This disclosure discloses a power conversion system including a first power converter, a second power converter, and a power storage device. The second power converter includes a control signal generation part, a detection signal processing part, and a state diagnosis part. The control signal generation part is configured to perform at least one of superposition of a predetermined AC voltage on a DC voltage in a second DC power and superposition of a predetermined AC current on a DC current in the second DC power. The detection signal processing part is configured to detect at least one of a detection value of the DC voltage superposed with the AC voltage and a detection value of the DC current superposed with the AC current. The state diagnosis part is configured to diagnose a state of the power storage device based on the detection value.
