Multilevel Converters: An Enabling Technology for High-Power Applications

| Multilevel converters are considered today as the state-of-the-art power-conversion systems for high-power and power-quality demanding applications. This paper presents a tutorial on this technology, covering the operating principle and the different power circuit topologies, modulation methods, technical issues and industry applications. Special attention is given to established technology already found in industry with more in-depth and self-contained information, while recent advances and state-of-the-art contributions are addressed with useful references. This paper serves as an introduction to the subject for the not-familiarized reader, as well as an update or reference for academics and practicing engineers working in the field of industrial and power electronics.Ministerio de Ciencia y Tecnología DPI2001-3089Ministerio de Eduación y Ciencia d TEC2006-0386

New techniques to improve power quality and evaluate stability in modern all-electric naval ship power systems

This dissertation focuses on two crucial issues in the design and analysis of the power electronic systems on modern all-electric naval ships, i.e., power quality control and stability evaluation. It includes three papers that deal with active power filter topology, active rectifier control, and impedance measurement techniques, respectively. To mitigate harmonic currents generated by high-power high-voltage shipboard loads such as propulsion motor drives, the first paper proposes a novel seven-level shunt active power filter topology, which utilizes tapped reactors for parallel operations of switching devices. The multi-level system has been implemented in both regular digital simulation and real-time digital simulator for validation. In the second paper, a harmonic compensation algorithm for three-phase active rectifiers is proposed. Based on the theory of multiple reference frames, it provides fast and accurate regulation of selected harmonic currents so that the rectifier draws balanced and sinusoidal currents from the source, even when the input voltages are unbalanced and contain harmonics. Extensive laboratory tests on a 2 kW prototype system verifies the effectiveness of the proposed control scheme. The last paper presents a new technique for impedance identification of dc and ac power electronic systems, which significantly simplifies the procedure for stability analysis. Recurrent neural networks are used to build dynamic models of the system based on a few signal injections, then the impedance information can be extracted using off-line training and identification algorithms. Both digital simulation and hardware tests were used to validate the technique --Abstract, page iv

A review on DC collection grids for offshore wind farms with HVDC transmission system

Abstract: Traditionally, the internal network composition of offshore wind farms consists of alternating current (AC) collection grid; all outputs of wind energy conversion units (WECUs) on a wind farm are aggregated to an AC bus. Each WECU includes: a wind-turbine plus mechanical parts, a generator including electronic controller, and a huge 50-or 60-Hz power transformer. For a DC collection grid, all outputs of WECUs are aggregated to a DC bus; consequently, the transformer in each WECU is replaced by a power converter or rectifier. The converter is more compact and smaller in size compared to the transformer. Thus reducing the size and weight of the WECUs, and also simplifying the wind farm structure. Actually, the use of offshore AC collection grids instead of offshore DC collection grids is mainly motivated by the availability of control and protection devices. However, efficient solutions to control and protect DC grids including HVDC transmission systems have already been addressed. Presently, there are no operational wind farms with DC collection grids, only theoretical and small-scale prototypes are being investigated worldwide. Therefore, a suitable configuration of the DC collection grid, which has been practically verified, is not available yet. This paper discussed some of the main components required for a DC collection grid including: the wind-turbine-generator models, the control and protection methods, the offshore platform structure, and the DC-grid feeder configurations. The key component of a DC collection grid is the power converter; therefore, the paper also reviews some topologies of power converter suitable for DC grid applications

Kesan penularan wabak Covid-19 terhadap sektor perumahan dari perspektif kemampuan pemilikan rumah

Rumah menjadi hak setiap individu seperti termaktub dalam Universal Declaration of Human Rights 1948 : Everyone has a right to a standard of living adequate for the health and well-being of himself and of his family, including food, clothing, housing and medical care and necessary social services and the right to security in the event of unemployment, sickness, disability, widowhood, old age or the lack of livelihood in circumstances beyond his control. (United Nations, 1948) Kemampuan perumahan menjadi agenda penting bagi majoriti negara di peringkat global. Keperluan manusia untuk mempunyai rumah sebagai keperluan asas yang perlu dipenuhi meletakkan isu kemampuan perumahan sentiada diberi tumpuan dan dibahaskan sepanjang tahun..