Improved error performance for generalised spatial modulation with enhanced spectral efficiency

The existing analytical average bit error rate (ABER) expression of conventional generalised spatial modulation (CGSM) does not agree well with the Monte Carlo simulation results in the low signal‐to‐noise ratio (SNR) region. Hence, the first contribution of this paper is to derive a new and easy way to evaluate analytical ABER expression that improves the validation of the simulation results at low SNRs. Secondly, a novel system termed CGSM with enhanced spectral efficiency (CGSM‐ESE) is presented. This system is realised by applying a rotation angle to one of the two active transmit antennas. As a result, the overall spectral efficiency is increased by 1 bit/s/Hz when compared with the equivalent CGSM system. In order to validate the simulation results of CGSM‐ESE, the third contribution is to derive an analytical ABER expression. Finally, to improve the ABER performance of CGSM‐ESE, three link adaptation algorithms are developed. By assuming full knowledge of the channel at the receiver, the proposed algorithms select a subset of channel gain vector (CGV) pairs based on the Euclidean distance between all CGV pairs, CGV splitting, CGV amplitudes, or a combination of these.     

Broken rotor bar detection in induction machines with transient operating speeds

Previous work on condition monitoring of induction machines has focused on steady-state speed operation. Here, a new concept is introduced based on an analysis of transient machine currents. The technique centers around the extraction and removal of the fundamental component of the current and analyzing the residual current using wavelets. Test results of induction machines operating both as a motor and a generator shows the ability of the algorithm to detect broken rotor bars.     

Resonance Overvoltages in Medium-Voltage Multilevel Drive Systems

Simulations and field tests indicate that unacceptable motor-terminal overvoltages and waveform shapes can occur in the normal operating range with high-output-voltage multilevel drive systems. These waveforms (if unattended) can result in premature motor insulation failures. A case study of an 11-kV multilevel system is presented. Simulations and calculations confirm the theory of resonance overvoltages. Different solution possibilities are analyzed. Further simulations and investigations are performed to determine the optimal carrier frequency. Test results confirm that the proposed modification has the desired effect, with waveforms well within limits stipulated by international standards. Simplified equations and recommendations are provided to determine suitable application solutions. Further simulated resonance case studies are presented, considering the effect of the system configurations, motor size, and cable length. Suitable carrier-frequency selection methods are presented to solve the problem.     

An informed genetic algorithm for the examination timetabling problem

This paper presents the results of a study conducted to investigate the use of genetic algorithms (GAs) as a means of inducing solutions to the examination timetabling problem (ETP). This study differs from previous efforts applying genetic algorithms to this domain in that firstly it takes a two-phased approach to the problem which focuses on producing timetables that meet the hard constraints during the first phase, while improvements are made to these timetables in the second phase so as to reduce the soft constraint costs. Secondly, domain specific knowledge in the form of heuristics is used to guide the evolutionary process. The system was tested on a set of 13 real-world problems, namely, the Carter benchmarks. The performance of the system on the benchmarks is comparable to that of other evolutionary techniques and in some cases the system was found to outperform these techniques. Furthermore, the quality of the examination timetables evolved is within range of the best results produced in the field.     

An investigation into vibration in switched reluctance motors

Two disadvantages of the switched reluctance motor (SRM) are its torque ripple and acoustic noise. Previous work on vibration modes and resonant frequencies of the laminations of an 8-6 SRM is extended here to include the effects of the frame. Both a smooth frame and a ribbed frame are examined, and the presence of numerous additional vibratory modes in the ribbed frame demonstrated. Accelerometer tests behind a pole verify some of the theoretical predictions     

Modelling a sustainability yardstick in modern energisation of rural sub-Saharan Africa

The bulk of rural Africa (as well as much of the third world) remains un-electrified and is underserved or poorly served by any other form of modern energy infrastructure. In case of a deep sub-Sahara African country like Kenya it is often dismissively argued that lack of finance and appropriate technology are the obvious causes. This argument would however not hold when applied to the more technologically advanced South Africa where a whopping 50% of rural households still suffer a similar fate. The common perception is that in the presence of modern technology the desired social change process will automatically commence. Unfortunately (and possibly due to pressure from donors) typical post project reports from the third world often contain deliberate commissions or omissions that essentially belie the grim reality on the ground. What seems to lack is a well-defined yardstick or standard check-off list as to the essential attributes of a sustainable energy dissemination project.