Polarization contributions to the tunable properties of Ba0.8Sr0.2TiO3 ceramics were quantitatively studied by microwave measurements. The width of the ferroelectric domain walls (90° domain walls) decreased with decreasing average grain size. The variation in domain size with grain size for grains smaller than 10 µm was roughly proportional to the square root of the grain size, consistent with previous reports on BaTiO3. The smaller size of the 90° domains (i.e., higher domain-wall density) resulted in greater tunability at an applied DC electric field of 6.7 kV/cm. The tunability of the specimen with a domain size of 161 nm was 26.5%, which was 4.4 times that of the specimen with a domain size of 259 nm (T = 6.0%). Under a relatively low DC field, the density of the domain-wall motion was the dominant factor determining the overall tunable properties, while the contributions of the ionic and electronic polarizations were relatively small in Ba0.8Sr0.2TiO3.
The effect of Mg loading on the high-frequency tunable properties and dielectric loss of Ba 0.8 Sr 0.2 Ti 1%x Mg x O 3 (BSTM) ceramics was investigated. Variation in the lattice parameters and the 90°domain configuration with Mg loading indicated a decrease in the tetragonal distortion. Additionally, the 90°domain size decreased slightly with a low Mg loading, up to 0.1 mol %, resulting in a higher domain-wall density compared with the nondoped specimen. The 0.075 mol % Mg-loaded BSTM ceramic exhibited the highest tunability; this was attributed to the domain-size effect. The loss tangent (tan δ) roughly decreased with Mg loading, due to loaded oxygen vacancies. The maximum figure of merit value (FOM = tunability/tan δ) at 10 MHz was achieved for the 0.075 mol % Mg specimen, twice that of the non-doped specimen, due to an increase in the tunability and a decrease in the loss tangent with Mg loading.
Constant power factor control of a power conditioning system in a large-scale photovoltaic generation system (PV system), such as a mega-solar system, is introduced to mitigate voltage variations on a distribution line. However, it is difficult for the control to mitigate the voltage variation on a long distribution line because of the loss on the distribution line. This paper proposes an advanced reactive power control, in which the power factor of the PV system is adjusted both by output power of the PV system and by apparent power of loads not to minimize the voltage variation at the interconnection point but to minimize the voltage variation over the whole distribution line, and reports the result examined by numerical analysis about mitigating the voltage variation by applying the control. This paper shows that the proposed control can mitigate the voltage variation more than constant power factor control and there is a probability that it will be applied as a measure of suppressing the voltage variation on the long distribution line.Index Terms--mega solar, reactive power control, distribution line, voltage variation I.
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