JP2000028659A - Frequency detecting apparatus and method - Google Patents

Abstract

(57) [Summary] In a conventional technique, when a DC component or a harmonic component is superimposed on an AC signal, the frequency cannot be detected stably because the zero crossing time of the signal varies. An AC signal that follows the phase of a fundamental wave component of an AC signal is generated, and a frequency is continuously detected from the AC signal that follows the fundamental wave component. The frequency of the fundamental wave can be calculated without being affected by the component and the DC component.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for detecting the frequency of an AC signal, and more particularly to a frequency detection apparatus for detecting the frequency of a fundamental wave component or a normal phase component.

[0002]

2. Description of the Related Art Conventionally, for detecting a frequency, for example,
As disclosed in Japanese Patent Application Laid-Open No. 7-12860, the frequency is obtained from the detected value of the AC signal near the zero cross and the previous value of the AC signal near the zero cross.

[0003]

In the above conventional technique, when a DC component or a harmonic component is superimposed on an AC signal,
The frequency cannot be detected stably because the zero crossing time of the signal varies.

Further, when calculating the frequency using the zero crossing of the detection signal, the result of the frequency calculation cannot be obtained unless there is a half cycle.

[0005] Therefore, when a system for detecting power fluctuations in the system using the system frequency detected in this way and stabilizing the power fluctuations is constructed, the fluctuations may be expanded or detected due to unbalance or the like. May not fulfill a sufficient function due to the delay.

An object of the present invention is to detect the frequency of an AC signal stably and at high speed even when a DC component or a harmonic component is superimposed on the AC signal.

[0007]

Means for Solving the Problems To solve the above problems, there is provided means for producing an AC signal following the phase of a fundamental wave component of an AC signal and detecting a frequency from the AC signal following the fundamental wave component. I have.

Further, there is provided a means for producing a plurality of AC signals having a phase shifted from that of the AC signal following the phase of the fundamental wave component of the AC signal, and detecting a frequency from the AC signal.

Means are provided for generating an AC signal following the positive-phase component of the polyphase AC and calculating the frequency from the AC signal following the positive-phase component.

[0010]

(Embodiment 1) An embodiment of the present invention will be described below with reference to FIG.

FIG. 1 shows an embodiment of the frequency detecting apparatus according to the present invention.

In FIG. 1, the voltage of an AC power supply 503 is detected by a voltage detector 501, and the detected voltage is adjusted in amplitude by a gain adjuster 502. The adjusted AC voltage Vi is input to the fundamental wave calculating means 100 constituting the frequency detector 500. The fundamental wave calculation means 100 outputs an AC signal Va that follows the fundamental wave component of the AC signal Vi and a signal Vb having a phase difference of 90 degrees. The frequency calculating means 200 calculates the frequency fb of the AC signal Vi by using both the AC signals Va and Vb.
0 outputs the frequency fb.

FIG. 2 shows the fundamental wave calculating means 100 shown in FIG.
2 shows a detailed configuration. In the figure, the input AC voltage Vi of the fundamental wave calculating means 100 is
Input to 2d. Further, the internal oscillator 305 generates an AC signal cosA and an AC signal sinA delayed by 90 degrees from the AC signal cosA, and outputs the signals to the multipliers 302c and 302d. The multipliers 302c and 302d output the AC signal Vi
Is multiplied by each of the outputs cosA and sinA of the internal oscillator 305 and the results are multiplied by one-cycle integrators 306a and 306
b. The one-cycle integrator 306 corresponds to the time of one cycle of the AC signal output from the internal oscillator 305.
a and 306b integrate the input values and calculate integration calculation results VaR and VaI.

The fundamental frequency ω ₀ of the input signal Vi and the frequency ω ₁ , k of the output cosA of the internal oscillator 305 are represented by time, Vi
And the phase difference of cosA and φ, and the ω ₀ = ω _1, VaR
And VaI are values obtained from the results of the Fourier transform shown in Expression (1) and Expression (2).

