Patent ID: 8174241

Claim:
A method of protecting an electricity storage device in a hybrid DC power supply system, which includes an electric power generating device and a DC/DC converter, the electricity storage device being connected to the electric power generating device through the DC/DC converter, comprising the steps of: controlling a voltage of the electric power generating device through the DC/DC converter so that the voltage tracks a command voltage; monitoring whether a voltage of the electricity storage device falls outside of a prescribed range or not while the voltage of the electric power generating device is being controlled to track the command voltage; if the voltage of the electricity storage device falls outside of the prescribed range, interrupting the step of controlling the voltage of the electric power generating device to track the command voltage, and controlling a current passing through the DC/DC converter to track a passing current limit value as a target current for protecting the electricity storage device; and monitoring the voltage of the electric power generating device and returning to the step, which has been interrupted, of controlling the voltage of the electric power generating device, depending on the monitored voltage.