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Nonlinear phenomena in power electronic circuits are generally studied through discrete-time maps. However, there exist very few circuit configurations (like, for example, the current-mode-controlled dc--dc converters or current programmed H-bridge inverter) for which the map can be obtained in closed form. In this paper, we show that, in a voltage-mode-controlled dc--dc converter, if the switching is governed by pulse-width modulation of the first kind (PWM-1), an explicit form of the stroboscopic map can be obtained. The resulting discrete-time state space is piecewise smooth, divided into five regions, each with a different functional form. We then analyze the bifurcation behavior using the explicit map and demonstrate the different types of border collision bifurcations that may occur in this system as a fixed point moves from one region to another. This includes the very interesting case of a direct transition from periodicity to quasi-periodicity through the route of border collision bifurcation. Mode-locking periodic windows are also obtained at certain ranges of the parameters. The two-parameter bifurcation diagram is presented, showing the domains of existence of different oscillatory modes in the system parameter plane. Index Terms--Bifurcation, border collision bifurcation, dc--dc converter, puisewidth modulation of first kind (PWM-1), quasiperiodicity.

This paper presents a simplified analytical model of a silicon-controlled-rectifier based, load-commutated inverter driven, commutatorless series motor to predict its speed-current, torque-current and torque-speed characteristics. The model has been formulated, keeping in view the steady state equivalent circuit of a conventional dc series motor. The proposed analytical expressions relating torque and current with speed are found to follow an inverse law and that relating torque and current is found to be parabolic, as is expected in a 'series' machine. The drive has been implemented, loaded with a dc generator and experimentally similar characteristics have been obtained, as predicted by the analytical model. The characteristics obtained experimentally are seen to follow the ones, predicted by the analytical model closely. Index Terms--Commutatorless series motor, load commutated inverter, self-controlled synchronous motor, steady state analysis.

Sintering of alumina from 1500°C to 1650°C and tribo‐mechanical properties at room temperature had been investigated using nano CuO as a sintering aid. Bulk density gradually increases with sintering temperature from 1500°C to 1600°C and is optimized at 1600°C, beyond this, bulk density does not significantly increase at 1650°C. The addition of 2 wt% CuO showed the best result on densification. Densification of about 97.74% was attained at 1600°C with the incorporation of 2 wt% CuO. Nano CuO at grain boundaries forms CuAl2O4 liquid which modifies the morphology of the grain and improves mechanical properties. The formation of self‐lubricating tribo‐film on the wear track results in a low coefficient of friction <0.2 and reduces specific wear rate. 4 wt% CuO addition increases contact tensile stress (σmax) by 51.2% and high Hertzian contact pressure (Pmax≈1.51 GPa) causes plastic deformation of wear track. The re‐solidified strengthening bond phase on the wear track simultaneously increases in friction coefficient and wear resistance with CuO addition. The optimizing effect of CuO addition shows that 2 wt% significantly decreases wear rate, and increases hardness and fracture toughness. [ABSTRACT FROM AUTHOR]

This investigation reports the adsorption effect of Cobalt and Zinc ions on the antibacterial properties of Silicon Carbide (SiC) added fired Porcelain based ceramics against Escherichia coli and Staphylococcus aureus. Incorporation of SiC in porcelain composition shows decrease in bulk density and increase in apparent porosity gradually upto 15 weight percent addition. The bulk density and apparent porosity of 15 wt% SiC added porcelain are 2.01 g/cm3 and 24.03%, respectively. Phase and microstructural charecterization reveals that fine grained interlocked mullite network with little unconverted quartz and carborandum are uniformly distributed in the microstructure. Co+2 and Zn+2 adsorption on exposed surface is calculated to be ~0.42 mg/cm2 and Inductively coupled mass plasma spectroscopy (ICP‐MS) shows that 1641.41 ppm of Co+2 and 1936.37 ppm of Zn+2 are leached in water from adsorbed surface. This is the first report where, transition metal specific antibacterial efficacy of SiC added porcelain‐based ceramics are investigated. This report reveals that both Co+2 and Zn+2 adsorption results in antibacterial efficacy against E coli and S aureus and Co+2 adsorption is superior to (zone of inhibition is ~1.3 cm more depending on bacteria and sample specifications) Zn+2 adsorption. [ABSTRACT FROM AUTHOR]

This paper examines the starting and variable-speed performance of a silicon-controlled-rectifier-based commutatorless series motor with special emphasis on the commutating process for the operation of a self-controlled synchronous machine in the load-commutated mode, unassisted by extra components or special techniques, even at very low speeds, including starting. A dynamic simulation of the drive, in which the field winding of the synchronous machine is located in the dc !ink has been presented, the results of which are validated by comparison with those of an experimental prototype. The influence of the damper windings on the commutation process and in the suppression of the voltage spikes so generated, and in reducing overlap times, has also been studied. A phasor-diagram-based steady-state analysis predicts the parameters of suitable machines for such an operation. The inherent series characteristics of this drive, its high power factor, and self-starting capability will find applications in large-power traction drives, flywheel energy storage systems, centrifugal pumps, etc. Index Terms--Commutatorless series motor, load-commutated inverter, self-controlled synchronous motor, unaided startup.