JP2016224014A - Frequency detection device, frequency detection method, and inverter device using detected frequency - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a frequency detection device that detects the frequency of power swing by a simple method without requiring multipoint data.SOLUTION: Provided is a power swing frequency detection device 1 for detecting the frequency fof power swing in a utility grid A, the device comprising: a frequency detection unit 12 for detecting the grid frequency f of the utility grid A on the basis of a voltage signal v detected by a voltage sensor 11; and a frequency search unit 16 for searching for the frequency of a detection signal fx' that is a deviation signal based on the grid frequency f. The frequency search unit 16, provided with a filter F to which the detection signal fx' is inputted, performs nonlinear optimization for causing an angular frequency ρ inputted to the filter F to change so that an evaluation value based on the error signal e of the filter F is optimized, and outputs the angular frequency ρ for optimizing the evaluation value as the frequency fof power swing. The power swing frequency detection device 1 can easily detect the frequency fof power swing with only data from detection performed at one point with a small calculation amount.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a frequency detection device, a frequency detection method, and an inverter device that uses the detected frequency of power oscillation in a power system.

  In the power system, power fluctuations, which are phenomena in which the system frequency and power flow oscillate, occur due to system faults and load fluctuations. If the power fluctuation becomes large, the generator will step out. In the future, the instability of power fluctuations may increase due to the heavy current flow and the liberalization of power associated with power trading. A system monitoring method has been developed for accurately grasping the state of the power fluctuation and performing operation and control of the power system (see Patent Document 1, Non-Patent Documents 1 to 3, etc.).

JP 2009-77589 A

"Western Japan 60Hz system dynamic characteristics observation system based on multi-point synchronized phasor measurement", Hashiguchi et al., Denki Theory B, Vol. 123, No. 9, 2003, pp. 1083-1090 “Identification of characteristic coefficient of power fluctuation based on multipoint synchronous phasor measurement”, Hashiguchi et al., Denki Theory B, Vol. 125, No. 4, 2005, pp. 417-424 “Smart power monitoring technology using phase-synchronized measurement”, Mitani, Denki B, 130, 9, 2010, pp. 791-794

  In each of the above methods, a phase difference is derived from multipoint phase data (frequency data), and power fluctuation is detected and analyzed by FFT analysis, analysis using wavelet transform, analysis based on eigenvalues, and the like. However, such an analysis method has a problem that the calculation amount is very large. In addition, it is necessary to accurately synchronize the time in order to handle multi-point data.

  The present invention has been conceived under the circumstances described above, and it is an object of the present invention to provide a frequency detection device that does not require multi-point data and detects the frequency of power oscillation by an easy method. Yes.

  In order to solve the above problems, the present invention takes the following technical means.

  The frequency detection device provided by the first aspect of the present invention is a frequency detection device that detects the frequency of power fluctuations in a power system, and is a power line connected to the system frequency of the power system or the power system. Detecting means for detecting the active power flowing through the frequency detector, and frequency searching means for searching for the frequency of the detection signal continuously detected by the detecting means, wherein the frequency searching means is a deviation signal based on the detection signal. And an optimization means for changing a frequency input to the filter so as to optimize an evaluation value based on an output signal of the filter, and an optimum frequency for optimizing the evaluation value Is output as the frequency of the power fluctuation. The “frequency” searched by the frequency search means and the “frequency” changed by the optimization means include “angular frequency”.

  In a preferred embodiment of the present invention, the filter is a notch filter, which attenuates an input frequency component from an input deviation signal and outputs the attenuated signal, and the optimization means minimizes the evaluation value. To do.

  In a preferred embodiment of the present invention, the filter is a band pass filter, attenuates components other than the input frequency from the input deviation signal, and outputs the evaluation value. Maximize.

  In a preferred embodiment of the present invention, the filter is a bandpass filter, attenuates components other than the input frequency from the input deviation signal and outputs the deviation signal. The evaluation value based on the signal obtained by subtracting the output signal of the filter from is minimized.

  In a preferred embodiment of the present invention, the evaluation value is a value corresponding to the square of the magnitude of the output signal of the filter.

  In a preferred embodiment of the present invention, the optimization means performs optimization using a Gauss-Newton method.

  In a preferred embodiment of the present invention, the frequency search means changes an initial value of the frequency input to the filter by the optimization means, and outputs an optimum frequency when each initial value is input.

  In a preferred embodiment of the present invention, the frequency detection device further includes a band-pass filter that attenuates a component other than a predetermined frequency band from the detection signal and outputs the attenuated component to the frequency search means.

  In a preferred embodiment of the present invention, the frequency detection device includes a recording unit that records a detection value detected by the detection unit, and a power oscillation detection unit that detects that power oscillation has occurred in the power system. And the frequency search means detects the detection value recorded by the recording means during a first predetermined time from when the power fluctuation detection means detects that power fluctuation has occurred. The signal is searched for the frequency of the detection signal.

  In a preferred embodiment of the present invention, the frequency search means is recorded by the recording means during a second predetermined time before the power fluctuation detection means detects that power fluctuation has occurred. The detection value is also used as the detection signal.

  In a preferred embodiment of the present invention, the power fluctuation detection means detects that power fluctuation has occurred when a detection value detected by the detection means changes by a predetermined value or more.

  In a preferred embodiment of the present invention, the frequency detection device further includes second detection means for detecting an electrical signal that changes in accordance with a state of the power system, and the power fluctuation detection means includes the first When the detection value detected by the second detection means changes by a predetermined value or more, it is detected that the power fluctuation has occurred.

  The inverter device provided by the second aspect of the present invention is an inverter device that converts DC power into AC power and outputs the AC power to the power system, and the frequency detection provided by the first aspect of the present invention. And the AC power is output by attenuating the frequency component of the power fluctuation detected by the frequency detector.

  A frequency detection method provided by a third aspect of the present invention is a frequency detection method for detecting a frequency of power fluctuation of an electric power system, the system frequency of the electric power system, or an electric power line connected to the electric power system. A first step of detecting active power flowing through the second step, and a second step of searching for the frequency of the detection signal continuously detected by the first step, wherein the second step includes the step of A third step of inputting a deviation signal based on the detection signal to the filter; a fourth step of changing a frequency input to the filter so as to optimize an evaluation value based on the output signal of the filter; And a fifth step of outputting an optimum frequency for optimizing the value as the frequency of the power fluctuation.

