Seven-Level Hybrid Cascaded H-Bridge Multilevel Inverter Fed Single Phase Induction Motor Drive

The poor quality of voltage and current of a con-ventional inverter fed induction machine is due to the presence of harmonics and hence there is significant level of energy losses. The Multilevel inverter is used to reduce the harmonics. The inverters with a large number of steps can generate high quality voltage waveforms. The higher levels can follow a voltage refer-ence with accuracy and with the advantage that the generated voltage can be modulated in amplitude instead of pulse-width modulation. An active harmonic elimination method is applied to eliminate any number of specific higher order harmonics of multilevel converters with unequal dc voltages. a cascaded H-bridge multilevel inverter that can be implemented using only a single dc power source and capacitors. Standard cascaded multilevel inverters require "n" dc sources for "2n + 1" levels. Without requiring transformers, the scheme proposed here allows the use of a single dc power source with the remaining "n-1" dc sources being capacitors, which is referred to as hybrid cascaded H-bridge multilevel inverter (HCMLI). HCMLI using only a single dc source for each phase is promising for high-power motor drive applications as it significantly decreases the number of required dc power supplies, provides high-quality output power due to its high number of output levels, and results in high conversion efficiency and low thermal stress as it uses a fundamental frequency switching scheme.