JP2020072586A - Snubber circuit and power conversion system - Google Patents

Abstract

To provide a snubber circuit capable of suppressing a ripple current and a power conversion system.SOLUTION: A snubber circuit 3 absorbs electric energy from a main circuit 2. The snubber circuit 3 includes a first capacitor C1, a second capacitor C2, an inductor L1, and a switching circuit 31. The first capacitor C1 and the second capacitor C2 store the electric energy absorbed from the main circuit 2. The inductor L1 regenerates the electric energy stored in the first capacitor C1 and the second capacitor C2 to the main circuit 2 or a load 5. The switching circuit 31 switches the supply source that supplies electric energy to the inductor L1 between the first capacitor C1 and the second capacitor C2 such that the direction of a current supplied from the first capacitor C1 to the inductor L1 is opposite to a direction of a current supplied from the second capacitor C2 to the inductor L1.SELECTED DRAWING: Figure 1

Description

  The present disclosure generally relates to a snubber circuit and a power conversion system, and more specifically, to a snubber circuit that suppresses a surge voltage and a power conversion system using the snubber circuit.

  Conventionally, there is a DC / DC converter (power conversion system) including a snubber circuit (for example, see Patent Document 1).

  The DC / DC converter of Patent Document 1 turns on a semiconductor switch in a snubber circuit in synchronization with the timing at which a secondary surge voltage of a transformer is generated, and loads the power stored in a snubber capacitor through a choke coil. Regenerate into.

JP, 2005-70716, A

  The snubber circuit described in Patent Document 1 cannot suppress the ripple current of the DC / DC converter.

  The present disclosure has been made in view of the above circumstances, and an object thereof is to provide a snubber circuit and a power conversion system that can suppress a ripple current.

  A snubber circuit according to one aspect of the present disclosure absorbs electrical energy from a main circuit. The snubber circuit includes a first capacitance component, a second capacitance component, an inductance component, and a switching circuit. The first capacitive component stores the electric energy absorbed from the main circuit. The second capacitance component stores the electric energy absorbed from the main circuit. The inductance component regenerates the electric energy stored in the first capacitance component and the second capacitance component to the main circuit or the load. The switching circuit is configured so that the direction of the current supplied from the first capacitance component to the inductance component and the direction of the current supplied from the second capacitance component to the inductance component are opposite to each other. A supply source for supplying electric energy to the inductance component is switched between the first capacitance component and the second capacitance component.

  A power conversion system according to an aspect of the present disclosure includes the snubber circuit and the main circuit.

  The present disclosure has an effect that the ripple current can be reduced.

FIG. 1 is a circuit diagram of a power conversion system including a snubber circuit according to an embodiment of the present disclosure. FIG. 2 is an operation explanatory diagram of the power conversion circuit in the above power conversion system. FIG. 3 is an operation explanatory diagram of the snubber circuit in the above power conversion system. FIG. 4 is an equivalent circuit of the power conversion system when the snubber circuit of the above is in the first operation mode. FIG. 5 is an equivalent circuit of the power conversion system when the snubber circuit of the above is in the second operation mode. FIG. 6 is an equivalent circuit of the power conversion system when the snubber circuit of the above is in the third operation mode. FIG. 7 is an equivalent circuit of the power conversion system when the snubber circuit of the above is in the fourth operation mode. FIG. 8A is an equivalent circuit of the power conversion circuit when the snubber circuit of the above is in the first mode and the second mode. FIG. 8B is an equivalent circuit of the power conversion circuit when the snubber circuit in the above is in the third mode and the fourth mode. FIG. 9A is an equivalent circuit of the snubber circuit when the above snubber circuit is in the first mode and the fourth mode. FIG. 9B is an equivalent circuit of the snubber circuit in the case where the snubber circuit in the above is in the second mode and the third mode. FIG. 10 is a circuit diagram of a power conversion system according to a first modified example of the present disclosure. FIG. 11 is a circuit diagram of a power conversion system according to a second modified example of the present disclosure.

  Each embodiment and modification described below are merely examples of the present disclosure, and the present disclosure is not limited to the embodiment and the modification. Other than this embodiment and modifications, various modifications can be made according to the design and the like as long as they do not depart from the technical idea of the present disclosure.

(1) Overview First, an overview of the snubber circuit 3 according to the present embodiment and a power conversion system 1 using the snubber circuit 3 will be described with reference to FIG.

  The power conversion system 1 includes a main circuit 2 and a snubber circuit 3. The main circuit 2 is a power conversion circuit 2 that converts electric power. Hereinafter, the main circuit 2 is also referred to as the power conversion circuit 2. The power conversion circuit 2 converts an AC voltage into a DC voltage. The snubber circuit 3 is a protection circuit for suppressing a surge voltage generated in the power conversion circuit 2. When the AC voltage is converted into the DC voltage in the power conversion circuit 2, resonance may occur due to the leakage inductance of the transformer 21 described later and the parasitic capacitance of the rectifier circuit 22 described later to generate a surge voltage. In the power conversion system 1 according to the present embodiment, such a surge voltage can be suppressed by the snubber circuit 3. The snubber circuit 3 corresponds to a sub circuit with respect to the main circuit 2.

  The main circuit 2 (power conversion circuit 2) is an AC / DC converter that converts AC power supplied from the power supply circuit 20 into DC power and outputs the DC power. The main circuit 2 includes a transformer 21 to which an AC voltage is input from the power supply circuit 20, a rectifier circuit 22 provided on the secondary side of the transformer 21, a smoothing filter (inductor L21) for smoothing the output voltage of the rectifier circuit 22, and And a smoothing capacitor (output capacitor Co). The load 5 is electrically connected across the output capacitor Co.

  The snubber circuit 3 absorbs electric energy from the main circuit 2. The snubber circuit 3 includes a first capacitance component (first capacitor C1), a second capacitance component (second capacitor C2), an inductance component (inductor L1), and a switching circuit 31. The first capacitance component (C1) stores the electric energy absorbed from the main circuit 2. The second capacitance component (C2) stores the electric energy absorbed from the main circuit 2. The inductance component (L1) regenerates the electric energy stored in the first capacitance component (C1) and the second capacitance component (C2) to the main circuit 2 or the load 5. In the switching circuit 31, the direction of the current supplied from the first capacitance component (C1) to the inductance component (L1) and the direction of the current supplied from the second capacitance component (C2) to the inductance component (L1) are mutually different. The supply source for supplying the electric energy to the inductance component (L1) is switched between the first capacitance component (C1) and the second capacitance component (C2) so as to be in the opposite direction.

  The electric energy absorbed from the main circuit 2 is supplied to the inductance component (L1) from the first capacitance component (C1) or the second capacitance component (C2). At this time, the direction of the current flowing through the inductance component (L1) is switched by the switching circuit 31. Therefore, the polarity of the voltage generated in the inductance component (L1) is switched, so that when the inductance component (L1) regenerates electric energy in the main circuit 2 or the load 5, a ripple current (second ripple current Ir2) flowing in the main circuit 2 is switched. The direction of) changes. Since the inductance component (L1) causes the ripple current (Ir2) to flow in the main circuit 2 so as to cancel the ripple current flowing in the main circuit 2, the ripple current flowing in the main circuit 2 can be suppressed.

(2) Configuration As shown in FIG. 1, the power conversion system 1 includes a power conversion circuit 2, a snubber circuit 3, and a control circuit 4.

(2.1) Power Converter Circuit The power converter circuit 2 includes a transformer 21, a rectifier circuit 22, a (second) inductor L21, and an output capacitor Co. The power conversion circuit 2 converts the AC power supplied from the power supply circuit 20 into DC power and outputs the DC power to the load 5. The power conversion circuit 2 further includes a pair of first terminals H11, H12 and a pair of second terminals H21, H22. However, the “terminal” here does not have to be a component for connecting an electric wire or the like, and may be, for example, a lead of an electronic component or a part of a conductor included in a circuit board.

  The transformer 21 is a high frequency insulating transformer having a primary winding L11 and a secondary winding L12 magnetically coupled to each other, and the primary winding L11 and the secondary winding L12 are electrically insulated. The primary winding L11 is electrically connected to the power supply circuit 20. The power supply circuit 20 is, for example, a DC / AC inverter circuit. The power supply circuit 20 converts a DC voltage into an AC voltage and applies it to the primary winding L11. The secondary winding L12 is electrically connected to the rectifier circuit 22 via the pair of first terminals H11 and H12. Specifically, one end of the secondary winding L12 is electrically connected to the first terminal H11, and the other end of the secondary winding L12 is electrically connected to the first terminal H12. By applying an AC voltage from the power supply circuit 20 to the primary winding L11 of the transformer 21, an AC voltage is generated across the secondary winding L12.

