Patent Description:
In the fast frequency response market, high-speed and highly-accurate measurement technology of the average apparent energy of a power system is desirable to realize high-speed control of power generation and storage plants and the like.

For example, in a known method for measuring apparent power, the instantaneous value of the active power and the instantaneous value of the reactive power are determined by acquiring the three-phase AC voltage and the thee-phase alternating current of the power system by high-speed sampling and by performing a Clarke transformation of the three-phase AC voltage and the thee-phase alternating current.

Also, harmonics, distorted waves, and the like are easily mixed into the instantaneous value of the active power and/or the instantaneous value of the reactive power when system disturbances such as an unbalanced state or the like occur in power electronics control in which a semiconductor element switches a large current. Therefore, it has also been proposed to calculate an average value synchronized with the power supply period based on the instantaneous value of the active power and the instantaneous value of the reactive power.

For example, a moving average filter is used to calculate the average value. However, in a moving average filter fixed at the nominal period, it is difficult to calculate an accurate average value under fluctuating power supply frequency conditions. It is therefore desirable for a power measurement device to be capable of more accurately measuring the average apparent power even when frequency fluctuation occurs in the presence of a system disturbance.

The document <CIT> discloses calculating instantaneous real power and instantaneous imaginary power of two phases from the power phase voltage and the load current of the three phases of a power system, and calculating the respective DC components using the moving average of these powers.

Embodiments of the invention provide a power measurement device that can more accurately measure the average apparent power even when frequency fluctuation occurs in the presence of a system disturbance.

According to an embodiment of the invention, a power measurement device includes: a first three-phase to two-phase converter converting a three-phase voltage signal of three-phase AC power into a two-phase voltage signal; a second three-phase to two-phase converter converting a three-phase current signal of the three-phase AC power into a two-phase current signal; an instantaneous power calculator calculating an instantaneous value of active power of the three-phase AC power and an instantaneous value of reactive power of the three-phase AC power based on the two-phase voltage signal and the two-phase current signal; a first moving average calculator including multiple first moving average filters calculating moving averages, wherein the multiple first moving average filters use different data quantities, and the first moving average calculator causes the multiple first moving average filters to respectively calculate multiple active power average values of different moving average data quantities; a second moving average calculator including multiple second moving average filters calculating moving averages, wherein the multiple second moving average filters use different data quantities, and the second moving average calculator causes the multiple second moving average filters to respectively calculate multiple reactive power average values of different moving average data quantities; a first average value calculator calculating an average value of the active power corresponding to a frequency of the three-phase AC power based on the multiple active power average values and frequency information representing the frequency of the three-phase AC power; and a second average value calculator calculating an average value of the reactive power corresponding to the frequency of the three-phase AC power based on the multiple reactive power average values and the frequency information representing the frequency of the three-phase AC power.

According to embodiments of the invention, a power measurement device is provided that can more accurately measure the average apparent power even when frequency fluctuation occurs in the presence of a system disturbance.

Embodiments will now be described with reference to the drawings.

The drawings are schematic and conceptual; and the relationships between the thicknesses and widths of portions, the proportions of sizes among portions, etc., are not necessarily the same as the actual values. The dimensions and/or the proportions may be illustrated differently among drawings even in the case where the same portion is illustrated.

In the specification and drawings, components similar to those described previously or illustrated in an antecedent drawing are marked with the same reference numerals; and a detailed description is omitted as appropriate.

<FIG> is a block diagram schematically illustrating a power measurement device according to a first embodiment.

As illustrated in <FIG>, the power measurement device <NUM> includes a three-phase to two-phase converter <NUM> (a first three-phase to two-phase converter), a three-phase to two-phase converter <NUM> (a second three-phase to two-phase converter), an instantaneous power calculator <NUM>, a moving average calculator <NUM> (a first moving average calculator), a moving average calculator <NUM> (a second moving average calculator), an average value calculator <NUM> (a first average value calculator), and an average value calculator <NUM> (a second average value calculator).

The power measurement device <NUM> measures the average apparent power of a power system of three-phase AC power. For example, the power measurement device <NUM> is used to measure the average apparent power at a connection point of the power system and a distributed power source such as solar power generation, wind power generation, etc. However, the average apparent power that is measured by the power measurement device <NUM> is not limited thereto, and may be the average apparent power of any three-phase AC power.

Three-phase voltage signals Va, Vb, and Vc of the three-phase AC power are input to the three-phase to two-phase converter <NUM>. The three-phase to two-phase converter <NUM> converts the three-phase voltage signals Va, Vb, and Vc into two-phase voltage signals Vα and Vβ of the α-phase and the β-phase by performing an α-β transformation (a Clarke transformation). The three-phase to two-phase converter <NUM> inputs the voltage signals Vα and Vβ after the conversion to the instantaneous power calculator <NUM>.

The three-phase voltage signals Va, Vb, and Vc may be input to the three-phase to two-phase converter <NUM> from a voltmeter that measures the voltage at the connection point, etc., or may be input to the three-phase to two-phase converter <NUM> from a higher-level controller, etc. The method for inputting the three-phase voltage signals Va, Vb, and Vc to the three-phase to two-phase converter <NUM> may be any method that can appropriately input the three-phase voltage signals Va, Vb, and Vc to the three-phase to two-phase converter <NUM>.

Three-phase current signals Ia, Ib, and Ic of the three-phase AC power are input to the three-phase to two-phase converter <NUM>. The three-phase to two-phase converter <NUM> converts the three-phase current signals Ia, Ib, and Ic into two-phase current signals Iα and Iβ of the α-phase and the β-phase by performing an α-β transformation (a Clarke transformation). The three-phase to two-phase converter <NUM> inputs the current signals Iα and Iβ after the conversion to the instantaneous power calculator <NUM>.

The three-phase current signals Ia, Ib, and Ic may be input to the three-phase to two-phase converter <NUM> from an ammeter that measures the current at the connection point, etc., or may be input to the three-phase to two-phase converter <NUM> from a higher-level controller, etc. The method for inputting the three-phase current signals Ia, Ib, and Ic to the three-phase to two-phase converter <NUM> may be any method that can appropriately input the three-phase current signals Ia, Ib, and Ic to the three-phase to two-phase converter <NUM>.

The instantaneous power calculator <NUM> calculates an instantaneous value Pinst of the active power and an instantaneous value Qinst of the reactive power of the three-phase AC power based on the voltage signals Vα and Vβ input from the three-phase to two-phase converter <NUM> and the current signals Iα and Iβ input from the three-phase to two-phase converter <NUM>. For example, the instantaneous power calculator <NUM> calculates the instantaneous value Pinst of the active power by the following formula (A), and calculates the instantaneous value Qinst of the reactive power by formula (B). <MAT> <MAT>.

The instantaneous power calculator <NUM> inputs the calculated instantaneous value Pinst of the active power to the moving average calculator <NUM>, and inputs the calculated instantaneous value Qinst of the reactive power to the moving average calculator <NUM>.

<FIG> are block diagrams schematically illustrating the moving average calculators.

As illustrated in <FIG>, the moving average calculator <NUM> includes multiple moving average filters 18a to <NUM> (first moving average filters) that calculate moving averages and use different data quantities.

The moving average calculator <NUM> inputs the instantaneous value Pinst of the active power input from the instantaneous power calculator <NUM> to each of the multiple moving average filters 18a to <NUM>, and causes the moving average filters 18a to <NUM> to respectively calculate multiple active power average values Pmaf of different moving average data quantities. The moving average calculator <NUM> inputs the multiple active power average values Pmaf respectively calculated by the moving average filters 18a to <NUM> to the average value calculator <NUM>.

The data quantities of the multiple moving average filters 18a to <NUM> correlate with sampling periods when acquiring the frequency of the three-phase AC power and the data (the voltage signals Va, Vb, and Vc and the current signals Ia, Ib, and Ic).

