Power Quality Enhancement in Electricity Grids with Wind Energy Using Multicell Converters and Energy Storage

In recent years, the wind power industry is experiencing a rapid growth and more wind farms with larger size wind turbines are being connected to the power system. While this contributes to the overall security of electricity supply, large-scale deployment of wind energy into the grid also presents many technical challenges. Most of these challenges are one way or another, related to the variability and intermittent nature of wind and affect the power quality of the distribution grid. Power quality relates to factors that cause variations in the voltage level and frequency as well as distortion in the voltage and current waveforms due to wind variability which produces both harmonics and inter-harmonics. The main motivation behind work is to propose a new topology of the static AC/DC/AC multicell converter to improve the power quality in grid-connected wind energy conversion systems. Serial switching cells have the ability to achieve a high power with lower-size components and improve the voltage waveforms at the input and output of the converter by increasing the number of cells. Furthermore, a battery energy storage system is included and a power management strategy is designed to ensure the continuity of power supply and consequently the autonomy of the proposed system. The simulation results are presented for a 149.2 kW wind turbine induction generator system and the results obtained demonstrate the reduced harmonics, improved transient response, and reference tracking of the voltage output of the wind energy conversion system.Peer reviewedFinal Accepted Versio

Pengaruh adukan dan kepekatan partikel silicon karbida sebagai penguat terhadap kelakuan salutan komposit matriks nikel

Affordable quality housing is vital in developing countries to meet its growing population. Development of a new cost effective system is crucial to fulfill these demands. In view of this, a study is carried out to develope a Precast Lightweight Foamed Concrete Sandwich Panel (PLFP), as a new affordable building system. Experimental investigation and finite element analysis to study the structural behaviour of the PLFP panel under axial load is undertaken. The panel consists of two foamed concrete wythes and a polystyrene insulation layer in between the wythes. The wythes are reinforced with high tensile steel bars and tied up to each other through the polystyrene layer by steel shear connectors bent at an angle of 45º. The panels are loaded with axial load until failure. The ultimate load carrying capacity, load-lateral deflection profile, strain distributions, and the failure mode are recorded. Partial composite behaviour is observed in all specimens when the cracking load is achieved. Finite element analysis is also carried out to study the effect of slenderness ratio and shear connectors which are the major parameters that affect the strength and behaviour of the panels. An empirical equation to predict the maximum load carrying capacity of the panels is proposed. The PLFP system proposed in this research is able to achieve the intended strength for use in low rise building. Considering its lightweight and precast construction method, it is feasible to be developed further as a competitive IBS building system

Comparative Study of Power Semiconductor Devices in a Multilevel Cascaded H-Bridge Inverter

This thesis compares the performance of a nine-level transformerless cascaded H-bridge (CHB) inverter with integrated battery energy storage system (BESS) using SiC power MOSFETs and Si IGBTs. Two crucial performance drivers for inverter applications are power loss and efficiency. Both of these are investigated in this thesis. Power devices with similar voltage and current ratings are used in the same inverter topology, and the performance of each device is analyzed with respect to switching frequency and operating temperature. The loss measurements and characteristics within the inverter are discussed. The Saber® simulation software was used for the comparisons. The power MOSFET and IGBT modeling tools in Saber® were extensively utilized to create the models of the power devices used in the simulations. The inverter system is also analyzed using Saber-Simulink cosimulation method to feed control signals from Simulink into Saber. The results in this investigation show better performances using a SiC MOSFET-based grid-connected BESS inverter with a better return of investment

Direct usage of photovoltaic solar panels to supply a freezer motor with variable DC input voltage

In this paper, a single-phase photovoltaic (PV) inverter fed by a boost converter to supply a freezer motor with variable DC input is investigated. The proposed circuit has two stages. Firstly, the DC output of the PV panel that varies between 150 and 300 V will be applied to the boost converter. The boost converter will boost the input voltage to a fixed 300 V DC. Next, this voltage is supplied to the single-phase full-bridge inverter to obtain 230 V AC. In the end, The output of the inverter will feed a freezer motor. The PV panels can be stand-alone or grid-connected. The grid-connected PV is divided into two categories, such as with a transformer and without a transformer, a transformer type has galvanic isolation resulting in increasing the security and also provides no further DC current toward the grid, but it is expensive, heavy and bulky. The transformerless type holds high efficiency and it is cheaper, but it suffers from leakage current between PV and the grid. This paper proposes a stand-alone direct use of PV to supply a freezer; therefore, no grid connection will result in no leakage current between the PV and Grid. The proposed circuit has some features such as no filtering circuit at the output of the inverter, no battery in the system, DC-link instead of AC link that reduces no-loads, having a higher efficiency, and holding enough energy in the DC-link capacitor to get the motor started. The circuit uses no transformers, thus, it is cheaper and has a smaller size. In addition, the system does not require a complex pulse width modulation (PWM) technique, because the motor can operate with a pulsed waveform. The control strategy uses the PWM signal with the desired timing. With this type of square wave, the harmonics (5th and 7th) of the voltage are reduced. The experimental and simulation results are presented to verify the feasibility of the proposed strategy

An On-line Diagnostic Method for Open-circuit Switch Faults in NPC Multilevel Converters

On-line condition monitoring is of paramount importance for multilevel converters used in safety-critical applications. A novel on-line diagnostic method for detecting open-circuit switch faults in neutral-point-clamped (NPC) multilevel converters is introduced in this paper. The principle of this method is based on monitoring the abnormal variation of the dc-bus neutral-point current in combination with the existing information on instantaneous switching states and phase currents. Advantages of this method include simpler implementation and faster detection speed compared to other existing diagnostic methods in the literature. In this method, only one additional current sensor is required for measuring the dc-bus neutral-point current, therefore the implementation cost is low. Simulation and experimental results based on a lab-scale 50 kVA adjustable speed drive (ASD) with a three-level NPC inverter validate the efficacy of this novel diagnostic method

Coconut dehusker machine

Generally, coconut is dehusked manually using either a machete or a spike. These methods required skill labor and tiring to use. Attempts made so far in development of dehusking tools have been only partially successful and not effective in replacing manual methods. The reasons quoted for the failure of these tools include unsatisfactory and incomplete dehusking, breakage of the coconut shell while dehusking, spoilage of useful coir, greater effort needed than manual methods, etc

A Review on Control Strategies and Topologies of Multi Level Converter System

In recent decades, high-performance and medium voltage energy management for academia and industry have been attracted by multi-level converter topologies. In addition, the multi-level principle is used without decreasing the inverter power output to synthesise the harmonic distortion on the output waveform. For the reduction of harmonic distortion in the output waveform, the multi-level principle is used. The following topologies are presented: diode clamped inverters (neutral point clamped), condenser clamped (flying condenser), multi-level cascading (dc source, etc.) and the most effective modulation methods built for this converter category: multi-level, selective harmonic removal and space m vectors. A series of different topologies are given in this paper. Multi-level inverters have been gaining popularity in research teams and in the production of industrial applications for high and medium voltage applications for 20 years. Moreover, compared to a conventional converter, multi-level inverters can generate switched waveforms with reduced harmonic slopes. Recently, multi-level inverters have increased interest in their ability to generate high-quality wave forms at lower frequencies; the multi-level topology used in dynamic restaurant voltages reduces the harmonic distortion of the inverter output waveform without inverter output losses. By integrating control techniques for multi-level inverters, this paper discusses the most common topologies, making their implementations flexible in some power applications in many industrial areas