  According to the present invention, the frequency of the detection signal continuously detected by the detection means is searched for by the frequency search means. The frequency search means searches for a frequency that optimizes the evaluation value by changing the frequency input to the filter, and outputs the frequency as a frequency of power fluctuation. Since the frequency of power fluctuation can be detected only by the data detected at one point by the detecting means, multi-point data is not required. Further, since the search is only performed based on the data at one point, the amount of calculation is small, and the frequency of power fluctuation can be easily detected.

  Other features and advantages of the present invention will become more apparent from the detailed description given below with reference to the accompanying drawings.

It is a figure for demonstrating the power fluctuation frequency detection apparatus which concerns on 1st Embodiment. It is a figure for demonstrating simulation. It is a figure which shows a simulation result. It is a figure for demonstrating an inverter apparatus provided with the electric power oscillation frequency detection apparatus which concerns on 1st Embodiment. It is a functional block diagram for demonstrating the internal structure of the control circuit of an inverter apparatus. It is a control block diagram for demonstrating the modification of the frequency search part which concerns on 1st Embodiment. It is a figure for demonstrating the power fluctuation frequency detection apparatus which concerns on 2nd and 3rd embodiment. It is a figure for demonstrating the electric power oscillation frequency detection apparatus which concerns on 4th and 5th embodiment.

  Embodiments of the present invention will be specifically described below with reference to the drawings.

  FIG. 1 is a diagram for explaining the power oscillation frequency detection device according to the first embodiment. Fig.1 (a) is a functional block diagram for demonstrating the internal structure of a power fluctuation frequency detection apparatus. FIG. 1B is a control block diagram for explaining the frequency search unit.

The power oscillation frequency detection device 1 detects the frequency of power oscillation of the power system A. The power fluctuation frequency detection device 1 includes a voltage sensor 11, a frequency detection unit 12, a recording unit 13, a power fluctuation detection unit 14, a prefilter 15, and a frequency search unit 16. The power oscillation frequency detection device 1 detects the system frequency f from the voltage signal detected by the voltage sensor 11 and detects the frequency f _SW of the fluctuation of the system frequency f. The frequency f _SW is the frequency of power fluctuation. Instead of the frequency f _SW , the angular frequency ω _SW (= 2π · f _SW ) may be detected.

  The voltage sensor 11 detects a voltage signal. The voltage sensor 11 is arrange | positioned at the power line connected to the electric power grid | system A, such as a power transmission line, a distribution line, a lead-in line, indoor wiring, for example, and detects the instantaneous value of a voltage with the said power line. Then, the detected instantaneous value is digitally converted and output to the frequency detector 12 as a voltage signal v. The voltage sensor 11 may be attached to an outlet and detect a voltage signal of the indoor wiring. Moreover, you may make it arrange | position on the power line of the installation connected to electric power systems, such as a power conditioner (refer the voltage sensor 24 of FIG. 4). In the case of three-phase alternating current, any one phase voltage signal may be detected. Note that the power oscillation frequency detection device 1 may not be provided with the voltage sensor 11, and the voltage signal v may be input from a voltage sensor provided in another device.

  The frequency detector 12 detects the frequency of the voltage signal v input from the voltage sensor 11. Since the voltage signal v is a voltage detected by a power line connected to the power system A, the frequency of the voltage signal v is the system frequency f. For example, the frequency detection unit 12 may detect a frequency by a PLL (Phase Locked Loop) method, or may detect a frequency by a zero-cross point counting method. Further, the frequency may be detected by other methods. The frequency detection unit 12 outputs the detected system frequency f to the recording unit 13 and the power fluctuation detection unit 14.

The power fluctuation detection unit 14 detects the occurrence of power fluctuation based on the system frequency f input from the frequency detection unit 12. The power fluctuation is a phenomenon in which the system frequency f and the power flow are vibrated due to a system fault or load fluctuation, and does not always occur. In the present embodiment, in order to reduce the amount of calculation, the frequency f _{SW of the} power fluctuation is detected using the data before and after the power fluctuation occurs at the timing when the power fluctuation occurs. The power fluctuation detecting unit 14 determines that the power fluctuation has occurred when the input system frequency f changes significantly, for example, when the amount of change Δf of the system frequency f is greater than or equal to a threshold value, and trigger signal Tr Is output to the recording unit 13.

The recording unit 13 records the system frequency f, and includes, for example, a RAM or a flash memory that is a nonvolatile semiconductor memory as a storage area. The recording unit 13 cyclically writes the system frequency f input from the frequency detection unit 12 in the storage area. When the trigger signal Tr is input from the power fluctuation detection unit 14, the recording unit 13 stores data for X ₁ second before the trigger signal Tr is input and X ₂ seconds after the trigger signal Tr is input. Data is read out and continuously output to the prefilter 15 as a detection signal fx. The storage area can record data for at least (X ₁ + X ₂ ) seconds. In this embodiment, both X ₁ and X ₂ are set to several seconds, and data for several seconds before and after the trigger signal Tr is input are used. Note that the amount of data to be used is not limited to this, and data for a longer time may be used, or data for a shorter time may be used. Further, only data after the trigger signal Tr is input may be used without using the data before the trigger signal Tr is input. In this case, data recording may be started when the trigger signal Tr is input (data is not recorded until the trigger signal Tr is input).

The pre-filter 15 is, for example, a band-pass digital filter, and passes only the frequency component in a predetermined frequency band of the detection signal fx input from the recording unit 13 and outputs it to the frequency search unit 16. . Hereinafter, a signal that passes through the prefilter 15 and is output to the frequency search unit 16 is referred to as a detection signal fx ′. The degree of the power fluctuation frequency f _SW is known for each target power system. For example, in Western Japan 60 Hz system, it is known that power fluctuation with a frequency of 0.2 to 1 [Hz] occurs. Therefore, in this embodiment, in order to extract only the frequency components in the frequency band of 0.2 to 1 [Hz], the prefilter 15 attenuates frequency components other than the frequency band of 0.2 to 1 [Hz]. I am letting. Since the prefilter 15 also cuts off a component (DC component) of 0 [Hz], the detection signal fx ′ output from the prefilter 15 is a signal indicating a deviation from a reference value (for example, 60 [Hz]). .

The frequency search unit 16 searches for the frequency of the detection signal fx ′ input from the prefilter 15. As shown in the control block of FIG. 1B, the frequency search unit 16 inputs the detection signal fx ′ to the filter F and optimizes the error signal e that is the output of the filter F with an optimal solution. A certain angular frequency ρ is searched by a nonlinear optimization technique.
The frequency search unit 16 outputs the frequency corresponding to the angular frequency ρ that is the optimum solution as the frequency of the detection signal fx ′, that is, the power fluctuation frequency f _SW . Instead of the angular frequency ρ, the frequency (ρ / 2π) may be searched.

