Robust controller for a brushless DC motor based on the gain and phase margin

In comparison to classical DC motors, brushless DC motors are very reliable. Nevertheless, they can also fail, caused by overheating or mechanical wear. This paper proposes a design of robust controller (via H^∞ technique) for a brushless DC motor with requirement for gain (m_k) and phase (γ_k) margin. A simple way to include the amplitude and phase margins in a design is to include a dynamic uncertainty block in configuration. This block contains one parameter (k_m), that is a measure of the stability margins to be imposed on the closed loop system. The overall gain from input to output depends on the uncertainties (Δ) and the parameter (k_m), and it is placed where the margin is needed. The advantages of this modeling of unstructured uncertainties are illustrated on a brushless DC motor.