Low Voltage Direct Current Supply and Utilization System:Definition,Key Technologies and Development

With rapid increase of distributed solar power generation and direct current(DC)based loads such as data centers,electric vehicles(EVs),and DC household appliances,the development trend of the power system is changed from conventional alternate current(AC)to DC.Traditional AC power systems can scarcely meet the development demand of new DC trends,especially since both the generation side and load side are comprised of DC-based electronic power components.With this background,low voltage direct current supply and utilization system(LVDCSUS)has attracted more and more attention for its great advantages over an AC grid to overcome challenges in operation,reliability,and energy loss in renewable energy connection,DC load power utilization and a number of other aspects.However,the definition of the LVDCSUS is still not clear even though many demonstration projects have been put into planning and operation.In order to provide a clear description of LVDCSUS,first,the characteristics of LVDCSUS are illustrated in this paper to show the advance of the LVDCSUS.Second,the potential application scenarios of LVDCSUS are presented in this paper.Third,application of LVDCSUS technologies and some demonstration projects in China are introduced.Besides the development of the LVDCSUS,key technologies,including but not limited to planning and design,voltage levels,control strategies,and key equipment of LVDCSUS,are discussed in this paper.Finally,future application areas and the research orientations of LVDCSUS are analyzed.

Research on Sports Public Service Supply in the Chengdu-Chongqing Twin-City Economic Circle under the Background of Regional Economic Development

Using literature,questionnaires,interviews,and mathematical statistics to investigate the current situation of sports public services in the Chengdu-Chongqing Twin-city Economic Circle.The results show that there are some problems in Chengdu-Chongqing sports public services,such as big difference in the development level of supply between urban and rural areas,low supply level,low efficiency,supply mechanism defect,lack of social sports instructors,an outstanding contradiction between the quality of sports public service and residents’demand.To address the problems,government departments should accelerate the transformation of government functions,improve the relevant regulations and systems,increase the investment in sports public services,improve the quality of supply,cultivate the backbone team,integrate resources,and combine the national characteristics with regional characteristics,take into account the personalized needs of the residents,combine the sports public services with intelligence,and build the service system of“Internet+Fitness.”

Mathematical Modeling of ESR Process for Hollow Ingot with Current Supplying Mould

With ificreasing demand for large cylindrical forgings, a new technology--electroslag remelting （ESR） for direct manufacture of hollow ingots rather than solid ingots has been developed. The main features of the process include a T-shaped current supplying mould （CSM）, double power supply, an ingot withdrawing system, a metal level automatic control system based on a level sensor using the electromagnetic eddy current method, and the exchange of a consumable multi-electrode. ANSYS software was used to calculate the fluid flow and heat transfer in the slag bath 1 and metal pool of this ESR hollow ingot process with its T-shaped CSM. The mathematmal model was Verified by measuring the geometry of the liquid metal pool as observed in the macrostructure of 4650 mm （external diameter）/ 4450 mm （internal diameter） hollow ingots by sulphur print method： the. observed shape and depth of the s!ag bath were consistent with the simulated results. Simulation of the ESR process can improve understanding of the process and allow better operating parameters to be selected.

Application of a Current and Voltage Mixed Control Mode for the New Fast Control Power Supply at EAST

A feedback control system is needed to restrain plasma vertical displacement in EAST （Experimental Advanced Superconducting Toknmak）. A fast control power supply excites active feedback coils, which produces a magnetic field to control the plasma＇s displacement. With the development of EAST, new demands on the new fast control power supply have led to an enhanced ability of fast response and output current, as well as a new control mode. The structure of cascaded and paralleled H-bridges can meet the demand of extended capacity, and digital control can reMize current and voltage mixed control mode. The validity of the proposed scheme is confirmed by experiments.

Oscillation Test Strategy for Analog Filters by Monitoring Output Voltage and Supply Current

A test strategy for analog filters was proposed. The output voltage and supply current of the circuit were monitored when using the oscillation test technique. The frequency, average value, maximum value and amplitude of both output voltage and supply current were taken as test parameters. Tolerance bands of test parameters were analyzed. Fault detectabilities of test parameters were compared and combined, and optimal parameter sets were derived. Experimental results show that both the output voltage and supply current give significant contribution to fault detection. Considering catastrophic, single and double parametric faults, the fault coverage in testing the benchmark circuit can be raised from 90.6% for traditional voltageonly oscillation test strategy to 97.2% by monitoring both output voltage and current parameters.