JPS61142959A - Higher harmonic current compensator - Google Patents

Abstract

PURPOSE:To organize an apparatus of high performance suppressing the generation of higher harmonic current over al operation range, by providing a current limiting circuit eliminating non-linear property for control based on current limiting function. CONSTITUTION:A higher harmonic current compensator 30 is set on AC bus connected to a load 10 generating the higher harmonic current of an AC power source system 1, a cycloconverter, and the like. The hither harmonic current compensator 30 is provided with a current indicator 300A and a current generator 350 and works actively, and the higher harmonic current is different from the current generated from the cycloconverter 10 by just 180 deg. in phase, and current of the same amplitude is generated as compensating current. The current is synthesized at points 352U-352W, and the higher harmonic current is prevented from flowing toward the AC power source system 1.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to a harmonic current compensator, which is effective in a system that supplies power from an AC power supply system to a load that generates a large amount of harmonic current via an AC bus. The present invention relates to a harmonic current compensation device for performing harmonic current compensation.

[Technical background and problems of the invention]

In recent years, large-capacity cycloconverters have been installed and operated in AC power systems. As is well known, a cycloconverter generates a complex harmonic current on the input power supply side based on equation (1) related to both the power supply frequency fl and the output frequency fo of the cycloconverter.

If this harmonic current flows directly into the AC power system, the power system will oscillate due to the anti-resonance phenomenon with the power system impedance, the harmonic current will flow to the power factor correction capacitor, causing burnout of the capacitor, and the capacitor installed in parallel in the power system Problems such as interference with communication lines may occur. For this reason, measures are taken to prevent harmonic currents from flowing into the AC power supply system, such as installing a series resonant passive filter consisting of a capacitor and a reactor to absorb harmonic currents. However, since the frequency of the harmonics that passive filters can compensate for is fixed, there is a problem in that in principle, it is difficult to obtain a sufficient filtering effect when the frequency changes in a complex manner, such as the harmonics generated by a cycloconverter. . To solve this drawback of passive filters, actively harmonic current compensators (also referred to as active filters) using power converters have recently been proposed. In principle, this device can provide sufficient compensation for harmonics that change in a complex manner; however, if used incorrectly, the harmonic current compensator itself becomes a new source of harmonic current. However, there was a need for a solution to this problem. In the following, we will clarify the configuration and problems of the conventional actively acting harmonic current compensator, and show how to solve them.

FIG. 3 is a diagram in which a conventional harmonic current compensator is applied to an AC power supply system.

In FIG. 3, a cycloconverter 10 operates the induction motor 12 at variable speed. 3U to 3W are system impedances present in the AC power system.

1 is a power supply source such as a three-phase AC power supply or a power transmission/distribution/bus bar. 30 is a harmonic current compensator that acts actively, and includes first current detectors 301U to 301W, and a current command device 3.
00. It consists of a current generator 350. That is, the first current detectors 301U to 301W detect the current of the cycloconverter 10 including harmonics and output the first detection signals jUL to 1wl,
output to lines 302U to 302W. Current command device 3
00 introduces the first detection signal 1UL-iwb and outputs the harmonic current command wind υ plate to wire to the lines 311U to 311WE. The current generator 350 is a harmonic current command true υ plate ~ IWHR
and the corresponding compensation current +uo -iwo is connected to line 3.
It is generated at 57U to 357w and acts to flow to the AC buses 40 to 4W. This device works actively, i.e. it compensates for the harmonic currents generated by the cycloconverter 10 by compensating the currents with a phase difference of exactly 1800 and the same amplitude.
o”iwo, therefore, this current and the harmonic current generated by the cycloconverter 10 are at the point 352U.
~352W and cancel each other out (or it can also be said that the harmonic current compensator 30 absorbs the harmonic current generated by the cycloconverter 10), and as a result, the harmonics flowing toward the AC power supply system 1 are This type of harmonic current compensator is a type of waveform-following current generator, and in principle, there are no restrictions on the current waveform that can be generated, so any harmonic current can be absorbed. is possible.

