JP2020030969A - Overvoltage suppression circuit and cutoff device - Google Patents

Abstract

To prevent over-specification of a switch by expanding a selection range of the switch and a nonlinear element such as a varistor.SOLUTION: An overvoltage suppression circuit 102 connected in parallel to a main switch 101 of a main circuit 300 connecting a power supply 200 and a load includes a first auxiliary switch S1 and a first nonlinear element V1 provided in parallel with the main switch 101 and provided in series with each other, and a second auxiliary switch S2 and a second nonlinear element V2 that are provided in parallel with the main switch 101, the first auxiliary switch S1, and the first nonlinear element V1 and provided in series with each other, and a voltage generated in the first nonlinear element when a predetermined reference current flows through the first nonlinear element V1 is set to be lower a voltage generated in the second nonlinear element when the predetermined reference current flows through the second nonlinear element V2.SELECTED DRAWING: Figure 2

Description

  The present invention relates to an overvoltage suppression circuit and a shutoff 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.

  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), and the surge voltage can be absorbed and the surge voltage can be reduced to a somewhat lower voltage. It is known that there is a relationship of V1 × 2 <V2 between the maximum voltage and the maximum limit voltage V2.

  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 connected in parallel to a main switch of a main circuit that connects a power supply and a load, provided in parallel with the main switch, and A first auxiliary switch and a first nonlinear element provided in series;
A second auxiliary switch and a second nonlinear element that are provided in parallel with the main switch, the first auxiliary switch, and the first nonlinear element, and that are provided in series with each other; A voltage generated in the first nonlinear element when a predetermined reference current flows through the second nonlinear element is lower than a voltage generated in the second nonlinear element when the predetermined reference current flows in the second nonlinear element. It is characterized by the following.

According to the overvoltage suppression circuit configured as described above, first, if the first auxiliary switch and the second auxiliary switch are turned off while the main switch is off, the first nonlinear element and the second nonlinear element are turned off. Since no voltage is applied from the power supply of the main circuit, the maximum allowable circuit voltage of the first nonlinear element and the second nonlinear element does not need to be higher than the circuit voltage of the main circuit. Thereby, in selecting the first nonlinear element and the second nonlinear element, the restriction on the maximum allowable circuit voltage is relaxed, so that the selection range of these nonlinear elements can be expanded.
Therefore, a first non-linear element whose voltage generated in the first non-linear element when a predetermined reference current flows is lower than voltage generated in the second non-linear element when the same reference current flows. By selection, as shown in FIG. 2, the cutoff current I1 generated by turning off the main switch flows through the first nonlinear element. That is, the overvoltage generated by turning off the main switch can be absorbed by the first nonlinear element. For this reason, by using an element having a low maximum limiting voltage as the first non-linear element, an element having a low rated voltage can be selected as the main switch, and an excessive specification of the main switch can be prevented.

  On the other hand, by using an element having a low maximum limiting voltage as the first nonlinear element, as shown in FIG. 2, a current due to a voltage applied from a power supply of the main circuit (hereinafter, referred to as a circuit voltage) is applied to the first nonlinear element. Will flow. Therefore, when the first auxiliary switch is turned off, an overvoltage still occurs, but this overvoltage can be absorbed by the second nonlinear element. From this, in selecting the second nonlinear element, as shown in FIG. 2, the interruption current I2 generated by turning off the first auxiliary switch flows, and the voltage generated in the second nonlinear element is mainly reduced. What is necessary is just to select so that it may become smaller than the rated voltage of a switch. That is, the second non-linear element does not necessarily have to have a maximum limiting voltage lower than the rated voltage of the main switch, and can be selected without being restricted by the rated voltage of the main switch.

  As described above, according to the above-described overvoltage suppression circuit, the selection range of the nonlinear element and the main switch can be expanded, and the rated voltage of the main switch can be reduced. Can be.

  In order to protect the main switch from overvoltage generated by turning off the main switch, the main switch is turned off from a state where the main switch, the first auxiliary switch, and the second auxiliary switch are on. Preferably, the voltage generated in the first nonlinear element is lower than the rated voltage of the main switch.

