Control Loop Interactions and Their Mitigation Schemes in VSC-HVDC Systems

In line with two goals of the United Nations, i.e., providing affordable and clean energy as well as combating climate change, various converter-interfaced renewable energy sources (RESs) are being integrated into the power systems. The transfer of renewable power generated by the RESs such as offshore wind farms to remote load centers may require the use of direct current (DC) lines, which are connected to the alternating current (AC) grid via AC-DC converters. In addition to facilitating the reliable connection of RESs to the power grid, high-voltage DC (HVDC) lines may be used for the transcontinental exchange of power to transfer power over long distances. One of the major challenges in the evolution of AC systems to hybrid AC-DC systems is the control of converters. Each converter station owns various control loops that require proper tuning in their stand-alone mode of operation. Furthermore, control loops of adjacent converters may also impact one another, and as a result, there must be coordination among the control design of converters to guarantee stability and appropriate dynamic response of the entire grid. The control loop interactions among the converters worsen with increasing the size of the system and the number of converters, especially when one converter station is already in operation and re-tuning the converter's controllers is not an option. Another important aspect of future AC-DC power grids is the employment of converters built by multiple vendors, who will take part in the development of converter controllers with unique designs and know-how. These independently designed controllers will form a part of the grid control system. In this scenario, the stability of the entire system is of great importance and needs to be verified due to control loop interactions. This thesis studies both internal and external control loop interactions in voltage-sourced converters (VSCs) embedded in AC-HVDC systems. This thesis, first, studies the internal control loop interactions, where the control loops within one single converter interact with one another, and develops a method to design the individual control loops within a VSC such that the converter stability is ensured. A metric is proposed to measure interaction levels, and the impact of interactions on set-point tracking capability is also investigated. This thesis, next, considers the connections among various converters either from the AC side or the DC side and studies the external control loop interactions among the adjacent converters. Regarding the external control loop interactions caused by DC side connections, suitable system models are introduced to enable individual control design for the converters in a multi-terminal DC (MTDC)-HVDC grid. As for the AC side external control loop interactions, two scenarios are considered: 1) the converters are in the grid-following (GFL) mode of operation, and 2) the converters are in the grid-forming (GFM) mode of operation. Regarding the GFL mode of operation, the impact of control modes on the interactions is studied, and the control modes causing the highest interaction levels are identified. A novel control design framework is designed to relate the control design of each converter to the interconnected system stability. The multi-vendor issue then is considered, and the interactions are mitigated by designing individual robust controllers or by employing interaction filters. The interaction analyses are then extended to the parallel connection of GFM converters and hybrid connections of GFL and GFM converters. Stability and coupling analyses are performed among GFL and GFR converters. small-signal stability of parallel GFM converters is proved, and real-time simulations and hardware-in-the-loop-test are performed for validating the studies

Ekspresija mRNA agutiju srodnog peptida i mRNA melanokortin-4 receptora u arkuatnoj jezgri za vrijeme gravidnosti i laktacije štakorica.

