Stability analysis based on birfurcation theory of the DSTATCOM operating in current control mode

This paper presents the stability analysis for a distribution static compensator (DSTATCOM) that operates in current control mode based on bifurcation theory. Bifurcations delimit the operating zones of nonlinear circuits and, hence, the capability to compute these bifurcations is of important interest for practical design. A control design for the DSTATCOM is proposed. Along with this control, a suitable mathematical representation of the DSTATCOM is proposed to carry out the bifurcation analysis efficiently. The stability regions in the Thevenin equivalent plane are computed for different power factors at the point of common coupling. In addition, the stability regions in the control gain space, as well as the contour lines for different Floquet multipliers are computed. It is demonstrated through bifurcation analysis that the loss of stability in the DSTATCOM is due to the emergence of a Neimark bifurcation. The observations are verified through simulation studies.

Coast control for mass rapid transit railways with searching methods

With daily commercial and social activity in cities, regulation of train service in mass rapid transit railways is necessary to maintain service and passenger flow. Dwell-time adjustment at stations is one commonly used approach to regulation of train service, but its control space is very limited. Coasting control is a viable means of meeting the specific run-time in an inter-station run. The current practice is to start coasting at a fixed distance from the departed station. Hence, it is only optimal with respect to a nominal operational condition of the train schedule, but not the current service demand. The advantage of coasting can only be fully secured when coasting points are determined in real-time. However, identifying the necessary starting point(s) for coasting under the constraints of current service conditions is no simple task as train movement is governed by a large number of factors. The feasibility and performance of classical and heuristic searching measures in locating coasting point(s) is studied with the aid of a single train simulator, according to specified inter-station run times.

Probabilistic load flow in AC electrified railways

System analysis within the traction power system is vital to the design and operation of an electrified railway. Loads in traction power systems are often characterised by their mobility, wide range of power variations, regeneration and service dependence. In addition, the feeding systems may take different forms in AC electrified railways. Comprehensive system studies are usually carried out by computer simulation. A number of traction power simulators have been available and they allow calculation of electrical interaction among trains and deterministic solutions of the power network. In the paper, a different approach is presented to enable load-flow analysis on various feeding systems and service demands in AC railways by adopting probabilistic techniques. It is intended to provide a different viewpoint to the load condition. Simulation results are given to verify the probabilistic-load-flow models.

Railway junction traffic control by heuristic methods

Traffic conflicts at railway junctions are very conmon, particularly on congested rail lines. While safe passage through the junction is well maintained by the signalling and interlocking systems, minimising the delays imposed on the trains by assigning the right-of-way sequence sensibly is a bonus to the quality of service. A deterministic method has been adopted to resolve the conflict, with the objective of minimising the total weighted delay. However, the computational demand remains significant. The applications of different heuristic methods to tackle this problem are reviewed and explored, elaborating their feasibility in various aspects and comparing their relative merits for further studies. As most heuristic methods do not guarantee a global optimum, this study focuses on the trade-off between computation time and optimality of the resolution.

Optimal traffic control at railway junctions

Conflict occurs when two or more trains approach the same junction within a specified time. Such conflicts result in delays. Current practices to assign the right of way at junctions achieve orderly and safe passage of the trains, but do not attempt to reduce the delays. A traffic controller developed in the paper assigns right of way to impose minimum total weighted delay on the trains. The traffic flow model and the optimisation technique used in this controller are described. Simulation studies of the performance of the controller are given.

