A Reduced Switch Count Five Level Inverter With Extended Linear Modulation Range Up to Full Base Speed

This article proposes an 18-switch five-level inverter topology for induction motor (IM) drives, enabling an extended linear modulation range (LMR) till full base speed. The power circuit consists of a conventional NPC three-level inverter and a standard two-level inverter feeding the opposite phase winding ends of an open-ended winding IM. The proposed inverter achieves a voltage space vector radius of <inline-formula> <tex-math notation="LaTeX">$0.955~{V}_{\text {dc}}$ </tex-math></inline-formula> and a maximum peak fundamental phase voltage of <inline-formula> <tex-math notation="LaTeX">$0.637~{V}_{\text {dc}}$ </tex-math></inline-formula> in its LMR compared to a conventional five-level inverter with the corresponding figures of 0.866 and <inline-formula> <tex-math notation="LaTeX">$0.577~{V}_{\text {dc}}$ </tex-math></inline-formula>, respectively. This improvement arises from the fact that in the overmodulation region spanning from 0.577 to <inline-formula> <tex-math notation="LaTeX">$0.637~{V}_{\text {dc}}$ </tex-math></inline-formula>, the standard five-level inverter operates in a six-step mode, resulting in the voltage space vector trace a hexagonal path producing a lower-order harmonic-rich phase voltage. The proposed power circuit effectively addresses this issue by ensuring a circular locus for the voltage space vector up to a radius of <inline-formula> <tex-math notation="LaTeX">$0.955~{V}_{\text {dc}}$ </tex-math></inline-formula> resulting in a maximum peak fundamental voltage of <inline-formula> <tex-math notation="LaTeX">$0.637~{V}_{\text {dc}}$ </tex-math></inline-formula>. Consequently, it extends the linear speed range of the motor to the full base speed without lower-order harmonic problems.