  The rectifier circuit 22 is electrically connected to the secondary winding L12 of the transformer 21 via the pair of first terminals H11 and H12. The pair of first terminals H11 and H12 function as a pair of input terminals of the rectifier circuit 22. Hereinafter, the voltage between the pair of first terminals H11 and H12 (AC voltage between both ends of the secondary winding L12) is referred to as the input voltage Vi.

  The rectifier circuit 22 is a full-wave rectifier circuit that full-wave rectifies the input voltage Vi. The rectifier circuit 22 generates a full-wave rectified voltage (bus voltage Vbus) of the input voltage Vi between the pair of second terminals H21 and H22. The pair of second terminals H21 and H22 function as a pair of output terminals of the rectifier circuit 22.

  In the present embodiment, the rectifier circuit 22 is a synchronous rectification type full-wave rectifier circuit having four switching elements Q11 to Q14 as rectifier elements. As an example, each of the switching elements Q11 to Q14 is composed of a depletion type n-channel MOSFET (Metal Oxide Semiconductor Field Effect Transistor). The switching elements Q11 to Q14 are full-bridge connected. A series circuit of switching elements Q11 and Q12 and a series circuit of switching elements Q13 and Q14 are electrically connected in parallel between the second terminal H21 on the high potential side and the second terminal H22 on the low potential side. There is. A connection point between the switching elements Q11 and Q12 is electrically connected to the first terminal H11, and a connection point between the switching elements Q13 and Q14 is electrically connected to the first terminal H12.

  Specifically, the switching element Q11 has a drain electrically connected to the second terminal H21 and a source electrically connected to the first terminal H11. The switching element Q12 has a drain electrically connected to the first terminal H11 and a source electrically connected to the second terminal H22. The switching element Q13 has a drain electrically connected to the second terminal H21 and a source electrically connected to the first terminal H12. The switching element Q14 has a drain electrically connected to the first terminal H12 and a source electrically connected to the second terminal H22.

  The switching elements Q11 to Q14 have parasitic diodes D11 to D14, respectively. Each of the parasitic diodes D11 to D14 is configured such that its anode is electrically connected to its source and its cathode is electrically connected to its drain.

  In the rectifier circuit 22, the switching elements Q11 to Q14 are turned on / off in synchronization with the phase of the input voltage Vi, so that the bus voltage Vbus obtained by full-wave rectifying the input voltage Vi is applied between the pair of second terminals H21 and H22. To generate. The on / off states of the switching elements Q11 to Q14 are individually controlled by the drive signals S11 to S14 from the control circuit 4, respectively.

  The output capacitor Co is a smoothing capacitor electrically connected between a pair of output terminals of the rectifier circuit 22 (between the pair of second terminals H21 and H22). Specifically, the output capacitor Co has a high-potential-side terminal electrically connected to the high-potential-side second terminal H21 via the inductor L21, and a low-potential-side terminal connected to the inductor L1 of the snubber circuit 3. Via, it is electrically connected to the second terminal H22 on the low potential side. The inductor L21 is a choke coil and functions as a smoothing filter that smoothes the bus voltage Vbus. Between both ends of the output capacitor Co, a DC output voltage Vo obtained by averaging the bus voltage Vbus between the second terminals H21 and H22 is generated. The load 5 is electrically connected between both ends of the output capacitor Co. The load 5 operates when the output voltage Vo is applied.

(2.2) Snubber circuit The snubber circuit 3 is electrically connected to the power conversion circuit 2. Specifically, the snubber circuit 3 is electrically connected to the pair of second terminals H21 and H22 which are the pair of output terminals of the rectifier circuit 22 in the power conversion circuit 2. That is, the power conversion circuit 2 has the pair of second terminals H21 and H22 to which the snubber circuit 3 is electrically connected.

  The snubber circuit 3 absorbs electric energy from the power conversion circuit 2 to clamp the voltage (bus voltage Vbus) between the pair of second terminals H21 and H22 so as not to exceed a predetermined clamp value. When the magnitude of the bus voltage Vbus exceeds the clamp value, the snubber circuit 3 extracts electric energy that exceeds the clamp value to clamp the upper limit value of the bus voltage Vbus to the clamp value.

  The snubber circuit 3 of the present embodiment causes the load 5 or the power conversion circuit 2 to regenerate the electric energy absorbed from the power conversion circuit 2. Thereby, the power loss due to the snubber circuit 3 can be suppressed. Further, the snubber circuit 3 has a second ripple in a phase opposite to the first ripple current Ir1 generated by the power conversion circuit 2 when the electric energy absorbed from the power conversion circuit 2 is regenerated by the load 5 or the power conversion circuit 2. A current Ir2 is generated. As a result, the first ripple current Ir1 and the second ripple current Ir2 are canceled out, the ripple current flowing through the power conversion circuit 2 is reduced, and the capacitance of the output capacitor Co can be reduced.

  The snubber circuit 3 includes a first capacitor C1 (first capacitance component), a second capacitor C2 (second capacitance component), a (first) inductor L1 (inductance component), a diode D3, a switching circuit 31, Is equipped with. The switching circuit 31 is configured to switch the direction of the current supplied from the first capacitor C1 or the second capacitor C2 to the inductor L1. The switching circuit 31 includes a first switching element Q1 and a second switching element Q2.

  A series circuit of a diode D3 and a first capacitor C1 is electrically connected between the pair of second terminals H21 and H22 of the power conversion circuit 2. The diode D3 has an anode electrically connected to the second terminal H21 on the high potential side and a cathode electrically connected to the second terminal H22 on the low potential side via the first capacitor C1.

  A series circuit of the first switching element Q1, the second capacitor C2, and the inductor L1 is electrically connected between both ends of the first capacitor C1. That is, the discharge path of the first capacitor C1 includes the first switching element Q1, the second capacitor C2, and the inductor L1.

  The first switching element Q1 is composed of a depletion type n-channel MOSFET. The first switching element Q1 has a drain electrically connected to the first capacitor C1 and a source electrically connected to the second capacitor C2.

  The inductor L1 has one end electrically connected to the second capacitor C2 and the other end electrically connected to the first capacitor C1. Further, one end of the inductor L1 (the connection point between the inductor L1 and the second capacitor C2) is electrically connected to the low potential side terminal of the output capacitor Co in the power conversion circuit 2. That is, the inductor L1 is electrically connected in series between the pair of second terminals H21 and H22 together with the inductor L21 and the output capacitor Co, and also serves as a smoothing filter in the power conversion circuit 2. The inductor L21 is a high potential side smoothing filter, while the inductor L1 is a low potential side smoothing filter. In the present embodiment, the inductor L1 and the inductor L21 have the same magnitude of inductance (for example, 500 μH), but may have different magnitudes of inductance.

  The second switching element Q2 is electrically connected between both ends of the second capacitor C2 together with the inductor L1. That is, the second switching element Q2 and the inductor L1 are included in the discharge path of the second capacitor C2.

  The second switching element Q2 is composed of a depletion type n-channel MOSFET. The second switching element Q2 has a drain electrically connected to one end of the second capacitor C2 (a connection point between the second capacitor C2 and the first switching element Q1), and a source of the second capacitor C2 via the inductor L1. It is electrically connected to the other end.

  The first switching element Q1 and the second switching element Q2 have parasitic diodes D1 and D2, respectively. Each of the parasitic diodes D1 and D2 has an anode electrically connected to the source and a cathode electrically connected to the drain.

  With the above configuration, if the magnitude of the voltage Vc1 across the first capacitor C1 is set to the clamp value, when the bus voltage Vbus exceeds the clamp value, the diode D3 is turned on (conducting state), and the current Id3 flows to the first capacitor C1. Flowing. Strictly speaking, the voltage obtained by adding the forward drop voltage of the diode D3 to the voltage Vc1 across the first capacitor C1 becomes the clamp value. However, since the forward drop voltage of the diode D3 is sufficiently smaller than the clamp value, the forward drop voltage of the diode D3 is zero, that is, the magnitude of the voltage Vc1 across the first capacitor C1 is the clamp value. As described below.