Reverse immigration

This book (256 pages, written in Korean) is a critical essay that reviews, questions, and criticises Korean and Eastern immigrants’ thinking and behaviour styles in Australia from their cultural perspectives, and discuss and proposes a creative cultural dimension for their better life in a multicultural context. Multiculturalism is not supportive of Eastern cultures because of individualistic collection of cultures, while transculturalism facilitates nurture of their culture in a community-oriented way within multicultural circumstances. Korean and Eastern immigrants, sharing oriental cultural systems and values, should approach to the Australian multicultural context with transculturalism which allows creating new cultural values in collaboration with and by participation into local communities. ------------------------------------------------------------ Many Eastern immigrants live in their own ethnic communities without or less interacting with Australian (communities). The author defines this phenomenon as “reverse immigration”. Reverse immigration refers to re-immigrating to their ethnic community in Australia or to their birth country despite they did not anticipate that this would happen to them before immigration to Australia. The author argues that Easterners’ collectivistic culture often devalues individuality and vice versa. Cultural clash between West and East often forces the immigrants to choose reverse immigration because of their lack of understanding of Western culture and their cultural characteristics such as low individuality, high power distance, and high uncertainty avoidance. For example, a vague boundary between individualist and collectivist in a collectivistic context (within their ethnic group) often leads to maladjustment to local communities and enhancement of cultural conservatism. The author proposes that the cultural clash can be overcome by cross-cultural activities named “transculturalism”. To Eastern immigrants, transculturalism can be achieved by acculturation of their two predominant cultures, the third-person perspective and generalised others. In a multicultural context, the former refers to the ability to share another person's feelings and emotions as if they were your own, and the latter does the ability to manage community and public expectations. When both cultural values are used for quality interactions between East and West, they allow Eastern immigrants to be more creative and critical and Australian to be more socially inclusive and culturally tolerant. With these discussions, the author discusses cultural differences throughout the book with four topics (chapters) and proposes transculturalism as a solution to the reverse immigration. ------------------------------------------------------------ Chapter 1 criticises Koreans’ attitudes and methods towards learning English that is less pragmatic and practical, but more likely to be a scholarly study. The author explains that Koreans’ non-pragmatic towards learning English has been firmly built based on their traditional systems and values that Koreans view English as a discipline and an aim of academic achievements rather than a means of communication. Within their cultural context, English can be perceived as more than a language, but something like vastly superior to their language and culture. Their collectivistic culture regards English as an unreachable and heterogeneous one that may threaten their cultural identity, so that “scholarly studying” is only the way to achieve (not learn) it. This discourages the immigrants to engage and involve in daily dialogues by “using” English as a second language. The author further advises the readers to be aware of Eastern collectivistic culture in communication and interaction that sometimes completely reverses private and public topics in a Western context. This leads them to feel that they have no content to talk to natives. ------------------------------------------------------------ Chapter 2 compares between Korea and Australia in terms of their educational systems and values, and proposes how Eastern overseas students can achieve critical and creative thinking within a Western educational setting. Interestingly, this chapter includes an explanation of why Eastern overseas students easily fail assessments including essay writing, oral presentations and discussions. One of the reasons the author explains is that Eastern students are not familiar to criticise others and think creatively, especially when they recognise that their words and ideas may harm the collectivistic harmony. Western educational systems focuses on enhancement of individuality such as self-confidence, self-esteem, and self-expression, while Eastern educational systems foster group-oriented values such as interpersonal relationship, and strong moral and spiritual values. Yet, the author argues that the collectivistic approach to criticism and creativity is often more critical and creative than Western individuals when they know what they are supposed to do for a group (or a community). Therefore, Eastern students need to think their cultural merits and demerits by using an individual perspective rather than generalised others’ perspective. The latter often discourages individual participation in a community, and the generalised others in a Western culture is weaker than Eastern. Furthermore, Western educational systems do not educate students to transform (loose) their individuality to fit into a group or a community. Rather they cultivate individuality for community prosperity. ------------------------------------------------------------ Chapter 3 introduces various cases of reverse immigration in workplaces that many immigrants return to their country or their ethnic community after many trials for acculturation. Reverse immigration is unexpected and not planned before immigration, so that its emotional embarrassment increases such severe social loneliness. Most Eastern immigrant workers have tried to adjust themselves in this new cultural environment at the early stages of immigration. However, their cultural features of collectivism, high power distance, high uncertainty avoidance, and long-term oriented cultures suppress individual initiative and eliminate the space for experiments in ways of acculturation. The author argues that returning to their ethnic community (physically and psychologically) leads to two significant problems: their distorted parenting and becoming more conservatives. The former leads the first generation of immigrants to pressure their children to pursue extrinsic or materialist values, such as financial success, fame and physical appearance, rather than on intrinsic values, while the latter refers to their isolated conservative characters because of their remoteness from the changes of their own country. The author also warns that their ethnic and religious groups actively strengthens immigrants’ social loneliness and systematically discourages immigrants’ interests and desire to be involving into local communities. The ethnic communities and leaders have not been interacting with Australian local communities and, as a result, are eager to conserve outdated cultural systems values. Even they have a tendency to weed out those people who wish to settle down within Australian local communities. They believe that those people can threaten their community’s survival and continuity. ------------------------------------------------------------ Chapter 4 titled multiculturalism argues that Korean and Eastern immigrants should more precisely understand Australia as a multicultural society in a way of collaboratively creating new cultural values. The author introduces multiculturalism with its definitions and history in Australia and argues the limitations of multiculturalism from an Easterner’s perspective. With well known tragedies of the second generations of U.S. immigrants, Cho Seung-Hui, a university student, massacred 32 people on the Virginia Tech before committing suicide and Hidal Hassan, an Army psychiatrist, killed 13 people at Fort Hood and the responses of ethnic community, the author explains that their mental illness may be derived from their parents’ (or ethnic group) culturally isolated attitude and socially static viewpoint of U.S. (Western system and values). The author insists that multiculturalism may restrict Eastern immigrants’ engagement and involvement in local communities. Multiculturalism has been systematically and historically developed based on Western systems and cultural values. In other words, multiculturalism requires high self-confidence and self-esteem that Eastern immigrants less prioritise them. It has been generally known that Easterners put more weight on human relationship than Westerners, but the author claims that this is not true. Within an individualistic culture, Westerners are more interested in building person-to-person connections and relationships. While Easterners are more interested in how individuals can achieve a sense of belonging within a group and a community. Therefore, multiculturalism is an ideology which forces Eastern immigrants to discard their strong desire to be part of a group and does not give a sense of belonging. In a consequence, the author advises that Eastern immigrants should aim towards “transculturalism” which allows them to actively participate in and contribute to their multicultural community. Transculturalism does not ask Easterners to discard their cultural values, but enables them to be a collectivistic individualist (a community leader) who is capable of developing new cultural values in a more creative and productive way. Furthermore, transculturalism encourages Western Australians in a multicultural context to collaborate with ethnic minorities to build a better community.