Pregnancy is associated with a range of physiological adjustments to adapt the body to the demands of the growth of the fetus and subsequent lactation. It has been observed that agouti-related peptide (AGRP) and melanocortin-4 receptor (MC4R) are involved in energy homeostasis. A randomized controlled experimental study was planned to investigate the expression of AGRP and MC4R mRNAs in the stages of pregnancy and lactation in rat arcuate nucleus (ARC) of the hypothalamus. Thirty-two adult female rats were randomly divided into six groups. Pregnant rats were assigned into three groups (n = 6) of 7, 14, and 21 days of pregnancy. Two more groups were also assigned of non-suckling rats (n = 5), immediately separated from their pups after parturition, and suckling rats (n = 5), allowed to suckle five pups until day 8 (increasing milk). The sixth group consisted of four ovariectomized rats, which were assigned two weeks after surgery and served as control. Using real-time PCR, the relative expressions (compared to controls) of MC4R and AGRP mRNAs in ARC were calculated in the pregnant, suckling and non-suckling rats. Expression of AGRP mRNAs in pregnant rats on days 14 and 21 was higher than that observed in suckling and non-suckling rats (P<0.05). Expression of MC4R mRNAs in pregnant rats on days 14 and 21 was lower than that observed in suckling rats, and was higher on day 7 than that observed in both suckling and non-suckling rats (P<0.05). In conclusion, expression of AGRP in pregnancy and MC4R in lactation in ARC of rats controls energy homeostasis.Gravidnost je povezana s nizom fizioloških prilagodbi kojima tijelo odgovara zahtjevima povezanima s rastom fetusa i kasnije laktacije. Uočeno je da su agutiju srodan peptid (AGRP) i melanokortin-4 receptor (MC4R) uključeni u energetsku homeostazu. Randomiziranim kontroliranim pokusom planirano je u arkuatnoj jezgri (ARC) hipotalamusa štakorica istražiti ekspresiju mRNA AGRP i mRNA MC4R tijekom gravidnosti i laktacije. Trideset dvije odrasle štakorice nasumično su bile podijeljene u šest skupina. Gravidne su štakorice podijeljene u tri skupine (n = 6), s obzirom na 7., 14. i 21. dan gravidnosti. Još dvije skupine (n = 5) činile su nedojne štakorice koje su odvojene od svoje mladunčadi odmah nakon porođaja te dojne štakorice kojima je dozvoljeno dojenje 5 mladunaca do osmog dana rastuće laktacije. Četiri ovarijektomizirane štakorice, dva tjedna nakon operacije, dodijeljene su u 6. kontrolnu skupinu. Koristeći PCR u stvarnom vremenu, relativna ekspresija (usporedba s kontrolama) mRNA MC4R i mRNA AGRP u ARC izračunata je za gravidne, nedojne i dojne štakorice. Ekspresija mRNA AGRP kod gravidnih štakorica 14. i 21. dan bila je veća od one opažene kod dojnih i nedojnih štakorica (P<0,05). Ekspresija MC4R mRNA u gravidnih štakorica 14. i 21. dan bila je manja u odnosu na dojne štakorica i veća 7. dan u odnosu na skupine dojnih i nedojnih štakorica (P<0,05). Zaključno, ekspresija AGRP u ARC tijekom gravidnosti i MC4R u ARC tijekom laktacije kontrolira energetsku homeostazu štakorica

Promjene u RF-amidu srodnom peptidu-3 hipotalamusa i ekspresijama gena Kiss1 tijekom spermatogeneze kod štakora u uvjetima kroničnog stresa.