It is favorable for the data quantities of the moving average filters 18a to <NUM> and the sampling periods to be set to values that acquire data of precisely one period of the three-phase AC power. In other words, it is favorable for the moving average filters 18a to <NUM> to calculate the moving average of the data (the instantaneous value Pinst of the active power) of one period of the three-phase AC power.

For example, when the frequency of the three-phase AC power is <NUM> and the sampling period is <NUM>, the period of the three-phase AC power is <NUM>; it is therefore favorable for the data quantity to be <NUM>/<NUM>, i.e., <NUM>. Thus, when the frequency of the three-phase AC power is <NUM> and the sampling period is <NUM>, <NUM> data points are acquired, and the moving average is calculated based on the <NUM> data points. The moving average of the data of one period of the three-phase AC power is calculated thereby, and the superimposition on the instantaneous value Pinst of the active power of the fluctuation of components at the frequency of the three-phase AC power and the fluctuation of components at integer multiples of the frequency of the three-phase AC power can be suppressed.

For example, as illustrated in formula (A) and formula (B) recited above, the instantaneous value Pinst of the active power and the instantaneous value Qinst of the reactive power are represented by the product of the voltage signals Vα and Vβ and the current signals Iα and Iβ. Therefore, for example, when an imbalance occurs in the voltage signals Va, Vb, and Vc and the current signals Ia, Ib, and Ic, according to trigonometric identities, the instantaneous value Pinst of the active power and the instantaneous value Qinst of the reactive power undesirably fluctuate at a frequency that is twice the frequency of the three-phase AC power. Thus, even when the instantaneous value Pinst of the active power and the instantaneous value Qinst of the reactive power fluctuate at twice the frequency, the effects of the fluctuation can be suppressed as described above by calculating the moving average of the data of one period of the three-phase AC power. For example, even when a system disturbance such as an unbalanced state or the like occurs in the three-phase AC power, the effects of the system disturbance can be suppressed, and the fluctuation of the average value Pmaf of the active power caused by the system disturbance can be suppressed.

Thus, a data quantity L can be represented by the following formula (C), where L is the data quantities of the moving average filters 18a to <NUM>, T is one period of the three-phase AC power, and Δt is the sampling period of the data.

It is favorable to set the sampling period Δt to be sufficiently small with respect to one period T of the three-phase AC power. For example, it is favorable to set the sampling period Δt to be not more than <NUM>/<NUM> of one period T of the three-phase AC power.

<FIG> shows an example in which the moving average calculator <NUM> includes the seven moving average filters 18a to <NUM> having the data quantities L respectively set to <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and <NUM>. The moving average filter 18a that has the data quantity L set to <NUM> corresponds to a three-phase AC power frequency of <NUM>. The moving average filter 18b that has the data quantity L set to <NUM> corresponds to a three-phase AC power frequency of <NUM>. The moving average filter 18c that has the data quantity L set to <NUM> corresponds to a three-phase AC power frequency of <NUM>. The moving average filter 18d that has the data quantity L set to <NUM> corresponds to a three-phase AC power frequency of <NUM>. The moving average filter 18e that has the data quantity L set to <NUM> corresponds to a three-phase AC power frequency of <NUM>. The moving average filter 18f that has the data quantity L set to <NUM> corresponds to a three-phase AC power frequency of <NUM>. The moving average filter <NUM> that has the data quantity L set to <NUM> corresponds to a three-phase AC power frequency of <NUM>.

When the frequency of the three-phase AC power is <NUM>, the fluctuation of the average value Pmaf of the active power can be suppressed as described above by using the calculation result of the moving average filter 18d having the data quantity L set to <NUM>. On the other hand, when the frequency of the three-phase AC power fluctuates from <NUM>, it is difficult to appropriately suppress the fluctuation of the average value Pmaf of the active power even when using the calculation result of the moving average filter 18d.

Therefore, the moving average calculator <NUM> prepares the multiple moving average filters 18a to <NUM> that calculate moving averages by using different data quantities. Thereby, the moving average calculator <NUM> can adapt to multiple frequencies of the three-phase AC power. For example, the calculation results of the other moving average filters 18a to 18c and 18e to <NUM> are used when the frequency of the three-phase AC power fluctuates from <NUM>. Thereby, the moving average calculator <NUM> can suppress the fluctuation of the average value Pmaf of the active power even when the frequency of the three-phase AC power fluctuates.

The data quantities L set for the multiple moving average filters 18a to <NUM> are not limited to those described above. For the multiple moving average filters 18a to <NUM>, it is sufficient for at least a data quantity L that corresponds to the nominal frequency of the three-phase AC power (in the example, <NUM>) to be set for one of the moving average filters 18a to <NUM>.

For example, it is favorable to set the data quantities L of the multiple moving average filters 18a to <NUM> to be on the high frequency side and the low frequency side of the nominal frequency of the three-phase AC power, such as the three-phase AC power nominal frequency ±<NUM>, ±<NUM>,. , ±n as in the example described above. Thereby, fluctuation on the high side and fluctuation on the low side of the frequency of the three-phase AC power can be appropriately adapted to. However, the method for setting the data quantities L of the moving average filters 18a to <NUM> is not limited to that described above, and may be any method. For example, when a tendency of the fluctuation of the frequency of the three-phase AC power, such as the fluctuation on the high frequency side being large, is known beforehand, etc., the setting of the data quantities L may be biased to the high or low frequency side. Also, the number of moving average filters located in the moving average calculator <NUM> is not limited to seven and may be any number.

As illustrated in <FIG>, the moving average calculator <NUM> includes multiple moving average filters 20a to <NUM> (second moving average filters) that calculate moving averages by using different data quantities.

The moving average calculator <NUM> inputs the instantaneous value Qinst of the reactive power input from the instantaneous power calculator <NUM> to each of the multiple moving average filters 20a to <NUM> and causes the moving average filters 20a to <NUM> to respectively calculate multiple reactive power average values Qmaf by using different moving average data quantities. The moving average calculator <NUM> inputs the multiple reactive power average values Qmaf respectively calculated by the moving average filters 20a to <NUM> to the average value calculator <NUM>. The configuration of the moving average calculator <NUM> is similar to the configuration of the moving average calculator <NUM>, and a detailed description is therefore omitted below.

<FIG> are graphs schematically illustrating an example of the operation of the power measurement device according to the first embodiment.

<FIG> schematically illustrates an example of the voltage signal Va and the current signal Ia.

<FIG> schematically illustrates an example of the voltage signal Vb and the current signal Ib.

<FIG> schematically illustrates an example of the voltage signal Vc and the current signal Ic.

<FIG> schematically illustrates an example of the instantaneous value Pinst of the active power calculated by the instantaneous power calculator <NUM> and the average value Pmaf of the active power calculated by the multiple moving average filters 18a to <NUM> of the moving average calculator <NUM>.

<FIG> schematically illustrates an example of the instantaneous value Qinst of the reactive power calculated by the instantaneous power calculator <NUM> and the average value Qmaf of the reactive power calculated by the multiple moving average filters 20a to <NUM> of the moving average calculator <NUM>.

<FIG> schematically illustrates an example of the average value Pmaf of the active power calculated by the multiple moving average filters 18a to <NUM> of the moving average calculator <NUM>.

In the example as illustrated in <FIG>, an example of an unbalanced state is illustrated in which the voltage signal Va = <NUM> pu (Per Unit), the voltage signal Vb = <NUM> pu, the voltage signal Vc = <NUM> pu, the current signal Ia = <NUM> pu, the current signal Ib = <NUM> pu, and the current signal Ic = <NUM> pu. Also, in the example, the frequency of the voltage signals Va, Vb, and Vc and the current signals Ia, Ib, and Ic is <NUM>.