Next, details of the current command device 300 and the current generator 350 will be explained. In the current command device 300 of FIG. 4, the line 302U~
302W is connected to the power station with the same symbol in FIG. 3 as the first detection signal I. L-1vF1. is input to the harmonic detection circuit 304, in which the fundamental wave component is removed, and the first harmonic signal i'uH-iI (only w is the line 305U) corresponds to the madder harmonic current component generated by the cycloconverter 10. ~305W.The first harmonic signal i'uH"iIvIH is introduced into the inverter 306, where only the phase is inverted by 180°,
The second harmonic signal iUH””iWH is the line 307U to 307
w is output. 308 is a maximum current setting device, which commands the maximum value of current that the current generator 350 (@31k) can generate, and sets a maximum value command. 310
is a limiter which introduces the second harmonic signals 1t7H to j1yH and the maximum value command arc, performs an amplitude limiting operation having the characteristics shown in FIG. 5, and outputs harmonic current commands 1ki to inn. That is, in FIG. 5, in the range where the second harmonic signal iυu-1■ is smaller than the maximum value command IH, the second harmonic signal itru
=iw is passed as is as the harmonic current command 1iiac~'WHR, and the second harmonic signal IIJH-! When □ becomes larger than the maximum value command rH (= limits the maximum value of the second harmonic signal □~i1 to the maximum value command 17., and the signal is set as the harmonic current command IσHR~1). Out′j
Tr'r is also 9, and for example, the relationship between the signals is shown in Figure 6 (
Figure a) (no restrictions) and Figure 6(b) (with restrictions). This amplitude limiter is an essential element when operating an actual power converter, and without this circuit, when an excessive harmonic current is detected, a corresponding compensation current is generated by the current generator 350 (third Figure 7 shows the details of the current generator 350 shown in Figure 3. show.

In FIG. 7, the harmonic current commands 1811 to ii□ are introduced to lines 311U to 311W. 355U~35
5W is a second current detector and is a compensation current lυ generated by the current generator 350. ~Detects iwo and generates current signal IUOF~
Create 1vray. 1UOF~Dark. 1 is comparator 35
It is fed back to 1U to 351W, where it is compared with the harmonic current command 1ifHB''iLi to generate voltage commands v. to .mo. 353 is a main circuit section, and an example of the circuit is shown in FIG.

The main circuit section 353 generates output voltages vU□ to − specified by voltage commands VMH to ■h. In the main circuit section of FIG. 8, 362 is a DC power supply, 363 is a three-phase inverter composed of gate turn-off thyristors, etc., and 360 is a gate control circuit for the three-phase inverter 363. The voltage commands Vi) I to I described in FIG. 7 are input, and corresponding output voltages VUH to VWH are generated on the lines 354U to 354W. Current generator 350 configured in this way
(@Figure 7), harmonic current command jt5m −
ij; Compensation current iuo to two indicated by HB is
It can be poured into points 352U to 352W in the figure.

The above configuration shown in FIG. 3 operates as follows. That is, the third
In the figure, the current of the cycloconverter 10 (current containing harmonics) is detected by the first current detectors 301U to 301W (iuL to IWL), and it is detected by the harmonic detection circuit in the current command device 300 of FIG. 304, where a first harmonic signal 1'u)i""'1'WH corresponding to the harmonic component of the current generated by the cycloconverter IO is obtained, and the phase of this signal is inverted by an inverter 306. A second harmonic signal +1 to iwu is obtained. Second harmonic signal tuH
-iw) I passes through the limiter 310 and harmonic current command 1
8□~tea is obtained. Here, the harmonic current command i[delta]~I is a signal whose phase is exactly 180[deg.] inverted from the harmonic component of the current of the cycloconverter 10. The harmonic current command igm~ and 1LtB are the current generator 3 in Fig. 7.
50 becomes the current command, and 1! The flow generator 350 is (8,
A compensation current 1110-t, . . At this time, the compensation current box. ~The phase relationship between iWo and the harmonic components of the current of the cycloconverter 10 is exactly 18
Since they are inverted by 0°, they are therefore points 352υ~3
The harmonic currents are combined and cancel each other out at the five points, and as a result, the harmonic currents no longer flow toward the AC power supply system 1.

