on the simulation model, dynamic characteristics of the above S-CO₂ boiler under step disturbance of different boundary conditions, such as fuel flow rate, working fluid flow rate, and working fluid temperature, are analyzed. The results show that, the S-CO₂ boiler has large thermal inertia, stability times of working fluid temperature at the boiler outlet are different under disturbance of different boundary conditions. With the increase of disturbance range of boundary conditions, stability times become longer. With the increase of boiler heat load, the working fluid pressure at the S-CO₂ boiler outlet decreases, and the working fluid flow rate at the S-CO₂ boiler outlet increases instantaneously in the initial stages of a dynamic process.

Against the shortcomings of intermittency and instability of photovoltaic power generation in microgrids, a hybrid energy storage system composed of vanadium redox batteries (VRB) and super capacitors (SC) is utilized to smooth out the power fluctuations in standalone microgrids, thus to improve the power supply reliability of standalone microgrids. Considering the capacity allocation problem of the hybrid energy storage system, a multi-objective hybrid energy storage system capacity optimization model that minimizes the average annual cost of the hybrid energy storage system and the load shortage rate is developed. Aiming at the poor local search ability of the conventional elite non-dominated solution sorting genetic algorithm (NSGA-II) algorithm for solving the multi-objective optimization problem, an NSGA-II algorithm based on the improved elite retention strategy is proposed. By introducing a new fitness function, the algorithm is sorted and reasonably retains the elite individuals, so it improves the optimization effect, thus to enhance the local search ability, continuously approach the Pareto true frontier, and obtain better capacity configuration solutions. Finally, the rationality of the proposed method is verified by arithmetic examples.

In order to improve the performance and efficiency of the battery in vanadium redox battery (VRB) system, a multi-stack equivalent loss circuit model is developed based on the composition and principles of VRBs, which includes electrochemical, hydrodynamic, temperature, bypass current, and vanadium batteries. Moreover, the effects of pumping loss and bypass current on vanadium batteries in the pipeline system of all-vanadium flow batteries are investigated. The relationship between pumping loss and pumping current, the bypass current model, and the equivalent circuit model of vanadium battery with multiple stacks connected in series are established, and the core mechanism of the vanadium battery taking into account the dynamic response is elaborated by transforming each model into a whole. The key factors involved in modelling of the VRB, including the pumping loss and bypass current, are discussed in detail. The influencing factors of battery performance and efficiency are also analyzed. The results show that, parameters such as the length and cross-sectional area of the pipeline affect the pipeline resistance, and the resistance of longer main and branch pipes will reduce the bypass current but increase the pumping loss current. Longer and thicker pipelines are conducive to the simultaneous reduction of both the bypass current and the pumping loss, which improves the energy efficiency of the battery. The research provides an idea for design of the manufacturer’s pipeline.

Against the cooling problem of engine heat exchangers, the flow and heat transfer characteristics of hydrogen in vertical and U-shaped tubes at supercritical pressures are studied. The influence of pressure and mass flow rate on heat transfer of the pipeline is studied by numerical method, and the heat transfer law is obtained. The heat transfer mechanism of the elbow section is discussed in depth, and the effect of dimensionless force on heat transfer is analyzed. The results show that, the closer the pressure is to the quasi-critical or when the mass flow rate increases, the convective heat transfer coefficient will increase, resulting in heat transfer enhancement. The bend section of the U-shaped tube can enhance heat transfer effectively, reaching a peak near θ=90°. There is a buoyancy effect in the straight pipe section at the inlet, but when the pressure is higher than 2.0 MPa, the buoyancy effect can be ignored after the hydrogen flows through the elbow section due to the influence of density difference. The Dean vortex caused by the secondary flow is the main factor to enhance the heat transfer performance of the elbow section, and the influence on the inlet section is significantly weaker than that on the outlet section.

The cost of underwater assets in offshore wind farms is relatively low compared with the total cost of offshore wind power projects, yet the quality of these assets is vital for safe and stable operation of the offshore wind farms. The quality issues that can arise with wind turbines, underwater steel structures and foundations of offshore substations, and submarine cables during the construction and operation and maintenance phases are analyzed. Based on cases from practical offshore wind power generation projects, the inspection requirements and methods stipulated by relevant standards are evaluated, and comprehensive and effective underwater inspection methods for various types of quality defects are put forward. These methods have been verified in real cases, forming industry standards and specifications, which provides significant technical guidance and reference value for quality control and operational maintenance of underwater assets in offshore wind farms.

