Under grid voltage sags, over current protection and exploiting the maximum capacity of the inverter are the two main goals of grid-connected PV inverters. To facilitate low-voltage ride-through ...(LVRT), it is imperative to ensure that inverter currents are sinusoidal and remain within permissible limits throughout the inverter operation. An improved LVRT control strategy for a two-stage three-phase grid-connected PV system is presented here to address these challenges. To provide over current limitation as well as to ensure maximum exploitation of the inverter capacity, a control strategy is proposed, and performance the strategy is evaluated based on the three generation scenarios on a 2-kW grid connected PV system. An active power curtailment (APC) loop is activated only in high power generation scenario to limit the current's amplitude below the inverter's rated current. The superior performance of the proposed strategy is established by comparison with two recent LVRT control strategies. The proposed method not only injects necessary active and reactive power but also minimizes overcurrent with increased exploitation of the inverter's capacity under unbalanced grid voltage sag.
The rapid increase in the penetration of photovoltaic (PV) power plants results in an increased risk of grid failure, primarily due to the intermittent nature of the plant. To overcome this problem, ...the flexible power point tracking (FPPT) algorithm has been proposed in the literature over the maximum power point tracking (MPPT) algorithm. These algorithms regulate the PV power to a certain value instead of continuously monitoring the maximum power point (MPP). The proposed work carries out a detailed comparative study of various constant power generation (CPG) control strategies. The control strategies are categorized in terms of current-, voltage-, and power-based tracking capabilities. The comparative analysis of various reported CPG/FPPT techniques was carried out. This analysis was based on some key performance indices, such as the type of control strategy, irradiance pattern, variation in G, region of operation, speed of tracking, steady-state power oscillations, drift severity scenario, partial shading scenario, implementation complexity, stability, fast dynamic response, robustness, reactive power, cost, and tracking efficiency. Among existing FPPT algorithms, model-based control has a superior performance in terms of tracking speed and low steady-state power oscillations, with a maximum tracking efficiency of 98.57%.
Over the last few decades, multilevel inverters (MLIs) are being extensively utilized in many industrial and grid connected applications due to their numerous merits. With the recent development of ...renewable energy systems (RES), applications of classical MLI topologies are hindered due to their performance issues such as poor power quality, uneconomical structure and low efficiency. These performance issues and limitations in classical MLI topologies have attracted the researchers toward evolving new hybrid MLI topologies. In this article, a comprehensive analysis of these recent hybrid MLI topologies is done on the basis of some qualitative and quantitative performance indices. Special focus has been given to extensively review the influence of MLIs in grid connected renewable energy applications such as photovoltaic (PV) systems, wind energy conversion systems (WECS) and micro-grid. In order to provide the better insight about the working and performance of these MLI topologies, simulation results performed in MATLAB/Simulink environment are also presented.
In multilevel inverters (MLI), output voltage waveform consists of dominant low order harmonics, which needs to be minimized. Simultaneously, good control over the fundamental voltage for desirable ...operation is needed. In this paper, an atom search optimization (ASO) based selective harmonic elimination (SHE) method is proposed for a variable dc bus based reduced component count (RCC) MLI. ASO is a population-based metaheuristic algorithm, which mathematically models the motion of atoms in nature to accurately determine the optimum firing angle of the switches by solving SHE fitness function. The proposed ASO SHE method outperforms recent metaheuristics based SHE methods such as bee algorithm, imperialistic colonial algorithm (ICA), firefly, particle swarm optimization (PSO), and teaching learning-based optimization (TLBO) in solving SHE problem for 11-level multilevel inverter. Detailed simulation case studies are presented to effectively demonstrate the performance of the proposed ASO SHE method on a stand-alone photovoltaic (PV) based RCC MLI subjected to sudden changes in irradiance, load and dc-link capacitor voltage. The experimental results on a PV based variable dc bus multilevel inverter validate the excellent performance of ASO SHE method in minimizing the total harmonic distortion (THD) and dominant order harmonics under sudden change in operating conditions.
This article presents a hybrid method to solve the selective harmonic elimination (SHE) problem for an adaptive DC bus multilevel inverter (MLI) topology. The proposed hybrid method combines the Grey ...wolf optimization (GWO) technique and Newton-Raphson (NR) numerical method which drastically minimizes the computational time and further improves the accuracy of the SHE solution. The technique is essentially divided into two stages. In the exploration stage, GWO explores the entire search space of SHE problem and provides initial values of switching angles for a given modulation index with a fast rate of exploration. In the exploitation stage, the NR method uses these initial switching angles as input to iteratively determine the optimum value of the firing angles. This GWO-inspired iterative methodology is implemented on a hybrid MLI topology for photovoltaic (PV) system applications. The performance of proposed SHE method is compared with recently developed metaheuristic SHE techniques based on some key performance indices. From an application point of view, the 11-Level MLI is tested on a PV battery-based stand-alone system to determine the effectiveness of the proposed method in MATLAB/Simulink environment. Finally, a small-scale experimental prototype is developed to validate the proposed method.
