JP2020030967A - Overvoltage suppression circuit and DC cutoff device - Google Patents

Abstract

To provide an overvoltage suppression circuit capable of preventing over-specification or the like of a switch by expanding a selection range of the switch and a nonlinear element such as a varistor.SOLUTION: An overvoltage suppression circuit that suppresses overvoltage of a main switch of a main circuit connecting a power supply and a load includes a nonlinear element connected in parallel to the main switch and an auxiliary switch connected in series to the nonlinear element, and the auxiliary switch is configured to turn off in conjunction with turning off of the main switch, and to turn on in conjunction with turning on of the main switch.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an overvoltage suppression circuit and a DC cutoff device using the overvoltage suppression circuit.

  As a conventional overvoltage suppression circuit, there is one that protects a switch provided in a main circuit that connects a power supply and a load from overvoltage, as disclosed in Patent Document 1. Specifically, this overvoltage suppression circuit includes a varistor as a surge absorber connected in parallel to the switch, and is configured so that the varistor absorbs an overvoltage generated by turning off the switch.

  By the way, generally, as characteristics of a non-linear element such as a varistor, the maximum allowable circuit voltage V1, which is the maximum voltage that can be continuously applied (used) for a long time, and the surge voltage is absorbed, and the surge voltage is reduced to a somewhat lower voltage. It is known that there is a relation of V1 × 2 <V2 between the maximum voltage V2, which is the maximum voltage that can be generated.

  For this reason, for example, if the circuit voltage of the main circuit is 700 V, when a switch provided in the main circuit is to be protected from overvoltage, the varistor must first have a maximum allowable circuit voltage V1 higher than 700 V. Must be selected. As a result, the maximum limiting voltage V2 of the varistor becomes higher than 1400 V. Therefore, it is necessary to select a switch having a rated voltage higher than the maximum limiting voltage V2, for example, a rated voltage of about 1700 V. As a result, the rated voltage of the switch becomes higher than the circuit voltage 700 V of the main circuit, and the switch is over-specified.

  On the other hand, if a switch having a low rated voltage is used, a varistor having a low maximum limit voltage V2 is selected, and the maximum allowable circuit voltage V1 of the varistor is reduced. As a result, when the maximum allowable circuit voltage V1 of the varistor is lower than the circuit voltage of the main circuit, the varistor is destroyed by overheating or the like.

  As described above, the attempt to lower the rated voltage of the switch and the attempt to ensure the use of the varistor for the circuit voltage are in a contradictory relationship. Therefore, the selection range of the switch and the varistor is restricted, and there is a possibility that an increase in cost due to an over-specification of the switch or the like may be caused.

JP 2010-238391 A

  Therefore, the present invention has been made to solve the above problems, and has as its main object to prevent over-specification of switches by expanding the selection range of non-linear elements such as varistors and switches. is there.

  That is, the overvoltage suppression circuit according to the present invention is an overvoltage suppression circuit that suppresses overvoltage of a main switch of a main circuit that connects a power supply and a load, and includes a non-linear element connected in parallel to the main switch, and a non-linear element. And an auxiliary switch connected in series, wherein the auxiliary switch is configured to turn off in conjunction with turning off of the main switch, and to turn on in conjunction with turning on of the main switch.

According to the overvoltage suppression circuit configured as described above, the auxiliary switch is also turned off in conjunction with the turn-off of the main switch, so that the circuit voltage of the main circuit is continuously applied to the nonlinear element when the main switch is turned off. There is no.
On the other hand, since the auxiliary switch is turned on in conjunction with the turn-on of the main switch, the main switch is conductive when the auxiliary switch is turned on, and the circuit voltage of the main circuit is continuously applied to the non-linear elements connected in parallel to this. I will not continue.

  As described above, according to the overvoltage suppression circuit of the present invention, the circuit voltage of the main circuit is not continuously applied to the nonlinear element both when the main switch is turned on and when the main switch is turned off. There is no need to make the allowable circuit voltage higher than the circuit voltage of the main circuit. Thereby, in selecting the nonlinear element, the restriction on the maximum allowable circuit voltage is relaxed, so that the selection range of the nonlinear element can be expanded. Therefore, by using a non-linear element having a low maximum limiting voltage, a main switch having a low rated voltage can be selected, and an excessive specification of the main switch can be prevented.

