Robust Decentralized Voltage Tracker of Islanded Multi-DG AC Microgrids Using Invariant Ellipsoids

This chapter develops a robust decentralized voltage tracker for islanded MGs. The proposed controller is robust against the plug and play operation of the MG, loads, and line parameter uncertainties. The problem is solved in the framework of linear matrix inequality (LMI). The proposed robust control represents the load changes and the parameter variations of lines connecting the DGs as a norm-bounded uncertainty. The proposed controller utilizes local measurements from DGs (i.e., it is totally decentralized). Control decentralization is accomplished by decomposing the global system into subsystems. The effect of the rest of the system on a specific subsystem is considered as a disturbance to minimize (disturbance rejection control). The controller is designed by the invariant-sets (approximated by the invariant ellipsoids). Different time-domain simulations are carried out as connecting and disconnected one or more DGs, connecting and disconnecting local loads DGs and transmission line parameters variation.

APPLICATION OF ANALYTICAL SOLUTIONS FOR BENDING BEAMS IN THE METHOD OF MOVEMENT

Introduction: Usually, to analyze statically indeterminate rod systems, the classical displacement method and preprepared tables for two types of rods of the main system are used. A mathematically correct representation of local loads with the use of generalized functions makes it possible to find an accurate solution of the differential equation for the equilibrium of a beam exposed to an arbitrary transverse load. Purpose of the study: We aimed to obtain analytical expressions for functions of deflection, rotation angles, transverse forces, and bending moments depending on four types of local loads for beams with different boundary conditions, so as to apply accurate solutions in the displacement method. Methods: We propose an analytical form of the displacement method to analyze rod structural models. For beams exposed to different types of transverse load (uniformly distributed force, concentrated force, or a couple of forces), accurate analytical solutions were obtained for functions of deflection, bending moments, and transverse forces at different types of beam ends’ restraint. This is possible due to the fact that concentrated load and load in the form of the moment of force can be specified by using unit column functions. By transforming Mohr’s integrals, using integration by parts, we show that the system of canonical equations of the displacement method was obtained based on the Lagrange principle. Results: Based on the analysis of a statically indeterminate frame, the effectiveness of the proposed analytical method is shown as compared with the classical displacement method.

Recommendations for deck primary supporting members design as applied to pillarless construction of ro-ro ships

Статья посвящена вопросам определения размеров набора грузовых стационарных палуб морских стальных судов типа Ro-Ro на ранних стадиях проектирования. В силу большого расстояния между поперечными переборками в случае отсутствия пиллерсов карлингсы палуб не являются опорами для рамных бимсов. Однако, как показывает практика, они всегда включаются в конструктивную схему палубы, так как позволяют разнести локальную нагрузку между соседними рамными бимсами, обеспечивают устойчивость их стенок, а также вовлекаются в работу в составе перекрытия при некоторых сценариях нагружения. В литературе отсутствуют рекомендации по выбору расчётной ширины их присоединенного пояска, расчётных значений изгибающих моментов и перерезывающих сил при восприятии нагрузки от разного типа груза. Исследование выполнялось на примере перекрытия грузовой палубы длиной 64,4 м на основе МКЭ. Были разработаны КЭ-модели палубы в балочной и оболочечно-балочной идеализациях. Вторая модель использовалась для оценки адекватности результата, получаемого на более простой модели. Рассмотрены 8 сценариев нагрузки. При определении ширины присоединенного пояска за величину условного пролёта принималось расстояние между точками, в которых величина изгибающего момента принимает нулевое значение. Показано, что карлингсы активно вовлекаются в работу при частичной загрузке трюма контейнерами в несколько ярусов, а также при работе погрузчика. Расчётная ширина их присоединенного пояска составила 0,60…0,75 расстояния между карлингсами при действии нагрузки от колёсной техники и оказалась близка к этому расстоянию при восприятии нагрузки от контейнеров при их поперечной укладке. Авторами предложено в качестве первого приближения значение расчётного изгибающего момента для карлингсов определять в долях от соответствующего значения для рамных бимсов. The paper deals with a design of deck primary structures of Ro-Ro vessels at early design stages. Due to the large distance between transverse bulkheads, in the case of no pillar construction, deck girders cannot be considered as supports for deck transverses. The common practice however, is to provide deck structures with deck girders anyway. It helps to distribute the local loads between transverses and to ensure the stability of deck transverses web plates. In addition, for a localized loads on deck structures girders to some extent contribute to local strength of the deck. Practically, deck girder scantlings are usually larger than those based on the minimum thickness, web depth and slenderness requirements of classification society rules. There are no publications proposing recommendations for deck girders design in pillarless structures of ro-ro ships at the early stages. Prescriptive recommendations should primarily include design bending moment value and effective breadth of the attached plate in different loading scenarios. The results presented in this paper are based on the linear finite element (FE) analysis of Ro-Ro deck having a length of 64.4 meters. Since the goal of the study was to develop recommendations for structural design aligned with prescriptive requirements of RS rules the research is provided with beam analysis carried out for 8 different loading scenarios. All of the reference calculations were made in FESTA-2020 software developed in SMTU as a part of CAD/СAE software ALMAZ-K. Verification is made with more sophisticated shell model analysis carried out in ANSYS with similar assumptions. The effective breadth of deck girders attached plate is calculated considering a distance between zero bending moment points as a nominal span. It is shown that the deck girders are highly stressed in loading cases with stacked containers and working fork lift. The calculated width of their attached plate which is in range from 0.60 to 0.75 of the distance between girders S under the load from the wheeled vehicles turns out to be close to Sin case of loading of transversely stacked containers. The authors propose to determine value of the design bending moment for deck girders at the early stages depending on span and loading of deck transverses.

