Current source wave voltage inverter voltage-clamping and soft-switching techniques, and fuel cell system using the same

A fuel cell system, comprising:

• a fuel cell for providing a direct current (DC) voltage, the fuel cell comprising an anode, a cathode, a catalyst and an electrolyte, wherein the anode, used as a negative post in the fuel cell, disperses hydrogen gases equally over the entire catalyst surface and conducts electrons for being used as power in an external circuit, and the cathode, used as a positive post in the fuel cell, distributes oxygen fed to it onto the catalyst surface and conducts electrons back from the external circuit, and the catalyst is a special material used to facilitate the oxygen and hydrogen reaction;
• a DC to DC converter circuit comprising a first and second coupled windings, a third capacitor having an electrode connected to coupled ends of the first and second winding, and a transistor cascaded between the anode of the fuel cell and the coupled ends of the first and second windings;
• and
• a current-source sine-wave voltage inverter for converting the DC voltage to an alternating (AC) voltage, the current-source sine-wave voltage inverter comprising:
• a current source circuit having a primary side inductance of a transformer;
• a clamping circuit comprising a first switch cascaded with a first diode, a second diode cascaded with a second switch, a first capacitor connected between an anode of the first diode and a cathode of the second diode, a secondary side inductance of the transformer cascaded with a third diode, the secondary side inductance of the transformer and the third diode connected to two ends of the DC source, and a cathode of the third diode connected to an anode of the DC source;
• an inverting circuit, being a full-bridge dc-ac inverting circuit which comprising diagonally opposite a third switch and a fourth switch, a fifth switch and a sixth switch from two legs, a fourth diode, a fifth diode, a sixth diode and a seventh diode used for avoiding the short current from a second capacitor to pass through the first, second, third, fourth, fifth and sixth switches or the first, second, third, fourth, fifth, sixth, and seventh diodes;
• and
• a control and driving circuit comprising a single-phase voltage and frequency command signal and then further makes a logic determination, a delay operation, isolates an amplified driving current and triggers and cuts off the first, second, third, fourth, fifth and sixth switches;
• when an output voltage is at an upper half cycle of the sine wave, current flowing from the DC source through the primary side inductance and the first and second switches, then via the third and fourth switches to charge the second capacitor;
• when an output voltage is at a lower half cycle of the sine wave, the first, second, third, and fourth switches turn on at the same time to discharge the second capacitor;
• when the primary side inductance is forward-biased, the third diode is reverse-biased, no current flowing through the secondary side inductance, and current on the primary side inductance storing energy at the transformer;
• when the first and second switches cut off, the primary side inductance reverses a voltage polarity (the polarity of the black spots is negative), the third diode is forward-biased, a current on the secondary side inductance will release the energy stored in the transformer to the DC source;
• and during the energy releasing time, the voltage value of the secondary side inductance is the same as the source's, and the voltage value of the primary side inductance will be limited by turns ratio, therefore the structure disclosed herein is able to clamp two times the voltage of the DC source;
• wherein the first capacitor and the first and second diodes all connect either sides of the first and second switches to enable a zero voltage switching (ZVS) property of the first and second switches when the first and second switches cut off;
• when a current on the secondary side inductance is zero, which means all stored energy in the transformer has been released, then if any one of the first, second, third, fourth, fifth and sixth switches on the primary side turns on, it will have a zero current switching (ZCS) property.