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Quarterly published "Inventi Impact: Electrical Engineering" publishes high quality unpublished as well as high impact pre-published research and reviews related to all the areas of electrical engineering including power engineering, electrical machines,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 BÃ¢â?¬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\nchargeÃ¢â?¬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....
This paper proposes a high-performance indirect control scheme for torque rippleminimization in the switched reluctancemotor
(SRM) drive system. Firstly, based on the nonlinear torque-angle characteristic of SRM, a novel torque sharing function is
developed to obtain the optimal current profiles such that the torque ripple is minimized with reduced copper losses. Secondly, in
order to track current accurately and indirectly achieve high-performance torque control, a robust current controller is derived
through the Lyapunov stability theory. The proposed robust current controller not only considers the motor parameter modeling
errors but also realizes the fixed frequency current control by introducing the pulse width modulation method. Further, a
disturbance-observer-based speed controller is derived to regulate the motor speed accurately, and the load torque is considered
an unknown disturbance................................
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....
Prediction of available energy storage power is essential for increasing the energy management performance of fuel cell hybrid
electric systems (FCHES). A simple yet effective power prediction index is proposed to estimate the supercapacitor state of power.
It prevents the supercapacitor’s total depletion in the battery/supercapacitor combination. Modern energy management is
equipped with an equivalent consumption minimization strategy. The power prediction index is simple compared with other
predictive algorithms while providing excellent efficiency compared with supercapacitor-based management strategies. A
supercapacitor-based strategy is presented which extends battery life, at the cost of increased fuel consumption. However, it
cannot predict the future low state of charge for the supercapacitor. In such conditions, the battery provides the demand power
while fuel cells generate more current. On the other hand, the modern power prediction index energy management strategy
significantly increases battery life without adding extra hardware. Moreover, fuel consumption decreased by 15.1 percent. The
results show that the modern energy management strategy provides outstanding performance for battery life and fuel consumption
compared with other energy management strategies due to its power limitation prediction....
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 ...
Increasing industrial development puts forward high requirements for the performances of
stator permanent magnet (PM) machines, such as torque density and efficiency. The paper proposes
a new dual stator PM machine based on field modulation theory (DSPMM), which employs the
intermediate rotor participating in the electromechanical energy conversion of the internal and
external machine. The proposed machine has the advantages of high torque density and high
efficiency and solves the problem of insufficient space utilization of a single stator machine. The
evolution process and working principle of the proposed DSPMM are studied. The flux-switchingtype
PM (FSPM) and the flux-reversal-type PM (FRPM) are employed in the proposed DSPMM,
which forms four representative machines. For a fair comparison, the proposed machines employ
identical key parameters, i.e., PM volume, the outer radius of the outer stator, and active airgap length.
Based on finite element analysis (FEA), the electromagnetic performances of the four representative
DSPMM under no-load and rated load, and different copper consumption conditions are analyzed
and compared. The calculated results show that the proposed DSPMM with inner FSPM stator
and outer FRPM stator can provide high output torque, low torque ripple, high power factor, and
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 faultÃ¢â?¬â?¢s position....
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