  In order to protect the main switch from an overvoltage generated by turning off the first auxiliary switch, the main switch is turned off, and the first auxiliary switch and the second auxiliary switch are turned on. It is preferable that a voltage generated in the second nonlinear element by turning off the first auxiliary switch is lower than a rated voltage of the main switch.

  In order to minimize the overvoltage generated by turning off the second auxiliary switch, the current flowing through the second nonlinear element due to the applied voltage from the power supply is reduced by the applied voltage from the power supply. It is preferable that the current is smaller than the current flowing through one nonlinear element.

By the way, when the first auxiliary switch or the second auxiliary switch in the off state is turned on, the electrostatic energy accumulated in the capacitance of the first nonlinear element or the second nonlinear element is discharged, and the rush exceeding the rating of the main switch is performed. Current may be generated.
Therefore, a diode connected in series to the positive side of the first auxiliary switch and the second auxiliary switch, the forward direction of which is directed to the first auxiliary switch and the second auxiliary switch, and a resistor connected in parallel to the diode. It is preferable to further include
With such a configuration, the diode is reverse-biased with respect to the discharge current generated by turning on the first auxiliary switch and the second auxiliary switch, so that the discharge current flows through the resistor and is consumed. Thereby, when turning on the first auxiliary switch or the second auxiliary switch, it is possible to prevent an inrush current exceeding the rating from flowing into the main switch.

Further, the shut-off device according to the present invention includes a main switch provided in a main circuit connecting a power supply and a load, and an overvoltage suppression circuit connected in parallel to the main switch, wherein the overvoltage suppression circuit is A first auxiliary switch and a first non-linear element provided in parallel with the main switch and provided in series with each other, and the first switch, the first auxiliary switch, and the first non-linear element, A second auxiliary switch and a second nonlinear element provided in parallel and in series with each other, and a voltage generated in the first nonlinear element when a predetermined reference current flows through the first nonlinear element However, the voltage is lower than the voltage generated in the second nonlinear element when the predetermined reference current flows through the second nonlinear element.
With such an interrupting device, it is possible to exhibit the same operational effects as those of the above-described overvoltage suppression circuit.

  According to the present invention configured as described above, the selection range of the main switch and the non-linear element can be widened, and the rated voltage of the main switch can be reduced.

The figure which shows typically the circuit structure of the shut-off device of this embodiment. 4 is a graph showing voltage characteristics of a first varistor and a second varistor of the same embodiment. 4 is a flowchart for explaining the operation of the shutoff device of the embodiment. 4 is a graph for explaining an operation and a current flow of the shutoff device of the embodiment.

  Hereinafter, an embodiment of a shutoff device according to the present invention will be described with reference to the drawings.

  As shown in FIG. 1, the cutoff device 100 of 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), and switches between supply and cutoff of DC power to the load. Things.

  Specifically, the 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 cut off, and specifically includes a first commutation circuit 10, a second commutation circuit 20, and an overcurrent suppression circuit 30. .

The first commutation circuit 10 has a first auxiliary switch S1 and a first nonlinear element V1 provided in parallel with the main switch 101 and in series with each other. The first auxiliary switch S1 is, for example, a semiconductor switch. The first nonlinear element V1 is an element in which the applied voltage is not proportional to the current flowing through the element, and is a varistor made of, for example, ceramics such as ZnO. Hereinafter, the first nonlinear element V1 is also referred to as a first varistor V1 for convenience of description.
Note that the first auxiliary switch S1 and the first varistor V1 are connected in series to the above-described line switch SW. Here, the first auxiliary switch S1 is disposed on the positive side of the first varistor V1.

