اندلس میں مسلمانوں کے ادوار حکومت کا تحقیقی و تنقیدی جائزہ

The golden Islamic history cannot be completed without the mention of Spain which was a bright star. It became one of the great Muslim civilizations; reaching its summit with the Umayyad caliphate of the tenth century. The heartland of Muslim rule was Southern Spain or Andulus. Different eras of Muslim rule in Andulus have been described in this research with an aim to highlight their apex and glory they achieved and then a focus on the reasons of their downfall as well. A brief introduction of the rulers in all eras with their major achievements and immersion in evil habits that led to their downfall has been the prime focus of this research. It gives us various glimpses from the course of history to reflect upon Muslim rule in Spain from a new perspective.

Control and Analysis of Switching Power Electronic Converter.

The suggested research is focused on the analysis, design, and development of the single-phase direct AC-to-AC converters. They are classified as voltage and frequency controllers. The AC voltage controllers are employed to solve the power system disturbances. The problem of voltage sag and swell is very common in the power distribution system that degrades the performance of the connected load and may cause their failure. In these circumstances, the power conditioning units such as dynamic voltage restorers (DVRs) are employed for their proper and safe operation that are realized with AC-to-AC converters. The voltage sags and swells issues are tackled by increasing and decreasing the line voltage respectively. The in-phase and out-of-phase output voltages are generated if AC voltage controllers can be operated with bipolar voltage gain. These characteristics can be realized if they operate in non-inverting and inverting modes. The voltage controllers having these features may also be employed as direct frequency changers (DFC) for variable speed drives and induction heating systems. The circuit and control complexity in these converters depend upon the number of controlled switching devices. The power conversion efficiency in these converters is directly related to unwanted switching and conduction losses caused by the switching devices. These losses depend on the number of switching devices, switching voltages, switching frequency, and switching currents. The high switching voltages and currents are the main problems in these converters. They not only increase the unwanted conversion losses but also increase the voltage and current rating of the switching devices. These problems become very serious in frequency boost operation. In variable frequency operation, the output is not in pure sinusoidal form, and it contains unwanted harmonics as it is obtained by inverting and non-inverting the input voltage. So here, we propose a novel AC-to-AC converter that has voltage and frequency regulation characteristics. It is capable of operating in the buck and boost fashion with non-inverting and inverting characteristics. Its operation is realized with a low count of the switching devices having low switching voltages and currents. These characteristics reduce the conversion losses and hence improve efficiency. The detailed analysis related to switching voltages and currents and conversion losses is also presented. The regulation of the output voltage is achieved through the pulse width modulation (PWM) control of one switch directly and other as indirectly. The direct PWM controlled (DPWM) switch is controlled with a high-frequency gating sequence. Its switching controls the operating states of the other switch called indirect PWM (IDPWM) controlled switch. The power quality problem in variable output frequency mode is determined by computing their harmonics coefficients analytically through the pulse selective approach. The problem of high voltage and current overshoots in boost frequency mode is tackled by developing a new DFC with low count of switching devices. Its output is realized through simple switching control scheme that is generated with any PWM generator as there is no need to synchronize the gating signals with input voltage. The worth of the proposed work is proved by comparing its performance parameters with the existing topologies. The simulation and practical results validate the effectiveness of the proposed research.