  The electric energy absorbed from the power conversion circuit 2 is stored in the first capacitor C1. A series circuit of the first switching element Q1, the second capacitor C2, and the inductor L1 is electrically connected between both ends of the first capacitor C1. Therefore, when the first switching element Q1 is turned on, a closed loop including the first capacitor C1, the first switching element Q1, the second capacitor C2, and the inductor L1 is formed. In this case, the first capacitor C1 is discharged, and a current flows from the first capacitor C1 to the first switching element Q1, the second capacitor C2, and the inductor L1 in this order. The second capacitor C2 is charged by this current. That is, in the snubber circuit 3, the electric energy absorbed from the power conversion circuit 2 is stored in the first capacitor C1 and the second capacitor C2. The voltage Vc2 across the second capacitor C2 is a voltage obtained by stepping down the voltage Vc1 across the first capacitor C1.

  A series circuit of the second switching element Q2 and the inductor L1 is electrically connected between both ends of the second capacitor C2. Therefore, when the second switching element Q2 is turned on, a closed loop including the second capacitor C2, the second switching element Q2, and the inductor L1 is formed. In this case, the second capacitor C2 is discharged, and a current flows from the second capacitor C2 to the second switching element Q2 and the inductor L1 in this order.

  That is, the direction in which the discharge current of the first capacitor C1 flows and the direction in which the discharge current of the second capacitor C2 flows in the inductor L1 are opposite to each other. The switching circuit 31 including the first switching element Q1 and the second switching element Q2 switches the direction of the current flowing through the inductor L1 by turning on / off the first switching element Q1 and the second switching element Q2. In the switching circuit 31, the first switching element Q1 and the second switching element Q2 are alternately turned on to periodically switch the direction of the current flowing through the inductor L1. On / off of the first switching element Q1 and the second switching element Q2 are individually controlled by drive signals S1 and S2 from the control circuit 4.

(2.4) Control Circuit The control circuit 4 is composed of a microcomputer having a processor and a memory. That is, the control circuit 4 is realized by a computer system having a processor and a memory. Then, the computer system functions as the control circuit 4 by the processor executing an appropriate program. The program may be pre-recorded in the memory, or may be provided through an electric communication line such as the Internet or in a non-transitory recording medium such as a memory card.

  The control circuit 4 is configured to control the power conversion circuit 2 and the snubber circuit 3. Specifically, the control circuit 4 outputs to the power conversion circuit 2 drive signals S11 to S14 for driving the switching elements Q11 to Q14, respectively. Further, the control circuit 4 outputs drive signals S1 and S2 to the snubber circuit 3, which drive the first switching element Q1 and the second switching element Q2, respectively.

  In the present embodiment, one control circuit 4 controls both the power conversion circuit 2 and the snubber circuit 3, but the control circuit controlling the power conversion circuit 2 and the control circuit controlling the snubber circuit 3 are controlled. It may be divided into and. Further, the control circuit 4 may be configured to further control the power supply circuit 20.

(3) Operation example (3.1) Operation of power conversion circuit The operation of the power conversion circuit 2 will be described below with reference to FIG. 2. FIG. 2 is an operation waveform diagram of the power conversion circuit 2 with the horizontal axis as the time axis. In FIG. 2, the input voltage Vi is shown in the first stage from the top. In FIG. 2, switching elements Q11 and Q14 are turned on / off in the second stage from the top, and switching elements Q12 and Q13 are turned on / off in the third stage from the top. In FIG. 2, the bus voltage Vbus and the output voltage Vo are shown at the fourth stage from the top.

  An AC voltage is applied from the power supply circuit 20 to the primary winding L11 of the transformer 21. The primary winding L11 and the secondary winding L12 of the transformer 21 are magnetically coupled to each other, and both ends of the secondary winding L12 correspond to the winding ratio of the primary winding L11 and the secondary winding L12. An alternating voltage having a voltage value (input voltage Vi) is generated. The input voltage Vi is an AC voltage having the same phase as the AC voltage applied to the primary winding L11. In the present embodiment, the AC voltage output from the power supply circuit 20 is a rectangular wave (pseudo sine wave), so the input voltage Vi is also a rectangular wave.

  The control circuit 4 outputs drive signals S11 to S14 for driving the switching elements Q11 to Q14 in synchronization with the output voltage (input voltage Vi) of the power supply circuit 20. Specifically, when the polarity of the input voltage Vi is “positive”, the control circuit 4 outputs the drive signals S11 to S14 so that the switching elements Q11 and Q14 turn on and the switching elements Q12 and Q13 turn off. .. When the polarity of the input voltage Vi is “negative”, the control circuit 4 outputs the drive signals S11 to S14 so that the switching elements Q12 and Q13 are turned on and the switching elements Q11 and Q14 are turned off. Further, when the voltage value of the input voltage Vi is zero, the control circuit 4 outputs the drive signals S11 to S14 so that the switching elements Q11 to Q14 are turned off.

  As a result, the bus voltage Vbus obtained by full-wave rectifying the input voltage Vi is generated between the pair of second terminals H21 and H22 which are the pair of output terminals of the rectifier circuit 22. A DC output voltage Vo obtained by smoothing the bus voltage Vbus by the inductor L21, the output capacitor Co, and the inductor L1 of the snubber circuit 3 is output to the load 5.

  The output voltage Vo is a voltage obtained by averaging the bus voltage Vbus. Specifically, the absolute value of the voltage value when the polarity of the input voltage Vi is “positive” or “negative” is vi. The cycle of the bus voltage Vbus is T1. A period in which the pair of switching elements Q11 and Q14 or the pair of switching elements Q12 and Q13 is on (on period) is Ton1. The duty ratio of the bus voltage Vbus is Dr1. The duty ratio Dr1 of the bus voltage Vbus is a ratio of the on period Ton1 to the cycle T1 of the bus voltage Vbus, and is represented by Ton1 / T1. The voltage value of the output voltage Vo is vi × Dr1.

(3.2) Operation of Snubber Circuit Next, the operation of the snubber circuit 3 will be described with reference to FIGS. 1 and 3. FIG. 3 is an operation waveform diagram of the power conversion circuit 2 and the snubber circuit 3 with the horizontal axis as the time axis. In FIG. 3, the bus voltage Vbus, the output voltage Vo, and the voltage Vc1 across the first capacitor C1 are shown in the first stage from the top. In FIG. 3, the second stage from the top shows ON / OFF of the switching elements Q11 to Q14, and the third stage from the top shows ON / OFF of the first switching element Q1 and the second switching element Q2. There is. In FIG. 3, the fourth stage from the top shows the current Id3 flowing through the diode D3, and the fifth stage from the top shows the voltage Vc2 across the second capacitor C2, the voltage VL21 across the inductor L21, and the voltage across the inductor L1. VL1 is shown. In FIG. 3, the sixth stage from the top shows the current Ic2 flowing through the second capacitor C2, and the seventh stage from the top shows the first ripple current Ir1 and the snubber circuit flowing through the power conversion circuit 2 (power supply circuit 20). 3 shows the second ripple current Ir2 flowing by 3 and the current Ico flowing through the output capacitor Co. In addition, regarding the polarities of the current and the voltage in FIG. 3, the direction of the arrow described in FIG. 1 is “positive”.

(3.2.1) Clamp Operation First, the clamp operation of the snubber circuit 3 will be described.

  A surge may occur in the bus voltage Vbus due to the operation of the power conversion circuit 2 described above. The switching elements Q11 to Q14 of the rectifier circuit 22 are electrically connected to the secondary winding L12 of the transformer 21. Therefore, the series resonance circuit is configured by the leakage inductance of the secondary winding L12 and the parasitic capacitances of the switching elements Q11 to Q14. Therefore, during the switching operation of the switching elements Q11 to Q14, the surge voltage may be superimposed on the bus voltage Vbus.

  When a surge voltage occurs in the bus voltage Vbus, the snubber circuit 3 absorbs electric energy from the power conversion circuit 2 to clamp the bus voltage Vbus to a clamp value (voltage value of the voltage Vc1 across the first capacitor C1). To do. That is, when a surge voltage occurs in the bus voltage Vbus and the voltage value exceeds the clamp value (voltage value of the voltage Vc1), the diode D3 is turned on. At this time, a pulsed current Id3 flows through the diode D3 as the electric energy is absorbed (see FIG. 3). Therefore, when the magnitude of the bus voltage Vbus exceeds the clamp value (voltage value of the voltage Vc1), the snubber circuit 3 extracts from the power conversion circuit 2 the electric energy for the amount exceeding the clamp value and outputs the electric energy as the first value. It can be stored in the capacitor C1. Therefore, even if a surge voltage occurs in the bus voltage Vbus, the maximum value of the bus voltage Vbus is suppressed to the clamp value.

