JP2019103234A - Dc active filter and converter - Google Patents

Abstract

To provide a direct current active filter that can miniaturize a transformer and can reduce vibration and noise generated in the transformer, and a converter including the same.SOLUTION: A DC active filter 1 according to an embodiment includes a current detection device 3 provided in an electric path 2, an arithmetic device 5 obtaining a current flowing through the electric path 2 by taking the output of the current detection device 3, a converter 4 connected in parallel to the electric path 2 and outputting a DC current to the electric path 2, a control device 6 outputting a control signal to the converter 4 on the basis of the calculation result of calculation device 5. The arithmetic device 5 calculates the magnitude of the direct current component included in the current flowing through the electric path 2, and the control unit 6 controls the converter 4 to output a direct current having the same magnitude as the calculated direct current component and having an opposite sign.SELECTED DRAWING: Figure 1

Description

  Embodiments of the present invention relate to a direct current active filter that reduces a direct current component flowing in an electrical path, and a converter including the same.

  Conventionally, in a transformer connected to a conversion device such as a voltage type inverter, a core with a gap may be used in order to suppress DC bias magnetism due to the flow of DC (see, for example, Patent Document 1). .

JP, 2008-289267, A

  However, providing a gap in the iron core complicates the iron core structure and can not obtain a large iron core magnetic flux density, which causes a problem of increasing the size of the transformer. In the case of a core with a gap, there is also a problem that vibration and noise during operation increase.

  Therefore, a DC active filter capable of miniaturizing a transformer and reducing vibration and noise generated in the transformer, and a converter including the same are provided.

The DC active filter according to the embodiment is connected in parallel with the current path, a current detection device provided in the electrical path, an arithmetic device for obtaining the current flowing in the electrical path by capturing the output of the current detection device, and outputting DC current to the electrical path And a control device that outputs a control signal to the converter based on the calculation result of the calculation device, the calculation device calculates the magnitude of the DC component included in the current flowing through the electric path, and the control device The converter is controlled to output a DC current which is the same as the calculated DC component size and opposite in sign.
Moreover, the converter of embodiment is provided with the above-mentioned DC active filter.

The figure which shows typically the electric constitution of the direct current | flow active filter by embodiment, and the converter. Diagram schematically showing the filter effect by the DC active filter Diagram to explain the principle of operation of a DC active filter A diagram schematically showing an electrical configuration of a current detection circuit Diagram schematically showing the electrical configuration of the converter

Hereinafter, embodiments will be described with reference to the drawings.
As shown in FIG. 1, the DC active filter 1 of the present embodiment includes a current detection device 3 provided in the electric path 2, a converter 4 connected in parallel with the electric path 2 and outputting DC current to the electric path 2, The arithmetic device 5 obtains an electric current flowing in the electric path 2 by taking the output of the current detection device 3, and the control device 6 outputs a control signal to the converter 4 based on the arithmetic result.

  The DC active filter 1 is disposed between the inverter 7 and the transformer 8, more specifically, on the output side of the inverter 7 and on the front side of the transformer 8. The inverter 7 adopts, for example, a known configuration in which IGBTs are bridge-connected and PWM-controlled by a control unit (not shown). The DC active filter 1 and the inverter 7 constitute a power converter that converts DC to AC in the converter 9 here, and supplies power to the load 10 connected to the secondary side of the transformer 8 .

  Here, the current output from the inverter 7 will be described. As shown in FIG. 2, the output current (Ii) of the inverter 7 may include not only an AC component but also a DC component, that is, a DC current (Ioff). Then, when this direct current (Ioff) flows through the transformer 8, a biased magnetization in which a direct current component is superimposed on the magnetic flux density of the iron core is caused, and magnetic saturation occurs in the iron core of the transformer 8, causing vibration and noise. It becomes.

  Therefore, in the present embodiment, the direct current (Ic) from the converter 4, more strictly, the direct current having the same magnitude as the direct current component (Ioff) included in the output current (Ii) of the inverter 7 and the direction being reverse By outputting the current (Ic) to the electric path 2, the direct current does not flow to the transformer 8 or the load 10 side. The specific method will be described below.

