434,487 research outputs found
Power system analysis / John J. Grainger, William D. Stevenson, Jr.
No full textBased on: Elements of power system analysis, by William D. Stevenson.sventeenth reprint 2011.Includes index.xix, 787 pages. :Covering such topics as power flow, power-system stability and transmission lines, this senior/graduate text teaches the fundamental topics of power system analysis accompanied by discussions and numerous examples
Stability Analysis and Control Design for Hybrid AC-DC More-Electric Aircraft Power Systems
Get PDFThis thesis studies the stability of a more-electric aircraft (MEA) power system with hybrid converters and loads, and proposes a control design method using state feedback. The MEA is aimed to replace the conventional nonelectric power in aircraft with electric power in order to reduce the size and weight of the aircraft power system. This thesis considers a model of the MEA power system consisting of the following components: converters with uncontrolled diodes and controlled rectifiers, ideal constant power loads (CPL), and non-ideal CPL driven by electromechanical actuators. The system has narrow stability range under the conventional two-loop PI control. To improve control performance, a full-state feedback control method is developed that can significantly increase the stability margin of the MEA power system
An Advance Distributed Control Design for Wide-Area Power System Stability
Get PDFThe development of control of a power system that supply electricity is a major concern in the world. Some trends have led to power systems becoming overstated including the rapid growth in the demand for electrical power, the increasing penetration of the system from renewable energy, and uncertainties in power schedules and transfers. To deal with these challenges, power control has to overcome several structural hurdles, a major one of which is dealing with the high dimensionality of the system.
Dimensionality reduction of the controller structure produces effective control signals with reduced computational load. In most of the existing studies, the topology of the control and communication structure is known prior to synthesis, and the design of distributed control is performed subject to this particular structure. However, in this thesis we present an advanced model of design for distributed control in which the control systems and their communication structure are designed simultaneously. In such cases, a structure optimization problem is solved involving the incorporation of communication constraints that will punish any communication complexity in the interconnection and thus will be topology dependent. This structure optimization problem can be formulated in the context of Linear Matrix Inequalities and l1-minimization.
Interconnected power systems typically show multiple dominant inter-area low-frequency oscillations which lead to widespread blackouts. In this thesis, the specific goal of stability control is to suppress these inter-area oscillations. Simulation results on large-scale power system are presented to show how an optimal structure of distributed control would be designed. Then, this structure is compared with fixed control structures, a completely decentralized control structure and a centralized control structure
Power Quality in DC railway systems
Get PDFThe topic of the power quality in railway systems has more and more interest driven by the need of having a reliable, efficient and resilient system. The paper contributes to the identification and cataloguing of transient and power quality events and power quality indices that affect the DC metro and railway systems. Several transient events detecting on-board the 3 kV and 1.5 kV traction units and in a 3 kV substation are presented and described. The behaviour of the amplitude and frequency content of the voltage and current ripple under a particular operating condition is described. The events have been extracted by the measurement campaigns performed in the framework of the European project MyRailS
Control of mineral scaling in power plant recirculating cooling systems using treated municipal wastewater
Get PDFThe global energy demand is projected to increase by 77% from 2006 to 2030 along with a projected 38% increase in freshwater withdrawal for cooling in power industry. Finding alternative sources of water for cooling has become essential for future energy generation in thermoelectric power plants because of water scarcity in many parts of the US. Treated municipal wastewater is considered as one of the most promising alternative water sources because of its geographic distribution and abundant quantity. However, its impaired water quality makes the cooling tower management more challenging. Therefore, effective approaches are required to prevent scaling, corrosion, and biological growth to promote the reuse of treated municipal wastewater as cooling water in power plants.
This study focuses on understanding mineral scale formation and developing effective mitigation methods when using tertiary treated municipal wastewater as power plant cooling makeup. Two types of tertiary-treated municipal wastewater that were evaluated included secondary-treated water with pH adjustment (MWW_pH) and water from secondary-treatment followed by nitrification and sand filtration (MWW_NF). Laboratory-scale studies and pilot-scale cooling systems were used to evaluate mineral scaling formation and inhibition on non-heated surfaces (e.g., pipelines, tower packing, etc.) under conditions relevant to full-scale cooling systems. Results showed that pH adjustment to 7.8 plus the addition of 5 ppm polymaleic acid (PMA) could reduce the scaling significantly with MWW_pH. MWW_NF exhibited little scaling potential, which is related in part to the lower pH and alkalinity in this water. Amorphous calcium phosphate (ACP) was the primary form of mineral scale on non-heated surface with the above two-types of tertiary-treated municipal wastewater.
A bench-scale experimental system was designed to simulate the condenser surface to study the impacts of mineral scaling on the heated surfaces and the effectiveness of proposed scaling control strategies under these conditions. Heated surface favored the formation of hydroxyapatite (HAP), the most thermodynamically stable calcium phosphate, was the main reason for the crystalline fouling with MWW_pH at pH 7.8. 10 ppm PMA addition could suppress the crystalline fouling of MWW_pH at 7.8 to a low level by inhibiting the transformation of amorphous calcium phosphate to hydroxyapatite during the test period. Significant crystalline fouling was identified with MWW_NF at pH 7.2 while pH adjustment to 7.8 resulted in negligible fouling.