(3.2.2) Regenerative Operation Next, the regenerative operation of the snubber circuit 3 will be described. Here, it is assumed that the power conversion circuit 2 is operating in the continuous current mode.

  The snubber circuit 3 supplies the electrical energy absorbed from the power conversion circuit 2 to the inductor L1 to treat the inductor L1 as a power source and regenerate the electrical energy to the power conversion circuit 2 or the load 5. Further, the snubber circuit 3 regenerates electric energy in the power conversion circuit 2 or the load 5 so as to reduce the ripple current flowing in the output capacitor Co.

  The snubber circuit 3 has four operation modes (first mode to fourth mode) in the regenerative operation. In the first mode, the first switching element Q1 turns on and the second switching element Q2 turns off. In the second mode and the fourth mode, the first switching element Q1 and the second switching element Q2 are turned off. In the third mode, the first switching element Q1 is turned off and the second switching element Q2 is turned on.

  The snubber circuit 3 switches the operation mode in synchronization with the bus voltage Vbus. In other words, in the switching circuit 31, the first switching element Q1 and the second switching element Q2 are turned on / off in synchronization with the output voltage (bus voltage Vbus) of the rectifier circuit 22. The snubber circuit 3 has the first value during the ON period Ton1 in which the bus voltage Vbus has a voltage value of vi, that is, the set of switching elements Q11 and Q14 of the rectifier circuit 22 or the set of switching elements Q12 and Q13 is ON. Mode and the second mode. The snubber circuit 3 operates in the third mode and the fourth mode in a period in which the voltage value of the bus voltage Vbus is zero, that is, in an off period Toff1 in which the switching elements Q11 to Q14 of the rectifier circuit 22 are off. In FIG. 3, a period T11 is a period in which the snubber circuit 3 is operating in the first mode, a period T12 is a period in which the snubber circuit 3 is operating in the second mode, and a period T13 is a snubber circuit. 3 is a period in which the snubber circuit 3 is operating in the third mode, and a period T14 is a period in which the snubber circuit 3 is operating in the fourth mode. That is, the period T12 in the second mode and the period T14 in the fourth mode are dead times Td during which the first switching element Q1 and the second switching element Q2 are off.

  Hereinafter, the first mode to the fourth mode will be described with reference to FIGS. 4 to 7. Each arrow shown in FIGS. 4 to 7 represents the polarity of current or voltage in the operation mode.

First Mode FIG. 4 is an equivalent circuit of the snubber circuit 3 and the power conversion circuit 2 when the snubber circuit 3 is in the first mode. Since the first mode is executed during the on period Ton1 in which the switching elements Q11, Q14 (or Q12, Q13) of the rectifier circuit 22 are on, the voltage value of the bus voltage Vbus is constant at vi. Therefore, in FIG. 4, the power supply circuit 20, the transformer 21, and the rectifier circuit 22 are collectively shown as a power supply E1 that outputs a DC voltage.

  The first mode is executed after the fourth mode described later. In the first mode, the first switching element Q1 is turned on and the second switching element Q2 is turned off in the on period Ton1. Specifically, the control circuit 4 turns on the first switching element Q1 in synchronization with turning on of the switching elements Q11 and Q14 (or Q12 and Q13). As a result, the first switching element Q1 is turned on in synchronization with the rising of the output voltage (bus voltage Vbus) of the rectifier circuit 22.

  When the first switching element Q1 is turned on, a closed loop including the first capacitor C1, the second capacitor C2, and the inductor L1 is formed.

  Then, the current Ic2 flows through the second capacitor C2 and the inductor L1 with the first capacitor C1 as a supply source. The current Ic2 charges the second capacitor C2. The voltage Vc2 across the second capacitor C2 is lower than the voltage Vc1 across the first capacitor C1. Specifically, the duty ratio of the first switching element Q1 is Dr2. The duty ratio Dr2 of the first switching element Q1 is the ratio of the ON period (period T11) of the first switching element Q1 to the cycle T1 of the bus voltage Vbus, and is represented by T11 / T1. The voltage Vc2 across the second capacitor C2 is represented by Vc1 × Dr2. The voltage Vc2 across the second capacitor C2 is expressed as follows using the dead time Td during which the first switching element Q1 and the second switching element Q2 are off. The voltage Vc2 across the second capacitor C2 is (Dr1-Td / T1) Vc1.

  In the first mode, a current flows in the inductor L1 from the connection point between the inductor L1 and the second capacitor C2 toward the connection point between the inductor L1 and the first capacitor C1.

  In the first mode, the voltage VL1 across the inductor L1 is a voltage (Vc1-Vc2) obtained by subtracting the voltage Vc2 across the second capacitor C2 from the voltage Vc1 across the first capacitor C1. The voltage Vc2 across the second capacitor C2 is a voltage obtained by stepping down the voltage Vc1 across the first capacitor C1. Therefore, in the voltage VL1 across the inductor L1, the connection point between the inductor L1 and the first capacitor C1 is on the low potential side, and the connection point between the inductor L1 and the second capacitor C2 is on the high potential side.

  The voltage VL21 across the inductor L21 in the first mode is determined by the voltage VL1 across the inductor L1, the bus voltage Vbus, and the output voltage Vo. Specifically, the voltage VL21 across the inductor L21 is obtained by VL1- (Vbus-Vo). Here, the polarity of the voltage VL21 across the inductor L21 is calculated assuming that the connection point between the inductor L21 and the output capacitor Co is “positive”. In the first mode, the voltage VL1 across the inductor L1 is Vc1-Vc2. The voltage Vc2 across the second capacitor C2 is (Dr1-Td / T1) Vc1. The output voltage Vo is Dr1 × Vbus. Therefore, the voltage VL21 across the inductor L21 is obtained by the following equation 1.

  The voltage Vc1 across the first capacitor C1 is the sum of the bus voltage Vbus and the surge voltage. Therefore, since (Vc1-Vbus) becomes positive, the voltage VL21 across the inductor L21 obtained by the above equation 1 becomes "positive". That is, in the voltage VL21 across the inductor L21, the connection point between the inductor L21 and the output capacitor Co is on the high potential side.

  The second ripple current Ir2 flows through the output capacitor Co due to the voltage VL1 across the inductor L1. Regarding the both-end voltage VL1, the connection point between the inductor L1 and the output capacitor Co is on the high potential side. Therefore, the second ripple current Ir2 flows in the direction in which the output capacitor Co is discharged. In the first mode, the set of switching elements Q11 and Q14 or the set of switching elements Q12 and Q13 in the rectifier circuit 22 is on. Therefore, the second ripple current Ir2 flows through the secondary winding L12 of the transformer 21, and the electric energy is transmitted to the power supply circuit 20 via the primary winding L11.

  That is, in the first mode, the snubber circuit 3 regenerates the electric energy absorbed from the power conversion circuit 2 to the power conversion circuit 2 (power supply E1) using the inductor L1 as a power supply. As a result, the power loss of the power conversion circuit 2 can be reduced as compared with the configuration in which the snubber circuit 3 consumes the electric energy absorbed from the power conversion circuit 2 by a resistor or the like.

  At this time, a current Ico, which is the sum of the first ripple current Ir1 flowing from the power source E1 and the second ripple current Ir2 flowing from the snubber circuit 3, flows through the output capacitor Co. The current Ico flowing through the output capacitor Co is a regenerative current regenerated from the snubber circuit 3 to the power conversion circuit 2. The regenerative power regenerated from the snubber circuit 3 to the power conversion circuit 2 is obtained by multiplying the voltage VL1 across the inductor L1 and the regenerative current (current Ico) (VL1 × Ico).

-Second Mode FIG. 5 is an equivalent circuit of the snubber circuit 3 and the power conversion circuit 2 when the snubber circuit 3 is in the second mode. The second mode is executed during the on period Ton1 in which the switching elements Q11, Q14 (or Q12, Q13) of the rectifier circuit 22 are on, so the voltage value of the bus voltage Vbus is constant at vi. Therefore, in FIG. 5, the power supply circuit 20, the transformer 21, and the rectifier circuit 22 are collectively shown as a power supply E1 that outputs a DC voltage.

  The second mode is executed after the first mode, and the first switching element Q1 is turned off from the state of the first mode. Specifically, the control circuit 4 turns on the first switching element Q1 after turning on the first switching element Q1 for a predetermined period T11 (<ON period Ton1).