The above is the operation of the actively acting harmonic current compensator shown in FIG. 3, but the device with this configuration has the following problems.

That is, although the current generator 350 shown in FIG. 3 is constructed using a power converter such as the three-phase inverter shown in FIG.
Therefore, the limiter 3 is included in the current command device 300 shown in FIG.
10 is provided to limit the maximum current of the current generator 350.

From this, for example, when the harmonic current component of the cycloconverter lO is small, the limiter 310 in FIG. 4 does not substantially operate, and as a result, the limiter 3100 inputs as shown in FIG. Signal 1Ul (~- and output signal iim
~ I-8 in terms of waveform and linearity is maintained), therefore, the compensation current box is necessary to compensate for the harmonic current components of Nylon Conher 910 (7). ~iwo (Figure 1) is generated normally and there is no problem.

However, when the harmonic components generated by the cycloconverter 10 increase, the limiter 310 in the current command device 300 in FIG. 4 operates, and the current generated by the current generator 350 (FIG. 3) decreases. will be restricted.

The input signal i of the limiter 310 at this time. H-iWH and output signal! The relationship between δ path and I path is as shown in FIG. 6(b).

That is, signals iUH to iWH and signal 18HR" I:HB
The linearity between them will no longer be maintained. In this state, the harmonic current compensator (9) in FIG.
Compensation current iυ indicated by R-uR. ~iwo will be generated, which means that the cycloconverter 10
This means that the harmonic compensator 30 newly generates harmonics with a frequency completely different from the harmonic components generated by the harmonic component, and injects them into the AC power system, which is very dangerous and problematic in terms of compensation operation.

As is clear from the above explanation, when applying a harmonic current compensator, such a problem, that is, a situation where the compensator becomes a new harmonic generation source, must never occur. Therefore, in order to expand the range of application of harmonic current compensators, there is a strong need to solve this problem.

[Purpose of the invention]

The present invention has been made in view of the problems of the prior art described above.
The purpose of this is to install an improved type of harmonic current compensator in a device that compensates for harmonic current generated by a load such as a cycloconverter, which can eliminate control nonlinearity caused by the current limiting function. A current limiting circuit is provided, which suppresses the harmonic current compensator from generating unintended harmonic currents due to control nonlinearity over the entire operating range of the harmonic current compensator, making it possible to apply it with high performance. The object of the present invention is to provide a harmonic current compensator with a wide range.

[Summary of the invention]

In order to achieve the above object, the present invention provides a device for compensating harmonic current in an AC power system, which includes: means for detecting current in the AC power system; means for extracting harmonic components from the detected current signal; It comprises means for limiting the amplitude of the detected harmonic component signal, and a current generating section that operates using the output signal of the limiting means as a command value, generates a compensation current based on the command value, and supplies the current to the power supply system. , a harmonic current compensator configured to compensate harmonic components of the current flowing in the AC power system with the compensation current, and its operation is such that while the harmonic current in the AC power system is small, the detected The harmonic component signal passes through the amplitude limiting means without any influence, and a compensation current is generated based on it, and the harmonic current of the AC power supply system is within the range of the current that can be generated by the current generating section. When the harmonic component signal becomes larger than , the detected harmonic component signal is affected by the amplitude limiting means. The amplitude of the output signal is limited so that a proportional relationship (or similarity relationship) is always maintained, and a compensation current is generated based on the limited output signal. Regardless, the harmonic current compensator is controlled to maintain linearity, and as a result, the harmonic current compensator is prevented from generating unintended harmonic current.