In view of the complex variation law and strong autocorrelation of nitrogen oxides emission mass concentration of circulating fluidized bed (CFB) boiler, by using relevant variables and their historical information, ensemble learning online models of nitrogen oxides emission mass concentration are established. The ensemble learning online models include the autoregressive integrated moving average (ARIMA), random forest (RF), gradient boosting (GBDT), and eXtreme gradient boosting (XGBoost) model. The prediction results are compared and selected, among which the GBDT regressor is the best. In order to further improve the prediction effect of the model, a GBDT differential regression model is established by combining the first-order difference with the GBDT regression algorithm. The tests show that the established GBDT differential regression model has better prediction performance than the aforementioned models. The mean squared error of the predicted value is 20.2% lower than that of the simple GBDT regressor, and 46.5% lower than that of the online sequential extreme learning machine (OS-ELM) model used in the reference. The online model also fully considers avoiding the influence of the instrument purge process, and has strong practicability.

With the increasingly prominent problem of load fluctuations in high proportion renewable energy grids, improving the fast load response ability of large-scaled thermal power units under full operating conditions has become an urgent need to maintain the safe and stable operation of the power system. Therefore, a rapid load change strategy combined with the high-pressure bypass transformation technology under the flexibility demand of supercritical power units is proposed. Firstly, the high-pressure bypass is added to the high-pressure regenerative system to flexibly change the steam extracted amount from turbine, thus to accelerate the energy supply rate of once-through boiler. Secondly, to adapt to the high ramping rate, a load change scheme is designed with the limitations of main steam pressure, temperature and their change rate that boiler can withstand at sliding-pressure operation mode and the decoupling of load-main steam pressure for unit. Finally, test on a 600 MW coal-fired thermal power unit shows that, the unit can successfully achieve a high load ramping rate of 3%Pe/min under full operating conditions. Moreover, the main steam pressure, position of main steam valve and other parameters are maintained stable. In addition, the load regulation ability of the unit with load ramping rate of 5% Pe/min is verified, confirming the effectiveness of the proposed load rapid regulation strategy.

Direct discharging of saturated flue gas from coal-fired utility boiler can lead to significant low-grade waste heat loss. The saturated flue gas waste heat recovery and utilization for centralized heating system is constructed, the operating parameters of the heating system in coal-fired power plant are analyzed, and the feasibility that the saturated flue gas waste heat can be used to heat the return water of the heating system is verified. Finally, the economic efficiency of the centralized heating system is investigated for operation with different targets, and the influence characteristics of the operating parameters are revealed for the thermal performance of the centralized heating system. The research results show that, the temperature of flue gas waste heat can be increased by 30~40 ℃ by absorption heat pump. With the 350 MW coal-fired heating unit as an example, the absorption heat pump recovers the saturated flue gas waste heat with 50.23 MW for re-utilization. The economic benefits brought by enhancing the heating capacity are significantly better than those corresponding to the increase in power generation, and the heating capacity of the coal-fired power plant is increased by 13.4%, and the annual heating revenue is increased by 19 752 000~34 423 200 yuan. The research provides technical references for the saturated flue gas waste heat recovery and utilization in coal-fired power plants.

In response to significant increase in energy consumption caused by low-grade waste heat and energy waste in coal-fired power plants, a 350 MW unit is selected as the research object, the Ebsilon software is used to model and simulate different deep recovery schemes for low-grated waste heat and residue. The operating data of the unit under two schemes of “organic Rankine cycle (ORC)” and “Heater” are calculated. The energy consumption characteristics, revenue characteristics and differences are analyzed, and the mechanism and optimization plan for deep recovery of waste heat and energy are obtained. The results show that, the energy consumption characteristics of the unit improve significantly under both schemes, and the “heater” scheme has lower energy consumption. As the organic working fluid flow rate increases, the power generation of the ORC system gradually increases, but the thermoelectric efficiency of the ORC system gradually increases at first and then tends to stabilize and has a downward trend, with a range of 6.94%~7.75%. The organic working fluid flow rate has a relatively small effect on circulation efficiency of the ORC system. Both schemes are technically and economically feasible. The “ORC” scheme can bring direct electricity benefits to the power plant, while the “Heater” scheme is slightly more economical.

In order to provide effective repair and rust prevention treatment for hot surface pipe of utility boilers, and to ensure safe operation of the equipment, cold metal transfer (CMT) cladding process is adopted for water-cooled wall tubes. Four cladding process paths are designed, and the reliability of the numerical simulation data is verified through ANSYS numerical simulation and the CMT cladding experimental platform. Comparison based on the process developed in the simulation process shows that, design of the CMT heat source function has a higher degree of agreement in characterizing the temperature field than the conventional arc heat source. Along the material thickness direction, the change rule of the temperature gradient is consistent with the actual morphology of the specimen cross-section. In the case of the same heat input, the average temperature of the cross-melting path is 30 ℃ lower than that of the sequential melting path, the thermal effect of the cross-melting path on the substrate is smaller, and the stress is 22.0 MPa lower. Pipe deformation reduces by 0.18 mm in the cross-over reverse welding path compared with that in the sequential reverse welding path. Comprehensively considering the effects of the residual stresses and the deformations, the cross-reversed melting path is the optimal process route for CMT.