  When the first switching element Q1 is turned off, the current supply from the first capacitor C1 to the inductor L1 is stopped. As a result, the polarity of the voltage VL1 across the inductor L1 is inverted, and the connection point between the inductor L1 and the second capacitor C2 is on the low potential side.

  Due to the voltage VL1 across the inductor L1, the current Ic2 flows in the direction of charging the second capacitor C2 via the parasitic diode D2 of the second switching element Q2. At this time, the voltage VL1 across the inductor L1 is the same as the voltage Vc2 across the second capacitor C2. Note that the forward drop voltage of the parasitic diode D2 is neglected here because it is sufficiently smaller than the both-end voltage Vc2.

  The voltage VL21 across the inductor L21 in the second mode is determined by the voltage VL1 across the inductor L1, the bus voltage Vbus, and the output voltage Vo. Specifically, the voltage VL21 across the inductor L21 is obtained by -VL1-Vbus + Vo. Here, the polarity of the voltage VL21 across the inductor L21 is calculated assuming that the connection point between the inductor L21 and the output capacitor Co is “negative”. The voltage VL21 across the inductor L21 is calculated by the following equation 2.

  Since the voltage Vc1 across the first capacitor C1 is the sum of the bus voltage Vbus and the surge voltage, (Vc1-Vbus) is positive. The dead time Td is a value that is sufficiently smaller than the period T1. Therefore, the voltage VL21 across the inductor L21, which is obtained by the above equation 2, becomes "negative". That is, in the voltage VL21 across the inductor L21, the connection point between the inductor L21 and the output capacitor Co is on the low potential side.

  The second ripple current Ir2 is generated in the output capacitor Co due to the voltage VL1 across the inductor L1. Since the connection point between the inductor L1 and the output capacitor Co is on the low potential side, the second end voltage VL1 causes the second ripple current Ir2 to flow in the direction in which the output capacitor Co is charged. In the second mode, the set of switching elements Q11 and Q14 or the set of switching elements Q12 and Q13 in the rectifier circuit 22 is on. Therefore, the second ripple current Ir2 flows to the output capacitor Co via the set of switching elements Q11 and Q14 or the set of switching elements Q12 and Q13.

  That is, in the second mode, the snubber circuit 3 regenerates the electric energy absorbed from the power conversion circuit 2 to the load 5 by using the inductor L1 as a power source. As a result, the power loss of the power conversion circuit 2 can be reduced as compared with the configuration in which the snubber circuit 3 consumes the electric energy absorbed from the power conversion circuit 2 by a resistor or the like.

  In the second mode, the current Ico flowing through the output capacitor Co is the regenerative current regenerated from the snubber circuit 3 to the load 5. The regenerative power regenerated from the snubber circuit 3 to the load 5 is obtained by multiplying the voltage VL1 across the inductor L1 and the regenerative current (current Ico) (VL1 × Ico).

Third Mode FIG. 6 is an equivalent circuit of the snubber circuit 3 and the power conversion circuit 2 when the snubber circuit 3 is in the third mode. The third mode is executed during the off period Toff1 in which the switching elements Q11 to Q14 of the rectifier circuit 22 are off. Therefore, in FIG. 6, the parasitic diodes D11 to D14 of the switching elements Q11 to Q14 are collectively shown as the diode D10.

  The third mode is executed after the second mode. In the third mode, in the off period Toff1, the first switching element Q1 is off and the second switching element Q2 is on. Specifically, the control circuit 4 turns on the second switching element Q2 in synchronization with turning off of the switching elements Q11 and Q14 (or Q12 and Q13). As a result, the second switching element Q2 is turned on in synchronization with the fall of the output voltage (bus voltage Vbus) of the rectifier circuit 22.

  When the second switching element Q2 is turned on, a closed loop including the second capacitor C2 and the inductor L1 is formed.

  Then, the current Ic2 flows through the inductor L1 via the second switching element Q2 with the second capacitor C2 as a supply source. That is, in the third mode, a current flows in the inductor L1 in the opposite direction to that in the first mode. In the voltage VL1 across the inductor L1, the connection point between the inductor L1 and the second capacitor C2 is on the low potential side. The voltage VL1 across the inductor L1 is the same as the voltage Vc2 across the second capacitor C2.

  The voltage VL21 across the inductor L21 in the third mode is obtained by the voltage VL1 across the inductor L1 and the output voltage Vo. Specifically, the voltage VL21 across the inductor L21 is calculated by −VL1 + Vo. Here, the polarity of the voltage VL21 across the inductor L21 is calculated assuming that the connection point between the inductor L21 and the output capacitor Co is “negative”. The voltage VL21 across the inductor L21 is calculated by the following expression 3.

  Since the voltage Vc1 across the first capacitor C1 is the sum of the bus voltage Vbus and the surge voltage, (Vc1-Vbus) is positive. The dead time Td is a value that is sufficiently smaller than the period T1. Therefore, the voltage VL21 across the inductor L21, which is obtained by the above equation 3, becomes "negative". That is, in the voltage VL21 across the inductor L21, the connection point between the inductor L21 and the output capacitor Co is on the low potential side.

  The second ripple current Ir2 flows through the output capacitor Co due to the voltage VL1 across the inductor L1. Since the connection point between the inductor L1 and the output capacitor Co is on the low potential side in the voltage VL1 at the both ends, the second ripple current Ir2 is generated by the parasitic diodes D11 to D14 of the switching elements Q11 to Q14 of the rectifier circuit 22 (diodes in FIG. D10) and flows in a direction to charge the output capacitor Co.

  That is, in the third mode, the snubber circuit 3 regenerates the electric energy absorbed from the power conversion circuit 2 to the load 5 by using the inductor L1 as a power source. As a result, the power loss of the power conversion circuit 2 can be reduced as compared with the configuration in which the snubber circuit 3 consumes the electric energy absorbed from the power conversion circuit 2 by a resistor or the like.

  In the third mode, the current Ico flowing through the output capacitor Co is a regenerative current regenerated from the snubber circuit 3 to the load 5. The regenerative power regenerated from the snubber circuit 3 to the load 5 is obtained by multiplying the voltage VL1 across the inductor L1 and the regenerative current (current Ico) (VL1 × Ico).

Fourth Mode FIG. 7 is an equivalent circuit of the snubber circuit 3 and the power conversion circuit 2 when the snubber circuit 3 is in the fourth mode. In the fourth mode, the switching elements Q11 to Q14 of the rectifier circuit 22 are off. Therefore, in FIG. 6, the parasitic diodes D11 to D14 of the switching elements Q11 to Q14 are collectively shown as the diode D10.

  The fourth mode is executed after the third mode, and the second switching element Q2 is turned off from the state of the third mode. Specifically, the control circuit 4 turns on the second switching element Q2 after turning on the second switching element Q2 for a predetermined period T13 (<off period Toff1).

  When the second switching element Q2 is turned off, the current supply from the second capacitor C2 to the inductor L1 is stopped. As a result, the polarity of the voltage VL1 across the inductor L1 is inverted, and the connection point between the inductor L1 and the second capacitor C2 is on the high potential side.

  Due to the voltage VL1 across the inductor L1, a current Ic2 flows in a direction to charge the first capacitor C1 via the second capacitor C2 and the parasitic diode D1 of the first switching element Q1. The voltage VL1 across the inductor L1 is a voltage (Vc1-Vc2) obtained by subtracting the voltage Vc2 across the second capacitor C2 from the voltage Vc1 across the first capacitor C1. The forward drop voltage of the parasitic diode D1 is neglected here because it is sufficiently smaller than the both-end voltages Vc1 and Vc2.

  The voltage VL21 across the inductor L21 in the fourth mode is determined by the voltage VL1 across the inductor L1 and the output voltage Vo. Specifically, the voltage VL21 across the inductor L21 is obtained by VL1 + Vo. Here, the polarity of the voltage VL21 across the inductor L21 is calculated assuming that the connection point between the inductor L21 and the output capacitor Co is “positive”. The voltage VL21 across the inductor L21 is calculated by the following equation 4.

  Further, the second ripple current Ir2 flows through the output capacitor Co due to the voltage VL1 across the inductor L1. Regarding the both-end voltage VL1, the connection point between the inductor L1 and the output capacitor Co is on the high potential side. Therefore, the second ripple current Ir2 flows in the direction in which the output capacitor Co is discharged.

