Frequency: Quarterly E- ISSN: New Release P- ISSN: New Release
Quarterly published â??Inventi Rapid/Impact: Electrical Engineeringâ?? publishes high quality unpublished as well as high impact pre-published research and reviews related to all the areas of electrical engineering including power engineering, electrical machines, instrumentation and control, electric power generation, transmission and distribution etc.
This paper takes a typical 220 kV three-phase three-limb oil-immersed transformer as\nan example, this paper building transient field-circuit coupled model and 3D coupled magneto\n-fluid-thermal model. Considering a nonlinear Bââ?¬â??H curve, the magneto model uses the field-circuit\ncoupled finite element method (FEM) to calculate the magnetic flux distribution of the core and the\ncurrent distribution of the windings when the transformer is at a rated current and under direct\ncurrent (DC) bias. Taking the electric power losses of the core and windings as a heat source,\nthe temperature inside the transformer and the velocity of the transformer oil are analyzed by\nthe finite volume method (FVM) in a fluid-thermal field. In order to improve the accuracy of the\ncalculation results, the influence of temperature on the electrical resistivity of the windings and\nthe physical parameter of the transformer oil are taken into account in the paper. Meanwhile, the\nconvective heat transfer coefficient of the FVM model boundary is determined by its temperature.\nBy iterative computations, the model is updated according to the thermal field calculation result\nuntil the maximum difference in hot spot temperature between the two adjacent steps is less than\n0.01 K. The result calculated by the coupling method agrees well with the empirical equation result\naccording to IEC 60076-7....
Hybrid excitation synchronous motor (HESM) offers the advantages of a convenient flux regulation and a wide range of available\nspeeds. As such, it may be conveniently employed in the fields of electric vehicle and aerospace. In this paper, based on a suitable\ncontrol strategy for vector and speed partition, we put forward a speed control method for HESM which shows optimal efficiency.\nOn the one hand, our method aims at minimizing the copper loss by an optimal configuration of the q-axis current, the d-axis\ncurrent, and the excitation current under the constraint voltage at the armature end. On the other hand, we conduct a comprehensive\nanalysis of the effects of the flux-weakening speed coefficient on the operating performance of the motors and suggest a\nself-adaptive control method to regulate that coefficient and further improve the overall performance of the motors, including\ntheir speed-range regulation, their efficiency, and their dynamical properties. The proposed flux-weakening control method has\nbeen assessed by simulations and HESM-driven experiments. Results have confirmed the feasibility and optimality of our method....
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....
A high-input voltage 2-phase series-capacitor (2-pscB) DC-DC buck converter is theoretically analyzed, designed, and implemented.\nA new design approach for an automatic current sharing scheme was presented for a 2-phase series-capacitor synchronous\nbuck converter. The series-capacitor voltage is used to achieve current sharing between phases without a current sensing\ncircuit or external control loop as each phase inductor charges and discharges the series capacitor to maintain its average capacitor\nvoltage constant. A novel isolated gate driver circuit to accommodate an energy storage capacitor is proposed to deliver isolated\ngate voltages to the switching transistors. An I2 control scheme that uses only one feedback path control for the four gate drivers is\nproposed to enable higher voltage conversion. An experimental 110-12V 6A load prototype converter was designed, and its\ncurrent sharing characteristics were experimentally verified....
In this paper, an U-shape flux barrier rotor concept for a hybrid excited synchronous\nmachine with flux magnetic bridges fixed on the rotor is presented. Using 3D finite element\nanalysis, the influence of axial flux bridges on the field-weakening and -strengthening characteristics,\nelectromagnetic torque, no-load magnetic flux linkage, rotor iron losses and back electromotive force\nis shown. Three different rotor designs are analyzed. Furthermore, the field control characteristics\ndepending on additional DC control coil currents are shown....
