Modular multilevel converter with modified half-bridge submodule and arm filter for dc transmission systems with DC fault blocking capability

Although a modular multilevel converter (MMC) is universally accepted as a suitable converter topology for the high voltage dc transmission systems, its dc fault ride performance requires substantial improvement in order to be used in critical infrastructures such as transnational multi-terminal dc (MTDC) networks. Therefore, this paper proposes a modified submodule circuit for modular multilevel converter that offers an improved dc fault ride through performance with reduced semiconductor losses and enhanced control flexibility compared to that achievable with full-bridge submodules. The use of the proposed submodules allows MMC to retain its modularity; with semiconductor loss similar to that of the mixed submodules MMC, but higher than that of the half-bridge submodules. Besides dc fault blocking, the proposed submodule offers the possibility of controlling ac current in-feed during pole-to-pole dc short circuit fault, and this makes such submodule increasingly attractive and useful for continued operation of MTDC networks during dc faults. The aforesaid attributes are validated using simulations performed in MATLAB/SIMULINK, and substantiated experimentally using the proposed submodule topology on a 4-level small-scale MMC prototype

Relationship between ethical corporate social responsibility and customer loyalty: the mediating role of customers’ gratitude

The purpose of this study was to examine whether customer gratitude mediates the association between ethical corporate social responsibility and customer loyalty. A cross-sectional survey was adopted. A total of 430 individual customers of retail banks located in some selected towns in north-east region of Nigeria were selected using convenience sampling. Structured questionnaires were used to collect. Descriptive statistics and partial least square structural equation modeling were used in data analysis. Finding showed that ethical corporate social responsibility positively and significantly affected customer loyalty. Also, a positive and significant effect of ethical corporate social responsibility on customer gratitude was observed. Furthermore, it was observed that customer gratitude and customer loyalty are positively associated. Also, customer gratitude mediated between ethical corporate social responsibility and customer loyalty. This study concluded that customer gratitude mediated the influence of ethical corporate social responsibility on customer loyalty. The finding of this study will help managers of Nigerian retail banks to develop ethical corporate social practices which strongly create feelings of gratitude among their banks’ customers in order to take advantage of customers’ gratitude, and eventually cultivate customers’ loyalty

Current source back to back converter for wind energy conversion systems

This paper proposes a new back-to-back current source converter (BTB-CSC) suitable for mediumvoltage high power wind energy conversion systems (WECS). It employs a dual three-phase permanent magnet synchronous generator and two current source inverters with a phase-shift transformer at the grid side. The proposed BTB-CSC has the following advantages: reduced power circuit and control complexity; low switching losses (zero switching losses at the inverter side); and independent control of active and reactive power. PSCAD/EMTDC simulations are used as to assess the steady-state and dynamic behaviour of the proposed system under different operating conditions. It is shown that the proposed WECS can ride-through ac faults. Experimental results from scaled prototype of the proposed WECS are used to validate the simulations

Do grain reserves necessarily contribute to prices stability and food security in Sudan? An assessment

AbstractMost governments in Africa implement policies aiming to stabilize the prices of staple foods, which often include building up grain reserves, besides other trade measures insulating their domestic market from the world market. The mechanism should ideally work as follows, grains should be bought and stored from areas, during the surplus seasons (after harvest) so as to assure fair prices to producers and should be distributed during deficit seasons, in deficit areas besides in cases of emergencies. However, ideal approaches are not necessarily followed in many developing countries due to different constraints and situations. The Strategic Reserve Corporation (SRC) is an institution that is established ten years ago to play such a role in Sudan. This paper tries to assess the performance of the SRC against the overall goals and to study the related obstacles if any. We use a sample of 112 respondents from the SRC staff, related and grain farmers as our data source. Results of the research revealed numerous financial and administrative constraints that obstruct SRC from playing the intended role, which need to be considered so as to contribute to price stability and food security in Sudan

Single-stage ac–dc buck–boost converter for medium-voltage high-power applications

This study proposes three topologies based on single-stage three-phase ac-dc buck-boost converters suitable for medium-voltage high-power applications. The first two topologies are based on a dual three-phase buck-boost converter, with a three-winding phase-shifted transformer to achieve sinusoidal input currents, with relatively small ac filters. The limitation of these two topologies is the switching devices are exposed either to a high voltage beyond that tolerable by a single device. The third topology is based on three single-phase buck-boost converters; with their dc output terminals connected in series to generate high voltage. By using this approach, voltage stresses on the switching devices are greatly reduced, and sinusoidal input currents with nearly unity power factor is achieved over the entire operating range when using small ac filters. Analysis, PSCAD/EMTDC simulations and experimentation are used to assess the feasibility of the proposed topologies during normal operation. Major findings of this study are discussed and summarised as a comparison between the three topologies

