  Accurate plasma shape control is the basis of tokamak plasma experiments and
physical research. Modeling of the linearized control response of plasma shape
and position has been widely used for shape controller design in the last
several years. But it usually contains much of the uncertainty, such as
structured uncertainties and unmodeled dynamics. EAST tokamak plasma shape
controller design is also based on a linear rigid plasma response model which
integrated within a Matlab-based toolset known as TokSys. Meanwhile the PID
control approach is currently used for EAST plasma shape control. This leads to
strong coupling between different parameters describing the plasma shape. To
handle these problems, a H_infinity robust control scheme for EAST multi-input
multi-output (MIMO) shape control has been proposed. First, the plasma response
is modeled as the linearized rigid RZIp model. Then, the controller design
technique is introduced with two main stages: 1) loop shaping is used to shape
the nominal plant singular values to give desired open-loop properties at
frequencies of high and low loop gain; 2) a normalized coprime factorization
and H_infinity technique is used to decouple the most relevant control channels
and minimize the tracking errors. Finally, the simulation results show that the
H_infinity robust controller combines good robust stability margins, speed of
response, dynamic tracking characteristics, and closed-loop decoupling for EAST
plasma shape control.