Who's afraid of the dark? Transpower New Zealand Ltd

On 12 June 2006, the lights went out in New Zealand’s largest city and major commercial centre, Auckland. Business was disrupted and many thousands of people inconvenienced. The unscheduled power cut was the latest in a series of electric power problems in New Zealand over the past decade. Attention turned to state-owned enterprise [SOE] Transpower, which was in charge of maintaining and developing New Zealand’s national electricity grid. The problem of 12 June was traced to two shackles in poor condition, small but essential parts of the electricity grid infrastructure. Closer examination of New Zealand’s electricity sector indicated these shackles were merely the tip of a power supply iceberg. Transpower’s Chief Executive, Ralph Craven, was now answerable to the Prime Minister for the issues creating the problems, and a workable solution to fix them. Transpower Chief Executive Ralph Craven needed to produce answers that went well beyond the problem of the two faulty shackles. The power crisis had brought to the fore wider issues of roles, responsibilities, and expectations in relation to the supply of electric power in New Zealand. Transpower was contending with these issues on a daily basis; however, the incident on 12 June publicly highlighted the urgent need for solutions that served the stakeholders in this critical industry.

A new unequal DC link voltage configuration for a single phase multilevel converter to reduce low order harmonics

Multilevel converters are used in high power and high voltage applications due to their attractive benefits in generating high quality output voltage. Increasing the number of voltage levels can lead to a reduction in lower order harmonics. Various modulation and control techniques are introduced for multilevel converters like Space Vector Modulation (SVM), Sinusoidal Pulse Width Modulation (SPWM) and Harmonic Elimination (HE) methods. Multilevel converters may have a DC link with equal or unequal DC voltages. In this paper a new modulation technique based on harmonic elimination method is proposed for those multilevel converters that have unequal DC link voltages. This new technique has better effect on output voltage quality and less Total Harmonic Distortion (THD) than other modulation techniques. In order to verify the proposed modulation technique, MATLAB simulations are carried out for a single-phase diode-clamped inverter.