[Embodiments of the invention]

An embodiment of the harmonic current compensation device of the present invention is shown in FIGS. 3 and 7.
This will be explained with reference to FIGS. 1 and 2. The present invention relates to an improvement of a conventional harmonic current compensator, and the harmonic current compensator according to the present invention and the conventional device have some overlapping structural requirements. The drawings used in the installation of the prior art will be used for components having substantially the same configuration and function, and detailed description thereof will be omitted.

In FIG. 3, a harmonic/sleep current compensator 30 according to the present invention is installed on an AC bus connecting an AC power supply system 1 and a load 10 such as a cycloconverter that generates harmonic current. In the harmonic current compensator 30, the first current detector 301U~
Cycloconverter 10 containing harmonic components at 301W
detects the current and outputs it to the lines 302U to 302W as the lth detection signals lto and NiwL. 300A is an improved current command device and harmonic current command 1i5Ha to ijinHR
is output to lines 311U to 311W. 350 is the current corresponding to the supplementary current 1uo" iwo the line 357U~
357W is generated and acts to flow to the AC bus bar.

The harmonic current compensator 30 consisting of these elements acts actively, that is, the harmonic current generated by the cycloconverter 10 and the current having a phase difference of 180 degrees and the same amplitude are compensated for by a compensation current 100 to iWo. As line 357U~357
Therefore, these currents are generated at point 352U
~35 bis, they are combined and cancel each other out, and as a result, it is possible to prevent harmonic currents from flowing toward the AC power supply system 1.

Next, details of the improved current command device 300A according to the present invention will be explained using FIGS. 1 and 2. Note that the current command device 300A according to the present invention (FIG. 1) and the conventional current command device 300 (FIG. 4) having the same symbol have the same function.

In the current command device 300A in Fig. 1, the line 302U~
302W is connected to the power station with the same symbol in FIG.
A first harmonic signal i'un-i'uw corresponding to the harmonic current component generated by 0 is obtained. 1st harmonic signal i'U
H"I'WM is the second harmonic signal IU which is introduced into the inverter 306 and whose phase is inverted by 1800 with respect to the original signal.
H~IWH is obtained. A maximum current setting device 308 sets the maximum current value that can be generated by the current generator 350 (FIG. 3), and outputs a maximum value command 18. 320 is a comparator that compares the maximum value command I profit and the second harmonic signal lυHivni
322U to 322W are multipliers that multiply the second harmonic signals iυ8 to 5 by the limiting coefficient signal KU-w Kw,
The result is output as a harmonic current command i~l:HR. Note that here, the comparator 320 and the multipliers 322U to 3
The combination of 22W and 22W is tentatively called a linear limiter 330, which operates as follows. That is, in FIG.
The second harmonic signal 1oH-iw is the maximum value command I; in a smaller range, the output of the comparator 320, that is, the limiting coefficient signal Ko
= The value of Kw becomes 1, so the second harmonic signal 1
trn~i□ is multiplier 322U without changing its size.
It appears in the output of ~322W and the harmonic current command 1uI (R
= iwax. The situation at this time is shown in FIG. 2(a). Next, the second harmonic signal IUH' in FIG.
If there is a part of the waveform of IWH that is larger than the maximum value command I8, the comparator 320 detects this state and decreases the output limiting coefficient signal Kt, ~, and does so (the multiplier 322U ~ Harmonic current command 1 of 322W output
Make sure that the waveforms from iHR to iYoke5 do not exceed the maximum value command H. In other words, the situation at this time is shown in FIG. 2 (b) IIJ. Since there is a part of the waveform of the input second harmonic signal 1UH=1vn (which is larger than the maximum value command B), the limiting coefficient signal K
The amplitude of the harmonic current command i, ~ iLg, which is the result of the multiplication of the second harmonic signal I. The value is controlled to match the maximum value command Is.What should be noted here is that the second harmonic signal i
A proportional relationship is always established between UH"""IWH and the harmonic current commands 1Rua to iLa, and the proportionality coefficient is υ to Kw with respect to the aforementioned limiting coefficient.