The filter F is a so-called notch filter, which attenuates a predetermined frequency component and allows other frequency components to pass through without being attenuated. In the present embodiment, as the filter F, for example, a filter having a second-order transfer function represented by the following equation (1) is used. The filter F is not limited to this.

In this embodiment, the following equation (2) is used as an evaluation function for nonlinear optimization, and an angular frequency ρ that minimizes the evaluation value J is searched using the Gauss-Newton method. The evaluation function is not limited to this, and may be designed as appropriate. Further, the nonlinear optimization method is not limited to this, and for example, a Newton method, a quasi-Newton method, a Levenberg-Markert method, a conjugate gradient method, a steepest descent method, or the like may be used. An appropriate method may be used in accordance with the transfer function of the filter F and in consideration of the amount of calculation and accuracy.

  The frequency search unit 16 changes the angular frequency ρ, which is the cutoff angular frequency of the filter F (notch filter), so that the evaluation value J based on the error signal e (see the above equation (2)) becomes smaller. Search for the frequency ρ. Since the filter F outputs a signal obtained by attenuating the frequency component of the angular frequency ρ from the deviation signal Δfx ′ as the error signal e, the angular frequency ρ corresponds to the frequency of the deviation signal Δfx ′ (the frequency of the detection signal fx ′). The closer to the frequency, the smaller the amplitude of the error signal e and the smaller the evaluation value J. Therefore, the angular frequency ρ when the evaluation value J is minimized is an angular frequency corresponding to the frequency of the detection signal fx ′.

Further, depending on the power system, there may be a plurality of frequency components of power fluctuation. In order to cope with this, in the present embodiment, a plurality of initial values of the angular frequency ρ when nonlinear optimization is performed are prepared, and the optimum solution when each initial value is used is searched for. In the present embodiment, assuming that the frequency f _{SW of} power fluctuation is in the range of 0.2 to 1 “Hz”, 0.2 [Hz], 0.3 [Hz], 0.4 [Hz] ], 0.5 [Hz], 0.6 [Hz], 0.7 [Hz], 0.8 [Hz], 0.9 [Hz], and 1.0 [Hz], respectively. That is, a value obtained by multiplying 2π) is an initial value of the angular frequency ρ. In nonlinear optimization such as the Gauss-Newton method, an optimal solution close to the initial value is searched.By setting multiple initial values at equal intervals between the upper and lower limits of the optimal solution, the optimal solution can be obtained. Even when there are a plurality of them, each optimum solution can be searched. The number and range of initial values are not limited to this. As the number of initial values increases, a finer search becomes possible, but the calculation amount increases. On the other hand, if the number of initial values is reduced, the amount of calculation can be reduced, but the search becomes rough, and there is a possibility that a certain optimum solution is not searched. The initial value range needs to be set in a range including values that the optimal solution can take. Note that if it is known in advance that there is only one frequency component of power fluctuation, only one initial value may be used.

  The frequency detection unit 12, the recording unit 13, the power fluctuation detection unit 14, the prefilter 15, and the frequency search unit 16 are realized by, for example, a computer. Note that the processing performed by each unit may be designed by a program, and the program may be executed by a general-purpose computer so that these functions are performed, or a dedicated computer for the processing may be used. The voltage sensor 11 may transmit the voltage signal v wirelessly to a computer that implements the frequency detection unit 12, the recording unit 13, the power fluctuation detection unit 14, the prefilter 15, and the frequency search unit 16, or a cable. You may connect with and send by wire. In addition, the power fluctuation frequency detection device 1 includes a circuit board on which a CPU and a RAM that implement a frequency detection unit 12, a recording unit 13, a power fluctuation detection unit 14, a prefilter 15, and a frequency search unit 16 are mounted. It is good also as an independent apparatus provided with the voltage sensor 11 to connect.

Next, a simulation for detecting the power fluctuation frequency f _SW will be described with reference to FIGS.

FIG. 2A shows the amplitude characteristic of the pre-filter 15. As shown in the figure, the pre-filter 15 attenuates frequency components other than the frequency band of 0.2 to 1 “Hz”. FIG. 2B shows the detection signal f output from the frequency detection unit 12. FIG. 2C shows an output signal obtained by passing the detection signal f through the prefilter 15. The output signal is a signal obtained by extracting only the frequency component in the frequency band of 0.2 to 1 “Hz” from the detection signal f. The output signal was input to the frequency search unit 16 to search for the power fluctuation frequency f _SW . In this simulation, data recorded when power fluctuation actually occurs is used, and the functions of the recording unit 13 and the power fluctuation detection unit 14 are omitted.

  FIG. 3 shows the simulation result. In each figure, the horizontal axis represents the number of search steps, and the vertical axis represents the evaluation value J by the evaluation function shown in the above equation (2). The evaluation value J is plotted for each search step, and the search is terminated when the evaluation value J stops changing (specifically, the amount of change in the evaluation value J becomes equal to or less than a predetermined value).

  FIG. 3A shows a simulation result when the initial value of the angular frequency ρ is 2π · 0.2 [rad / sec]. The evaluation value J at the initial value is about 4.2, and in the 74th step, the evaluation value J becomes about 2.8, and the search is completed. The angular frequency ρ at this time was about 0.403 [Hz].

  FIG. 3B shows a simulation result when the initial value of the angular frequency ρ is 2π · 0.4 [rad / sec]. In the 18th step, the evaluation value J reached about 2.815, and the search was completed. The angular frequency ρ at this time was 0.403 [Hz].

  FIG. 3C shows a simulation result when the initial value of the angular frequency ρ is 2π · 0.6 [rad / sec]. The evaluation value J at the initial value is about 3.95, and the evaluation value J becomes about 2.8 at the 74th step, and the search is completed. The angular frequency ρ at this time was about 0.403 [Hz].

  FIG. 3D shows a simulation result when the initial value of the angular frequency ρ is 2π · 0.8 [rad / sec]. The evaluation value J at the initial value is about 4.15. In the 105th step, the evaluation value J becomes about 2.8, and the search is completed. The angular frequency ρ at this time was about 0.403 [Hz].

