Dual 18-pulse rectifier for high-power multilevel inverters

This paper presents a new rectifier topology that uses 18-pulse transformers to achieve 36-pulse harmonic cancellation. The proposed rectifier can be used to reduce the input current harmonics for several multilevel inverters, such as 3-level neutral point clamped (NPC), 5-level cascaded H-bridge (CHB) and 5-level NPC/H-bridge inverters. It can also be used to neutralize harmonics between two 18-pulse drives. Compared to conventional multi-pulse topologies, it uses less secondary windings and simpler transformers to achieve better current THD. Fourier analysis shows that the topology is able to achieve 36-pulse harmonic cancellation. It also provides additional harmonic cancellation for the 5^th and 7^th harmonics for non-ideal transformers or between two drives. The simulated current waveforms, current spectra and DC bus voltages are given to confirm the theoretical analysis. Experiments are performed to verify the performance.