Abstract
This paper presents an H∞ control system design for a levitation transport equipment by electromagnets attraction with nonlinear characteristics. The control systems consist of a levitation system, a guide system and a run system. As the feature of this system, state variables and outputs evolve in continuoustime and others evolve in discrete-time in the system, and controllers are restricted to be digital controllers through samplers and zero order holds with a fixed sampling period. In the control system design, we consider the influence of both disturbances and uncertainties in the model. The main disturbances stem from the position sensors. The electromagnetic uncertainties are due to the gain change in the current amplifier, the influence of leakage flux and linearization error in the magnetic circuit, and the mechanical uncertainties are due to the changes of the mass and the moment of inertia of the vehicle. The controller design is based on the H∞ type control problem for sampled-data control systems.
The results of several experiments show that the H∞ controller designed for sampled-data control systems gives a higher performance as the sampling period gets longer compared with the H∞ controller designed for continuous-time control systems.
