JPH11103527A - Higher harmonics compensating system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To correct and surely compensate amplitude and phase by detecting k-th higher harmonics current without delays. SOLUTION: A k-th higher harmonics constituent of a load current detected by a current transformer CT1 is converted into a DC part with a three-phase/kω coordinate transformer 22, which rotates with a value kω obtained by multiplying the k-th higher harmonics with a degree k and power source angular frequency, and the rest of the constituents into an AC part. The DC part is extracted with low-pass filters 23, 24 and converted with a kω/three-phase coordinate transformer 25, which rotates with the value kω for detecting three-phase k-th higher harmonics. Since control cycle, delays in current detection by CT and delay in current control exist, amplitude and phase are each corrected for the k-th higher harmonics current with a amplitude/ phase correcting circuit 27 after the three-phase k-th higher harmonics is converted into the k-th higher harmonics current of dq axis with a three-phase/dq coordinate transformer 26. Then, it is converted into three-phase k-th higher harmonics current, whose amplitude and phase are corrected with a dq/three-phase coordinate transformer 28. The k-th higher harmonics current of a three-phase power source is corrected by PWM control, in such a way that the deviation between the k-th higher harmonics current and the output current of an inverter 10 becomes zero.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an active filter having an active filter function for compensating harmonics of a power system, and a harmonic compensation system suitable for high-order harmonic compensation in a power line conditioner.

[0002]

2. Description of the Related Art FIG. 3 shows a circuit configuration of a conventional active filter. In the figure, an inverter 10 for outputting a harmonic compensation power to the grid, 12 3 for converting the load current i _LU through i _LW detected by the current detector CT1 of dq coordinates d, q-axis current i _d, the i _q phase / dq coordinate transformation circuit, the d, AC component (harmonic current component) of the q-axis current 13, 14 through i _d, through i _q
Is a dq / 3-phase coordinate conversion circuit for converting the d- and q-axis harmonic current components into a three-phase current, and 31 is the harmonic current and the output of the inverter 10 detected by the current detector CT2. A subtractor 32 for detecting a deviation from the current; a current controller 32 for performing PI calculation of the current deviation and outputting a current command; and a comparator 33 for comparing the current command with a triangular carrier to convert the current command into a PWM control signal. Is a PWM control circuit for controlling This method is an example of current control by a PI controller and PWM control by triangular wave comparison. However, the present invention can be similarly applied to a hysteresis comparator method and a space vector method. (The hysteresis comparator method and space vector method use the current controller and P
The WM control unit is together. ) Three-phase load current i _LU detected by current detector CT1
Through i _LW and a rotating coordinate system that rotates at the power supply frequency omega d, current of the q-axis i _d, the relationship between the i _q is (1).

[0003]

(Equation 1)

The current _id is an invalid component of the load current, and the current _iq is an effective component. The current i _d, the DC component of the i _q is the fundamental wave current components, AC component becomes harmonic component.

[0005] Thus, to detect only the AC component by the high-pass filters 13 and 14 from the current i _d, i _q as shown in FIG. 3, and converts the current through i _d, a through i _q to the three-phase voltage by the current control The harmonic current contained in the load current can be compensated by generating a harmonic current from the inverter and injecting it into the system. This generally corresponds to the function of an active power filter.

[0006] can compensate the reactive power by extracting the DC component of the coordinate transformed current i _d (the reactive component fundamental) a low-pass filter. Further, the load current is converted by reverse 3-phase / dq coordinate conversion circuit coordinate is reversely rotated, the converted current i _d, i _q DC component negative-phase power when extracting the (fundamental wave negative phase component) low-pass filter Can be compensated. The one that performs the reactive power compensation and the negative phase power compensation in addition to the function of the active filter corresponds to the function of the power line conditioner.

[0007]

SUMMARY OF THE INVENTION An active filter,
When compensating for higher harmonics in harmonic compensation in a power line conditioner or the like, sufficient compensation cannot be performed due to a control cycle, a delay in current detection by a current detection device, and a delay in current control. As a countermeasure, a method of adding a control delay compensation circuit can be considered. However, since the differential operation is performed, stability is lacking and control becomes difficult.

The present invention has been made in view of such a problem, and an object thereof is to detect a high-order harmonic current of an electric power system without delay and correct the amplitude and phase to reliably compensate. It is an object of the present invention to provide a harmonic compensating method that can be performed.