The recent trend in multilevel inverters (MLIs) is to produce the high quality staircase ac voltage waveform while utilizing the optimum number of switching devices. In this context, this article ...presents a combination of topological and modulation scheme-based solution for the optimum performance of MLI. A concept of adaptable dc voltage link in conjunction with modified H-bridge unit is introduced to reduce the number of switching devices. Further to improve the quality of voltage waveform and to reduce the switching losses in the proposed topology, a hybrid gravitational search algorithm (GSA) selective harmonic elimination (SHE) technique is proposed and implemented on the newly developed MLI topology with symmetric dc sources. Comparative analysis is performed with the conventional and existing hybrid cascaded MLI topologies, which exhibits the superiority of the proposed topology in terms of reduction in count of switching devices, count of components, and conduction losses. The efficacy of the proposed hybrid GSA SHE technique is shown in the simulated results. The feasibility of the proposed MLI topology and SHE technique is further verified by the experimental results of a nine-level inverter with both equal and unequal dc sources.
In multilevel inverters (MLIs), the selective harmonic elimination (SHE) technique is becoming popular owing to its twofold prime advantages. The first advantage is its ability to compute the desired ...switching angles such that the actual fundamental output voltage is maximized to desired voltage level while simultaneously minimizing the dominant low order harmonics. The second advantage of this scheme is that it can operate in low switching frequency mode which reduces switching losses in medium voltage and high power inverters. However, SHE method requires solution of transcendental nonlinear equations using conventional means such as algebraic and iterative methods which is quite cumbersome task. In order to alleviate this problem, a heuristic based optimization technique particle swarm optimization (PSO) is being used in this paper. Performance of PSO based SHE technique has been compared with continuous genetic algorithm (CGA) based SHE method which shows the superiority of proposed PSO based SHE technique. Simulations and programming have been performed using MATLAB/Simulink software environment for an eleven-level inverter.
Selective harmonic elimination (SHE) techniques are widely employed in multilevel inverters (MLIs) for the calculation of switching angles in such a manner that the desired fundamental output voltage ...is obtained while simultaneously eliminating the dominant low order harmonics. In order to obtain this objective, the solution of nonlinear transcendental equations by means of algebraic, iterative and optimization techniques is required. In this article, Gravitational Search Algorithm (GSA) based SHE technique is applied to find the optimum switching angles for 11-level cascaded MLI. A comparative study has been carried out which showed that the GSA based SHE method provided more precise results with less number of iterations as compared to the Genetic Algorithm (GA) based SHE method. GSA based SHE technique has been programmed in MATLAB/Simulink software environment. Simulation and harmonic analysis results exhibit the efficacy of GSA in the elimination of low order harmonics while obtaining the desired fundamental voltage at the same time.
In this paper; a variable dc link based novel multilevel inverter (MLI) topology is proposed. This proposed topology comprises two variable dc links and a modified H-bridge unit. This new ...single-phase topology offers advantages such as reduction in count of switches; gate drivers and dc sources while simultaneously improving the power quality. The proposed topology has been analyzed for both symmetric and asymmetric modes of operation. A comparative study of the proposed topology with some recent MLI topologies has been presented. The comparative study indicates that the proposed topology requires less number of dc sources; switches and driver circuits as compared to other topologies. The proposed topology has been simulated for 31-level asymmetric configuration in MATLAB/SIMULINK environment to verify the proper operation of proposed topology. Harmonic analysis was also performed for 31-level inverter which showed significant reduction in the total harmonic distortion (THD) for phase voltage and current waveforms. The proposed topology is suitable for low voltage applications such as standalone photovoltaic (PV) systems and hybrid electric vehicles (HEVs).
Aim: The study is aimed at determining the characters of roots of Aerva javanica (A.javanica) assessing acute oral toxicity of hydroalcoholic extract of roots of Aerva javanica.
Place and Duration of ...Study: the physicochemical and phytochemical evaluation was carried out at Faculty of Pharmacy, Maulana Azad University Jodhpur, Rajasthan. Acute Oral Toxicity was studied at Bilwal Medchem and Research Laboratory, Jaipur Rajasthan. The duration of study June 2021 – July 2021
Methodology: The pharmacognostical characters were evaluated in terms of organoleptic property, physico-chemical parameters, and preliminary phytochemical investigation. The acute oral toxicity was determined using the 423, OECD guideline for testing of chemical, acute toxic class method.
Results: The physico-chemical analysis revealed total ash; water soluble ash and, acid insoluble ash to be 6.36 ± 0.26%, 0.79 ±0.23 % and, 1.23 ± 0.34%. The water, alcohol and petroleum ether soluble extractive values were found to be 17.88± 3.54 %, 15.58 ± 1.13% and, 0.3 ± 0.13 %. The percentage yield of hydroalcoholic extract of root of A.javanica was found to be 24%. The phytochemical screening of hydroalcoholic extract revealed the presence of carbohydrates, flavonoids, steroids, alkaloids, tannins, proteins, and fixed oil. The acute oral toxicity of hydroalcoholic extract of root of A.javanica revealed that the extract was found to be safe till 2000 mg/kg BW.
Conclusion: The results of the present study will furnish data helpful in the correct identification and authentication of roots of A.javanica. The extractive value shed light on the most suitable solvent to be chosen to obtain extract rich in phytoconstituents. The physicochemical screening furnished data on important phytoconstituents present in the hydroalcoholic extract which could be helpful in isolation and purification of desired phytoconstituents. Acute oral toxicity study revealed that the extract is safe till 2000 mg/kg BW which could be helpful in selection of dose for future pharmacological activities.
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