ABSTRACT:A single phase five level inverter with a dual reference single carrier Pulse Width Modulated (PWM) control scheme is presented. The inverter is capable of producing five levels of output voltage levels (Vdc, Vdc/2, 0, −Vdc/2, −Vdc) from the dc supply voltage. For this, the proposed multilevel inverter needs a single dc voltage source with a series connection of two capacitors, a bidirectional switch formed with four diodes and a switch, and an Hbridge cell. The proposed approach helps in reducing the number of independent dc voltage sources and number of switches as compared with conventional circuits KEYWORDS:Multilevel Inverter (MLI), Pulse Width Modulation, Total Harmonic Distortion (THD).
I.INTRODUCTIONMultilevel inverter technology has emerged recently as a very important alternative in the area of high-power mediumvoltage applications. Researches are going on to improve their capabilities further through optimized control techniques, and to minimize both component count and manufacturing cost. The multilevel inverter has been implemented in various applications, such as motor drives, power conditioning devices, renewable energy generation and distribution. PWM inverters can simultaneously control output voltage, frequency and it can reduce the amount of harmonics in output current which results in better THD content.Several multilevel topologies have been developed, but as the output voltage levels increases, it also increases the number of switches, number of independent dc sources, switching stresses, losses, voltage unbalancing across capacitors etc. Half and Full bridge inverters requires large input and output filters, lower voltage operating capability, harmonic distortion is high, high Electro Magnetic Interference (EMI) [1]. The mainly used MLI topologies are flying capacitor, diode clamped and H-bridge converter with separate DC sources. Diode clamped MLI requires large number of diodes as no: of level increases. Flying capacitor MLI uses a large no: of capacitors to hold voltages. Cascaded H bridge MLI requires least no: of components but needs separate dc voltage sources for each H bridges [2]. Among conventional multilevel inverters, cascaded H-bridge multilevel inverter (CHB) is one of the best approaches to increase the number of output voltage levels. As CHB increases H-bridge cells, it also increases the number of switches and also independent dc input voltage sources. One of the solutions to reduce the number of components in CHB is to use asymmetrical dc voltage sources. But the main disadvantage of asymmetric cascaded H-bridge inverter is the requirement of asymmetric DC sources for its operation. Using H Bridge with Multiple Transformer reduces the number of switches and provides proper isolation. It also uses a combination of asymmetrical voltage sources to synthesize multilevel output voltages. This technique employs only a single dc voltage source. But it uses two low frequency transformers and thus makes the system bulky and costly [3]. In case of CHB with single voltage s...