Limitations in Inner-Loop PI Controllers in IM Drive With an $LC$ Filter and Its Remedies

Abstract

This article presents the proportional&#x2013;integral (PI) controller design, its limitation, and remedies for <inline-formula><tex-math notation="LaTeX">$dq$</tex-math></inline-formula>-axis currents in a vector-controlled voltage-source-inverter-fed induction motor (IM) drive with an inverter output <inline-formula><tex-math notation="LaTeX">$LC$</tex-math></inline-formula> filter. The idea of designing PI controllers by incorporating the <inline-formula><tex-math notation="LaTeX">$LC$</tex-math></inline-formula> filter dynamics into the IM dynamics is applied for the vector-controlled IM + <inline-formula><tex-math notation="LaTeX">$LC$</tex-math></inline-formula> filter drive. This article shows that the PI controller, a first-order controller, has limitations of stability margins and performance criteria for an IM + <inline-formula><tex-math notation="LaTeX">$LC$</tex-math></inline-formula> filter system. These limitations in the PI controller are demonstrated by deriving the complete range of stabilizing PI gains (<inline-formula><tex-math notation="LaTeX">$K_{p}$</tex-math></inline-formula> and <inline-formula><tex-math notation="LaTeX">$K_{i}$</tex-math></inline-formula>) for the IM + <inline-formula><tex-math notation="LaTeX">$LC$</tex-math></inline-formula> filter system and segregating them to satisfy the desired frequency-domain specifications. As a remedy to the limitations, this article proposes to use a second-order controller instead of a PI controller to provide better stability margins, attenuation at the resonance frequency, and more robustness. The controller design and resulting closed-loop stability are thoroughly analyzed, and the experimental results are presented to validate the same.