JPH08223803A - Method and device for controlling active filter - Google Patents

Abstract

PURPOSE: To perform high accurate compensation for harmonics by adding the harmonics obtained by adding an active filter current to a load current to a compensating command value computed on the basis of the load current as a correction value. CONSTITUTION: In a control device 22, the functions of detecting and correcting a harmonic current ISH made to flow into an active filter(AF) from a power supply is added to the function of a harmonic detection circuit 23. To the input stage, a current transformer 24 for detecting the current IAF, of the AF, an adder 25 for adding a load current IL to the detected current IAF and a changeover switch circuit 26 for switching and inputting the added value (IAF+IL) and the load current IL to the harmonic detection circuit 23. Namely, the harmonic current ISH made to flow into the AF from the power supply is obtained from the addition of a harmonic current ILH contained in the load current IL and the AF current IAF and added to a harmonic current ILH separated and extracted from the load current IL as a connection value, thereby obtaining a compensating aommand value IREF.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an active filter (harmonic suppressing device) for suppressing a harmonic current generated on a load side from flowing into a power source side.

[0002]

2. Description of the Related Art As shown in FIG. 4, an active filter 1 allows a harmonic compensation current I _AF to flow out to a system and be offset by a harmonic current I _LH generated by a load side harmonic generation source 2. By (I _AF + I _LH = 0), harmonics flowing into the power source 3 such as a substation are suppressed.

The active filter 1 shown in FIG. 4 is of an injection circuit type, in which a series circuit of a capacitor C and a reactor L is connected to a system bus 4 and inverters 5 connected to both ends of the reactor L lead to harmonics in the system. The current I _AF is flowing. This injection circuit system has X _C >
X _L, by establishing the relationship between X _C <X _L against harmonics, to reduce the inverter capacity output voltage of the inverter 5 as low corresponding to harmonics, simultaneously improving the power factor of the system by the capacitor C It has the feature of being able to Command value I of the compensation current I _AF of the active filter
_REF is determined by the control device 6 of the active filter shown in FIG.

In FIG. 5, 7 is the voltage V _{L of the} system bus 4.
For detecting the load current I _L , a current transformer for detecting the load current I _L , a synchronization detection circuit 9 for generating a power supply synchronization signal f _S from the system voltage V _L, and a load current I for the power supply synchronization signal f _S. harmonics detection circuit for separating and extracting the harmonic current I _LH from _L, 11 the detected harmonic current I _LH [(X _L -X _C)
/ _XL ] to convert the output current of the inverter 5 into a compensation command value I _REF .

This compensation command value I _REF is
It is subtracted by the presently detected current inverter output current I _INV and output to the comparator 13. Inverter control is performed by the output of the comparator 13.

The harmonic detection circuit 10 is constructed as shown in FIG. 6, and calculates the harmonic current I _LHn contained in the load current I _L based on the power supply synchronizing signal f _S according to the following Fourier transform formula.

[Equation 1]

In FIG. 6, 14 is a sample hold command circuit for generating a sample hold signal S _H at the end of each Fourier calculation cycle based on the power supply synchronizing signal f _S , and 15
Is a reset circuit that generates the reset signal R immediately after the generation of the sample hold signal. Reference numeral 16a is a cos wave generation circuit, 16b is a sin wave generation circuit, and a harmonic voltage cos nω synchronized with the system voltage V _L based on the power supply synchronization signal f _S.
t and sin nωt, where n is the harmonic order.
Numerals 17a and 17b are multipliers for obtaining a product value of the synchronous harmonic voltage and the load current I _L. Reference numerals 18a and 18b denote integrating circuits, which are reset by the reset signal R and integrate the multiplied value for each Fourier calculation cycle. 19a, 19b
Is a sample and hold circuit, which samples and holds the integrated value as coefficients (a _n , b _n ) of the sine term and the cosine term in the corresponding order of the Fourier expansion at the end of each Fourier calculation cycle. Reference numerals 20a and 20b _denote multipliers, which multiply the synchronous harmonic voltage by the coefficient (a _n , b _n ) to generate voltages of a sine term and a cosine term. Reference numeral 21 denotes an adder, which adds the voltages of the sine term and the cosine term to obtain a harmonic (I
_LHn = a _n · sin nωt + b _n · cos nωt) is created.