This paper presents a new 12-bit digital to analog converter (DAC) circuit based on a low-offset bandgap reference (BGR) circuit\nwith two cascade transistor structure and two self-contained feedback low-offset operational amplifiers to reduce the effects of\noffset operational amplifier voltage effect on the reference voltage, PMOS current-mirror mismatch, and its channel modulation. A\nStart-Up circuit with self-bias current architecture andmultipoint voltagemonitoring is employed to keep the BGR circuit working\nproperly. Finally, a dual-resistor ladderDAC-Core circuit is used to generate an accuracyDACoutput signal to the buffer operational\namplifier.The proposed circuit was fabricated in CSMC 0.5 ...
Owing to the installation of autotransformers at regular intervals along the line, distance\nprotection relays cannot be used with the aim of locating ground faults in 2 Ã?â?? 25 kV railway power\nsupply systems. The reason is that the ratio between impedance and distance to the fault point is not\nlinear in these electrification systems, unlike in 1 Ã?â?? 25 kV power systems. Therefore, the location of\nground faults represents a complicated task in 2 Ã?â?? 25 kV railway power supply systems. Various\nmethods have been used to localize the ground fault position in 2 Ã?â?? 25 kV systems. The method\ndescribed here allows the location of a ground fault to be economically found in an accurate way\nin real time, using the modules of the circulating currents in different autotransformers when the\nground fault occurs. This method first needs to know the subsection and the conductor (catenary or\nfeeder) with the defect, then localizes the ground faultââ?¬â?¢s position....
An active voltage doubler utilizing a single supply op-amp for energy harvesting system is presented.The proposed doubler is used\nfor rectification process to achieve both acceptably high power conversion efficiency (PCE) and large rectified DC voltage. The\nincorporated op-amp is self-biased, meaning no external supply is needed but rather it uses part of the harvested energy for its\nbiasing. The proposed active doubler achieves maximum power conversion efficiency (PCE) of 61.7% for a 200Hz sinusoidal input\nof 0.8V for a 20K�© load resistor. This efficiency is 2 times more when compared with the passive voltage doubler.The rectified DC\nvoltage is almost 2 times more than conventional passive doubler.The relation between PCE and the load resistor is also presented.\nThe proposed active voltage doubler is designed and simulated in LF 0.15 ...
The mixed power flow analysis method decreases the computational complexity and\nachieves a high level of simulation accuracy. The mixed approach combines the ac with the dc\npower flow models, depending on the area of interest. The accurate ac model is used in the study\narea of interest to obtain high simulation accuracy, while the approximate dc model is used in the\nremainder of the system to reduce the required computations. In the original mixed approach,\nthe errors originating from the use of the dc model may propagate to the area of interest where\naccurate simulation outcomes are required; thus, the simulation accuracy might not be satisfactory.\nThis paper presents a new method of enhancing the simulation accuracy of the mixed power flow\nanalysis using available information. In the proposed approach, a modified dc model is used instead\nof the traditional one and is constructed from an initial base-case ac solution. The new dc model\ncompensates for the errors originating from the neglect of the real power losses and the assumption of\na flat voltage magnitude in the conventional dc model. Thus, the proposed method can improve the\nsimulation accuracy in the area of interest. The superior computational benefits can also be preserved\nby maintaining linear characteristics of the dc model. Case studies with the IEEE 118-bus system are\nprovided to validate the enhanced accuracy of the proposed method....
Copper wire is a major conduction material that carries a variety of signals in\nindustry. Presently, automatic wire elongating machines to produce very thin wiresare available for\nmanufacturing. However, the original wires for the elongating process to thin sizes need heating,\ndrawing and then threadingthrough the die molds by the manpower before the machine starts to\nwork. This procedure repeatsuntil the wire threads through all various die molds. To replace the\nmanpower, this paper aims to develop an automatic wire die molds threading system for the wire\nelongation process. Three pneumatic grippers are designed in the proposed system. The first gripper\nis used to clamp the wire. The second gripper fixed in the rotating mechanism is to draw the heated\nwire. The third gripper is used to move the wire for threading through the dies mold. The force\ndesigned for drawing the wire can be adjusted via the gear ratio. The experimental results confirm\nthat the proposed system can accomplish the wiredies mold threading processin term of robustness,\nrapidness and accuracy....
Loading....