A VRC H∞ Design for Dynamic Thermal Derating of Induction Machines

Induction machines exhibit thermal derating in their performance during operation that causes sheer uncertainties in the controlling parameters such as stator and rotor resistances. It does not only affect the steady-state but also the dynamic response of an induction machine (IM). An output feedback variable resistance controller (VRC), which is inherently an H∞ linear parameter varying (LPV) controller, is proposed to compensate this thermal derating caused by stator resistance variations. An L2 gain bound and internal stability are ensured by linear matrix inequalities (LMIs). IM speed control is established by using input/output feedback linearization (I/O-FL). The proposed controller is implemented for a 30 kW induction motor in MATLAB® Simulink environment. Nonlinear simulation results show excellent performance tracking for the thermally derated dynamic IM characteristics in the presence of varying stator resistance and an applied load torque.