1,721,030 research outputs found
Medium Voltage DC integrated power systems for large all electric ships
Get PDFThe Medium Voltage Direct Current (MVDC) distribution represents a promising technology for future shipboard power systems. In such a topic, during the last years, universities and reserch centers have proposed technical solutions to achieve the important targets of MVDC technology, for instance fuel saving, reducing power system weight/space, reconfigurability in case of fault and enhanced power quality. Conversely, the main challenge to face regards voltage control, which has to be capable for guaranteeing the paramount requirement of stability. In regards to this aspect, a possible instability may arise due to the presence of high-bandwidth controlled load converters, modeled as Constant Power Loads (CPLs). Such non-linear loads are seen from the system as negative incremental resistances which are the cause of voltage instability in presence of a perturbation (e.g. load connection, generating system disconnection).
The thesis has been realized in the Laboratory of Grid Connected and Marine Electric Power Generation and Control (EPGC Lab.), at the University of Trieste. The aim is to develop voltage control strategies to solve the CPL issue in a realistic multi-converter MVDC Integrated Power System, which is conveniently designed considering a real cruise line MVAC distribution. In such a system, voltage instability may be engage by different approaches, exploiting plant solutions (addition of dedicated filters, addition of energy storage devices) or control solutions. The latter is followed in this thesis: in this case voltage actuators (DC/DC power converters) are used to compensate for the voltage instability: therefore, on one hand (load side) power converters are responsible for the non-linear loads’ issue but, on the other (generators side), they may be utilized to contribute in its solution, thus ensuring a stable behavior. The stabilizing approach foresees the employment of different control techniques, whose theory is focused in the thesis. Starting from the simplier State Feedback (SF), two techniques are mostly studied in the multi-converter arrangement, i.e the Active Damping (AD) and the Linearization via State Feedback (LSF).
The AD is a control method to transiently increase the filter resistances in order to damp the voltage oscillations: one of the main pros is the simple implementation on digital controllers, whereas the drawback regards its limited stabilizing action. Therefore, strategies based on Active Damping are to be used to stabilize non-critical systems. Conversely, LSF is a well-performing technique to obtain a notable cancellation of the non-linearities related to CPLs, by exploiting the DC/DC converters to apply a proper non-linear control function. Against the notable capability in stabilizing critical systems, great attention is to be paid in control function’s estimation: inaccurate system parameters or errors in controller’ feedbacks may invalidate the LSF approach, determining a partial loop-cancellation, therefore a non-linear resulting power system. Final simulations are aimed in testing AD and LSF, implemented in global and local control strategies: the former strategy has the purpose to solve the instability directly on CPLs, whereas the second one ensures the bus stability
The WBM Reconfiguration to Prevent the Instability on DC Shipboard Microgrids
Get PDFMost innovative DC shipboard microgrids are designed to feed high-performance loads with advanced flexibility feature. The onboard loads not only require great amounts of power, but also their management results dynamically demanding. To this aim, tightly controlled power converters are employed to supply the loads by the filtered DC distribution. In such an islanded system, high-bandwidth converters and LC filters can negatively interact thus finally jeopardizing the ship operation. Smart procedures are to be conceived to preserve the system stability by reconfiguring the online shipboard loads. As the system stability depends on power/bandwidth of each load, the Weighted Bandwidth Method (WBM) is adopted to aggregate the effect of the several controlled loads. Once the WBM identifies two controlled loads as representative of the total dynamics demand, a 3D map results consequent. It reveals the loads combination to be fed without impairing the stability. If the Power Management System (PMS) exploits the outcomes from the 3D map to perform planned reconfigurations, the onboard stable operation is certainly ensured
Analytical Approach to Define the Stability Boundaries in Controlled DC Microgrids
No full textThe DC technology is envisioned as the most promising alternative for the design of the new generation of shipboard power systems. The superior flexibility that the DC grids guarantee in respect to their AC counterpart make them the ideal candidate for the integration of demanding and high power loads. One of the components that make it possible to enhance the dynamics performance of such grids are definitely the power electronics converters. These fully controllable interfaces make it possible to easily coordinate the combination of generating sources, storages and loads, while guaranteeing adequate power quality. The price to pay for guaranteeing performing controls is the possibility to jeopardize the power system. Indeed, one of the risks of not properly controlled DC grids is the insurgence of voltage instability, an event that can possibly lead to a ship blackout. Considering systems with many converters the study of the voltage stability is not an easy task and certainly not doable with a full analytical approach. This is why this paper proposes a reduced-order approach for the problem to obtain a simplified analytical, yet approximated, expression of the system stability conditions
On the Influence of Switch Inductance in Zonal DC System Stability
