JP7101334B2 - Snubber circuit - Google Patents

Description

The present invention relates to a snubber circuit.

In a power supply device such as a DC-DC converter, a snubber circuit is provided in order to protect the switching element itself and other circuit elements from a surge voltage generated when the switching element is switched or a short circuit accident occurs.

As a conventional snubber circuit, for example, as disclosed in Patent Document 1, a circuit in which resistors and capacitors connected in series with each other are provided in parallel with a switching element is known. In this snubber circuit, the energy of the surge voltage is stored in the capacitor and then consumed as heat in the resistance element.

Japanese Unexamined Patent Publication No. 01-202161

In the above-mentioned conventional snubber circuit, when an excessive surge voltage is generated due to an unexpected short circuit accident or the like, an overvoltage exceeding the rated voltage may be applied to the capacitor, which may cause an abnormality in the snubber circuit.

The present invention has been made in view of the above problems, and its main object is to provide a snubber circuit having excellent durability against surge voltage.

That is, the snubber circuit according to the present invention is a snubber circuit for absorbing the surge voltage generated at the turn-off of the main switching element that controls the supply of current from the DC power supply to the load, and is connected in parallel to the main switching element. A sub-switching element and a sub-capacitor having a main capacitor and a surge energy consuming circuit connected in parallel to the main capacitor, the surge energy consuming circuit being connected in parallel to the main capacitor and connected in series with each other, and the sub-capacitor. It includes an auxiliary switching element and a resistance element that are connected in parallel to the capacitor and connected in series with each other. When the voltage of the main capacitor exceeds a predetermined threshold value, the sub-switching element is turned on and the auxiliary switching is performed. The first state in which the element is off and the second state in which the sub-switching element is off and the auxiliary switching element is on are alternately switched.

In such a snubber circuit, when the voltage of the main capacitor exceeds a predetermined threshold value, the energy of the surge voltage accumulated in the main capacitor in the first state is distributed to the sub-capacitor, and then in the second state. The energy of the surge voltage accumulated in the auxiliary capacitor can be consumed by the resistance element. By alternately switching between the first state and the second state, the energy of the surge voltage accumulated in the main capacitor can be transferred to the resistance element one after another like a bucket relay and consumed in this resistance element. can. Therefore, even if an excessive surge voltage is generated due to an unexpected short-circuit accident or the like, it is possible to prevent an overvoltage exceeding the rated voltage from being applied to the main capacitor, and the durability of the snubber circuit against the surge voltage can be improved. Can be enhanced.
Further, since the energy of the surge voltage can be consumed in the resistance element while being stored in the main capacitor, it is not necessary to increase the size of the main capacitor, and the snubber circuit itself can be miniaturized.

In the snubber circuit, it is preferable that the sub-switching element and the auxiliary switching element are semiconductor switches.
In such a case, the switching speed of the sub-switching element and the auxiliary switching element can be increased as compared with the case of a mechanical switch, so that the first state and the second state can be switched at a higher speed. The energy of the surge voltage accumulated in the main capacitor can be quickly consumed. This makes it possible to more reliably prevent the main capacitor from becoming overvoltage.

The snubber circuit also preferably has the surge energy consumption circuit in the first state at the time of turn-off of the main switching element.
In such a case, the voltage applied to the main switching element can be borne by dividing the voltage between the sub-capacitor and the sub-switching element, so that the required withstand voltage of each switching element can be reduced and the size can be further reduced. ..

The snubber circuit also includes a plurality of the surge energy consuming circuits connected in parallel to the main capacitor, and when the voltage of the main capacitor exceeds a predetermined threshold value, each of the plurality of surge energy consuming circuits is provided. It is preferable that the sub-switching element is configured to operate in an interleaved manner.
In such a case, the switching frequency of the sub-switching element and the auxiliary switching element in each surge energy consuming circuit can be reduced as compared with the one provided with only one surge energy consuming circuit. Also, compared to the one equipped with only one surge energy consumption circuit, the peak of the voltage applied to the main switch becomes smaller due to interleaving, so each surge energy consumption circuit is proportional to the difference in voltage between the main capacitor and the sub capacitor. The current flowing through the sub-switching element and the auxiliary switching element in the above can be reduced.

According to the present invention configured as described above, it is possible to provide a snubber circuit having excellent durability against surge voltage.

