1,720,990 research outputs found
Spectrum Estimation of Input Current Ripple on a Wide Class of Multilevel Grid-Tied Converters
Full text linkMultilevel (ML) converters are frequently used to implement grid-tied ac-dc conversion systems. Their design may benefit from multiobjective optimization techniques, which typically involves time-consuming circuit simulations in order to obtain input current estimations suitable for input inductor and electromagnetic interference filter design. Herein, a closed-form expression of the input current ripple is derived to ease harmonic content estimations. The proposed approach separates the fundamental grid-current component from its ripple and models the latter like an amplitude modulation, where the modulating signal is its envelope and the carrier is the triangular current waveform. First, a general waveform analysis of ML converters is performed to derive the voltage across the grid-side inductor, then the associated current ripple is modeled. Experimental results on an ML converter prototype are reported to validate the analytical results
AC Grid-interface Bidirectional Buck-Type Converters for DC microgrids: A Comparative Study
No full textThis paper discusses the power converter interface between the 400 VDC DC microgrid and the European threephase grid (400 VLL). Therefore, power bidirectional step-down topologies are considered in this paper. Among the various topologies, three single-stage non-isolated topologies are compared in terms of semiconductor losses, magnetic component size and heat sink size. These topologies are the seven-switch buck converter, the SWISS converter and the Y-converter. The comparative evaluation is conducted for a 10-kW converter targeting residential or small commercial applications
Remaining Useful Lifetime Prediction of Discrete Power Devices by Means of Artificial Neural Networks
Full text linkThis work proposes a deep learning-based model for predicting the lifetime of power devices subjected to power cycling. To this purpose, a neural network based on bidirectional long short-term memory is adopted. The neural network is trained with experimental on-voltage degradation profiles. The application of the proposed method is based on the monitoring of a precursor, that is the on-voltage degradation. According to considered precursor, the model allows predicting the remaining useful lifetime (RUL) of power components. In order to prove the accuracy of the model, TO-247 power devices are stressed under power cycling and their wear-out is experimentally investigated. RUL predicted by the neural network is then compared with the experimental lifetime of power devices. Thanks to the proposed deep learning model, the accuracy in the lifetime estimation improves as long as more information about the state of health of the device under test is acquired
Multidimensional Ripple Correlation Technique for Optimal Operation of Triple Active-Bridge Converters
Full text linkThe paper presents a multidimensional ripple correlation search technique of optimal operating points of triple active bridge (TAB) converters. Such converters present multiple modulation parameters that should be exploited to achieve high operation efficiency. On the other hand, the several degrees of freedom available make the identification of optimal parameters a challenging task, not easily tackled analytically or in closed form. A model-free on-line search method based on the ripple correlation technique is then proposed in this paper. The proposed method finds the optimum modulation parameters of TAB converters utilizing a three-dimensional ripple correlation control. The key property of the proposed solution is the adoption of orthogonal perturbation signals, where the orthogonality is simply obtained using different injection frequencies. The multidimensional correlation technique originally shown herein can be applied to other generic optimization problems. The proposed search is verified through a hardware-in-the-loop validation setup and an experimental prototype rated
Per-Phase Power Controller for Smooth Islanded Transitions in Three-Phase Three-Wire Systems
Full text linkThis manuscript describes the operation of a droop-based controller for three-phase converters in the case of the absence of a neutral connection to the grid. The controller is capable of output power tracking and smooth transitions into the islanded operation. While independent per-phase control of the converter output power is possible if a neutral connection is present, its absence implies additional constraints to be considered. Focusing on this latter case, the controller described herein allows the independent control of the active power at the output of each phase of the converter and a smooth transition to the islanded operation. These features are paramount in future smart power systems, such as smart microgrids, for implementing demand–response, power-flow management, and uninterrupted power operation
Isolated Active Front-End with Integrated Bidirectional GaN Switches for Battery Chargers
No full textA Power and Unbalanced-Current Inverter Controller for Three-Phase Microgrids capable of Islanded Operation
No full textA power and unbalanced-currents controller for three-phase inverters in microgrids is presented herein. Based on symmetric sequences, it allows tracking positive-sequence active and reactive power setpoints and negative-sequence currents setpoints during grid-tied operation. Moreover, if islanded operation occurs, the controller can seamlessly transition into this mode of operation without the need for data exchange (i.e., communication) among the units. Islanded operation with other inverters connected in parallel is fully supported. The control principle and design guidelines are discussed, and experimental results are reported. The controller is useful to provide i) active and reactive power tracking to support demand-response and reactive power compensation, ii) unbalanced current compensation, iii) balanced power injection also in case of unbalanced grid voltages, iv) uninterrupted operation in case of islanding
A Multiport Converter for Flexible Active Balancing in Li-Ion Batteries
Full text linkActive balancing techniques have become increasingly popular for mitigating voltage mismatches in series-connected lithium-ion (Li-ion) batteries. These techniques outperform passive balancing in enhancing battery capacity as the battery ages, leading to an increased lifetime, especially in the electric transportation sector, where residual capacitance plays a crucial role in determining battery lifespan. This study proposes a circuit configuration that utilizes a multiport active half-bridge converter for active cell balancing. The proposed method offers a high degree of flexibility owing to multiple operating modes and a relatively straightforward circuit configuration. Based on the state of charge of each cell, bidirectional power flow can be controlled between two or more arbitrary cells or between the entire battery string and a group of batteries. The proposed approach has been experimentally validated in a battery pack of seven Li-ion cells
A Two-Stage DC-DC Isolated Converter for Battery-Charging Applications
Full text linkThis paper proposes and analyzes a two-stage dc-dc isolated converter for electric vehicle charging applications, where high efficiency over a wide range of battery voltages is required. The proposed conversion circuit comprises a first two-output isolation stage with CLLC resonant structure and a second two-input buck regulator. The transformer of the first stage is designed such that its two output voltages correspond, ideally, to the minimum and maximum expected voltage to be supplied to the battery. Then, the second stage combines the voltages provided by the previous isolation stage to regulate the output voltage of the whole converter. The first stage is always operated at resonance, with the only function of providing isolation and fixed conversion ratios with minimum losses, whereas the second stage allows output voltage regulation over a wide range of battery voltages. Overall, it is shown that the solution features high conversion efficiency over a wide range of output voltages. This paper comprehensively describes the solution, including modeling, analyses, design considerations for the main circuit components (e.g., magnetics, switches), and modulation choices. Experimental results are reported considering a converter module prototype rated 10 kW, input voltage 800 V, and output range 250 V to 500 V, employing silicon-carbide and gallium-nitride semiconductors
Online Loss Reduction of Isolated Bidirectional DC-DC Quad-Active Bridge Converters
No full textIsolated multi-port converters can interconnect several sources and loads operating at different voltage levels by their ports, with the advantage of galvanic isolation and shared magnetics. However, challenges exist for such converters, due to coupling between the ports, the high number of modulation variables, and, in general, their modeling complexity. This paper discusses the operation of the quad-active bridge (QAB) and presents its improved operation by a model-free four-dimensional ripple correlation control (4D-RCC). First, fundamental component analysis of the converter is carried out for the QAB, driving a decoupling matrix that ensures good closed-loop control performance for each port individually. Then, the 4D-RCC is presented in the case of the QAB to perform an online optimization of the overall converter efficiency. The presented optimization exploits orthogonal signals for the simultaneous adjustment of the duty-cycles of the four ports of the QAB. The validation of the analytical results and the proposed optimization approach are reported by Matlab/Simulink simulations and experimental results considering a converter prototype rated 5kW
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