A Robustness Evaluation Method for the Robust Control of Electrical Drive Systems Based on Six-Sigma Methodology

Numerous uncertainties in practical production and operation can seriously affect the drive performance of permanent magnet synchronous machines (PMSMs). Various robust control methods have been developed to mitigate or eliminate the effects of these uncertainties. However, the robustness to uncertainties of electrical drive systems has not been clearly defined. No systemic procedures have been proposed to evaluate a control system's robustness (how robust it is). This paper proposes a systemic method for evaluating control systems' robustness to uncertainties. The concept and fundamental theory of robust control are illustrated by considering a simple uncertain feedback control system. The effects of uncertainties on the control performance and stability are analyzed and discussed. The concept of design for six-sigma (a robust design method) is employed to numerically evaluate the robustness levels of control systems. To show the effectiveness of the proposed robustness evaluation method, case studies are conducted for second-order systems, DC motor drive systems, and PMSM drive systems. Besides the conventional predictive control of PMSM drive, three different robust predictive control methods are evaluated in terms of two different parametric uncertainty ranges and three application requirements against parametric uncertainties.