First, the operation principle of the DC active filter 1 will be described with reference to FIG. As shown in FIG. 3, when the AC power supply 11 and the DC power supply 12 exist in the power path 2, as shown in the following equation (1), the AC current (Iac) from the AC power source 11 is present in the power path 2. And a DC current (Idc) from the DC power supply 12 is added to flow a current (Ix).
Ix = Iac + Idc (1)

At this time, assuming that the voltage of the AC power supply 11 is Eac and the impedance of the load 10 is Z, the alternating current (Iac) can be obtained as in the following equation (2).
Iac = Eac / Z (2)

Further, the direct current (Idc) can be obtained as in the following equation (3), assuming that the voltage of the direct current power supply 12 is Edc and the resistance of the load 10 is R.
Idc = Edc / R (3)

At this time, assuming that the direct current source 13 is controlled to output the current having the same magnitude and the opposite direction as the magnitude of the direct current (Idc) determined by the current detection device 3, the direct current source The relationship between the output current (Iα) from 13 and the direct current (Idc) is expressed by the following equation (4).
Iα = −Idc (4)

Further, since the current (Iy) flowing to the load 10 side is the sum of the current (Ix) flowing through the electric path 2 and the output current (Iα) of the DC current source 13, the table (5) below Be done.
Iy = Ix + Iα (5)

Then, when the above equations (1) and (4) are substituted into the equation (5), as shown in the following equation (6), the load 10 side does not contain a DC component, that is, It turns out that you can assistant professor DC component.
Iy = (Iac + Idc) + (− Idc) = Iac (6)

  Now, as shown in FIG. 4, the current detection device 3 of the present embodiment is configured by an optical CT (Current Transformer) that uses the optical fiber 20 as a sensor. More specifically, the current detection device 3 is provided in the electric path 2 and has the optical fiber 20 on each of the electromagnetic CT 21 (Current Transformer) with the secondary side closed and the electric path 2 and the secondary side of the electromagnetic CT 21. It is comprised by optical CT of the state wound in series.

  The light CT includes an arithmetic unit 5, an optical fiber 20, and a mirror 22 provided at an end of the optical fiber 20. In the present embodiment, the arithmetic unit 5 is provided integrally with the control unit 6 for controlling the converter 4, and the arithmetic unit 5 and the control unit 6 are realized by a single microcomputer. .

  In light CT, the light emitted from the light source 23 propagates through the half mirror 24 in the optical fiber 20 in the direction indicated by the broken arrow as Tx, and the mirror 22 provided at the end of the optical fiber 20 As a result of the reflection of light, the light propagates in the direction shown by the broken arrow with the inside of the optical fiber 20 as Rx and returns to the control device 6.

  Now, the principle of detection of current by optical CT is well known, and thus detailed description will be omitted. However, when the optical fiber 20 is wound around the electric path 2, light propagating in the optical fiber 20 is a magnetic field generated around the electric path 2. The plane of polarization rotates along. At this time, the Faraday rotation angle, which is the rotation angle of the polarization plane, is proportional to the product of the number of turns of the optical fiber 20 and the strength of the magnetic field, that is, the magnitude of the current flowing through the electric path 2. Further, since the rotation direction in which the polarization plane rotates is dependent on the winding direction in which the optical fiber 20 winds the electric path 2, if the winding direction is reversed, the rotation direction is also reversed. Therefore, the magnitude and direction of the current can be computed by the computing device 5.

  Specifically, the light returned to the control device 6 is reflected by the half mirror 24 and then converted into an electrical signal in the photoelectric conversion unit 25 and subjected to filter processing and the like in the signal processing unit 26, and then the calculation is performed. It is calculated by the device 5. Then, as described above, since the rotation of the polarization plane is determined by the magnitude and direction of the current flowing through the electric path 2, the magnitude and the direction of the current flowing through the electric path 2 can be determined by calculation based on the rotation angle of the polarization plane. it can. This is the detection principle by optical CT.

