A boundary voltage control (BVC) strategy suitable for single-phase current-source inverters has been proposed to achieve zero current switching (ZCS) by dynamically adjusting the resonant capacitor voltage, and this control strategy has low requirements for DC side current ripple, which can effectively reduce the DC side inductance value. Therefore, this control method can reduce circuit losses and decrease the size of the inverter. In this article, the working principle and conditions for achieving ZCS are analyzed by combining BVC and bipolar modulation strategy; Based on the principle of area equivalence, a quantitative model of DC side inductor current and output current is established, revealing the mechanism of the impact of second harmonic current ripple on output harmonics. The optimization design criteria for DC side inductance parameters are derived, and the reasons for the decrease in inductance value are analyzed. On this basis, a three loop grid-connected control strategy based on BVC is proposed. Finally, based on theoretical analysis, simulation and experimental research are conducted. The simulation and experimental results have verified the feasibility of the proposed BVC strategy.
In this paper,a scale model experimental platform was built to research the effect of the stratified discharge on the thermal stratification by combining the evaluation methods of outlet temperature,Nmix number,and Ri number.The results show that the closer the outlet is to the top of the thermal storage tank,the more obvious the decreasing trend of the water temperature and outlet temperature is,the thinner the thermocline is,and the Nmix number increases faster,indicating that the degree of thermal stratification of the water body decreases.The Ri number is mostly determined by volume flow rates,and the position of the outlets has little bearing on it.The discharge efficiency increases with time when the outlet is located above the middle line of the pool volume.With fixed outlet positions,as flow rate increases,the water temperature,Nmix number,and discharge efficiency vary faster,and the closer the outlet is to the top,the more the volume flow rates affect the thermal stratification of the water body.The change in volume flow rates affects thermal stratification more than the change in outlet height.
To advance the achievement of dual carbon goals and fully utilize the low-carbon potential of the microgrid load side,this paper proposes a bi-level low-carbon dispatch strategy for the power-carbon coupling of multi-microgrid systems and distribution networks,considering cooperative game theory.Firstly,to consider the impact of energy storage charging and discharging on carbon emissions,a carbon emission model for storage systems is established,integrating carbon flow analysis into the demand response model on the load side of the microgrids.A bi-level dispatch model,considering node carbon potential,is constructed,where the upper-level model addresses optimal economic dispatch for the distribution network,and the lower-level model incorporates the interests of microgrid operators and users within integrated energy systems.A joint operation model is designed under a carbon trading mechanism based on node carbon potential,facilitating cooperation between multiple microgrid operators and an aggregator representing the interests of all microgrid users.Secondly,leveraging Nash bargaining theory,energy interactions and cooperative operations between microgrid operators and the load aggregator are achieved.After demonstrating that the Nash bargaining model can minimize operational costs,the problem is decomposed into two sub-problems and solved using the alternating direction multiplier method(ADMM),achieving optimal low-carbon economic dispatch for the microgrid coalition.Finally,the model is applied to a modified IEEE 33-node system,and results demonstrate that the proposed approach effectively reallocates carbon emission responsibilities from the source side to the load side.It also accurately reflects the dynamics of competition and cooperation among stakeholders in the carbon trading market,enhancing both the low-carbon profile and economic efficiency of the system.
In order to improve energy utilization and reduce carbon emissions, this paper presents a comprehensive energy system economic operation strategy of Incineration power plant Power-to-gas (P2G) with waste heat recovery. First, consider the coordinated operation of Incineration power plant - P2G, introduce the refined Power-to-gas two-stage operation process, add Hydrogen fuel cells on the basis of traditional Power-to-gas to reduce the energy ladder loss, and recycle the Methanation reaction heat; Secondly, in order to improve the energy utilization efficiency of Incineration, it is considered to install a waste heat recovery device containing a water source heat pump to recover the waste heat of flue gas and consume some electric energy, sourced from wind power, and add a CO2 separation device to combine the recovered CO2 with P2G to synthesize CH4 to achieve carbon recycling. Finally, within the framework of a tiered carbon trading mechanism an IES optimization model for electricity-heat with the goal of minimizing the system operating cost is constructed, and the GUROBI modeling optimization engine is used to solve this model. The results verify the effectiveness of the model.
A wireless power transmission system powered by photovoltaics is proposed,which is mainly applied to the constant current(CC)and constant voltage(CV)charging topologies for electric vehicles(EVs),and only needs to adjust the switching state of the relay to realize the CC output of inductive capacitor-inductive capacitor(LCC-LCC)and the CV output of inductive capacitor in series(LCC-S).Compared with other topologies,no redundant components are required and the switching frequency is fixed during operation with high error tolerance.The proposed topology also enables bidirectional CC and CV charging without the need for communication between the primary and secondary sides.To verify the effectiveness of the topology,a 6 kW prototype is built in the laboratory with a maximum efficiency of 94%.