FIG. 6 shows a Fourier calculation circuit for separating / extracting harmonics of one order. In reality, however, a Fourier calculation circuit is provided for each order of the harmonics to be compensated, and the calculated value of each order is calculated. Will be added to determine the compensation command value I _REF .

According to the compensation command value I _REF , the active filter 1 supplies the compensation current I _AF to the system, so that I _AF + I _LH = 0 and the harmonic current I _L can be suppressed from flowing out to the power supply. .

[0010]

The conventional active filter described above calculates the compensation command value I _REF only from the load current I _L.

Therefore, there is a harmonic generation source (such as a load on the upstream side) on the power source side, and the active filter 1 is connected from the power source side.
When a harmonic current flows in, since it is not detected, it appears that IL _H + I _AF ≠ 0, and the harmonic current I _SH flowing to the power source side seems to remain as a compensation error ( (Fig. 4).

Therefore, the present invention provides a control method and apparatus for an active filter which can be improved so that the harmonic current flowing on the power supply side becomes zero even if there is a harmonic generation source on the power supply side. To aim.

[0013]

A method of controlling an active filter provided by the present invention is to detect a harmonic current I _LH from a load current I _L by Fourier series expansion to obtain a compensation command value I _L.
In the active filter to be _REF ,

The harmonic current I _LH contained in the load current and the output current I _AF of the active filter are added to obtain the harmonic current I _SH flowing into the active filter from the power supply, and the harmonic current I _SH detected from the load current is calculated. It is characterized in that the compensation command value I _REF is added to the current I _LH as a correction value. An active filter control device embodying the above control method includes a current transformer for detecting a load current I _L , a current transformer for detecting an output current I _AF of the active filter, a detected load current I _L and an active filter. Output current I _AF
An adder for adding the correction value calculation timing and a correction value calculation timing determination circuit for generating a correction value calculation signal f _S ^* for a predetermined cycle period synchronized with the power supply at predetermined intervals.

Normally, the load current I _L is passed as an input signal for Fourier calculation, and when the correction value calculation signal f _S ^* is generated, the added value (I _L + I _AF ) is passed as an input signal for Fourier calculation. A changeover switch circuit,

Receives an input signal that has passed through the changeover switch circuit.
And the integration circuit that performs the Fourier integration.
The result is sent to the correction value calculation signal at the end of each Fourier calculation cycle.
No. f _S ^*For load current and added value according to
A sample and hold circuit that distinguishes and stores things
Sample value corresponding to load current (a_n, B_n) To the added value
Corresponding sample value (a_n ^*, B_n ^*) Is added to correct
Equipped with an adder to separate and extract harmonics from the input signal
A harmonic detection circuit,

The output of the harmonic detection circuit is multiplied by a predetermined coefficient to be converted into the output current of the active filter, and the counter is used as the compensation command value I _REF .

[0018]

According to the above active filter control method, the harmonic current I _SH flowing from the power supply into the active filter is replaced with the harmonic current I _LH included in the load current I _L at predetermined intervals.
And the active filter current I _AF are added, and this is added as a correction value to the harmonic current I _LH separated and extracted from the load current I _L to obtain a compensation command value I _REF . Therefore, even if there is a harmonic generation source on the power supply side, the harmonic current flowing on the power supply side can be suppressed to zero.

