JP2020054119A - Line filter - Google Patents

Abstract

To provide a line filter capable of suppressing flowing of a large current to each capacitor when switching the connection of a plurality of capacitors between serial connection and parallel connection in a power applying state.SOLUTION: A line filter comprises: a pair of electric power lines 2; a voltage measurement unit 6; a plurality of capacitors 3; a serial-parallel switching circuit 40 formed by a plurality of switches 4; and a control unit 5. The serial-parallel switching circuit 40 switches a connection of the plurality of capacitors 3 between parallel connection and serial connection. Each of the switches 4 is configured to be able to assume an on-state, an off-state, and a high-impedance conduction state. The control unit 5 turns on a switch 4 in the off-state after placing it in the high impedance conduction state when switching the connection of the plurality of capacitors 3.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a line filter used for electric equipment.

  2. Description of the Related Art Conventionally, a line filter used for an electric device has been known (see Patent Document 1 below). This line filter includes a pair of power lines for electrically connecting a DC power supply and an electric device, and a plurality of capacitors. Using this capacitor, noise contained in the power line is removed, and the DC power supply is stabilized. Thus, the DC power supply is stabilized while suppressing transmission of noise from the DC power supply to the electric device and from the electric device to the DC power supply.

  The line filter includes a series-parallel switching circuit that switches a connection of a plurality of capacitors between a series connection and a parallel connection (see FIGS. 35 to 37). The line filter is configured to connect a plurality of capacitors in parallel when a voltage between the pair of power lines is lower than a predetermined threshold. When the voltage exceeds the threshold, a plurality of capacitors are connected in series. This reduces the voltage applied to each capacitor. This suppresses the application of a voltage exceeding the withstand voltage to the capacitor, allows the use of a small capacitor having a low withstand voltage, and reduces the size of the line filter.

JP 2009-268324 A

However, in the line filter, when switching the connection of the plurality of capacitors between the serial connection and the parallel connection, a large current may flow. That is, for example, switching the two capacitors from parallel connection to series connection (FIG. 35, see FIG. 36), the voltage applied to each capacitor, decreases from the supply voltage V _B to V _B / 2. Therefore, a large discharge current flows from the capacitor. Therefore, it is necessary to increase the current capacity of switches, capacitors, power lines, and the like that constitute the series-parallel switching circuit, and there is a problem that the line filter becomes large.

Similarly, for example, switching the two capacitors in parallel connection connected in series (see FIG. 36, FIG. 37), the voltage applied to each capacitor rises from V _B / 2 to V _B. Therefore, a large inrush current flows through the capacitor, and it is necessary to increase the current capacity of the switch, the capacitor, and the like. Therefore, there is a problem that the line filter becomes large.

  The present invention has been made in view of such a problem, and when a connection of a plurality of capacitors is switched between a serial connection and a parallel connection, a large current caused by the voltage of each capacitor is suppressed. It is intended to provide a line filter that can be used.

One embodiment of the present invention includes a pair of power lines (2) for electrically connecting a DC power supply (7) and an electric device (8),
A voltage measuring unit (6) for measuring a voltage between the pair of power lines,
A plurality of capacitors (3) electrically connected between the pair of power lines;
A plurality of switches (4) connected in series to the individual capacitors, wherein the plurality of switches are in an on state in which a current flows and in an off state in which no current flows; A series-parallel switching circuit (40) for switching the connection of the plurality of capacitors between parallel connection and series connection by changing a combination with the switch;
A control unit (5) for controlling the operation of the switch;
Each of the switches is configured to be able to take three types of states: the on state, the off state, and a high impedance conduction state in which a current flows and the impedance is higher than the on state.
The control unit, when the measured value of the voltage by the voltage measurement unit is lower than a predetermined threshold, the plurality of capacitors are connected in parallel, when the measured value of the voltage exceeds the threshold Is a series connection of the plurality of capacitors,
The control unit, when switching the connection of the plurality of capacitors between the parallel connection and the series connection, the switch in the off state, the high impedance conduction state, and then the on state In the line filter (1).

The switch of the line filter is configured to be able to take three types of states: the on state, the off state, and the high impedance conduction state. Further, when switching the connection of the plurality of capacitors between the parallel connection and the series connection, the control unit sets the switch in an off state to a high impedance conduction state and then to an on state.
Therefore, even if a discharge current or an inrush current occurs when the connection of the capacitor is switched, a large current does not easily flow because the current flows through the switch in the high impedance conduction state. Therefore, the current capacity of switches, capacitors, power lines, and the like can be reduced, and the reliability can be improved while reducing the size of these components. Therefore, the entire line filter can be reduced in size and reliability can be improved.

As described above, according to the above aspect, it is possible to provide a line filter that can suppress a large current from flowing through each capacitor when the connection of a plurality of capacitors is switched between series connection and parallel connection. .
Note that reference numerals in parentheses described in the claims and means for solving the problems indicate the correspondence with specific means described in the embodiments described below, and limit the technical scope of the present invention. Not something.