Due to the unbalanced state as illustrated in <FIG>, an oscillating component of <NUM> appears in the instantaneous value Pinst of the active power. Conversely, in the average value Pmaf of the active power, the oscillating component of the instantaneous value Pinst of the active power can be suppressed after <NUM> of data.

In <FIG>, the average values Pmaf of the active power calculated by the multiple moving average filters 18a to <NUM> are superimposed and appear as one line. Similarly, in <FIG>, the average values Qmaf of the reactive power calculated by the multiple moving average filters 20a to <NUM> are superimposed and appear as one line.

<FIG> is an enlarged illustration of a portion of the average values Pmaf of the active power of the moving average filters 18a to <NUM> illustrated in <FIG> from <NUM>. In the example as illustrated in <FIG>, the frequency of the voltage signals Va, Vb, and Vc and the current signals Ia, Ib, and Ic is <NUM>; therefore, the oscillating component of the instantaneous value Pinst of the active power is best suppressed for the average value Pmaf of the active power calculated by the moving average filter 18d having the data quantity L set to <NUM>. Also, it can be seen that the remaining effects of the oscillating component of the instantaneous value Pinst of the active power undesirably increase away from the data quantity L of <NUM>.

Thus, the fluctuation of the component having twice the frequency of the three-phase AC power superimposed onto the instantaneous value Pinst of the active power can be appropriately suppressed by calculating the moving average of the data of one period of the three-phase AC power.

The multiple active power average values Pmaf from the moving average calculator <NUM> is input to the average value calculator <NUM>, and frequency information f representing the frequency of the three-phase AC power is input to the average value calculator <NUM>. For example, the frequency information f is input to the average value calculator <NUM> from an external frequency detector, a higher-level controller, or the like via a network, etc..

The average value calculator <NUM> calculates an average value Pave of the active power corresponding to the frequency of the three-phase AC power based on the frequency information f and the multiple active power average values Pmaf input from the moving average calculator <NUM>.

<FIG> is a graph schematically illustrating an example of the operation of the average value calculator.

<FIG> illustrates an example of the relationship between the data quantity L (the frequency of the three-phase AC power) and the average value Pmaf of the active power calculated by the moving average calculator <NUM>. In the example illustrated in <FIG>, an example is illustrated in which the moving average calculator <NUM> calculates more average values Pmaf of the active power than the example illustrated in <FIG>. <FIG> illustrates an example in which nineteen average values Pmaf of the active power are calculated.

As illustrated in <FIG>, the average values Pmaf of the active power calculated by the moving average calculator <NUM> are acquired as discrete data corresponding to prescribed data quantities L. Therefore, when the current frequency of the three-phase AC power is between the data quantities L, it is difficult to appropriately suppress the fluctuation of the component having twice the frequency of the three-phase AC power superimposed onto the instantaneous value Pinst of the active power based on the calculation results of the moving average calculator <NUM>.

On the other hand, as illustrated in <FIG>, the change of the average value Pmaf of the active power between the data quantities L is determined to be continuous and monotonous between the average values Pmaf of the active power of the data quantities L.

Therefore, the average value calculator <NUM> calculates the average value Pave of the active power corresponding to the frequency of the three-phase AC power by selecting a prescribed number of active power average values Pmaf at frequencies (data quantities L) near the frequency represented by the frequency information f among the multiple active power average values Pmaf calculated by the moving average calculator <NUM>, and by performing a linear interpolation of the selected prescribed number of active power average values Pmaf. It is favorable for the prescribed number to be, for example, about two or three. However, the prescribed number is not limited thereto; it is sufficient for the prescribed number to be any number corresponding to the settings such as the sampling period Δt, the data quantities L, etc..

For example, when the frequency represented by the frequency information f is <NUM>, the corresponding data quantity L is about <NUM> according to formula (C) described above. In such a case, for example, the average value calculator <NUM> calculates the average value Pave of the active power corresponding to the frequency of the three-phase AC power by selecting the average value Pmaf of the active power of the data quantity L = <NUM> and the average value Pmaf of the active power of the data quantity L = <NUM> in <FIG>, and by performing linear interpolation of the selected two average values Pmaf of the active power. Thereby, the average value Pave of the active power can be obtained in which the fluctuation of the component having twice the frequency of the three-phase AC power superimposed onto the instantaneous value Pinst of the active power is appropriately suppressed, even when the frequency of the three-phase AC power fluctuates and the current frequency of the three-phase AC power is between the data quantities L.

The method for calculating the average value Pave of the active power by the average value calculator <NUM> is not limited to that described above. For example, as illustrated by the broken line in <FIG>, an approximate curve CA of the multiple active power average values Pmaf calculated by the moving average calculator <NUM> may be calculated, and the average value Pave of the active power may be calculated based on the approximate curve CA.

However, in such a case, there is a possibility that the calculation of the approximate curve CA may become complex, and a deviation in the power value may undesirably occur at some portion of the multiple active power average values Pmaf. As described above, the average value Pave of the active power corresponding to the frequency of the three-phase AC power is calculated by selecting a prescribed number of active power average values Pmaf having frequencies near the frequency represented by the frequency information f among the multiple active power average values Pmaf calculated by the moving average calculator <NUM>, and by performing a linear interpolation of the selected prescribed number of active power average values Pmaf. Thereby, the average value Pave of the active power can be more appropriately calculated by a relatively simple calculation.

The multiple reactive power average values Qmaf from the moving average calculator <NUM> are input to the average value calculator <NUM>, and the frequency information f representing the frequency of the three-phase AC power is input to the average value calculator <NUM>. Similarly to the average value calculator <NUM>, the average value calculator <NUM> calculates an average value Qave of the reactive power corresponding to the frequency of the three-phase AC power based on the frequency information f and the multiple reactive power average values Qmaf input from the moving average calculator <NUM>.

Thereby, the average value Qave of the reactive power can be obtained in which the fluctuation of the component having twice the frequency of the three-phase AC power superimposed is the instantaneous value Qinst of the reactive power is appropriately suppressed even when the frequency of the three-phase AC power fluctuates and the current frequency of the three-phase AC power is between the data quantities L.

Thus, in the power measurement device <NUM> according to the embodiment, the average value Pave of the active power and the average value Qave of the reactive power can be obtained in which the fluctuation is appropriately suppressed even when frequency fluctuation occurs in the presence of a system disturbance. Accordingly, according to the power measurement device <NUM> according to the embodiment, the average apparent power can be more accurately measured based on the average value Pave of the active power and the average value Qave of the reactive power even when frequency fluctuation occurs in the presence of a system disturbance. The average apparent power can be measured using the formula of S<NUM> = Pave<NUM> + Qave<NUM>, where S is the average apparent power.

<FIG> is a block diagram schematically illustrating a power measurement device according to a second embodiment.

As illustrated in <FIG>, the power measurement device 10a further includes a median filter <NUM> (a first median filter) and a median filter <NUM> (a second median filter). Components that are substantially the same in function and configuration as those of the first embodiment described above are marked with the same reference numerals, and a detailed description is omitted.

The average value Pave of the active power calculated by the average value calculator <NUM> is input to the median filter <NUM>. The median filter <NUM> calculates a median value Pmed of a prescribed number of active power average values Pave calculated by the average value calculator <NUM>.

The average value Qave of the reactive power calculated by the average value calculator <NUM> is input to the median filter <NUM>. Similarly to the median filter <NUM>, the median filter <NUM> calculates a median value Qmed of a prescribed number of reactive power average values Qave calculated by the average value calculator <NUM>.

The prescribed numbers used by the median filters <NUM> and <NUM> to calculate the median values Pmed and Qmed are, for example, about <NUM> to <NUM>. However, the prescribed numbers are not limited thereto and may be any number. The prescribed numbers are not necessarily the same between the median filters <NUM> and <NUM>, and may be different.

