Gain-scheduled state variable controller for SMES power conditioning system

Averaging techniques are used to model a bi-directional DC-DC converter with input filter supplying a superconducting magnet energy storage (SMES) device. The third order transfer function between converter duty-ratio and the SMES coil current is dominated by a pair of undamped complex poles and a pair of complex zeros and becomes nonminimum phase under some operating conditions. A state-variable feedback controller is designed for the system, however to achieve well-behaved transient responses under all conditions, the feedback gains must be varied with converter duty-ratio. A simple scheduling regime is therefore devised for the feedback gains. The converter model and control design are verified by MATLAB/Simulink simulations