  FIG. 3E shows a simulation result when the initial value of the angular frequency ρ is 2π · 1.0 [rad / sec]. The evaluation value J at the initial value is about 4.2. At the 118th step, the evaluation value J becomes about 2.8, and the search is completed. The angular frequency ρ at this time was about 0.403 [Hz].

As described above, in all initial values, the search result of the angular frequency ρ is about 0.403 [Hz]. That is, it was detected that the frequency f _{SW of} power fluctuation was one and was about 0.403 [Hz].

  Next, the operation and effect of the power fluctuation frequency detection device 1 according to this embodiment will be described.

According to the present embodiment, based on the voltage signal v detected by the voltage sensor 11, the frequency detection unit 12 detects the system frequency f, and the recording unit 13 records the system frequency f in the storage area. The power fluctuation detection unit 14 detects the occurrence of power fluctuation based on the system frequency f and outputs a trigger signal. The recording unit 13 reads data before and after the trigger signal is input from the power fluctuation detection unit 14 and outputs the data as a detection signal fx. The frequency search unit 16 searches for and outputs the power fluctuation frequency f _SW based on the detection signal fx ′ in which the frequency components other than the predetermined frequency band are attenuated by the pre-filter 15. The power oscillation frequency detection device 1 according to the present embodiment can detect the power oscillation frequency f _SW only by data detected at one point by the voltage sensor 11, and therefore does not need multi-point data. . Further, since the search is only performed based on the data at one point, the amount of calculation is small and the frequency f _{SW of the} power fluctuation can be easily detected.

Further, according to the present embodiment, since the search is performed using a plurality of initial values, each frequency f _SW can be detected even when there are a plurality of power fluctuation frequencies f _SW .

  Next, as a usage example of the power oscillation frequency detection device 1 according to the first embodiment, with reference to FIG. 4 and FIG. 5, the power oscillation frequency detection device 1 is provided to suppress causing or increasing power oscillation. The inverter device 2 that can be used will be described.

  FIG. 4A is a diagram for explaining the overall configuration of the inverter device 2. The inverter device 2 is a so-called power conditioner, and includes an inverter circuit 21, a control circuit 22, a current sensor 23, a voltage sensor 24, a DC voltage sensor 25, and the power oscillation frequency detection device 1. The inverter device 2 is linked to a three-phase power system A. Hereinafter, the three phases are referred to as a U phase, a V phase, and a W phase. The inverter device 2 converts DC power input from the DC power source B into AC power by the inverter circuit 21 and supplies the AC power to a load (not shown). The load is also supplied with power from the power system A. The inverter device 2 is a system with a reverse power flow, and supplies AC power to the power system A. Although not shown, a transformer for boosting (or stepping down) the AC voltage is provided on the output side of the inverter circuit 21.

  The DC power source B outputs DC power and includes, for example, a solar battery. A solar cell generates direct-current power by converting solar energy into electrical energy. The DC power source B outputs the generated DC power to the inverter device 2. Note that the DC power source B is not limited to one that generates DC power from a solar cell. For example, the DC power source B may be a fuel cell, a storage battery, an electric double layer capacitor, a lithium ion battery, or AC power generated by a diesel engine generator, a micro gas turbine generator, a wind turbine generator, or the like. It may be a device that converts to DC power and outputs it.

  The inverter circuit 21 converts DC power input from the DC power source B into AC power and outputs the AC power. The inverter circuit 21 includes a PWM control inverter and a filter (not shown). The PWM control inverter is a three-phase inverter provided with three sets of six switching elements (not shown). Based on the PWM signal input from the control circuit 22, each switching element is turned on and off to generate DC power. Convert to AC power. The filter removes high frequency components due to switching. Since the positive and negative electrodes on the input side of the inverter circuit 21 are connected to the positive and negative electrodes of the DC power supply B, respectively, the input voltage of the inverter circuit 21 matches the output voltage of the DC power supply B.

The current sensor 23 detects an instantaneous value of the three-phase output current of the inverter circuit 21. The current sensor 23 digitally converts the detected instantaneous value and outputs it to the control circuit 22 as current signals i _u , i _v , i _w . The voltage sensor 24 detects an instantaneous value of the three-phase output voltage of the inverter circuit 21. The voltage sensor 24 digitally converts the detected instantaneous value and outputs it to the control circuit 22 as voltage signals v _u , v _v , v _w . The voltage sensor 24 also serves as the voltage sensor 11 (see FIG. 1) of the power fluctuation frequency detection device 1, and any one of the voltage signals v _u , v _v , and v _w is used as the voltage signal v. The frequency is input to the frequency detector 12 (see FIG. 1). Note that the voltage sensor 11 may be provided separately from the voltage sensor 24.

  The DC voltage sensor 25 detects an instantaneous value of the input voltage of the inverter circuit 21 (that is, the output voltage of the DC power supply B). The DC voltage sensor 25 digitally converts the detected instantaneous value and outputs it to the control circuit 22 as a DC voltage signal e. The DC voltage sensor 25 detects a voltage between terminals of an electrolytic capacitor (not shown) provided between the positive electrode and the negative electrode on the input side of the inverter circuit 21. As will be described later, since the control circuit 22 performs DC voltage control, the DC voltage is controlled to a constant voltage, and the electric power stored in the electrolytic capacitor is also constant. Therefore, the power input to the inverter circuit 21 matches the power output from the DC power supply B.

The power oscillation frequency detection device 1 is configured such that the voltage signal v is input from the voltage sensor 24 instead of the voltage sensor 11 in the power oscillation frequency detection device 1 shown in FIG. The power oscillation frequency detection device 1 detects the power oscillation frequency f _SW based on the voltage signal v input from the voltage sensor 24 and outputs the detected frequency to the control circuit 22. Instead of inputting the voltage signal v detected by the voltage sensor 24, the voltage sensor 11 may be provided separately and the voltage signal v detected by the voltage sensor 11 may be used. Further, as shown in FIG. 4B, the power fluctuation frequency detection device 1 may be arranged separately from the inverter device 2 so as to transmit and receive signals to and from the inverter device 2 in a wired or wireless manner. .

The control circuit 22 controls the inverter circuit 21 and is realized by, for example, a microcomputer. The control circuit 22 receives current signals i _u , i _v , i _w input from the current sensor 23, voltage signals v _u , v _v , v _w input from the voltage sensor 24, and a DC voltage sensor 25. A PWM signal is generated based on the DC voltage signal e to be output to the inverter circuit 21.

  FIG. 5A is a functional block diagram for explaining the internal configuration of the control circuit 22.

