Design considerations for large space electric power systems

As power levels of spacecraft rise to the 50 to 100 kW range, it becomes apparent that low voltage (28 V) dc power distribution and management systems will not operate efficiently at these higher power levels. The concept of transforming a solar array voltage at 150 V dc into a 1000 V ac distribution system operating at 20 kHz is examined. The transformation is accomplished with series-resonant inverter by using a rotary transformer to isolate the solar array from the spacecraft. The power can then be distributed in any desired method such as three phase delta to delta. The distribution voltage can be easily transformed to any desired load voltage and operating frequency. The reasons for the voltage limitations on the solar array due to plasma interactions and the many advantages of a high voltage, high frequency at distribution system are discussed

Full- & Reduced-Order State-Space Modeling of Wind Turbine Systems with Permanent-Magnet Synchronous Generator

Wind energy is an integral part of nowadays energy supply and one of the fastest growing sources of electricity in the world today. Accurate models for wind energy conversion systems (WECSs) are of key interest for the analysis and control design of present and future energy systems. Existing control-oriented WECSs models are subject to unstructured simplifications, which have not been discussed in literature so far. Thus, this technical note presents are thorough derivation of a physical state-space model for permanent magnet synchronous generator WECSs. The physical model considers all dynamic effects that significantly influence the system's power output, including the switching of the power electronics. Alternatively, the model is formulated in the $(a,b,c)$- and $(d,q)$-reference frame. Secondly, a complete control and operation management system for the wind regimes II and III and the transition between the regimes is presented. The control takes practical effects such as input saturation and integral windup into account. Thirdly, by a structured model reduction procedure, two state-space models of WECS with reduced complexity are derived: a non-switching model and a non-switching reduced-order model. The validity of the models is illustrated and compared through a numerical simulation study.Comment: 23 pages, 11 figure

Switched-battery boost-multilevel inverter with GA optimized SHEPWM for standalone application

This paper presents a boost-multilevel inverter design with integrated battery energy storage system for standalone application. The inverter consists of modular switched-battery cells and a full-bridge. It is multifunctional and has two modes of operation: the charging mode which charges the battery bank and the inverter mode which supplies AC power to the load. This inverter topology requires significantly less power switches compared to conventional topology such as cascaded H-bridge multilevel inverter, leading to reduced size/cost and improved reliability. To selectively eliminate low-order harmonics and control the desired fundamental component, nonlinear system equations are represented in fitness function through the manipulation of modulation index and the Genetic Algorithm is employed to find the optimum switching angles. A 7-level inverter prototype is implemented and experimental results are provided to verify the feasibility of the proposed inverter design

Performance analysis of PV powered multilevel inverter

This article deals with the PV based DC/DC boost chopper integrated nine level inverter. This topology requires 7 switches in minimum to obtain a nine level stepped wave output. So the main objective of this paper is to develop a 9 level AC output using PV based DC/DC boost chopper. In the case of conventional multi-level inverter, 16 switches were utilized and the number of sources needed was also more. Here the proposed system comprises of single PV panel and the switches used are also less. Also PV is integrated with DC/DC boost chopper is used to increase the source input level of the inverter. Using MATLAB platform, the proposed system is simulated with a resistive and inductive load. The similar results are obtained in prototype which validates the designed converter

Index to 1984 NASA Tech Briefs, volume 9, numbers 1-4

Short announcements of new technology derived from the R&D activities of NASA are presented. These briefs emphasize information considered likely to be transferrable across industrial, regional, or disciplinary lines and are issued to encourage commercial application. This index for 1984 Tech B Briefs contains abstracts and four indexes: subject, personal author, originating center, and Tech Brief Number. The following areas are covered: electronic components and circuits, electronic systems, physical sciences, materials, life sciences, mechanics, machinery, fabrication technology, and mathematics and information sciences

Pushing the Boundary of the 48 V Data Center Power Conversion in the AI and IoT Era