[0015]

(Equation 1)

[0016]

(Equation 2)

In Equations (1) and (2), ω ₀ = n
Since the components of ω ₁ (n = ...- 2, -1, 0, 2, 3 ...) become zero, the nth-order harmonic component contained in ω ₀ can be removed. FIG. 3 shows the characteristics of the Fourier transform expressed by Equation (Equation 1) or Equation (Equation 2). The horizontal axis indicates the order of the harmonic, and the vertical axis indicates the magnitude of the fundamental frequency component as 1. The result of calculating 1) or the value of equation (Equation 2) is shown. From the figure, it can be seen that the magnitude of the n-th harmonic component is 0 and has been removed. It can also be seen that the frequency can be detected even if ω ₀ deviates slightly from the fundamental frequency.

The integration operation results VaR and VaI are converted by the coordinate converter 307 according to the equation (Equation 3) into the phase co of the internal oscillator.
The signals are converted into AC signals Va and Vb using sA and sinA.

[0019]

(Equation 3)

Therefore, the AC signals Va and Vb are AC signals having a phase difference of 90 degrees.

FIG. 4 shows the frequency calculating means 200 shown in FIG.
2 shows a detailed configuration. In the figure, the input signals Va and Vb of the frequency calculating means 200 are provided by multipliers 302a and 30
2b and the delay circuits 301a and 301b. The two input signals Va and Vb are AC signals, and the phase relationship is different by 90 degrees, so that the relationship between the cos function and the sin function is established, and Va and Vb are defined as cos (ω · k) and sin, respectively.
(Ω · k). Here, k is time, and ω is the angular frequency of the AC signal. The delay circuits 301a and 301b
Outputs the signals Vaold and Vbold obtained by delaying the input signals Va and Vb by one sample to the multipliers 302b and 302a, respectively. Assuming that the delay time of the delay circuits 301a and 301b is Ts, Vaold and Vbold can be expressed by Expressions (4) and (5).

[0022]

[Equation 4] Vaold = cosｓω (k−Ts)} (Equation 4)

[0023]

Vbold = sin {ω (k−Ts)} (Equation 5) Vaold and Vbold are multiplied by the input values Vb and Va by multipliers 302b and 302a, respectively, and Vba and V
ab is output to the adder / subtractor 303a. Adder / subtractor 303a
Calculates the difference between the input Vab and Vba and outputs a signal w1. The signal w1 can be expressed by Expression (Equation 6) by using the addition theorem.

[0024]

W1 = cos {ω · k} · sin {ω (k−Ts)} − sin {ω · k} · cos {ω (k−Ts)} = sin {ω · Ts} (Equation 6) The arithmetic operation of the arc sine of w1 is performed by the arithmetic unit 304.
The fundamental frequency fb is obtained by dividing by π · Ts (π: pi).

If the delay time Ts in the equation (Equation 6) is sufficiently smaller than the period (2π / ω) of the input AC signals Va and Vb, the equation (Equation 6) is linearly approximated. Is done.

[0026]

(Equation 7)

Even if this w1 is divided by 2.pi.Ts, the fundamental frequency fb can be obtained.

According to the present embodiment, since the frequency fb is calculated from the AC signal that follows the fundamental wave of the input AC signal Vi, the harmonic component and the DC component included in the input AC signal Vi of the frequency detector 500 are calculated. The frequency of the fundamental wave can be stably calculated without being affected.

Further, since the AC signal Vb having a phase shifted by 90 degrees from the signal Va following the fundamental wave of the input AC signal Vi is generated, the frequency can be continuously calculated by using the addition theorem.

When the delay time Ts is sufficiently short with respect to the AC signal to be obtained, the addition theorem and linear approximation are used.
The frequency can be calculated continuously with simple calculations.

The fundamental wave calculating means 100 outputs the AC signal V
Since the Fourier transform is performed by weighting the fundamental wave component of i, the AC signal output from the fundamental wave calculating means 100 is obtained by removing the harmonic component and the DC component of the input signal Vi, and the AC signal following the fundamental wave component of the input signal. Is obtained.

Next, another embodiment of the present invention will be described. Note that the same reference numerals are given to the same components throughout the drawings, and detailed description will be omitted.

(Embodiment 2) FIG. 5 shows a second embodiment for realizing the frequency detecting apparatus according to the present invention. FIG.
3 shows a detailed configuration of the fundamental wave calculation means 100 shown in FIG.

