System frequency detector

A system frequency detector, comprising:

• 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 an orthogonal two-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 after calculating the moving average generated by the orthogonal coordinate signal generator, and
• an arithmetic unit calculating a system frequency of the power system from the angular frequency by multiplying the angular frequency by ½π,
• the angular frequency calculator calculating the angular frequency by performing a proportional-integral control based on the two-phase voltage signal,
• the frequency calculator further including
• a rate limiter limiting a change of the system frequency equal to or greater than a prescribed change rate, the rate limiter feeding back an output-input difference of the rate limiter to the calculation of the proportional-integral control of the angular frequency calculator,
• a prediction calculator calculating a predicted value of the angular frequency after a prescribed period of time has elapsed based on the angular frequency output from the rate limiter and a differential of the angular frequency, and
• a switching circuit selectively switching a first state of inputting the angular frequency output from the rate limiter to the arithmetic unit, and a second state of inputting the predicted value output from the prediction calculator to the arithmetic unit,
• the switching circuit detecting a phase jump of the power system based on the voltage signal of the rotating coordinate system calculated by the orthogonal coordinate signal generator, selecting the first state in a state in which the phase jump of the power system is not detected, selecting the second state for a constant amount of time when the phase jump of the power system is detected, and returning the second state to the first state after the constant amount of time has elapsed.