A method of controlling a DC power source, wherein the DC power source is a fuel cell power plant with a fuel cell stack, having a critical parameter, wherein the critical parameter is cell voltage of the fuel cell stack, with a limiting value which should not be exceeded, and providing power to a DC/DC converter, in which power conversion is controlled by a control strategy, to convert the output power of said DC power source to provide a desired output of the DC/DC converter; the method being characterized by: a) determining if the output voltage of the DC/DC converter is greater than an output voltage command of the DC/DC converter, b) if the output voltage is greater than said output voltage command, determining if the limiting value of said critical parameter has been exceeded, c) if the limiting value of said critical parameter has not been exceeded, causing a change in the output of the DC/DC converter by reaching a step of decrementing the duty cycle, which will make it less likely that said critical parameter will exceed said limiting value, d) if the limiting value of said critical parameter has been exceeded, the two following tests are performed for determining if either d1) the value of a second critical parameter, of the DC power source, is in excess of a second limiting value, wherein the second critical parameter is output current of the fuel cell stack, or d2) the value of a third critical parameter, of the DC/DC converter, is in excess of a third limiting value, wherein the third critical parameter is output current of DC/DC converter, e) if the second limiting value of said second critical parameter has been exceeded, changing control of the DC/DC converter to cause a change in the output of the DC/DC converter by reaching the step of decrementing the duty cycle, tending to reduce currents, which will make it less likely that said second critical parameter will exceed said second limiting value, or f) if the third limiting value of said third critical parameter has been exceeded, changing control of the DC/DC converter to cause a change in the output of the DC/DC converter by reaching the step of decrementing the duty cycle, tending to reduce currents, which will make it less likely that said third critical parameter will exceed said third limiting value. a) determining if the output voltage of the DC/DC converter is greater than an output voltage command of the DC/DC converter, b) if the output voltage is greater than said output voltage command, determining if the limiting value of said critical parameter has been exceeded, c) if the limiting value of said critical parameter has not been exceeded, causing a change in the output of the DC/DC converter by reaching a step of decrementing the duty cycle, which will make it less likely that said critical parameter will exceed said limiting value, d) if the limiting value of said critical parameter has been exceeded, the two following tests are performed for determining if either d1) the value of a second critical parameter, of the DC power source, is in excess of a second limiting value, wherein the second critical parameter is output current of the fuel cell stack, or d2) the value of a third critical parameter, of the DC/DC converter, is in excess of a third limiting value, wherein the third critical parameter is output current of DC/DC converter, either d1) the value of a second critical parameter, of the DC power source, is in excess of a second limiting value, wherein the second critical parameter is output current of the fuel cell stack, or d2) the value of a third critical parameter, of the DC/DC converter, is in excess of a third limiting value, wherein the third critical parameter is output current of DC/DC converter, e) if the second limiting value of said second critical parameter has been exceeded, changing control of the DC/DC converter to cause a change in the output of the DC/DC converter by reaching the step of decrementing the duty cycle, tending to reduce currents, which will make it less likely that said second critical parameter will exceed said second limiting value, or f) if the third limiting value of said third critical parameter has been exceeded, changing control of the DC/DC converter to cause a change in the output of the DC/DC converter by reaching the step of decrementing the duty cycle, tending to reduce currents, which will make it less likely that said third critical parameter will exceed said third limiting value.