Aiming at the problems of inaccurate hyper-parameter optimization and low prediction accuracy of Informer in wind power prediction,an ultra-short-term wind power prediction model based on MGWO-Informer is proposed.Firstly,in order to solve the shortcomings of the traditional Grey Wolf evolutionary algorithm,which has the disadvantages of poor solution accuracy and easy to fall into the local optimum in some of the optimization searching processes,a Modified Grey Wolf Optimizer(MGWO)algorithm is proposed to enhance the global searching,which proposes 2 kinds of improvement strategies:the new convergence factor and the staged position updating.Second,the Informer model parameters are optimized using the improved Gray Wolf algorithm to improve the accuracy of model hyperparameter optimization.Finally,taking the measured data of a wind farm in Northwest China as an example,the prediction results are compared with gate recurrent unit(GRU),long short term memory(LSTM)and transformer.The results indicate that the improved Informer model has high prediction accuracy and operational efficiency,with a decrease of 26.74%in mean absolute error and 19.74%in root mean square error,and an increase of 1.41%in fitting coefficient.
The configuration and operational validation of wind solar hydrogen storage integrated systems are critical for achieving efficient energy utilization, ensuring economic viability, and maintaining system stability. This study proposed an off-grid multi-energy system capacity configuration and control optimization framework based on the Grey Wolf Optimization (GWO) algorithm, which enhances system revenue through an improved capacity allocation model. The results demonstrate the following: Firstly, the proposed system achieves a significant financial improvement, with an annual revenue increase of 33.79 % compared to a hydrogen production scheme relying solely on wind power without energy storage. Secondly, the adoption of a wind solar complementary hydrogen production approach increases the annual revenue of the system by 33.33 % compared to the single wind power hydrogen production scheme. Furthermore, a system operation control strategy based on the State of Charge (SOC) of lithium batteries is proposed. Using operational data from the Zhangjiakou Chongli wind solar complementary coupling hydrogen production project, the effectiveness of the proposed control strategy is validated, demonstrating its ability to ensure stable system operation. Results show that in wind and solar power excess scenarios, the SOC rises from 45.8 % to 49.8 %, and declines to 47.2 % when there's a power deficit, indicating its potential for peak shaving and valley filling, thereby mitigating fluctuations in wind and solar power output.
To achieve a more economical and stable operation, the power output operation strategy of the electrochemical energy storage plant is studied because of the characteristics of the fluctuation of the operation efficiency in the long time scale. Second, an optimized operation strategy for an electrochemical energy storage station is presented based on the proposed efficiency transformation model. The energy storage station's economic efficiency and load-smoothing effect are studied. Finally, the proposed optimization strategy and operation indexes are verified by calculation and simulation comparison with an example of an energy storage station in Guangdong. The results show that the proposed operation strategy of electrochemical energy storage station has an excellent technical economy.
With the deepening of the energy revolution, the power terminal will also usher in significant transformations, DC home appliances in building “photovoltaics-energy storage-DC-flexibility (PEDF)” system have typical features of storage-use integration, DC power supply and flexible electricity consumption. This paper focuses on the technologies and standards of DC household appliances, compares the relevant standards at home and abroad. Thus, a standard system for DC household appliances was built based on the above review, the key technologies that hinder the industrialization of DC household appliances were analyzed, and the key research contents of technical standards were proposed. Conclusively, the outlook of the future research was proposed to provide reference for further in-depth research and exploration of “PEDF” DC household appliances.
SummaryThe prestressed anchor bolt system is a reasonable connection mode between the upper steel tower and the bottom concrete foundation for multi‐megawatt wind turbines. This prestressed anchor bolt connection with forged flanges has a similar form to the prestressed high‐strength bolt connection with forged flanges between steel tubes for the tower. However, their mechanical performances have a great difference because of the influence of the stiffness of the anchorage zone in the concrete foundation. Based on the Petersen's method, the engineering calculation method of the prestressed anchor bolt system for wind turbine foundation is derived. The tensile force of the anchor bolt, the anchorage stiffness and clamping force of the base are all deduced according to the theories of mechanics of materials. The numerical models of the segment foundation with the unfavorable anchor bolt and the overall foundation with all anchor bolts are developed for researching the influence of the spatial effect of adjacent segments on the restraint stiffness of the concrete foundation. The numerical analyses of four engineering cases designed by engineering calculation method are carried out for verifying the effectiveness of engineering calculation method. The analysis results show the spatial effect of adjacent segments can be neglected and the Petersen's method can be directly applied for the design of the prestressed anchor bolt system for wind turbine foundation in engineering practice. The engineering calculation method meets the accuracy requirements in engineering practice and can be used to design the prestressed anchor bolt system of wind turbine foundation.
