Solar energy as one type of the renewable energy becomes more and more popular which has led to increase the photovoltaic (PV) installations recently. One of the PV installations is the power conditioning system which is to convert the maximum available power output of the PV modules to the utility grid. Single-phase microinverters are commonly used to integrate the power to utility grid in modular power conditioning system. In the two-stage microinverter, each PV module is connected with a power converter which can transfer higher output power due to the tracking maximum power point (MPP) capability. However, it also has the disadvantages of lower power conversion efficiency due to the increased number of power electronics converters. The primary objective of this thesis is to develop a high-efficiency microconverter to increase the output power capability of the modular power conditioning systems. A topology with hybrid modes of operation are proposed to achieve wide-input regulation while achieving high efficiency. Two operating modes are introduced in details. Under high-input conditions, the converter acts like a buck converter, whereas the converter behaves as a boost converter under low-input conditions. The converter operates as the series resonant converter with normal-input voltage to achieve the highest efficiency. With this topology, the converter can achieve zero-voltage switching (ZVS) and/or zero-current switching (ZCS) of the primary side MOSFETs, ZCS and/or ZVS of the secondary side MOSFETs and ZCS of output diodes under all operational conditions. The experimental results based on a 300 W prototype are given with 98.1% of peak power stage efficiency and 97.6% of weighted California Energy Commission (CEC) efficiency including all auxiliary and control power under the normal-input voltage condition. / Master of Science

The perpetual conflict in Darfur, Sudan, which started anew in 2003, had dire humanitarian consequences and threatened international peace and security. The UN Security Council, which has the primary responsibility for maintaining international peace and security, adopted Resolution 1769 on 31 July 2007 and authorised a 26 000 person-strong joint African Union/United Nations hybrid operation in Darfur (UNAMID) to take over from AMIS (the African Union peace operation in Darfur). UNAMID was established with dual command and control linked to both the African Union and the United Nations and both organisations would have an equal say in its mandate and operations. Given this unique and unprecedented arrangement between a regional organisation and the United Nations in terms of maintaining international peace and security, the aim of this research was to: • Understand and describe the political motivations/reasons why the United Nations formed a hybrid peace operation with the African Union; • Establish in which way the aforementioned impacted on future efforts of the United Nations to maintain international peace and security, especially on the African continent; and, based on this, • To determine whether or not hybrid operations were a viable alternative for the United Nations to maintain international peace and security. By means of a thorough analysis of the theoretical underpinnings of international peace and security, an assessment of the peace and security architecture of the United Nations and the African Union, an investigation into the origins of the Darfur conflict, an examination of the structure and mandate of UNAMID, and through an empirical investigation, a new theoretical proposition is provided in the conclusion of the thesis. It is concluded that the UNAMID model, in practical terms, is not an optimal mechanism for the United Nations to use to maintain international peace and security because it suffers from numerous internal political inequities and operational inadequacies. / Thesis (Ph.D. (Political Studies))--North-West University, Potchefstroom Campus, 2012

The perpetual conflict in Darfur, Sudan, which started anew in 2003, had dire humanitarian consequences and threatened international peace and security. The UN Security Council, which has the primary responsibility for maintaining international peace and security, adopted Resolution 1769 on 31 July 2007 and authorised a 26 000 person-strong joint African Union/United Nations hybrid operation in Darfur (UNAMID) to take over from AMIS (the African Union peace operation in Darfur). UNAMID was established with dual command and control linked to both the African Union and the United Nations and both organisations would have an equal say in its mandate and operations. Given this unique and unprecedented arrangement between a regional organisation and the United Nations in terms of maintaining international peace and security, the aim of this research was to: • Understand and describe the political motivations/reasons why the United Nations formed a hybrid peace operation with the African Union; • Establish in which way the aforementioned impacted on future efforts of the United Nations to maintain international peace and security, especially on the African continent; and, based on this, • To determine whether or not hybrid operations were a viable alternative for the United Nations to maintain international peace and security. By means of a thorough analysis of the theoretical underpinnings of international peace and security, an assessment of the peace and security architecture of the United Nations and the African Union, an investigation into the origins of the Darfur conflict, an examination of the structure and mandate of UNAMID, and through an empirical investigation, a new theoretical proposition is provided in the conclusion of the thesis. It is concluded that the UNAMID model, in practical terms, is not an optimal mechanism for the United Nations to use to maintain international peace and security because it suffers from numerous internal political inequities and operational inadequacies. / Thesis (Ph.D. (Political Studies))--North-West University, Potchefstroom Campus, 2012