The impact of flow velocity on particle deposition was analyzed in a quantitative model, showing positive deposition potential for bulk precipitates at flow velocity of 0.5 and 0.4 m/s while little particulate fouling was theoretically predicted at 0.6 m/s in the test situation. Bench-scale studies were consistent the model prediction, confirming that the model could be used to identify optimal hydrodynamic conditions to control depositions of bulk precipitates.
The mechanism of calcium phosphate scale control by common antiscalants included PMA and 1-hydroxyethane 1,1-diphosphonic acid (HEDP) was elucidated to provide scientific background for the effective scaling mitigation when treated municipal wastewater is used as make-up in thermoelectric power plant cooling systems. Both PMA and HEDP inhibited the transformation of ACP to HAP by preventing the aggregation of ACP particles. However, PMA dispersed the ACP particles mainly through electrostatic repulsive force while hydration force was hypothesized to be the reason for the function of HEDP in dispersion.
The key findings of this study indicate that it is possible to control mineral scaling through direct chemical addition at proper operating conditions when treated municipal wastewater is used as makeup water in the recirculating cooling system. This study not only evaluated scaling control methods in cooling systems, but also revealed the fundamentals of scaling formation and inhibition
Lifecourse social position and D-dimer; findings from the 1958 British birth cohort
Get PDFThe aim is to examine the association of lifecourse socioeconomic position (SEP) on circulating levels of D-dimer. Data from the 1958 British birth cohort were used, social class was determined at three stages of respondents' life: at birth, at 23 and at 42 years. A cumulative indicator score of SEP (CIS) was calculated ranging from 0 (always in the highest social class) to 9 (always in the lowest social class). In men and women, associations were observed between CIS and D-dimer (P<0.05). Thus, the respondents in more disadvantaged social classes had elevated levels of D-dimer compared to respondents in less disadvantaged social class. In multivariate analyses, the association of disadvantaged social position with D-dimer was largely explained by fibrinogen, C-reactive protein and von Willebrand Factor in women, and additionally by smoking, alcohol consumption and physical activity in men. Socioeconomic circumstances across the lifecourse at various stages also contribute independently to raised levels of D-dimer in middle age in women only. Risk exposure related to SEP accumulates across life and contributes to raised levels of D-dimer. The association of haemostatic markers and social differences in health may be mediated by inflammatory and other markers
Magnetic Design Considerations to Improve Non-Linear Characteristics of Inductively Coupled Power Transfer Systems
No full textThe paper discusses the magnetic features of various pick-up arrangements of Inductively Coupled Power Transfer systems. The performance of the standard monorail system containing an E-pickup can be improved by using S- or Z-shaped magnetic circuits. Moreover, in the case of the Z-pickup, it is possible to benefit from the positive mutual coupling if an alternate-direction configuration is adopted
Ultra-Low Idle Power Class-D Amplifier
No full textClass-D amplifiers are widely used in automotive audio systems because of their high efficiency. In modern car sound systems, multiple amplifiers are used to provide good audio effect. However, typical class-D amplifiers have a high idle-power, which can drain the battery quickly. To solve this problem, an ultra-low idle power class-D amplifier is proposed in this thesis. The simulation results show that this amplifier can achieve very low idle power while maintaining competitive linearity and efficiency.Electrical Engineering | Microelectronic
Impact of wind power on the unit commitment, operating reserves and market design
No full textPaper presented at the 2011 IEEE Power and Energy Society General Meeting, San Diego, CA, 24-29 July 2011This article highlights and demonstrates the new requirements variable and partly unpredictable wind power will bring to unit commitment and power system operations.
Current practice is described and contrasted against the new requirements. Literature specifically addressing questions about wind power and unit commitment related power system operations is surveyed. The scope includes forecast errors, operating reserves, intra-day markets, and sharing reserves across interconnections. The discussion covers the critical issues arising from the research.Science Foundation Irelandau, ti, ke, ab, co - TS 10.04.1
Dynamic Reserve Power Point Tracking in Grid-Connected Photovoltaic Power Plants
No full textThis article introduces a dynamic power reserve control methodology called reserve power point tracking (RPPT) for grid-connected photovoltaic (PV) plants. The proposed RPPT methodology is employed to ensure availability of the required power reserve to support the grid and accordingly facilitate high penetration of PV generation in the grid. Implementing this control methodology does not require any extra hardware. The proposed methodology regulates the average PV power dynamically by periodically operating on and off the maximum power point (MPP) in order to inject a constant desired power into the grid. Tracking a desired power reference implies that the proposed methodology is a form of flexible power point tracking (FPPT). However, unlike a traditional FPPT, the proposed methodology also provides updated information of the available maximum PV power. Hence, the RPPT fulfills both FPPT and maximum power point tracking (MPPT) functionalities simultaneously. The proposed methodology extracts the MPP information and uses this information to calculate and regulate the amount of PV reserve power. One of the main advantages of the proposed algorithm is its applicability under partial shading conditions. Its effectiveness is demonstrated by experimental results under changing solar irradiance, grid frequency deviation, and partial shading conditions
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