• Energy Research

With penetration of plug-in electrical vehicles (PEV), fast charging stations (FCS) are expected to constitute be a considerable portion of total energy consumptions. This paper proposes a hybrid power coordinating control strategy implemented in a fast charging station equipped with flywheel energy storage system, in order to provide a comfortable charging circumstance for PEV as well as some ancillary services (active power and reactive power support) for grid by four-quadrate bidirectional operation. The distributed bus signaling (DBS) method is employed for coordinating the control between grid converter and flywheel converter to avoid the highly dependent on communication. Finally, the experimental results based on dSPACE1006 are presented to show the effectiveness of the proposed control structure.

Harmonics have been considered as one of the major issues in modern power grids. Considering the high penetration level of power electronic converter interfaced distributed generators (DGs), it is of interest to provide ancillary services through DG interfacing converters, such as harmonic compensation. In case of that, multiple DG interfacing converters are utilized to compensate harmonics, and the compensation effort should be properly shared among these converters. However, it is rarely considered in existing literatures that converters operating in different modes, such as voltage-controlled mode (VCM) and current-controlled mode (CCM), need to cooperatively provide the compensation function. Aiming at this objective, this paper proposes a unified voltage harmonic mitigation strategy for VCM and CCM converters with high harmonic current sharing accuracy. Another advantage of the proposal is that grid-side and load-side current measurements are avoided which reduces implementation cost. Experimental results are presented to demonstrate the effectiveness of the method.

In this paper, we propose a secondary consensus-based control layer for current sharing and voltage bal-ancing in DC microGrids (mGs). To this purpose, we assume that Distributed Generation Units (DGUs) areequipped with decentralized primary controllers guaranteeing voltage stability. This goal can be achievedusing, for instance, Plug-and-Play (PnP) regulators, which allow one to analyze the behavior of the closed-loop mG by approximating local primary control loops with either unitary gains or first-order transferfunctions. Besides proving exponential stability, current sharing, and voltage balancing, we describe howto design secondary controllers in a PnP fashion when DGUs are added or removed. Theoretical results arecomplemented by simulations, using a 7-DGUs mG implemented in Simulink/PLECS, and experiments ona 3-DGUs mG.

Next generation power management at all scales is highly relying on the efficient scheduling and operation of different energy sources to maximize efficiency and utility. The ability to schedule and modulate the energy storage options within energy systems can also lead to more efficient use of the generating units. This optimal planning and operation management strategy becomes increasingly important for off-grid systems that operate independently of the main utility, such as microgrids or power systems on marine vessels. This work extends the principles of optimal planning and economic dispatch problems to shipboard systems where some means of generation and storage are also schedulable. First, the question of whether or how much energy storage to include into the system is addressed. Both the storage power rating in MW and the capacity in MWh are optimized. Then, optimal operating strategy for the proposed plan is derived based on the solution from a mixed-integer nonlinear programming (MINLP) problem. Simulation results showed that including well-sized energy storage options together with optimal operation management of generating units can improve the economic operation of the test system while meeting the system’s constraints.

Abstract Parallel-wiring cables are often used in multi-phase AC aircraft Electrical Power Systems (EPSs). However, it complicates the ac resistance estimation. To solve this issue, an analytical resistance calculation method for parallel-wiring cables in multi-phase EPS was proposed. Firstly, the existing calculation formula of proximity factor was optimized, and the calculation error was reduced from 16% to 2% when two conductors are close to each other. Afterwards, the superposition effect on current density distribution between multi-conductors was considered based on orthogonal decomposition method, and the position of the equivalent charged points were easily determined. Finally, the ac resistance calculation formula was derived according to characteristics of parallel-wiring strategy, and the general ac resistance calculation methods of multi-phase parallel-wiring cables were presented. The proposed approach considerably enhances the applicability of ac resistance analytical calculation method for multi-conductor cables. Thanks to the accuracy of the proposed method, it can be used in many cases to avoid case-by-case simulation work and facilitate efficient system design and analysis.

Microgrids are energy systems that can work independently from the main grid in a stable and self-sustainable way. They rely on energy management systems to schedule optimally the distributed energy resources. Conventionally, the main research in this field is focused on scheduling problems applicable for specific case studies rather than in generic architectures that can deal with the uncertainties of the renewable energy sources. This paper contributes a design and experimental validation of an adaptable energy management system implemented in an online scheme, as well as an evaluation framework for quantitatively assess the enhancement attained by different online energy management strategies. The proposed architecture allows the interaction of measurement, forecasting and optimization modules, in which a generic generation-side mathematical problem is modeled, aiming to minimize operating costs and load disconnections. The whole energy management system has been tested experimentally in a test bench under both grid-connected and islanded mode. Also, its performance has been proved considering severe mismatches in forecast generation and load. Several experimental results have demonstrated the effectiveness of the proposed EMS, assessed by the corresponding average gap with respect to a selected benchmark strategy and ideal boundaries of the best and worst known solutions.

This paper presents the system integration and hierarchical control implementation in an inverter-based microgrid research laboratory (MGRL) in Aalborg University, Denmark. MGRL aims to provide a flexible experimental platform for comprehensive studies of microgrids. The structure of the laboratory, including the facilities, configurations and communication network, is first introduced. The complete control system is based on a generic hierarchical control scheme including primary, secondary and tertiary control. Primary control loops are developed and implemented in digital control platform, while system supervision, advanced secondary and tertiary management are realized in a microgrid central controller. The software and hardware schemes are described. Several example case studies are introduced and performed in order to achieve power quality regulation, energy management and flywheel energy storage system control. Experimental results are presented to show the performance of the whole system