JP7095711B2 - Switching power supply - Google Patents

Description

The techniques disclosed herein relate to switching power supplies with snubber circuits.

In a switching power supply device, LCR resonance (ringing) may occur during switching of a switching element, and electromagnetic noise may be radiated. As shown in the example of Non-Patent Document 1, there is known a technique of consuming ringing energy and suppressing electromagnetic noise by inserting a snubber circuit between a high power line and a low power line.

Kenichi Yatsugi, Katsuya Nomura, Yoshiyuki Hattori, “Analytical technique for designing an RC snubber circuit for ringing suppression in a phase-leg configuration”, IEEE TRANSACTIONS ON POWER ELECTRONICS, 33, 4736 (2018)

In a snubber circuit as shown in the example of Non-Patent Document 1, a snubber capacitor is arranged on a connection path between a high power supply line and a low power supply line. If this snubber capacitor breaks down, the high power line and the low power line will be short-circuited.

One embodiment of the switching power supply disclosed herein comprises a main circuit and a snubber circuit. The main circuit includes a switching element. The snubber circuit includes a closed circuit in which a resistance portion, a capacitance portion, and a coupling portion are connected in series. The snubber circuit is isolated from the main circuit. The coupling portion is magnetically or electrically coupled to the first conductive wire provided in the main circuit.

A snubber circuit is coupled to the first conductive wire provided in the main circuit. Therefore, the ringing energy generated from the switching element of the main circuit can be consumed by the coupled snubber circuit. Further, since the energy is consumed by coupling, it is not necessary to arrange the capacitance portion on the connection path between the high power supply line and the low power supply line. It is possible to avoid the situation where a short circuit occurs due to dielectric breakdown of the capacitive part.

The first conductive wire may include at least a part of the first plane portion. The coupling portion may be a conductive wire provided with a second plane portion. The second plane portion may be insulated from the first plane portion and may be arranged substantially in parallel. Details of the effect will be described in Examples.

When the loss rate of the main circuit is γ ₁ and the loss rate of the snubber circuit is γ ₂ , the magnetic coupling constant κ between the coupling portion and the first conductive wire is κ> (γ ₁ − γ ₂ ) / 2. A relationship may be established. Details of the effect will be described in Examples.

The coupling portion may be a capacitor that connects the snubber circuit and the first conductive wire.

The main circuit may include a control unit in which a switching element is arranged and a smoothing unit in which a smoothing capacitor is arranged. The first conductive wire may be a bus bar connecting between the control unit and the smoothing portion, or a bus bar connecting between the front sliding portion and the external load.

The main circuit may include a conductive plate connected to the switching element, a switching element, and a resin portion covering the connection portion between the switching element and the conductive plate. The first conductive wire may be a region of the conductive plate covered with the resin portion. Details of the effect will be described in Examples.

It is a schematic circuit diagram of the electric system 1. It is a schematic block diagram of a part of a switching power supply 2. It is a schematic circuit diagram of the switching power supply 102 of the comparative example. It is a schematic sectional drawing of a part of a power module 30. It is a schematic block diagram of a part of a switching power supply 2b.

(Configuration of electric system 1)
FIG. 1 shows a schematic circuit diagram of an in-vehicle electric system 1. The electric system 1 includes a switching power supply 2, an inverter 3, a motor 4, and a controller 5. The switching power supply 2 boosts the voltage of the battery 11 and applies it to the inverter 3 which is an external load. The inverter 3 converts direct current into three-phase alternating current and applies it to the motor 4. The controller 5 controls the operation of the switching power supply 2 and the inverter 3.

(Configuration of switching power supply 2)
The switching power supply 2 includes a battery 11, a control unit 12, a snubber circuit 13, a smoothing unit 14, and bus bars 21 and 22. The main circuit is composed of the control unit 12, the smoothing unit 14, and the bus bars 21 and 22. The bus bars 21 and 22 are copper plates. The control unit 12 includes switching elements SW1 and SW2 connected in series between the bus bars 21 and 22. The positive terminal of the battery 11 is connected to the intermediate connection node of the switching elements SW1 and SW2 via the inductor L1. The negative terminal of the battery 11 is connected to the bus bar 22. The bus bar 22 is connected to the reference voltage portion GND. The bus bar 22 is a low-level power line, and the bus bar 21 is a high-level power line. Further, the control unit 12 has a parasitic inductance L _p3 .