It is a schematic diagram which shows the structure of the snubber circuit of this embodiment. It is a time chart explaining the basic surge voltage absorption operation of the snubber circuit of the same embodiment. It is a figure explaining the surge voltage absorption operation of the snubber circuit of the same embodiment. It is a figure explaining the surge voltage absorption operation of the snubber circuit of the same embodiment. It is a schematic diagram which shows the structure of the snubber circuit of another embodiment. It is a figure explaining the surge voltage absorption operation of the snubber circuit of another embodiment. It is a figure explaining the surge voltage absorption operation of the snubber circuit of another embodiment. It is a figure explaining the surge voltage absorption operation of the snubber circuit of another embodiment.

Hereinafter, an embodiment of the snubber circuit according to the present invention will be described with reference to the drawings.

As shown in FIG. 1, the snubber circuit 100 of the present embodiment is connected in parallel to a main switching element S provided in a main circuit such as a power conversion circuit (not shown), and occurs when the main switching element S is turned off or the like. This is to protect the main switching element S and peripheral circuit elements from surge voltage.
A coil L and a resistance element R are connected in series to a main circuit (not shown), and a current flows through the coil L and the resistance element R of the main circuit before the main switching element S is turned off.

Specifically, this snubber circuit 100 includes a main capacitor 1 connected in parallel to a switching element and a surge energy consumption circuit 2 connected in parallel to the main capacitor 1. The surge energy consumption circuit 2 has a sub-switching element 211 and a sub-capacitor 212 connected in parallel to the main capacitor 1 and connected in series to each other, and an auxiliary switching element 221 and a resistance element connected in parallel to the sub-capacitor 212 and connected in series to each other. It is equipped with 222.

The main capacitor 1 and the sub-capacitor 212 are for absorbing the energy of the surge voltage, and specifically, for example, a ceramic capacitor or the like.

The sub-switching element 211 switches on / off the current flowing through the sub-capacitor 212. The auxiliary switching element 221 switches on / off the current flowing through the resistance element 222. Both the sub-switching element 211 and the auxiliary switching element 221 of the present embodiment are semiconductor switches, for example, MOSFETs and the like.

The resistance element 222 is for consuming the energy of the surge voltage, and has a resistance value of V ₁ / _Im [Ω] or less. Here, V ₁ is a threshold value set with respect to the voltage value applied to the main capacitor 1 described later, and _Im is the current value flowing through the main circuit.

The snubber circuit 100 further includes a control circuit 3 for controlling the on / off of the sub-switching element 211 and the auxiliary switching element 221. The control circuit 3 is configured to detect the voltage values applied to the main capacitor 1 and the sub-capacitor 212, and to switch on / off the sub-switching element 211 and the auxiliary switching element 221 based on the detected voltage values. ing.

In the snubber circuit 100 of the present embodiment, the control circuit 3 controls the on / off of the sub-switching element 211 and the auxiliary switching element 221 so that the surge energy consumption circuit 2 has the sub-switching element 211 turned on and the sub-switching element 211 is turned on. The first state in which the auxiliary switching element 221 is off and the second state in which the auxiliary switching element 211 is off and the auxiliary switching element 221 is on are alternately switched.

Specifically, the control circuit 3 is limited to the case where the voltage value applied to the main capacitor ₁ is larger than the predetermined threshold value V1 and the voltage value applied to the sub _- capacitor 212 is larger than the predetermined threshold value V2. , The surge energy consumption circuit 2 is set to the second state, and in other cases, the surge energy consumption circuit 2 is set to the first state. Here, the threshold value V ₁ is set to be larger than the threshold value V ₂ .

Next, the surge voltage absorption operation of the snubber circuit 100 of the present embodiment when a short-circuit accident occurs in the main circuit will be described with reference to FIGS. 2 to 4. In the following description, the surge energy consumption circuit 2 is in the first state immediately before the short circuit accident occurs.

A surge voltage is generated in the main circuit due to the occurrence of a short circuit accident or the like. When the current value _Im of the current flowing through the main circuit exceeds the set value, the overcurrent protection circuit (not shown) turns off the main switching element S. Then, as shown in FIGS. 2 and 3, the energy of the surge voltage is accumulated in the main capacitor 1 and the sub- _capacitor 212, and the voltage value VC1 applied to the main capacitor 1 and the voltage value _VC2 applied to the sub-capacitor 212. Both rise above the threshold V ₂ .

As shown in FIGS. 2 and 4, when the voltage value VC1 applied to the main _{capacitor 1} (and the voltage value _VC2 applied to the sub-capacitor 212) continues to rise and exceeds the threshold value V1, the control circuit 3 Turns off the sub-switching element 211 and turns on the auxiliary switching element 221 to switch the surge energy consumption circuit 2 to the second state. Then, the auxiliary capacitor 212 discharges the accumulated electric charge, and a current flows through the resistance element 222. As a result, the energy of the surge voltage accumulated in the auxiliary capacitor 212 is consumed in the resistance element 222. _The voltage value _VC2 of the auxiliary capacitor 212 drops to the threshold value V2 due to the discharge. Here, the time t ₁ required for the voltage value _VC2 of the sub _- capacitor 212 to drop from the threshold value V1 to the threshold value V2 due to the discharge is expressed by the following equation ( ₁ ). In the equation (1), _RA is the resistance value of the resistance element 222, and C ₂ is the capacitance of the sub-capacitor 212.