Aiming at the problem of controlling the excess ratio of oxygen in the air supply subsystem of proton exchange membrane fuel cells.Firstly,a control-oriented fourth-order nonlinear dynamic model of the proton exchange membrane fuel cells system is established,and a fitting curve equation between the stack load current and the optimal oxygen excess ratio is constructed.Subsequently,a sliding mode controller using a new compound reaching law is designed,and the parameters in the sliding mode control are optimized and tuned using the sand cat swarm optimization algorithm.Finally,the improved sliding mode controller is simulated and verified,and compared with PID and other three sliding mode controllers.The simulation results show that when the load current of the stack changes,the improved sliding mode controller can adjust the driving voltage of the air compressor according to the cathode flow deviation parameter.At this time,the real-time oxygen excess ratio of the system will quickly approach the optimal oxygen excess ratio.The deviation between the two can be controlled within 0.1%,and the required average adjustment time and error performance indicators are better than those of the comparison group.
This paper proposed a model predictive control(MPC)secondary frequency control method considering wind and solar power generation stochastics.The extended state-space matrix including unknown stochastic power disturbance is established,and a Kalman filter is used to observe the unknown disturbance.The maximum available power of wind and solar DGs is estimated for establishing real-time variable constraints that prevent DGs output power from exceeding the limits.Through setting proper weight coefficients,wind and photovoltaic DGs are given priority to participate in secondary frequency control.The distributed restorative power of each DG is obtained by solving the quadratic programming(QP)optimal problem with variable constraints.Finally,a microgrid simulation model including multiple PV and wind DGs is built and performed in various scenarios compared to the traditional secondary frequency control method.The simulation results validated that the proposed method can enhance the frequency recovery speed and reduce the frequency deviation,especially in severe photovoltaic and wind fluctuations scenarios.
The energy storage virtual synchronous generator (VSG), which can provide inertial support for the grid, has attracted wide attention. However, there is a problem that the dynamic characteristics and the characteristics of primary frequency modulation of grid-connected active power cannot be satisfied at the same time. Therefore, the dynamic oscillations suppression strategy of energy storage VSG grid-connected active power based on frequency feedforward compensation is proposed in this paper. This strategy uses the rated frequency to feed forward to the grid-connected active power closed-loop modulation loop through the compensation link and increases the transient damping of the system without affecting the characteristics of primary frequency modulation of the energy storage VSG, to effectively suppress the dynamic oscillations of its grid-connected active power. Finally, the effectiveness and superiority of the proposed strategy are verified by the Matlab/Simulink simulation model of the energy storage VSG grid-connected system.
As one of the main types of wind power generation, doubly-fed induction generator (DFIG) has been widely used with the rapid development of new energy. In this paper, the mechanism of insufficient stability of DFIG control system under weak grid is investigated. By constructing small signal model of DFIG in weak grid, the influence loop of phase-locked loop (PLL) on current closed-loop control is analyzed. Based on the small signal model, a compound decoupling control strategy considering the effect of PLL is proposed, which effectively improves the stability margin of DFIG in weak grid. The effectiveness of the proposed strategy is verified by experiments.
When the PV power supply participates in reactive power regulation of distribution network, its output reactive power will affect the reliability of IGBT in the PV inverter. Aiming at this problem, this paper first qualitatively analyzed the influence of photovoltaic power supply participating in reactive power regulation of distribution network on the reliability of photovoltaic power supply. Then, a quantitative evaluation method of IGBT reliability based on data-driven was proposed. This method uses LightGBM machine learning model to replace the traditional thermoelectric coupling model, which effectively improves the calculation efficiency of IGBT junction temperature and reduces the dependence of IGBT reliability evaluation results on IGBT model parameters. Through this method, the reliability of core power electronic devices in photovoltaic inverters is quantitatively evaluated according to active power, reactive power, solar irradiance and ambient temperature. Finally, based on the IEEE 33 node distribution system, the reliability of IGBT in PV inverters participating in reactive power regulation of the distribution network was evaluated.
To address the limitations of single renewable energy applications in cold regions, a novel photovoltaic thermal curtain wall assisted dual-source (air and ground source) heat pump system is proposed. The performance of the system was investigated using numerical simulations and experimental tests. Furthermore, a multi-objective optimization based on the non-dominated sorting genetic algorithm was employed to achieve the optimal design of the hybrid renewable system for a nearly zero-energy building in Shenyang, China. The energy consumption, life cycle cost, and photovoltaic power generation of the system were considered as objective functions. A sensitivity analysis was performed to study the effect of the design variables on the objective functions. The results showed that the seasonal coefficient of performance (COP) of the unit and the proposed system were 3.30 and 2.80, which are increases of 6 % and 5 %, respectively, compared with the dual-source heat pump system. According to the Pareto front obtained, life cycle cost is negatively correlated with energy consumption and positively correlated with photovoltaic power generation. When the area of the photovoltaic thermal curtain wall increased from 0 to 15 m2, the energy consumption and life cycle cost were reduced by 253 kWh and 1118 CNY, respectively.