FIG. 2 is a circuit diagram of a line filter according to the first embodiment in which a plurality of capacitors are connected in parallel. FIG. 2 is a circuit diagram in which the positive side parallel switch is switched to a high impedance conduction state from FIG. 1. FIG. 3 is a circuit diagram in which the negative side parallel switch is switched to a high impedance conduction state from FIG. 2. FIG. 4 is a circuit diagram in which a positive side parallel switch is switched to an off state from FIG. 3. FIG. 5 is a circuit diagram in which the negative side parallel switch is switched to the off state from FIG. 4. FIG. 6 is a circuit diagram in which the series switch is switched to a high impedance conduction state from FIG. 5. FIG. 7 is a circuit diagram in which a series switch is switched to an ON state from FIG. 6, and is a circuit diagram of a line filter in a state where a plurality of capacitors are connected in series. FIG. 8 is a circuit diagram in which the series switch is switched to a high impedance conduction state from FIG. 7. FIG. 9 is a circuit diagram in which the series switch is turned off from FIG. 8. FIG. 10 is a circuit diagram in which the negative side parallel switch is switched to a high impedance conduction state from FIG. 9. FIG. 11 is a circuit diagram in which the positive side parallel switch is switched to a high impedance conduction state from FIG. 10. FIG. 12 is a circuit diagram in which the negative side parallel switch is turned on from FIG. 11. FIG. 9 is a circuit diagram of a line filter according to a second embodiment in which a plurality of capacitors are connected in parallel. FIG. 14 is a circuit diagram in which the positive side parallel switch is switched to a high impedance conduction state from FIG. 13. FIG. 15 is a circuit diagram in which the negative-side parallel switch is switched to a high impedance conduction state from FIG. 14. FIG. 16 is a circuit diagram in which the positive side parallel switch is turned off from FIG. 15. FIG. 17 is a circuit diagram in which the negative side parallel switch is turned off from FIG. 16. FIG. 18 is a circuit diagram in which the series switch is switched to a high impedance conduction state from FIG. 17. FIG. 19 is a circuit diagram in which a series switch is switched to an ON state from FIG. 18 and a circuit diagram of a line filter in a state where a plurality of capacitors are connected in series. FIG. 20 is a circuit diagram in which the series switch is switched to a high impedance conduction state from FIG. 19. FIG. 21 is a circuit diagram in which the series switch is turned off from FIG. 20. FIG. 22 is a circuit diagram in which the negative side parallel switch is switched to the high impedance conduction state from FIG. 21. FIG. 23 is a circuit diagram in which the positive side parallel switch is switched to a high impedance conduction state from FIG. 22. FIG. 24 is a circuit diagram in which the negative side parallel switch is switched to the ON state from FIG. 23. FIG. 9 is a circuit diagram when a simulation is performed in the second embodiment. 9 is a simulation result of the voltage V _B of the power line, the current of the capacitor, the on / off state of each switch unit, and the current of each switch unit in the second embodiment. FIG. 27 is an enlarged view of FIG. 26 at the moment of switching from parallel connection to series connection. FIG. 27 is an enlarged view of FIG. 26 at the moment of switching from series connection to parallel connection. FIG. 13 is a circuit diagram of a line filter according to the third embodiment. FIG. 13 is a circuit diagram of a line filter according to a fourth embodiment. FIG. 15 is a circuit diagram of a line filter according to the fifth embodiment. FIG. 15 is a circuit diagram of a line filter according to a sixth embodiment. FIG. 4 is a circuit diagram of a line filter in a comparative embodiment. In comparative embodiment, the voltage V _B of the power line, and on-off state of each switch unit, a simulation result of the current of each switch. FIG. 7 is a schematic circuit diagram of a line filter in which a plurality of capacitors are connected in parallel in a comparative embodiment. FIG. 36 is a schematic circuit diagram of the line filter immediately after switching a plurality of capacitors to series connection from FIG. 35. FIG. 37 is a schematic circuit diagram of the line filter immediately after switching a plurality of capacitors to parallel connection from FIG. 36.

(Embodiment 1)
An embodiment according to the line filter will be described with reference to FIGS. As shown in FIG. 1, the line filter 1 of the present embodiment includes a pair of power lines 2 (2 _P , 2 _N ), a voltage measuring unit 6, a plurality of capacitors 3 (3 _A , 3 _B ), and a series-parallel switching circuit. And a control unit 5.

  The power line 2 electrically connects the DC power supply 7 and the electric device 8. The voltage measuring unit 6 measures a voltage between the pair of power lines 2. The capacitor 3 is electrically connected between the pair of power lines 2. The capacitor 3 removes noise included in the power line 2 and stabilizes the DC power supply 7. The series / parallel switching circuit 40 includes a plurality of switches 4 connected in series to the individual capacitors 3. The series-parallel switching circuit 40 changes the combination of the switch 4 in the ON state where the current flows and the switch 4 in the OFF state where the current does not flow, among the plurality of switches 4, The connection of the capacitor 3 is switched between a parallel connection (see FIG. 1) and a series connection (see FIG. 7).

The control unit 5 controls the operation of the switch 4.
Each switch 4 has an on state (see the positive side parallel switch 4 _{P in} FIG. 1), an off state (see the series switch 4 _{S in} FIG. 1), and a high impedance conduction state (the positive side parallel switch in FIG. 2). 4 _P ). The high impedance conduction state is a state in which a current flows and the impedance is higher than the ON state.

When the measured value of the voltage by the voltage measuring unit 6 is lower than a predetermined threshold value V _TH , the control unit 5 connects the plurality of capacitors 3 in parallel (see FIG. 1). When the measured value of the voltage exceeds the threshold value V _TH , the control unit 5 connects the plurality of capacitors 3 in series (see FIG. 7).

When switching the connection of the plurality of capacitors 3 between parallel connection and series connection, the control unit 5 sets the switch 4 in the off state to a high impedance conduction state and then to the on state. are (see the series switch 4 _S in FIGS. 5 to 7).

  The line filter 1 of the present embodiment is a vehicle-mounted line filter to be mounted on a vehicle. The line filter 1 stabilizes the DC power supply 7 while suppressing transmission of noise from the DC power supply 7 to the electric device 8 and from the electric device 8 to the DC power supply 7.

