Buffer circuit and power conversion device

Abstract

In recent years, there has been a desire to more reliably prevent component damage and reduce circuit loss. A snubber circuit and a power conversion device are provided. The snubber circuit comprises: N charging paths, each comprising a positive-side capacitor, a first diode, and a negative-side capacitor connected in series between a positive-side wiring and a negative-side wiring, allowing current to flow from the positive side to the negative side; N+1 discharging paths, each comprising a second diode connected between the negative-side capacitor in the kth charging path and the positive-side capacitor in the k+1th charging path, allowing current to flow from the negative side to the positive side via the negative-side capacitor and the positive-side capacitor; and another charging path comprising an inductor between the positive-side capacitor in the ith charging path and the negative-side capacitor in the i+1th charging path, allowing current to flow from the positive side to the negative side, wherein the capacitance of the positive-side capacitor and the negative-side capacitor included in the another charging path is greater than the capacitance of each of the positive-side capacitor and the negative-side capacitor not included in the another charging path.

Description

Technical Field

[0001] The present invention relates to a buffer circuit and a power conversion device. Background Art

[0002] Conventionally, various snubber circuits for reducing surge voltage have been proposed (for example, see Patent Documents 1 to 3).

[0003] Patent Document 1: Japanese Patent Application Laid-Open No. 2016-144340

[0004] Patent Document 2: Japanese Patent Application Laid-Open No. 2009-247132

[0005] Patent Document 3: Japanese Patent No. 5516055 Summary of the Invention

[0006] Technical issues

[0007] In recent years, there has been a demand for more reliable prevention of element destruction and reduction of circuit loss.

[0008] Technical Solution

[0009] To address the above-mentioned issues, a first aspect of the present invention provides a snubber circuit. The snubber circuit may include N (where N is an integer greater than or equal to 2) parallel charging paths, each of which includes a positive-side capacitor, a first diode, and a negative-side capacitor connected in series between a positive-side wiring and a negative-side wiring, and allows current to flow from the positive-side wiring to the negative-side wiring. The snubber circuit may also include N+1 parallel discharging paths, each of which includes a second diode connected between the negative-side wiring or the negative-side capacitor in the kth (where k is an integer 0 ≤ k < N) of the N charging paths, and the positive-side capacitor or the positive-side wiring in the k+1th (where k is an integer 0 ≤ k < N) of the N charging paths. The N+1 discharging paths allow current to flow from the negative-side wiring to the positive-side wiring via at least one of the negative-side capacitor and the positive-side capacitor. The snubber circuit may include an additional charging path having an inductor connected in series with a second diode between a positive-side capacitor in the i-th charging path (where i is an integer 1 ≤ i ≤ N-1) and a negative-side capacitor in the i+1-th charging path among N charging paths, and allowing current to flow from the positive-side wiring side to the negative-side wiring side via the positive-side capacitor in the i-th charging path, the second diode, the inductor, and the negative-side capacitor in the i+1-th charging path. Of the positive-side capacitors and negative-side capacitors in the i-th and i+1-th charging paths, the capacitance of the positive-side capacitor and the negative-side capacitor included in the additional charging path may be greater than the capacitance of each of the positive-side capacitor and the negative-side capacitor not included in the additional charging path.

[0010] The capacitances of the negative side capacitor and the positive side capacitor in the other charging path may be equal to each other. The capacitances of the negative side capacitor and the positive side capacitor in the discharge path through the second diode and the inductor may be equal to each other.

[0011] N can be 2.

[0012] The inductance of each charging path may be smaller than the inductance of each discharging path.

[0013] In a second aspect of the present invention, a power conversion device is provided. The power conversion device may include a transformer whose primary side is connected to an AC power supply. The power conversion device may include a rectifier circuit connected to the secondary side of the transformer and outputting a DC voltage corresponding to the output from the secondary side of the transformer between positive and negative wiring. The power conversion device may include the buffer circuit of the first aspect connected between the positive and negative wiring.

[0014] In a third aspect of the present invention, a power conversion device is provided. The power conversion device may include an inverter or a chopper that outputs a DC voltage between a positive-side wiring and a negative-side wiring. The power conversion device may include the buffer circuit of the first aspect connected between the positive-side wiring and the negative-side wiring.

[0015] At least one of the positive-side wiring and the negative-side wiring may have inductance. A resonance period between the inductance of the wiring and the inductance of the inductor in the snubber circuit and the positive-side capacitor and the negative-side capacitor in another charging path may be an even multiple of a resonance period between the inductance of the wiring and the positive-side capacitor and the negative-side capacitor in each of the i-th charging path and the (i+1)-th charging path.

[0016] The resonance period between the inductance of the wiring and the inductance of the inductor in the snubber circuit and the positive-side capacitor and the negative-side capacitor in another charging path can be twice the resonance period between the inductance of the wiring and the positive-side capacitor and the negative-side capacitor in each of the i-th charging path and the i+1-th charging path.

