16 research outputs found
A Simplified Model for the Battery Ageing Potential Under Highly Rippled Load for Battery Management and Active Degradation Control
Whereas in typical standardized tests batteries are almost exclusively loaded
with constant current or relatively slowly changing cycles, real applications
involve rapid load ripple, which do not contribute to the net energy. The trend
to reduced filter capacitors and even dynamically reconfigurable batteries
further increases the ripple. The influence of rippled load on lithium
batteries is therefore receiving increased attention. According to recent
studies, accelerated ageing strongly depends on the frequency of the ripple. We
use electrochemical models to derive a highly simplified regression model that
catches the asymptotic behavior and allows parameter identification and
calibration to specific cells. The model allows quantitative monitoring of the
additional ageing due to ripple current in battery management systems.
Furthermore it enables active control of the ageing potential by influencing
the frequency content in modern battery systems, such as reconfigurable
batteries.Comment: 7 page
Ageing Mitigation and Loss Control Through Ripple Management in Dynamically Reconfigurable Batteries
Dynamically reconfigurable batteries merge battery management with output
formation in ac and dc batteries, increasing the available charge, power, and
life time. However, the combined ripple generated by the load and the internal
reconfiguration can degrade the battery. This paper introduces that the
frequency range of the ripple matters for degradation and loss. It presents a
novel control method that reduces the low-frequency ripple of dynamically
reconfigurable battery technology to reduce cell ageing and loss. It
furthermore shifts the residual ripple to higher frequencies where the lower
impedance reduces heating and the dielectric capacitance of electrodes and
electrolyte shunt the current around the electrochemical reactions.Comment: 8 pages, 8 figure
A proposed single-phase five-level PFC rectifier for smart grid applications: an experimental evaluation
The use of PFC rectifiers has assumed an increasingly preponderance, contributing in a decisive way to improve the power quality indices, since they allow to operate with sinusoidal current on the ac side and with controlled voltage on the dc side. In this paper is proposed a novel PFC rectifier that allows five levels of voltage. As noted in the paper, it presents a number of interesting advantages when compared to the conventional five level PFC rectifier, mainly because it requires less passive and active semiconductors to produce the different voltage levels and requires less hardware resources to implement the gate driver circuits. The proposed five level PFC (5L PFC) rectifier operates in boost mode and has a single dc link (although with a midpoint to achieve the various levels), being an important feature for applications in smart grids (e.g., smart electrical appliances and electric mobility chargers). The key topics of the 5L PFC rectifier are addressed and discussed based on the analysis of the principle of operation. As current control strategy it was adopted the model predictive control. Experimental results in steady and transient state were considered for an effective validation of the 5L PFC rectifier, verifying the operation with: sinusoidal current on the ac side; multi level operation with five levels; controlled dc link voltage.FCT - Fundação para a Ciência e Tecnologia within the Project Scope: UID/CEC/00319/2019. This work has been supported by FCT Project newERA4GRIDs PTDC/EEI-EEE/30283/2017 and by ERDF - European Regional Development Fund through the Operational Programme for Competitiveness and Internationalisation - COMPETE 2020 Programme, and by National Funds through the Portuguese funding agency, FCT, within project. Mr. Tanta was supported by FCT PhD grant with a reference PD/BD/127815/2016
Review of Five-Level Front-End Converters for Renewable Energy Applications
Provisional fileWith the objective of minimizing environment and energy issues, distributed renewable energy sources have reached remarkable advancements along the last decades, with special emphasis on wind and solar photovoltaic installations, which are deemed as the future of power generation in modern power systems. The integration of renewable energy sources into the power system requires the use of advanced power electronics converters, representing a challenge within the paradigm of smart grids, e.g., to improve efficiency, to obtain high power density, to guarantee fault-tolerance, to reduce the control complexity and to mitigate power quality problems. This paper presents a specific review about front-end converters for renewable energy applications (more specifically the power inverter that interfaces the renewable energy source with the power grid). It is important to note that the objective of this paper is not to cover all types of front-end converters; the focus is only on single-phase multilevel structures limited to five voltage levels, based on a voltage-source arrangement and allowing current or voltage feedback control. The established review is presented considering the following main classifications: (a) Number of passive and active power semiconductors; (b) Fault tolerance features; (c) Control complexity; (d) Requirements of specific passive components as capacitor or inductors; (e) Number of independent or split dc-link voltages. Throughout the paper, several specific five-level front-end topologies are presented and comparisons are made between them, highlighting the pros and cons of each one of them as a candidate for the interface of renewable energy sources with the power grid.Fundação para a Ciência e Tecnologia (FCT
A Generic Scheduling Algorithm for Low-Frequency Switching in Modular Multilevel Converters With Parallel Functionality
Predictive Control of Low-Cost Three-Phase Four-Switch Inverter-Fed Drives for Brushless DC Motor Applications
An Accurate Practical Technique for Real-Time State-of-Charge Estimation of Li-Ion Batteries Using Neural Networks
Compensated State-Space Model of Diode-Clamped MMCs for Sensorless Voltage Estimation
Modular multilevel converters are well known in the energy sector. Generally, their stable operation is at the expense of numerous sensors, communication burden, and computationally expensive balancing strategies that challenge their expansion to cost-driven applications. Hence, introducing a sensorless voltage-balancing strategy with a simple controller is an attractive objective. Diode-clamped modular multilevel converters (MMCs) offer a simple and effective solution by providing a unidirectional balancing path between two modules through a diode. Ideally, the modulation technique should compensate for the lack of bidirectional energy transfer; hence open-loop operation is possible. Although the sensorless operation is desirable to reduce costs, good knowledge of the modules' voltages for system monitoring, and protection functions still improves operation in some applications or is mandatory in others. However, information should not be at the cost of additional sensors and communication bandwidth. This article develops a compensated state-space model for diode-clamped MMCs to estimate module voltages using an optimal estimator without any direct measurement at module levels. The model considers the effect of the diode-clamped branches and their balancing effect, resulting in 30%-50% reduction in estimation error compared to the conventional models using similar estimators. Simulations and experiments further confirm the provided analysis, where the estimator achieves >97.5% accuracy.</p