Arithmetic unit 5 detects the DC component contained in the current (I1 = Iac + Idc) flowing through electrical path 2, that is, the magnitude and direction of DC current (Idc). In the current detection device 3, the electromagnetic CT 21 in which the number of turns on the electric path 2 is N1 and the number of turns on the secondary side is N2 is provided in series in the electric path 2. In this case, the current (I2) flowing through the secondary side is expressed by the following equation (7).
I2 = (N2 / N1) · I1 (7)

  The optical fiber 20 is wound on the electric path 2 at a position (Fa) on the electric path 2 side, and at a position (Fb) on the secondary side of the electromagnetic CT 21, a path on the secondary side of the electromagnetic CT 21 It is wound around 21a.

  More specifically, in the position (Fa), the optical fiber 20 rotates in the clockwise (CW) winding direction as viewed from the right side with respect to the direction of the current (I1) flowing through the electric path 2 , And the number of turns is n1. The optical fiber 20 also has a winding direction in the counterclockwise direction (CCW) when viewed from the right side with respect to the direction of the current (I2) flowing to the secondary side of the electromagnetic CT 21 at the position (Fb) And the number of turns is n2.

In this case, the output (Pa) of the light CT at the position (Fa) is obtained as in the following equation (8).
Pa = n1 · I1 = n1 · (Iac + Idc) (8)

Further, the output (Pb) of the light CT at the position (Fb) is calculated as in the following equation (9). In addition, since electromagnetic type CT21 does not pass a direct current, the electric current (I2) which flows to a secondary side becomes the magnitude | size resulting from alternating current (Iac). In other words, by winding the optical fiber 20 at the position (Fb), it is possible to obtain the output (Pb) caused by only the alternating current (Iac) of the current (I1) flowing through the electric path 2.
Pb =-n2 · I2 =-n2 · (N2 / N1) · Iac (9)

At this time, the total output (Pa + Pb) of the optical fiber 20 can be expressed as the following equation (10) based on the equations (7) to (9).
Pa + Pb = n1 · (Iac + Idc) + (− n2 · (N2 / N1) · Iac)
= N1 · Idc + (n1-n2 · (N2 / N1)) · Iac (10)

In the equation (10), n 1, n 2, N 1 and N 2 are the number of turns of the optical fiber 20 and the number of turns of the electromagnetic CT 21, which are mechanically determined values. Can be expressed as
K = n1-n2 (N2 / N1) (11)

When the constant (K) is 0, that is, when n1, n2, N1, and N2 satisfy the relationship of the following equation (12), the equation (10) becomes as the following equation (13) It can be represented only by direct current (Idc).
(N1 / n2) = (N2 / N1) (12)
Pa + Pb = n1 · Idc (13)

  Depending on the specifications of the electromagnetic CT 21, the constant (K) may be substantially zero although it may be assumed that the relationship of the equation (12) is not necessarily satisfied, that is, the number of turns of the optical fiber 20 on the electric path 2 side If the ratio between n1) and the number of turns on the secondary side (n2) matches the turns ratio (N2 / N1) of the windings of the electromagnetic CT 21 within a predetermined range, the total output (Pa + Pb) Can be approximated as in equation (13). The predetermined range can be appropriately set, for example, several percent.

  At this time, as described above, n1 is a value that is determined mechanically, so the DC current (Idc) can be obtained by calculation from this equation (13). At this time, the direction of the direct current (Idc) flowing through the electric path 2, that is, the sign of the direct current (Idc) can also be determined from the rotation direction of the Faraday rotation angle. Further, the overall output (Pa + Pb) can be determined more accurately by performing the FFT process in the signal processing unit 26 in consideration of the conversion error in the photoelectric conversion unit 25 and the like.

  Then, if the magnitude and the sign of the direct current (Idc) included in the current (I1) flowing in the electric path 2 are determined, the converter 4 outputs a direct current (Ic) having the same magnitude and opposite sign. The direct current (Idc) included in the current (I1) flowing through the electrical path 2 can be canceled. That is, direct current can be prevented from flowing in the transformer 8.

  In the present embodiment, as shown in FIG. 5, the converter 4 is provided with two groups of rectifier circuits 30 having different direct current output directions. Each rectifier circuit 30 has a configuration in which a series circuit in which two thyristors 31 are connected in series is connected in parallel, and outputs a direct current controlled by the control device 6. Power is supplied from a power supply transformer 32 connected in parallel to the electric path 2 to a connection point where the thyristors 31 of the series circuits are connected to each other. In the present embodiment, the rectifier circuit 30 on the left side in the figure outputs a positive direct current, and the rectifier circuit 30 on the right side in the figure outputs a negative direct current.

