H∞ control with minor feedback for a pneumatic actuator system

The uncertainty model used in the H_∞ control is norm bounded, while the actual modeling error is not so in general, and hence such uncertainty model can be conservative in certain applications. Therefore, the resulting system performance might be conservative if we simply apply the H_∞ control. To reduce the conservativeness, the H_∞ control scheme with minor feedback is examined in this paper. Since the minor feedback loop changes both the nominal plant and uncertainty models, we cannot conclude immediately that it improves the system performance even if the magnitude of the uncertainty model is reduced. A disturbance rejection problem is introduced to investigate the effect of the minor feedback and a sufficient condition is derived on which the minor feedback improves the disturbance rejection performance. Experimental results for a pneumatic control system confirm the effectiveness of the proposed method