Transient stability studies are primarily concerned with the generator response of ac power systems and use only steady state type equations to model HVdc converter terminals. These equations are adequate for small disturbances at the converter terminals but cannot accurately represent a converters behaviour during, and through its recovery of, a significant transient disturbance. A detailed three phase electromagnetic analysis is necessary to describe the converters correct behaviour. This thesis describes an accurate and effective hybrid method combining these two types of studies, for analyzing dynamically fast devices such as HVdc converters within ac power systems. Firstly, conventional techniques are reviewed for both a transient stability analysis of power systems and for an electromagnetic transient analysis of HVdc converters. This review deals in particular with the two programs that constitute the hybrid developed in this thesis. Various techniques are then examined to efficiently and accurately pass the dynamic effects of an HVdc link to an ac system stability study, and the dynamic effects of an ac system to a detailed HVdc link study. An optimal solution is derived to maximise the inherent advantages of a hybrid. Finally, the hybrid is applied to a test system and its effectiveness in performing its task is shown.

Renewable energy sources including photovoltaic cells, fuel cells, and wind turbines require converters with high voltage gain in order to interface with power transmission and distribution networks. These conversions are conventionally made using bulky, complex, and costly transformers. Multiple modules of single-switch, single-inductor DC-DC converters can serve these high-gain applications while eliminating the transformer. This work generally classifies multiple modules of single-switch, single-inductor converters as high gain DC-DC converters transformers. The gain and efficiency of both series and cascade configurations are investigated analytically, and a method is introduced to determine the maximum achievable gain at a given efficiency. Simulations are used to verify the modeling approach and predict the performance at different power levels. Experimental prototypes for both low power and high power applications demonstrate the value of multiple module converters in high gain DC-DC converters for renewable energy applications.

This thesis investigates the feasibility of hybrid converter based arrangements for High Voltage direct current (HVdc) transmission systems. The conventional HVdc transmission systems, which use Line Commutated Converter (LCC) technology, require ac voltage and large amounts of reactive power to operate; Voltage-Sourced Converter (VSC) based HVdc schemes, on the other hand, while maintaining most of the advantages of LCC-based systems, have overcome a number of disadvantages inherent to conventional LCC systems. Their ability to provide voltage support to very weak ac networks through generating reactive power, while delivering real power, makes them an ideal option for providing reliable power to remote locations. These converters suffer disadvantages such as higher costs, sensitivity to dc-side faults, and smaller ratings in comparison to conventional converters. This research exploits a new approach and introduces a hybrid configuration of VSC and LCC converters. The hybrid converter combines the advantages of these two converter types, while trying to stay far from their disadvantages. The thesis investigates and discusses the benefits of using VSC-LCC hybrid converters for HVdc transmission systems in stations where support of ac voltage is mostly absent (very weak ac system). It concludes that Series Hybrid Converter (SHC) configuration is a promising option for very weak ac system applications comparing to Parallel Hybrid Converter (PHC) option. Using simplified mathematical models and extensive effort on digital time simulation with PSCAD / EMTDC program, the technical feasibility of implementing SHC has been demonstrated.

This thesis investigates the feasibility of hybrid converter based arrangements for High Voltage direct current (HVdc) transmission systems. The conventional HVdc transmission systems, which use Line Commutated Converter (LCC) technology, require ac voltage and large amounts of reactive power to operate; Voltage-Sourced Converter (VSC) based HVdc schemes, on the other hand, while maintaining most of the advantages of LCC-based systems, have overcome a number of disadvantages inherent to conventional LCC systems. Their ability to provide voltage support to very weak ac networks through generating reactive power, while delivering real power, makes them an ideal option for providing reliable power to remote locations. These converters suffer disadvantages such as higher costs, sensitivity to dc-side faults, and smaller ratings in comparison to conventional converters. This research exploits a new approach and introduces a hybrid configuration of VSC and LCC converters. The hybrid converter combines the advantages of these two converter types, while trying to stay far from their disadvantages. The thesis investigates and discusses the benefits of using VSC-LCC hybrid converters for HVdc transmission systems in stations where support of ac voltage is mostly absent (very weak ac system). It concludes that Series Hybrid Converter (SHC) configuration is a promising option for very weak ac system applications comparing to Parallel Hybrid Converter (PHC) option. Using simplified mathematical models and extensive effort on digital time simulation with PSCAD / EMTDC program, the technical feasibility of implementing SHC has been demonstrated.