JP2001057737A - Method of identifying frequency characteristics of electric power system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To remove the effect caused by the generating source of harmonic current as a disturbance at the time when the frequency characteristics of an electric power system is identified by treating the value obtained by dividing mutual spectral density by the self-spectral density of an identification signal as the identified value of frequency characteristics. SOLUTION: The phase of each sine wave signal that makes up an identification signal x(t) from an identification circuit 50 is injected into an electric power system 1b by being displaced by 2 π/n (rad) ('n' is a plural number) from the previous one. From the responses of the electric power system 1b based on these injected identification signals, the correlation functions of the responses to the identification signal x(t) are obtained to calculate mutual spectral density by performing the Fourier transform of the average of the addition of each correlation functions so obtained. The value obtained by dividing this mutual spectral density by the self-spectral density of the identification signals is treated as the identified value of the frequency characteristics. This method can prevent the occurrence of a resonance phenomenon and the like.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for identifying a frequency characteristic of a power system via a semiconductor power converter or the like operated in connection with the power system.

[0002]

2. Description of the Related Art With the spread of semiconductor power converters typified by inverters for driving motors, deterioration of the power environment, such as an increase in harmonic distortion of the power system, has become a problem. For example, an active filter or the like is installed as a semiconductor power converter that is operated in an interconnected manner.

In this active filter, it is necessary to identify the frequency characteristics of the power system in order to better correct the above-described deterioration of the power environment, and an identification signal obtained by combining a plurality of sinusoidal signals having different oscillation frequencies [ x (t)], a conventional method for identifying the frequency characteristic [G (jω)] based on the block diagram of FIG.
This will be described below with reference to the flowchart (b).

In FIG. 4A, a response y (t) based on the identification signal injected into the power system is a voltage or a current between the illustrated power system and a higher-level power system.

[0005] As shown in FIG.
As a correlation function [R _xx (τ)] of (t), the following equation (1)
Is calculated.

[0006]

(Equation 1)

Here, τ is a virtual time parameter in calculating the correlation function, and x ^* (t) is a conjugate function of x (t).

In step S2, the identification signal x (t) is injected into the power system, and y (t) is detected (step S3).

Next, in step S4, the following equation (2)
Is calculated, and a correlation function [R _xy] between x (t) and y (t) is calculated.
(Τ)].

[0010]

(Equation 2)

Here, y ^* (t) is a conjugate function of y (t).

Further, in step S5, each of the above equations (1) and (2) is subjected to Fourier transform, and the transform results are used as the self-spectral density and the cross-spectral density, and the process proceeds to step S6.

In step S6, the calculation of the cross-spectral density / self-spectral density is performed.
The identification value of the frequency characteristic G (jω) of the power system shown in FIG.

The method for identifying the frequency characteristic of the power system in steps S1 to S6 is called a spectrum analysis method, and is relatively resistant to noise. Therefore, the frequency characteristic can be identified by a weak identification signal, and the Fourier transform is used. Since the characteristics at a plurality of frequency points can be obtained at one time, the frequency characteristics can be identified in a short time.

[0015]

FIG. 5 is a conceptual configuration diagram of a device for suppressing harmonic components of a power system by an active filter.

In FIG. 5, reference numeral 1a denotes an upper power system,
b is a lower power system to which the present invention is applied, 2 is a harmonic current generation source as a load of the lower power system 1b, 4 is a voltage matching transformer, 5 is an upper power system 1a and a lower power. A current detector for detecting a current between the system 1b, 6 is a general load, 7 is an LC filter, 10 is an active filter, 14 is a current detector for detecting the output current of the active filter 10, 20, 30 and 40 Either one is an identification circuit for deriving the frequency characteristic of the lower power system 1b and transmitting this derived value to the active filter 10. The identification circuit 20 activates the identification signal command value [x ^* (t)]. A command is sent to the filter 10, and based on this command, assuming that the output current of the active filter 10 becomes [x (t)], the operation of the flowchart shown in FIG.

In the identification circuit 20, the frequency characteristic G (jω) of the power system 1b = [the detection value y (t) of the current detector 5]
/ Detection value x (t) of current detector 14].