The effects were evaluated of chronic stress and the glucocorticoid receptor antagonist (RU486) on mRNA expressions of RF-amide related peptide-3 (RFRP-3) in the dorsomedial hypothalamic nucleus (DMH) and Kiss1 in the arcuate nucleus (ARC) of male rats. Twenty-four male rats were allocated to four equal sized groups: the stress, RU486, stress/RU486, and control groups. In the stress group the rats were restrained 1 hour/day for 12 days. In the RU486 group, the rats were injected with RU486 for 12 days. In the stress/RU486 group, the rats were injected with RU486 1 hour before the stress process for 12 days. Relative expressions of RFRP-3 and Kiss1 mRNAs were determined using real-time PCR. The relative expression of RFRP-3 mRNA in the stress group was higher than that in the RU486 and control rats. The relative expression of RFRP-3 mRNA did not differ between the stress group and the stress/RU486 rats. Furthermore, the relative expressions of Kiss1 mRNA in the stress, RU486, and stress/RU486 groups were less than that of the control rats. The relative expression of Kiss1 mRNA did not differ between the stress, RU486, and stress/RU486 groups. In conclusion, dysfunction in male rat fertility caused by the chronic stress may be the result of the increase in REFP-3 and the decrease in Kiss1 mRNA expression.Istražen je učinak kroničnog stresa i antagonista glukokortikoidnog receptora (RU486) na ekspresiju mRNA RF-amidu srodnog peptida-3 (RFRP-3) u dorzomedijalnoj jezgri hipotalamusa (DMH), te na ekspresije gena Kiss1 u arkuatnom nukleusu (ARC) štakora. Dvadeset i četiri štakora bila su raspodijeljena u četiri jednake skupine: stresna skupina, RU486 skupina, stresna/RU486 skupina i kontrolna skupina. U stresnoj skupini štakori su 12 dana bili obuzdani tijekom jednog sata dnevno. U skupini RU486, štakorima je tijekom 12 dana bio primijenjivan RU486. U skupini stres/RU486, štakorima je tijekom 12 dana apliciran RU486 jedan sat prije postupka obuzdavanja. Relativne ekspresije RFRP-3 i Kiss1 mRNA određene su lančanom reakcijom polimerazom u stvarnom vremenu. Relativna ekspresija RFRP-3 mRNA u stresnoj skupini bila je veća nego u skupini RU486 i kontrolnoj skupini. Relativna ekspresija RFRP-3 mRNA nije bila različita između stresne skupine i stres/RU486 skupine. Nadalje, relativne ekspresije Kiss1 mRNA u stresnoj skupini, skupini RU486, i stresnoj skupini/RU486 bile su manje u odnosu na kontrolnu skupinu. Relativna ekspresija Kiss1 mRNA nije se razlikovala između stresne skupine, skupineRU486 i stresne skupine/RU486. Zaključno, disfunkcija plodnosti kod štakora izloženih kroničnom stresu može biti uzrokovana putem povećane ekspresije RFRP-3 i smanjene ekspresije Kiss1 mRNA

Investigation on adaptability and performance of species and provenances of Eucalyptus in Markazi province (Saveh)

The aim of the present study was selection of adaptable species with proper growth and wood production and resistant to cold with the aim of wood production and cultivation in the urban green space and infertile lands of Saveh. Seedlings of Eucalyptus suggrandis ssp. Suggrandis, E. microcarpa, E. suggrandis ssp. Alipe, E. camaldulensis 41-sh, E. camaldulensis var. camaldulensis, E. rubida 166-sh, E. viminalis 168-sh, E. sargentii and E. camaldulensis 41-ch were planted in 3×3m spacing on late March 2010 in three replications with 25 seedlings based on Randomized Complete Block design (RCB). Also, some physic-chemical properties of soilwere examined. Results of the data analysis showed that the maximum total height, crown diameter and trees quality were observed in E. camaldulensis 41-sh. While E. viminalis 168-sh showed maximum diameter at breast height and E. camaldulensis 41-ch the heigheststanding stock volume, volume increment and quality in compare to other species. Eucalyptus suggrandis ssp. Suggrandis, E. camaldulensis 41-sh and E. microcarpa were most resistant to cold. The maximum rate of survival was measured in E. sargentii and the lowest in E. rubida 166-sh. Total height was found to be the most important factor in extraction data variance. E. camaldulensis is recommended for wood production and E. sargentii is suggested for soil and water conservation in infertile lands of Saveh

Effect of soil composition on seed germination of Pinus halepensis Mill.

Present research was aimed to study 1- the effect of soil-media on seed germination of Pinus halepensis Mill. and 2- the increase of seed germination and seedling production in nursery of Koloudeh, located in Amol city, Iran. Seeds were sown in plastic pots at four different soil treatments including: a- nursery soil (control), b- control soil+ cattle manure (5:1), c- control soil+ litter (5:1), d- control soil+ cattle manure+ litter (5:1:1). The experiment was set up as completely randomized design (CRD) with four replications. Results demonstrated that among the soil treatments there was a significant difference in attributes as germination rate, mean daily germination and germination energy but no significant differences were found in maximum mean daily germination, germination speed, mean germination time, germination value and Kotowski coefficient of velocity. There was a highly significant correlation between germination rate and mean daily germination with different soil composition. Seed germination rate was highest where decomposed litter was mixed with control soil+ cattle manure+ litter (5:1:1). From this investigation it is deduced that organic matter improves seed germination of Pinus halepensis, due to the suitability of seedbed. Thus, it can be proposed that in order to enhance the qualitative and quantitative of seedling production of this species, the condition of soil-media should be better considered in nurseries

Ekspresija mRNA agutiju srodnog peptida i mRNA melanokortin-4 receptora u arkuatnoj jezgri za vrijeme gravidnosti i laktacije štakorica.

