Cost-Optimized Control of DC Microgrids based on Characteristic Diagrams

This paper presents a novel approach for an energy control of a DC microgrid. It combines decentralized grid management and energy management. For this purpose, the conventional voltage droop curves are extended to a characteristic diagram with electricity costs as a further dimension. The support points of these characteristic diagrams are then optimized with a particle swarm optimizer. The target criterion of this optimization is a monetary cost function, that takes several effects, such as depth of discharge, on the operating costs into account. The optimized characteristic diagrams are designed more robust by a sensitivity analysis. The proposed method has been tested successfully in simulations and experiment and was always more cost-efficient than the initial characteristics diagram

Decentralized Cost-Optimized Fuzzy Control of DC Microgrids

This paper presents a novel method for designing a decentralized fuzzy controller for DC microgrids, aiming to reduce operating costs. Therefore, a classical fuzzy control is created for each power supplying grid user based on the voltage droop control. The control of the active rectifier is then extended with respect to the electric costs as an additional input. The input membership functions of this controller are in a next step optimized with a genetic algorithm, whereas two different approaches were used: first, only the membership function of the rectifier was optimized, secondly, the energy storage system was added to the optimization. The optimization was performed in terms of minimizing the operative costs of the DC microgrid. This method and its results were in the end compared with the optimized characteristic diagrams presented in [1]. These diagrams were an extension of the voltage droop curves and the optimization was also based on the operating costs of the grid. Results achieved with the new concept are as good as in the previously presented characteristic diagrams approach. In addition optimization time is reduced significantly (up to 50 times) and the definition of membership functions is more handy

An improved voltage compensation approach in a droop-controlled DC power system for the more electric aircraft

This paper proposes an improved voltage regulation method in multi-source based DC electrical power system in the more electric aircraft. The proposed approach, which can be used in terrestrial DC microgrids as well, effectively improves the load sharing accuracy under high droop gain circumstance with consideration of cable impedance. Since no extra communication line and controllers are required, it is easily implemented and also increases the system modularity and reliability. By using the proposed approach the DC transmission losses can be reduced and system stability is not deteriorated for normal and fault scenarios. In this paper optimal droop gain settings are investigated and the selection of individual droop gains as well as the proportional power sharing ratio has been described. Experimental results validate the effectiveness of the proposed method

Future of electromechanical switchgear

The current development of the electrical networks towards a DC system imposes certain changes in the design and functionality of several network components. This paper aims to offer an overview of the challenges and the opportunities that are raised by the DC system over the electromechanical switchgear in order to identify its future path in the electrical network. The paper starts with a review process of the previous statements regarding the future of the low-voltage (LV) electromechanical switchgear. In the second part, the existing developments in the LV technology towards a mixed (centralized and decentralized) DC grid are presented. The third part presents the main influencing factors and the developments in the classic electromechanical switchgear as well as in the relatively new switchgear technologies represented by the hybrid and power electronic switches. Following, several questions concerning the standardization and the DC ageing behaviour of the insulating materials will be presented and discussed. The last part will present the conclusions of the current overview

A novel decentralized economic operation in islanded AC microgrids

Droop schemes are usually applied to the control of distributed generators (DGs) in microgrids (MGs) to realize proportional power sharing. The objective might, however, not suit MGs well for economic reasons. Addressing that issue, this paper proposes an alternative droop scheme for reducing the total active generation costs (TAGC). Optimal economic operation, DGs’ capacity limitations and system stability are fully considered basing on DGs’ generation costs. The proposed scheme utilizes the frequency as a carrier to realize the decentralized economic operation of MGs without communication links. Moreover, a fitting method is applied to balance DGs’ synchronous operation and economy. The effectiveness and performance of the proposed scheme are verified through simulations and experiments

Power-Electronic-Based DC Distribution Systems for Electrically Propelled Vessels: A multivariable Modeling Approach for Design and Analysis

The benefits of using power-electronic-based dc distribution systems in electrically propelled vessels are well known. However, some aspects must be deeply analyzed to guarantee a safe, robust, and stable system by design. This paper presents a multivariable dc distribution system mathematical model, where all the transmission lines and filters impedances are considered. The model has been tackled under a holistic approach in which the average small-signal model of the drives/converters can be easily added and “connected” to the main grid model. The stability and power quality analysis, as well as the design and tuning of controls and active damping strategies, can be conducted through this mathematical model at low computational cost. In this paper, the usefulness of this model in the early design stages is presented through its application over a realistic design scenario. Moreover, the performance of the proposed model is proven into a real test bench, which presents a configuration and architecture quite close to the one used in a real vessel. The carried out tests prove the suitability of the proposed model, becoming a significant tool to get an improved design

A Comparative Study on the Influence of DC/DC-Converter Induced High Frequency Current Ripple on Lithium-Ion Batteries

Modern battery energy systems are key enablers of the conversion of our energy and mobility sector towards renewability. Most of the time, their batteries are connected to power electronics that induce high frequency current ripple on the batteries that could lead to reinforced battery ageing. This study investigates the influence of high frequency current ripple on the ageing of commercially available, cylindrical 18,650 lithium-ion batteries in comparison to identical batteries that are aged with a conventional battery test system. The respective ageing tests that have been carried out to obtain numerous parameters such as the capacity loss, the gradient of voltage curves and impedance spectra are explained and evaluated to pinpoint how current ripple possibly affects battery ageing. Finally, the results suggest that there is little to no further influence of current ripple that is severe enough to stand out against ageing effects due to the underlying accelerated cyclic ageing