Hydrogen generator, method of operating hydrogen generator, and fuel cell system

A method of operating a fuel cell system, the method comprising:

• (a) heating a reformer by a heater;
• (b) causing a steam reforming reaction to proceed to generate a reformed gas by said reformer
• (c) causing a shift reaction of carbon monoxide in the reformed gas to proceed by a shift converter;
• (d) counting the number of times of start-up and/or stop of said fuel cell system comprising said hydrogen generator including said reformer, said shift converter, and said heater, and a fuel cell;
• and
• (e) counting an accumulated operation time of said hydrogen generator,
• wherein the step (c) includes:
• step (c1) causing the shift reaction to proceed at a first controlled temperature if the counted number of times of start-up and/or stop of said hydrogen generator is less than a predetermined number of times,
• step (c2) causing the shift reaction to proceed at a second controlled temperature higher than the first controlled temperature if the counted number of times of start-up and/or stop of said hydrogen generator is not less than the predetermined number of times,
• (c3) causing the shift reaction to proceed at a third controlled temperature if the counted accumulated operation time of said hydrogen generator is less than a predetermined time, and
• (c4) causing the shift reaction to proceed at a fourth controlled temperature higher than the third controlled temperature if the counted accumulated operation time of said hydrogen generator is not less than the predetermined time.