The output terminal of the control unit 12 is connected to the smoothing unit 14 and the inverter 3 via the bus bars 21 and 22. The bus bar 21 has a parasitic inductance L _p1 . The smoothing section 14 includes a capacitor C1 and an equivalent series resistance R _ESR connected in series between the bus bars 21 and 22. The smoothing unit 14 smoothes the surge voltage and the like generated when the switching elements SW1 and SW2 are turned on / off.

The snubber circuit 13 is a closed circuit in which a resistance portion R _snb , a capacitance portion C _snb , and a parasitic inductance L _p2 are connected in series by a conductive plate 23. The snubber circuit 13 is insulated from the main circuit (control unit 12, smoothing unit 14, bus bar 21 and 22). Further, the snubber circuit 13 is connected to the reference voltage portion GND. The conductive plate 23 has a parasitic inductance L _p2 . The parasitic inductance L _p2 is magnetically coupled to the parasitic inductance L _p1 of the bus bar 21.

FIG. 2 shows a schematic configuration diagram of a part of the electric system 1. The electric system 1 has a configuration in which a control unit 12, a smoothing unit 14, and an inverter 3 are connected by a bus bar 21. Further, the bus bar 21 has a configuration in which the snubber circuit 13 is arranged in the vicinity of the region connecting between the control unit 12 and the smoothing unit 14. Although the bus bar 21 is briefly described as one component in FIG. 2, it may actually be composed of a plurality of components. The bus bar 21 includes a first plane portion P1 parallel to the xy plane. An insulating sheet IS is arranged on the surface of the first flat surface portion P1. The insulating sheet IS may be wound around the bus bar 21. A snubber circuit 13 is arranged on the first flat surface portion P1 via an insulating sheet IS. The snubber circuit 13 is insulated from the main circuit by the insulating sheet IS.

The snubber circuit 13 is formed by processing the conductive plate 23 into an annular shape. The conductive plate 23 is cut by slits S1 and S2 extending in the y direction. Further, the capacitance portion C _snb and the resistance portion R _snb are connected so as to straddle the slits S1 and S2. Further, the conductive plate 23 includes a second plane portion P2 parallel to the xy plane in a region facing the bus bar 21. The second plane portion P2 is arranged substantially parallel to the first plane portion P1. As a result, as described above, the snubber circuit 13 and the main circuit are magnetically coupled by the parasitic inductances L _p1 and L _p2 . A magnetic material for increasing the magnetic coupling constant κ between the snubber circuit 13 and the main circuit is not arranged. The magnetic coupling constant κ can be adjusted by the area where the first plane portion P1 and the second plane portion P2 overlap and the distance between the first plane portion P1 and the second plane portion P2.

ここで、κは結合定数、ω_１は主回路の共振周波数、ω_２はスナバ回路の共振周波数、γ_１は主回路の損失率、γ_２はスナバ回路の損失率である。損失率γ_１およびγ_２は、下式２および式３で表される。

上式１は、下式４に書き換えられる。

ここでω_０は、ω_１＝ω_２としたときの共振周波数である。また、β、χ、Ａ_１およびＡ_２は、下式で表される。

(Magnetic coupling constant)
The magnetic coupling constant κ will be described. The resonance mode of the snubber circuit 13 is a ₁ , and the resonance mode of the main circuit (control unit 12, smoothing unit 14, bus bars 21 and 22) is a ₂ . In this case, the behavior of the entire system is expressed by the following equation 1.

Here, κ is the coupling constant, ω ₁ is the resonance frequency of the main circuit, ω ₂ is the resonance frequency of the snubber circuit, γ ₁ is the loss rate of the main circuit, and γ ₂ is the loss rate of the snubber circuit. The loss rates γ ₁ and γ ₂ are represented by the following equations 2 and 3.

The above equation 1 is rewritten into the following equation 4.

Here, ω ₀ is the resonance frequency when ω ₁ = ω ₂ . Further, β, χ, A ₁ and A ₂ are expressed by the following equations.

従って、スナバ回路１３に効率よくエネルギーを伝達する条件は、κ＞βである。すなわち、主回路の損失率がγ_１であり、スナバ回路１３の損失率がγ_２である場合に、磁気結合定数κに、κ＞（γ_１－γ_２）／２の関係が成立すればよい。 When the eigenvalues of the 2 × 2 matrix of the first term on the right side of the above equation 4 are real numbers, the resonance energies of the main circuit and the snubber circuit 13 become equal. That is, the energy transmitted to the snubber circuit 13 is maximized. The eigenvalue is expressed by the following formula. Here, ω is the resonance frequency when ω ₁ = ω ₂ .