During this period, a charge of Im × _{t 1} [q] flows into the main capacitor 1, and the voltage value VC1 of the main _capacitor 1 is expressed by the following equation (2).

When the sub-capacitor 212 continues to discharge and its voltage value _VC2 becomes less than V ₂ , the control circuit 3 turns on the sub-switching element 211 and turns off the auxiliary switching element 221 as shown in FIGS. 2 and 3. Then, the surge energy consumption circuit 2 is switched to the first state again. Then, the electric charge accumulated in the main capacitor 1 flows into the sub-capacitor 212, and the voltage value _VC1 of the main capacitor 1 and the voltage value _VC2 of the sub-capacitor 212 become equal and are expressed by the following equation (3). .. Here, C ₁ is the capacitance of the main capacitor 1.

After that, when the voltage value _VC1 of the main capacitor ₁ and the voltage value _VC2 of the sub-capacitor 212 are boosted and exceed the threshold value V1, the control circuit 3 switches the surge energy consumption circuit 2 to the second state again, and the above operation is performed. repeat.

As described above, a plurality of cycles are repeated with one cycle being the period from when the voltage value VC1 of the main _{capacitor 1} exceeds the threshold value V1 to when the voltage value VC1 exceeds the threshold value V1 again after stepping down. The energy E consumed by the resistance element 222 during this one cycle is represented by the following equation (4).

Then, when the current value _Im of the current flowing through the main circuit becomes equal to or less than a predetermined value, the snubber circuit 100 is stopped.

<Effect of this embodiment>
According to the snubber circuit 100 of the present embodiment configured in this way, when the voltage of the main capacitor ₁ exceeds the threshold value V1, the energy of the surge voltage accumulated in the main capacitor 1 in the first state is used as the sub-capacitor 212. Then, in the second state, the energy of the surge voltage accumulated in the auxiliary capacitor 212 can be consumed by the resistance element 222. Then, by alternately switching between the first state and the second state, the energy of the surge voltage accumulated in the main capacitor 1 is transferred to the resistance element 222 one after another like a bucket relay and consumed in the resistance element 222. can do. Therefore, even if an excessive surge voltage is generated due to an unexpected short-circuit accident or the like, it is possible to prevent an overvoltage exceeding the rated voltage from being applied to the main capacitor 1, and the durability of the snubber circuit 100 against the surge voltage can be prevented. It can enhance the sex.
Further, since the surge voltage energy can be consumed in the resistance element 222 while the surge voltage energy is stored in the main capacitor 1, it is not necessary to increase the size of the main capacitor 1, and the snubber circuit 100 itself can be miniaturized.

Further, since the surge energy consumption circuit 2 is in the first state at the time of turn-off of the main switching element S, the voltage applied to the main switching element S can be shared by the sub-capacitor 212 and the sub-switching element 211, respectively. The required withstand voltage of the switching element can be reduced, and the size can be further reduced.

Further, since the sub-switching element 211 and the auxiliary switching element 221 are semiconductor switches, the switching speed of the sub-switching element 211 and the auxiliary switching element 221 can be increased, and the first state and the second state can be switched at high speed. .. As a result, the energy of the surge voltage accumulated in the main capacitor 1 can be quickly consumed.

The present invention is not limited to the above embodiment.

In the description of the surge voltage absorption operation of the snubber circuit 100 described above, the surge energy consumption circuit 2 was in the first state immediately before the short circuit accident occurred, but the surge energy consumption circuit 2 is not limited to this and may be in the second state.

The snubber circuit 100 of another embodiment may include n surge energy consuming circuits 2 (where n is a natural number of 2 or more) connected in parallel to the main capacitor 1. For example, as shown in FIG. 5, two surge energy consuming circuits 2a and 2b having the same configuration connected in parallel to the main capacitor 1 may be provided.

In the snubber circuit 100 of this embodiment, the control circuit 3 detects the voltage value of the main capacitor 1 and turns on / off the plurality of sub-switching elements 211 and the plurality of auxiliary switching elements 221 based on the detected voltage value. It is configured to control.