  The control circuit 22 includes a DC voltage control unit 221, a power fluctuation component attenuation unit 222, a reactive power calculation unit 223, a reactive power control unit 224, a current control unit 225, and a PWM signal generation unit 226. Although not shown, the control circuit 22 includes a protection mechanism that detects overvoltage, overcurrent, isolated operation, and the like, and disconnects the inverter device 2 from the power system A.

The DC voltage control unit 221 is for controlling the input voltage of the inverter circuit 21. The DC voltage control unit 221 receives the deviation Δe (= e ^* −e) between the DC voltage signal e output from the DC voltage sensor 25 and the DC voltage target value e ^*, and makes the deviation zero. The DC voltage compensation signal is output to the power fluctuation component attenuation unit 222. The DC voltage control unit 221 performs, for example, PI control (proportional integration control).

The power fluctuation component attenuating unit 222 removes the same frequency component as the power fluctuation frequency f _SW (hereinafter referred to as “power fluctuation component”) from the DC voltage compensation signal. The power fluctuation component attenuating unit 222 is a so-called notch filter, which attenuates a predetermined frequency component and passes other frequency components as they are without being attenuated. The power fluctuation component attenuating unit 222 receives the DC voltage compensation signal from the DC voltage control unit 221, removes the power fluctuation component based on the frequency f _SW input from the power fluctuation frequency detection device 1, and the current control unit 225. Output to.

The transfer function F _N (s) of the power fluctuation component attenuation unit 222 is expressed by the following equation (3), for example. f ₀ is the center frequency of the frequency band to be attenuated, and a and b are parameters that determine the attenuation characteristics. The parameters a and b are appropriately determined based on actual machine verification based on the stability of the control system and the efficiency of MPPT control. The frequency f _SW input from the power fluctuation frequency detection device 1 is set as the center frequency f ₀ . The power fluctuation component attenuating unit 222 is not limited to the transfer function F _N (s) expressed by the following equation (3), and may be any unit that attenuates a predetermined frequency component.

The power oscillation component attenuating unit 222 may be configured by connecting a plurality of notch filters in multiple stages so as to cope with a case where there are a plurality of power oscillation frequencies f _SW .

The reactive power calculator 223 calculates reactive power output from the inverter circuit 21. The reactive power calculation unit 223 is based on the current signals i _u , i _v , i _w input from the current sensor 23 and the voltage signals v _u , v _v , v _w input from the voltage sensor 24. Q is calculated and output.

The reactive power control unit 224 is for controlling the reactive power output from the inverter circuit 21. The reactive power control unit 224 receives the deviation (Q ^* −Q) between the reactive power value Q output from the reactive power calculation unit 223 and the reactive power target value Q ^*, and is used to make the deviation zero. The power compensation signal is output to the current control unit 225. The reactive power control unit 224 performs PI control, for example. In this embodiment, “0” is set as the reactive power target value Q ^* so that the power factor becomes “1”.

The current control unit 225 is for controlling the output current of the inverter circuit 21. The current control unit 225 generates a compensation signal based on the current signals i _u , i _v , i _w input from the current sensor 23, and outputs the compensation signal to the PWM signal generation unit 226.

  FIG. 5B is a functional block diagram for explaining the internal configuration of the current control unit 225.

  The current controller 225 includes a three-phase / two-phase converter 225a, a rotational coordinate converter 225b, an LPF 225c, an LPF 225d, a PI controller 225e, a PI controller 225f, a stationary coordinate converter 225g, and a two-phase / three-phase converter. 225h.

The three-phase / two-phase conversion unit 225a performs a so-called three-phase / two-phase conversion process (αβ conversion process). The three-phase / two-phase conversion process is a process that converts a three-phase AC signal into an equivalent two-phase AC signal. The three-phase AC signal is a stationary orthogonal coordinate system (hereinafter referred to as “static coordinate system”). In this case, the signals are decomposed into orthogonal α-axis and β-axis components and the components of the respective axes are added to each other, thereby converting into an AC signal of the α-axis component and an AC signal of the β-axis component. The three-phase / two-phase converter 225a converts the three-phase current signals i _u , i _v , i _w input from the current sensor 23 into an α-axis current signal iα and a β-axis current signal iβ, and rotates coordinates The data is output to the conversion unit 225b.

The conversion process performed by the three-phase / two-phase conversion unit 225a is represented by a determinant represented by the following equation (4).

The rotation coordinate conversion unit 225b performs a so-called rotation coordinate conversion process (dq conversion process). The rotation coordinate conversion process is a process of converting a two-phase signal in the stationary coordinate system into a two-phase signal in the rotation coordinate system. The rotating coordinate system is an orthogonal coordinate system having orthogonal d-axis and q-axis and rotating in the same rotational direction at the same angular velocity as the fundamental wave of the system voltage of the power system A. The rotation coordinate conversion unit 225b converts the α-axis current signal iα and β-axis current signal iβ of the stationary coordinate system input from the three-phase / two-phase conversion unit 225a into rotation coordinates based on the phase θ of the fundamental wave of the system voltage. System d-axis current signal i _d and q-axis current signal i _q are converted and output.

The conversion process performed by the rotation coordinate conversion unit 225b is expressed by a determinant represented by the following expression (5).

LPF225c and LPF225d is a low-pass filter, to pass only the DC component of the d-axis current signal i _d and the q-axis current signal i _q, respectively. By rotating the coordinate transformation process, the fundamental wave component of the α-axis current signal iα and β-axis current signal iβ has been converted into a DC component of the d-axis current signal i _d and the q-axis current signal i _q, respectively. That is, the LPF 225c and the LPF 225d remove the unbalanced component and the harmonic component, and pass only the fundamental wave component.

The PI control unit 225e performs PI control (proportional integration control) based on the deviation between the DC component of the d-axis current signal i _d and the target signal, and outputs a compensation signal x _d . Signal input from the power fluctuation component attenuation unit 222 (signal obtained by removing the power fluctuation component from a DC voltage compensation signal) is used as a target signal of the d-axis current signal i _d.

PI control unit 225f performs PI control based on a deviation between the DC component and the target signal of the q-axis current signal i _q, and outputs the compensation signal x _q. The reactive power compensation signal input from the reactive power control unit 224 is used as a target signal for the q-axis current signal _iq .