The second commutation circuit 20 is provided in parallel with the main switch 101, the first auxiliary switch S1, and the first varistor V1, and the second auxiliary switch S2 and the second nonlinear element V2 provided in series with each other. have. The second auxiliary switch S2 is, for example, a semiconductor switch. The second nonlinear element V2 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, the second nonlinear element V2 is also referred to as a second varistor V2 for convenience of description.
The second auxiliary switch S2 and the second varistor V2 are connected in series to the above-described line switch SW, and here, the second auxiliary switch S2 is arranged on the positive side of the second varistor V2.

However, the overvoltage suppression circuit 102 of the present embodiment is characterized in that the varistor voltage of the first varistor V1 is lower than the varistor voltage of the second varistor V2.
Here, the varistor voltage is a voltage generated in the varistor when a predetermined reference current (for example, 1 mA) is passed through the varistor.

Describing in more detail, the first varistor V1 and the second varistor V2 have, for example, the voltage characteristics shown in FIG. That is, the first varistor V1 has lower voltage characteristics than the second varistor V2, and generates a smaller voltage when a current of the same magnitude flows. Here, the change in the voltage with respect to the change in the magnitude of the flowing current (the slope of the voltage characteristic shown in FIG. 2) is larger in the second varistor V2 than in the first varistor V1.
Further, regarding the maximum allowable circuit voltage, which is a kind of voltage characteristic, that is, the maximum voltage that can be continuously applied (used), the second varistor V2 is larger than the first varistor V1.
Further, with respect to the maximum limit voltage, which is a type of voltage characteristic, that is, the maximum voltage that can absorb the surge voltage and reduce the surge voltage to a somewhat lower voltage, the second varistor V2 has a higher voltage than the first varistor V1. Is big.
Note that there is a relationship between the maximum allowable circuit voltage and the maximum limit voltage such as “maximum allowable circuit voltage × 2 <maximum limit voltage”.

  The overcurrent suppression circuit 30 suppresses an overcurrent caused by turning on the first auxiliary switch S1 and the second auxiliary switch S2 in the off state, and includes the first commutation circuit 10 and the second commutation circuit 20. It is provided on the more positive side. Specifically, the overcurrent suppression circuit 30 is connected in series to the positive side of the first auxiliary switch S1 and the second auxiliary switch S2, and has a diode 31 whose forward direction is directed to the first auxiliary switch S1 and the second auxiliary switch S2. , And a resistor 32 connected in parallel with the diode 31. Note that the overcurrent suppression circuit 30 includes only passive elements.

  Next, the operation of the shut-off device 100 according to the present embodiment will be described with reference to the flowchart of FIG. 3 while also describing the method of selecting each varistor and the like described above.

  First, in a state where the main switch 101, the first auxiliary switch S1, and the second auxiliary switch S2 are turned on and the power from the power supply 200 is supplied to the load, for example, the load of the load is detected by a current detector (not shown). An overcurrent caused by a short circuit or the like is detected (S1).

  When an overcurrent is detected, the control device (not shown) shuts off the main switch 101 (S2). Then, when the main switch 101 is shut off, an overvoltage occurs due to the impedance L (see FIG. 1) of the distribution line forming the main circuit 300.

  At this time, in the present embodiment, the varistor voltage of the first varistor V1 is lower than the varistor voltage of the second varistor V2, in other words, the first varistor V1 generates a voltage when a predetermined reference current flows. Since it is lower than the second varistor V2, as shown in FIGS. 2 and 4, the interruption current I1 generated by the interruption of the main switch 101 flows into the first varistor V1. That is, the overvoltage generated when the main switch 101 is shut off is absorbed by the first varistor V1.

Here, in selecting the first varistor V1, as shown in FIG. 2, the voltage V1 generated by the flow of the cutoff current I1 generated by the cutoff of the main switch 101 becomes lower than the rated voltage Vx of the main switch 101. , The first varistor V1 is selected.
Conversely, when selecting the main switch 101, the main switch 101 may be selected so that the rated voltage Vx is higher than the voltage Va generated by the interruption current I1 flowing through the selected first varistor V1. .