The calculation analysis and experimental study of blade fracture of a certain type of steam and static adjustable induced draft fan are carried out. Vibration signals and blade natural frequencies of fans at different speeds and openings are obtained through vibration tests and modal experiments. Performance curves of fans at different speeds are drawn according to the similarity theory, and the rotation-opening curves corresponding to the flow rate are obtained. The fan operation restricted zone is delimited by the stall line. The test results show that, when the rotation speed is constant, the amplitude of the blade passing frequency and its harmonic component increase with the stator blade opening. Combining with the modal experiment, it is found that the natural frequency of the blade and the blade passing frequency and its harmonic component coincide when the fan runs in the rotation speed range of 796~912 r/min, resulting in blade resonance. The fan should avoid running in the resonance speed range and avoid running in the speed restricted area.

With the large-scale development and grid integration of new energy sources, the fundamental control and operational mechanisms of power system have undergone significant changes to power balance and safety stability control. Low-frequency oscillation events in power systems have typically been simulated and analyzed using standard speed control system models. However, these standard models fail to reflect the regulation characteristics of the units and cannot accurately reproduce the low-frequency oscillation process. Based on the nonlinear characteristics of steam turbine valves and combined with the actual frequency control logic, a small frequency deviation compensation module and a valve flow module are introduced into the typical speed control system model to establish low-frequency oscillation model. The accuracy and effectiveness of the model are verified using actual operational data. Moreover, low-frequency oscillation evaluation indicators are established, by employing the analytic hierarchy process (AHP) and fuzzy evaluation methods, online identification and grading evaluation of low-frequency oscillations are achieved. On this basis, a phased suppression strategy for low-frequency oscillations on the prime mover side of thermal power units is proposed. The corresponding suppression measures are executed based on low-frequency oscillation evaluation results, and the low frequency oscillation model is used to carry out simulation verification. The results demonstrate the suppression strategy can effectively eliminate low-frequency oscillations on the prime mover side and improve operation safety of thermal power units.

The continuous penetration of internet technology into industrial control field has given rise to conceptual systems such as Industry 4.0 and Industrial Internet. Consequently, power plants are evolving towards digitization and informatization, with the intelligence and complexity of field-controlled objects increasing steadily. Control functions of conventional distributed control systems (DCS) are gradually becoming inadequate to meet these new demands. To enhance the maturity level of intelligent manufacturing in China, it is essential to strengthen the core computational control functions of DCS. In response, a novel collaborative control platform is proposed based on software-defined principles. This platform decouples the software and hardware of conventional DCS using software-defined concepts, reconstructs the control and configuration functions on the host computer, and designs and develops a dual-redundant computing engine and configuration and debugging tools. Additionally, protection mechanisms are established to ensure the operational security of the platform and the security of third-party data. This platform inherits the conventional configuration and control functions of conventional DCS while additionally supporting the implementation of various advanced intelligent algorithms. In terms of application, it can both enhance the control performance of conventional DCS and serve as an independent product providing high-quality computing services for other control systems. Consequently, it can be widely applied to various process control scenarios, offering users a reliable, efficient, flexible and cost-effective production control solution. Moreover, it provides an optional platform foundation for the future integration of cutting-edge computer technologies such as artificial intelligence and big data into DCS.

The safe and stable operation of submarine oil-filled cables is critical, but the internal dodecylbenzene (DDB) insulating oil is subject to rapid pyrolysis and gas production at localized high temperatures due to thermal faults. Against this issue, the pyrolysis and gas production processes of dodecylbenzene insulating oil are investigated based on reactive molecular dynamics simulations (ReaxFF-MD) and thermogravimetric-infrared spectroscopy (TG-IR) experiments. The pyrolysis simulation results show that, the initial cracking reaction of the dodecylbenzene molecule is mainly the breaking of C—C bond to produce long-chain macromolecules, and then the gradual pyrolysis produces small alkyl radicals and olefinic molecules, and the DDB will eventually be pyrolyzed to the short-chain alkylbenzene molecules with the side chains of ·C₂H₅, ·CH₃ and ·C₃H₇ groups. The main characteristic gases during pyrolysis are C₂H₄, H₂, and CH₄, which are the same as the results of IR experiments, and the main reaction mechanisms for the generation of the characteristic gases are: (i) the breaking of the C—C bond at the β-position, the hydrogenation reaction, and the dehydrogenation reaction; (ii) the attack of -H radicals to the H atoms on other radicals; and (iii) the reaction of the methyl radicals (·CH₃) with the free hydrogen (·H) radicals, respectively. The kinetic results show that the activation energies of the TG experiment and ReaxFF-MD are 86.606 kJ/mol as well as 99.867 kJ/mol, respectively, and the similar activation energies further validate the reasonableness of the simulation results. The study conclusion provides theoretical support for deep understanding of the cracking and gas production mechanism of dodecylbenzene insulating oil.