Load modelling : induction motors

Modelling the power systems load is a challenge since the load level and composition varies with time. An accurate load model is important because there is a substantial component of load dynamics in the frequency range relevant to system stability. The composition of loads need to be charaterised because the time constants of composite loads affect the damping contributions of the loads to power system oscillations, and their effects vary with the time of the day, depending on the mix of motors loads. This chapter has two main objectives: 1) describe the load modelling in small signal using on-line measurements; and 2) present a new approach to develop models that reflect the load response to large disturbances. Small signal load characterisation based on on-line measurements allows predicting the composition of load with improved accuracy compared with post-mortem or classical load models. Rather than a generic dynamic model for small signal modelling of the load, an explicit induction motor is used so the performance for larger disturbances can be more reliably inferred. The relation between power and frequency/voltage can be explicitly formulated and the contribution of induction motors extracted. One of the main features of this work is the induction motor component can be associated to nominal powers or equivalent motors

Security constrained economic dispatch considering wind energy conversion systems

The available wind power is stochastic and requires appropriate tools in the OPF model for economic and reliable power system operation. This paper exhibit the OPF formulation with factors involved in the intermittency of wind power. Weibull distribution is adopted to find the stochastic wind speed and power distribution. The reserve requirement is evaluated based on the wind distribution and risk of under/over estimation of the wind power. In addition, the Wind Energy Conversion System (WECS) is represented by Doubly Fed Induction Generator (DFIG) based wind farms. The reactive power capability for DFIG based wind farm is also analyzed. The study is performed on IEEE-30 bus system with wind farm located at different buses and with different wind profiles. Also the reactive power capacity to be installed in the wind farm to maintain a satisfactory voltage profile under the various wind flow scenario is demonstrated.

From the Editor

The five articles appearing in this issue of the journal reflect the breadth of project management research and the cross-fertilization of ideas from other management disciplines with project management. These articles focus on the evolution of project management theory (“A Bibliometric View on the Use of Contingency Theory in Project Management Research” by Hanisch and Wald), interfirm knowledge management and learning in project networks (“Exploring Negotiation Through Boundary Objects in Global Design Project Networks” by Di Marco, Alin, and Taylor), learning within one project organization (“Organizational Learning in Project-Based Companies: A Process Thinking Approach” by Koskinen), identifying the factors affecting project performance (“Factors Causing Design Schedule Delays in Turnkey Projects in Taiwan: An Empirical Study of Power Distribution Substation Projects” by Yau and Yang), and considering the antecedents of negative employee behavior and its consequences for project team performance (“Counteracting Free-Riding With Team Morale—An Experimental Study” by He).

A new technique for optimal allocation and sizing of capacitors and setting of LTC

An iterative based strategy is proposed for finding the optimal rating and location of fixed and switched capacitors in distribution networks. The substation Load Tap Changer tap is also set during this procedure. A Modified Discrete Particle Swarm Optimization is employed in the proposed strategy. The objective function is composed of the distribution line loss cost and the capacitors investment cost. The line loss is calculated using estimation of the load duration curve to multiple levels. The constraints are the bus voltage and the feeder current which should be maintained within their standard range. For validation of the proposed method, two case studies are tested. The first case study is the semi-urban 37-bus distribution system which is connected at bus 2 of the Roy Billinton Test System which is located in the secondary side of a 33/11 kV distribution substation. The second case is a 33 kV distribution network based on the modification of the 18-bus IEEE distribution system. The results are compared with prior publications to illustrate the accuracy of the proposed strategy.

Transmission system expansion planning considering combined operation of wind farms and energy storage systems

An energy storage system (ESS) can provide ancillary services such as frequency regulation and reserves, as well as smooth the fluctuations of wind power outputs, and hence improve the security and economics of the power system concerned. The combined operation of a wind farm and an ESS has become a widely accepted operating mode. Hence, it appears necessary to consider this operating mode in transmission system expansion planning, and this is an issue to be systematically addressed in this work. Firstly, the relationship between the cost of the NaS based ESS and its discharging cycle life is analyzed. A strategy for the combined operation of a wind farm and an ESS is next presented, so as to have a good compromise between the operating cost of the ESS and the smoothing effect of the fluctuation of wind power outputs. Then, a transmission system expansion planning model is developed with the sum of the transmission investment costs, the investment and operating costs of ESSs and the punishment cost of lost wind energy as the objective function to be minimized. An improved particle swarm optimization algorithm is employed to solve the developed planning model. Finally, the essential features of the developed model and adopted algorithm are demonstrated by 18-bus and 46-bus test systems.