The harmonic current component F, which is the output of the linear limiter 330 obtained in this way, is calculated by the current generator 350 of the next stage.
(Figure 7).

FIG. 7 is a detail of the current generator 350 of FIG.

In FIG. 7, 351U to 351W are comparators, and 353 is a main circuit section, an example of which is shown in FIG.

353U to 355w are second current detectors. These operations are as described in the description of the prior art described above, and they operate in response to the output signal of the current command device 300A shown in FIG. ~
Compensated flow directed by 5th. ~iwo is generated and poured into points 352U to 352W in FIG.

The harmonic current compensator of the present invention configured as described above operates as follows. That is, in FIG. 3, the current of the cycloconverter 10 (current containing harmonics) is detected by the first current detectors 301U to 301W (iuh to 'WL
), the harmonic detection circuit 304 in the current command device 300A in FIG.
on ” i 'W)l is obtained, and the phase of the signal is inverted by the inverter 306 to produce a second harmonic signal IUH~iw)I
is obtained. The second harmonic signal ioH-iwH is processed by the linear limiter 330 and becomes the harmonic current command jaHR-iw.
na is obtained. Here, harmonic current command i: HB −
i6m is a signal whose phase is exactly 1800 inverted from the harmonic component of the current of the cycloconverter 10, and this 1
3g1s ~ Compensation current 1oo indicated by mu1. is generated by current generator 350, which is at point 352U in FIG.
~352W is poured. At this time, the compensation current iuo
= iwo and 1 (Since the harmonic components of the current of the chromatographic converter 10 are out of phase by exactly 180 degrees, they are combined at points 352U to 352W, cancel each other out, and the result is , harmonic current will no longer flow toward the AC power system.

This is the general operation of the harmonic current compensator according to the present invention. Next, detailed operation of the linear limiter 330 shown in FIG. 1, which is the main part of the invention, will be described.

First, the harmonic current component generated by a load such as a cycloconverter is detected as the second harmonic signal 1trH~iwH in Fig. 1, but this second harmonic signal IuH"iwo If it is small, the output signal KU-K, (limiting coefficient signal) of the comparator 320 becomes 1, so the second harmonic signal iuL-iwI and the harmonic current command I
Lta~1, etc. are completely equal (operation waveform 2nd (a
), control nonlinearity does not enter this part.

Next, if the harmonic current generated by a load such as a cycloconverter increases, and as a result, the waveform of the second harmonic signal - iWH in Figure 1 becomes larger than the maximum value command, the comparator 320 detects this state and reduces -Kw to the control coefficient signal, thereby limiting the waveform of the harmonic current command jaHR-iLi so that it does not exceed the maximum value command I; 2nd harmonic signal 1
0□~IWH and harmonic current command 1ffHR” I:ui
The similarity (or linearity) of the waveform between .

From the above explanation, in the harmonic current compensator according to the present invention, for example, if the harmonic current of the AC power supply system is within a range smaller than the maximum current capacity of the compensator, it is natural that the compensation control includes nonlinear control. There is no sexual intrusion, and in addition,
Even if the harmonic current of the AC power supply system becomes larger than the maximum current capacity of the compensator and the compensator is operated while operating the current limiting function, control nonlinearity should not be introduced into the compensation control. I can see that it has been improved.

′ As explained earlier, in conventional harmonic current compensators, when the harmonic current in the AC power system increases, nonlinearity of control enters into the compensation control due to its configuration, and as a result, harmonics in the AC power system increase. The compensating device itself generates harmonic components that are completely unrelated to the wave current and injects them into the AC power supply system, which has caused problems, but with the harmonic current compensating device of the present invention, such a situation does not occur. That is, in the harmonic current compensator of the present invention, control nonlinearity is introduced into the compensation control regardless of the magnitude of the harmonic current to be compensated.
Therefore, it is clear that no unintended harmonics are generated.

