| Summary: | 博士 === 國立臺灣科技大學 === 電機工程系 === 95 === This dissertation presets the application of fuel cell power conversion systems based on proton exchange membrane fuel cells. The system introduces multi-leg dc-dc power converters, buck/boost converters, and single-phase three-wire dc-ac converters for fuel cells, batteries, and ac/dc outputs. The presented fuel cell power conversion system overcomes low-voltage-high-current behavior and slow dynamic response of fuel cells, and meets current ripple requirements.
For low-voltage-high-current behavior of fuel cells, multi-leg dc-dc converters is adopted to decrease current standing rating of switches, while interleaved switching techniques and current sharing control are introduced. This dissertation proposes a novel phase-interleaved pulse-width modulation for the converter, which can significantly minimize the number of timer to one regardless of the number of PWM outputs. On the other hand, the current sharing control with duty feedforward not only achieves equal current distribution, but also save computation time of digital signal processors.
As to fuel cell slow dynamic response, the system uses batteries to serve an energy buffer to dynamically and quickly sustain energy balance by battery discharging. In addition to discharging, the system charges batteries, when fuel cells are able to supply this extra load from charging.
The dc-dc and dc-ac converters of the proposed system bring current ripples at switching frequency and twice utility frequency for fuel cells. To meet the power conditioning requirements for fuel cells, multi-leg boost converter with phase interleaving pulse-width modulation is proposed for the system. The converter always operates in continuous conduction mode to conform to the current ripple specification with designed input inductors. However, this method which is only for high frequency current ripples can not depress the current ripples at twice utility frequency. A notch filter with designed dc-link capacitors are presented to reduce voltage ripples of dc-link capacitors, which can indirectly decrease low frequency current ripples.
The control parameters of regulators for fuel cell power converters are designed by frequency response and direct design method through small-signal models. This analytic method can save the time of parameters tuning, and compromise system dynamic response and stability. The relative control of the system is realized by a 32bit digital signal processor, TMS320F2812.
Finally, experimental results of a 1 kW prototype are given to justify the feasibility of the implemented fuel cell power converter system through a digital signal processor. The system inputs use fuel cell and 24V batteries, and can supply dc and ac loads. Besides, experimentally it shows an efficiency of 94.8% at dc loads and of 89.2% at ac loads, and current ripple factors under 4%.
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