As is clear from FIG. 5, it is necessary to identify the frequency characteristic of the lower power system 1b in a state where all the devices other than the active filter 10 are operating. As shown in the block diagram of FIG. 6, the harmonic current [h (t)] becomes a disturbance because the harmonic current generation source 2 exists in the device, and the identification value derived by the identification circuit 20 is disturbed. An error will be included.

That is, the detection value y (t) of the current detector 5
= [Detected value x (t) of current detector 14 + harmonic current [h (t)] of harmonic current generator 2].

It is an object of the present invention to provide a method of identifying frequency characteristics of a power system while extracting only a component based on the identification signal from a detected value between an upper power system and a lower power system. .

[0021]

According to the first aspect of the present invention, when identifying frequency characteristics of a power system based on an identification signal obtained by synthesizing a plurality of sine-wave signals having different oscillation frequencies, the identification signal is used. The phase of each constituent sine wave signal is injected into the power system while being displaced by 2π / n [rad] (n: plural) from the previous time, and the power system response based on the injected identification signal is A correlation function between the identification signal and the response is obtained, and an average value of the obtained correlation functions is Fourier-transformed to obtain a cross-spectral density, and the cross-spectral density is divided by the self-spectral density of the identification signal. The calculated value is used as an identification value of the frequency characteristic.

According to a second aspect of the present invention, when identifying frequency characteristics of a power system based on an identification signal obtained by combining a plurality of sine wave signals having different oscillation frequencies, the amplitudes of the sine wave signals are made equal to each other. , The phase of the sine wave signal is shifted into the power system by 2π / n [rad] (n: plural) from the previous time, and injected into the power system. From the response of the power system based on the injected identification signal, the identification is performed. A correlation function between the signal for use and the response is obtained, and a value obtained by Fourier transforming an average value of the obtained correlation functions is used as an identification value of the frequency characteristic.

In a third aspect based on the first or second aspect, the identification signal is based on an identification signal command value additionally commanded to a semiconductor power conversion device that operates in connection with a power system. It is characterized by being generated by a power converter.

In a fourth aspect based on the third aspect, the identification signal is an output current or an output voltage of the semiconductor power converter, and the response is a current or a voltage between a higher power system and the power system. And calculating an identification value of the frequency characteristic.

In a fifth aspect based on the third aspect, the identification signal is the identification signal command value, and the response is a current or a voltage between a higher power system and the power system. Is calculated.

The present invention has been made by paying attention to the following operations.

For example, a cos waveform signal, one of which is Aco
s (ωt + φ ₁ ) and the other is Bcos (ωt + φ ₂ )
Then, the correlation function between the two is represented by equation (3).

[0028]

(AB / 2) cos {ωt + (φ ₂ −φ ₁ )} (3) That is, the phase difference component between the two appears in the correlation function.

Therefore, the Acos (ωt + φ ₁ ) is made a part of the sine wave signal constituting the identification signal,
If cos (ωt + φ ₂ ) is the response only,
The above φ ₁ is 2π / n [rad] from the previous time, (n: plural)
[Φ ₂ −φ ₁ ] of each of the n sets of correlation functions shown in the above equation (3) obtained by injecting into the electric power system while displacing each other.
Are the same, the correlation function value corresponding to each identification signal does not change even if φ ₁ is displaced as described above.

However, the harmonic current h shown in FIG.
Of the response including the component due to (t), the response component due to h (t) has a certain fixed phase irrelevant to the response component due to the identification signal. [Φ ₂ −φ ₁ ] in the indicated correlation function is φ φ as described above.
_{When 1} is displaced, the vector-wise average value of each of the obtained correlation functions becomes zero, and as a result, the response component due to the h (t) can be eliminated.

[0031]

FIG. 1 is a flow chart showing a first embodiment of the present invention. The identification circuit 3 shown in FIG.
The operation at 0 is shown.

When the identification signal command value [x ^* (t)] is instructed to the active filter 10, the active filter 10 generates a current as the identification signal [x (t)] based on this command. At this time, x (t) is a plurality of cos
Assuming that wave currents are combined, x (t) is expressed by equation (4).