  In order to reliably absorb the overvoltage caused by turning off the main switch by the nonlinear element, the auxiliary switch may be configured to turn off at a timing delayed from the turn-off of the main switch.

  In order to reduce the overvoltage caused by turning off the auxiliary switch, after turning off the main switch, the switch is turned off at the timing when the current flowing in the nonlinear element or the voltage generated in the nonlinear element becomes equal to or less than a predetermined value. It is preferable to be configured so that

  In order to prevent the circuit voltage of the main circuit from being constantly applied to the non-linear element during the turn-on operation of the main switch, the auxiliary switch may be operated at the same time as the turn-on of the main switch or at a timing delayed from the turn-on of the main switch. What is necessary is just to be configured to turn on.

By the way, when the auxiliary switch in the off state is turned on, electrostatic energy accumulated in the capacitance of the nonlinear element is discharged, and there is a possibility that an inrush current exceeding the rating of the main switch is generated.
Therefore, it is preferable to further include a diode connected in parallel to the main switch, connected in series to the positive side of the nonlinear element, and having a forward direction facing the nonlinear element, and a resistor connected in parallel to the diode. .
With such a configuration, the diode is reverse-biased for a discharge current generated by turning on the auxiliary switch, and the discharge current flows through the resistor and is consumed. This can prevent a rush current exceeding the rating from flowing into the main switch when the auxiliary switch is turned on.

  Further, the DC cutoff device according to the present invention is a main switch of a main circuit that connects a power supply and a load, and an overvoltage suppression circuit that suppresses an overvoltage of the main switch, wherein the overvoltage suppression circuit is connected in parallel to the main switch. A non-linear element connected thereto, and an auxiliary switch connected in series to the non-linear element, wherein the auxiliary switch turns off in conjunction with the turn-off of the main switch and turns on in conjunction with the turn-on of the main switch. It is characterized by comprising.

  According to the present invention configured as described above, by expanding the selection range of the non-linear element such as the varistor and the switch, it is possible to prevent the switch from being over-specified.

FIG. 2 is a diagram schematically illustrating a circuit configuration of the DC cutoff device according to the embodiment. 4 is a flowchart for explaining the operation of the DC cutoff device of the embodiment. 5 is a graph schematically showing a time change of a voltage and a current at the time of interruption of the DC interruption device of the embodiment. 4 is a graph schematically showing a time change of a voltage and a current at the time of closing of the DC cutoff device of the embodiment. The figure which shows typically the circuit structure of the DC cutoff apparatus of other embodiment.

  Hereinafter, an embodiment of a DC cutoff device having an overvoltage suppression circuit according to the present invention will be described with reference to the drawings.

<Configuration of DC cutoff device>
As shown in FIG. 1, the DC cutoff device 100 according to the present embodiment is provided in a main circuit 300 that connects a power supply 200 such as a DC power supply and a load (not shown) to supply and cut off DC power to the load. Switch.

  Specifically, the DC cutoff device 100 includes a main switch 101 for switching between supply and cutoff of DC power, and an overvoltage suppression circuit 102 provided in parallel with the main switch 101.

  The main switch 101 is a circuit breaker such as a semiconductor switch element provided in a main circuit 300 connecting the power supply 200 and a load, and is opened and closed by a gate drive circuit controlled by a control device (not shown). On both sides (positive side and negative side) of the main switch 101 in the main circuit 300, open / close switches such as a line switch SW are provided.

  The overvoltage suppression circuit 102 suppresses an overvoltage generated when the main switch 101 is shut off. Specifically, it includes a commutation circuit section 10 and an overcurrent suppression circuit section 20.

The commutation circuit unit 10 includes an auxiliary switch 11 connected in parallel to the main switch 101 and connected in series with each other, and a nonlinear element 12. The auxiliary switch 11 is, for example, a semiconductor switch. The non-linear element 12 is an element in which the applied voltage and the current flowing through the element are not proportional, and is a varistor made of ceramics such as ZnO. Hereinafter, for convenience of explanation, the nonlinear element 12 is also referred to as a varistor 12.
Note that the auxiliary switch 11 and the varistor 12 are connected in series to the above-described line switch SW, and the auxiliary switch 11 is arranged on the positive side of the varistor 12 here. The auxiliary switch 11 may be arranged on the negative side of the varistor 12.

