No description available.

Multi-level converters that provide more than two levels of voltage to achieve an output waveform closer to sinusoidal waveform with less distortion are very attractive to power applications. This thesis investigates several multi-level converter topologies and different modulation strategies such as pulse-width modulation and space vector modulation. Attention is paid in particular to SVM strategy. Although SVM strategy is applicable for N-level converter, this thesis only focuses on five-level and three-level diode clamped converter (DCC). Despite their appealing harmonic spectrum and low losses, multi-level converters are known to suffer from inherent voltage imbalance on their dc side. The thesis presents a method in order to balance the dc side capacitor voltages for an N-level converter. The presented balancing method is based on minimizing a cost function which is related to voltage divergence of the dc capacitors. This method is used for a three-level SVM to overcome the voltage drifting problem.

Multi-level converters that provide more than two levels of voltage to achieve an output waveform closer to sinusoidal waveform with less distortion are very attractive to power applications. This thesis investigates several multi-level converter topologies and different modulation strategies such as pulse-width modulation and space vector modulation. Attention is paid in particular to SVM strategy. Although SVM strategy is applicable for N-level converter, this thesis only focuses on five-level and three-level diode clamped converter (DCC). Despite their appealing harmonic spectrum and low losses, multi-level converters are known to suffer from inherent voltage imbalance on their dc side. The thesis presents a method in order to balance the dc side capacitor voltages for an N-level converter. The presented balancing method is based on minimizing a cost function which is related to voltage divergence of the dc capacitors. This method is used for a three-level SVM to overcome the voltage drifting problem.

Zugl.: Kassel, Univ., Diss., 2007

Zugl.: Mannheim, Univ. Diss., 2007

Zugl.: Mannheim, Univ., Diss., 2007

Zugl.: Kassel, Universiẗat, Diss., 2007.

The new concept of Multi-Level Current Reinjection (MLCR) combines the advantages of DC ripple reinjection, multi-level conversion and soft-switching technique. Taking advantage of the soft-switching technique which uses zero current switching for the main bridge switches, thyristor based MLCR current source converter (CSC) is proposed. This concept adds self-commutation capability to thyristors and produces high quality line current waveforms. Various thyristor based MLCR CSC topologies have been simulated extensively using PSCAD/EMTDC in this thesis and their performance characteristics investigated. Questions have been raised about the ability to force the main thyristors off using the reinjection bridge in a real-world implementation, where there are inevitable stray capacitances and inductances which may influence the thyristor turn-off; and simulation switching models may not represent the switching characteristics fully or accurately. For this proof of concept, a small scale prototype has been built in the laboratory. The 3-level MLCR CSC, which increases the pulse number from 12 to 24, is chosen to verify the concept. The experimental investigation of the 3-level MLCR CSC, under steady-state conditions, verified the following: • The reinjection current allows the main bridge thyristors to be switched at negative firing angles. • This current reinjection technique allows self-commutation capability in a practical system despite the finite turn-off times of the thyristor. • This current reinjection technique improves the harmonic characteristics of the thyristor based converter. • It is observed that the deviation of the actual waveforms from the theoretical waveforms is mainly due to the snubber across the reinjection switch, and a trade-off in the choice of snubber components is required.

Multi-level security is prevalent within the military; however, the private sector has not yet invested in the approach. As big data, Internet of things, and artificial intelligence drive businesses to collaborate (share data, algorithms, and tools) the need to secure such resources while simultaneously sharing them will push towards an alternative approach-–namely Multi-level security. The military labels data according to the sensitivity it carries as related to national security. Furthermore, the military restricts access by both the overall trust in the individual and by their need-to-know. To put it another way, data has a certain level of sensitivity and only those individuals that can be trusted with the data and have a need-to-know shall have access to such data. Military organizations not only limit access to digital data but also to sensitive discussions, often having sensitive talks within a Sensitive Compartmented Information Facility referred to as a SCIF. Irrespective of the media, all data must be secured and disseminated in order to produce value. Inaccessible data has no real value, as data must be accessible in order to be actionable and produce value. Along the same lines, data often requires aggregation to become actionable. Creating a security domain with multiple levels of trust and need-to-know ensures that data can both be accessed and aggregated. Multi-level secure domains exist in military organizations today, however, the challenge arises when two domains want to share data—hence the need for multi-level secure data dissemination. One way to accomplish this objective is for Domain X to contact Domain Y and together identify how their two security domains can map to one another. After determining the mapping Domain X can send Domain Y data, however, what if Domain Z wants access to the same data? Should Domain Z request the data from Domain Y? Would Domain Y violate the trust of Domain X, if Domain Y disseminates the data? Perhaps, Domain Z is only cleared to a portion of the data. These are the issues related to the dissemination of MLS data within a multi-domain environment. The objective of this project is to propose a solution that would allow domains to securely disseminate data without the need to repackage the data for each domain. The solution outlined in this project, leverages Simple Public Key certificates, Active Bundle, and a directory server. When combined, the three technologies allow domains: to convey both trust and authorization policies, learn about trust and authorization policies of external domains, and provide a mechanism to securely disseminate data.

No description available.