No full textMost advanced navy ships are nowadays conceived to attain a totally controlled power grid with high reconfigurability and resiliency. The latter are the key-features of DC zonal microgrids, where the widespread adoption of power electronics ensures the load supply even during critical events, like a zone blackout. In the zonal configuration, a remote-maneuverable DC switch is to be installed on the mutual interconnection among buses to independently provide power to the feeders. As the DC switch is characterized by an intrinsic inductive nature, its presence could be negative in regarding to the DC system stability. Basing on this possible criticality, the paper wants to explore the influence of DC switch inductance on the stability of a zonal DC power system. A convenient modeling will provide a simplified equivalent circuit on which the stability conditions are made evident, thus clarifying the switch effect. Final tests on Hardware In the Loop platform will prove the validity of analytical stability boundaries
Assessment of an Alpine Microgrid in a Ski Resort for Integrating RES and Electrical Mobility
No full textIn the Alps area, the ski-resorts are powered by the electrical distribution network, especially to ensure the snow making operations throughout the ski slopes. Such grids can be characterized by low capacity on one hand, whereas on the other one the line lengths are far from being negligible due to natural obstacles and altitude changes. These aspects result in remarkable voltage drops when feeding several power loads on the low voltage section. Basing on this, a smart redesign of alpine power grids is advisable for enhancing the grid operation, while at the same time enabling electric mobility and renewable energy exploitation. In this context, the evolution towards the alpine microgrid appears consequent for ensuring some important pros, such as power system safety, reliability and sustainability. The present paper is aimed at modeling the electrical distribution system installed in the ski-resort of San Vito di Cadore, Italy. After a power flow analysis, the voltage profiles will be carried out, focusing on bottlenecks and feasible options for the system optimization. Finally, some solutions will be proposed for increasing the power system smartness
Sistemi elettrici integrati con distribuzione in corrente continua per navi a propulsione elettrica
No full textStability-Oriented Analysis of a DC Shipboard Zonal Distribution System
Get PDFThe Medium Voltage Direct Current technology and the flexible zonal topology are the enablers to renovate the onboard power use. The several benefits due to DC zonal electrical distributions are possible only in presence of a smart management of the grid. On one side, the tomorrow DC ships must thus rely on a high-performing control, on the other the related large bandwidths can negatively influence the poles positioning of LC filtered systems. Indeed, a not-concurrent design of filters and control system can provide unsuitable solutions, where even a small perturbation can lead to unstable phenomena. To solve this issue, the integrated design procedure is proposed as effective to assure both power quality and stability target. This paper presents an optimized filter design to ensure the DC system stability by taking into account the control requirements. The new stability-oriented method is adopted to conceive the filtering solutions, later verified through eigenvalues analysis and Hardware-In-the-Loop simulations
Inland waterway gas-fueled vessels: CASM-based electrification of a pushboat for the European network
Get PDFThe peculiarities of the European inland waterway transport are analyzed, and a novel design of a pushboat for barges convoys is proposed and optimized for the Rhine-Danube corridor. To this aim, a hybrid parallel electric propulsion system is adopted with the perspective to define an eco–friendly vessel. The present work is to be intended as the early-stage in the proof-of-concept (POC) for commercial technologies useful for the electrification of pushboats employed in inland waterway navigation. Specifically, the optimal design solution is highlighted by evaluating of proper attribute weights, which determine the degree of closeness among possible solution and the design target. In particular, CASM methodology to minimize CAPEX and OPEX of a pushboat is adopted
Multi-criteria Methodology for the Sustainable Powering of an Industrial DC Microgrid Cluster
No full textIn the most developed economies, the industrial growth cannot be promoted while ignoring the effect on climate change. Therefore, industrial clusters are to be coupled with renewable energy plants in order to minimize the CO2 production. To pursue the sustainability in industries, the most effective approach foresees the widespread installation of photovoltaic modules within the industry boundary. By hypothesizing the presence of a DC microgrid to collect sources-loads, the paper wants to explore a multi-criteria methodology to identify the most convenient renewable plant. Different alternatives are compared by adopting battery energy storage on one hand, by optimizing the PV size on the other. The best solution is declared by intersecting different domains, therefore economic, energetic and environmental outcomes
Considerations on the design of voltage control for multi-machine MVDC power systems on large ships
No full textMedium Voltage Direct Current (MVDC) distribution is an enabling technology for future large ships, e.g. cruise liners or military vessels. In MVDC systems, shipboard loads are normally fed through power-converters directly connected to the MVDC bus. For such systems a key design goal is voltage stability, impaired by the presence of high-bandwidth controlled loads (Constant Power Loads, CPLs). The paper proposes an approach to stabilize the MVDC bus using the generating systems as sources of stabilizing power. Fast controlled DC/DC converters, interfacing generators to MVDC bus, are employed to control it in a stable way and to provide power sharing among the generators. To this aim, an Active Damping method is exploited. A supplementary Linearization via State Feedback control is utilized to stabilize DC/DC load converters feeding particularly impacting CPLs. Proposed controls are verified by means of time-domain numerical simulations. Shipboard feasibility and performance of the proposed control systems are most considered in the work as conclusions
- …