The stationary coordinate conversion unit 225g converts the compensation signals x _d and x _q respectively input from the PI control unit 225e and the PI control unit 225f into the compensation signals xα and xβ of the stationary coordinate system, and the rotational coordinate conversion unit 225b is the reverse conversion process. The stationary coordinate conversion unit 225g performs a so-called stationary coordinate conversion process (inverse dq conversion process). The compensation signal x _d , x _q of the rotating coordinate system is used as the compensation signal xα of the stationary coordinate system based on the phase θ. , convert to xβ.

The conversion process performed by the stationary coordinate conversion unit 225g is represented by a determinant represented by the following expression (6).

The two-phase / three-phase converter 225h converts the compensation signals xα, xβ input from the stationary coordinate converter 225g into three-phase compensation signals x _u , x _v , x _w . The two-phase / three-phase conversion unit 225h performs a so-called two-phase / three-phase conversion process (reverse αβ conversion process), and performs a reverse conversion process to the three-phase / two-phase conversion unit 225a.

The conversion process performed by the two-phase / three-phase conversion unit 225h is represented by a determinant represented by the following equation (7).

Returning to FIG. 5A, the PWM signal generator 226 generates a PWM signal. The PWM signal generation unit 226 is a command signal for commanding the waveform of the output voltage of each phase of the inverter circuit 21 based on the three-phase compensation signals x _u , x _v , x _w input from the current control unit 225. And a PWM signal is generated by a triangular wave comparison method based on the command signal and the carrier signal. For example, a pulse signal that is high when the command signal is larger than the carrier signal and low when the command signal is equal to or less than the carrier signal is generated as a PWM signal. The generated PWM signal is output to the inverter circuit 21. Note that the PWM signal generation unit 226 is not limited to the case where the PWM signal is generated by the triangular wave comparison method, and for example, the PWM signal may be generated by a hysteresis method.

In the control circuit 22 of the inverter 2, the current control unit 225, the removed signal power fluctuation component from a DC voltage compensation signal output from the DC voltage control unit 221 as a target signal of the d-axis current signal i _d, the reactive power Current control is performed using the reactive power compensation signal input from the control unit 224 as a target signal of the q-axis current signal _iq . Then, the PWM signal generation unit 226 generates a PWM signal based on the compensation signals x _u , x _v , x _w generated by the current control unit 225 and outputs the PWM signal to the inverter circuit 21. The inverter circuit 21 performs power conversion based on the PWM signal.

  The control circuit 22 controls the DC voltage input to the inverter circuit 21 and the reactive power output from the inverter circuit 21. In addition, the control circuit 22 also controls the DC power input by controlling the DC voltage, thereby controlling the output power. Therefore, the control circuit 22 also controls the output power by controlling the DC voltage.

Since a signal obtained by attenuating the frequency component of power fluctuation from the DC voltage compensation signal for controlling the output power is used as the target signal of the d-axis current signal _id , the output power of the inverter circuit 21 also suppresses the frequency component. It will be done. Therefore, the inverter apparatus 2 can suppress causing or increasing power fluctuation. The power fluctuation frequency f _SW to be suppressed by the inverter device 2 can be easily detected by the power fluctuation frequency detection device 1 based on the voltage signal v detected by the voltage sensor 24. As in the prior art, in order to detect the power fluctuation frequency f _SW , multipoint data is not required, and it is not necessary to perform many complicated calculations.

The control circuit 22 may perform active power control instead of performing DC voltage control. That is, in the control circuit 22 shown in FIG. 5A, the current signals i _u , i _v , i _w input from the current sensor 23 and the voltage signal input from the voltage sensor 24 instead of the DC voltage control unit 221. An active power calculation unit that calculates an active power value P based on v _u , v _v , and v _w , and a deviation (P ⁾ between the active power value P output from the active power calculation unit and the active power target value P ^{* *} -P) may be input, and an active power control unit that outputs an active power compensation signal for setting the deviation to zero to the power fluctuation component attenuation unit 222 may be provided.

  In the first embodiment, the case where the filter F of the frequency search unit 16 is a notch filter has been described. However, the present invention is not limited to this. For example, a band pass filter may be used. In this case, the angular frequency ρ may be searched so that the evaluation value J is maximized. Further, if the frequency search unit 16 is a control block diagram shown in FIG. 6, the search can be made to minimize the evaluation value J by using the filter F as a bandpass filter.

In the first embodiment, the case where the power fluctuation frequency f _SW is detected only when the power fluctuation detection unit 14 detects the occurrence of the power fluctuation has been described, but the present invention is not limited to this. The power fluctuation detection unit 14 cannot reliably detect the occurrence of power fluctuations, and there is power fluctuation that the power fluctuation detection unit 14 cannot detect. Therefore, the power fluctuation frequency f _SW may always be detected without providing the power fluctuation detection unit 14. However, in this case, it is necessary to always perform a search by the frequency search unit 16. In this case, the recording unit 13 may not be provided. That is, in FIG. 1A, the system frequency f output from the frequency detection unit 12 may be directly input to the prefilter 15 without providing the recording unit 13 and the power fluctuation detection unit 14.

  In the first embodiment, the case where the pre-filter 15 passes only frequency components in a predetermined frequency band has been described. However, the present invention is not limited to this. The detection signal fx output from the recording unit 13 may be directly input to the frequency search unit 16. In this case, the detection signal fx needs to be converted into a signal indicating a deviation from a reference value (for example, 60 [Hz]) and then input to the filter F.

In the first embodiment, the case where the frequency f _{SW of} power fluctuation is detected based on the system frequency f has been described, but the present invention is not limited to this. The influence of power fluctuation appears in, for example, the system voltage and active power. Therefore, the frequency f _{SW of} power fluctuation may be detected using these. The case where it detects based on active power is demonstrated below as 2nd Embodiment.

  Fig.7 (a) is a figure for demonstrating the electric power fluctuation frequency detection apparatus which concerns on 2nd Embodiment. In the same figure, the same code | symbol is attached | subjected to the element which is the same as that of the electric power oscillation frequency detection apparatus 1 (refer FIG. 1) which concerns on 1st Embodiment (refer FIG. 1). As illustrated in FIG. 7A, the power fluctuation frequency detection device 1 </ b> A further includes a current sensor 17, and includes a power detection unit 18 instead of the frequency detection unit 12. Different from the oscillation frequency detector 1.