As shown in FIG. 1, the power lines 2 include a positive power line 2 _P connected to the positive electrode of the DC power supply 7 and a negative power line 2 _N connected to the negative electrode (GND) of the DC power supply 7. Further, as described above, the series-parallel switching circuit 40 includes the plurality of switches 4. The switches 4 include a positive side parallel switch 4 _P , a negative side parallel switch 4 _N, and a series switch 4 _S. Positive parallel switch 4 _P is provided between the positive electrode 31 _P and the positive power line 2 _P of the first capacitor 3 _A. Negative parallel switch 4 _N is provided between the negative electrode 31 _N and the negative power line 2 _N of the second capacitor 3 _B. The series switch 4 _S is provided between the positive electrode 31 _P of the first capacitor 3 _A and the negative electrode 31 _N of the second capacitor 3 _B.

As shown in FIG. 1, a series switch 4 _S off state, when the two parallel switches 4 _P, 4 _N with positive parallel switches 4 _P and the negative side parallel switch 4 _N to the ON state, the two capacitors 3 is connected in parallel. As shown in FIG. 7, when the two parallel switches 4 _P and 4 _N are turned off and the series switch 4 _S is turned on, the two capacitors 3 are connected in series.

Further, as shown in FIG. 1, the line filter 1 is provided with a withstand voltage capacitor 11 having a higher withstand voltage than the capacitor 3. As described later, in this embodiment, since there is a moment when all the switches 4 are turned off (see FIGS. 5 and 9), a withstand voltage capacitor 11 is provided so that noise can be removed even at this moment. The withstand voltage of the withstand voltage capacitor 11 is higher than the threshold value V _TH . The withstand voltage capacitor 11 is made of a ceramic capacitor or the like. The capacitor 3 is made of a capacitor having a lower withstand voltage than the withstand voltage capacitor 11, for example, an electrolytic capacitor, and the capacitance of each electrolytic capacitor is set to be large. With this configuration, the line filter 1 is made smaller than when all the capacitors 3 are the same type of capacitor (for example, a ceramic capacitor) as the withstand voltage capacitor 11 and have the same capacitance. .

As shown in FIG. 1, an alternator 71 for charging the DC power supply 7 is connected to the DC power supply 7. When the load of the alternator 71 fluctuates rapidly, a surge voltage may be generated. In this case, the voltage V _B between the pair of power lines 2 _P and 2 _N sharply increases. Further, even if the DC power supply 7 was connected to an external power source 79 for charging (see FIG. 25), there may be a voltage V _B between a pair of power lines 2 _P, 2 _N rises sharply. As a capacitor 3, when used as a withstand voltage is high enough to sufficiently withstand the increased voltage V _B, the capacitor 3 is likely to increase in size. In Therefore this embodiment, if the voltage V _B becomes high, and switches the connection of a plurality of capacitors 3, the parallel connection (see FIG. 1) connected in series (see FIG. 7). This suppresses the application of a high voltage to the individual capacitors 3, so that the capacitors 3 having low withstand voltage and easy to be miniaturized can be used. Further, if the voltage V _B decreases, switching the capacitor 3 connected in parallel to increase the capacitance.

As shown in FIG. 1, the switch 4 of the present embodiment includes a series body 44 in which a first switch section 41 capable of on / off operation and a resistor 43 are connected in series, and a second switch section 42 connected in parallel to the series body 44. Prepare. These switch units 41 and 42 can be configured using a mechanical switch or a semiconductor switching element such as a MOSFET described later. When the second switch section 42 is turned on, the switch 4 is turned on. When the two switch units 41 and 42 are turned off, the switch 4 is turned off. When only the first switch section 41 is turned on, as in the case of the positive side parallel switch 4 _P in FIG. 2, the switch 4 enters a high impedance conducting state.

The positive side parallel switch 4 _P includes a positive side first switch section 41 _P and a positive side second switch section 42 _P as the switch sections 41 and 42. Further, the negative side parallel switch 4 _N includes a negative first switch section 41 _N and a negative second switch section 42 _N as the switch sections 41 and 42. Further, the series switch 4 _S includes, as the switch sections 41 and 42, a first switch section 41 _S for series and a second switch section 42 _S for series.

Hereinafter, as shown in FIG. 1, a plurality of capacitors 3 from a state of being connected in parallel, when a voltage V _B of the power line 2 rises, the operation of each switch 41, 42. When the voltage V _B of the power line 2 increases and exceeds the threshold value V _TH , the control unit 5 turns off the positive second switch unit 42 _P as shown in FIG. As a result, the positive side parallel switch 4 _P is brought into a high impedance conducting state.

Thereafter, the control unit 5, as shown in FIG. 3, turns off the second negative switch unit 42 _N. Thus, the negative side parallel switch 4 _N in a high-impedance conductive state. When the voltage V _B of the power line 2 to rise, but the current I flows into the capacitor 3, the current I for the passage of parallel switch 4 _P, 4 _N that is a high-impedance conductive state, can be suppressed amount of current. Therefore, as the parallel switch 4 _P, 4 _N, etc., can be used as a small current capacity can be miniaturized these parallel switch 4 _P, 4 _N.

Thereafter, as shown in FIG. 4, the control unit 5 turns off the first positive switch unit 41 _P. As a result, the positive side parallel switch 4 _P is turned off.
Then, as shown in FIG. 5, the control unit 5 turns off the first negative switch unit 41 _N. Thus, the negative side parallel switch _4N is turned off.