Specifically, in this snubber circuit 100, when the voltage value of the main capacitor 1 exceeds a predetermined value, the respective sub-switching elements 211 of the first surge energy consumption circuit 2a and the second surge energy consumption circuit 2b operate in an interleave operation. It is configured to do. That is, the cycle in which the second state is switched to the first state in the first surge energy consumption circuit 2a and the cycle in which the second state is switched to the first state in the second surge energy consumption circuit 2b are 360 / n ° (that is, that is). Here, it is configured to shift by 180 °).

The surge voltage absorption operation when a short-circuit accident occurs in the main circuit of the snubber circuit 100 of this embodiment will be described with reference to FIGS. 6 to 8. Here, as shown in FIG. 6, both the first surge energy consumption circuit 2a and the second surge energy consumption circuit 2b are in the second state immediately before the short circuit accident occurs.

When a surge voltage is generated in the main circuit due to a short circuit accident or the like and the current value _Im of the current flowing through the main circuit exceeds the set value, an overcurrent protection circuit (not shown) turns off the main switching element S. Then, as shown in FIG. 6, the energy of the surge voltage is accumulated in the main capacitor 1, and the voltage value of the main capacitor 1 rises.

When the voltage value of the main capacitor ₁ exceeds a predetermined threshold value V3, the first surge energy consumption circuit 2a switches from the second state to the first state as shown in FIG. 7. Then, the electric charge accumulated in the main capacitor 1 flows into the first sub-capacitor 212a, the voltage value of the main capacitor 1 drops, and then the voltage value of the main capacitor 1 rises again.

When the voltage value of the main capacitor ₁ exceeds the predetermined threshold value V3 again, as shown in FIG. 8, the first surge energy consumption circuit 2a switches from the first state to the second state, and the second surge energy consumption circuit 2b Switches from the second state to the first state. Then, the electric charge accumulated in the main capacitor 1 flows into the second sub-capacitor 212b, the voltage value of the main capacitor 1 drops, and the electric charge accumulated in the first sub-capacitor 212a is discharged to generate energy in the first resistance element 222a. Is consumed.

After that, the voltage value of the main capacitor 1 rises again, and the switching operation of the first surge energy consumption circuit 2a and the second surge energy consumption circuit 2b described above is repeated. As a result, the energy of the surge voltage is alternately consumed by the first resistance element 222a of the first surge energy consumption circuit 2a and the second resistance element 222b of the second surge energy consumption circuit 2b. When the current value _Im of the current flowing through the main circuit becomes equal to or less than a predetermined value, the snubber circuit 100 is stopped.

When a plurality of surge energy consuming circuits 2 are provided, the resistance element 222 for discharging may be configured to be shared by the plurality of surge energy consuming circuits 2. With such a case, the number of parts of the snubber circuit 100 can be reduced, and the mounting area can be reduced accordingly.

In the combination of the snubber circuit 100 according to the embodiment and the main switching element S to which the snubber circuit 100 is applied, a plurality of sets may be connected in series to each other, a plurality of sets may be connected in parallel to each other, or they may be combined. good.

In addition, the present invention is not limited to the above-described embodiment, and it goes without saying that various modifications can be made without departing from the spirit of the present invention.

100 ... Snubber circuit 1 ... Main capacitor 2 ... Surge energy consumption circuit 211 ... Sub switching element 212 ... Sub capacitor 221 ... Auxiliary switching element 222 ... Resistance element 3 ... Control circuit S: Main switching element

Claims (4)

It is a snubber circuit for absorbing the surge voltage generated at the turn-off of the main switching element that controls the supply of current from the DC power supply to the load.
The main capacitor connected in parallel to the main switching element,
It is equipped with a surge energy consumption circuit connected in parallel to the main capacitor.
The surge energy consumption circuit
Sub-switching elements and sub-capacitors connected in parallel to the main capacitor and connected in series with each other,
It includes an auxiliary switching element and a resistance element that are connected in parallel to the sub-capacitor and connected in series with each other.
When the voltage of the main capacitor exceeds a predetermined threshold value, the first state in which the sub-switching element is on and the auxiliary switching element is off, and the sub-switching element is off and the auxiliary switching element is off. A snubber circuit configured to switch alternately with the second state in which is on. The snubber circuit according to claim 1, wherein the sub-switching element and the auxiliary switching element are semiconductor switches. The snubber circuit according to claim 1 or 2, wherein the surge energy consumption circuit is in the first state when the main switching element is turned off. It is equipped with a plurality of the surge energy consumption circuits connected in parallel to the main capacitor.
The invention according to any one of claims 1 to 3, wherein each of the sub-switching elements of the plurality of surge energy consuming circuits is configured to perform interleave operation when the voltage of the main capacitor exceeds a predetermined threshold value. Snubber circuit.

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