[0017] The inductance of the wiring and the inductance of the inductor in the snubber circuit may be equal.

[0018] The power conversion device may further include a smoothing inductor provided in at least one of the positive-side wiring and the negative-side wiring.

[0019] The power conversion device may include a plurality of snubber circuits between the positive-side wiring and the negative-side wiring.

[0020] It should be noted that the above summary of the invention does not list all the essential features of the present invention. In addition, sub-combinations of these feature groups can also constitute other inventions. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a circuit diagram of the power conversion device 1 according to this embodiment.

[0022] Figure 2 The flow of current when a surge voltage is absorbed via the charging path 21 is shown.

[0023] Figure 3 The flow of current when a surge voltage is absorbed via the charging path 23 is shown.

[0024] Figure 4 The flow of current when the surge voltage is released via the discharge path 22 is shown.

[0025] Figure 5 1 and 2 show the operating waveforms of the buffer circuit 2.

[0026] Figure 6 A power conversion device 1A according to a modified example is shown.

[0027] Explanation of symbols

[0028] 1 Power conversion device, 2 Snubber circuit, 3 Inverter, 4 Load, 10 AC power supply, 11 Transformer, 12 Rectifier circuit, 12a to 12d diodes, 16 Smoothing inductor, 17 Smoothing capacitor, 21 Charging path, 22 Discharging path, 23 Charging path, 101 Positive output terminal, 102 Negative output terminal, 103 Positive wiring, 104 Negative wiring, 110 Leakage inductance, 120 Parasitic capacitance, 211 Positive capacitor, 213 Negative capacitor, 221 Second diode, 231 Inductor DETAILED DESCRIPTION

[0029] The present invention will be described below by way of embodiments of the invention, but the following embodiments are not intended to limit the invention as claimed. Furthermore, not all combinations of features described in the embodiments are necessarily essential to the solution provided by the invention.

[0030] [1. Circuit Structure of Power Converter]

[0031] Figure 1This is a circuit diagram of a power conversion device 1 according to this embodiment. The power conversion device 1 converts AC power into DC power and outputs it. The power conversion device 1 includes an AC power source 10, a transformer 11, a rectifier circuit 12, a snubber circuit 2, a smoothing inductor 16, and a smoothing capacitor 17. The rectifier circuit 12, snubber circuit 2, and smoothing capacitor 17 of the power conversion device 1 can be arranged between a positive-side wiring 103 and a negative-side wiring 104. The power conversion device 1 can output a DC voltage from a positive-side output terminal 101 connected to the positive-side wiring 103 and a negative-side output terminal 102 connected to the negative-side wiring 104. One or more loads (not shown) can be connected to the positive-side output terminal 101 and the negative-side output terminal 102.

[0032] [1-1. AC power supply 10]

[0033] The AC power supply 10 outputs AC power. In this embodiment, the AC power supply 10 is a DC / AC inverter, but it may also be a commercial power supply. The AC power supply 10 can supply AC power to the transformer 11.

[0034] [1-2. Transformer 11]

[0035] The primary side of the transformer 11 is connected to the AC power supply 10, and the secondary side is connected to the rectifier circuit 12. The transformer 11 insulates the AC power supply 10 from the rectifier circuit 12, transforms the AC power from the AC power supply 10, and supplies it to the rectifier circuit 12. In this embodiment, as an example, an electromotive force E can be generated in the secondary coil of the transformer 11.

[0036] Note that a leakage inductance 110 may be present on the secondary side of the transformer 11. Thus, at least one of the positive-side wiring 103 and the negative-side wiring 104 may have inductance.

[0037] [1-3. Rectifier circuit 12]

[0038] The rectifier circuit 12 is connected to the secondary side of the transformer 11 and outputs a DC voltage corresponding to the output from the secondary side of the transformer 11 between the positive side wiring 103 and the negative side wiring 104. In this embodiment, as an example, the rectifier circuit 12 is a diode bridge that performs full-wave rectification on the AC power output from the secondary side of the transformer 11. The rectifier circuit 12 can have four diodes 12a to 12d, wherein the diode 12a and the diode 12b, and the diode 12c and the diode 12d can be connected in series between the positive side wiring 103 and the negative side wiring 104, respectively. Parasitic capacitance 120a to 120d may exist in each of the diodes 12a to 12d. The parasitic capacitance 120a to 120d can resonate with the leakage inductance 110 of the transformer 11. The rectifier circuit 12 can supply the rectified voltage to the load (not shown) via the buffer circuit 2, the smoothing inductor 16, and the smoothing capacitor 17.