<FIG> is a block diagram schematically illustrating an example of the operation of the power measurement device according to the second embodiment.

<FIG> schematically illustrates an example of the average value Pave of the active power calculated by the average value calculator <NUM>, the median value Pmed of the average value Pave of the active power calculated by the median filter <NUM>, and a reference average value Pref of the active power. The reference average value Pref of the active power is the moving average value of the active power calculated by a moving average filter using a data quantity L corresponding to the nominal frequency of the three-phase AC power.

<FIG> schematically illustrates an example of the operation of the power measurement device 10a when an unbalanced state occurs in which the voltage and the current of one phase among the three-phase AC power are zero, and the frequency fluctuates from <NUM> to <NUM> between a timing t1 and a timing t2.

As illustrated in <FIG>, the reference average value Pref of the active power for which the data quantity L of the moving average filter is fixed greatly fluctuates between the timing t1 and the timing t2 in which the fluctuation of the frequency occurs.

Conversely, compared to the reference average value Pref of the active power, the fluctuation can be appropriately suppressed for the average value Pave of the active power calculated by the average value calculator <NUM> even between the timing t1 and the timing t2 when the fluctuation of the frequency occurs. Also, compared to the average value Pave of the active power, the fluctuation can be better suppressed for the median value Pmed of the average value Pave of the active power calculated by the median filter <NUM> between the timing t1 and the timing t2 when the fluctuation of the frequency occurs.

Thus, the power measurement device 10a further includes the median filters <NUM> and <NUM>, and calculates the median value Pmed of the average value Pave of the active power and the median value Qmed of the average value Qave of the reactive power. Thereby, in the power measurement device 10a according to the embodiment, the average apparent power can be more accurately measured based on the median value Pmed of the average value Pave of the active power and the median value Qmed of the average value Qave of the reactive power even when frequency fluctuation occurs in the presence of a system disturbance.

<FIG> is a block diagram schematically illustrating a power measurement device according to a third embodiment.

As illustrated in <FIG>, the power measurement device 10b further includes a frequency detector <NUM>. The frequency detector <NUM> detects the frequency of the three-phase AC power and inputs the frequency information f of the detected frequency to the average value calculators <NUM> and <NUM>.

In the power measurement device 10b, the average value calculator <NUM> calculates the average value Pave of the active power corresponding to the frequency of the three-phase AC power based on the multiple active power average values Pmaf input from the moving average calculator <NUM> and the frequency information f input from the frequency detector <NUM>. Similarly, the average value calculator <NUM> calculates the average value Qave of the reactive power corresponding to the frequency of the three-phase AC power based on the multiple reactive power average values Qmaf input from the moving average calculator <NUM> and the frequency information f input from the frequency detector <NUM>.

<FIG> is a block diagram schematically illustrating the frequency detector.

As illustrated in <FIG>, the frequency detector <NUM> includes an orthogonal coordinate signal generator <NUM> and a frequency calculator <NUM>. The frequency detector <NUM> detects the frequency of the power system of the three-phase AC power.

The orthogonal coordinate signal generator <NUM> generates orthogonal two-phase voltage signals Vα' and Vβ' from the three-phase voltage signals Va, Vb, and Vc of the three-phase AC power. For example, the three-phase voltage signals Va, Vb, and Vc are detected by a voltage detector or the like, and are input to the orthogonal coordinate signal generator <NUM>. The three-phase voltage signals Va, Vb, and Vc are, for example, instantaneous values of a three-phase AC voltage input at a prescribed sampling period.

The orthogonal coordinate signal generator <NUM> includes a three-phase to two-phase converter <NUM>, a rotating coordinate converter <NUM>, moving average filters <NUM> and <NUM>, and an inverse converter <NUM>.

The three-phase to two-phase converter <NUM> converts the three-phase voltage signals Va, Vb, and Vc into the two-phase voltage signals Vα and Vβ of the α-phase and the β-phase by performing an α-β transformation (a Clarke transformation).

The two-phase voltage signals Vα and Vβ are input to the rotating coordinate converter <NUM>, and a nominal phase θn obtained by integrating a nominal angular frequency ωn of the power system is input to the rotating coordinate converter <NUM>. The rotating coordinate converter <NUM> performs a rotating coordinate transformation of the voltage signals Vα and Vβ of the orthogonal two-axis coordinates into voltage signals Vd and Vq of a coordinate system (dq coordinates) synchronized with the phase θn by a so-called dq transformation (a Park transformation). The voltage signal Vd is a voltage signal of the d-axis component of the three-phase AC power (the voltage signals Va, Vb, and Vc); and the voltage signal Vq is a voltage signal of the q-axis component of the three-phase AC power (the voltage signals Va, Vb, and Vc) of the power system.

The moving average filter <NUM> outputs a voltage signal Vd' after the moving average calculation by calculating the moving average of the voltage signal Vd. Similarly, the moving average filter <NUM> outputs a voltage signal Vq' after the moving average calculation by calculating the moving average of the voltage signal Vq. Thus, the moving average filters <NUM> and <NUM> suppress the high frequency components of the voltage signals Vd and Vq by calculating the moving averages of the voltage signals Vd and Vq. For example, the moving average filters <NUM> and <NUM> suppress the harmonic components included in the voltage signals Vd and Vq. For example, undesirable effects on the detection of the frequency due to trouble at the power system side such as voltage imbalance of the three phases, harmonics, noise, etc., can be suppressed thereby.

By performing an inverse transformation of the voltage signals Vd' and Vq' of the rotating coordinate system into an orthogonal two-axis coordinate system, the inverse converter <NUM> converts the voltage signals Vd' and Vq' into the voltage signals Vα' and Vβ' of the orthogonal two-axis coordinates after the moving average calculation. Thereby, the orthogonal coordinate signal generator <NUM> generates the orthogonal two-phase voltage signals Vα' and Vβ' from the three-phase voltage signals Va, Vb, and Vc.

The frequency calculator <NUM> calculates the frequency information f based on the two-phase voltage signals Vα' and Vβ' generated by the orthogonal coordinate signal generator <NUM>. By using a PLL (Phase-Locked-Loop) calculation, the frequency calculator <NUM> detects a synchronous phase θαβPLL synchronized with the voltage signals Vα' and Vβ' after the two-phase conversion and calculates the frequency information f from an angular frequency ω obtained in the detection process of the synchronous phase θαβPLL.

The frequency calculator <NUM> includes an angular frequency calculator AFP. The angular frequency calculator AFP includes, for example, arithmetic units <NUM>, <NUM>, and <NUM>, multipliers <NUM> and <NUM>, a subtractor <NUM>, arithmetic units <NUM> and <NUM>, an integrator <NUM>, adders <NUM> and <NUM>, an integrator <NUM>, an arithmetic unit <NUM>, and a subtractor <NUM>.

The arithmetic unit <NUM> calculates cosθn and sinθn from the two-phase voltage signals Vα' and Vβ'. The arithmetic unit <NUM> calculates cosθn by using the formula <MAT>, and calculates sinθn by using the formula <MAT>. The arithmetic unit <NUM> inputs the calculated cosθn to the multiplier <NUM>, and inputs the calculated sinθn to the multiplier <NUM>.

The arithmetic unit <NUM> calculates sinθαβPLL based on the detected synchronous phase θαβPLL, and inputs sinθαβPLL to the multiplier <NUM>.

The arithmetic unit <NUM> calculates cosθαβPLL based on the detected synchronous phase θαβPLL, and inputs cosθαβPLL to the multiplier <NUM>.

The multiplier <NUM> multiplies the input cosθn and sinθαβPLL and inputs the multiplication result to the subtractor <NUM>.

The multiplier <NUM> multiplies the input sinθn and cosθαβPLL and inputs the multiplication result to the subtractor <NUM>.

