Impedance interaction between islanded parallel voltage source inverters and the distribution network

In an islanded microgrid consisting of parallel-connected inverters, the interaction between an inverter’s output impedance (dominated by the inverter’s filter and voltage controller) and the impedance of the distribution network (dominated by the other paralleled inverters’ output impedances and the interconnecting power cables) might lead to instability. This paper studies this phenomenon using root locus analysis. A controller based on the second derivative of the output capacitor voltage is proposed to enhance the stability of the system. Matlab simulation results are presented to confirm the validity of the theoretical analysis and the robustness of the proposed controlle

Interaction of Retinol with HSA using Spectroscopic Techniques

The interaction between retinol and HSA has been investigated using UV-absorption spectrophotometry, fluorescence spectroscopy and Fourier Transform Infrared (FT-IR) spectroscopy.UV-absorption spectrophotometry showed an increase in the absorption intensity with increasing the molecular ratios of retinol to HSA, it is found that the value of the binding constant is estimated to be1.7176×102 M-1. FTIR spectroscopy is used in the mid infrared region with Fourier self deconvolution, second derivative, difference spectra, peak picking and curve fitting were used to determine the effect of Retinol on the protein secondary structure in the amides I, II and Ill regions. Analysis of FTIR absorbance spectra is found that the intensity of the absorption bands increased with increasing the molecular ratios of retinol, however from the deconvoluted and curve fitted spectra found that the absorbance intensity for α-helix decreases relative to β-sheets, this decrease in intensity is related to the formation of H- bonding in the complex molecules

Comparative studies on the interactions between human serum albumin, bovine serum albumin and cholesterol: ftir and fluorescence spectroscopy

The interaction of the human serum albumin (HSA), bovine serum albumin (BSA) with cholesterol has been investigated. The basic binding interaction was studied by FTIR and fluorescence spectroscopy. From spectral analysis cholesterol showed a strong ability to quench the intrinsic fluorescence of HSA and BSA through a static quenching mechanism. The binding constant (k) between HSA and cholesterol is estimated to be K=2.14 × 103 M-1 at 293 K while between BSA and cholesterol is estimated to be K=.1.12 × 103 M-1 at the same temperature. FTIR spectroscopy with Fourier self-deconvolution technique was used to determine the protein secondary structure and cholesterol binding mechanisms. The observed spectral changes indicate a higher percentage of H-bonding between cholesterol and -helix compared to the percentage of H-bonding to cholesterol and -sheets.This work is supported by the German Research Foundation DFG grant No. DR228/24-

DC link voltage control during sudden load changes in AC microgrids

Parallel inverters in AC microgrids can achieve accurate power sharing using droop control. However, different grid line impedances will result in different transient power and thus different energy being delivered or absorbed by the inverters during sudden load changes. This might lead the DC link voltage to rise beyond the trip limit causing the inverter to shut down, which reduces the reliability of the whole microgrid. This paper investigates the effect of the mismatch in line impedances on the stability of the DC link voltage during a sudden load changes and proposes a scheme to control the DC link voltage during disturbances. Simulation and experimental results are presented to verify the efficacy of the proposed controller

Assessment of Supercapacitor performance in a hybrid energy storage system with an EMS based on the discrete wavelet transform

This is the author accepted manuscript.When battery and supercapacitor (SC) Energy Storage Systems (ESSs) coexist in electric vehicles, energy management is imperative to ensure efficient power distribution based on the strengths and weaknesses of each ESS. The decoupling of highly dynamic power demands into components that match the dynamic nature of each ESS is essential. The Discrete Wavelet Transform (DWT) has been widely recommended for this purpose as part of real time energy management systems. However, due to DWT signal processing, delays in the frequency components can undermine the benefits of hybridization. This paper analyses the contribution of the SC to alleviate the battery when the DWT is used with and without time delay compensation using future demand prediction. Four different implementation strategies for a DWT based EMS have been evaluated using different metrics to quantify energy circulation and SC assistance during acceleration and braking. Simulation results using urban and highway driving cycles, show that obtaining the SC current reference as the difference between the real time current demand and the DWT low frequency component enhances SC assistance during acceleration and braking at the expense of higher energy circulation. The complexity added by future demand prediction does not reap SC performance benefits

Design optimisation of a current-fed solid-state transformer for MV grid-connected applications

This is the final version. Available from MDPI via the DOI in this record. For integrating large batteries in the medium voltage grid, current fed solid-state transformers offer galvanic isolation and a significant weight and size reduction. While the power losses increase with frequency and flux density, the core volume is contrariwise. Therefore, a design optimisation to achieve minimum losses and/or a minimum volume is essential. An optimisation strategy is proposed in this paper to find the optimum operating frequency and core flux density under certain practical constraints such as winding voltage per turn, clearance between transformer windings, saturation flux density and minimum efficiency. Differently from previous works, the proposed strategy provides a holistic approach for the design considering all main power losses from all main components using nonsinusoidal voltage waveforms and different operating conditions. Analytical equations for the power losses calculation and the cores design are derived and validated using ANSYS and MATLAB Simulink software packages. Simulation results of the power loss calculation under different operating frequencies and duty cycles are presented and compared with the analytical results. A case study for designing a 1.0 MW, 0.6/18 kV current fed solid-state transformer is presented. The results of two optimisation objectives, minimum power losses or minimum total cores housing volume are also shownIntelligent Community Energy (ICE) projec

AN INVESTIGATION OF THE PHASE BEHAVIOR OF AN AQUEOUS SYSTEM THAT CONTAINS A POLYAMPHOLYTE AND POLY(ETHYLENE GLYCOL)

The phase behavior of aqueous two-phase polymer system containing poly(ethylene glycol) and a synthetic polyampholyte in 0.1 N KCl was studied as a function of pH. The top phase was poly(ethylene glycol)-rich and the bottom phase was polyampholyte-rich. The binodal curve was found to move towards lower concentrations of polymers with increasing pH as a result of decreased solubility of the polyampholyte. Phase compositions were correlated using a model based on Flory- Huggins theory. Also, a model based on excluded volume theory was used to correlate the binodal curve