ABSTRACT – A new single-phase 15-level inverter with a reduced number of components is proposed in this paper. It is incorporate the proposed inverter which aids to generate fifteen stepped output voltage levels with lower THD. The proposed inverter can improve efficiency and reduce losses, cost, and complexity of the overall system. The work not only to show its efficiency but also to the effectiveness under different circumstances of linear and non-linear loads. The inverter is stable during the non-linear loads and well suits for grid-connected systems. The simulation is carried out in MATLAB/Simulink software.
INTRODUCTION
The world has been experiencing an everlasting bloom in both developments and population; there is a huge power demand. The world is also trying to shift towards greener and sustainable energy. Researchers are coming up with fresh ones and complex approaches for using complex methods to tackle both the power demands and the pollution caused by extracting power. However, the extraction of power from a renewable source is not as simple as from conventional sources. DC is the form of energy derived from renewable sources such as solar energy, and our current transmission systems use AC. However, the recent advancements made in power electronic converters along with controllers have made integrating renewable energy sources into a grid. Different control methods, and various topologies of converters, are researched to a great extent. In most of the papers cited below it is seen that research is being done extensively to connect three-phase grids using inverters with pulse width modulation and for a low to microgrid, single-phase inverters with medium power are being preferred. Microgrids connected to renewable can reduce the demand for power in residential area energy. However, renewable energy sources tend to supply fluctuating power depending on time and several other factors; hence it is essential to optimize getting energy. With solar panels and wind turbines, the sun and wind respectively depend on the energy that can be generated from them. Therefore, the systems are in charge of them should be capable of adjusting themselves to these varying factors. Thus, the output voltage and current solar panel have to be adjusted for different temperatures, times of the day so that the energy generated from the panel is heavily optimized and the system has to be at the maximum power point. DC-DC converters are, therefore, used to power the PV panel’s variable output voltage [4]. Since there is a strong demand for applications with low and medium power, multilevel (MLIs) inverters are common because they can increase the output voltage without the use of transformers. The cascaded type of multilevel inverter is preferred in microgrids for RES as it is possible to connect individual H bridges. To individually even with other various sources of renewable energy, such for example solar panels, using wind turbines fuel cells that have been stacked and for power distribution purpose the step-up transformers are possible to be eliminated by including the use of DC-DC converters and connections of H bridge outputs through cascading. This paper deals with the development of an inverter to be used for micro-grids powered by renewable energy. There is a constant demand for clean and sustainable energy all over the world as the existing fossil fuel resources are being depleted, and the condition of the environment we live in is getting worse each day. This calls for a major shift towards renewable energy for a better and stable future. As most of our existing systems are built around fossil fuel, it is not possible to just shift to other energy instantly; the process has to be slow. It associates the grid with a photovoltaic system, which could be seamlessly integrated into our existing system. Since the output produced from solar panels is in DC, and the grid distributes current as AC, inverters have to play a huge role in converting the DC to AC. Therefore, the inverter used has a direct influence on the overall performance of this integrated system. Prefer an inverter with low total harmonic distortion and high efficiency. Multilevel inverters are used as they have higher efficiency and (THD) lower total harmonic distortion when compared to the other inverters. However, the number of switches used in the circuit must decrease to minimize losses. As the switches play an essential role in the multilevel inverters, instead of trying to directly decrease the switches, have used here the PWM technique. There are three relevant kinds of multilevel inverters, H bridge, Neutral point clamped MLI, and flying capacitor MLI. Cascaded H Bridge MLI. Besides these are formed by connecting in sequence with the H bridge MLI with each other. The H bridge is called so, as the circuit when connected looks like ‘‘H’’. Comprising four switches, using the H bridge for both single and three-phase conversion. Based on the required mechanical or solid-state switches may be used, although mechanical switches are rare nowadays. This system has the least number of switches but is mostly used when there are two or more sources. The H bridge rectifier has the least amount of Total harmonic distortion but is less preferred as the device makes use of two different power sources, which is what is present in almost all real-life scenarios. In flying capacitor multilevel inverter, the diodes are also replaced by capacitors. They have a tree-like structure comprising capacitors, where each capacitor has a different voltage. For the flying capacitor, the number of switches required is given by doubling the level of the MLI and then subtracting two from the result, and for the capacitor, the number of levels in MLI is doubled, and then one is subtracted from it. The real and reactive power flow is better controlled, during the outage the capacitors present makes way for the inverter to save itself; however, the circuit and design are much more complex, and switching efficiency is low, it is costlier than the other setups. Neutral point clamped inverters have a lot of numbers of switches when compared to H bridge but work ideally better with a single source. The THD levels and efficiency are quite better than H-bridge for a singular source. With the increase in the number of switches, the overall (THD)total harmonic distortion also increases, which is eliminated by bringing in a filter at the end of the circuit. In the Neutral point Clamped Multilevel inverter, diodes clipping devices, and use the capacitors as instruments for clamping. The number of switches varies depending on the stage of the converter; the switches are less concerning the levels, and dynamic loads have been tested experimentally and well suits for renewable energy applications.