In the figure, an input AC signal Vi is input to a phase difference detecting means 309. The output signal Va of the oscillator 100a is multiplied by the amplitude Vabs of the input signal Vi by the multiplier 302e to generate a signal Vc. The signal Vc is input to the phase difference detection means 309. The phase difference detecting means 3
09 calculates the phase difference Δθ2 between the input signals Vi and Vc. The calculated phase difference Δθ2 is input to the adder 311a. The reference angular frequency wa is integrated by the integrator 308, and the integrator 308 outputs the phase θa to the adder 311a.

The adder 311a outputs an addition result θb of the phase difference Δθ2 and the phase θa. The signal θb is input to the internal oscillator 312a and the adder / subtractor 303b. The adder / subtractor 303b subtracts the phase θc from θb and outputs a signal θd to the internal oscillator 312b. Assuming that θc is 90 degrees, the internal oscillators 312a and 312b output a sine wave Va having a phase of θb and a sine wave Vb delayed by 90 degrees, respectively.

As described above, the output signal Va is fed back so that the phase of the internal oscillator 312a follows the phase of the input signal Vi, and the phase of the internal oscillator is corrected.

In this embodiment, the phase θb following the fundamental wave
And a phase θd delayed by 90 degrees is output, but it is also possible to output a plurality of output AC signals with an arbitrary phase difference by using a plurality of means for calculating the phase θd.

According to the present embodiment, the output signal Va is fed back so that the phase of the internal oscillator 312a matches the phase of the input AC signal Vi to correct the phase of the internal oscillator. An AC signal that follows the fundamental wave of the signal and is unaffected by the harmonic components and the DC component of the input AC signal is obtained.

(Embodiment 3) FIG. 6 shows a third embodiment for realizing frequency detection according to the present invention. FIG. 6 shows a detailed configuration of the frequency calculation means 200 shown in FIG.

The input signals Va and Vb of the frequency calculating means 200a are input to differential calculators 314a and 314b, respectively. The differential calculators 314a and 314b calculate the differential results Vas and Vbs by the square calculators 315a and 315b.
5b. The square calculators 315a and 315
15b outputs the result Vas2 and Vbs2 of squaring the input values Vas and Vbs to the adder 311b.

The two input signals Va and Vb are alternating signals, and are cos (ω · k) and s, respectively, as in the first embodiment.
If in (ω · k), Vas2 and Vbs2 are represented by Expression (8) and Expression (9).

[0042]

(Equation 8)

[0043]

(Equation 9)

The output wx of the adder 311b is represented by the sum of Vas2 and Vbs2, and is input to the route calculator 316. The route calculator 316 calculates and outputs the frequency fb according to the equation (Equation 10).

[0045]

(Equation 10)

According to this embodiment, since the frequency is calculated using the addition theorem for the sum of squares of the differential result of the input AC signal, the frequency can be calculated continuously.

(Embodiment 4) FIG. 7 shows a fourth embodiment for realizing frequency detection according to the present invention. FIG. 7 shows a detailed configuration of the frequency calculation means 200 shown in FIG.

The input signals Va and Vb of the frequency calculator 200b are input to the angle calculator 317. The input signal Va
And Vb are AC signals. If cos (ω · k) and sin (ω · k) are set as in the first embodiment, the angle calculator 317 calculates the calculation result according to the equation (Equation 11). Output θnew.

[0049]

[Equation 11]

The operation result θnew is input to the delay circuit 318 and the adder / subtractor 303c, and the delay circuit 318 outputs the delay time Ts
The previous value θold is output to the adder / subtractor 303c. The adder / subtractor 303c calculates the difference between the current value θnew and θold, and the result θ
def is output to the multiplier 319. θdef is the equation (Equation 12)
Represented by

[0051]

(12) θdef = θnew−θold = (ω · k) − (ω · k−ω · Ts) = ω · Ts (Expression 12) The multiplier 319 calculates the time change θdef of the angle by 2 · π · T
Divide by s to find the frequency fb.

According to this embodiment, the cos function of the input signal and s
The frequency can be calculated stably and continuously from the vector phase θnew determined from the two in functions.

(Embodiment 5) FIG. 8 shows a fifth embodiment for realizing frequency detection according to the present invention. FIG. 8 shows a detailed configuration of the frequency calculation means 200 shown in FIG. The figure shows a case where the output Va of the fundamental wave calculating means is used for the input of the frequency calculating means.