An optimization method based on economic stochastic model prediction control is proposed to address the impact of uncertainty on both sides of the source and load of the wind-solar-hydrogen coupling system.Firstly,according to the characteristics of the equipment in the wind-solar-hydrogen coupling system,a state-space model considering the start-stop state of the equipment is established.Then,the scenario generation technology is used to process wind and solar output,as well as electrical load prediction data to generate a scenario set that describes the system uncertainty.Finally,based on the generated scenarios,a mixed-integer linear programming problem is formulated under the designed economic stochastic model predictive control framework,and then the system is economically optimized and controlled.A scenario generation mechanism based on nonparametric prediction is proposed,which provides a scenario set that accurately describes the system's uncertainty for the economic stochastic model prediction control method.Simulation results demonstrate the effectiveness of the proposed method in addressing uncertainty in the wind-solar-hydrogen coupling system,achieving a 5.89%reduction in operating costs compared to conventional stochastic model predictive control method,and a 13.25%reduction compared to conventional model predictive control method.
The thermoelectric generation cycle system is widely used, and different cycle processes have their own advantages. This study utilized simulation method, through the modeling of Rankine cycle, Kalina cycle and Uehara cycle, the differences in thermal efficiency ( η ) and leveled cost of energy (LCOE) between different cycle processes were analyzed under different heat source temperature conditions. Meanwhile, the effects of evaporation temperature and turbine inlet pressure on thermal-economic performance in different cycle systems were also explored. The results show that Kalina cycle has high thermal efficiency in each temperature condition of heat source, but its economic performance is poor. In low temperature heat source, the LCOE of Rankine cycle with pure ammonia work flow is the lowest under the same conditions. Rankine cycle should be set in saturated steam state, and designers should as far as possible to increase the turbine inlet pressure and reduce the evaporation superheat. Instead, in high temperature heat source, the LCOE of Uehara cycle is the lowest. Moreover, there is a deviation of the turbine inlet pressure corresponding to the minimum LCOE and the maximum thermal efficiency of Kalina cycle and Uehara cycle. Designed according to the minimum LCOE principle at this point, more power generation and less equipment cost can be obtained. Therefore, thermal-economic performance of different cycles under different heat source temperature conditions should be considered in cycle flow design.
In view of the growing depletion of traditional fossil fuels and their adverse impact on natural environment, wind energy has gained increasing popularity across the globe. Characterized by wide distribution, low cost, and well-rounded technology, it has achieved fast-growing installed capacity in recent years. However, wind power is volatile and random in nature and the power ramping events caused by extreme weather always threaten the safe, stable, and economic operation of the power grid. To address the problems of insufficient sample data and low prediction accuracy in existing ramping prediction methods, a new way of wind power prediction considering ramping events based on Generative Adversarial Network (GAN) is proposed. First of all, the ramping events get identified and separated from the database of historical wind power, and the feature set of historical ramping events is then extracted according to the waveform and meteorological factors. Taking the feature set which integrates similar feature with historical one as the input of GAN, the simulated ramping data are continuously produced through the adversarial training of the generator and discriminator, thus enriching the ramping database. After that, the expanded ramping database can be applied to predict the ramping power through the LSTM model. An experiment based on the wind power dataset in a certain area of northwest China further verifies the effectiveness and superiority of this method compared with traditional ones.
In HSCW (Hot Summer and Cold Winter) climate zone of China, the building heat load is usually less than the cooling load which caused the problem of thermal accumulation of underground soil to damaged the COP of the heat pump system. PV/T-GCHPs (Photovoltaic/photothermal - Ground-coupled heat pump system) is a system that realizes the complementary utilization of geothermal energy and solar energy to solve the problem. The experimental platform of the system was designed and built, and the effect of the temperature of the outlet water from the ground buried pipes on the photoelectric efficiency of the PV panel was analyzed through experiments and simulations under the heating conditions of the PV/T-GCHPs system, and the heating performance coefficients of PV/T-GCHPs and GCHPs were compared. The results show that the PV plate temperature reaches the lowest when the heat pump load is 75% and the circulating water flow is 0.28 kg/s, when the outlet temperature of buried pipe is 8℃. The maximum photoelectric efficiency increased by 6.4% under above conditions, the average heating performance coefficient of PV/T-GCHPs is increased by 2.2% compared with GCHPs. The daily average comprehensive efficiency is 63.32%, the maximum comprehensive efficiency of the system is 74.67%. The maximum heat collection efficiency of PV/T collector is 48.33%. This paper hopes to provide a theoretical basis for the promotion of PV/T-GCHPs in HSCW climate zone of China.