Thereafter, as shown in FIG. 6, the control unit 5 turns on the first switch unit 41 _S for series. As a result, the series switch 4 _S is brought into a high impedance conducting state.
In this way, a discharge current _ID is generated from each capacitor 3. That is, (see FIG. 1) because it was connected in parallel immediately before the individual capacitor 3, the capacitors 3, had applied voltage V _B of the power line 2, as shown in FIG. 6, the first switch unit for series When 41 _S is turned on, the two capacitors 3 are connected in series, and the voltage of each capacitor 3 becomes V _B / 2. Therefore, the voltage of the capacitor 3 drops suddenly, and the discharge current _ID occurs. However, the discharge current I _D, since through the resistor 43 of the series switch 4 _S, can be suppressed that a large discharge current I _D flows. Therefore, as a first switch unit 41 _S for series, it is possible to use a current capacity is small, it can be downsized first switch unit 41 _S for series.
When the voltage V _B of the power line 2 is twice or more that of the parallel connection when the two capacitors 3 are switched from the parallel connection to the series connection, a charging current flows through each capacitor 3. Also in this case, since the charging current flows through the resistor 43, it is possible to suppress a large charging current from flowing.

After generation of the discharge current I _D is completed, as shown in FIG. 7, the control unit 5 turns on the second switch 42 _S for series. As a result, the series switch 4 _S is turned on. This state (that is, a state in which two capacitors 3 are connected in series) is maintained while the voltage V _B of the power line 2 exceeds the threshold value V _TH .

Control unit 5, once the voltage V _B of the power line 2 becomes smaller than the threshold value V _TH, as shown in FIG. 8, and turns off the second switch 42 _S for series. As a result, the series switch 4 _S is brought into a high impedance conducting state. When the voltage V _B of the power line 2 decreases, the current I flows out from the capacitor 3, the current I for the passage of the series switch 4 _S that is a high-impedance conductive, it can be suppressed amount of current. Thereafter, the control unit 5 as shown in FIG. 9, turns off the first switch unit 41 _S for series.

Thereafter, as shown in FIG. 10, the control unit 5 turns on the first negative switch unit 41 _N. Then, as shown in FIG. 11, the control unit 5 turns on the first positive switch unit 41 _P. As a result, the two parallel switches 4 _P and 4 _N are brought into a high impedance conduction state.
In this way, the current I _R flows through each capacitor 3. That is, since the two capacitors 3 were connected in series until immediately before (see FIG. 7), the voltage applied to each capacitor 3 was V _B / 2, but the positive-side first switch unit 41 _P and the negative-side When one switch unit 41 _N is turned on, the capacitors 3 _A and 3 _B are connected in parallel, so that the voltage V _B of the power line 2 is applied to each capacitor 3. Therefore, the voltage applied to the capacitor 3 rises rapidly, and the current I _R flows. However, since the current I _R passes through the resistor 43, the amount of current can be suppressed. Therefore, as the switch section 41 _P, 41 _N, can be used as current capacity is small, these switch portions 41 _P, 41 _N can be miniaturized.
When the two capacitors 3 are switched from series connection to parallel connection and the voltage V _B of the power line 2 becomes 以下 or less of that in the case of series connection, a discharge current flows from each capacitor 3. Also in this case, since the discharge current passes through the resistor 43, the amount of current can be suppressed.

After completing the flow of current I _R, as shown in FIG. 12, the control unit 5 turns on the second negative switch unit 42 _N. Then, as shown in FIG. 1, to turn on the second positive switch unit 42 _P. As a result, the two capacitors 3 are connected in parallel.

Next, the operation and effect of this embodiment will be described. The switch 4 of the line filter 1 according to the present embodiment is configured to be able to take three types of states: an ON state, an OFF state, and a high impedance conduction state. Further, when switching the connection of the plurality of capacitors 3 between the parallel connection and the series connection, the control unit 5 sets the switch 4 in the off state to the high impedance conduction state and then to the on state ( 5 to 7).
Therefore, when switching the connection of the capacitor 3, even if the discharge current I _D and the rush current I _R is generated, these currents to flow a switch 4 which is in a high impedance conducting state, hardly a large current flows Become. Therefore, a switch having a small current capacity can be used as the switch 4, the capacitor 3, the power line 2, and the like, and these components can be downsized.

Further, in this embodiment, when the voltage V _B of the power line 2 is higher than the threshold value V _TH, connected in series a plurality of capacitors 3.
Therefore, the voltage applied to the capacitor 3 can be reduced. Therefore, a capacitor 3 having a small withstand voltage but a small size and a large capacitance, such as an electrolytic capacitor, can be used. Therefore, the line filter 1 can be reduced in size and inexpensive.

Further, when the capacitor 3 having a large capacitance is used, a large discharge current I _D and a rush current I _R are likely to be generated when the series-parallel connection of the capacitor 3 is switched. In the present embodiment, however, these currents I _D , I _R can be passed through the switch 4 which is in a high impedance conducting state, so that the current value can be suppressed. Therefore, it is easy to use the capacitor 3 having a large capacitance, and it is easy to reduce the size of the line filter 1 while enhancing the noise removing effect.

Further, when switching the connection of the capacitor 3 between the parallel connection and the series connection, the control unit 5 of the present embodiment turns the switch 4 in an on state into a high impedance conduction state and then turns it off. (See FIGS. 1-5).
Therefore, even if the voltage V _B of the power line 2 fluctuates and a current flows through the capacitor 3, this current passes through the switch 4 that is in a high-impedance conducting state, so that the current amount can be suppressed. Therefore, the current capacity of the switch 4 and the like can be reduced, and the reliability can be ensured while the size of the switch 4 and the like is reduced.

Further, as shown in FIG. 1, the switch 4 of the present embodiment includes a series body 44 in which a resistor 43 and a first switch section 41 are connected in series, and a second switch section 42 in parallel with the series body 44.
Therefore, by turning on only the first switch section 41, the switch 4 can be reliably brought into a high impedance conduction state.