Further, an active filter control device embodying the above method intermittently provides a correction value calculation period, and normally performs a Fourier operation on the load current I _L to detect the harmonic current I _LH . Then, during the calculation period of the correction value, the Fourier calculation is performed on the added value of the load current I _L and the active filter current I _AF to detect the harmonic current I _SH flowing from the power supply into the active filter. These calculation results are the coefficient values (a _n , b _n of the Fourier calculation formula.
And a _n ^* , b _n ^* ) in separate sample and hold circuits. The compensation command value I _REF is the sum (a _n +
a _n ^* , b _n + b _n ^* ) and is calculated according to the Fourier transform formula.

Thus, the compensation command value I _REF of the active filter control performed by detecting the harmonic current I _LH contained in the load current I _L for each cycle is intermittently measured and updated. It can be corrected with I _SH .

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to FIGS.

The controller 22 for the active filter of FIG.
Has added the function of detecting the harmonic current I _SH flowing from the power supply to the active filter to the harmonic detection circuit 23 in addition to the function of the conventional harmonic detection circuit 10 shown in FIGS. (Fig. 2).

With the improvement of the harmonic detection circuit 23,
The input stage of the device of FIG. 1 is the same as the device of FIG. 5, _except that a current transformer 24 that detects the current I _{AF of the} active filter, an adder 25 that adds the detected current I _AF to the load current I _L ,
A changeover switch circuit 26 for additionally inputting the added value (I _AF + I _L ) and the load current I _L to the harmonic detection circuit 23 is added.

Other components of the apparatus of FIG. 1 are the same as those of FIG.
Common. That is, the system voltage V _LVoltage change to detect
Generator 7, load current I_LTransformer 8 for detecting current, system power
Pressure V_LTo power supply synchronization signal f_SDetection circuit 9 for detecting
Harmonic current (I_LH＋ I_{S H}) Is the output voltage of the inverter
Compensation command value I converted to flow_REFAnd the coefficient unit 11,
Compensation command value I_REFTo the current inverter output current I_INVTo
Adder 12 for subtraction, ratio for outputting inverter control signal
The same comparator 13 as that shown in FIG. 5 is used. 1 high
The harmonic detection circuit 23 is configured as shown in FIG.
It First, the parts added / changed from FIG. 6 will be explained.
It

Reference numeral 27 denotes a correction value calculation timing determination circuit, which generates a correction value calculation signal f _S ^* for a predetermined cycle period in synchronization with the power source at predetermined intervals. This is shown in FIG.
As shown in, the output is set to a high level for the length of one cycle every 30 shots of the power supply synchronization signal f _S (30 cycle periods), and this is used as the correction value calculation signal f _S ^* .

28a and 28b are the added values (I _AF + I)
_L ) sample hold circuit for integrating circuits 18a, 1
When 8b integrates the Fourier calculation with respect to the added value (I _AF + I _L ), at the end of the calculation cycle, each integrated value is a correction value of each coefficient of the sine term and cosine term of the Fourier calculation formula. It is individually stored as (a _n ^* , b _n ^* ).

29a and 29b are adders, which are load currents I _L
Outputs (a _n , b _n ) of the sample hold circuits 19a and 19b that store the integrated value when Fourier calculation is performed on
And the correction outputs (a _n ^* , b _n ^* ) of the sample and hold circuits 28a and 28b for the added value (I _AF + I _L ) are added together (a _n + a _n ^* , b _n + b). _n ^* ).

A sample and hold command circuit 14 'generates a sample and hold signal S _H at the end of each Fourier calculation cycle based on the power supply synchronizing signal f _S. This circuit has a function similar to that of the circuit 14 shown in FIG. 6, but the present invention performs a Fourier operation on the added value (I _AF + I _L ) in addition to the Fourier operation on the load current I _L. Therefore, it has two outputs, a signal line for the sample and hold circuits 19a and 19b and an output line for the sample and hold circuits 28a and 28b, corresponding to each calculation. At the end of the Fourier calculation cycle, which signal line to output is determined by the correction value calculation signal f _S ^{* of the} determination circuit 27.