  After the overvoltage generated by the interruption of the main switch 101 is absorbed by the first varistor V1, as shown in FIGS. 2 and 4, the first varistor V1 is supplied with an applied voltage Vy (hereinafter referred to as a voltage) from the power supply 200 of the main circuit 300. , A circuit voltage Vy). The current I2 is larger than the zero current because the first varistor V1 is selected to have a relatively low voltage characteristic. Therefore, when the first auxiliary switch S1 is turned off (S3), an overvoltage occurs as in the case where the main switch 101 is turned off.

Therefore, the overvoltage suppression circuit 102 of the present embodiment is configured so that the overvoltage generated by turning off the first auxiliary switch S1 can be absorbed by the second varistor V2.
For this reason, in selecting the second varistor V2, as shown in FIG. 2, the voltage Vb generated by the flow of the cut-off current I2 generated by turning off the first auxiliary switch S1 changes the rated voltage of the main switch 101. What is necessary is just to select so that it may become smaller than Vx. That is, it is not necessary to select the second varistor V2 whose maximum limit voltage is lower than the rated voltage Vx of the main switch 101.

  After the overvoltage generated by turning off the first auxiliary switch S1 is absorbed by the second varistor V2, a current I3 due to the circuit voltage flows through the second varistor V2 as shown in FIGS. Will be. This current I3 becomes zero current or near zero current by selecting a second varistor V2 having a higher voltage characteristic than at least the first varistor V1.

Thereafter, in a state where the current flowing through the second varistor V2 becomes zero current or near zero current, the second auxiliary switch S2 is turned off (S4), so that the shut-off operation of the main circuit 300 is performed without generating an overvoltage. Complete.
Note that the line switch SW may be turned off after the second auxiliary switch S2 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) obtains a supply start signal indicating the start of power supply in a state where the main circuit 300 is shut off (S5), the control device turns on the main switch 101 (S6). Then, the first auxiliary switch S1 and the second auxiliary switch S2 are turned on (S7). At this time, the line switch SW has been turned on in advance, and the order in which the first auxiliary switch S1 and the second auxiliary switch S2 are turned on may be appropriately selected.

As described above, when the first auxiliary switch S1 and the second auxiliary switch S2 are turned on, the electrostatic energy accumulated in the capacitance (not shown) constituting the first varistor V1 and the second varistor V2 is discharged. Therefore, in the present embodiment, the overcurrent suppression circuit 30 suppresses the overcurrent generated when the first auxiliary switch S1 and the second auxiliary switch S2 are turned on from flowing into the main switch 101.
Specifically, the diode 31 constituting the overcurrent suppression circuit 30 has a reverse bias to the discharge current generated by turning on the first auxiliary switch S1 and the second auxiliary switch S2. It flows to the resistor 32 of the suppression circuit 30 and is consumed.

  According to the shutoff device 100 configured as described above, the shutoff operation of the main circuit 300 turns off all of the main switch 101, the first auxiliary switch S1, and the second auxiliary switch S2. No circuit voltage is applied to the varistor V1 and the second varistor V2. Therefore, it is not necessary to make the maximum allowable circuit voltage of the first varistor V1 or the second varistor V2 higher than the circuit voltage, and the restriction on the maximum allowable circuit voltage is reduced in selecting the first varistor V1 or the second varistor V2. Therefore, the selection range of these varistors can be expanded.

  Further, the overvoltage generated by shutting off the main switch 101 is absorbed stepwise by using the first varistor V1 and the second varistor V2, so that the main switch 101 has a voltage higher than the maximum voltage limit of the first varistor V1. Also, if the rated voltage is high, the rated voltage does not need to be higher than the maximum limit voltage of the second varistor V2, and an over-specification of the main switch 101 can be avoided.

  As the first varistor V1, the overvoltage generated by turning off the first varistor V1 is absorbed by the second varistor V2. Therefore, if the overvoltage generated by turning off the main switch 101 can be absorbed, the voltage characteristics are relatively high. May be low.

  The second varistor V2 only needs to have a voltage lower than the rated voltage of the main switch 101 when the cutoff current I2 generated by turning off the first auxiliary switch S1 flows. It need not be lower than the voltage.