openThe increasing interest in cloud-based services, the Internet-of-Things and the take-over of artificial intelligence computing require constant improvement of the power distribution network. Electricity consumption of data centers, which drains a consistent slice of modern world energy production, is projected to increase tremendously during the next decade. Data centers are the backbone of modern economy; as a consequence, energy-aware resource allocation heuristics are constantly researched, leading the major IT services providers to develop new power conversion architectures to increase the overall webfarm distribution efficiency, together reducing the resulting carbon footprint and maximizing their investments. As higher voltage distribution yields lower conduction losses, vendors are moving from the 12 V rack bus to 48 V solutions together with research centers and especially data center developers. As mentioned, efficiency is crucial to address in this scenario and the whole conversion chain, i.e. from the 48 V bus to the CPU/GPU/ASIC voltage, must be optimized to decrease wasted energy inside the server rack. Power density for this converters family is also paramount to consider, as the overall system must occupy as less area and volume as possible. LLC resonant converters are commonly used as IBCs (intermediate bus converters), together with their GaN implementations because of their multiple advantages in efficiency and size, while multiphase-buck-derived topologies are the most common solution to step-down-to and regulate the final processor voltage as they're well-know, easy to scale and design. This dissertation proposes a family of non-isolated, innovative converters capable of increasing the power density and the efficiency of the state-of-the-art 48 V to 1.8/0.9 V conversion. In this work three solutions are proposed, which can be combined or used as stand-alone converters: an ASIC on-chip switched-capacitor resonant voltage divider, two unregulated Google-STC-derived topologies for the IBC stage (48 V to 12 V and 48 V to 4.8 V + 10.6 V dual-output) and a complete 48 V to 1.8 V ultra-dense PoL converter. Each block has been thoroughly tested and researched, therefore mathematical and experimental results are provided for each solution, together with state-of-the-art comparisons and contextualization.The increasing interest in cloud-based services, the Internet-of-Things and the take-over of artificial intelligence computing require constant improvement of the power distribution network. Electricity consumption of data centers, which drains a consistent slice of modern world energy production, is projected to increase tremendously during the next decade. Data centers are the backbone of modern economy; as a consequence, energy-aware resource allocation heuristics are constantly researched, leading the major IT services providers to develop new power conversion architectures to increase the overall webfarm distribution efficiency, together reducing the resulting carbon footprint and maximizing their investments. As higher voltage distribution yields lower conduction losses, vendors are moving from the 12 V rack bus to 48 V solutions together with research centers and especially data center developers. As mentioned, efficiency is crucial to address in this scenario and the whole conversion chain, i.e. from the 48 V bus to the CPU/GPU/ASIC voltage, must be optimized to decrease wasted energy inside the server rack. Power density for this converters family is also paramount to consider, as the overall system must occupy as less area and volume as possible. LLC resonant converters are commonly used as IBCs (intermediate bus converters), together with their GaN implementations because of their multiple advantages in efficiency and size, while multiphase-buck-derived topologies are the most common solution to step-down-to and regulate the final processor voltage as they're well-know, easy to scale and design. This dissertation proposes a family of non-isolated, innovative converters capable of increasing the power density and the efficiency of the state-of-the-art 48 V to 1.8/0.9 V conversion. In this work three solutions are proposed, which can be combined or used as stand-alone converters: an ASIC on-chip switched-capacitor resonant voltage divider, two unregulated Google-STC-derived topologies for the IBC stage (48 V to 12 V and 48 V to 4.8 V + 10.6 V dual-output) and a complete 48 V to 1.8 V ultra-dense PoL converter. Each block has been thoroughly tested and researched, therefore mathematical and experimental results are provided for each solution, together with state-of-the-art comparisons and contextualization.Dottorato di ricerca in Ingegneria industriale e dell'informazioneopenUrsino, Mari

Power Flow Control In Hybrid Ac/Dc Microgrids

Microgrid structures allow for more efficient utilization of renewable resources as well as autonomous operation. Ideally, a centralized controller would be available to allow for an optimizer to take all components into account so that they may collaboratively work towards a shared goal. To this end, a centralized optimization method was developed called the squared slack interior point method. The novelty of this method is that it incorporates the fraction to bound rule to alleviate the known ill-conditioning introduced by utilizing squared slack variables to handle inequality constraints. In addition, this method also allows for inequality constraint violations to be quantified in the same manner that equality constraints are quantified. The proposed method is found to quickly and accurately calculate the optimal power flow and reject solutions that violate the inequality constraints beyond some specified tolerance. Where centralized information is not available, a decentralized method is required. In this method, constrained game theoretical optimization is utilized. However, due to unknown information about remote loads, inconsistent solution among players result in overloaded generators. To alleviate this issue, two perturbation methods are introduced. The first is overload feedback and the second is the perturb and observe squeeze method. In both methods, the goal is to adjust voltage angles and magnitudes to locally manage generator output. Both methods are found to rapidly drive overloaded sources back within their desired tolerances. Moreover, the game theoretical approach is found to have poor performance in the absence of shared load information among players. It is determined that the localized optimizers should be removed to reduce cost and that the operating condition should be perturb starting from the most recently available power flow calculation or starting from the nominal value. Also, to manage voltage stability in the absence of communication, a Hamiltonian approach is implemented for the voltage source rectifier. This approach resulted in a highly stable voltage and a fast response to large step changes. The method was able to maintain the reference dc output at unity power factor while not requiring any information about loading or interconnection

Planning and Operation of DSTATCOM in Electrical Distribution Systems

In present day scenario, it is most essential to consider the maximum asset performance of the power distribution systems to reach the major goals to meet customer demands. To reach the goals, the planning optimization becomes crucial, aiming at the right level of reliability, maintaining the system at a low total cost while keeping good power quality. There are some problems encountered which are hindering the effective and efficient performance of the distribution systems to maintain power quality. These problems are higher power losses, poor voltage profile near to the end customers, harmonics in load currents, sags and swells in source voltage etc. All these problems may arise due to the presence of nonlinear loads, unpredictable loads, pulse loads, sensor and other energy loads, propulsion loads and DG connections etc. Hence, in order to improve the power quality of power distribution systems, it is required to set up some power quality mitigating devices, for example, distribution static synchronous compensator (DSTATCOM), dynamic voltage restorer (DVR), and unified power quality conditioner (UPQC) etc. The goal of this project work is to devise a planning of optimal allocation of DSTATCOM in distribution systems using optimization techniques so as to provide reactive power compensation and improve the power quality

SINGLE PHASE MULTILEVEL INVERTER FOR GRID-TIED PHOTOVOLTAIC SYSTEMS

Multilevel inverters offer many well-known advantages for use in high-voltage and high-power applications, but they are also well suited for low-power applications. A single phase inverter is developed in this paper to deliver power from a residential-scale system of Photovoltaic panels to the utility grid. The single-stage inverter implements a novel control technique for the reversing voltage topology to produce a stepped output waveform. This approach increases the granularity of control over the PV systems, modularizing key components of the inverter and allowing the inverter to extract the maximum power from the systems. The adaptive controller minimizes harmonic distortion in its output and controls the level of reactive power injected to the grid. A computer model of the controller is designed and tested in the MATLAB program Simulink to assess the performance of the controller. To validate the results, the performance of the proposed inverter is compared to that of a comparable voltage-sourced inverter