Therefore, the condition for efficiently transmitting energy to the snubber circuit 13 is κ> β. That is, when the loss rate of the main circuit is γ ₁ and the loss rate of the snubber circuit 13 is γ ₂ , if the relationship of κ> (γ ₁ − γ ₂ ) / 2 is established for the magnetic coupling constant κ. good.

(effect)
FIG. 3 shows a switching power supply 102 of a comparative example. In the switching power supply 102 of the comparative example, the snubber circuit 113 is connected between the bus bar 21 (high power line) and the bus bar 22 (low power line). The snubber circuit 113 has a configuration in which a resistance portion R ₁₀₀ , a capacitance portion C ₁₀₀ , and a parasitic inductance L ₁₀₀ are connected in series. The snubber circuit 113 consumes ringing energy and can suppress electromagnetic noise. However, the capacitance unit C ₁₀₀ is arranged on the connection path between the bus bars 21 and 22. When the capacitance portion C ₁₀₀ is subjected to dielectric breakdown, the bus bars 21 and 22 are short-circuited. On the other hand, the switching power supply 2 (FIG. 1) according to the present embodiment has a structure in which the snubber circuit 13 is magnetically coupled to the bus bar 21 included in the main circuit. The ringing energy generated from the switching elements SW1 and SW2 of the main circuit can be consumed by the magnetically coupled snubber circuit 13. Since the snubber circuit 13 consumes energy by magnetic coupling, it is not necessary to arrange the capacitance unit C _snb on the connection path between the bus bars 21 and 22. It is possible to avoid the situation where a short circuit occurs due to dielectric breakdown of the capacitance portion C _snb .

When a snubber circuit is magnetically coupled to a main circuit using a magnetic material, magnetic saturation becomes a problem. This is because a large current is used in the in-vehicle electric system. Also, because the switching frequency is relatively low, the current flowing through the parasitic inductance can be regarded as direct current. In the switching power supply 2 (FIG. 2) according to the present embodiment, the second plane portion P2 of the snubber circuit 13 and the first plane portion P1 of the bus bar 21 are arranged in parallel and close to each other. This makes it possible to magnetically couple the snubber circuit 13 to the main circuit without using a magnetic material. The magnetic saturation phenomenon can be suppressed.

In the second embodiment, an embodiment in which the snubber circuit according to the present specification is incorporated in a power module will be described. FIG. 4 shows a schematic cross-sectional view of a part of the power module 30. The power module 30 is a component mounted on the control unit 12 described above. The power module 30 includes a heat sink 31, lead wires 32 and 36, solder layers 33 and 35, a power element 34, a snubber circuit 13, and a resin layer 37. The structure of the snubber circuit 13 has already been described in the first embodiment.

The power element 34 is formed in a substantially rectangular parallelepiped shape, and accommodates a plurality of the above-mentioned switching elements SW1 and SW2 and diodes. A source electrode, a drain electrode, a gate electrode, and the like (not shown) are provided on the surface of the power element 34. One end of the lead wire 32 is connected to the gate electrode by a solder layer 33. The other end of the lead wire 32 is connected to the controller 5 described above. Further, one end of the lead wire 36 is connected to each of the source electrode and the drain electrode by a solder layer 35. The other end of the lead wire 36 is connected to the bus bars 21 and 22 described above. FIG. 4 shows only the lead wire 36 connected to the drain electrode for simplification.

The lead wire 36 includes a first plane portion P1a parallel to the xy plane. A snubber circuit 13 is arranged on the surface of the first flat surface portion P1a via an insulating sheet IS. The conductive plate 23 included in the snubber circuit 13 includes a second flat surface portion P2a parallel to the xy plane in a region facing the lead wire 36. The second plane portion P2a and the first plane portion P1a are arranged substantially in parallel. As a result, the snubber circuit 13 and the lead wire 36 are magnetically coupled.

The resin layer 37 is formed by curing the filled liquid resin (eg, epoxy resin). The resin layer 37 is formed so as to cover the ends of the power element 34, the snubber circuit 13, and the lead wires 32 and 36. Specifically, the vicinity of the connection portion between the lead wire 36 and the power element 34 is covered with the resin layer 37. The snubber circuit 13 is arranged in the region covered with the resin layer 37.