The current sensor 17 detects a current signal. The current sensor 17 is disposed on a power line on which the voltage sensor 11 is disposed, and detects an instantaneous value of current on the power line. Then, the detected instantaneous value is digitally converted and output to the power detector 18 as a current signal i. In the case of a three-phase alternating current, the voltage sensor 11 detects a current signal of the same phase as the voltage signal v is detected. The voltage sensor 11 may detect the three-phase voltage signals v _u , v _v and v _w , and the current sensor 17 may detect the three-phase current signals i _u , i _v and i _w . In addition, the power fluctuation frequency detection device 1A may not be provided with the current sensor 17, and the current signal i may be input from a current sensor provided in another device. For example, in the case of the inverter device 2 described in FIG. 4, the current signal i may be input from the current sensor 23.

The power detection unit 18 detects active power. The power detection unit 18 calculates the active power value P using the voltage signal v input from the voltage sensor 11 and the current signal i input from the current sensor 17. The voltage sensor 11 and the current sensor 17 detect a three-phase signal, and the power detection unit 18 uses the voltage signals v _u , v _v , v _w and the current signals i _u , i _v , i _w , The active power value P may be calculated. The power detection unit 18 outputs the calculated active power value P to the recording unit 13 and the power fluctuation detection unit 14.

  The power fluctuation detection unit 14 detects the occurrence of power fluctuation based on the active power value P input from the power detection unit 18. The power fluctuation detection unit 14 determines that the power fluctuation has occurred when the input active power value P changes greatly, for example, when the amount of change ΔP of the active power value P is equal to or greater than a threshold, and triggers The signal Tr is output to the recording unit 13.

  The recording unit 13 cyclically writes the active power value P input from the power detection unit 18 in the storage area. When the trigger signal Tr is input from the power fluctuation detection unit 14, the recording unit 13 reads data before and after the trigger signal Tr is input, and continuously outputs the data to the prefilter 15 as the detection signal Px.

  The pre-filter 15 passes only the frequency component of a predetermined frequency band in the detection signal Px input from the recording unit 13 and outputs it to the frequency search unit 16. Hereinafter, a signal that passes through the prefilter 15 and is output to the frequency search unit 16 is referred to as a detection signal Px ′.

The frequency search unit 16 searches for the frequency of the detection signal Px ′ input from the prefilter 15. The frequency search unit 16 searches for an angular frequency ρ that is an optimal solution based on the detection signal Px ′. The frequency search unit 16 outputs the frequency corresponding to the angular frequency ρ that is the optimal solution as the frequency of the detection signal Px ′, that is, the frequency f _SW of the power fluctuation.

Also in the second embodiment, similarly to the first embodiment, the frequency f _SW of the power fluctuation can be detected only by data detected at one point. Therefore, also in 2nd Embodiment, there can exist an effect similar to 1st Embodiment.

In the first and second embodiments, the same detection value (system frequency f or effective frequency) is used for the detection of the power fluctuation by the power fluctuation detection unit 14 and the detection of the frequency f _SW of the power fluctuation by the frequency search unit 16. Although the case where the power value P) is used has been described, the present invention is not limited to this. Different detection values may be used in the power fluctuation detection unit 14 and the frequency search unit 16. For example, the case where the power fluctuation detection unit 14 uses the system frequency f and the frequency search unit 16 uses the active power value P will be described below as a third embodiment.

  FIG.7 (b) is a figure for demonstrating the electric power oscillation frequency detection apparatus which concerns on 3rd Embodiment. In the same figure, the same code | symbol is attached | subjected to the element which is the same as that of the electric power oscillation frequency detection apparatus 1A (refer FIG. 7 (a)) based on 2nd Embodiment, or similar. As shown in FIG. 7 (b), the power oscillation frequency detection device 1B includes a frequency detection unit 12 in addition to the power detection unit 18, and the power oscillation frequency detection device 1A according to the second embodiment. Different.

The frequency detection unit 12 is the same as the frequency detection unit 12 of the power oscillation frequency detection device 1 (see FIG. 1) according to the first embodiment. In the present embodiment, the system frequency f detected by the frequency detection unit 12 is input to the power fluctuation detection unit 14, and the power fluctuation detection unit 14 detects the occurrence of power fluctuation based on the system frequency f. On the other hand, the active power value P detected by the power detection unit 18 is input to the recording unit 13, and the frequency search unit 16 detects the frequency f _{SW of} power fluctuation based on the active power value P.

Also in the third embodiment, similarly to the first embodiment, the frequency f _SW of the power fluctuation can be detected using only the data detected at one point. Therefore, also in the third embodiment, the same effect as in the first embodiment can be obtained.

Fig.8 (a) is a figure for demonstrating the electric power oscillation frequency detection apparatus which concerns on 4th Embodiment. In the same figure, the same code | symbol is attached | subjected to the element which is the same as that of the electric power oscillation frequency detection apparatus 1B (refer FIG.7 (b)) based on 3rd Embodiment, or similar. In the power fluctuation frequency detection device 1C shown in FIG. 8A, the effective power value P detected by the power detection unit 18 is the power fluctuation detection unit, contrary to the power fluctuation frequency detection device 1B according to the third embodiment. 14, the power fluctuation detection unit 14 detects the occurrence of power fluctuation based on the active power value P, the system frequency f detected by the frequency detection unit 12 is input to the recording unit 13, and the frequency search unit 16 detects the frequency f _{SW of the} power fluctuation based on the system frequency f.

In the fourth embodiment, similarly to the first embodiment, the frequency f _SW of the power fluctuation can be detected using only the data detected at one point. Therefore, also in the fourth embodiment, the same effect as in the first embodiment can be obtained.

  The power fluctuation detecting unit 14 may detect the occurrence of power fluctuation based on a detection value other than the system frequency f and the active power value P, for example, the voltage signal v detected by the voltage sensor 11. Good. Any detection value that detects an electrical signal that changes in accordance with the state of the power system A can be used. The power fluctuation detection unit 14 may detect the occurrence of power fluctuation based on some detection values. For example, the case where the power fluctuation detection unit 14 detects the occurrence of power fluctuation based on both the system frequency f and the active power value P will be described below as a fifth embodiment.

  FIG.8 (b) is a figure for demonstrating the power fluctuation frequency detection apparatus which concerns on 5th Embodiment. In the figure, elements that are the same as or similar to those in the power oscillation frequency detection device 1C according to the fourth embodiment (see FIG. 8A) are denoted by the same reference numerals. The power oscillation frequency detection device 1D shown in FIG. 8B is configured to detect the power oscillation frequency according to the fourth embodiment in that the system frequency f detected by the frequency detection unit 12 is also input to the power oscillation detection unit 14. Different from the device 1C.