  In the present embodiment, as described above, the switch 4 having the resistor 43 and the two switch units 41 and 42 is used, but the present invention is not limited to this. That is, as will be described later, the switch 4 is configured using only the semiconductor switching element without using the resistor 43 (see FIG. 32), and by adjusting the gate voltage of the semiconductor switching element, the switch 4 is turned on with high impedance. It may be in a state.

  As described above, according to the present embodiment, it is possible to provide a line filter that can suppress a large current from flowing through each capacitor when the connection of a plurality of capacitors is switched between series connection and parallel connection. .

  In this embodiment, two capacitors 3 are used, but the present invention is not limited to this, and three or more capacitors 3 may be used to switch between serial and parallel.

  In the following embodiments, among the reference numerals used in the drawings, the same reference numerals as those used in the first embodiment represent the same components and the like as those in the first embodiment unless otherwise specified.

(Embodiment 2)
This embodiment is an example in which the circuit configuration of the line filter 1 is changed. As shown in FIG. 13, the line filter 1 of the present embodiment includes a current measurement unit 10 for measuring the current of the capacitor 3. The current measuring unit 10 includes a shunt resistor 101 and a voltage sensor 102 for measuring a voltage drop of the shunt resistor 101.

Control unit 5 of this embodiment, as in Embodiment 1, when the voltage V _B of the power line 2 exceeds the threshold value V _TH, switches the two capacitors 3 from parallel connection to series connection. Further, when the voltage V _B of the power line 2 is below the threshold value V _TH switches the two capacitors 3 connected in series to the parallel connection. In addition to these controls, the control unit 5 switches the two capacitors 3 from parallel connection to series connection even when the measured value of the current I by the current measurement unit 10 exceeds a predetermined value I _TH. Or switching from serial connection to parallel connection. Hereinafter, this control will be described.

As shown in FIG. 13, when the voltage V _B of the power line 2 is equal to or lower than the threshold value V _TH , the control unit 5 connects two capacitors 3 in parallel. That is, the two parallel switches 4 _P and 4 _N are turned on, and the series switch 4 _S is turned off. In this state, when the voltage V _B of the power line 2 begins to rise, before the voltage V _B exceeds the threshold value V _TH, there is a case where a large current I flowing into the capacitor 3 _A, 3 _B. Control unit 5, if the measured value of the current I by the current measuring unit 10 exceeds a predetermined value I _TH, as shown in FIG. 14, and turns off the second positive switch unit 42 _P, then shown in FIG. 15 As a result, the negative second switch unit _42N is turned off. As a result, the two parallel switches 4 _P and 4 _N are brought into a high impedance conduction state. This suppresses the flow of the large current I.

Thereafter, the control unit 5 (see FIG. 16) turns off the first positive switch unit 41 _P, then turns off the first negative switch unit 41 _N (see Figure 17). Thereafter, as shown in FIG. 18, to turn on the first switch unit 41 _S for series. At this time, the voltage of the capacitor 3, since in order to reduce the V _B is a value immediately before the V _B / 2, the discharge current I _D flows but from the capacitor 3, through the discharge current I _D resistor 43, The current value can be suppressed.

Then, the control unit 5 turns on the second switch 42 _S for series (see FIG. 19). During the voltage V _B of the power line 2 above the threshold V _TH maintains this state (i.e., a state where the two capacitors 3 connected in series).

Thereafter, when the voltage V _B begins to fall, before the voltage V _B falls below the threshold value V _TH, it may flow out large discharge current from the capacitor 3. Control unit 5 of this embodiment, when the measured value of the current I by the current measuring unit 10 exceeds a predetermined value I _TH is, as shown in FIG. 20, turns off the second switch 42 _S for series. As a result, the series switch 4 _S is brought into a high impedance conducting state, and a large discharge current is suppressed from flowing. Thereafter, the control unit 5 turns off the first switch unit 41 _S for series (see FIG. 21).

Then, the control unit 5 turns on the first negative switch unit 41 _N (see FIG. 22), turns on the first positive switch section 41 _P (see FIG. 23). As a result, the two parallel switches 4 _P and 4 _N are brought into a high impedance conduction state. Since the voltage of the capacitor 3 rises from V _B / 2, which is the immediately preceding value, to V _B , a current I _R flows into each capacitor 3, but the current I _R is supplied to the parallel switch 4 _{P in a} high impedance conducting state. , _4N , so that the current value can be suppressed.

Thereafter, the control unit 5 turns on the second negative switch unit 42 _N (see FIG. 24), then turn on the second positive switch section 42 _P (see FIG. 13).

  A simulation was performed to confirm the effects of the present invention. The result will be described. In this simulation, the circuit shown in FIG. 25 was assumed. As shown in the figure, an external power supply 79 different from the DC power supply 7 is provided, and the power switch 78 is turned on so that the voltage (24 V) of the external power supply 79 is applied to the power line 2. The voltage of the DC power supply 7 was set to 10V. The resistance 43 was set to 0.16Ω, and the capacitance of the capacitor 3 was set to 800 mF.

After the power switch 78 was switched from off to on, and the voltage V _B of the power line 2 was set to 24 V, the power switch 78 was turned off again to lower the voltage V _B to 10 V. Then, as shown in FIG. 26, the voltage V _B of the power line 2, the voltage V _C of the capacitor 3, the capacitors 3 _A, 3 _B of the current I _3A, I _3B, the on / off operation of the switches 41 and 42, positive side first switch portion 41 _P of the current I _41P, negative current I _41N of the first switch section 41 _N, a first switch unit 41 _S of the current I _41S for series, the second switch section 42 _P, 42 _N, 42 _S The current I _42P , I _42N , and I _42S waveforms were examined. Pspice was used for the simulation software.

