This paper presents a new control strategy based on Lyapunov-function and proportional-resonant (PR) controller for single-phase grid-connected LCL-filtered voltage-source inverters (VSIs). While ...Lyapunov-function-based control guarantees the global stability of the system, the PR controller is employed to process the grid current error and determine the inverter current reference. However, it is shown that the conventional Lyapunov-function-based control (CLFBC) together with the PR control cannot damp the inherent resonance of the LCL filter. Therefore, this control approach is modified by adding a capacitor voltage loop so as to achieve the desired resonance damping. In addition, a transfer function from the reference grid current to actual grid current is formulated in terms of the LCL-filter parameters and their possible variations in the proposed control strategy. An important consequence of using the PR controller is that the need for performing first and second derivative operations in the generation of inverter current reference is eliminated. Also, a zero steady-state error in the grid current is guaranteed in the case of variations in the LCL-filter parameters. The computer simulations and experimental results obtained from a 3.3-kW system show that the proposed control strategy exhibits a good performance in achieving the required control objectives such as fast dynamic response, zero steady-state error, global stability, and sinusoidal grid current with low total harmonic distortion (THD).
In this paper, a sliding-mode control (SMC) strategy is proposed for three-phase grid-tied LCL -filtered voltage source inverters in the natural frame. The SMC in the natural frame is based on ...controlling the sliding surface functions of phase-legs a and b. The sliding surface function of phase-leg c is obtained from the sliding surface functions of phase-legs a and b. This eliminates the need for sensing capacitor voltage and grid current of phase-leg c . The capacitor voltage references are generated by the proportional-resonant (PR) controllers which result in zero steady-state error in the grid current. The feasibility and performance of the proposed SMC strategy is investigated under steady-state, transient, unbalanced, and distorted grid conditions. Experimental results taken from a 9.8 kW system are provided to demonstrate the validity of the proposed SMC strategy.
► We propose a dSPACE based neuro-fuzzy controlled grid interactive inverter. ► The membership functions and rule base of fuzzy logic controller by using ANFIS. ► A LCL output filter is designed. ► A ...high performance controller is designed.
In this study, design, simulation and implementation of a dSPACE based grid interactive voltage source inverter are proposed. This inverter has adaptive neuro-fuzzy controller and capable of importing electrical energy, generated from renewable energy sources such as the wind, the solar and the fuel cells to the grid. A line frequency transformer and a LCL filter are used at the output of the grid interactive inverter which is designed as current controlled to decrease the susceptibility to phase errors. Membership functions and rule base of the fuzzy logic controller, which control the inverter output current, are determined by using artificial neural networks. Both simulation and experimental results show that, the grid interactive inverter operates synchronously with the grid. The inverter output current which is imported to the grid is in sinusoidal waveform and the harmonic level of it meets the international standards (4.3
<
5.0%). In addition, simulation and experimental results of the neuro-fuzzy and the PI controlled inverter are given together and compared in detail. Simulation and experimental results show that the proposed inverter has faster response to the reference variations and lower steady state error than PI controller.
In this paper, an enhanced Lyapunov-function based control scheme is proposed for three-phase grid-tied LCL-filtered voltage source inverters (VSIs). The grid-tied VSI is modeled in the synchronously ...rotating dq-frame. Motivated from the energy distribution in the system, an energy-like function (referred to as Lyapunov-function) is defined. Then, Lyapunov-function based control scheme is derived, which guarantees the global stability of the system. However, the derived Lyapunov-function based control scheme with single-loop cannot exhibit a satisfactory damping performance due to the poles located near imaginary axis. Therefore, an enhanced Lyapunov-function based control scheme is proposed by adding a second loop into the control variable. Unlike the existing control schemes where cross-coupling interaction exists between d and q-axes actual currents, the cross coupling in the proposed control scheme is dependent on the inverter current references. The performance and validity of the proposed control scheme are verified by computer simulations and experimental results.