  In the above-described first to fourth modes, the magnitude of the regenerative power by the snubber circuit 3 is substantially constant regardless of the magnitude of the load 5 (the magnitude of the output current Io). When the load 5 is unloaded (the output current Io is zero), all the regenerative current flows to the power conversion circuit 2 (power supply circuit 20). When the load 5 is a light load (for example, the output current Io is 15 A), the regenerative current flows through both the power conversion circuit 2 (power supply circuit 20) and the load 5. Further, when the load 5 is a heavy load (for example, the output current Io is 60 A), all of the regenerative current flows to the load 5.

Reduction of Ripple Current Next, reduction of the ripple current flowing through the output capacitor Co by the snubber circuit 3 will be described with reference to FIGS. 8A to 9B.

  As described above, the snubber circuit 3 switches the direction of the second ripple current Ir2 flowing through the output capacitor Co by sequentially performing the first mode to the fourth mode. In the first mode, the snubber circuit 3 generates the second ripple current Ir2 in the ON period Ton1 in the direction in which the output capacitor Co is discharged. At this time, since the switching elements Q11, Q14 (or Q12, Q13) of the rectifier circuit 22 are turned on, the voltage value of the bus voltage Vbus becomes vi, and the power supply E1 (power conversion circuit 2) charges the output capacitor Co. The first ripple current Ir1 is generated in the direction to do so.

  In the third mode, the snubber circuit 3 generates the second ripple current Ir2 in the off period Toff1 so as to charge the output capacitor Co. At this time, since the switching elements Q11 to Q14 of the rectifier circuit 22 are off, the voltage value of the bus voltage Vbus becomes zero, and the power supply E1 (power conversion circuit 2) causes the first ripple to discharge the output capacitor Co. A current Ir1 is generated.

  That is, the snubber circuit 3 generates the second ripple current Ir2 opposite to the first ripple current Ir1 which the power source E1 flows. The ripple current flowing through the output capacitor Co is the sum of the first ripple current Ir1 and the second ripple current Ir2. Therefore, the first ripple current Ir1 is canceled by the second ripple current Ir2, and the ripple current flowing through the output capacitor Co is reduced.

  Specifically, the first ripple current Ir1 in the on period Ton1 in which the switching elements Q11, Q14 (or Q12, Q13) of the rectifier circuit 22 are on and the off period Toff1 in which the switching elements Q11 to Q14 are off are , As follows.

  8A is an equivalent circuit in the on period Ton1 (first mode, second mode), and FIG. 8B is an equivalent circuit in the off period Toff1 (third mode, fourth mode). 8A and 8B, the snubber circuit 3 (including the inductor L1) is ignored.

  In the on period Ton1, since the switching elements Q11, Q14 (or Q12, Q13) are on, the voltage value of the bus voltage Vbus is constant at vi. Therefore, in FIG. 8A, the power supply circuit 20, the transformer 21, and the rectifier circuit 22 are collectively shown as a power supply E1 that outputs a DC voltage.

  In the on period Ton1 (first mode, second mode), the bus voltage Vbus having a voltage value vi is applied to the output capacitor Co via the inductor L21. Therefore, the first ripple current Ir1 flows from the power source E1 through the inductor L21 in the direction to charge the output capacitor Co (see FIG. 8A and FIG. 3). The first ripple current Ir1 at this time is obtained by the following equation 5 based on the bus voltage Vbus, the output voltage Vo, and the inductance of the inductor L21.

  In the off period Toff1 (third mode and fourth mode), the voltage value of the bus voltage Vbus becomes zero. Therefore, the first ripple current Ir1 flows in the direction in which the output capacitor Co is discharged (see FIGS. 8B and 3). The first ripple current Ir1 at this time is obtained by the following equation 6 based on the output voltage Vo and the inductance of the inductor L21.

  The second ripple current Ir2 in the first to fourth modes is as follows.

  9A is an equivalent circuit in the first mode and the fourth mode, and FIG. 9B is an equivalent circuit in the second mode and the third mode. In FIG. 9A and FIG. 9B, the power source E1, the load 5, etc. are ignored.

  In the first mode and the fourth mode, the voltage VL1 across the inductor L1 is at the high potential side at the connection point between the inductor L1 and the output capacitor Co. In FIG. 9A, the inductor L1 is described as a DC power supply. In the first mode and the fourth mode, the inductor L1 is used as a power source and the second ripple current Ir2 flows in the direction in which the output capacitor Co is discharged (see FIGS. 9A and 3). The second ripple current Ir2 at this time is obtained by the following formula 7 based on the voltage VL1 across the inductor L1 and the inductance of the inductor L21.

  Further, in the second mode and the third mode, the voltage VL1 across the inductor L1 is at the low potential side at the connection point between the inductor L1 and the output capacitor Co. In FIG. 9B, the inductor L1 is described as a DC power supply. In the second mode and the third mode, the inductor L1 is used as a power source and the second ripple current Ir2 flows in the direction in which the output capacitor Co is charged (see FIGS. 9B and 3). The second ripple current Ir2 at this time is obtained by the following equation 8 based on the voltage VL1 across the inductor L1 and the inductance of the inductor L21.

  As described above, in the period T11 in which the snubber circuit 3 is in the first mode, the first ripple current Ir1 flows in the direction of charging the output capacitor Co, while the second ripple current Ir2 is in the direction of discharging the output capacitor Co. Flow to. Further, during the period T13 in which the snubber circuit 3 is in the third mode, the first ripple current Ir1 flows in the direction of discharging the output capacitor Co, whereas the second ripple current Ir2 flows in the direction of charging the output capacitor Co. .. That is, since the first ripple current Ir1 and the second ripple current Ir2 have opposite phases, the ripple current flowing through the output capacitor Co is reduced. Note that the first ripple current Ir1 and the second ripple current Ir2 are not exactly in opposite phases, but are out of phase by the dead time Td when the snubber circuit 3 is in the second mode and the fourth mode.

  As described above, the current Ico flowing through the output capacitor Co is a current that is the sum of the first ripple current Ir1 and the second ripple current Ir2 due to the reason of overlapping. Therefore, the magnitude of the current Ico in the period T11 in which the snubber circuit 3 is in the first mode is a value obtained by adding the first ripple current Ir1 obtained by the above equation 5 and the second ripple current Ir2 obtained by the above equation 7. Becomes The magnitude of the current Ico in the period T12 in which the snubber circuit 3 is in the second mode is a value obtained by adding the first ripple current Ir1 obtained by the above-mentioned equation 5 and the second ripple current Ir2 obtained by the above-mentioned equation 8. .. The magnitude of the current Ico in the period T13 in which the snubber circuit 3 is in the third mode has a value obtained by adding the first ripple current Ir1 obtained by the above-mentioned equation 6 and the second ripple current Ir2 obtained by the above-mentioned equation 8. .. The magnitude of the current Ico in the period T14 in which the snubber circuit 3 is in the fourth mode is a value obtained by adding the first ripple current Ir1 obtained by the above-mentioned equation 6 and the second ripple current Ir2 obtained by the above-mentioned equation 7. ..

  In this way, the snubber circuit 3 regenerates the electric energy absorbed from the power conversion circuit 2 into the power conversion circuit 2 or the load 5 so that the ripple current flowing through the output capacitor Co is reduced. As a result, the capacitance of the output capacitor Co can be reduced and the size can be reduced. For example, in the power conversion circuit 2 to which the snubber circuit 3 of the present embodiment is not connected, the ripple current flowing through the output capacitor Co is 3 Ap-p and the capacitance of the output capacitor Co is 330 μF. When the snubber circuit 3 of this embodiment is connected to the power conversion circuit 2, the ripple current flowing through the output capacitor Co can be reduced to 1.5 Ap-p or less. As a result, a capacitor having a capacity of 120 μF can be used as the output capacitor Co, and the power conversion circuit 2 can be downsized.

(4) Modified Example (4.1) First Modified Example Hereinafter, a first modified example of the power conversion system 1 will be described with reference to FIG. 10.

  In the above-described example, the rectifier circuit 22 is a synchronous rectification type full-wave rectifier circuit including the switching elements Q11 to Q14 as rectifier elements, but is not limited to this.

  As shown in FIG. 10, the rectifier circuit 22 may be a diode bridge circuit including diodes D11a to D14a as rectifier elements. The diodes D11a to D14a are full-bridge connected. The series circuit of the diodes D11a and D12a and the series circuit of the diodes D13a and D14a are electrically connected in parallel between the second terminal H21 on the high potential side and the second terminal H22 on the low potential side. The connection point between the diode D11a and the diode D12a is electrically connected to the first terminal H11, and the connection point between the diode D13a and the diode D14a is electrically connected to the first terminal H12.