The subtractor <NUM> calculates an error phase Δθ between the phase θn of the power system and the synchronous phase θαβPLL by calculating sinθn·cosθαβPLL - cosθn·sinθαβLL. The frequency calculator <NUM> calculates the error phase Δθ as <MAT>.

The arithmetic unit <NUM> multiplies the error phase Δθ by a proportional gain KP and inputs the multiplication result to the adder <NUM>.

The arithmetic unit <NUM> multiplies the error phase Δθ by an integral gain KI and inputs the multiplication result to the integrator <NUM>.

The integrator <NUM> integrates the multiplication result of the error phase Δθ and the integral gain KI and inputs the integral to the adder <NUM>.

The adder <NUM> adds the integral of the multiplication result of the arithmetic unit <NUM> and the integrator <NUM>. The arithmetic units <NUM> and <NUM>, the integrator <NUM>, and the adder <NUM> calculate a command value Δω of the angular frequency for setting the error phase Δθ to zero by a so-called proportional-integral control.

The command value Δω of the angular frequency calculated by the adder <NUM> is input to the adder <NUM>, and the nominal angular frequency ωn of the power system is input to the adder <NUM>. The adder <NUM> calculates the angular frequency ω of the power system by adding the command value Δω of the angular frequency and the nominal angular frequency ωn of the power system. Thus, the angular frequency calculator AFP calculates the angular frequency ω by performing the proportional-integral control based on the two-phase voltage signals Vα' and Vβ'.

The integrator <NUM> calculates a synchronous phase θ from the angular frequency ω by integrating the angular frequency ω calculated by the adder <NUM>. The integrator <NUM> inputs the calculated synchronous phase θ to the subtractor <NUM>.

The arithmetic unit <NUM> calculates a correction value by multiplying the integration result of the integrator <NUM> by a constant Kϕ. The constant Kϕ is determined by Kϕ = (Tω - TSP)/<NUM>. TSP is the sampling period of the voltage signals Va, Vb, and Vc. Tω is the window length of the moving average filters <NUM> and <NUM>. Tω is represented by N·TSP, where N is the averaging number of the moving average filters <NUM> and <NUM>. The arithmetic unit <NUM> inputs the calculated correction value to the subtractor <NUM>.

The subtractor <NUM> corrects the synchronous phase θ by subtracting the correction value from the synchronous phase θ. The subtractor <NUM> calculates the synchronous phase θαβPLL by the correction.

The angular frequency calculator AFP synchronizes the synchronous phase θαβPLL with the phase θn of the power system by feeding back the detected synchronous phase θαβPLL to the arithmetic units <NUM> and <NUM>. Thus, based on the angular frequency ω, the angular frequency calculator AFP detects the synchronous phase θαβPLL synchronized with the two-phase voltage signals Vα' and Vβ' after calculating the moving averages, calculates the error phase Δθ between the nominal phase θn of the power system and the synchronous phase θαβPLL, and calculates the angular frequency ω to cause the error phase Δθ to be zero. For example, the configuration of the PLL of the angular frequency calculator AFP (the frequency calculator <NUM>) of the example may be called an αβEPMAFPLL (αβ Enhanced Pre-filtering Moving Average Filter PLL).

The frequency calculator <NUM> further includes an arithmetic unit <NUM>, a rate limiter <NUM>, subtractors <NUM> and <NUM>, a prediction calculator <NUM>, a switching element <NUM>, and a switching circuit <NUM>. The frequency calculator <NUM> calculates the frequency information f from the calculated angular frequency ω. The adder <NUM> inputs the calculated angular frequency ω to the integrator <NUM> and inputs the angular frequency ω to the rate limiter <NUM>.

The rate limiter <NUM> limits a change of the frequency information f equal to or greater than a prescribed change rate by limiting a change of the angular frequency ω equal to or greater than a prescribed change rate. For example, the rate limiter <NUM> suppresses the change of the frequency information f equal to or greater than <NUM>/sec.

Thus, by providing the rate limiter <NUM>, even when a phase jump or the like occurs in the three-phase AC power, an abrupt fluctuation of the frequency information f can be suppressed, and the error of the calculation of the frequency information f can be reduced.

The subtractor <NUM> is connected with the input and output sides of the rate limiter <NUM>. The subtractor <NUM> subtracts the output value of the rate limiter <NUM> from the input value of the rate limiter <NUM>. In other words, the subtractor <NUM> calculates the difference between the input value and the output value of the rate limiter <NUM>. The difference is calculated by the subtractor <NUM> when the calculated value of the angular frequency ω abruptly increases, the angular frequency ω is limited by the rate limiter <NUM>, and the output value of the rate limiter <NUM> drops below the input value of the rate limiter <NUM>. The subtractor <NUM> inputs the calculation result of the difference to the subtractor <NUM>.

The subtractor <NUM> is located between the arithmetic unit <NUM> and the integrator <NUM> of the angular frequency calculator AFP. The subtractor <NUM> subtracts the calculation result of the difference of the subtractor <NUM> from the multiplication result of the arithmetic unit <NUM> multiplying the error phase Δθ by the integral gain KI. In other words, when the rate limiter <NUM> limits the angular frequency ω, the subtractor <NUM> subtracts the amount limited by the rate limiter <NUM> from the calculation of the integration operation of the proportional-integral control.

Thus, in the frequency calculator <NUM>, the subtractors <NUM> and <NUM> are included and feed back the output-input difference of the rate limiter <NUM> to the calculation of the proportional-integral control of the angular frequency calculator AFP. Even when a phase jump or the like occurs in the three-phase AC power, an abrupt fluctuation of the frequency information f can be more reliably suppressed thereby, and the error of the calculation of the frequency information f can be further reduced. For example, such control of the feedback may be called anti reset wind up.

The prediction calculator <NUM> is arranged in series with the rate limiter <NUM>. The prediction calculator <NUM> calculates a predicted value ω' of the angular frequency ω after a prescribed time interval has elapsed based on the angular frequency ω output from the rate limiter <NUM> and the derivative of the angular frequency ω.

The switching element <NUM> selectively switches between the state in which only the rate limiter <NUM> is connected in series to the arithmetic unit <NUM> and the state in which the rate limiter <NUM> and the prediction calculator <NUM> are connected in series to the arithmetic unit <NUM>. At this time, when the switching element <NUM> is in either state, the output of the rate limiter <NUM> is input to the subtractor <NUM>; and the output-input difference of the rate limiter <NUM> is fed back to the calculation of the proportional-integral control of the angular frequency calculator AFP.

The switching circuit <NUM> selectively switches between a first state in which the angular frequency ω output from the rate limiter <NUM> is input to the arithmetic unit <NUM>, and a second state in which the predicted value ω' output from the prediction calculator <NUM> is input to the arithmetic unit <NUM>. For example, the switching circuit <NUM> selectively switches between the first state and the second state by controlling the switching of the path by the switching element <NUM>.

However, switching between the first state and the second state is not limited thereto. For example, the first state may be taken to be when only the rate limiter <NUM> operates; and the second state may be taken to be when the rate limiter <NUM> and the prediction calculator <NUM> operate. In such a case, the switching element <NUM> is omissible.

The voltage signal Vd of the d-axis component and the voltage signal Vq of the q-axis component that are calculated by the rotating coordinate converter <NUM> of the orthogonal coordinate signal generator <NUM> are input to the switching circuit <NUM>. The switching circuit <NUM> detects a phase jump of the power system based on the input voltage signals Vd and Vq. In the state in which the phase jump of the power system is not detected, the switching circuit <NUM> selects the first state and inputs the angular frequency ω to the arithmetic unit <NUM>. Then, when the phase jump of the power system is detected, the switching circuit <NUM> selects the second state for a constant interval, and inputs the predicted value ω' to the arithmetic unit <NUM> for the constant interval. The switching circuit <NUM> returns from the second state to the first state after the constant interval has elapsed.