Design of protection and control scheme for hybrid nanogrid

Nanogrid is “The new ray of hope” for people living in remote isolated locations as well as where power supply reliability is poor. A nanogrid is a small power capacity distribution system with the ability to operate standalone or with a utility grid. It consists of local power production supplying local loads and energy storage systems. In this paper, an innovative inverter design is presented, which converts the power in a single stage. It is superior to the traditional two-stage inverter system and can supply hybrid loads (AC and DC loads) with a single input. System AC and DC bus voltages are regulated under both steady-state and dynamic load variation conditions in the nanogrid. Simulation results are presented which confirm the suitability of the inverter and its control strategy for a hybrid nanogrid system.

Microgrid modeling for contribution to the frequency control of power system

Recently, Distributed Energy Resources (DERs) are becoming more attractive to supply local loads under the concept of microgrids. These new parts of the power system have basically different dynamics compared with conventional power plants. Most of them are connected to the grid by power electronic interfaces, and their dynamic is determined by their controller. In this paper, the effect of the increased penetration of DERs on the load frequency problem of power systems is studied. The DERs of microgrids in each area are controlled to change their active power at Point of Common Coupling (PCC) after a disturbance in the power system. It is shown that with appropriate control of DERs in microgrids, the frequency deviation of the power system will decrease and the stability margin can be increased.

Operating Behavior of Sliding Planet Gear Bearings for Wind Turbine Gearbox Applications—Part I: Basic Relations

The application of sliding planet gear bearings in wind turbine gearboxes has become more common in recent years. Assuming practically applied helix angles, the gear mesh of the planet stage causes high force and moment loads for these bearings involving high local loads at the bearing edges. Specific operating behavior and suitable design measures to cope with these challenging conditions are studied in detail based on a thermo-hydrodynamic (THD) bearing model. Radial clearance and axial crowning are identified as important design parameters to reduce maximum pressures occurring at the bearing edges. Furthermore, results indicate that a distinct analysis of the gear mesh load distribution is required to characterize bearing operating behavior at part-load. Here, operating conditions as critical as the ones reached at nominal load might occur. Wear phenomena can improve the shape of the gap in the circumferential as well as in axial direction incorporating a significant reduction of local maximum pressures. The complexity of the combination of these aspects and the additionally expected impact of structure deformation gives an insight into the challenges in the design processes of sliding planet gear bearings for wind turbine gearbox applications.

AI Based system Performance Enhancement Fed by BESS with grid Integration

The electric lattice should have the generation ability to satisfy the needs of power consumers. The point of this examination is to research how the force limit and situation of a battery energy stockpiling framework influence the force quality in a frail force lattice with variable loads. The system performance is expected to be improved by designing a compensator in line with the variable loads and whose control system is guided by artificial intelligence (AI) based techniques and algorithms. The grid performance enhancement shall be done in terms of power factor and active power improvement with stable outputs. The analysis has been focused on the low tension line (local loads) after the grid connection where the system is also driving the electric drive and reactive loads at the high tension line. The effect has been studied on of 400V phase to phase load line. The infers that the BESS framework is made effective for driving the heaps having improved dynamic force yield at its terminal. The voltage accessible has been made less mutilated to 3.07% and the THD level in current yield has also come down to 2.93%.

Run-of-the-River Hydro-PV Battery Hybrid System as an Energy Supplier for Local Loads

Hybrid hydro energy systems are usually analysed with pumped hydro storage systems, which can facilitate energy accumulation from other sources. Despite the lack of water storage, run-of-the-river hydropower plants are also attractive for hybrid systems owing to their low investment cost, short construction time, and small environmental impact. In this study, a hybrid system that contains run-of-the-river small hydro power plants (SHPs), PV systems, and batteries to serve local loads is examined. Low-power and low-head schemes that use variable-speed operation are considered. The novelty of this study is the proposal of a dedicated steady-state model of the run-of-the-river hydropower plant that is suitable for energy production analysis under different hydrological conditions. The presented calculations based on a real SHP of 150 kW capacity have shown that a simplified method can result in a 43% overestimation of the produced energy. Moreover, a one-year analysis of a hybrid system operation using real river flow data showed that the flow averaging period has a significant influence on the energy balance results. The system energy deficiency and surplus can be underestimated by approximately 25% by increasing the averaging time from day to month.