The overcurrent suppression circuit unit 20 suppresses an overcurrent generated at the time of re-closing.
Specifically, the overcurrent suppression circuit unit 20 is connected in parallel to the main switch 101 and connected in series to the varistor 12, and a diode 21 whose forward direction is directed to the varistor 12 and a resistor connected in parallel to the diode 21. 22.
The overcurrent suppression circuit section 20 is composed of only passive elements.

  Thus, the overvoltage suppression circuit 102 of the present embodiment is configured such that the auxiliary switch 11 is turned off in conjunction with the turn-off of the main switch 101 and turned on in conjunction with the turn-on of the main switch 101.

When the main switch 101 is turned off, the auxiliary switch 11 is configured to turn off at a timing delayed from the turn-off of the main switch 101. More specifically, after the main switch 101 is turned off, the auxiliary switch 11 is turned off at a timing when the value of the current commutated to the commutation circuit unit 10 becomes a predetermined value or less (for example, zero current or near zero current). It is configured to be.
The auxiliary switch 11 is turned off at a timing when the value of the current flowing through the varistor 12 becomes equal to or less than a predetermined value after the main switch 101 is turned off, or after a predetermined time elapses after the main switch 101 is turned off. Is also good.

When the main switch 101 is turned on, the auxiliary switch 11 is configured to turn on at a timing delayed from the turn on of the main switch 101. More specifically, the auxiliary switch 11 is turned on after a lapse of a predetermined time after the main switch 101 is turned on.
The auxiliary switch 11 may be configured to be turned on at the same time as the main switch 101 is turned on. Further, after turning on the main switch 101, the auxiliary switch 11 may be turned on at a timing when the voltage between both ends of the main switch 101 becomes equal to or less than a predetermined value.

<Operation of DC cutoff device 100>
Subsequently, the operation of the DC blocking device 100 of the present embodiment will be described with reference to FIGS.

  First, in a state where the main switch 101 and the auxiliary switch 11 are turned on and the power from the power supply 200 is being supplied to the load, an overcurrent caused by, for example, a short circuit of the load is detected by a current detector (not shown). (Step S1).

When the overcurrent is detected, the control device (not shown) turns off (cuts off) the main switch 101 (step S2). This creates an overvoltage due to the impedance of the distribution line L (see FIG. 1) constituting the main circuit 300 at the time of interruption of the main switch 101, breaking current I _s flows into the varistor 12 (commutation). That is, the overvoltage generated when the main switch 101 is turned off is absorbed by the varistor 12.

Here, in the selection of the varistor 12, so that the voltage V generated by the flow cutoff current I _s generated by interrupting the main switch 101 is lower than the rated voltage Vx of the main switch 101, which selects the varistor 12 .
Conversely, in the selection of the main switch 101, as rated voltage Vx than the voltage Va generated by the flow cutoff current I _s to the varistor 12 selected is high, may be selected to the main switch 101.

  After the overvoltage generated by turning off the main switch 101 is absorbed by the varistor 12, a current flows from the power supply 200 of the main circuit 300 by the applied voltage Vy (hereinafter, referred to as a circuit voltage Vy). Here, as shown in FIG. 3, a varistor 12 having a voltage characteristic such that this current becomes zero current or near zero current is selected.

Thereafter, in a state where the current flowing through the varistor 12 becomes equal to or near the zero current, the auxiliary switch 11 is turned off (step S3), whereby the shutoff operation of the main circuit 300 is completed without generating an overvoltage. Here, the auxiliary switch 11 is turned off after a predetermined time has elapsed since the main switch 101 was turned off.
The line switch SW may be turned off after the auxiliary switch 11 is turned off in order to disconnect the main switch 101 for maintenance or the like.

  On the other hand, when the control device (not shown) acquires a supply start signal indicating the start of power supply in a state where the main circuit 300 is shut off (step S4), the control device turns on the main switch 101 (closes). The auxiliary switch 11 is turned on after a predetermined time has elapsed (step S5) (step S6). At this time, the line switch SW is in a state of being turned on in advance.