The input AC signal Va of the frequency calculator 200c
Is input to the zero-crossing detector 320 to detect a zero-crossing time Tnew of the AC signal Va. Zero crossing time Tnew is a storage device
Stored in 321. The zero crossing time Tnew is stored in the storage device 321.
At the same time as the zero cross time Told
Is extracted from the storage device 321, and the difference from the current value Tnew is calculated by the adder / subtractor 303d, whereby the half cycle ΔT of the AC signal is obtained. This value is calculated by the reciprocal calculator 322.
The frequency fb can be obtained by calculating the reciprocal by doubling the frequency.

According to the present embodiment, the zero-crossing time is obtained from two AC signals whose phases are different from each other by 90 degrees.
A zero-crossing point is obtained in a quarter cycle, and frequency detection can be performed quickly. Furthermore, when a plurality of AC signals are input to the frequency calculator, the frequency can be calculated at a higher speed.

(Embodiment 6) FIG. 9 shows a sixth embodiment for realizing frequency detection according to the present invention.

In FIG. 9, the voltage of the three-phase AC power supply 504 is detected by a voltage detector 501a, and the detected voltage is adjusted in amplitude by a gain adjuster 502a to output AC voltages Vu, Vv, Vw. AC voltage Vu, Vv, V
The w is input to the three-phase to two-phase converter 323 constituting the frequency detector 500b, and the real-axis component Vx and the imaginary-axis component Vy of the positive-phase component are calculated based on the instantaneous symmetric coordinate method according to the equation (Equation 13). You.

[0058]

(Equation 13)

The fundamental wave calculating means 100c is provided with the AC signal Vx
And Vy are used to output AC signals Vscos and Vssin that follow the phase of the positive-phase component of the AC signals Vu, Vv, Vw, and the frequency calculating means 200d calculates the frequency fs from Vscos and Vssin, The detector 500b outputs the frequency fs.

FIG. 10 is a diagram for explaining the details of the fundamental wave calculating means 100c. Vx and V input in FIG.
From each of y, V is given by Equation (Equation 1) and Equation (Equation 2).
xR, VxI and VyR, VyI are obtained. These four signals have the harmonics and DC components removed,
Using these, the positive-phase operation means 326 calculates the real-phase component VsR and the imaginary-axis component VsI according to Equations (14) and (15).

[0061]

VsR = VxR + VyI (Equation 14)

[0062]

VsI = VyR−VxI (Equation 15) The coordinate converter 327 converts VsR and VsI into an AC signal by the coordinate conversion shown in the equation (Equation 16), and outputs Vscos and Vssin.
Is output.

[0063]

(Equation 16)

Various methods described in the above embodiments can be used for the frequency calculating means 200d.

According to this embodiment, since the frequency is detected from the AC signal that follows the positive-phase component of the polyphase AC, the positive-phase component is not affected by the negative-phase component, the harmonic component, and the DC component. Can be calculated.

Further, instead of the fundamental wave calculating means 100c, the normal phase component may be calculated by using the fundamental wave calculating means described in the second embodiment.

(Embodiment 7) FIG. 11 shows an embodiment in which the frequency detecting device of Embodiment 6 is applied to a system connected to a power system to absorb or discharge power.

In the figure, power converter 700 constituting power conversion system 800 is connected to power system 504 via main transformer 505. The power converter 700 absorbs or discharges power from the system according to a command from the control device 600.

Further, the voltage of the power system is
1b, 501c, and 501d. The detected voltage is adjusted in amplitude by a gain adjuster 502a, and the adjusted signals Vu, Vv, Vw are output to a frequency detector 500c. The frequency detector 500c calculates the frequency f from Vu, Vv, and Vw, and outputs the calculated frequency f to the control device 600 included in the power conversion system 800.

When the frequency of the power system is decreasing, the load on the power system is large. Therefore, the control device 600 operates the power converter 700 to output the active power. By operating to absorb power, the frequency of the power system is kept constant.

Further, even in a device capable of controlling an AC voltage, by changing the system voltage, the amount of power transmitted from the generator connected to the system can be adjusted, so that the frequency fluctuation can be suppressed.