  The two groups of rectifier circuits 30 are always driven in the present embodiment, and the control device 6 adjusts the magnitudes of the DC currents output from the respective rectifier circuits 30 so that The direct current (Ic) that is the difference is output to the cable 2 via the smoothing reactor 33. Although one smoothing reactor 33 is shown in the present embodiment, each rectifying circuit 30 may be configured to be provided with the smoothing reactor 33.

  As described above, in the present embodiment, the DC active current is supplied to the transformer 8 by providing the DC active filter 1 on the output side of the inverter 7 and on the front side of the transformer 8, that is, the electric path 2 input to the transformer 8. To prevent the flow.

According to the embodiment described above, the following effects can be obtained.
The DC active filter 1 according to the embodiment is connected in parallel to the current path 2 with the current detection device 3 provided in the current path 2, the operation device 5 for obtaining the current flowing in the current path 2 by taking the output of the current detection device 3 2 includes a converter 4 for outputting a direct current to 2 and a control device 6 for outputting a control signal to the converter 4 based on the calculation result of the calculation device 5. The controller 6 calculates the magnitude of the DC component to be output, and the control device 6 controls the converter 4 to output a DC current which is the same as the magnitude of the calculated DC component but opposite in sign.

  If a gap is provided in the iron core in order to suppress the biased magnetization generated in the transformer 8, the iron core structure becomes complicated and the iron core magnetic flux density can not be made large, so there is a problem that the transformer 8 becomes large. In the case of a core with a gap, there is also a problem that vibration and noise during operation increase.

On the other hand, the DC active filter 1 of the present embodiment is provided on the output side of the inverter 7 and on the front side of the transformer 8. This prevents the direct current from flowing through the transformer 8 and suppresses the occurrence of biased magnetism, so that special measures such as adopting a core with a gap are not necessary.
Therefore, the transformer 8 can be miniaturized, and vibrations and noise generated in the transformer 8 can be reduced.

  Further, unlike the conventional case, for the side of manufacturing the transformer 8, it becomes possible to easily design the iron core on the premise that no direct current is supplied. On the other hand, for the side that manufactures conversion device 9, as in the prior art, the pulse width etc. at the time of PWM control of inverter 7 is controlled based on the current detection state etc. on the primary side and secondary side of transformer 8 The design, in other words, the design which has to take into account the characteristics inherent to the transformer 8 is not necessary. In addition, adjustment after combining the transformer 8 and the conversion device 9 can be unnecessary or greatly simplified.

  Thus, by removing the DC current from the output of the inverter 7 by the DC active filter 1, in other words, the DC active filter 1 made on the basis of the technical idea of preventing the DC current from flowing in the transformer 8. By adopting this, it is possible to greatly improve manufacturability and workability both on the side of manufacturing the transformer 8 and on the side of manufacturing the conversion device 9. Of course, the performance can also be improved since the biased magnetization can be suppressed.

  The converter 4 includes two groups of rectifier circuits 30, and is configured to be able to output positive and negative direct currents whose directions are opposite to each other to the electric path 2. Thereby, the direct current can be appropriately removed for the inverter 7 in which the direction of the direct current to be superimposed changes.

  The two groups of rectifier circuits 30 are always driven, and output a difference between them to output positive and negative DC currents to the circuit 2. As a result, even when the direction of the output current changes frequently, for example, when driving a motor, the required output of converter 4 can be obtained quickly.

  The current detection device 3 is configured by an optical CT (Current Transformer) that uses the optical fiber 20 as a sensor. By this, it is possible to accurately detect a slight direct current (Idc) superimposed on the alternating current (Iac) outputted from the inverter 7 which is hard to receive external noise and may be several hundreds to several thousands of amperes. Can. Moreover, since it is sufficient to wind the optical fiber 20 around the electric path 2, the installation can be easily performed, the workability and manufacturability can be improved, and the required installation space is small. There is no hindrance to miniaturization.

