Current Issue : October - December Volume : 2017 Issue Number : 4 Articles : 5 Articles
Recently, the use of DC microgrid distribution system has become more attractive than\ntraditional AC systems due to their energy efficiency and ability to easily integrate with renewable\nenergy sources and batteries. This paper proposes a 500 V DC microgrid which consists of a 20 kWp\nphotovoltaic panel, batteries, and DC loads. A hierarchical control strategy to ensure balance power\nof the DC microgrid and the maintenance of common DC bus voltage is presented. The capability\nof exchanging power energy of the microgrid with the power system of neighborhood buildings\nis also considered. Typical operation modes are simulated in the Matlab/simulink environment to\nconfirm the good performance of the controllers and the efficiency of appropriately controlling the\nchargeââ?¬â??discharge of the battery system. This research is expected to bring benefits to the design\nand operation of the system, such as reducing the capacity of batteries, increasing the self-supply of\nbuildings, and decreasing the electricity demand from the AC grid....
On the basis of fluid approximation, an improved version of the model for the description of dc glow discharge plasma in the axial\nmagnetic field was successfully developed.The model has yielded a set of analytic formulas for the physical quantities concerned\nfrom the electron and ion fluids equations and Poisson equation.The calculated results satisfy the practical boundary conditions.\nResults obtained from the model reveal that although the differential equations under the condition of axial magnetic field are\nconsistent with the differential equations without considering the magnetic field, the solution of the equations is not completely\nconsistent. The results show that the stronger the magnetic field, the greater the plasma density....
This paper analyses the transient characteristics and breaking performance of direct-current\n(DC) forced-interruption vacuum interrupters in 270 V power-supply systems. Three stages\nare identified in forced interruption: the DC-arcing stage, current-commutation stage, and\nvoltage-recovery stage. During the current-commutation stage, the reverse peak-current coefficient\nk, which is a key design factor, is used to calculate the rate of current at zero-crossing (di/dt).\nMATLAB/Simulink simulation models are established to obtain the transient characteristics\ninfluenced by the forced-commutation branch parameters and the coefficient k. To study the breaking\nperformance of spiral-type contacts, experiments are conducted for different contact materials and\narcing times for currents less than 3.5 kA. During the DC-arcing stage, a locally intensive burning arc\nis observed in the CuW80 contact; however, it is not observed in the CuCr50 contact. On examining\nthe re-ignition interruption results of the CuW80 contact, the intensive burning arc is found to be\npositioned within a possible re-ignition region. When the arcing time is longer than 1 ms, the intensive\nburning arc occurs and affects the breaking performance of the spiral-type contacts. If the DC-arcing\nstage is prolonged, the total arcing energy increases, which leads to a lower breaking capacity....
Flux-switching permanent magnet (FSPM) motors have gained increasing attention in\nelectric vehicles (EVs) applications due to the advantages of high power density and high efficiency.\nHowever, the heat sources of both permanent magnet (PM) and armature winding are located on the\nlimited stator space in the FSPM motors, which may result in the PM overheating and irreversible\ndemagnetization caused by temperature rise, and it is often ignored in the conventional thermal\nanalysis. In this paper, a new electrical-thermal two-way coupling design method is proposed to\nanalyze the electromagnetic performances, where the change of PM material characteristics under\ndifferent temperatures is taken into consideration. First, the motor topology and design equations\nare introduced. Second, the demagnetization curves of PM materials under different temperatures\nare modeled due to PM materials are sensitive to the temperature. Based on the electrical-thermal\ntwo-way coupling method, the motor performances are evaluated in detail, such as the load PM\nflux linkage and output torque. The motor is then optimized, and the electromagnetic performances\nbetween initial and improved motors are compared. Finally, a prototype motor is manufactured,\nand the results are validated by experimental measurements....
In this paper, we propose a novel variable pole pitch (VPP) electromagnetic (EM) propulsion\ntechnique using a series of ladder-slot-secondary double-sided linear induction motors (LS-secondary\nDLIMs). An equivalent circuit is developed for the LS-secondary DLIM, which considers the\ndistribution of the eddy current in the ladders and the end effect. This equivalent circuit forms\nthe basis for the subsequent design, numerical analysis, and optimization. The primary purpose\nof the VPP EM propulsion system is to address several obstacles encountered in high-speed\nlarge-thrust applications of LIMs, such as power factor improvement, optimization considering\nsupply frequency constraint and operating kinetics, etc. The equivalent circuit of the LS-secondary\nDLIM, i.e., the theoretical foundation of the VPP EM propulsion, has been validated via simulation\nand experimentation on a small-scale platform, which proves that the numerical analysis of the VPP\nEM propulsion is effective....
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