When the auxiliary switch 11 is turned on in step S6, the electrostatic energy stored in the capacitance (not shown) of the varistor 12 is discharged. Thus, in the present embodiment, the overcurrent generated when the auxiliary switch 11 is turned on by the overcurrent suppression circuit unit 20 is suppressed from flowing into the main switch 101.
Specifically, since the diode 21 constituting the overcurrent suppression circuit has a reverse bias with respect to the discharge current generated by turning on the auxiliary switch 11, the discharge current flows to the resistor 22 of the overcurrent suppression circuit. Consumed.

<Effect of this embodiment>
According to the DC cutoff device 100 configured as described above, the auxiliary switch 11 is configured to turn off in conjunction with the turn-off of the main switch 101 and to turn on in conjunction with the turn-on of the main switch 101. The circuit voltage of the main circuit 300 does not continue to be applied to the varistor 12 for a long time regardless of whether the main switch 101 is on or off. Accordingly, it is not necessary to make the maximum allowable circuit voltage of the varistor 12 higher than the circuit voltage, and the restriction on the maximum allowable circuit voltage in selecting the varistor 12 is relaxed, so that the selection range of the varistor 12 can be expanded. .

  Further, since the overvoltage generated by shutting off the main switch 101 is absorbed by using the varistor 12, the main switch 101 only needs to have a rated voltage higher than the maximum limit voltage of the varistor 12. The over-specification of 101 can be avoided.

  Furthermore, since the discharge current generated by turning on the auxiliary switch 11 is consumed by the resistor 22 constituting the overcurrent suppression circuit unit 20, when the auxiliary switch 11 is turned on, the main switch 101 is inrushed beyond the rating. The current can be prevented from flowing.

<Other embodiments>
Note that the present invention is not limited to the above embodiment.

  For example, the overvoltage suppression circuit 102 of the above embodiment is connected in parallel to the main switch 101, and the auxiliary switch 11 is connected in series to the varistor 12, but is not limited to this. As shown in FIG. 5, the overvoltage suppression circuit 102 of another embodiment may be provided such that the auxiliary switch 11 is connected to both the main switch 101 and the varistor 12 in series.

  The non-linear element 12 is not limited to a zinc oxide varistor, but may be, for example, one having a pair of zener diodes facing each other or one having another configuration.

  The main switch 101 and the auxiliary switch 11 are not limited to semiconductor switches, but may be mechanical switches.

  In addition, the overvoltage suppression circuit 102 does not necessarily need to include the overcurrent suppression circuit unit 20.

  In addition, it goes without saying that the present invention is not limited to the above-described embodiment, but can be variously modified without departing from the gist thereof.

100 DC cutoff device 200 Power supply 300 Main circuit 101 Main switch 102 Overvoltage suppression circuit SW Line switch 10 Commutation circuit unit 11 Auxiliary Switch 12: Varistor (non-linear element)
20 overcurrent suppression circuit section 21 diode 22 resistor

Claims (6)

An overvoltage suppression circuit that suppresses an overvoltage of a main switch of a main circuit that connects a power supply and a load,
A non-linear element connected in parallel to the main switch;
An auxiliary switch connected in series with the nonlinear element,
An overvoltage suppression circuit configured to turn off the auxiliary switch in conjunction with turning off of the main switch and turn on in conjunction with turning on of the main switch.   2. The overvoltage suppression circuit according to claim 1, wherein the auxiliary switch is configured to turn off at a timing delayed from turning off of the main switch.   3. The overvoltage suppression circuit according to claim 2, wherein after the main switch is turned off, the switch is turned off at a timing when a current flowing in the non-linear element or a voltage generated in the non-linear element becomes equal to or less than a predetermined value.   4. The overvoltage suppression circuit according to claim 1, wherein the auxiliary switch is configured to be turned on at the same time as the turn-on of the main switch or at a timing delayed from the turn-on of the main switch. 5.   The device further comprising: a diode connected in parallel to the main switch and connected in series to a positive side of the nonlinear element, the forward direction of which is directed to the nonlinear element, and a resistor connected in parallel to the diode. 5. The overvoltage suppression circuit according to any one of 4. A main switch of a main circuit for connecting a power supply and a load,
An overvoltage suppression circuit that suppresses an overvoltage of the main switch,
The overvoltage suppression circuit,
A non-linear element connected in parallel to the main switch;
An auxiliary switch connected in series with the nonlinear element,
A DC cutoff device, wherein the auxiliary switch is turned off in conjunction with turning off of the main switch, and turned on in conjunction with turning on of the main switch.