Active and adaptive-passive control of acoustic impedance with thermoacoustic cooling applications
This thesis research involves active and adaptive-passive control problems that are related to thermoacoustic cooling. The basic issue is acoustic impedance control for one-dimensional sound wave in ducts. The goal is to replace the duct of a standing wave tube with a controlled or tunable boundary and thus reduce space requirements. In the active control approach a secondary driver is used to force the sound field as desired. Both single-input-single-output and two-input-two-output control schemes are formulated and implemented. Robust repetitive control was used for both cases, and satisfactory results from experiments have shown the feasibility of the proposed method. For the adaptive-passive control scheme, a tunable Helmholtz resonator is developed as an attachment to the existed thermoacoustic cooler to control the boundary conditions. A motor-driven mechanism drives the piston in the resonator such that the compliance of the end impedance can be changed. The cooling power is chosen as the variable to be maximized, as it is a better performance index to evaluate the cooling system. The acoustic impedance matching control is achieved implicitly. Extremum seeking control is applied for the adaptive-passive thermoacoustic cooler to maximize the cooling power via tuning the piston position and the driving frequency. Experimental results show the effectiveness of such control schemes in searching for the optimal cooling power with fixed and varying operating conditions. Improvement in terms of transient performance is observed by incorporating a proportional-derivative (PD) compensator in the control loop. ^
Major Professors: George T.-C. Chiu, Purdue University, Luc G. Mongeau, Purdue University.