[0009]

SUMMARY OF THE INVENTION The present invention detects a harmonic current of a system load current, compares the detected harmonic current with an output current of an inverter output to the system, and eliminates the current deviation. In an inverter that controls an inverter to compensate for harmonics, the detected load current is converted by a rotating coordinate conversion circuit that rotates at a value that is a multiple of the order of the harmonics to be compensated for the power supply angular frequency, and the order of the order to be compensated from the load current is Harmonics are obtained, these harmonics are converted to rotation vectors, their amplitude and phase are independently corrected, and the amplitude and phase corrected harmonics are compensated as detected harmonics. The amplitude and phase errors due to the current detection delay and the current control delay are eliminated.

Alternatively, the detected load current is converted by each rotating coordinate conversion circuit rotating at a value of each order multiple of the harmonic to be compensated for the power supply angular frequency, and the harmonic of each order to be compensated is obtained from the load current. The harmonics of each order are converted into rotation vectors, the amplitudes and phases of the harmonics are independently corrected, and the harmonics of the orders corrected for the amplitude and phase are added to compensate for harmonics as detected harmonics. The amplitude and phase errors due to the control cycle, current detection delay, and current control delay associated with harmonic compensation are eliminated.

Alternatively, a harmonic current of the order k, which is to be surely compensated from the detected load current, is converted into a k-th harmonic by a three-phase / kω rotational coordinate conversion circuit that rotates at a value obtained by multiplying the order k by the power supply frequency. Is converted to a DC component, the DC component is extracted by a low-pass filter, and converted into three phases by a kω / 3-phase rotation coordinate conversion circuit to obtain a k-th harmonic current. Is converted into d- and q-axis currents by a three-phase / dq coordinate conversion circuit that rotates at k, and the k-th harmonic current is corrected in amplitude and phase so that the amplitude and phase errors are eliminated.
A k-th harmonic current whose amplitude and phase have been corrected by converting it into a three-phase signal by a three-phase coordinate conversion circuit is removed. The k-th harmonic current whose amplitude and phase has been corrected is removed from the detected load current, and the k-th harmonic current is removed. 3 phase / d rotating load current with wave removed at power supply frequency
The d- and q-axis currents are converted by a q-coordinate conversion circuit, harmonic components are extracted by a high-pass filter, and converted into three phases by a dq / 3-phase coordinate conversion circuit to obtain a harmonic current that does not include the k-th harmonic. The harmonic current not including the k-th harmonic is added to the amplitude
The inverter is controlled by a harmonic current to which the k-th harmonic current whose phase has been corrected is added to perform harmonic compensation.

[0012]

FIG. 1 shows a circuit configuration of an active filter according to an embodiment.

In FIG. 1, S is a system three-phase AC power source, L
Is a system load, 10 is an inverter that outputs a compensation current of the active filter, 11 is an amplitude / phase correction detected by a k-order harmonic amplitude / phase correction block 21 described later from the load currents i _{LU to} i _LW detected by the current detector CT1. A subtractor for subtracting the k-th harmonic, a harmonic detection circuit for detecting a harmonic that does not require amplitude and phase correction, and a load current from which the k-th harmonic from the subtractor 11 has been removed. Is converted to a dq coordinate system rotating at the power supply frequency ω, and d, q-axis currents _id ,
i _q 3-phase / dq-axis coordinate converting circuit to obtain, this d, AC component (harmonic current component) of the q-axis current 13, 14 through i _d, ~
high pass filter, 15 is the d, dq / 3-phase coordinate conversion circuit for converting the q-axis higher harmonic current component in three-phase current to extract the i _q.

Reference numeral 21 (22 to 29) denotes a k-th harmonic amplitude / phase correction block. Reference numeral 22 denotes a dq coordinate system for rotating the load current detected by the CT1 by a value kω obtained by multiplying the harmonic order k by the rotational angular velocity ω. To convert only the k-th harmonic into a DC component
Phase / kW rotating coordinate conversion circuit, 23 and 24 to remove the harmonics other than that of k-th order, the d, DC component i _dk of the q-axis current, i _qk
Low-pass filter for extracting, 25 converts this d, DC component -i _dk of the q-axis, the -i _qk (9) to the 3-phase current of the formula k
ω / 3-phase rotation coordinate conversion circuit, 26 is the k-th harmonic component 3
Dq rotating phase currents i _ka , i _kb , i _kc at power frequency ω
A three-phase / dq coordinate conversion circuit for converting into a coordinate system, 27 is an amplitude-phase correction circuit for correcting the converted amplitude and phase of the k-th harmonic current according to equation (1), and 28 is dq after the amplitude-phase correction. axis k-th harmonic components through i _dk, dq / 3-phase coordinate conversion circuit for converting a through i _qk into three-phase current, the amplitude phase correction circuit for harmonics from dq / 3-phase coordinate conversion circuit path 15 29 27
, And the dq / 3-phase coordinate conversion circuit 28
An adder for adding the k-th harmonic current converted to three phases in the above.