[0033]

(Equation 4)

First, in step S11, the correlation function R _xx (τ) of the above equation (4) is calculated, and the result of this calculation is expressed by equation (5).

[0035]

(Equation 5)

Next, in step S12, the self-spectral density S _xx (jω) obtained by performing the Fourier transform on the equation (5) and expressed by the equation (6) is obtained.

[0037]

(Equation 6)

In step S13, x represented by equation (4)
Theta ₁ of (t), θ _2, ··· is an initial value state (i.e., the as n = n), the injection into the lower power system 1b shown in FIG.

This power system 1b includes a harmonic current source 2
Are operating, and this harmonic current becomes disturbance [h (t)] represented by the following equation (7).

[0040]

(Equation 7)

That is, [y detected at step S14
(T)] is represented by equation (8).

[0042]

(Equation 8)

[0043] Here, K _k is the gain of the power system 1b at frequency ω _k, ψ _k represents the phase delay at frequency omega _k, the first group on the right side shows the response by identification signal x (t), also , The second group on the right side shows the response due to the disturbance h (t).

In step S15, x (t) shown by the above equation (4) and y (t) shown by the above equation (8) are correlated with the correlation function R _xy (t) according to the definition of the above equation (2). ) Is obtained as shown in equation (9).

[0045]

(Equation 9)

The above steps S13 to S15
By the sequence of step S16 and step S17, the phase of each sine wave signal constituting the identification signal x (t) is changed by 2π / n [rad], (n: plural) from the previous time.
Injecting into the power system while displacing each time, and therefore, the correlation functions represented by n equations (9) based on the respective x (t) and y (t) are obtained, and the process proceeds to step S18.

In step S18, the average value of the obtained n correlation functions is obtained, and the bar of this average value R _xy (t) is expressed by equation (10).

[0048]

(Equation 10)

As is apparent from this equation, the disturbance h (t)
The term for has been eliminated.

In step S19, equation (10) is subjected to Fourier transform to obtain a mutual spectral density S _xy (jω) shown in equation (11).

[0051]

[Equation 11]

Further, in step S20, step S1
9 is divided by the self-spectral density obtained in step 12 to obtain the frequency characteristic G () of the lower power system 1b shown in FIG. jω).

[0053]

(Equation 12)

FIG. 2 is a flowchart showing the operation of the identification circuit 40 shown in FIG. 5 according to a second embodiment of the present invention.

When the identification signal command value [x ^* (t)] is commanded to the active filter 10, the active filter 10 generates a current as the identification signal [x (t)] based on the command. At this time, x (t) is a plurality of cos
When the wave currents are combined and normalized so that the amplitude of each of the cosine wave currents is “1”, x (t) is given by the formula (1)
It is represented by 3).

[0056]

(Equation 13)

First, in step S31, the values of θ ₁ , θ ₂ ,... Of x (t) shown in equation (13) are initial values (that is, n = n), as shown in FIG. It is injected into the lower power system 1b.

This power system 1b includes a harmonic current source 2
Are operating, and this harmonic current becomes disturbance [h (t)] represented by the above equation (7).

That is, [y detected at step S32
(T)] is represented by equation (14).

[0060]

[Equation 14]

[0061] Here, K _k is the gain of the power system 1b at frequency ω _k, ψ _k represents the phase delay at frequency omega _k, the first group on the right side shows the response by identification signal x (t), also , The second group on the right side shows the response due to the disturbance h (t).

In step S33, x (t) shown in the above equation (13) and y (t) shown in the above equation (14) are converted into a correlation function R _xy (t) according to the definition of the above equation (2). ) To the formula (1)
It is required as shown in 5).

[0063]

(Equation 15)

The above steps S31 to S33
By the sequence of steps S34 and S35, the phase of each sine wave signal constituting the identification signal x (t) is set to 2π / n [rad], (n: plural) from the previous time.
Injecting into the power system while displacing each time, and accordingly, n correlation functions represented by the equation (15) by x (t) and y (t) are obtained, and the process proceeds to step S36.

In step S36, the average value of the obtained n correlation functions is obtained, and the bar of this average value R _xy (t) is expressed by equation (16).

