Current Issue : April - June Volume : 2017 Issue Number : 2 Articles : 6 Articles
In this paper, a novel modulation function-based method including analyses of the\nmodulation index and phase is proposed for operation of modular multilevel converters (MMCs) in\nhigh voltage direct current (HVDC) transmission systems. The proposed modulation function-based\ncontrol technique is developed based on thorough and precise analyses of all MMC voltages and\ncurrents in the a-b-c reference frame in which the alternating current (AC)-side voltage is the first\ntarget to be obtained. Using the AC-side voltage, the combination of the MMC upper and lower\narm voltages is achieved as the main structure of the proposed modulation function. The main\ncontribution of this paper is to obtain two very simple new modulation functions to control MMC\nperformance in different operating conditions. The features of the modulation function-based control\ntechnique are as follows: (1) this control technique is very simple and can be easily achieved in a-b-c\nreference frame without the need of using Park transformation; and (2) in addition, the inherent\nproperties of the MMC model are considered in the proposed control technique. Considering these\nproperties leads to constructing a control technique that is robust against MMC parameters changes\nand also is a very good tracking method for the components of MMC input currents. These features\nlead to improving the operation of MMC significantly, which can act as a rectifier in the HVDC\nstructure. The simulation studies are conducted through MATLAB/SIMULINK software, and the\nresults obtained verify the effectiveness of the proposed modulation function-based control technique...
This paper presents a study of fractional order quadrature oscillators based on current-\ncontrolled current follower transconductance amplifiers (CCCFTA). The design\nrealisation and performance of the fractional order quadrature oscillators have been\npresented. The quadrature oscillators are constructed using three fractional capacitors\nof orders �± = 0.5. The fractional capacitor is not available on the market or in the\nPSPICE program. Fortunately, the fractional capacitor can be realised by using the\napproximate method for the RC ladder network approximation. The oscillation frequency\nand oscillation condition can be electronically/orthogonally controlled via\ninput bias currents. Due to high-output impedances, the proposed circuit enables\neasy cascading in current-mode (CM). The PSPICE simulation results are depicted,\nand the given results agree well with the anticipated theoretical outcomes....
In this article, a compact narrow-bandpass filter with high selectivity and improved rejection level is presented. For miniaturization,\na pair of double negative (DNG) cells consisting of quasi-planar chiral resonators are cascaded and electrically loaded to a microstrip\ntransmission line; short ended stubs are introduced to expand upper rejection band. The structure is analyzed using equivalent\ncircuit models and simulated based on EM simulation software. For validation, the proposed filter is fabricated and measured.The\nmeasured results are in good agreement with the simulated ones. By comparing to other filters in the references, it is shown that the\nproposed filter has the advantage of skirt selectivity and compact size, so it can be integrated more conveniently in modern wireless\ncommunication systems and microwave planar circuits....
The dielectric and magnetic properties of electric double layer (EDL) capacitor structures\nwith a perpendicularly magnetized Pt/Co/Pt electrode and an insulating cap\nlayer (MgO) are investigated. An electric field is applied through a mixed ionic liquid/\nMgO barrier to the surface of the top Pt layer, at which the magnetic moment\nis induced by the ferromagnetic proximity effect. The basic dielectric properties of\nthe EDL capacitor are studied by varying the thickness of the MgO cap layer. The\nresults indicate that the capacitance, i.e., the accumulated charge density at the Pt\nsurface, is reduced with increasing the MgO thickness. From the MgO thickness\ndependence of the capacitance value, the effective dielectric constant of the ionic\nliquid is evaluated. Almost no electric field effect on the magnetic moment, the coercivity,\nor the Curie temperature is confirmed in the top Pt layer with the thickness of\n1.3 nm, regardless of the presence or absence of the MgO cap layer, whereas the a\nclear change in the magnetic moment is observed when the top Pt layer is replaced\nby a Pd layer of 1.7 nm....
The shift register is a type of sequential logic circuit which is mostly used for storing digital\ndata or the transferring of data in the form of binary numbers in radio frequency identification\n(RFID) applications to improve the security of the system. A power-efficient shift register utilizing\na new flip-flop with an implicit pulse-triggered structure is presented in this article. The proposed\nflip-flop has features of high performance and low power. It is composed of a sampling circuit\nimplemented by five transistors, a C-element for rise and fall paths, and a keeper stage. The speed\nis enhanced by executing four clocked transistors together with a transition condition technique.\nThe simulation result confirms that the proposed topology consumes the lowest amounts of power\nof 30.1997 and 22.7071 nW for parallel in ââ?¬â??parallel out (PIPO) and serial in ââ?¬â??serial out (SISO) shift\nregister respectively covering 22 Ã?¼m2 chip area. The overall design consist of only 16 transistors and\nis simulated in 130 nm complementary-metal-oxide-semiconductor (CMOS) technology with a 1.2 V\npower supply....
Although various silicon carbide (SiC) power devices with very high blocking voltages\nover 10 kV have been demonstrated, basic issues associated with the device operation are still not\nwell understood. In this paper, the promise and limitations of high-voltage SiC bipolar devices are\npresented, taking account of the injection-level dependence of carrier lifetimes. It is shown that the\nmajor limitation of SiC bipolar devices originates from band-to-band recombination, which becomes\nsignificant at a high-injection level. A trial of unipolar/bipolar hybrid operation to reduce power loss\nis introduced, and an 11 kV SiC hybrid (merged pin-Schottky) diodes is experimentally demonstrated.\nThe fabricated diodes with an epitaxial anode exhibit much better forward characteristics than diodes\nwith an implanted anode. The temperature dependence of forward characteristics is discussed....
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