(effect)
The snubber circuit 13 can be coupled to the main circuit via the lead wire 36 inside the power module 30. Since the snubber circuit 13 can be built in the power module 30, the switching power supply 2 can be miniaturized.

FIG. 5 shows a schematic configuration diagram of a part of the switching power supply 2b according to the third embodiment. The switching power supply 2b of the third embodiment is different from the switching power supply 2 of the first embodiment (FIG. 2) in that it includes a coupling capacitor C _c . The same reference numerals are given to the parts common to both, and the description thereof will be omitted.

The bus bar 21 and the conductive plate 23 of the snubber circuit 13 are electrically coupled to each other via a coupling capacitor C _c . Further, the snubber circuit 13 is not connected to the reference voltage portion GND and is in a floating state.

(effect)
The ringing energy generated from the switching elements SW1 and SW2 in the control unit 12 can be consumed by the snubber circuit 13 electrically coupled by the coupling capacitor C _c . Further, since the snubber circuit 13 is in a floating state, it is possible to avoid the occurrence of a short circuit even when the capacitance portion C _snb is subjected to dielectric breakdown.

Although specific examples of the present invention have been described in detail above, these are merely examples and do not limit the scope of claims. The techniques described in the claims include various modifications and modifications of the specific examples exemplified above. Further, the technical elements described in the present specification or the drawings exhibit technical usefulness alone or in various combinations, and are not limited to the combinations described in the claims at the time of filing. In addition, the techniques exemplified in the present specification or the drawings can achieve a plurality of purposes at the same time, and achieving one of the purposes itself has technical usefulness.

(Modification example)
The snubber circuit 13 may be arranged at any position as long as it is on the path of the bus bar 21 provided in the main circuit. That is, the arrangement position of the snubber circuit 13 is not limited to the region (FIG. 2) of the bus bar 21 connecting between the control unit 12 and the smoothing unit 14. For example, the snubber circuit 13 may be arranged in a region of the bus bar 21 that connects the smoothing portion 14 and the inverter 3.

The snubber circuit 13 (FIG. 1) of the first embodiment may be in a floating state not connected to the reference voltage portion GND.

The switching power supply 2 of the present specification is not limited to an in-vehicle system, and can be applied to various uses.

The control unit 12, the smoothing unit 14, and the bus bars 21 and 22 are examples of the main circuit. The conductive plate 23 and the coupling capacitor C _c are examples of the coupling portion. The bus bar 21 is an example of the first conductive wire. The lead wire 36 is an example of a conductive plate. The inverter 3 is an example of an external load.

1: Electric system 2: Switching power supply 11: Battery 12: Control unit 13: Snubber circuit 14: Smoothing unit 21 and 22: Bus bar 23: Conductive plate SW1 and SW2: Switching element L _p1 to L _p3 : Parasitic inductance R _snb : Resistance Part, C _snb : Capacity part

Claims (6)

A switching power supply device including a main circuit including a switching element and a snubber circuit including a closed circuit in which a resistance portion, a capacitance portion, and a coupling portion are connected in series.
The snubber circuit is isolated from the main circuit.
The coupling portion is a switching power supply device that is magnetically or electrically coupled to the first conductive wire included in the main circuit. The first conductive wire has at least a part of the first plane portion.
The joint portion is a conductive wire provided with a second plane portion, and is a conductive wire.
The switching power supply device according to claim 1, wherein the second flat surface portion is insulated from the first flat surface portion and arranged substantially in parallel. When the loss rate of the main circuit is γ ₁ and the loss rate of the snubber circuit is γ ₂ , the magnetic coupling constant κ between the coupling portion and the first conductive wire is κ> (γ ₁ − γ ₂ ). The switching power supply device according to claim 2, wherein the relationship of) / 2 is established. The coupling portion is a capacitor that connects the snubber circuit and the first conductive wire.
The switching power supply device according to claim 1. The main circuit includes a control unit in which the switching element is arranged and a smoothing unit in which a smoothing capacitor is arranged.
The first conductive wire is any one of claims 1 to 4, wherein the first conductive wire is a bus bar connecting between the control unit and the smoothing portion, or a bus bar connecting between the smoothing portion and an external load. The switching power supply according to. The main circuit is
A conductive plate connected to the switching element and
The switching element, and the resin portion that covers the connection portion between the switching element and the conductive plate,
Equipped with
The switching power supply device according to any one of claims 1 to 5, wherein the first conductive wire is a region of the conductive plate covered with the resin portion.

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