SYSTEM FREQUENCY DETECTOR

According to an embodiment of the invention, a system frequency detector is provided and 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 by converting the three-phase voltage signal into a two-phase voltage signal orthogonal to the three-phase voltage signal, converting the two-phase voltage signal into a voltage signal of a rotating coordinate system, calculating a moving average of the voltage signal of the rotating coordinate system, and performing an inverse transformation of the voltage signal of the rotating coordinate system after calculating the moving average; 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 further including a low-pass filter provided in series with the arithmetic unit, the low-pass filter suppressing a high frequency component of the system frequency. Thus, 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.