Numeral 26 is a switch switch number described in FIG.
In order to show the connection relationship with the harmonic detection circuit 23,
Is also shown. That is, this changeover switch circuit 2
6 is the correction value calculation signal f_S ^*Receiving the reset signal R
Raw current, load current I _LPassing and the added value above
(I_L＋ I_AF) Switch the passage. Wait for reset signal R
Switching is performed by performing one Fourier calculation for each cycle.
This is to make it complete.

The other structure is common to the conventional harmonic wave detection circuit 10 of FIG. That is, the reset circuit 15, cos
Wave generator 16a, sin wave generator 16b, multiplier 17
a, 17b, integration circuits 18a, 18b, sample hold circuits 19a, 19b, multipliers 20a, 20b, and an adder 21. The operation of the circuit shown in FIG. 1 and FIG.
This will be described with reference to the operation timing chart of FIG.

The synchronization detection circuit 9 outputs a synchronization signal pulse f _S for each cycle of the commercial power supply cycle. As described above, the correction value calculation timing determination circuit 17 determines the correction value calculation signal f _S at a high level for the length of one cycle every 30 times (30 cycle periods) of the power supply synchronization signal f _S , for example. Generate ^* .

This output is input to the changeover switch circuit 26 and the sample hold command circuit 14 'and used for switching the input signal to the harmonic detection circuit 23 and for switching the sample hold target.

The sample and hold command circuit 14 'outputs a sample and hold signal to each sample and hold circuit at the timing of generation of the synchronizing signal pulse f _{S. When} there is a high level correction value calculation signal f _S ^* Is a sample hold circuit (28a, 2a) corresponding to the added value.
8b) only outputs S _H ^* , and in the normal state without this signal, the sample hold circuit (19
The output S _H is applied only to a, 19b). FIG. 6 shows that this switching is performed at the fall of the correction value calculation signal f _S ^* .

The reset circuit 15 outputs the reset signal R to the integrator circuits 18a and 18b immediately after the generation of the sample and hold signal, that is, at the end of one Fourier calculation, and enables integration of the next Fourier calculation.

The changeover switch circuit 26 is as described above.
And the high-level correction value calculation signal f _S ^*When occurs,
At the timing of generation of the reset signal, the load current I_LPassage of
From the above added value (I_L＋ I_AF) Switch to next time
Load signal I by the reset signal of_LReturn to the passing state
I do. As a result, the high-level correction value calculation signal f_S ^*
When the above occurs, the addition value (I_L+
I_AF) Of the load current I during the other period.
_LThe Fourier operation for is performed.

As described above, input switching to the harmonic detection circuit 23, switching output of the sample and hold signals S _H and S _H ^* , and resetting of the integration circuits (18a, 18b) are performed, so normally, For each cycle period, the load current I
Coefficients (a _n , b _n ) of the sine term and cosine term of the Fourier transform formula necessary for calculating the harmonic current I _LH contained in _L are sampled by the sample hold circuit (19a, 19b),
When the high-level correction value calculation signal f _S ^* is generated, the coefficients (a _n ^* , b _n ^* ) corresponding to the above added value (I _L + I _AF )
Are sampled by the sample hold circuit (28a, 28b).

These sample values are added by the adders corresponding to the sine term and those corresponding to the cosine term according to the Fourier transform formula, and the multiplier 20
a, 20b and the adder 21 calculate and output as a harmonic current I _LH + I _SH = (a _n + a _n ^* ) · sin nωt + (b _n + b _n ^* ) · cos nωt.

The output of the harmonics detection circuit 23 is multiplied by _{[(X L -X C) / X} L ] in the coefficient unit 11 is converted into an output current of the inverter 5 is output as compensation command value I _REF It Inverter control is performed by the adder 12 and the comparator 13 based on the compensation command value I _REF .

FIG. 2 shows a Fourier calculation circuit for separating / extracting harmonics of one order, but in reality, a Fourier calculation circuit is provided for each order of the harmonics to be compensated, and the calculated value of each order is set. Is added to obtain the compensation command value I _REF , similar to the circuit described in FIG.

