SINGLE PHASE INVERTER TOPOLOGIES BY USING SLIDING MODE CONTROL STRATEGIES

The field of power electronics can be defined as the development of devices that converts one type of power to another. There are four type of power conversion: AC-AC, DC-AC, AC-DC and DC-DC. An inverter circuit is used to convert to DC-AC at desired output voltage and frequency. This conversion can be achieved by Transistors, SCR's, MOSFETS, and IGBT's. For low and medium power outputs transistorized inverters are suitable, but for high power outputs SCR's use is advisable. One of the biggest problems in power quality aspects is the harmonic contents in the electrical systems. Generally, harmonics are of two types: [51], [65], [70], 1) Voltage harmonics. 2) Current harmonics. Current harmonics are usually generated by harmonics contained in voltage supply and depend on the type of load such as resistive, capacitive and inductive load. Both harmonics can be generated by either the source or the load side. Harmonics generated by load are caused by nonlinear operation of devices, including power converters, arc-furnaces, gas discharge lighting devices, etc. Load harmonics can cause the overheating of the magnetic cores of transformer and motors. On the other hand, source harmonics are mainly generated by power supply with non-sinusoidal voltage waveform. Voltage and current source harmonics imply power losses, Electromagnetic Interference (EMI) and pulsating torque in AC motor drives.[2], [28],[93] Multilevel inverters have been attracting in favor of a researchers, academia as well as industry in the recent decade for high-power and medium-voltage energy control. In addition, they can synthesize switched waveforms with lower levels of harmonic distortion than an equivalently rated two-level converter. The multilevel concept is used to decrease the harmonic distortion in the output waveform without decreasing the inverter power output. This paper presents the most important topologies like diode-clamped inverter (neutral- point clamped), capacitor-clamped (flying capacitor), and cascaded multilevel with separate dc sources. This paper also presents the most relevant modulation methods developed for this family of converters: multilevel sinusoidal pulse width modulation, multilevel selective harmonics elimination, and space-vector modulation.[86] Authors strongly believe that this survey article will be very much useful to the researchers for finding out the relevant references in the field of topologies and modulation strategies of multilevel inverter. To summarize many multilevel converter topologies have been proposed during last decade.