Fengyun-4 Geostationary Satellite-Based Solar Energy Nowcasting System and Its Application in North China

Surface solar irradiance(SSI)nowcasting(0-3 h)is an effective way to overcome the intermittency of solar energy and to ensure the safe operation of grid-connected solar power plants.In this study,an SSI estimate and nowcasting system was established using the near-infrared channel of Fengyun-4A(FY-4A)geostationary satellite.The system is composed of two key components:The first is a hybrid SSI estimation method combining a physical clear-sky model and an empirical cloudy-sky model.The second component is the SSI nowcasting model,the core of which is the derivation of the cloud motion vector(CMV)using the block-matching method.The goal of simultaneous estimation and nowcasting of global horizontal irradiance(GHI)and direct normal irradiance(DNI)is fulfilled.The system was evaluated under different sky conditions using SSI measurements at Xianghe,a radiation station in the North China Plain.The results show that the accuracy of GHI estimation is higher than that of DNI estimation,with a normalized root-mean-square error(nRMSE)of 22.4%relative to 45.4%.The nRMSE of forecasting GHI and DNI at 30-180 min ahead varied within 25.1%-30.8%and 48.1%-53.4%,respectively.The discrepancy of SSI estimation depends on cloud occurrence frequency and shows a seasonal pattern,being lower in spring-summer and higher in autumn-winter.The FY-4A has great potential in supporting SSI nowcasting,which promotes the development of photovoltaic energy and the reduction of carbon emissions in China.The system can be improved further if calibration of the empirical method is improved.

Experimental Study on Branch and Diffuse Type of Streamers in Leader Restrike of Long Air Gap Discharge

One of the main problems in the Ultra High Voltage(UHV) transmission project is to choose the external insulation distance,which requires a deep understanding of the long air gap discharge mechanism.The leader-streamer propagation is one of most important stages in long air gap discharge.In the conductor-tower lattice configuration,we have measured the voltage,the current on the high voltage side and the electric field in the gap.While the streamer in the leader-streamer system presented a conical or hyperboloid diffuse shape,the clear branch structure streamer in front of the leader was firstly observed by a high speed camera in the experiment.Besides,it is found that the leader velocity,width and injected charge for the branch type streamer are greater than those of a diffuse type.We propose that the phenomenon results from the high humidity,which was 15.5-16.5 g/m^3 in our experiment.

外包工程高风险作业“六步法”安全管理标准实践与探索（英文）

In accordance with the "six-step method",the unremitting improvement of all steps in safety management may result in effective reduction of safety risk in outsourcing operations to ensure the whole operation is carried out in a safe and well-organized way.

A DC Grid Benchmark Model for Studies of Interconnection of Power Systems

Reducing carbon emissions in the power sector is critical for transitioning to a sustainable and low-carbon future.Estimating carbon efficiency of demand side response(DSR)in the power system is an important step towards realizing potential environmental benefits.Marginal emission factor(MEF)is an effective tool for estimating incremental changes in carbon emissions as a result of a change in demand.However,estimation methods currently used for evaluating MEF can be improved upon,specifically,by factoring in the ramp-rate constraint of generators in the fuel cost based merit order dispatch.In this paper is described a new method for MEF assessment under ramp-rate constraints;the method is then compared with two conventional estimations in a British power system.Three fuel price scenarios are used to conduct a sensitivity analysis of MEFs to fuel prices.Conclusions are drawn that can pave the way for future improvements in estimating MEF in power systems.

Online Decision-Making and Control of Power System Stability Based on Super-Real-Time Simulation

During power grid cascading failure,the operating point changes frequently,resulting in a mismatch or inaccuracy of online pre-decision making emergency control strategy.To solve this problem,an online power system stability decisionmaking and control method based on super-real-time simulation is presented in this paper.A decision-making and control system is developed in which the three main operation modes,offline pre-decision-making,online pre-decision-making,and real-time control,are all coordinated.To verify the method,ADPSS(advanced digital power system simulator)is used to simulate a digital power grid with about 20,000 buses.The closed-loop operation of the digital power grid and the online decisionmaking and control system are implemented.Test results show that when online pre-decision making control strategies are mismatched,aided real-time control works well and can prevent power grid stability loss.

Stability and Accuracy Considerations in the Design and Implementation of Wind Turbine Power Hardware in the Loop Platform

There is increasing interest in the evaluation of wind turbine control capabilities for providing grid support.Power hardware in the loop(PHIL)simulation is an advanced method that can be used for studying the interaction of hardware with the power network,as the scaled-down actual wind turbine is connected with a simulated system through an amplifier.Special consideration must be made in the design of the PHIL platform to ensure that the system is stable and yields accurate results.This paper presents a method for stabilizing the PHIL interface and improving the accuracy of PHIL simulation in a real-time application.The method factors in both the power and voltage scaling level,and a phase compensation scheme.It uses the reactive power control capability of the wind turbine inverter to eliminate the phase shift imposed by the feedback current filter.This is accomplished with no negative impact on the dynamic behavior of the wind turbine.The PHIL simulation results demonstrate the effectiveness of the proposed stability analysis method and phase compensation scheme.The strength of the platform is demonstrated by extending the simulation method to wind turbine control validation.