As shown in FIG. 26, the power switch 78 is turned on at time t _1, increased the voltage V _B of the power line 2. Further, the power switch 78 is turned off at time t _2, the reduced voltage V _B. Until time t ₀ ~t ₁ has a low voltage V _B, the two capacitors 3 are connected in parallel. When the voltage V _B rises at time t ₁ , the switches 41 and 42 are switched, and the two capacitors 3 are connected in series. At this time, the discharge current I _D flows but from the capacitor 3, since the discharge current I _D through the resistor 43, the current amount is suppressed (see FIG. 18). In this simulation, the maximum value of the discharge current I _D at time t ₁ was confirmed to be about 120A.

Further, when the voltage V _B decreases at time t ₂ , the switches 41 and 42 are switched, and the two capacitors 3 are connected in parallel. At this time, the current I _R flows into the capacitor 3, but the current I _R passes through the resistor 43, so that the current amount is suppressed (see FIG. 23). In this simulation, it was confirmed that the maximum value of the current I _R at time t ₂ was about 150A.

An enlarged view of the vicinity of the time t ₁ shown in FIG. 27. As shown in the figure, when turning on the power switch 78 at time t _1, since the voltage V _B begins to rise, the current I (i.e. I _42P, I _42N) of the capacitor 3 starts to increase. When the current I exceeds a predetermined value, the positive second switch 42 _P and the negative second switch 42 _N are turned off (see FIG. 15). Therefore, the current I (I _42P , I _42N ) of these switch sections 42 _P , 42 _N becomes 0A. The current I flows to the resistor 43 through the positive first switch 41 _P or the negative first switch 41 _N. Therefore, the current I (I _41P , I _41N ) of these switch sections 41 _P , 41 _N increases. Since the currents I _41P and I _41N pass through the resistor 43, the current values are suppressed.

Further, an enlarged view of the vicinity of the time t ₂ in Figure 28. As shown in the figure, when turning off the power switch 78 at time t _2, the order in which the voltage V _B begins to decrease, capacitor 3 is discharged, the current I (i.e., I _42S) starts to flow. When the current I exceeds a predetermined value, the second switch unit for series _42S is turned off (see FIGS. 19 and 20). Therefore, the current I (I _42S ) of the second switch unit for series 42 _S becomes 0 _A. Further, the current I flows through the first switch unit 41 _S for series through the resistor 43. Therefore, the current I (I _41S ) of the series first switch unit 41 _S increases. Since the current I passes through the resistor 43, the current amount is suppressed.

Next, a similar simulation was performed for the conventional line filter 1. In this simulation, as shown in FIG. 33, the circuit of the conventional line filter 1 was configured using the switch 4 having no resistor 43. The switch 4 can switch between an on state and an off state, but cannot be in a high impedance conduction state. The switches 4 include parallel switches 4 _P and 4 _N and series switches 4 _S. When only the parallel switches 4 _P and 4 _N are turned on among the three switches 4, the two capacitors 3 are connected in parallel. When only the series switch 4 _S is turned on, the two capacitors 3 are connected in series. The voltages of the DC power supply 7 and the external power supply 79 and the capacitance of the capacitor 3 were the same as in the simulation according to the present embodiment.

In the above circuit, the power switch 78 is off, the up and down the voltage V _B of the power line 2. Then, as shown in FIG. 34, the voltage V _B of the power line 2, the voltage V _C of the capacitor 3, and on-off states of the parallel switch 4 _P, 4 _N, and on-off states of the series switches 4 _S, these switches 4 _P , 4 _N, 4 current flowing through the _S I _4P, I _4N, was investigated I _4S.

As shown in FIG. 34, from time t ₀ to t _1, since the voltage V _B of the power line 2 is low, the parallel switches 4 _P and 4 _N are turned on and the two capacitors 3 are connected in parallel. When the voltage V _B increases at time t ₁ , the parallel switches 4 _P and 4 _N are turned off, and the series switch 4 _S is turned on. Thus, two capacitors 3 are connected in series. At this time, the discharge current I _D of the capacitor 3 flows through the series switch 4 _S. Since the discharge current _ID does not flow through the resistor 43 as in the present embodiment, the current value is large. In the simulation, the maximum value of the discharge current I _D was confirmed to be about 12000 A.

Further, when the voltage V _B falls at time t _2, the series switch 4 _S is turned off, parallel switch 4 _P, 4 _N is turned on. Thereby, two capacitors 3 are connected in parallel. At this time, an inrush current I _R flows through the capacitor 3. Rush current I _R, since not flow through the resistor 43 as in this embodiment, a large current value. In the simulation, it was confirmed that the maximum value of the inrush current I _R was about 5000A.

The operation and effect of the present embodiment will be described. When the current measured by the current measuring unit 10 exceeds a predetermined value I _TH , the control unit 5 of the present embodiment _{brings the} switch 4 in the ON state into a high impedance conductive state.
Therefore, even when the voltage V _B of the power line 2 does not reach the threshold V _TH, it is possible using measurements of current, the switch 4 to the high-impedance conductive state. Therefore, the switch 4 can be more reliably and quickly brought into the high-impedance conduction state, and the flow of a large current through the capacitor 3 can be suppressed.
In addition, the second embodiment has the same configuration, operation and effect as those of the first embodiment.