[0066]

(Equation 16)

As is apparent from this equation, the disturbance h (t)
The term for has been eliminated.

In step S37, the equation (16) is Fourier-transformed. In step S38, as shown in the equation (17), the frequency characteristic G (jω) of the lower power system 1b shown in FIG. Value.

[0069]

[Equation 17]

FIG. 3 is a diagram showing a device configuration in a power system according to a third embodiment of the present invention. In this embodiment, the difference from the configuration shown in FIG. That is, an identification circuit 50 is provided.

That is, in the identification circuit 50, the identification signal command value [x
^* (T)], the frequency characteristic of the lower power system 1a is identified.
Alternatively, it may be the same as the flowchart shown in FIG.

In the above-described embodiment, an example in which a general current is used as the identification signal and the power system current is detected and performed is described. However, the voltage is used as the identification signal and the power system voltage is detected. Then, the identification method of the present invention may be performed.

[0073]

According to the present invention, it is possible to extract only the component of the power system from the detected value between the upper power system and the lower power system by the identification signal based on the spectrum analysis method. The effect of the harmonic current source as a disturbance when identifying the frequency characteristics of the filter is removed.For example, when removing the harmonic component using an active filter, a so-called resonance phenomenon, which has been a problem in the past, occurs. Will be blocked.

[Brief description of the drawings]

FIG. 1 is a flowchart showing a first embodiment of the present invention.

FIG. 2 is a flowchart showing a second embodiment of the present invention.

FIG. 3 is a device configuration diagram showing a third embodiment of the present invention.

FIG. 4 is a flowchart showing a conventional example.

FIG. 5 is a configuration diagram of an electric power system.

FIG. 6 is a block diagram of FIG. 5;

[Explanation of symbols]

1a: Upper power system, 1b: Lower power system, 2: Harmonic current generation source, 4: Transformer, 5: Current detector, 6: Load, 7: LC filter, 10: Active filter, 1
4. Current detector, 20, 30, 40, 50 ... Identification circuit.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2G028 BD02 BE10 CG20 DH04 FK01 FK02 GL06 5G066 EA03 EA10 5H740 NN03

Claims (5)

[Claims] When identifying a frequency characteristic of a power system based on an identification signal obtained by synthesizing a plurality of sine wave signals having different oscillation frequencies, a phase of each sine wave signal constituting the identification signal is set to a previous value. From the response of the power system based on the injected identification signal, the correlation function between the identification signal and the response. The Fourier transform is performed on the obtained average value of the obtained correlation functions to obtain a cross-spectral density, and the value obtained by dividing the cross-spectral density by the self-spectral density of the identification signal is used as the identification value of the frequency characteristic. A frequency characteristic identification method for a power system, comprising: 2. When identifying a frequency characteristic of a power system based on an identification signal obtained by synthesizing a plurality of sine wave signals having different oscillation frequencies, the amplitudes of the sine wave signals are made equal to each other, and The phase of the signal is 2π / n [rad],
(N: plural) are injected into the power system while being displaced, and from the response of the power system based on the injected identification signal, a correlation function between the identification signal and the response is obtained. A frequency characteristic identification method for a power system, wherein a value obtained by Fourier transforming an average value of a function is used as an identification value of the frequency characteristic. 3. The frequency characteristic identification method for a power system according to claim 1, wherein the identification signal is additionally commanded to a semiconductor power conversion device that operates in connection with the power system. A frequency characteristic identification method for a power system, wherein the frequency characteristic is generated by the power converter based on a signal command value. 4. The method for identifying frequency characteristics of a power system according to claim 3, wherein the identification signal is an output current or an output voltage of a semiconductor power conversion device, and the response is a response between an upper power system and the power system. A frequency characteristic identification method for a power system, wherein an identification value of the frequency characteristic is calculated as a current or a voltage between the two. 5. The frequency characteristic identification method for a power system according to claim 3, wherein the identification signal is the identification signal command value, and the response is a current or a current between an upper power system and the power system. A frequency characteristic identification method for a power system, comprising calculating an identification value of the frequency characteristic as a voltage.