  Specifically, the diode D11a has a cathode electrically connected to the second terminal H21 and an anode electrically connected to the first terminal H11. The diode D12a has a cathode electrically connected to the first terminal H11 and an anode electrically connected to the second terminal H22. The diode D13a has a cathode electrically connected to the second terminal H21 and an anode electrically connected to the first terminal H12. The diode D14a has a cathode electrically connected to the first terminal H12 and an anode electrically connected to the second terminal H22.

  The diodes D11a to D14a are turned on / off in synchronization with the phase of the input voltage Vi. Specifically, when the polarity of the input voltage Vi is “positive”, the diodes D11a and D14a are turned on (conductive state), and when the polarity of the input voltage Vi is “negative”, the diodes D12a and D13a are turned on ( Conductive state). As a result, the bus voltage Vbus obtained by full-wave rectifying the input voltage Vi is generated between the pair of second terminals H21 and H22 which are the pair of output terminals of the rectifier circuit 22.

  In the above-described embodiment (see FIG. 1), the rectifier circuit 22 is a synchronous rectification type full-wave rectifier circuit including the switching elements Q11 to Q14 as rectifier elements. Therefore, when the snubber circuit 3 is in the first mode, the second ripple current Ir2 flows through the secondary winding L12 of the transformer 21 via the switching elements Q11, Q14 (or Q12, Q13). As a result, the electric energy regenerated from the snubber circuit 3 was transmitted to the power supply circuit 20 via the transformer 21.

  In this modification, the rectifier circuit 22 is a diode bridge circuit including diodes D11a to D14a as rectifier elements. Therefore, when the snubber circuit 3 is in the first mode, the second ripple current Ir2 does not flow in the secondary winding L12 of the transformer 21, but flows in the diode D3 and the first capacitor C1 of the snubber circuit 3. That is, the second ripple current Ir2 flows through the closed loop including the output capacitor Co, the inductor L21, the diode D3, and the first capacitor C1. As a result, the second ripple current Ir2 flows in the opposite direction to the first ripple current Ir1, so that the ripple current flowing through the output capacitor Co can be reduced. As a result, the capacitance of the output capacitor Co can be reduced and the size can be reduced.

(4.2) Second Modification Hereinafter, a second modification of the power conversion system 1 will be described with reference to FIG. 11.

  As shown in FIG. 11, the rectifier circuit 22 may be a push-pull type full-wave rectifier circuit including switching elements Q15 and Q16 as rectifier elements.

  In the example shown in FIG. 11, the transformer 21 includes a primary winding L11, a first secondary winding L121, and a second secondary winding L122. The first secondary winding L121 and the second secondary winding L122 are magnetically coupled to the primary winding L11. One end of the first secondary winding L121 is electrically connected to the other end of the second secondary winding L122, and the other end thereof is electrically connected to the first terminal H12. One end of the second secondary winding L122 is electrically connected to the first terminal H11. A connection point between the first secondary winding L121 and the second secondary winding L122 (tap of the secondary winding of the transformer 21) is electrically connected to the second terminal H21 on the high potential side. In this modification, it is assumed that the first secondary winding L121 and the second secondary winding L122 have the same number of turns.

  By applying an AC voltage from the power supply circuit 20 to the primary winding L12 of the transformer 21, the first secondary winding L121 and the second secondary winding L122 are connected between both ends of the series circuit (a pair of first terminals H21. , H22), an AC input voltage Vi is generated.

  The rectifier circuit 22 has two switching elements Q15 and Q16 as rectifier elements. As an example, the switching elements Q15 and Q16 are composed of depletion type n-channel MOSFETs.

  The switching element Q15 has a drain electrically connected to the first terminal H12 and a source electrically connected to the second terminal H22. The switching element Q16 has a drain electrically connected to the first terminal H11 and a source electrically connected to the second terminal H22.

  The switching elements Q15 and Q16 have parasitic diodes D15 and D16, respectively. Each of the parasitic diodes D15 and D16 is configured such that its anode is electrically connected to its source and its cathode is electrically connected to its drain.

  In the rectifier circuit 22, the switching elements Q15 and Q16 are turned on / off in synchronization with the phase of the input voltage Vi, so that the bus voltage Vbus obtained by full-wave rectifying the input voltage Vi is applied between the pair of second terminals H21 and H22. To generate. The switching elements Q15 and Q16 are individually turned on / off controlled by drive signals S15 and S16 from the control circuit 4, respectively.

  The control circuit 4 outputs drive signals S15 and S16 for driving the switching elements Q15 and Q16 in synchronization with the output voltage (input voltage Vi) of the power supply circuit 20. Specifically, when the polarity of the input voltage Vi is “positive”, the control circuit 4 outputs the drive signals S15 and S16 so that the switching element Q15 turns on and the switching element Q16 turns off. When the polarity of the input voltage Vi is "negative", the control circuit 4 outputs the drive signals S15 and S16 so that the switching element Q16 turns on and the switching element Q15 turns off. Further, the control circuit 4 outputs the drive signals S15 and S16 so that the switching elements Q15 and Q16 are turned off when the voltage value of the input voltage Vi is zero.

  As a result, the bus voltage Vbus obtained by full-wave rectifying the input voltage Vi is generated between the pair of second terminals H21 and H22 which are the pair of output terminals of the rectifier circuit 22.

  In this modification, when the snubber circuit 3 is in the first mode, the second ripple current Ir2 passes through the switching element Q15 (or Q16) to the first secondary winding L121 (or the second secondary winding L21) of the transformer 21. L122). As a result, the electric energy regenerated from the snubber circuit 3 can be transmitted to the power supply circuit 20 via the transformer 21.

(4.3) Other Modifications Other modifications of the power conversion system 1 will be listed below.

  In the above example, the period T12 (dead time Td) in the second mode and the period T14 (dead time Td) in the fourth mode have the same time length, but the period T12 and the period T14 are different from each other. It may be the length of time.

  Further, in the above-described example, in the on period Ton1, the second mode is executed after the first mode, but the first mode may be executed after the second mode. That is, the dead time Td at which the first switching element Q1 and the second switching element Q2 are turned off may be set at the beginning of the on period Ton1 in which the rectifying element of the rectifying circuit 22 is turned on. Similarly, in the off period Toff1, the third mode may be executed after the fourth mode. That is, the dead time Td at which the first switching element Q1 and the second switching element Q2 are turned off may be set at the beginning of the off period Toff1 when the rectifying element of the rectifying circuit 22 is off.

  The first capacitance component and the second capacitance component are not limited to the capacitance elements (the first capacitor C1 and the second capacitor C2), but may be parasitic capacitances, for example.

  The inductance component is not limited to the inductance element (inductor L1) but may be, for example, a parasitic inductance.

  In the example described above, the inductor L1 also serves as the smoothing filter of the power conversion circuit 2, but a smoothing filter on the low potential side may be provided separately from the inductor L1.

  In the above-described example, the transformer 21 is an insulation type transformer in which the primary winding L11 and the secondary winding L12 are electrically insulated, but not limited to this, the primary winding and the secondary winding are It may be a non-insulated transformer electrically connected.

  Although the rectifier circuit 22 is a full-wave rectifier circuit that full-wave rectifies the AC input voltage Vi in the above-described example, it may be a half-wave rectifier circuit that half-wave rectifies the input voltage Vi.

(Summary)
The snubber circuit (3) according to the first aspect absorbs electric energy from the main circuit (2). The snubber circuit (3) includes a first capacitance component (first capacitor C1), a second capacitance component (second capacitor C2), an inductance component (inductor L1), and a switching circuit (31). The first capacitance component (C1) stores the electric energy absorbed from the main circuit (2). The second capacitance component (C2) stores the electric energy absorbed from the main circuit (2). The inductance component (L1) regenerates the electric energy stored in the first capacitance component (C1) and the second capacitance component (C2) to the main circuit (2) or the load (5). The switching circuit (31) has a direction of current supplied from the first capacitance component (C1) to the inductance component (L1) and a direction of current supplied from the second capacitance component (C2) to the inductance component (L1). So as to be opposite to each other, the supply source for supplying electric energy to the inductance component (L1) is switched between the first capacitance component (C1) and the second capacitance component (C2).