(Embodiment 3)
This embodiment is an example in which the configuration of the electric device 8 is changed. The electric device 8 of the present embodiment is an ozonizer for generating ozone. As shown in FIG. 29, the ozonizer includes an inverter 81 that converts DC power of the DC power supply 7 into AC power, and a discharge reactor 82 that generates discharge using the obtained AC power. This discharge is used to convert oxygen in the air into ozone. The exhaust gas from the vehicle is altered using the obtained ozone.

Inverter 81 is configured to perform an intermittent operation for switching the discharge period T _D and the discharge stop period T _S alternately. Discharge period T _D is a period for generating discharge by supplying an AC power to a discharge reactor 82. The discharge stop period T _S is a period during which the supply of AC power is stopped and no discharge is generated from the discharge reactor 82.

  Further, the control unit 5 of the present embodiment is configured to stop driving the electric device 8 (that is, the ozonizer) while any one of the plurality of switches 4 is in the high impedance conduction state.

The operation and effect of the present embodiment will be described. As described above, the control unit 5 of the present embodiment is configured to stop driving the electric device 8 while any of the plurality of switches 4 is in the high impedance conduction state.
By doing so, leakage of noise to the outside can be suppressed more reliably. That is, while the switch 4 is in the high-impedance conducting state, it is difficult for the capacitor 3 to absorb the noise current, and the noise current removal efficiency is reduced. In the present embodiment, while the switch 4 is in the high impedance conduction state, the driving of the electric device 8 is stopped, so that it is possible to suppress the leakage of noise from the electric device 8 to the outside during this time.

Further, the electric device 8 of the present embodiment is an ozonizer. The ozonizer is configured to perform intermittent operation alternately switching between the discharge period T _D the discharge stop period T _S.
Therefore, the effects of the present invention can be sufficiently exhibited. That is, the discharge reactor 82 cannot start discharging without supplying a certain amount of power. However, for example, in a vehicle-mounted ozonizer, the required amount of ozone may be small because the amount of exhaust gas discharged is small. In this case, if the discharge reactor 82 is continuously discharged, excessive ozone will be generated. Therefore, by performing the above-described intermittent operation, it is possible to prevent discharge of excess ozone while generating discharge in the discharge reactor 82. That is, the amount of generated ozone can be reduced as compared with the case of continuous discharge. When the intermittent operation is performed, the discharge period T _D and the discharge stop period T _S are alternately performed, so that low-frequency noise is likely to occur. To remove the low-frequency noise, a capacitor 3 having a large capacitance is required. However, the capacitor 3 having a large capacitance and a large withstand voltage tends to be large. In the present embodiment, as described above, when the voltage or the charging / discharging current of the capacitor 3 becomes larger than the threshold, the connection is switched to the series connection, so that the capacitor 3 can be protected and the capacitor 3 having a low withstand voltage is used. be able to. For example, a capacitor 3 having a low withstand voltage but a small size and a large capacitance, such as an electrolytic capacitor, can be used. Therefore, the size of the line filter 1 can be reduced and the cost can be reduced.
In addition, the second embodiment has the same configuration, operation and effect as those of the first embodiment.

(Embodiment 4)
This embodiment is an example in which the configuration of the capacitor 3 is changed. As shown in FIG. 30, in the present embodiment, a capacitor 3 is configured by connecting a plurality of capacitor cells 30 in series. Each of the capacitor cells 30 is composed of an electrolytic capacitor, an electric double layer capacitor or a lithium ion capacitor having a low withstand voltage and a large capacity.

With the above configuration, the voltage applied to each capacitor cell 30 can be reduced. Therefore, a capacitor with a low withstand voltage can be used as the capacitor cell 30, and the capacitor cell 30 can be downsized. Thus, the size of the capacitor 3 can be further reduced.
In addition, the second embodiment has the same configuration, operation and effect as those of the first embodiment.

(Embodiment 5)
This embodiment is an example in which the configuration of the switch 4 is changed. As shown in FIG. 31, in the present embodiment, the switch units 41 and 42 are configured by semiconductor switching elements (MOSFETs). When turning on the switch 4, the control unit 5 applies a voltage sufficiently higher than the threshold voltage to the gate electrode of the semiconductor switching element included in the second switch unit 42. As a result, the second switch section 42 is turned on, and the switch 4 is turned on. When the switch 4 is turned off, no voltage is applied to the gate electrodes of the semiconductor switching elements constituting the two switch sections 41 and 42, respectively. When the switch 4 is set to the high impedance conduction state, no voltage is applied to the gate electrode of the semiconductor switching element forming the second switch section 42, and the gate electrode of the semiconductor switching element forming the first switch section 41 Apply a voltage sufficiently higher than the threshold voltage. As a result, the first switch 41 is turned on while the second switch 42 is turned off, and the switch 4 is brought into a high impedance conduction state.

The operation and effect of the present embodiment will be described. As described above, in the present embodiment, each of the switch sections 41 and 42 is configured by a semiconductor switching element. Since the semiconductor switching element is faster switching speeds, when the voltage V _B of the power line 2 is changed, it is possible to switch the switching units 41 and 42 in a short time. Therefore, it is possible to suppress a large current from flowing through the capacitor 3.

Further, the switch units 41 and 42 of the series switch 4 _S are configured so as to be able to cut off current in both directions. More specifically, the switch units 41 and 42 of the series switch 4 _S are composed of two MOSFETs connected in series with each other. The direction in which the current flows through the body diode 411 of one of the two MOSFETs and the direction in which the current flows through the body diode 412 of the other MOSFET are opposite to each other.
In this way, it is possible to reliably turn off the series switch 4 _S. That is, one terminal 413 of the series switch 4 _S may have a higher potential, and the other terminal 414 may have a higher potential. According to the above configuration, no matter which of the terminals 413 and 414 has a high potential, no current flows through the body diodes 411 and 412, and the current can be reliably turned off.
In addition, the second embodiment has the same configuration, operation and effect as those of the first embodiment.

