| Summary: | 碩士 === 臺灣大學 === 機械工程學研究所 === 98 === This thesis proposes the design and implementation of robust PID controllers for a proton exchange membrane fuel cell (PEMFC) system. First, we model the PEMFC as a multivariable plant by identification techniques. Second, we apply multivariable robust control strategies to stabilize the output voltage, and to improve system performance and efficiencies. Finally, the designed robust PID controllers are implemented on a microcontroller for system miniaturization.
PEMFC systems are nonlinear and time-varying. However, from the system point of view, the dynamics of PEMFC can be represented as a two-input-two-output system, that has inputs of air flow rate and hydrogen flow rate, and outputs of stack voltage and current. By fixing the output resistance, the system can be further reduced to a two-input-single-output system. Because most electrical equipment requires steady voltage supply, we aim to maintain steady output voltage for the PEMFC system.
We first identify the models of the PEMFC system at different operating points, and regard the un-modeled dynamics as system uncertainties. Since robust control is well known for its ability to cope with system uncertainties and disturbances, we then design a standard robust controller to improve stability and performance of the PEMFC system. However, the standard robust controller might be too complex for implementation, because the order of the controller is determined by the orders of the plant and weighting functions. On the other hand, PID control has been widely applicable to industrials because of its simple structure, but it lacks stability analysis for systems with uncertainties. Therefore, combining the merits of robust control and PID control, we design robust PID controllers for the PEMFC system. The designed controllers are then implemented on Simulink to experimentally verify the system performance. Lastly, the robust controllers are implemented on a microcontroller unit for system miniaturization. From the results, the proposed robust PID controllers are shown to be effective.
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