Pregnancy is associated with a range of physiological adjustments to adapt the body to the demands of the growth of the fetus and subsequent lactation. It has been observed that agouti-related peptide (AGRP) and melanocortin-4 receptor (MC4R) are involved in energy homeostasis. A randomized controlled experimental study was planned to investigate the expression of AGRP and MC4R mRNAs in the stages of pregnancy and lactation in rat arcuate nucleus (ARC) of the hypothalamus. Thirty-two adult female rats were randomly divided into six groups. Pregnant rats were assigned into three groups (n = 6) of 7, 14, and 21 days of pregnancy. Two more groups were also assigned of non-suckling rats (n = 5), immediately separated from their pups after parturition, and suckling rats (n = 5), allowed to suckle five pups until day 8 (increasing milk). The sixth group consisted of four ovariectomized rats, which were assigned two weeks after surgery and served as control. Using real-time PCR, the relative expressions (compared to controls) of MC4R and AGRP mRNAs in ARC were calculated in the pregnant, suckling and non-suckling rats. Expression of AGRP mRNAs in pregnant rats on days 14 and 21 was higher than that observed in suckling and non-suckling rats (P<0.05). Expression of MC4R mRNAs in pregnant rats on days 14 and 21 was lower than that observed in suckling rats, and was higher on day 7 than that observed in both suckling and non-suckling rats (P<0.05). In conclusion, expression of AGRP in pregnancy and MC4R in lactation in ARC of rats controls energy homeostasis.Gravidnost je povezana s nizom fizioloških prilagodbi kojima tijelo odgovara zahtjevima povezanima s rastom fetusa i kasnije laktacije. Uočeno je da su agutiju srodan peptid (AGRP) i melanokortin-4 receptor (MC4R) uključeni u energetsku homeostazu. Randomiziranim kontroliranim pokusom planirano je u arkuatnoj jezgri (ARC) hipotalamusa štakorica istražiti ekspresiju mRNA AGRP i mRNA MC4R tijekom gravidnosti i laktacije. Trideset dvije odrasle štakorice nasumično su bile podijeljene u šest skupina. Gravidne su štakorice podijeljene u tri skupine (n = 6), s obzirom na 7., 14. i 21. dan gravidnosti. Još dvije skupine (n = 5) činile su nedojne štakorice koje su odvojene od svoje mladunčadi odmah nakon porođaja te dojne štakorice kojima je dozvoljeno dojenje 5 mladunaca do osmog dana rastuće laktacije. Četiri ovarijektomizirane štakorice, dva tjedna nakon operacije, dodijeljene su u 6. kontrolnu skupinu. Koristeći PCR u stvarnom vremenu, relativna ekspresija (usporedba s kontrolama) mRNA MC4R i mRNA AGRP u ARC izračunata je za gravidne, nedojne i dojne štakorice. Ekspresija mRNA AGRP kod gravidnih štakorica 14. i 21. dan bila je veća od one opažene kod dojnih i nedojnih štakorica (P<0,05). Ekspresija MC4R mRNA u gravidnih štakorica 14. i 21. dan bila je manja u odnosu na dojne štakorica i veća 7. dan u odnosu na skupine dojnih i nedojnih štakorica (P<0,05). Zaključno, ekspresija AGRP u ARC tijekom gravidnosti i MC4R u ARC tijekom laktacije kontrolira energetsku homeostazu štakorica