Numeral 31 denotes the harmonic current from the adder 29 and CT
A subtractor for detecting a deviation from the output current of the inverter detected in step 2; a current controller 32 for performing a PI operation on the current deviation to output a current command; and 33 for comparing the current command with a triangular carrier to perform PWM control. This is a PWM control circuit that converts the signal into a signal and controls the inverter 10.

The k-th harmonic amplitude / phase correction block 21
Will be described together with the principle. The low-order harmonics are detected without using a high-pass filter by converting them into a rotating coordinate system that rotates by a value obtained by multiplying the harmonic order k by the power supply angular frequency ω.

The load currents i _LU , i _LV , i _LW are defined as in equation (2).

[0018]

(Equation 2)

In the equation (2), n is an integer, which means the harmonic order k. Consider a case where the k-th harmonic is detected and compensated from the load current.

The load current in equation (2) is d, q transformed into a coordinate system rotating at a value kω obtained by multiplying the higher harmonic order k by the rotational angular velocity ω. The conversion equation in this case can be defined as equation (3).

[0021]

(Equation 3)

By substituting equation (2) into the above equation,

[0023]

(Equation 4)

## EQU1 ## Here, when the harmonic current is converted into a coordinate system rotating by kω, the harmonic current component n = k + i
The components of (i = 0, ± 1, ± 2, ± 3...) Are expressed by equations (6) and (7) from equations (4) and (5).

[0025]

(Equation 5)

From the equations (6) and (7), it is understood that the k-th harmonic current contained in the load current becomes a DC value, and the harmonic currents of the fundamental harmonic and other orders become AC values. . Therefore, if extract only the DC component by the low-pass filter 23, 24 from the current i _d, i _q converted by three-phase / kW rotating coordinate conversion circuit, included in the system current as shown in equation (8) The k-th harmonic can be detected. Since a high-pass filter that performs a differential operation is not used for high-order harmonic detection, detection can be performed with high accuracy.

[0027]

(Equation 6)

Next, the coordinates of the equation (8) are transformed by the equation (9).
Further, when the coordinates are transformed by Expression (10),

[0029]

(Equation 7)

[0030] The obtained current through i _dk, through i _qk is the rotation vector rotating at an angular frequency 3 milliohms (although k = 3m ± 1, m = integer) (see Fig. 2).

[0031] When the amplitude correction coefficient alpha _m, the phase correction coefficient and theta _m, the current value through i _dk2 corrected, through i _Qk2 can be calculated by equation (11).

[0032]

(Equation 8)

The kW / 3-phase rotating coordinate conversion circuit 25 converts the low-pass DC component -i _dk from the filter 23 and 24, the current i _ka of three phases in the -i _qk (9) equation, i _kb, the i _kc The k
Detect the second harmonic. Furthermore, three-phase currents i _ka , i _kb , i _kc
Was converted with 3-phase / dq coordinate conversion circuit 26 to the dq coordinate system rotating at the fundamental frequency omega, obtain current through i _dk, a through i _qk.

The amplitude and phase correction circuit 27 outputs currents ~ _idk , ~ i
through i _dk2 The _qk (11) the amplitude A and phase theta by the formula is corrected by the correction coefficient alpha _m and theta _m, and through i _Qk2, which dq / 3
The phase coordinate conversion circuit 28 converts the signal into three phases and outputs the k-th harmonic to which the amplitude and phase are corrected.

As described above, the control cycle,
It is possible to compensate for a delay in current detection by the current detector and a delay in current control. Since this compensation is performed on the rotation vector, there is no need for a differential operation like the conventional delay compensation,
Independent adjustment of phase and amplitude is possible.

The parameters such as the amplitude correction coefficient and the phase correction coefficient are determined from the specifications of the control circuit and are not affected by external circuits.

In FIG. 1, if a plurality of k-order harmonic amplitude / phase correction blocks 21 are provided in parallel, it is possible to simultaneously detect a plurality of high-order harmonics and correct the amplitude / phase.

