Search results

The purpose of this paper is to propose a method of optimal control of current commutation of switched reluctance motor drive.

The problem of optimal current commutation control is solved by off‐line selection of switching‐on and switching‐off angles. Selection of optimal values of angles is provided on computer model of the drive with help of particle swarm optimisation method. The optimal angle values are detected as functions of phase current and rotor speed. These calculated optimal values are stored in microcomputer control system memory in form of two‐input look‐up tables. The results are validated on laboratory set up.

Three different criteria of optimal control, which are taken into account: the maximum electromagnetic torque for given reference current, the maximum ratio of electromagnetic torque to root mean square value of phase current and the minimum electromagnetic torque ripples, gave a good results validated by simulation and experimental investigations.

A simple control method is proposed to optimise switched reluctance motors drive behaviour. Such an approach can be recommended for practical implementations.

The off‐line optimisation of switching angles, which is realised on computer model, is sufficient to obtain a good control effect.

Discusses the 27 papers in ISEF 1999 Proceedings on the subject of electromagnetisms. States the groups of papers cover such subjects within the discipline as: induction machines; reluctance motors; PM motors; transformers and reactors; and special problems and applications. Debates all of these in great detail and itemizes each with greater in‐depth discussion of the various technical applications and areas. Concludes that the recommendations made should be adhered to.

Gives introductory remarks about chapter 1 of this group of 31 papers, from ISEF 1999 Proceedings, in the methodologies for field analysis, in the electromagnetic community. Observes that computer package implementation theory contributes to clarification. Discusses the areas covered by some of the papers ‐ such as artificial intelligence using fuzzy logic. Includes applications such as permanent magnets and looks at eddy current problems. States the finite element method is currently the most popular method used for field computation. Closes by pointing out the amalgam of topics.

Recognition, measurement and disclosure of public sector assets constitute relevant matters for national and international public sector accounting standard-setting. This chapter develops a theoretical analysis drawing upon a dualistic approach contrasting current value and historical cost accounting models. Accordingly, the latter should be adapted and then preferred to cope with public sector specificities, with a view to providing information for and enforcing accountability to citizens and their political representatives. Drawing upon this theoretical setting, our analysis develops a consistent design for the overarching conceptual framework for assets in general, providing illustrative examples for specific categories such as financial, heritage, natural and military assets.

This study examines the value relevance of recognised and disclosed revaluations of land and buildings for a large sample of Australian firms from 1993 through 1997. In contrast to prior research, we control for risk and cyclical effects and find no difference between recognised and disclosed revaluations, using yearly‐cross‐sectional and pooled regressions and using both market and non‐market dependent variables. We also find only weak evidence that revaluations of recognised and disclosed land and buildings are value relevant.

During the 1990s the value to an intending professional accountant of undertaking a period of liberal (general) studies was promoted internationally by a number of individuals and organisations, including the International Federation of Accountants (IFAC) and the New Zealand Institute of Chartered Accountants (the “Institute”). The Institute significantly changed its admissions policy for Chartered Accountants in 1996 and one change was to require four years of degree level study with a compulsory liberal studies component. This study surveys the perceptions of New Zealand accounting practitioners on the impact of this compulsory liberal component. The results of this study demonstrate that there is little support from accounting practitioners for IFAC’s claim that liberal education “can contribute significantly to the acquisition of professional skills”, including intellectual, personal and communication skills. In addition, the majority of respondents did not perceive any improvements in the professional skills of the staff that had qualified under the Institute’s current admissions policy. However, any perceived improvements were mainly attributed to the Institute’s admissions policy change. Notwithstanding the lack of support for the assertion that liberal education develops professional skills, there is a strong belief by respondents in the value of liberal education for intending professional accountants.

The British North American colonies were the first western economies to rely on legislature-issued paper monies as an important internal media of exchange. This system arose piecemeal. In the absence of banks and treasuries that exchanged paper monies at face value for specie monies on demand, colonial governments experimented with other ways to anchor their paper monies to real values in the economy. These mechanisms included tax-redemption, land-backed loans, sinking funds, interest-bearing notes, and legal tender laws. I assess and explain the structure and performance of these mechanisms. This was monetary experimentation on a grand scale.

The purpose of this paper is to investigate whether the political setting (civil war versus temporary truce) in a country has an influence on firms' current narrative, visual, and numerical intellectual capital disclosure being included in the current market value of equity.

Using content analysis for data generation, this study identifies narrative, visual, and numerical intellectual capital disclosure in firms' annual reports. Financial data were obtained from firms' annual reports and the stock exchange. Fixed effect panel regression was conducted separately for the civil war period and temporary truce period.

The paper finds that during the period entirely beset by civil war, the current market value of equity includes net book value and current earnings only, and does not include narrative, visual, or numerical intellectual capital disclosure. During the period of temporary truce, the current market value of equity includes net book value, current earnings, and narrative disclosure, but not visual or numerical intellectual capital disclosure.

The findings provide insights into the effectiveness of disclosure strategies in politically unstable environments.

This study analyses the disclosure strategies in a civil war and temporary truce context.

Part 2 of this article appeared in the February issue. Basic principles were explained, followed by a description with illustrations of the various methods which could be used to produce flux in the required direction. This part will deal mainly with the values used in magnetic particle testing, the different current wave forms with a discussion on the advantages and limitation of each. A short abbreviated table of values used in various standards and codes is also included for comparison.

Flying‐capacitor multilevel converters (FCC) need a passive or active regulation of the capacitor voltages. Recently the trend is towards active control, often implemented separately from the current control. The advantages of a true multi‐variable control sparked the interest to apply Model Based Predictive Control (MBPC) for FCC. In this paper an objective analysis method to evaluate the effects of several design choices is presented. The effects of the weight factor selection, model simplification, and prediction horizon expansion for MBPC of a 3‐level FCC are analyzed in a systematical way.

The analysis is mainly based on the mean square error (MSE) of current and capacitor voltage. The results are analysed for different lengths of the prediction horizon and for a wide range of weight factor values. Similarly the effect of a model simplification, neglecting the neutral point voltage, is studied when implementing MBPC for FCCs while considering the computational aspects. Validation of the simulation results is done by experiments on an FPGA‐based setup.

Including the effect of the neutral point voltage considerably increases the current control quality and a much wider range of good values for the weight factor exists. As this good range is not critically dependent on the current amplitude it is possible to select one weight factor value for all operating points. Furthermore, it is concluded that increasing the prediction horizon increases the computational load without improving the control quality.

The effects of increasing the prediction horizon when including other controlled variables is to be investigated, as well as the robustness to modeling errors. The MSE analysis methodology is very suitable for this further research.

For practitioners of MBPC in power electronics the paper proves that by means of simulations and the MSE one value for weight factor can be chosen for all operating points. The paper clearly shows that a practical implementation is feasible and demonstrates that neglecting the neutral point voltage is not good practice.

The MSE‐based analysis is shown to be a systematical and unbiased methodology to evaluate the effects of design choices. The results from this analysis can be directly applied in practical setups.