Asymmetrical Pulse-Width Modulation Strategy for Current-Fed Dual Active Bridge Bidirectional Isolated Converter Applied to Energy Storage Systems

This paper proposes an asymmetrical pulse-width modulation (PWM) strategy for current-fed dual-active bridge (CFDAB) converters applied to energy storage systems (ESS). The ESS application considers low-voltage and high-capacity batteries, for low-power applications, such as data centers, residential photovoltaic systems (PV), and uninterruptable power supplies (UPS). The proposed modulation permits the use of an isolation transformer with negligible leakage inductance and, therefore, avoids the use of auxiliary circuits such as snubbers, active-clamp, or resonant cells. Hence, the converter implementation is simplified. The modulation also benefits the design of the control system because the converter can be modeled and controlled using simple strategies. A straightforward, large-signal model for the battery charge mode, which is valid over all the operation range of the converter, is obtained. Also, the converter operates with a fixed dc bus voltage on both charge and discharge modes. These characteristics represent a significant advantage when the CFDAB with PWM modulation is compared with phase-shifted or frequency modulations, commonly applied in these converters

Chromium removal on chitosan-based sorbents - An EXAFS/XANES investigation of mechanism

International audienceChitosan is known to be a good sorbent for metal-containing ions as the presence of amino groups and hydroxyl functions act as effective binding sites. Its crosslinking, employing glutaraldehyde or epichlorohydrin, may change the sorption properties (sorption capacity or diffusion properties) of this biopolymer, since the available functional groups are different in each case. X-ray absorption spectroscopy (XAS), including extended X-ray absorption fine structure (EXAFS) and X-ray absorption near-edge structure (XANES), Fourier-transformed infrared spectroscopy with attenuated total reflectance device (FTIR-ATR) was used along with speciation diagrams, in order to identify the binding groups involved in chromate sorption and its mechanisms. In pristine chitosan and epichlorohydrin-crosslinked chitosan membranes, amino groups are most likely responsible for adsorption, although the contribution of hydroxyl groups cannot be excluded (especially for metal-sorbent stabilization). In this case, when adsorbed about 70% of chromate ions remain in the Cr(VI) oxidation state. In the case of glutaraldehyde-crosslinked membranes, the functional groups involved are different. Carbonyl groups and imino bonds resulting from the reaction of the crosslinking agent and amino groups - may be involved in the adsorption mechanism. Additionally, a higher fraction of chromate anions, around 44% are reduced to Cr(III) oxidation state in loaded sorbent. The presence of free aldehyde groups may explain this partial reduction

Chromium removal on chitosan-based sorbents – An EXAFS/XANES investigation of mechanism

Chitosan is known to be a good sorbent for metal-containing ions as the presence of amino groups and hydroxyl functions act as effective binding sites. Its crosslinking, employing glutaraldehyde or epichlorohydrin, may change the sorption properties (sorption capacity or diffusion properties) of this biopolymer, since the available functional groups are different in each case. X-ray absorption spectroscopy (XAS), including extended X-ray absorption fine structure (EXAFS) and X-ray absorption near-edge structure (XANES), Fourier-transformed infrared spectroscopy with attenuated total reflectance device (FTIR-ATR) was used along with speciation diagrams, in order to identify the binding groups involved in chromate sorption and its mechanisms. In pristine chitosan and epichlorohydrin-crosslinked chitosan membranes, amino groups are most likely responsible for adsorption, although the contribution of hydroxyl groups cannot be excluded (especially for metal-sorbent stabilization). In this case, when adsorbed about 70% of chromate ions remain in the Cr(VI) oxidation state. In the case of glutaraldehyde-crosslinked membranes, the functional groups involved are different. Carbonyl groups and imino bonds – resulting from the reaction of the crosslinking agent and amino groups – may be involved in the adsorption mechanism. Additionally, a higher fraction of chromate anions, around 44% are reduced to Cr(III) oxidation state in loaded sorbent. The presence of free aldehyde groups may explain this partial reduction1433412417COORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIOR - CAPESFUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESPsem informação2004/13517-

Hybrid Inverter and Control Strategy for Enabling the PV Generation Dispatch Using Extra-Low-Voltage Batteries

This paper proposes a dispatchable photovoltaic (PV) hybrid inverter for output power tracking without any dependency on the converter’s efficiency and with no power closed loop. The system uses an extra-low-voltage battery energy storage system (BEES) based on a Li-ion battery pack to be applicable for use inside homes and other installations close to the end-user. A bidirectional isolated current-fed dual-active bridge (CF-DAB) converter associated with the batteries provides a wide conversion voltage ratio and ensures safety for the users. The proposed control system shares the DC bus voltage controller between the ac grid interfacing converter (AC-DC) and CF-DAB (DC-DC), eliminating the converter’s efficiency in the reference equations. When dispatchable power is not required, or according to the user’s request, the battery’s charge/discharge current can be specified. A disturbance rejection technique avoids low-frequency current ripple on the battery side. It contributes to the battery’s lifespan. Experimental results presenting the dc bus voltage control, current disturbance rejection, and power dispatching are included to validate the proposal

Hybrid Inverter and Control Strategy for Enabling the PV Generation Dispatch Using Extra-Low-Voltage Batteries

This paper proposes a dispatchable photovoltaic (PV) hybrid inverter for output power tracking without any dependency on the converter’s efficiency and with no power closed loop. The system uses an extra-low-voltage battery energy storage system (BEES) based on a Li-ion battery pack to be applicable for use inside homes and other installations close to the end-user. A bidirectional isolated current-fed dual-active bridge (CF-DAB) converter associated with the batteries provides a wide conversion voltage ratio and ensures safety for the users. The proposed control system shares the DC bus voltage controller between the ac grid interfacing converter (AC-DC) and CF-DAB (DC-DC), eliminating the converter’s efficiency in the reference equations. When dispatchable power is not required, or according to the user’s request, the battery’s charge/discharge current can be specified. A disturbance rejection technique avoids low-frequency current ripple on the battery side. It contributes to the battery’s lifespan. Experimental results presenting the dc bus voltage control, current disturbance rejection, and power dispatching are included to validate the proposal