Power control apparatus and method and power generating system using them

Power control apparatus and method for fetching the maximum electric power from a battery power source and a system using such apparatus and method are provided. For this purpose, the power control method comprises the steps of fluctuating an output voltage of the battery power source and obtaining (m) power values from at least (m) voltage signals from voltage detecting means and at least (m) current signals from current detecting means which were sampled at desired intervals, calculating a formula of function with a polar to approximate the relations between the (m) voltage values and (m) power values, obtaining a voltage at which a power is set to an extreme value from the formula of function with a polar, and setting the power at such a voltage into an output power set value and controlling the output power of the battery power source.