The above are the functions of the harmonic current compensator according to the present invention. Therefore, the harmonic current compensator according to the present invention can stably and efficiently compensate for the harmonic current that changes in a complicated manner generated by a cycloconverter or the like. can be understood.

〔Effect of the invention〕

As is clear from the above explanation, Fig. 3, Fig. 1, Fig. 7
The harmonic current compensator of the present invention configured as shown in the figure provides the following effects. That is, (1) Even if the operating conditions of a load that generates harmonics such as a cycloconverter change and the harmonic current it generates becomes larger than the maximum current that can be generated by the harmonic current compensator, harmonics The circuit is configured so that nonlinearity does not enter into the current compensation effect, so that the harmonic current compensator itself does not generate abnormal harmonics that are not intended under any operating conditions. This eliminates restrictions when applying the harmonic current compensator to an AC power supply system.

(2) Also, in relation to item (1) above, even if the harmonic current in the AC power supply system becomes excessive, the harmonic current compensator can continue harmonic current compensation while performing current limiting operation. Therefore, there is no possibility that the compensating device will be overloaded and the device will be damaged.

(3) Since the harmonic current compensator of the present invention acts actively, it is therefore different from conventional passive filters in that it generates harmonic currents in loads such as cycloconverters where the frequency of the generated flat waves constantly fluctuates. effective in compensating for

As described above, the harmonic current/compensation device based on the present invention has fewer restrictions when applied to an AC power supply system, and moreover, can efficiently perform harmonic current compensation function against harmonic currents that change in a complex manner. It is clear that the
Therefore, by placing the harmonic current compensator according to the present invention in an AC power supply system, a power supply system with less harmonic current and less voltage distortion can be realized.

[Brief explanation of drawings]

FIG. 1 is a diagram showing a specific example of the current command device 300A in FIG. 3 for realizing the present invention, FIG. 2 is an explanatory diagram of the operation of FIG. 1, and FIG. 3 is a diagram showing a harmonic current compensator. Figure 4 is a diagram showing a current command device used in a harmonic current compensator according to the prior art, Figures 5 and 6 are explanatory diagrams of the operation of Figure 4, and Figure 7 is in Figure 3. A diagram showing a specific example of a current generator 350,
The eighth factor is a diagram showing a specific example of the main circuit section 353 in FIG. 1... AC power supply system 3U to 3W... System impedance 10... Cycloconverter 30... Harmonic current compensator 301U to 301W... First current detector 300...
Conventional current command device 300A...Improved current command device of the invention 304...Harmonic detector 306...Inverter 308...Maximum current setter 301...Limiter 350...Current generation 351t)-351W...Comparator 353...Main circuit section 355U-355W...@2 current detector 363
... Three-phase inverter 330 ... Linear regulator 32
0... Comparator 322U-322W... Multiplier (7317) Agent Patent attorney Yu Chika (and 1 others)
Name) Figure 1 Figure 2 Co-) t! I) Figure 4 Figure 5 Figure 6

Claims (1)

[Claims] A harmonic current compensator connected to an AC power system through which harmonic current flows and for compensating the harmonic current, the harmonic current compensator includes means for detecting current in the AC power system, and detecting harmonic components from the detected current signal. means for extracting the detected harmonic component signal, means for limiting the amplitude of the detected harmonic component signal when it becomes excessive, and operating with the output signal of the limiting means as a command value to generate a compensation current based on the command value. a current generator that causes the current to flow through the AC power supply system, and the amplitude limiting means for the harmonic component signal limits the amplitude so that a proportional relationship is maintained between the input signal to the limiting means and the output signal. A harmonic current compensator characterized by: