A control apparatus configured to control an inverter , said inverter configured to be applied to a solar power generation system including a solar cell and to interconnect said solar power generation system with an alternating current power system , the control apparatus comprising: system voltage measurement means for measuring a system voltage (Vr) of the alternating current power system ; voltage drop detection means for detecting a voltage drop of the alternating current power system , based on the system voltage (Vr) measured by the system voltage measurement means ; characterized in that the control apparatus further comprises: first direct current voltage control means for controlling a direct current voltage (Vdc) of the DC side of the inverter through control of the inverter to enhance a power generation efficiency of the solar cell , when the voltage drop is not detected by the voltage drop detection means ; and second direct current voltage control means for controlling the direct current voltage (Vdc) of the inverter through control of the inverter to suppress a current output from the inverter , when the voltage drop is detected by the voltage drop detection means ; and an overcurrent relay ; an alternating current detector ; wherein the alternating current detector is configured to measure an output current (Iiv) of the inverter , and to output said current (Iiv) of the inverter as a detection signal to the control apparatus and the overcurrent relay ; and wherein the overcurrent relay is configured to perform a protecting operation, when an instantaneous value of the current output (Iiv) of the inverter measured by the alternating current detector is in excess of a beforehand setting value. system voltage measurement means for measuring a system voltage (Vr) of the alternating current power system ; voltage drop detection means for detecting a voltage drop of the alternating current power system , based on the system voltage (Vr) measured by the system voltage measurement means ; characterized in that the control apparatus further comprises: first direct current voltage control means for controlling a direct current voltage (Vdc) of the DC side of the inverter through control of the inverter to enhance a power generation efficiency of the solar cell , when the voltage drop is not detected by the voltage drop detection means ; and second direct current voltage control means for controlling the direct current voltage (Vdc) of the inverter through control of the inverter to suppress a current output from the inverter , when the voltage drop is detected by the voltage drop detection means ; and first direct current voltage control means for controlling a direct current voltage (Vdc) of the DC side of the inverter through control of the inverter to enhance a power generation efficiency of the solar cell , when the voltage drop is not detected by the voltage drop detection means ; and second direct current voltage control means for controlling the direct current voltage (Vdc) of the inverter through control of the inverter to suppress a current output from the inverter , when the voltage drop is detected by the voltage drop detection means ; and an overcurrent relay ; an alternating current detector ; wherein the alternating current detector is configured to measure an output current (Iiv) of the inverter , and to output said current (Iiv) of the inverter as a detection signal to the control apparatus and the overcurrent relay ; and wherein the overcurrent relay is configured to perform a protecting operation, when an instantaneous value of the current output (Iiv) of the inverter measured by the alternating current detector is in excess of a beforehand setting value. <EOS>