JP2000350364A - Harmonic current detecting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To speedily and accurately detect fundamental wave positive-phase component by performing the signal processing of the average section of the running average of instantaneous real power and instantaneous imaginary power as a specific value by the specific multiplication and electrical angle of a power supply frequency. SOLUTION: In running average high-pass filters 5p and 5q, the average section of running averaging is set to 180 deg. of a power supply frequency, namely 1/2f (S) (f: power supply frequency). As a result, the running averaging value of inverse-phase and harmonic components becomes zero, and only DC components for fundamental positive-phase components included in powers p and q can be detected, thus accurately detecting the fundamental wave positive-phase components and completely eliminating the fundamental wave inverse-phase components and harmonic components and also achieving a high- speed response that is approximately ten times larger than a conventional primary high-pass filter.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to harmonics in a power compensator (active filter) or the like having a compensation function such as a three-phase balancer, an unbalanced load in a power system, a reactive power compensation and a harmonic suppression. The present invention relates to a current detection device, and more particularly, to detection of a fundamental wave positive-phase component of a power system.

[0002]

2. Description of the Related Art For example, an active filter detects a harmonic current from a distorted load current and generates a current for compensating the harmonic current, thereby suppressing generation of the harmonic current in a power system. This function requires that the harmonic current can be accurately detected, and a detection method based on the pq theory has been proposed.

FIG. 5A shows a harmonic electric power based on the pq theory.
1 shows a flow detection device. The pq operation unit 1 is a three-phase power
Pressure V_a, V_b, V_cAnd load current i_a, I_b, I_cChanged to two-phase
The converted instantaneous real power p and instantaneous imaginary power q are obtained. Primary high
Pass filter 2_p, 2_qIs the DC component included in the power p, q
The AC component from which the component was removed (shown by adding
Out). The harmonic current calculator 3 calculates the powers p and q
AC component and three-phase voltage V _a, V_b, V_cConverted to three-phase
Harmonic current detection signal i_a*, I_b*, I_cAsk for *.

In this detection device, the lower the cutoff frequency of the high-pass filter, the higher the detection accuracy, but the lower the cutoff frequency, the greater the response delay.

Therefore, for example, in the paper “Pq Theory and a Method for Detecting the Harmonic Current of an Active Filter Using a Moving Average High-Pass Filter, IEEJ Industrial Application Division D, Vol.
No. 1998), as shown in FIG. 5B, proposes a detection method using moving average high-pass filters 4p and 4q, which is a kind of digital filter.

[0006]

In the detection device shown in FIG. 5, the calculation of the instantaneous real power p and the instantaneous imaginary power q by the pq calculation unit 1 is performed according to the following relationship.

First, when the power supply phase voltage and the load current are subjected to three-phase / two-phase conversion, the following equations (1) and (2) are obtained, and the instantaneous real power p and the instantaneous imaginary power q are expressed by the equation (3).

[0008]

(Equation 1)

[0009] Then, the power supply phase voltage V _a, V _b, V _c and the load current i _a, i _b, when the following (4) and (5) the i _c, the instantaneous real power p and instantaneous imaginary power q Is (6) and (7)
It is shown by the formula.

[0010]

(Equation 2)

[0011] Here, V _m is the phase voltage peak value, I _m is the load current peak value, n represents the order of the load current, theta denotes the delay of the load current.

By substituting n = 1 into the above equations (6) and (7), and obtaining the fundamental phase component of the load current, p and q are obtained as shown in the following equations (8) and (9). Is converted to a DC component.

[0013]

(Equation 3)

If m is an integer and f is the power supply frequency, the load current n = (6 _m
The ± 1) next component is converted into an f × 6 _m (H _Z ) component of p and q.

Here, when the fundamental component of the load current includes a negative-phase component, the negative-phase component of the load current is expressed by the following formula (10) from the above formula (5).

[0016]

(Equation 4)

At this time, the powers p and q corresponding to the fundamental component of the inverse phase of the fundamental wave are expressed by the following equations (11) and (12).

[0018]

(Equation 5)

From the above equations (11) and (12), the fundamental component of the load current in the negative phase is converted to a frequency 2f (Hz) component twice the power p and q.

Therefore, in the detection device shown in FIG. 5B, since the average section of the moving average is 1/6 f (s), the f.times.6 m (Hz) component can be removed, but the load current becomes ( When the fundamental wave reverse phase component as in the equation 8) is included, the moving average cannot completely remove the 2f (Hz) component of the fundamental wave reverse phase component, so that the fundamental wave normal phase component cannot be accurately detected. There's a problem.

It is an object of the present invention to provide a harmonic current detecting device capable of detecting a positive component of a fundamental wave at high speed and with high accuracy.

[0022]

SUMMARY OF THE INVENTION The present invention provides an instantaneous real power p.
And the average section of the moving average of instantaneous imaginary power q is 1 / 2f
(S) By performing signal processing with an electrical angle of 180 °, fundamentally, by removing the f × 6 m (Hz) component of the harmonic component and also removing the 2f (Hz) component of the fundamental wave reverse phase component. It is intended to accurately detect a wave positive phase component, and is characterized by the following device.

A pq calculation unit for obtaining a two-phase instantaneous real power p and an instantaneous imaginary power q from the three-phase power supply phase voltage and the load current of the power system; And a moving average high-pass filter that removes the DC components from the powers p and q to extract the AC components of the powers p and q;
In a harmonic current detection device comprising: a harmonic current calculating unit that detects a three-phase harmonic current from the AC component of q and the power supply phase voltage, the moving average high-pass filter supplies power to an average section of the moving average. It is characterized in that a moving average value of the fundamental wave reverse phase component and the harmonic component is set to 0 in a 180 ° section of the cycle.