Aims: We conducted this study to investigate the clinical significance of lactate kinetics in patients admitted to the intensive care unit (ICU) for diabetic ketoacidosis (DKA). Methods: This ...retrospective study was conducted between November 1, 2016, and December 31, 2020. Serial lactate measurements (at the hospital admission, ICU admission, and in 24 hours periods until 48 hours of ICU stay) of the patients admitted to our ICU with a diagnosis of DKA were recorded. Results: Forty patients were included in the study (mean age: 50.6+ or -19.4 years, female 60%). Eighty-five percent (n=34) of patients had increased (>2 mmol/L) blood lactate levels on admission. There was no significant difference between the low (lactate <4 mmol/L) and highlactate (lactate greater than or equal to 4 mmol/L) groups in mortality (p=0.195), ICU stay (p=0.966) and hospital length of stay (LOS) (p=0.274). However, the group with less than 40% decrease in lactate level from hospital admission to ICU had significantly higher Acute Physiology and Chronic Health Assessment II score 24 (12-46) vs. 18 (2-27), p=0.007, longer ICU stay 5 (1-40) vs. 3 (2-8) days, p=0.032, and higher mortality rate 6 (26.1) vs. 0 (0.0), p=0.030. Additionally, non-survivors (n=6) had significantly higher lactate levels at hospital admission 3.0 (1.3-15.0) vs. 5.1 (3.913.5) mmol/L, p=0.017, and ICU admission 2.3 (0.6-9.4) vs. 5.0 (2.4-16.0) mmol/L, p=0.010 than survivors. Conclusions: Although the ICU LOS and mortality did not differ between initial high and lowlactate groups in the present study, the lactate kinetics, especially in the early treatment period, can guide referral to the ICU level of care and determine the DKA patients at higher risk of death. Keywords: Diabetic ketoacidosis, lactate, diabetes mellitus, intensive care unit
In this study, the mediating role of book value between financial performance and market value is investigated by using mediated structural equation modelling as an alternative approach in the ...related literature. The theoretical frame of the study is constructed by benefit from the widely used value relevance of accounting models which treat earning and book value as exogenous to investigate the ability of information disclosed by financial statements to capture and summarize firm value. In the hypothesized meditation model book value is considered as a mediator while financial performance is used as an exogenous latent variable as the function of F-Score indicators instead of using a single proxy for earning. Quarterly announced accounting numbers and prices of active firms operating in Turkish electric power industry listed and traded on Borsa Istanbul between the years of 2009-2015 are used in construction of the dataset. The results of the model indicate that book value mediates the impact of financial performance on stock value. In other words, full mediator role of the book value makes the direct relationship between financial performance and stock value insignificant. Therefore, according to the findings, it is fair to say that (a) the effect of financial performance on stock value occurs indirectly through book value even financial performance has a primacy in investors’ decision making process and thus (b) investors make their decisions or shape their beliefs by comparing the book value with market value in the frame of realized financial performance in Turkey.
In this study, two transformers are designed using the ferrite N87 and the nanocrystalline core materials for the same power level and operating frequency. The operating frequency is defined as ...10 kHz, which is suitable␣for both materials. Modeling and simulation studies have been performed with the same finite element analysis software and the obtained results have been reported. The nanocrystalline and the ferrite N87 core materials have been compared according to both electrical and mechanical parameters. In these comparisons, many features such as core and winding losses, flux distributions, leakage flux, efficiency, and both electrical and mechanical performance have been reported comparatively in the case of rectangular waveform excitation of the transformer. Obtained results show that the weight and the volume of the transformer are reduced and more compact transformer is designed by using the nanocrystalline core material. In addition, besides the core loss, winding losses are also reduced in this design.
This paper introduces design and application of a novel one-axis sun tracking system which follows the position of the sun and allows investigating effects of one-axis tracking system on the solar ...energy in Turkey. The tracking system includes a serial communication interface based on RS 485 to monitor whole processes on a computer screen and to plot data as graphic. In addition, system parameters such as the current, the voltage and the panel position have been observed by means of a microcontroller. The energy collected is measured and compared with a fixed solar system for the same solar panel. The results show that the solar energy collected on the tracking system is considerably much efficient than the fixed system. The tracking system developed in this study provides easy installation, simple mechanism and less maintenance.
In this study, a maximum power point tracking DC–DC quadratic boost converter for high conversion ratio required applications is proposed. The proposed system consists of a quadratic boost converter ...with high step-up ratio and fuzzy logic based maximum power point tracking controller. The fuzzy logic based maximum power point tracking algorithm is used to generate the converter reference signal, and the change in PV power and the change in PV voltage are selected as fuzzy variables. Determined membership functions and fuzzy rules which are design to track the maximum power point of the PV system generates the output signal of the fuzzy logic controller's output. It is seen from MATLAB/Simulink simulation and experimental results that the quadratic boost converter provides high step-up function with robustness and stability. In addition, this process is achieved with low duty cycle ratio when compared to the traditional boost converter. Furthermore, simulation and experimental results have validated that the proposed system has fast response, and it is suitable for rapidly changing atmospheric conditions. The steady state maximum power point tracking efficiency of the proposed system is obtained as 99.10%. Besides, the output power oscillation of the converter, which is a major problem of the maximum power point trackers, is also reduced.
•A MPPT DC–DC quadratic boost converter is proposed for the high conversion ratio applications.•The fuzzy logic based control algorithm is used to track the maximum power point of the PV system.•The steady state MPPT efficiency of the proposed system is obtained as 99.10%.•The proposed system is suitable for rapidly changing atmospheric conditions.
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