The power conversion system 800 includes, for example, an SV
Devices connected to the system and capable of controlling electric power or voltage, such as C, SVG, a variable speed pumped-storage power generation system, and a variable speed flywheel system.

Since the frequency can be detected mainly when the variation of the number is about several tens%, it can be applied to the detection of the slip frequency for exciting the secondary winding of the electric motor.

According to the present embodiment, since the frequency detecting device according to the present invention is used, the frequency can be stably corrected without being affected by the harmonic component output from the power converter, the unbalanced voltage or the harmonic component of the system. The frequency of the phase component can be detected.

Further, in addition to the sixth embodiment, the frequency detector described in each embodiment may be used as the frequency detection device.

[0076]

Since the frequency is calculated from the AC signal following the fundamental wave of the input AC signal, the frequency of the fundamental wave is not affected by the harmonic components and the DC component contained in the input AC signal of the frequency detector. Computation can be performed stably.

[Brief description of the drawings]

FIG. 1 is a block diagram of a frequency detection device according to an embodiment of the present invention.

FIG. 2 is a diagram illustrating the configuration of FIG.

FIG. 3 is a frequency characteristic diagram illustrating the configuration of FIG.

FIG. 4 is a block diagram illustrating the configuration of FIG.

FIG. 5 is a block diagram illustrating the configuration of FIG.

FIG. 6 is a block diagram illustrating the configuration of FIG.

FIG. 7 is a block diagram illustrating the configuration of FIG.

FIG. 8 is a block diagram illustrating another embodiment of the present invention.

FIG. 9 is a block diagram illustrating the configuration of FIG.

FIG. 10 is a block diagram illustrating a frequency detection device according to another embodiment of the present invention.

FIG. 11 is a block diagram of a frequency detector according to another embodiment of the present invention.

[Explanation of symbols]

100, 100a, 100b... Fundamental wave calculating means, 20
0, 200a, 200b, 200c, 200d: frequency calculating means, 301a, 301b, 318, 321 ... delay circuit, 302a, 302b, 302c, 302d, 30
2e, 302f, 302g... Multipliers, 303a, 303
b, 303c, 303d... adder / subtractor, 304, 316, 3
19, 322: gain multiplier, 305: internal oscillator, 3
06a, 306b, 325a, 325b: one-period integrator, 307: coordinate converter, 308: integrator, 309: phase difference calculator, 310: phase difference setter, 311a, 311
b ... adder, 312a, 312b ... oscillator, 313 ... amplitude calculator, 314a, 314b ... differential calculator, 315
a, 315b: square operator, 317: arc tangent operator, 32
0: zero crossing time detector, 323: three-phase to two-phase converter, 32
4, internal oscillator, 326, positive phase calculator, 327, coordinate converter, 500, 500b, 500c, frequency calculator,
501, 501a, 501b, 501c, 501d: voltage detecting means; 502, 502a: voltage amplitude changing means;
03 ... AC power supply, 504 ... Three-phase AC power supply, 505 ... Transformer, 600 ... Control device, 700 ... Power converter, 800 ...
Power conversion system, Vi: AC signal detection value, Va: Fundamental wave following AC signal, Vb: 90 ° delayed AC signal, f, f
b, fs: detection frequency, ΔT: zero-crossing time interval, Va
b ... Va previous value Vb, Vba ... Vb x previous value Va, V
aold ... Va previous value, Vbold ... Vb previous value, w1, w
a, wx: angle, Vas: differential value of Va, Vbs: Vb
, Vas2 ... Vas squared, Vbs2 ... Vbs
, The power of Vabs: AC signal amplitude value, θnew: current calculation angle, θold: previous calculation angle, θdef: time change of angle, Vc: AC signal feedback, θa: phase, Δθ
2: phase difference, θb: phase addition result, θc: phase 90 degrees,
θd: 90-degree delayed phase, cosA, sinA: AC signal of internal oscillator, VaR: Real axis value of fundamental wave component, VaI: Imaginary axis value of fundamental wave component, Vx: α component, Vy: β component, Vscos, Vssin
... Positive phase component tracking AC signal, Vu, Vv, Vw... Three-phase AC signal, cosB, sinB ... Internal oscillator AC signal, VxR.
Component real axis value, VxI ... α component imaginary axis value, VyR ... β component real axis value, VyI ... β component imaginary axis value, VsR ... Positive phase component real axis component, VsI ... Positive phase component imaginary axis component.

