A power conversion apparatus comprising a converter for converting an AC power to a DC power and an inverter for converting the DC power to an AC power, comprising: a fluctuation detecting means to detect an input power source fluctuation; a gate blocking means to gate block the converter when the input power source fluctuation is detected by the fluctuation detecting means, and when a necessary condition of functional operation is satisfied; an inverter control changeover means to switch contents of inverter control when a converter gate blocking flag is outputted from the gate blocking means, and when a DC voltage of the DC power is under a threshold voltage; an inverter control means to control the inverter based on a inverter control changeover flag outputted from the inverter control changeover means; and wherein, when the input power source fluctuation is detected by the fluctuation detecting means, the converter is gate blocked by the converter gate blocking flag, and the inverter control means continuously operate the inverter while the inverter control changeover flag has been outputted, characterized in that the fluctuation detecting means has a first detecting means comprising a current fluctuation detector to detect a variation of converter d-axis current feedback as a converter control current, an absolute value detector and a converter control current level judgement part; and a second detecting means comprising an absolute value detector to compute an absolute value of voltage variation of a converter d-axis voltage feedback as a converter control voltage. a fluctuation detecting means to detect an input power source fluctuation; a gate blocking means to gate block the converter when the input power source fluctuation is detected by the fluctuation detecting means, and when a necessary condition of functional operation is satisfied; an inverter control changeover means to switch contents of inverter control when a converter gate blocking flag is outputted from the gate blocking means, and when a DC voltage of the DC power is under a threshold voltage; an inverter control means to control the inverter based on a inverter control changeover flag outputted from the inverter control changeover means; and wherein, when the input power source fluctuation is detected by the fluctuation detecting means, the converter is gate blocked by the converter gate blocking flag, and the inverter control means continuously operate the inverter while the inverter control changeover flag has been outputted, characterized in that the fluctuation detecting means has a first detecting means comprising a current fluctuation detector to detect a variation of converter d-axis current feedback as a converter control current, an absolute value detector and a converter control current level judgement part; and a second detecting means comprising an absolute value detector to compute an absolute value of voltage variation of a converter d-axis voltage feedback as a converter control voltage. a first detecting means comprising a current fluctuation detector to detect a variation of converter d-axis current feedback as a converter control current, an absolute value detector and a converter control current level judgement part; and a second detecting means comprising an absolute value detector to compute an absolute value of voltage variation of a converter d-axis voltage feedback as a converter control voltage.