Proton Exchange Membrane Fuel Cell (PEMFC) is difficult for application because of its high current and wide voltage output. A fractional order PID controller is introduced to a Four-Switch Buck-Boost DC/DC converter to stabilize the power output in this paper. To reduce the inductor current ripple, a kind of dual-triggered switch strategy is employed in detail, and an accurate dynamic model of DC/DC converter is proposed for fuel cell measurement and control system. Then a fractional order PID controller is designed for voltage module compensation, in which a stochastic inertia weight PSO algorithm is employed to optimize the parameters of this controller. The results of simulation and experiment indicate that the compensation effect of fractional order PID controller has better performance than the integer order controller, which is robust to the variation of fuel cell system dynamics and power request.
Summary As a kind of new energy power generation technology in the 21st century, hydrogen fuel cell plays an indispensable role in energy network. However, due to its characteristics of low output voltage and large fluctuation, direct current–direct current (DC–DC) converter with high step‐up voltage gain has become a key part for safe and stable operation of fuel cell. In this paper, by replacing the inductors on the input side of interleaved boost converter with switched‐inductor units (small current ripple) and adding a capacitor–diode unit with strong voltage multiplication to the output side, an innovative interleaved high step‐up DC–DC converter is proposed with high step‐up voltage gain, small inductor current, and low voltage/current stresses. In addition, working principle, steady‐state performance, device parameter design, and theoretical efficiency calculation for the entire duty cycle range (duty cycle D < 0.5 and D > 0.5) are carried out, respectively, to verify its validity and feasibility. Finally, a 150‐W experimental prototype of fuel cell front‐stage power conversion is established. When the input voltage and output current are 16 V and 1.25 A, respectively, the efficiency of the entire system can reach about 92.6%.
The conventional ultra capacitor charger uses computer to monitor the ultra capacitor's state of charge(SOC) and adopts different strategy to charge the ultra capacitor. It makes the system expensive and the control method is also inconvenient. For the above problems, a non-microcomputer ultra capacitor charging system is designed. The proposed system can achieve two-step charging modes, constant current limiting voltage(CCLV) mode and constant voltage limiting current(CVLC) mode. Finally, the designed charging system is presented at the last of the article. The ultra capacitor and its charging characteristic introduction Ultra capacitor is a high-capacity capacitor with capacitance values much higher than other capacitors, but lower voltage limits. It bridges the gap between electrolytic capacitors and rechargeable batteries and stores 10 to 100 times more energy per unit volume or mass than electrolytic capacitors. The ultra-capacitor can charge and discharge much faster than batteries, and tolerate many more charge and discharge cycles than rechargeable batteries. Constant voltage charging is also called as constant potential charging used to maintain the same voltage input to the ultra capacitor throughout the charging process, regardless of the ultra capacitor's state of charge. Constant voltage charging provides a high inrush current to the ultra capacitor because of the higher potential difference between ultra capacitor and charger. The charging curve is shown in figure. 1, a. Constant current charging supplies a relatively constant current, regardless of the ultra capacitor's temperature and state of charge. The charging curve is shown in figure. 1, b.
Due to defects of low-voltage and high-current output in new energy power generation system, it is necessary to raise the output voltage and realize further power conversion in the subsequent stage. In this paper, an innovative interleaved high step-up DC-DC converter is proposed. Considering the problems of non-common ground and limited gain in the previously proposed active network DC-DC boost converters, the active network structure is replaced by an interleaved parallel structure, in which charge pump units are employed, and a switched-capacitor unit is added to further improve the voltage gain. Finally, the experimental results of the 150W prototype show that the converter has higher gain, lower voltage stress in switch devices and higher efficiency. When the input voltage and output current are 16V and 1.25A respectively, the efficiency of the entire system can reach about 94.2%.
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