 ────────────────────────────────────────────────── ─── Continuing from the front page (72) Inventor Miyuki Miguchi 3-1-1, Sakaimachi, Hitachi-shi, Ibaraki Prefecture F-term in Hitachi Works, Ltd. Hitachi Plant 2G029 AA02 AA03 AB01 AC04 AD07 AH00 AH06

Claims (11)

[Claims] 1. An apparatus for detecting an AC signal and calculating the frequency of the AC signal, comprising: a detecting means for detecting the AC signal; and a second AC signal that follows a fundamental wave component of the detected AC signal. A frequency detecting apparatus comprising: a fundamental wave calculating means for calculating; and a frequency calculating means for calculating a frequency from the second AC signal. 2. An apparatus for detecting an AC signal and calculating the frequency of the AC signal, comprising: detecting means for detecting the AC signal; and a second AC signal that follows a fundamental wave component of the detected AC signal. Fundamental wave calculating means for calculating a plurality of AC signals having phases different from the second AC signal to output the second and the plurality of AC signals, and a frequency calculating means for calculating a frequency from an output of the fundamental wave calculating means A frequency detecting device comprising: 3. An apparatus for detecting a polyphase AC signal and calculating the frequency of the polyphase AC signal, comprising: means for detecting the polyphase AC signal; and calculating a positive phase component from the detected value of the polyphase AC signal. Means for calculating a second AC signal following the AC signal of the positive-phase component, a plurality of AC signals having different phases from the second AC signal, and a result of the fundamental wave calculating means A frequency detecting device comprising frequency calculating means for calculating a frequency from a signal. 4. A fundamental wave calculating means according to claim 1, wherein said fundamental wave calculating means separates the detected AC signal into an amplitude and a phase; and a phase amplitude calculating means for following the detected AC signal. And a phase calculating means for generating a phase different from the phase, and an AC signal generating means for generating a plurality of AC signals from a plurality of phases obtained from the phase calculating means. 5. The fundamental wave calculating means according to claim 1, wherein the fundamental wave component of the detected AC signal is Fourier-transformed, and a result of the Fourier calculating means is used. A frequency detecting device comprising an AC signal generating means for generating an AC signal that follows the phase of the fundamental wave component. 6. The frequency calculating means according to claim 1, wherein said frequency calculating means detects a time of a zero crossing point of an output signal of said fundamental wave calculating means, and a time of said zero crossing point. 1. A frequency detecting device comprising: a time calculating means for calculating a time interval from a signal; and a frequency calculating means for calculating a frequency from the obtained time interval. 7. The frequency calculating means according to claim 2, wherein the second AC signal and a third AC signal having a phase different from that of the second AC signal by 90 degrees are inputted. A frequency detecting device comprising: storage means for storing a third AC signal; and frequency calculating means for calculating a frequency using the second and third AC signals and the stored AC signal. . 8. The frequency calculating means according to claim 2, wherein said second AC signal and a third AC signal having a phase different from that of said second AC signal by 90 degrees are inputted, and each of said AC signals is inputted. A frequency detecting device comprising: a time change calculating means for calculating a time change of the signal; and a frequency calculating means for calculating a frequency from a result of the time change calculating means. 9. The frequency calculating means according to claim 2 or 3, wherein said second AC signal and a third AC signal having a phase different from that of said second AC signal by 90 degrees are input, and said second AC signal is inputted to said second AC signal. Phase calculation means for obtaining a phase from the AC signal and the third AC signal using arctangent calculation, and time change calculation means for calculating a time change of the phase obtained by the phase calculation means, A frequency detecting device comprising frequency calculating means for calculating a frequency from said time change calculating means. 10. A second AC signal that follows a fundamental wave component of the AC signal, a third AC signal having a phase difference of 90 degrees from the second AC signal, and one of the second and third AC signals. A frequency detection method comprising calculating a frequency from data of past samples. 11. A frequency detected by the frequency detecting apparatus or method according to claim 1 is input, and power is absorbed or released or system voltage is controlled based on the frequency detection signal. A grid interconnection system characterized by the following.