The arithmetic unit <NUM> calculates the frequency information f from the angular frequency ω or the predicted value ω' by multiplying the angular frequency ω or the predicted value ω' of the angular frequency ω by <NUM>/<NUM>π.

Thus, the frequency calculator <NUM> calculates the frequency information f of the three-phase AC power from the two-phase voltage signals Vα' and Vβ'. The frequency detector <NUM> detects the frequency information f of the three-phase AC power from the three-phase voltage signals Va, Vb, and Vc.

<FIG> is a block diagram schematically illustrating the switching circuit.

As illustrated in <FIG>, the switching circuit <NUM> includes a differential circuit <NUM>, an absolute value calculation circuit <NUM>, a differential circuit <NUM>, an absolute value calculation circuit <NUM>, an adder <NUM>, and a determination circuit <NUM>. The voltage signals Vd and Vq that are calculated by the rotating coordinate converter <NUM> are input to the switching circuit <NUM>.

The differential circuit <NUM> calculates the derivative of the voltage signal Vd. In other words, the differential circuit <NUM> calculates the slope of the voltage signal Vd. The absolute value calculation circuit <NUM> calculates the absolute value of the derivative of the voltage signal Vd calculated by the differential circuit <NUM>.

Similarly, the differential circuit <NUM> calculates the derivative of the voltage signal Vq. In other words, the differential circuit <NUM> calculates the slope of the voltage signal Vq. The absolute value calculation circuit <NUM> calculates the absolute value of the derivative of the voltage signal Vq calculated by the differential circuit <NUM>.

The adder <NUM> calculates the total value of the absolute value of the derivative of the voltage signal Vd and the absolute value of the derivative of the voltage signal Vq and inputs the calculated total value to the determination circuit <NUM>.

The determination circuit <NUM> determines whether or not the input total value is not less than a prescribed value. The voltage signal Vd of the d-axis component of the three-phase AC power and the voltage signal Vq of the q-axis component abruptly change when a phase jump occurs in the three-phase AC power. Therefore, when the total value of the absolute value of the derivative of the voltage signal Vd and the absolute value of the derivative of the voltage signal Vq reaches or exceeds the prescribed value, it can be considered that a phase jump has occurred in the three-phase AC power.

The determination circuit <NUM> switches the path of the switching element <NUM>. When the total value is less than the prescribed value, the determination circuit <NUM> sets the switching element <NUM> to the state in which the output of the rate limiter <NUM> is input to the arithmetic unit <NUM>. In other words, the first state is selected when the determination circuit <NUM> determines that a phase jump has not occurred in the power system.

When the total value is not less than the prescribed value, the determination circuit <NUM> sets the switching element <NUM> to the state in which the output of the prediction calculator <NUM> is input to the arithmetic unit <NUM>. In other words, the second state is selected when the determination circuit <NUM> determines that a phase jump has occurred in the three-phase AC power.

Thus, the switching circuit <NUM> selects the first state when the total value of the absolute value of the derivative of the voltage signal Vd and the absolute value of the derivative of the voltage signal Vq is less than the prescribed value, and selects the second state when the total value is not less than the prescribed value.

When switching from the first state to the second state, for example, the determination circuit <NUM> determines whether or not a constant interval has elapsed from the timing of switching from the first state to the second state, and returns the second state to the first state after the constant interval has elapsed.

In other words, the frequency calculator <NUM> calculates a system frequency f based on the angular frequency ω output from the rate limiter <NUM>, and when determining that a phase jump has occurred in the power system, switches to the predicted value ω' output from the prediction calculator <NUM> for a constant interval, and calculates the system frequency f based on the predicted value ω' for the constant interval from the determination of the occurrence of the phase jump.

The frequency detector <NUM> may have the function of externally outputting the detection result of the occurrence of the phase jump. Thereby, for example, in the power measurement device 10b that includes the frequency detector <NUM>, etc., it is possible to utilize the detection result of the occurrence of the phase jump; and the functionality of the frequency detector <NUM> can be further increased.

<FIG> is a block diagram schematically illustrating the prediction calculator.

As illustrated in <FIG>, the prediction calculator <NUM> includes an adder <NUM>, a differential circuit <NUM>, and an integration circuit <NUM>.

The prediction calculator <NUM> inputs the angular frequency ω output from the rate limiter <NUM> to the adder <NUM> and inputs the angular frequency ω output from the rate limiter <NUM> to the differential circuit <NUM>. More specifically, the prediction calculator <NUM> inputs, to the adder <NUM> and the differential circuit <NUM>, an angular frequency ω(t0) at a timing t0 at which it is determined that a phase jump occurred in the three-phase AC power.

The differential circuit <NUM> calculates a derivative dω(t0)/dt of the input angular frequency ω(t0) differentiated over time. The integration circuit <NUM> calculates the prediction change amount (t - t0)×dω(t0)/dt of the angular frequency ω after a prescribed time interval t has elapsed from the timing t0 at which it is determined that the phase jump occurred by integrating the derivative dω(t0)/dt, and inputs the prediction change amount (t - t0)×dω(t0)/dt to the adder <NUM>.

The adder <NUM> calculates the predicted value ω' of the angular frequency ω by adding the angular frequency ω(t0) at the timing t0 at which it is determined that the phase jump occurred and the prediction change amount (t - t0)×dω(t0)/dt. In other words, the prediction calculator <NUM> calculates the predicted value ω' using the following formula (<NUM>)
[Formula <NUM>] <MAT>.

Thus, the prediction calculator <NUM> calculates the predicted value ω' of the angular frequency ω after a prescribed time interval has elapsed based on the angular frequency ω and the derivative of the angular frequency ω. For example, as illustrated in formula (<NUM>), the prediction calculator <NUM> fixes the angular frequency ω and the derivative used in the calculation of the predicted value ω' to be the angular frequency ω(t0) and the derivative dω(t0)/dt at the timing t0 at which it is determined that the phase jump occurred.

<FIG> are graphs schematically illustrating examples of operations of the frequency detector.

The vertical axis of <FIG> is an example of the three-phase voltage signal Va.

The vertical axis of <FIG> is an example of the three-phase voltage signal Vb.

The vertical axis of <FIG> is an example of the three-phase voltage signal Vc.

The vertical axis of <FIG> is an example of the voltage signal Vd of the rotating coordinate system.

The vertical axis of <FIG> is an example of a reference system frequency f calculated by the arithmetic unit <NUM> as-is from the angular frequency ω calculated by the adder <NUM> without passing through the rate limiter <NUM>, etc..

The vertical axis of <FIG> is an example of a reference frequency information f calculated by the configuration of the frequency detector <NUM> in which the angular frequency ω output from the rate limiter <NUM> is input to the arithmetic unit <NUM> without switching to the prediction calculator <NUM> even when the phase jump occurs.

The vertical axis of <FIG> is an example of a frequency information f calculated by the configuration of the frequency detector <NUM>.

<FIG> illustrate examples when a phase jump of about <NUM> degrees occurs at a time T1. Also, in <FIG>, the actual frequency of the three-phase AC power is set to <NUM>.

As illustrated in <FIG>, the voltage signal Vd of the d-axis component of the three-phase AC power abruptly changes when the phase jump occurs. Similarly, the voltage signal Vq of the q-axis component also abruptly changes.

As illustrated in <FIG>, a mismeasurement of about <NUM> occurs when the phase jump occurs when the frequency information f is calculated without using the rate limiter <NUM>, etc..

Conversely, in a configuration in which the output-input difference of the rate limiter <NUM> is fed back to the calculation of the proportional-integral control as illustrated in <FIG>, the mismeasurement when the phase jump occurs can be suppressed to about <NUM>.