The timing for switching the correction value calculation signal f _S ^{* to} the high level, that is, the addition value (I _L +
The insertion interval of one cycle period for performing the Fourier calculation of I _AF ) is set appropriately according to the fluctuation period of the inflow from the power supply side. The correction value calculation period may be a plurality of Fourier calculation cycle periods, and an average value thereof may be used as the correction data.

[0041]

As described above, the current flowing into the active filter from the power source which causes an apparent compensation error is obtained by adding the load current I _L and the active filter current I _AF , and the harmonic I detected from this is obtained. By adding _SH as a correction value to the compensation command value calculated based on the load current, highly accurate harmonic compensation can be performed.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration example of a control device for an active filter according to the present invention.

FIG. 2 is a diagram showing a specific example of the harmonic detection circuit of FIG.

3 is a diagram showing the operation timing of each part with respect to the power supply synchronizing signal of the harmonic wave detection circuit of FIG.

FIG. 4 is a basic configuration diagram of an injection circuit type active filter.

FIG. 5 is a diagram showing a conventional active filter control device that determines a compensation current of an active filter only from a load current.

FIG. 6 is a diagram showing a specific example of the harmonic detection circuit of FIG.

[Explanation of symbols]

7 Voltage transformer for detecting system voltage 8 Current transformer for detecting load current I _L 9 Synchronization detection circuit 11 Coefficient device 12 Adder for detecting difference between compensation command value I _REF and current inverter output 13 Comparator 18a , 18b Integrator circuit for Fourier calculation 19a, 19b Sample-and-hold circuit for obtaining coefficients of Fourier transform formula 22 Control device for active filter of the present invention 23 Harmonic wave detection circuit 24 Current transformer for detecting active filter current I _AF 25 Active from power supply The current flowing into the filter
Adder 26 obtained by I _L + I _AF 26 Changeover switch circuit provided for interposing a correction value calculation cycle during the calculation period of the harmonic current I _LH contained in the load current 27 Correction value calculation timing determination circuit 28a , 28b Sample and hold circuits 29a and 29b for obtaining correction values of Fourier transform formula coefficients (a _n , b) obtained from load current I _L
adder for adding the correction value (a _n ^* , b _n ^* ) to ( _n )

Claims (2)

[Claims] 1. An active filter which detects a harmonic current I _LH from a load current I _L by Fourier series expansion and _sets it as a compensation command value I _REF , in which the harmonic current I _LH included in the load current and an output current of the active filter are included. A feature is that I _AF is added to obtain a harmonic current I _SH flowing from the power supply into the active filter, and this is added as a correction value to the harmonic current I _LH detected from the load current to obtain a compensation command value I _REF. Control method of active filter. 2. A current transformer for detecting the load current I _L , a current transformer for detecting the output current I _AF of the active filter, and an addition for adding the detected load current I _L and the output current I _AF of the active filter. And a correction value calculation timing determination circuit that generates a correction value calculation signal f _S ^* for a predetermined cycle period synchronized with the power supply at predetermined time intervals, and normally, the load current I _L is used as an input signal for Fourier calculation. A selector switch circuit that allows the addition value (I _L + I _AF ) to pass as a Fourier calculation input signal when the correction value calculation signal f _S ^* is generated, and a Fourier calculation that receives the input signal that has passed the selection switch circuit. And an integration circuit that performs the integration of the load current according to the correction value calculation signal at the end of each Fourier calculation cycle Includes a sample and hold circuit for storing the sample values (a _n, b _n) corresponding to the load current sample value corresponding to the addition value ^{_{(a n *, b n *}} ) an adder for performing an addition correction Te, An active filter comprising: a harmonic detection circuit for separating / extracting harmonics from an input signal; and a counter for multiplying an output of the harmonic detection circuit by a predetermined coefficient to obtain a compensation command value I _REF. Control device.