  As described above, when the switch 4 is set to the high impedance conducting state, the control unit 5 of the present embodiment does not apply a voltage to the gate electrode of the second switch unit 42 (that is, turns off the second switch unit 42). Then, a voltage sufficiently higher than the threshold voltage is applied to the gate electrode of the first switch unit 41 (that is, the first switch unit 41 is turned on), but the present invention is not limited to this. For example, a voltage slightly higher than the threshold voltage is applied to the gate electrodes of the switch units 41 and 42, whereby the switch units 41 and 42 are slightly turned on (that is, in a so-called half-on state), The switch 4 may be set to a high impedance conduction state. Alternatively, the switch 4 may be turned into a high impedance conduction state by turning off the second switch unit 42 and half-on only the first switch unit 41. As described above, by controlling the gate voltage applied to the semiconductor switching element by the control unit 5, the switch 4 can be brought into a high impedance conduction state.

(Embodiment 6)
This embodiment is an example in which the configuration of the switch 4 is changed. As shown in FIG. 32, in this embodiment, the switch 4 is configured using only semiconductor switching elements (MOSFETs). When turning on the switch 4, the control unit 5 applies a voltage sufficiently higher than the threshold voltage to the gate electrode of the MOSFET. When the switch 4 is turned off, no voltage is applied to the gate electrode. In the case of a high impedance conduction state, a voltage slightly higher than the threshold voltage is applied to the gate electrode. As a result, the MOSFET is slightly turned on and a slight current flows.

The operation and effect of the present embodiment will be described. In this embodiment, the switch 4 is configured using only semiconductor switching elements. The control unit 5 is configured to control the gate voltage applied to the semiconductor switching element to make the switch 4 into the high impedance conduction state.
By doing so, the configuration of the switch 4 can be simplified. Therefore, the manufacturing cost of the line filter 1 can be reduced.
In addition, the second embodiment has the same configuration, operation and effect as those of the first embodiment.

  The present invention is not limited to the above embodiments, and can be applied to various embodiments without departing from the gist thereof.

DESCRIPTION OF SYMBOLS 1 Line filter 2 Power line 3 Capacitor 4 Switch 40 Series-parallel switching circuit 5 Control part 6 Voltage measurement part 7 DC power supply 8 Electric equipment

Claims (10)

A pair of power lines (2) for electrically connecting the DC power supply (7) and the electric device (8);
A voltage measuring unit (6) for measuring a voltage between the pair of power lines,
A plurality of capacitors (3) electrically connected between the pair of power lines;
A plurality of switches (4) connected in series to the individual capacitors, wherein the plurality of switches are in an on state in which a current flows and in an off state in which no current flows; A series-parallel switching circuit (40) for switching the connection of the plurality of capacitors between parallel connection and series connection by changing a combination with the switch;
A control unit (5) for controlling the operation of the switch;
Each of the switches is configured to be able to take three types of states: the on state, the off state, and a high impedance conduction state in which a current flows and the impedance is higher than the on state.
The control unit, when the measured value of the voltage by the voltage measurement unit is lower than a predetermined threshold, the plurality of capacitors are connected in parallel, when the measured value of the voltage exceeds the threshold Is a series connection of the plurality of capacitors,
The control unit, when switching the connection of the plurality of capacitors between the parallel connection and the series connection, the switch in the off state, the high impedance conduction state, and then the on state A line filter (1) configured to:   When switching the connection of the plurality of capacitors between the parallel connection and the series connection, the control unit sets the switch in the on state to the high impedance conduction state, and then sets the switch to the off state. The line filter according to claim 1, wherein:   A current measuring unit (10) for measuring a current flowing through the capacitor, wherein the control unit enters the ON state when a measured value of the current by the current measuring unit exceeds a predetermined value. 3. The line filter according to claim 2, wherein said switch is configured to bring said switch into said high impedance conducting state.   Each of the switches is configured such that a first switch section (41) and a resistor (43) configured to be capable of on / off operation are connected in series, and a series body (44) is connected in parallel to the series body and capable of on / off operation. The line filter according to any one of claims 1 to 3, further comprising a second switch unit (42).   5. The line filter according to claim 4, wherein each of said switch sections is made of a semiconductor switching element. The switch includes a series switch (4 _S ) provided between a positive electrode of the capacitor and a negative electrode of another capacitor, and is turned on when the plurality of capacitors are connected in series, The line filter according to claim 5, wherein the switch section of the series switch includes the semiconductor switching element, and is configured to be capable of bidirectionally interrupting a current.   7. The line filter according to claim 5, wherein the control unit is configured to control the gate voltage applied to the semiconductor switching element to make the switch into the high impedance conduction state. 8.   Each of the switches is configured by a semiconductor switching element, and the control unit is configured to control the gate voltage applied to the semiconductor switching element to bring the switch into the high impedance conduction state. 4. The line filter according to any one of 3.   The line filter according to any one of claims 1 to 8, wherein the control unit stops driving the electric device while any of the plurality of switches is in the high impedance conduction state.   The electric device includes an inverter (81) that converts DC power supplied from the DC power supply into AC power, and a discharge reactor (82) that generates discharge using the AC power, and discharges ozone by the discharge. An inverter for generating the discharge, wherein the inverter supplies the AC power to the discharge reactor to generate the discharge, and a discharge for stopping the supply of the AC power and not generating the discharge from the discharge reactor. The line filter according to any one of claims 1 to 9, wherein the line filter is configured to perform an intermittent operation of alternately switching a stop period.