Also, the mismeasurement when the phase jump occurs can be further suppressed in the frequency detector <NUM> that switches from the angular frequency ω of the rate limiter <NUM> to the predicted value ω' of the prediction calculator <NUM> when the occurrence of the phase jump is detected. In the frequency detector <NUM>, the mismeasurement can be suppressed to about <NUM>.

For example, when the actual frequency of the three-phase AC power is substantially constant as in the example illustrated in <FIG>, the derivative dω(t0)/dt of the angular frequency ω(t0) at the timing t0 at which it is determined that the phase jump occurred is substantially <NUM>. Accordingly, in such a case, ω' = ω(t0), and the fluctuation of the frequency information f can be suppressed.

In <FIG>, the vertical axis is an example of a reference frequency information f calculated by the configuration of the frequency detector <NUM> in which the angular frequency ω output from the rate limiter <NUM> is input to the arithmetic unit <NUM> without switching to the prediction calculator <NUM> even when the phase jump occurs.

The vertical axis of <FIG> is an example of the frequency information f calculated by the configuration of the frequency detector <NUM>.

<FIG> schematically illustrate an example of the frequency information f calculated for conditions such that an actual frequency FT of the three-phase AC power fluctuates at a smaller change rate than the rate limiter <NUM>. Also, <FIG> illustrates an example when a phase jump occurs in the positive direction at a time T2. <FIG> illustrates an example when a phase jump occurs in a negative direction at the time T2.

As a result of diligent investigations, the inventor of the application discovered that when the actual frequency FT of the three-phase AC power fluctuates at a smaller change rate than the rate limiter <NUM> as illustrated in <FIG>, and when the frequency information f is calculated using the angular frequency ω output from the rate limiter <NUM>, a mismeasurement of the frequency information f occurs, and the frequency information f undesirably fluctuates according to the change rate of the rate limiter <NUM>. Also, the inventor of the application discovered that the frequency information f fluctuates in the increasing direction when the phase jumps in the positive direction, and the frequency information f fluctuates in the decreasing direction when the phase jumps in the negative direction as illustrated in <FIG>.

Conversely, when the frequency information f is calculated using the predicted value ω' of the prediction calculator <NUM>, the fluctuation (the slope) of the actual frequency FT of the three-phase AC power can be predicted based on the derivative dω(t0)/dt of the angular frequency ω(t0) at the timing t0 at which it is determined that the phase jump occurred.

Accordingly, in the frequency detector <NUM>, the mismeasurement of the frequency information f when the phase jump occurs can be suppressed even when the phase jump occurs in a state in which the actual frequency FT of the three-phase AC power fluctuates at a smaller change rate than the rate limiter <NUM> as illustrated in <FIG>.

As described above, the frequency detector <NUM> according to the embodiment calculates the frequency information f based on the angular frequency ω output from the rate limiter <NUM>, and when it is determined that a phase jump has occurred in the three-phase AC power, switches to the predicted value ω' output from the prediction calculator <NUM> for a constant interval and calculates the frequency information f based on the predicted value ω' for the constant interval from the determination of the occurrence of the phase jump. Even when a phase jump or the like occurs in the three-phase AC power, an abrupt fluctuation of the frequency information f can be suppressed thereby, and the error of the calculation of the frequency information f can be reduced. Also, the calculation of the frequency information f is an open loop; therefore, effects on the speed of the voltage phase tracking by PLL can be suppressed even when the rate limiter <NUM> is included in the part calculating the frequency information f. Accordingly, the frequency detector <NUM> can be provided in which the change of the frequency information f can be quickly tracked, and an erroneous detection of the frequency information f can be suppressed even when a system disturbance occurs.

The constant interval of switching the prediction calculator <NUM> is, for example, not less than about <NUM> msec and not more than about <NUM> msec. If the constant interval is too short, for example, there is a risk that the calculation of the frequency information f may be undesirably returned to using the rate limiter <NUM> in a state in which the frequency information f calculated by the rate limiter <NUM> is fluctuating as illustrated in <FIG>, etc. It is therefore favorable for the constant interval to be not less than <NUM> msec. On the other hand, if the constant interval is too long, there is a risk that an erroneous detection of the frequency information f may undesirably occur when the slope of the change of the actual frequency FT of the three-phase AC power fluctuates. It is therefore favorable for the constant interval to be not more than <NUM> msec. It is more favorable for the constant interval to be, for example, not less than about <NUM> msec and not more than about <NUM> msec. The erroneous detection of the frequency information f can be more appropriately suppressed thereby.

Thus, the power measurement device 10b according to the embodiment further includes the frequency detector <NUM> and calculates the average value Pave of the active power and the average value Qave of the reactive power corresponding to the frequency of the three-phase AC power based on the frequency information f detected by the frequency detector <NUM>. Thereby, the average value Pave of the active power and the average value Qave of the reactive power can be calculated based on a more accurate frequency information f even when a phase jump or the like occurs in the three-phase AC power; and the average apparent power can be more accurately measured.

<FIG> is a block diagram schematically illustrating a modification of the prediction calculator.

As illustrated in <FIG>, the prediction calculator 70a further includes a moving average filter <NUM> and an arithmetic unit <NUM>.

The moving average filter <NUM> calculates the moving average of the angular frequency ω output from the rate limiter <NUM> and inputs the angular frequency ω after the moving average calculation to the adder <NUM> and the differential circuit <NUM>.

The differential circuit <NUM> calculates the derivative dω(t0)/dt based on the angular frequency ω(t0) after the moving average calculation input from the moving average filter <NUM> and inputs the derivative dω(t0)/dt to the integration circuit <NUM> and the arithmetic unit <NUM>.

Similarly to the description above, the integration circuit <NUM> calculates the prediction change amount (t - t0)×dω(t0)/dt of the angular frequency ω by integrating the derivative dω(t0)/dt, and inputs the prediction change amount (t - t0)×dω(t0)/dt to the adder <NUM>.

The arithmetic unit <NUM> calculates the correction value of the prediction change amount calculated by the integration circuit <NUM> by multiplying the derivative dω(t0)/dt input from the differential circuit <NUM> by a prescribed coefficient delaycomp. The arithmetic unit <NUM> inputs the calculated correction value to the adder <NUM>.

The adder <NUM> calculates the predicted value ω' of the angular frequency ω by adding the angular frequency ω(t0) at the timing t0 at which it is determined that the phase jump occurred, the prediction change amount (t - t0)×dω(t0)/dt, and the correction value. In other words, the prediction calculator 70a calculates the predicted value ω' using the following formula (<NUM>). [Formula <NUM>] <MAT>.

Thus, the prediction calculator 70a calculates the predicted value ω' based on the angular frequency ω(t0), the prediction change amount (t - t0)×dω(t0)/dt, and the correction value.

There is a possibility that noise such as power supply noise, measurement noise, or the like may be superimposed onto the angular frequency ω output from the rate limiter <NUM>. If noise is superimposed onto the angular frequency ω(t0) when the derivative dω(t0)/dt is calculated by the differential circuit <NUM>, there is a possibility that a slope that corresponds to the noise may be erroneously calculated, and erroneous detection of the frequency information f may undesirably occur.

Therefore, the prediction calculator 70a further includes the moving average filter <NUM> and calculates the moving average of the angular frequency ω. Thereby, the effects of noise superimposed onto the angular frequency ω can be suppressed.

On the other hand, when the moving average filter <NUM> is included, there is a possibility that a lag may undesirably occur in the predicted value of the frequency information f based on the predicted value ω' due to a phase lag due to the moving average filter <NUM>. For example, when a phase jump occurs in a state in which the actual frequency FT of the three-phase AC power is fluctuating, there is a possibility that a lag may undesirably occur in the predicted value of the frequency information f.

Therefore, the prediction calculator 70a further includes the arithmetic unit <NUM>, calculates a correction value of the prediction change amount, and calculates the predicted value ω' based on the angular frequency ω(t0), the prediction change amount (t - t0)×dω(t0)/dt, and the correction value.

