DESIGN OF SINGLE PHASE AND THREE PHASE CASCADED MULTI LEVEL INVERTERS

Abstract

Multilevel Inverters (MLI) have received significant attention in recent times. Reduced distortion, better output power quality, minimum switching losses, reduced switching stress make multilevel architecture suitable for a variety of applications. Till date multilevel inverters are widely used in UPS (un-interruptible power supply), renewable energy systems, medium voltage industrial (induction motor) drives and many more. An extensive study and research is being carried out to design multilevel inverters for advanced industrial applications as well as efficient utilization and storage of renewable energy. A variety of control mechanisms (PI, Fuzzy, Hysteresis bands etc.) and switching/modulation techniques (SPWM, SVM, Selective harmonic elimination, wavelet modulation) have been proposed and demonstrated across the world. Our work deals with design and analysis of various control techniques for single phase and three phase MLI. In our work we demonstrated multilevel inverter systems following Generalized Proportional Integral (GPI) control mechanism. The design of the system is based on cascade H-bridge architecture. The cascade H-bridge architecture eliminates the problems observed with other architectures such as Diode Clamped and Flying Capacitor. We designed a single phase MLI and also a three phase MLI. Feedback is an important facet in the design of closed loop systems. Typical feedback in an inverter would be voltage or current or both. In our work we designed MLI using current feedback and voltage feedback independently. Each model is designed for a 7-level inverter following single phase and three phase. The switching scheme for these designs follows SPWM (Sinusoidal Pulse Width Modulation) technique. This makes the system less complex and easy to implement. Major limitation on the design of cascaded MLI is the number of switches required. To resolve this limitation and a novel design method was proposed. The proposed technique based on H-bridge. This design also reduces the number of DC voltage sources, each having different magnitudes of voltage and number of power electronic switches.