[0038]

The present invention converts a harmonic component into a vector rotating by a value obtained by multiplying the order of k of the corrected harmonic by the power supply angular frequency, and corrects the vector amplitude and phase. Higher-order harmonics can be corrected more accurately and more stably than the differential operation method using

Further, by setting the value of the order k of the higher harmonic, any harmonic can be amplitude-phase compensated. It is also possible to simultaneously correct a plurality of harmonics.

Therefore, harmonics of any order can be compensated for without any control delay.

[Brief description of the drawings]

FIG. 1 is a circuit configuration diagram of a power active filter according to an embodiment.

FIG. 2 is a rotation vector diagram illustrating amplitude / phase correction of a high-order harmonic current.

FIG. 3 is a circuit configuration diagram of a power active filter according to a conventional example.

[Explanation of symbols]

Reference Signs List 10 power inverter 12 three-phase / d _q coordinate conversion circuit 13, 14 high-pass filter 15 dq / 3-phase coordinate conversion circuit 21 k-th harmonic amplitude / phase correction block. 22: three-phase / kω rotation coordinate conversion circuit 23, 24: low-pass filter 25: kω / 3-phase rotation coordinate conversion circuit. 27: amplitude and phase correction circuit 32: current control circuit 33: PWM control circuit

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Junichi Shimomura 2-1-17-1 Osaki, Shinagawa-ku, Tokyo Inside Meidensha Co., Ltd.

Claims (3)

[Claims] 1. A method for detecting a harmonic current of a system load current, comparing the detected harmonic current with an output current of an inverter to be output to the system, and controlling the inverter so as to eliminate the current deviation. In this method, the detected load current is converted by a rotating coordinate conversion circuit that rotates at a value that is a multiple of the harmonic to be compensated for the power supply angular frequency, and a harmonic of the order to be compensated is obtained from the load current. Is converted to a rotation vector, the amplitude and phase of which are independently corrected, and the harmonics whose amplitude and phase are corrected are subjected to harmonic compensation as detected harmonics. The control cycle, current detection delay, and current control A harmonic compensation method characterized by eliminating amplitude and phase errors due to delay. 2. Harmonic compensation by detecting a harmonic current of a system load current, comparing the detected harmonic current with an output current of an inverter output to the system, and controlling the inverter to eliminate the current deviation. In each of the above, the detected load current is converted by each rotating coordinate conversion circuit rotating at a value of each order multiple of the harmonic to be compensated for the power supply angular frequency, and the harmonic of each order to be compensated is obtained from the load current, The harmonics of each order are converted into rotation vectors, the amplitudes and phases of the harmonics are independently corrected, and the harmonics of the orders corrected for the amplitudes and phases are added to perform harmonic compensation as detected harmonics. Control cycle due to wave compensation, current detection delay,
A harmonic compensation method characterized by eliminating an amplitude phase error due to a delay in current control. 3. A harmonic compensation system for detecting a harmonic current of a system load current, comparing the detected harmonic current with an output current of an inverter to be output to the system, and performing PWM control on the inverter to eliminate the current deviation. In the above, the harmonic current of the order k, which is to be surely compensated from the detected load current, is converted into a DC by a three-phase / kω rotational coordinate conversion circuit that rotates at a value obtained by multiplying the order k by the power supply frequency. And a DC component is extracted by a low-pass filter, and converted into three phases by a kω / 3-phase rotating coordinate conversion circuit to obtain a k-th harmonic current. The k-th harmonic current is rotated at the power supply frequency. 3 phase / dq
The d- and q-axis currents are converted by a coordinate conversion circuit, and the k-th harmonic current is corrected in amplitude and phase so that the amplitude and phase errors are eliminated, and converted into three phases by a dq / 3-phase coordinate conversion circuit. The k-th harmonic current whose amplitude and phase have been corrected is removed. The k-th harmonic current whose amplitude and phase has been corrected is removed from the detected load current, and the load current from which the k-order harmonic has been removed is rotated at the power supply frequency. A three-phase / dq coordinate conversion circuit converts the current into d- and q-axis currents, and a high-pass filter extracts harmonic components.
A dq / 3-phase coordinate conversion circuit converts the current into three phases to obtain a harmonic current that does not include the k-th harmonic. A harmonic compensation method characterized in that the inverter is controlled by the harmonic current to which the current is added to compensate the harmonic.