The arithmetic unit <NUM> calculates the correction value to suppress the phase lag due to the moving average filter <NUM>. For example, the coefficient delaycomp of the arithmetic unit <NUM> is set according to a window length Tω of the moving average filter <NUM>. For example, the coefficient delaycomp is set to a value that is about half (about <NUM> times to <NUM> times) of the window length Tω. For example, when the window length Tω of the moving average filter <NUM> is <NUM> msec, the coefficient delaycomp is set to the value of <NUM> msec (<NUM>). The phase lag due to the moving average filter <NUM> can be suppressed thereby.

The window length Tω of the moving average filter <NUM> is, for example, not less than <NUM> msec and not more than <NUM> msec. By setting the window length Tω of the moving average filter <NUM> to be not less than <NUM> msec, the noise that is superimposed onto the angular frequency ω can be appropriately suppressed. By setting the window length Tω of the moving average filter <NUM> to be not more than <NUM> msec, an excessively long phase lag due to the moving average filter <NUM> can be suppressed.

Thus, the prediction calculator 70a uses the moving average filter <NUM> to suppress the effects of the noise superimposed onto the angular frequency ω, and uses the arithmetic unit <NUM> to suppress the phase lag due to the moving average filter <NUM>. Thereby, even when noise is superimposed onto the angular frequency ω, the effects of the noise can be suppressed and the erroneous detection of the frequency information f can be more appropriately suppressed. The frequency information f can be more accurately detected.

For example, the moving average filter <NUM> and the arithmetic unit <NUM> may be omitted when the noise that is superimposed onto the angular frequency ω can be appropriately suppressed by the moving average filters <NUM>, <NUM>, etc., included in the orthogonal coordinate signal generator <NUM>, etc. In other words, the frequency information f can be predicted by the configuration of the prediction calculator <NUM> illustrated in <FIG>.

<FIG> is a block diagram schematically illustrating a modification of the frequency detector.

In the frequency detector 30a as illustrated in <FIG>, the frequency calculator <NUM> further includes a rate limiter <NUM> (a limiting part).

The rate limiter <NUM> is located between the arithmetic unit <NUM> and the rate limiter <NUM> and between the arithmetic unit <NUM> and the prediction calculator <NUM>. In other words, the rate limiter <NUM> is located between the arithmetic unit <NUM> and the switching element <NUM>. Thereby, one of the angular frequency ω output from the rate limiter <NUM> or the predicted value ω' output from the prediction calculator <NUM> is selectively input to the rate limiter <NUM>.

The rate limiter <NUM> limits the change of the frequency information f equal to or greater than the prescribed change rate by limiting the change of the angular frequency ω or the predicted value ω' equal to or greater than the prescribed change rate. For example, the rate limiter <NUM> suppresses the change of the frequency information f equal to or greater than <NUM>/sec.

Thus, by including the rate limiter <NUM>, an abrupt change of the frequency information f when the switching circuit <NUM> switches between the first state and the second state can be suppressed. In other words, the undesirable abrupt change of the frequency information f at the timing of switching from the angular frequency ω to the predicted value ω' or at the timing of switching from the predicted value ω' to the angular frequency ω can be suppressed.

In the frequency detector 30b as illustrated in <FIG>, the frequency calculator <NUM> further includes a low-pass filter <NUM>. The low-pass filter <NUM> is arranged in series with the arithmetic unit <NUM>. For example, the low-pass filter <NUM> is located between the arithmetic unit <NUM> and the rate limiter <NUM>.

The low-pass filter <NUM> suppresses the high frequency components of the angular frequency ω or the predicted value ω'. The low-pass filter <NUM> attenuates higher frequency components than a prescribed frequency of the angular frequency ω or the predicted value ω'. In other words, the low-pass filter <NUM> suppresses an abrupt fluctuation of the angular frequency ω or the predicted value ω'. The low-pass filter <NUM> may include, for example, a moving average filter. The low-pass filter <NUM> inputs the angular frequency ω or the predicted value ω' after the high frequency components are suppressed to the arithmetic unit <NUM>.

The low-pass filter <NUM> is arranged in series with the arithmetic unit <NUM>. The low-pass filter <NUM> suppresses the high frequency component of the frequency information f by suppressing the high frequency components of the angular frequency ω or the predicted value ω'. The low-pass filter <NUM> suppresses an abrupt fluctuation of the frequency information f.

Thus, by providing the low-pass filter <NUM>, even when a phase jump or the like occurs in the three-phase AC power, an abrupt fluctuation of the frequency information f can be suppressed, and the error of the calculation of the frequency information f can be further reduced.

The low-pass filter <NUM> is not limited to being located between the arithmetic unit <NUM> and the rate limiter <NUM>, and may be located before the rate limiter <NUM> or may be located after the arithmetic unit <NUM>. The configuration of the low-pass filter <NUM> may be any configuration that can be arranged in series with the arithmetic unit <NUM> and can suppress the high frequency components of the frequency information f.

According to embodiments described above, the configuration of an αβEPMAFPLL is schematically illustrated as the angular frequency calculator AFP of the frequency calculator <NUM>. The configuration of the angular frequency calculator AFP is not limited thereto. The configuration of the angular frequency calculator AFP may be, for example, an EPMAFPLL (Enhanced Pre-filtering Moving Average Filter PLL) configuration, a PMAFPLL (Pre-filtering Moving Average Filter PLL) configuration, an EPMAFPLL Type <NUM> configuration, etc..

Hereinabove, exemplary embodiments of the invention are described with reference to specific examples. However, embodiments of the invention are not limited to these specific examples. For example, one skilled in the art may similarly practice the invention by appropriately selecting specific configurations of components included in the power measurement devices <NUM>, 10a, and 10b from known art; and such practice is within the scope of the invention to the extent that similar effects can be obtained.

Furthermore, any two or more components of the specific examples may be combined within the extent of technical feasibility, and are within the scope of the invention.

Moreover, all power measurement devices practicable by an appropriate design modification by one skilled in the art based on the power measurement devices <NUM>, 10a, and 10b described above as exemplary embodiments of the invention also are within the scope of the invention.

Furthermore, various modifications and alterations will be readily apparent to those skilled in the art; and all such modifications and alterations should be seen as being within the scope of the invention.

Claim 1:
A power measurement device (<NUM>), comprising:
a first three-phase to two-phase converter (<NUM>) converting a three-phase voltage signal of three-phase alternating current power into a two-phase voltage signal;
a second three-phase to two-phase converter (<NUM>) converting a three-phase current signal of the three-phase alternating current power into a two-phase current signal;
an instantaneous power calculator (<NUM>) calculating an instantaneous value of active power of the three-phase alternating current power and an instantaneous value of reactive power of the three-phase alternating current power based on the two-phase voltage signal and the two-phase current signal;
characterised by:
a first moving average calculator (<NUM>) including a plurality of first moving average filters calculating moving averages, the plurality of first moving average filters using different data quantities, the first moving average calculator causing the plurality of first moving average filters to respectively calculate a plurality of active power average values of different moving average data quantities;
a second moving average calculator (<NUM>) including a plurality of second moving average filters calculating moving averages, the plurality of second moving average filters using different data quantities, the second moving average calculator causing the plurality of second moving average filters to respectively calculate a plurality of reactive power average values of different moving average data quantities;
a first average value calculator (<NUM>) calculating an average value of the active power corresponding to a frequency of the three-phase alternating current power based on the plurality of active power average values and frequency information representing the frequency of the three-phase alternating current power; and
a second average value calculator (<NUM>) calculating an average value of the reactive power corresponding to the frequency of the three-phase alternating current power based on the plurality of reactive power average values and the frequency information representing the frequency of the three-phase alternating current power.