A multiport bidirectional dc-dc converter with a diagnosis function for fuel cells that employs electrochemical impedance analysis was developed. The proposed converter, which is connected to electric double layer capacitors, can freely adjust the fuel cell voltage without fluctuation of the load voltage. A signal that consists of multiple frequency sinusoidal waves is superimposed as a duty ratio signal of the chopper circuit connected to the fuel cell, which enables simultaneous impedance measurement for these frequencies. The voltage and current values of the fuel cell are acquired by a digital signal processor to conduct fast Fourier transform calculations that give voltage and current spectra. The fraction of the spectra yields the electrochemical impedance. Experiments were conducted to validate the proposed method using a polymer electrolyte membrane fuel cell. The sinusoidal waves in the imposed signal have multiple frequencies to reduce the measuring time. The impedance characteristics determined using the proposed method are in good agreement with those obtained with an electrochemical instrument. To demonstrate the proposed method, the Nyquist plots when the fuel cell current, the operation temperature, and the stoichiometric ratios were changed and produced using the proposed method.Index Terms-DC-DC converter, digital signal processor, electric double layer capacitor, electrochemical impedance analysis, fuel cell.
The injection of hydrogen/deuterium pellets into a tokamak leads to a sudden increase in the electron density, and subsequently to a profile peaking of the density and an increase in the stored energy. Immediately after the injection, different types of oscillations are excited. On TEXTOR, the first type immediately follows the injection and the second one is excited with a delay of more than 10 ms. The oscillations show a 'snake-like' structure and occur close to the q = 1 surface with a frequency of 0.7-2 kHz. The radial location of the second oscillation is slightly shifted with respect to the first one. A fast-cooling phenomenon ('pre-cooling') in the core region of a plasma is often observed at pellet ablation phase. A study on the relation between the 'pre-cooling' and sawtooth oscillations suggests that the central value of safety factor of plasmas, q(0), is kept sufficiently below unity even just after the sawtooth crash. During pellet injection, the ablation rate is strongly modulated; these modulations cause so-called 'striations' in the ablation cloud. One model relates the striations to the energy reservoir on the plasma flux surfaces and describes the possibility of deriving the q-profile; the question of whether this method provides reliable results cannot yet be answered conclusively. The trajectory of the pellet in the plasma is in general not straight but deflected in the electron drift direction (OH discharges) or in the ion drift direction (CO-NBI discharges). The cloud develops a helically structured tail in the electron flow direction (toroidally) and in the electron diamagnetic drift direction (poloidally). The tail structure is attributed to charge-exchange processes and to plasma rotation.
Reduction of Carbondioxide by AC Glow Discharge has been studied. Main product is Carbononoxide and the maximum efficiency of Carbondioxide reduction is about 160 nmol/secW. It has been shown that the simple simulation model based on rate equations can reproduce the experimental results.
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