[0024]

FIG. 1 shows a harmonic current detecting device according to an embodiment of the present invention. 5 differs from FIG. 5B in the moving average high-pass filters 5p and 5q.

The moving average in the time domain by the moving average high-pass filters 5p and 5q is expressed by the following equation (13), and the pulse transfer function is expressed by the following equation (14).

[0026]

(Equation 6)

Here, x is an input, X is an output, N is the number of data of the moving average, T is a sampling time, and z is a unit delay.

Here, in the conventional moving average high-pass filters 4p and 4q, the average section of the moving average is set to 6
The interval is 0 °, and the sampling time T of the moving average high-pass filter at that time is represented by the following equation (15).

[0029]

(Equation 7)

On the other hand, in the moving average high-pass filters 5p and 5q in the present embodiment, the average section of the moving average is set to the 180 ° section of the power supply frequency, that is, 1 / 2f (s).
And As a result, 2f (Hz), which is the opposite phase component, is removed by the moving average.

At this time, the moving average high-pass filter 5
The sampling time T for p, 5q is given by the following equation (16).

[0032]

(Equation 8)

As described above, since the negative phase component is 2f (Hz) and the harmonic component is f × 6 m (Hz),
In the present embodiment, the moving average high-pass filters 5p, 5q
By setting the average section of the moving average at ｆf (s), the moving average value of the antiphase component and the harmonic component becomes 0,
It is possible to detect only the DC component of the fundamental wave positive phase component included in the powers p and q.

FIG. 2 shows a moving average high-pass filter 5p,
It is a flowchart for digital operation in 5q.

The conditions in this processing are as follows:
Hz, average section 10 ms, moving average data number 100
The sampling time is 100 μs.

In FIG. 2, first, a change is made by initial setting.
Number x (a) = 0, y (a) = 0, p _sum= 0, q_sum=
0, a = 0 is set (S1), and the timer is set to 100 μs.
(S2).

In this state, sampling data obtained by A / D conversion of the arithmetic outputs (analog signals) p and q from the pq arithmetic unit 1 are fetched (S3). When the number of sampling data a becomes 100, a = 0. Reset (S4
S5).

Next, the sum of the sampling data of the powers p and q, p _sum , q _sum , and the subtraction of the past sampling data x (a), y (a) from the current sampling data p, q are used as the current values. The sums p _sum and q _sum are updated (S6), and the current sums p _sum and q _sum are divided by the number of data 100 to obtain the current moving average values p _ave and q _ave of the sampling data (S7).

Next, the current sampling data p and q are set to the past sampling data x (a) and y (a) (S
8) The number of sampling data is incremented to a = a + 1 (S9), and the current moving average values p _ave and q _ave are D / A
The signal is converted into an analog signal by the conversion and output, and the timer is set to 100 μs to return to the next moving average calculation (S10).

FIGS. 3A and 3B are Bode diagrams (gain and phase difference) of the moving average high-pass filter according to the present embodiment, and show the fundamental and anti-harmonic components (the fifth and seventh components). , 11, 13, 17, and 19) can be obtained in principle, with the characteristic removed to 0%, and the fundamental wave normal phase component can be detected with high accuracy. FIG. 4 shows the step response of the moving average. The time required to attenuate the DC component to 0% is 10 ms, which is about three times as large as that of the conventional moving average high-pass filter. Phase components and harmonic components can be completely removed. Note that the response is about ten times faster than that of a conventional primary high-pass filter.

[0041]

As described above, according to the present invention, the average section of the moving average of the instantaneous real power p and the instantaneous imaginary power q is 1 / 2f.
(S) By removing the f × 6 m (Hz) component of the harmonic component and the 2f (Hz) component of the fundamental wave reverse phase component by performing a moving average process with an electrical angle of 180 °. Thus, there is an effect that the normal phase component of the fundamental wave can be accurately detected.

[Brief description of the drawings]

FIG. 1 is a harmonic current detection device showing an embodiment of the present invention.

FIG. 2 is a flowchart of a moving average high-pass filter according to the embodiment.

FIG. 3 is a Bode diagram of a moving average in the embodiment.

FIG. 4 shows a step response of a moving average in the embodiment.

FIG. 5 is a conventional harmonic current detection device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... pq calculation part 2p, 2q ... Primary high-pass filter 3 ... Harmonic current calculation part 4p, 4q ... Conventional moving average high-pass filter 5p, 5q ... Moving average high-pass filter of embodiment

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[Procedure amendment]

[Submission date] September 30, 1999 (September 9, 1999
0)

[Procedure amendment 1]

[Document name to be amended] Drawing

[Correction target item name] Fig. 4

[Correction method] Change

[Correction contents]

FIG. 4

Claims (1)

[Claims] 1. A pq calculation unit for obtaining a two-phase instantaneous real power p and an instantaneous imaginary power q from a three-phase power supply phase voltage and a load current of a power system, and a moving average of sampling data of these powers p and q, respectively. And a moving average high-pass filter that removes these DC components from the powers p and q to extract an AC component of the powers p and q, and a moving average high-pass filter from the AC components of the powers p and q and the power supply phase voltage. A harmonic current detection device comprising: a harmonic current calculation unit that detects a harmonic current of three phases. The moving average high-pass filter sets an average section of the moving average to a 180 ° section of a power supply cycle, and reverses a fundamental wave. A harmonic current detection device wherein a moving average value of a phase component and a harmonic component is set to 0.