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 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.

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.

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 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.

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.

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.

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.

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.