The Mediating Role of Value Co-creation on the Relationship between Structural supply Chain Orientation and Marketing Adaptiveness: A Structural Equitation Model

the success of the supply chain depends upon the ability to adjust theinterests of various stakeholders of the supply chain members, which is has become a necessity to maintain a competitive advantage in a dynamic environment. SCO affects not only the single firm performance within the supply chain but also the overall performance of the supply chain.Drawing on RBV this study seek to investigate the mediating effect of value co-creation on the relationship between Structural Supply chain orientation and marketing adaptiveness of industrial firms in sudan. the study collected a data from non probability sample of 180 manufacturing firms, This study applies structural equation modelling (SEM) method for data analysis using The result indicates. That both Cooperative Norms and value co-creation significantly contribute to the marketing adaptiveness , also credibility have significance effect on value co-creation . The finding also suggests that value co-creation partially mediates the relationship between structural supply chain orientation(credibility) and marketing adaptiveness. Moreover industrial firms can more adaptability in marketing by maintaining and developing cooperative norms and participating partners in the process of creating value Key Words: Supply chain orientation, Structural SCO, Value co-creation, marketing adaptivenes

Hybrid multilevel converter with cascaded H-bridge cells for HVDC applications : operating principle and scalability

Hybrid multilevel converters are contemplated in an attempt to optimize the performance of voltage source converters in terms of magnitude of semiconductor losses and converter footprint, and to achieve additional features such as dc short circuit proof, which is essential for a high integrity multiterminal HVDC grid. Therefore, this paper considers an emerging hybrid cascaded converter that offers the dc side short circuit proof feature at reduced loss and footprint compared to the existing multilevel and other hybrid converters. Its operating principle, modulation, and capacitor voltage balancing strategies are described in detail. Furthermore, hybrid converter scalability to high voltage applications is investigated. The validity of the modulation and capacitor voltage strategy presented are confirmed using simulation and experimentation. The hybrid cascaded converter is extendable to a large number of cells, making it applicable to high voltage applications, and operation is independent of modulation index and power factor. On these ground, the converter is expected to be applicable for both real and reactive power applications

Three-phase ac-dc buck-boost converter with a reduced number of switches

A single-switch, single-stage, three-phase ac-dc buck-boost converter suitable for medium-voltage applications is proposed. Basic relations that govern steady-state converter operation are established, confirmed using PSCAD/EMTDC simulations, and substantiated experimentally. Simulation and experimental results establish that the proposed converter has good dynamic performance in buck and boost modes, with near unity input power factor

Population structure and genetic diversity of Sudanese native chickens

The objectives of this study were to analyze genetic diversity and population structure of Sudanese native chicken breeds involved in a conservation program. Five Sudanese native chicken breeds were compared with populations studied previously, which included six purebred lines, six African populations and one Sudanese chicken population. Twenty-nine (29) microsatellite markers were genotyped individually in these five populations. Expected and observed heterozygosity, mean number of alleles per locus and inbreeding coefficient were calculated. A model based cluster analysis was carried out and a Neighbor net was constructed based on marker estimated kinships. Two hundred and one alleles were detected in all populations, with a mean number of 6.93 ± 3.52 alleles per locus. The mean observed and expected heterozygosity across 29 loci was 0.524 and 0.552, respectively. Total inbreeding coefficient (FIT) was 0.069±0.112, while differentiation of subpopulations (FST 0.026±0.049) was low indicating the absence of clear sub-structuring of the Sudanese native chicken populations. The inbreeding coefficient (FIS) was 0.036±0.076. STRUCTURE software was used to cluster individuals to 2 ≤ k ≤ 7 assumed clusters. Solutions with the highest similarity coefficient were found at K=5 and K=6, in which Malawian, Zimbabwean, and purebred lines split from Sudanese gene pool. The six Sudanese native chicken populations formed one heterogeneous cluster. We concluded that Sudanese native chickens are highly diverse, and are genetically separated from Malawian, Zimbabwean chickens and six purebred lines. Our study reveals the absence of population sub-structuring of the Sudanese indigenous chicken populations.Key words: Genetic diversity, microsatellites, population structure, Sudanese native chickens