Design of robust fractional-order controller for 4-leg inverter

This paper proposes design of fractional-order controller for a 4-leg inverter using the concept of Bode's ideal loop transfer function. The 4-leg inverters have been increasingly used to cater nonlinear loads and hence there control is a crucial issue. The linear model of 4-leg inverter has poor phase margin resulting in a highly oscillatory time-domain response. The designed controller makes the closed-loop system robust by maintaining a constant phase with desired phase margin in the selected frequency band. This makes closed-loop system insensitive to system parameters achieving the robustness. The performance of the desired controller is compared with the adaptive pole-placement controller available in the literature. It is shown via simulation studies that the proposed controller results in a better closed-loop performance.