SYSTEM FREQUENCY DETECTOR

According to one embodiment, a system frequency detector is provided. The system frequency detector includes an orthogonal coordinate signal generator generating an orthogonal two-phase voltage signal from a three-phase voltage signal of three-phase alternating current power of a power system; and a frequency calculator including an angular frequency calculator calculating an angular frequency of the power system based on the two-phase voltage signal, and an arithmetic unit calculating a system frequency of the power system from the angular frequency. The frequency calculator includes a prediction calculator calculating a predicted value of the angular frequency after a prescribed period of time has elapsed based on the angular frequency and a differential of the angular frequency. In a state in which the phase jump of the power system is not detected, the frequency calculator calculates the system frequency based on the angular frequency. When the phase jump of the power system is detected, the frequency calculator calculates the system frequency based on the predicted value for a constant amount of time. Accordingly, a system frequency detector is provided in which the change of the system frequency can be quickly tracked and an erroneous detection of the system frequency can be suppressed even when a system disturbance occurs.