  The current detection device 3 is provided in the electric path 2 and uses the electromagnetic CT 21 (Current Transformer) with the secondary side closed, and the optical fiber 20 as a sensor, and the optical path 2 and the secondary side of the electromagnetic CT 21 are respectively optical fibers The optical fiber 20 has a winding direction with respect to the direction of the current flowing through the electric path 2 and a direction of the current flowing to the secondary side of the electromagnetic CT 21. And the ratio of the number of turns (n1) on the electric path 2 side of the optical fiber 20 to the number of turns (n2) on the secondary side is opposite to that of the winding of the electromagnetic CT21. It is provided to match the turns ratio (N2 / N1) within a predetermined range.

  The electromagnetic CT 21 does not transmit a DC component to the secondary side, so by detecting the current on each of the primary side and the secondary side of the electromagnetic CT 21, the electric path 2 is detected from the magnitude of the current detected on the secondary side. The alternating current flowing to the current path can be obtained, whereby the direct current flowing to the electric path 2, that is, the direct current to be output from the converter 4 can be obtained. Therefore, the direct current flowing in the electric path 2 can be canceled.

  Further, since the electromagnetic CT 21 has a relatively large number of turns of the conductor, the ratio (n1 / n2) of the number of turns of the optical fiber 20 can not be completely matched with the turn ratio (N2 / N1) of the electromagnetic CT 21 Although there is a case, by matching in a predetermined range, it is possible to detect a direct current without excessively reducing the detection accuracy.

  The converter 9 comprises a DC active filter 1. As a result, unlike the conventional case, for the side that manufactures the transformer 8, the design based on the assumption that direct current is not supplied can be performed, so the core design can be easily performed.

  Although the control device 6 is shown alone in the embodiment, the arithmetic device 5 and the control device 6 can be configured by a control unit that performs PWM control of the inverter 7. Further, in order to ensure the detection accuracy of the light CT, the light CT may be provided with a dedicated arithmetic device 5 and control of the converter 4 may be performed from the control unit for the inverter 7.

  While certain embodiments of the present invention have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and the gist of the invention, and are included in the invention described in the claims and the equivalent scope thereof.

  In the drawing, 1 is a DC active filter, 2 is an electric path, 3 is a current detecting device (optical CT), 4 is a converter, 5 is a computing device, 6 is a control device, 7 is an inverter, 8 is a transformer, 9 is a converting device Reference numeral 20 denotes an optical fiber, 21 denotes an electromagnetic CT, and 30 denotes a rectifier circuit.

Claims (6)

A current detection device provided in the electrical path,
An arithmetic unit for obtaining the current flowing in the electric path by taking the output of the current detection device;
A converter connected in parallel with the power path and outputting a DC current to the power path;
A control device that outputs a control signal to the converter based on the calculation result of the calculation device;
Equipped with
The arithmetic unit calculates the magnitude of the DC component included in the current flowing in the electric path,
The control apparatus controls the converter so as to output a direct current having the same magnitude as that of the calculated direct current component and the opposite sign.   2. The DC active filter according to claim 1, wherein the converter comprises two groups of rectifier circuits and is capable of outputting positive and negative DC currents whose directions are opposite to each other to an electric path.   The DC active device according to claim 2, wherein the two groups of the rectifier circuits are driven at all times and controlled to output positive and negative DC currents to the electric path by outputting the difference. filter.   The direct current active filter according to any one of claims 1 to 3, wherein the current detection device is configured by an optical CT (Current Transformer) using an optical fiber as a sensor. The current detection device is provided in an electric path and has an electromagnetic CT (Current Transformer) with a closed secondary side, an optical fiber as a sensor, and an optical fiber for each of the electric path and the secondary side of the electromagnetic CT. It is composed of optical CT (Current Transformer) wound in series,
The optical fiber has an electric path side of the optical fiber such that the winding direction with respect to the direction of the current flowing through the electric path and the winding direction with respect to the direction of the current flowing to the secondary side of the electromagnetic CT are opposite. The ratio between the number of turns of the coil and the number of turns on the secondary side is set to coincide with the turns ratio of the winding of the electromagnetic CT within a predetermined range. DC active filter according to any one of the preceding claims.   A converter comprising the DC active filter according to any one of claims 1 to 5.

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