  As described above, according to the above-described shutoff device 100, the selection range of the main switch 101, the first varistor V1, and the second varistor V2 can be widened, and the rated voltage of the main switch 101 can be reduced. This prevents over-specification of the switch.

  Further, the discharge current generated by turning on the first auxiliary switch S1 and the second auxiliary switch S2 is consumed by the resistor 32 included in the overcurrent suppression circuit 30, so that the first auxiliary switch S1 and the second auxiliary switch are consumed. When turning on S2, it is possible to prevent a rush current exceeding the rating from flowing into the main switch 101.

  Note that the present invention is not limited to the above embodiment.

  For example, the overvoltage suppression circuit 102 of the embodiment includes the first commutation circuit 10 and the second commutation circuit 20, but further includes a third commutation circuit parallel to these commutation circuits. May be. That is, the number of commutation circuits provided in the overvoltage suppression circuit 102 is not limited to two, and may be three or more.

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

  The main switch 101, the first auxiliary switch S1, and the second auxiliary switch S2 are not limited to semiconductor switches, but may be mechanical switches.

  Further, the overvoltage suppression circuit 102 does not necessarily need to include the overcurrent suppression circuit 30.

  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.

Reference Signs List 100 cut-off device 200 power supply 300 main circuit 101 main switch 102 overvoltage suppression circuit SW line switch 10 first commutation circuit S1 1 auxiliary switch V1 ... first varistor (first non-linear element)
20 second commutation circuit S2 second auxiliary switch V2 second varistor (second nonlinear element)
30 ... overcurrent suppression circuit 31 ... diode 32 ... resistor

Claims (6)

An overvoltage suppression circuit connected in parallel to a main switch of a main circuit that connects a power supply and a load,
A first auxiliary switch and a first nonlinear element provided in parallel with the main switch and provided in series with each other;
A second auxiliary switch and a second nonlinear element provided in parallel with the main switch, the first auxiliary switch, and the first nonlinear element, and provided in series with each other;
A voltage generated in the first nonlinear element when a predetermined reference current flows in the first nonlinear element is generated in the second nonlinear element when the predetermined reference current flows in the second nonlinear element. Overvoltage suppression circuit that is lower than the voltage.   When the main switch, the first auxiliary switch, and the second auxiliary switch are on, a voltage generated in the first nonlinear element by turning off the main switch is higher than a rated voltage of the main switch. The overvoltage suppression circuit according to claim 1, wherein the overvoltage suppression circuit is also low.   The voltage generated in the second nonlinear element by turning off the first auxiliary switch from the state where the main switch is off and the first auxiliary switch and the second auxiliary switch are on, 3. The overvoltage suppression circuit according to claim 1, wherein the overvoltage suppression circuit is lower than a rated voltage of the main switch.   The current according to any one of claims 1 to 3, wherein a current flowing through the second nonlinear element due to a voltage applied from the power supply is smaller than a current flowing through the first nonlinear element due to a voltage applied from the power supply. Overvoltage suppression circuit. A diode connected in series to a positive side of the first auxiliary switch and the second auxiliary switch, and a forward direction of which is directed to the first auxiliary switch and the second auxiliary switch;
5. The overvoltage suppression circuit according to claim 1, further comprising: a resistor connected in parallel to the diode. 6. A main switch provided in a main circuit for connecting a power supply and a load,
An overvoltage suppression circuit connected in parallel to the main switch,
The overvoltage suppression circuit,
A first auxiliary switch and a first nonlinear element provided in parallel with the main switch and provided in series with each other;
A second auxiliary switch and a second nonlinear element provided in parallel with the main switch, the first auxiliary switch, and the first nonlinear element, and provided in series with each other;
A voltage generated in the first nonlinear element when a predetermined reference current flows in the first nonlinear element is generated in the second nonlinear element when the predetermined reference current flows in the second nonlinear element. A cut-off device that is lower than the voltage.