The power fluctuation detection unit 14 has an amount of change ΔP in the active power value P input from the power detection unit 18 that is equal to or greater than a threshold value, and a change Δf in the system frequency f input from the frequency detection unit 12. When the magnitude is greater than or equal to the threshold value, it is determined that power fluctuation has occurred, and the trigger signal Tr is output to the recording unit 13. That is, the power fluctuation detection unit 14 detects the occurrence of power fluctuation only when both the system frequency f and the active power value P change greatly. In this case, it is possible to detect a more reliable occurrence of power fluctuation, and to further reduce the amount of calculation for detecting the frequency f _SW of the power fluctuation. The power fluctuation detection unit 14 may use another detection value instead of either the system frequency f or the active power value P, or in addition to the system frequency f and the active power value P, Other detection values may also be used.

Further, the power fluctuation detection unit 14 has a change amount ΔP of the active power value P input from the power detection unit 18 equal to or greater than a threshold value, or a change in the system frequency f input from the frequency detection unit 12. When the magnitude of the amount Δf is equal to or greater than the threshold value, it may be determined that power fluctuation has occurred and the trigger signal Tr may be output to the recording unit 13. That is, the power fluctuation detection unit 14 may detect the occurrence of power fluctuation when either the system frequency f or the active power value P changes greatly. In this case, the occurrence of power fluctuation can be detected more reliably, and the failure of detecting the power fluctuation frequency f _SW can be suppressed. The power fluctuation detection unit 14 may use another detection value instead of either the system frequency f or the active power value P, or in addition to the system frequency f and the active power value P, Other detection values may also be used.

Also in the fifth embodiment, similarly to the first embodiment, the frequency f _SW of the power fluctuation can be detected only by data detected at one point. Therefore, also in the fifth embodiment, the same effect as in the first embodiment can be obtained.

  The frequency detection device, the frequency detection method, and the inverter device using the detected frequency according to the present invention are not limited to the above-described embodiments. The specific configuration of each part of the frequency detection device, the frequency detection method, and the inverter device using the detected frequency according to the present invention can be varied in design in various ways.

1, 1A, 1B, 1C, 1D Power oscillation frequency detection device (frequency detection device)
11 voltage sensor 12 frequency detector (detection means, second detection means)
13 Recording Unit 14 Power Fluctuation Detection Unit 15 Prefilter (Bandpass Filter)
16 Frequency search unit 17 Current sensor 18 Power detection unit (detection means, second detection means)
2 Inverter device 21 Inverter circuit 22 Control circuit 221 DC voltage control unit 222 Power fluctuation component attenuation unit 223 Reactive power calculation unit 224 Reactive power control unit 225 Current control unit 225a Three-phase / two-phase conversion unit 225b Rotational coordinate conversion unit 225c, 225d LPF
225e, 225f PI controller 225g Static coordinate converter 225h Two-phase / three-phase converter 226 PWM signal generator 23 Current sensor 24 Voltage sensor 25 DC voltage sensor A Power system B DC power supply

Claims (14)

A frequency detection device for detecting the frequency of power fluctuations in a power system,
Detection means for detecting system frequency of the power system or active power flowing through a power line connected to the power system;
Frequency search means for searching for the frequency of the detection signal continuously detected by the detection means;
With
The frequency search means includes
A filter that receives a deviation signal based on the detection signal;
Optimization means for changing a frequency input to the filter so as to optimize an evaluation value based on an output signal of the filter;
With
An optimal frequency that optimizes the evaluation value is output as the frequency of the power fluctuation.
A frequency detection apparatus characterized by that. The filter is a notch filter, which attenuates and outputs an input frequency component from an input deviation signal,
The optimization means minimizes the evaluation value;
The frequency detection apparatus according to claim 1. The filter is a band pass filter, and attenuates and outputs components other than the input frequency from the input deviation signal,
The optimization means maximizes the evaluation value;
The frequency detection apparatus according to claim 1. The filter is a band pass filter, and attenuates and outputs components other than the input frequency from the input deviation signal,
The optimization means minimizes an evaluation value based on a signal obtained by subtracting the output signal of the filter from the deviation signal;
The frequency detection apparatus according to claim 1. The evaluation value is a value corresponding to the square of the magnitude of the output signal of the filter.
The frequency detection device according to claim 1. The optimization means performs optimization using a Gauss-Newton method.
The frequency detection apparatus according to claim 1. The frequency search means changes an initial value of the frequency input to the filter by the optimization means, and outputs an optimum frequency when each initial value is input,
The frequency detection apparatus according to claim 1. A band pass filter that attenuates components other than a predetermined frequency band from the detection signal and outputs the attenuated component to the frequency search means;
The frequency detection apparatus according to claim 1. Recording means for recording the detection value detected by the detection means;
Power fluctuation detection means for detecting that power fluctuation has occurred in the power system;
Further comprising
The frequency search means uses the detection value recorded by the recording means during the first predetermined time from when the power fluctuation detection means detects that power fluctuation has occurred as the detection signal, and the detection signal Search for the frequency of
The frequency detection apparatus according to claim 1. The frequency search means uses the detection value recorded by the recording means during the second predetermined time before the power fluctuation detection means detects that power fluctuation has occurred as the detection signal.
The frequency detection apparatus according to claim 9. The power fluctuation detection means detects that power fluctuation has occurred when the detection value detected by the detection means has changed by a predetermined value or more.
The frequency detection apparatus according to claim 9 or 10. A second detection means for detecting an electrical signal that changes in accordance with the state of the power system;
The power fluctuation detection means detects that power fluctuation has occurred when the detection value detected by the second detection means has changed by a predetermined value or more.
The frequency detection apparatus according to claim 9 or 10. An inverter device that converts DC power to AC power and outputs the AC power to the power system,
A frequency detection device according to any one of claims 1 to 12,
Outputting the AC power in which the frequency component of the power fluctuation detected by the frequency detection device is attenuated,
An inverter device characterized by that. A frequency detection method for detecting the frequency of power fluctuations in a power system,
A first step of detecting a system frequency of the power system or an active power flowing through a power line connected to the power system;
A second step of searching for the frequency of the detection signal continuously detected by the first step;
With
The second step includes
A third step of inputting a deviation signal based on the detection signal to the filter;
A fourth step of changing a frequency input to the filter so as to optimize an evaluation value based on an output signal of the filter;
A fifth step of outputting an optimal frequency that optimizes the evaluation value as the frequency of the power fluctuation;
With
The frequency detection method characterized by the above-mentioned.