A power feeding system comprising: a direct-current power supply including a storage battery which charges power, and discharges a direct-current power to an electric power converter; the electric power converter which converts a direct-current power output from the direct-current power supply, and supplies the converted power to a power system; a voltage detector configured to detect a voltage at a connection point between the electric power converter and power system; a current detector configured to detect a current output from the electric power converter; an effective power detector configured to detect effective power (Pe) from a voltage value detected by the voltage detector and a current value detected by the current detector; characterized by a rotor speed computation unit configured to compute an angular frequency (ω) of the voltage output from the electric power converter, in order to increase the angular frequency when the effective power value (Pe) is decreased and decrease the angular frequency when the effective power value is increased, based on an effective power value detected by the effective power detector and an effective power set value to be output from the electric power converter; an electrical characteristics computation unit configured to compute an output voltage target value (Ec) of the electric power converter, in order to increase a difference between the phase angle of the output voltage target and the voltage phase angle of the power system in a leading direction when the frequency of the power system is decreased, based on a current value detected by the current detector, a set voltage value (Vref) which is a reference value as a target of the close voltage of the electric power converter, and the angular frequency; and a power conversion controller configured to control the electric power converter according to the output voltage target value (Ec). a direct-current power supply including a storage battery which charges power, and discharges a direct-current power to an electric power converter; the electric power converter which converts a direct-current power output from the direct-current power supply, and supplies the converted power to a power system; a voltage detector configured to detect a voltage at a connection point between the electric power converter and power system; a current detector configured to detect a current output from the electric power converter; an effective power detector configured to detect effective power (Pe) from a voltage value detected by the voltage detector and a current value detected by the current detector; the electric power converter which converts a direct-current power output from the direct-current power supply, and supplies the converted power to a power system; a voltage detector configured to detect a voltage at a connection point between the electric power converter and power system; a current detector configured to detect a current output from the electric power converter; an effective power detector configured to detect effective power (Pe) from a voltage value detected by the voltage detector and a current value detected by the current detector; characterized by a rotor speed computation unit configured to compute an angular frequency (ω) of the voltage output from the electric power converter, in order to increase the angular frequency when the effective power value (Pe) is decreased and decrease the angular frequency when the effective power value is increased, based on an effective power value detected by the effective power detector and an effective power set value to be output from the electric power converter; an electrical characteristics computation unit configured to compute an output voltage target value (Ec) of the electric power converter, in order to increase a difference between the phase angle of the output voltage target and the voltage phase angle of the power system in a leading direction when the frequency of the power system is decreased, based on a current value detected by the current detector, a set voltage value (Vref) which is a reference value as a target of the close voltage of the electric power converter, and the angular frequency; and a power conversion controller configured to control the electric power converter according to the output voltage target value (Ec). a rotor speed computation unit configured to compute an angular frequency (ω) of the voltage output from the electric power converter, in order to increase the angular frequency when the effective power value (Pe) is decreased and decrease the angular frequency when the effective power value is increased, based on an effective power value detected by the effective power detector and an effective power set value to be output from the electric power converter; an electrical characteristics computation unit configured to compute an output voltage target value (Ec) of the electric power converter, in order to increase a difference between the phase angle of the output voltage target and the voltage phase angle of the power system in a leading direction when the frequency of the power system is decreased, based on a current value detected by the current detector, a set voltage value (Vref) which is a reference value as a target of the close voltage of the electric power converter, and the angular frequency; and a power conversion controller configured to control the electric power converter according to the output voltage target value (Ec).