  According to this aspect, the electric energy absorbed from the main circuit (2) is supplied to the inductance component (L1) from the first capacitance component (C1) or the second capacitance component (C2). At this time, the direction of the current flowing through the inductance component (L1) is switched by the switching circuit (31). Therefore, since the polarity of the voltage generated in the inductance component (L1) is switched, when the inductance component (L1) regenerates electric energy to the main circuit (2) or the load, the ripple current (second The direction of the ripple current Ir2) is switched. The inductance component (L1) causes the ripple current (Ir2) to flow through the main circuit (2) so as to cancel the ripple current flowing through the main circuit (2), thereby suppressing the ripple current flowing through the main circuit (2). it can.

  In the snubber circuit (3) according to the second aspect, in the first aspect, the switching circuit (31) has a first switching element (Q1) and a second switching element (Q2). The discharge path of the first capacitance component (C1) includes the first switching element (Q1), the second capacitance component (C2), and the inductance component (L1). The discharge path of the second capacitance component (C2) includes the second switching element (Q2) and the inductance component (L1). By turning on the first switching element (Q1), a current is supplied from the first capacitance component (C1) to the inductance component (L1). When the second switching element (Q2) is turned on, a current is supplied from the second capacitance component (C2) to the inductance component (L1).

  According to this aspect, since the first switching element (Q1) and the second switching element (Q2) are turned on / off, the supply source that supplies the electrical energy to the inductance component (L1) is the first capacitance component (C1). And the second capacitance component (C2).

  In the snubber circuit (3) according to the third aspect, in the second aspect, the main circuit (2) is a power conversion circuit that converts an AC voltage (input voltage Vi) into a DC voltage (output voltage Vo). It has a rectifier circuit (22) for rectifying the voltage (Vi). In the switching circuit (31), the first switching element (Q1) and the second switching element (Q2) are turned on / off in synchronization with the output voltage (bus voltage Vbus) of the rectifier circuit (22).

  According to this aspect, the ripple current can flow from the snubber circuit (3) so as to cancel the ripple current due to the fluctuation of the output voltage (Vbus) of the rectifier circuit (22).

  In the third mode, the snubber circuit (3) according to the fourth mode has operation modes of a first mode, a second mode, a third mode, and a fourth mode. In the first mode, the first switching element (Q1) is turned on while the rectifying elements (switching elements Q11 to Q14, diodes D11a to D14a) of the rectifying circuit (22) are turned on, and the second switching element (Q2) is turned on. ) Turns off. In the second mode, the first switching element (Q1) and the second switching element (Q2) are turned off when the rectifying elements (Q11 to Q14, D11a to D14a) are turned on. In the third mode, the first switching element (Q1) is turned off and the second switching element (Q2) is turned on when the rectifying elements (Q11 to Q14, D11a to D14a) are off. In the fourth mode, the first switching element (Q1) and the second switching element (Q2) are turned off when the rectifying elements (Q11 to Q14, D11a to D14a) are off.

  According to this aspect, the ripple current can be made to flow from the snubber circuit (3) so as to cancel the ripple current due to the fluctuation of the output voltage (Vbus) of the rectifier circuit (22).

  In the snubber circuit (3) according to the fifth aspect, in the fourth aspect, the second mode is executed after the first mode, and the fourth mode is executed after the third mode.

  According to this aspect, it becomes easy to control the first switching element (Q1) and the second switching element (Q2).

  In the snubber circuit (3) according to the sixth aspect, in any one of the first to fifth aspects, the inductance component (L1) also serves as the smoothing filter of the main circuit (2).

  According to this aspect, the inductance component (L1) also serves as the smoothing filter of the main circuit (2), so that the main circuit (2) can be downsized.

  In the snubber circuit (3) according to the seventh aspect, in the sixth aspect, the inductance component is the first inductor (inductor L1) and the second inductor (inductor L21) and the output capacitor (inductor L21) included in the main circuit (2). Co) is connected in series. The first inductor (L1) is electrically connected to the low potential side of the output capacitor (Co). The second inductor (L21) is electrically connected to the high potential side with respect to the output capacitor (Co).

  According to this aspect, the ripple current flowing through the output capacitor (Co) can be suppressed.

  A power conversion system (1) according to an eighth aspect includes a snubber circuit (3) according to any one of the first to seventh aspects and a main circuit (2).

  According to this aspect, the ripple current flowing in the main circuit (2) can be suppressed.

  In the power conversion system (1) according to the ninth aspect, in the eighth aspect, the main circuit (2) is a power conversion circuit that converts an AC voltage (input voltage Vi) into a DC voltage (output voltage Vo), It has a rectifier circuit (22) for rectifying the AC voltage (Vi). The rectifier circuit (22) includes switching elements (Q11 to Q14) that are turned on / off in synchronization with the phase of the AC voltage (Vi) as a rectifier element.

  According to this aspect, the power conversion loss in the rectifier circuit (22) can be reduced.

  In the power conversion system (1) according to the tenth aspect, in the eighth aspect, the main circuit (2) is a power conversion circuit that converts an AC voltage (input voltage Vi) into a DC voltage (output voltage Vo), It has a rectifier circuit (22) for rectifying the AC voltage (Vi). The rectifier circuit (22) includes diodes (D11a to D14a) as rectifier elements.

  According to this aspect, the configuration of the rectifier circuit (22) can be simplified.

1 Power conversion system 2 Main circuit (power conversion circuit)
22 Rectifier circuit 3 Snubber circuit 31 Switching circuit 5 Load C1 First capacitor (first capacitance component)
C2 Second capacitor (second capacitance component)
Co output capacitor L1 (first) inductor (inductance component)
L21 (Second) inductor Q1 First switching element Q2 Second switching element Q11 to Q14 Switching element (rectifying element)
D11a to D14a Diodes (rectifying element)
Vi input voltage (AC voltage)
Vo output voltage (DC voltage)
Vbus bus voltage (output voltage)

Claims (10)

A snubber circuit that absorbs electrical energy from the main circuit,
A first capacitive component that stores the electrical energy absorbed from the main circuit;
A second capacitive component that stores the electrical energy absorbed from the main circuit;
An inductance component for regenerating the electric energy stored in the first capacitance component and the second capacitance component to the main circuit or the load,
Electrical energy is supplied to the inductance component such that the direction of the current supplied from the first capacitance component to the inductance component and the direction of the current supplied from the second capacitance component to the inductance component are opposite to each other. A switching circuit that switches a supply source for supplying the power between the first capacitance component and the second capacitance component.
Snubber circuit. The switching circuit includes a first switching element and a second switching element,
The discharge path of the first capacitance component includes the first switching element, the second capacitance component, and the inductance component,
The discharge path of the second capacitance component includes the second switching element and the inductance component,
When the first switching element is turned on, current is supplied from the first capacitance component to the inductance component,
When the second switching element is turned on, current is supplied from the second capacitance component to the inductance component,
The snubber circuit according to claim 1. The main circuit is a power conversion circuit that converts an AC voltage into a DC voltage, and has a rectifying circuit that rectifies the AC voltage,
The switching circuit turns on / off the first switching element and the second switching element in synchronization with the output voltage of the rectifier circuit.
The snubber circuit according to claim 2. The operation modes include a first mode, a second mode, a third mode, and a fourth mode,
In the first mode, when the rectifying element of the rectifying circuit is on, the first switching element is on, and the second switching element is off,
In the second mode, the first switching element and the second switching element are turned off when the rectifying element is turned on,
In the third mode, the first switching element is turned off and the second switching element is turned on while the rectifying element is off,
In the fourth mode, the first switching element and the second switching element are turned off when the rectifying element is off.
The snubber circuit according to claim 3. The second mode is executed after the first mode,
The fourth mode is executed after the third mode,
The snubber circuit according to claim 4. The inductance component also serves as a smoothing filter for the main circuit,
The snubber circuit according to any one of claims 1 to 5. The inductance component is a first inductor, which is connected in series with a second inductor and an output capacitor included in the main circuit,
The first inductor is electrically connected to the low potential side with respect to the output capacitor,
The second inductor is electrically connected to the high potential side with respect to the output capacitor,
The snubber circuit according to claim 6. A snubber circuit according to any one of claims 1 to 7,
And a main circuit,
Power conversion system. The main circuit is a power conversion circuit that converts an AC voltage into a DC voltage, and has a rectifying circuit that rectifies the AC voltage,
The rectifier circuit includes, as a rectifier element, a switching element that is turned on / off in synchronization with the phase of the AC voltage.
The power conversion system according to claim 8. The main circuit is a power conversion circuit that converts an AC voltage into a DC voltage, and has a rectifying circuit that rectifies the AC voltage,
The rectifying circuit includes a diode as a rectifying element,
The power conversion system according to claim 8.

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