Patent ID: 11965917
Assignee: TOSHIBA MITSUBISHI—ELECTRIC INDUSTRIAL SYSTEMS CORPORATION
Field: Measurement (Instruments)
Classification: CPC G | IPC G

Claim 4:
5. The power measurement device according to claim 4, wherein
the frequency detector includes:
an orthogonal coordinate signal generator generating an orthogonal two-phase voltage signal from the three-phase voltage signal of the three-phase alternating current power by
converting the three-phase voltage signal into an orthogonal two-phase voltage signal,
converting the orthogonal 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 calculates the angular frequency by performing proportional-integral control based on the two-phase voltage signal,
the frequency calculator further includes:
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 time interval has elapsed based on the angular frequency output from the rate limiter and a derivative of the angular frequency; and
a switching circuit selectively switching between 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, and

the switching circuit detects a phase jump of the power system based on the voltage signal of the rotating coordinate system calculated by the orthogonal coordinate signal generator, selects the first state in a state in which the phase jump of the power system is not detected, selects the second state for a constant interval when the phase jump of the power system is detected, and returns the second state to the first state after the constant interval has elapsed.