[0039] [1-4. Buffer Circuit 2]

[0040] The snubber circuit 2 is connected between the positive-side wiring 103 and the negative-side wiring 104. The snubber circuit 2 absorbs surge voltage generated when the direction of current is reversed within the rectifier circuit 12 (in this embodiment, as an example, when the AC current supplied from the secondary side of the transformer 11 to the rectifier circuit 12 passes through zero), thereby protecting the various components of the power conversion device 1 (for example, the diodes 12a to 12d of the rectifier circuit 12).

[0041] The buffer circuit 2 includes N parallel charging paths 21, N+1 parallel discharging paths 22, and one or more parallel additional charging paths 23. Note that the number N is an integer greater than or equal to 2. In this embodiment, the number N is 2 as an example. Furthermore, in this embodiment, the two charging paths 21 are described as, from the left side of the figure, the first charging path 211 and the second charging path 212. Furthermore, the three discharging paths 22 are described as, from the left side of the figure, the first discharging path 221, the second discharging path 222, and the third discharging path 223. The subscripts 1, ..., N indicate the path number. In the figure, the charging path 23 is represented by dots.

[0042] [1-4-1. Charging path 21]

[0043] Each charging path 21 k (where k is an integer of 1≤k≤N) having a positive side capacitor 211 (also referred to as a positive side capacitor 211) sequentially connected in series between the positive side wiring 103 and the negative side wiring 104. k ), the first diode 212 (also referred to as the first diode 212 k ) and the negative side capacitor 213 (also referred to as the negative side capacitor 213k The positive side capacitor 211 and the negative side capacitor 213 each function as a buffer capacitor, absorbing the instantaneous surge voltage generated when the current is converted within the rectifier circuit 12 (for example, a surge voltage applied to the element during a period greater than 10ns and less than 10μs). For example, the positive side capacitor 211 and the negative side capacitor 213 can suppress vibrations greater than 100kHz and less than 100MHz. As an example, the positive side capacitor 211 and the negative side capacitor 213 can be a film capacitor or a laminated ceramic capacitor.

[0044] The first diode 212 is disposed with its anode facing the positive wiring 103 and its cathode facing the negative wiring 104. Thus, current flows from the positive wiring 103 to the negative wiring 104 in each charging path 21.

[0045] [1-4-2. Discharge Path 22]

[0046] Each discharge path 22 k The second diode 221 (also referred to as the second diode 221) k ). Second diode 221 k connected to the negative side wiring 104 or the kth charging path 21 among the N charging paths 21 k Negative side capacitor 213 in k and the k+1th charging path 21 among the N charging paths 21 k+1 The positive side capacitor 211 in k+1 or between the positive side wiring 103. For example, the second diode 2211 of the first discharge path 221 is connected between the negative side wiring 104 and the positive side capacitor 2111 of the first charge path 211. The second diode 2212 of the second discharge path 222 is connected between the negative side capacitor 2131 of the first charge path 211 and the positive side capacitor 2112 of the second charge path 212. The second diode 2213 of the third discharge path 223 is connected between the negative side capacitor 2132 of the second charge path 212 and the positive side wiring 103. The anode of the second diode 221 faces the kth charge path 211. k or the negative wiring 104 side and the cathode toward the k+1th charging path 21 k+1 Thus, each discharge path 22 allows current to flow from the negative-side wiring 104 side to the positive-side wiring 103 side via at least one of the negative-side capacitor 213 and the positive-side capacitor 211 .

[0047] The inductance of each discharge path 22 can be greater than the inductance of each charge path 21. In other words, the inductance of each charge path 21 can be smaller than the inductance of each discharge path 22. For example, the wiring length of each charge path 21 can be shorter than the wiring length of each discharge path 22. As an example, the wiring length connecting the positive-side wiring 103 and the negative-side wiring 104 of each charge path 21 can be shorter than the wiring length connecting the positive-side wiring 103 and the negative-side wiring 104 of each discharge path 22.

[0048] [1-4-3. Charging path 23]

[0049] One or more charging paths 23 (also referred to as charging paths 23 i wherein i is at least one integer in the range of 1≤i≤N-1) having an inductor 231 (also referred to as an inductor 231 i ). Inductor 231 i Among the N charging paths 21, the i-th charging path 21 i (where i is an integer of 1≤i≤N-1) in the positive side capacitor 211 i and the i+1th charging path 21 i+1 Negative side capacitor 213 in i+1 Between the second diode 221 i are connected in series. Thus, the inductor 231 i Can be included in the discharge path 22 i In the second diode 221 i Can be included in the charging path 23 i Thus, each charging path 23 i From the positive side wiring 103 side to the negative side wiring 104 side via the i-th charging path 21 i The positive side capacitor 211 in i , second diode 221 i 、Inductor 231 i and the i+1th charging path 21 i+1 Negative side capacitor 213 in i+1 When the discharge path 22 includes the inductor 231, the inductance of the discharge path 22 may include the inductance of the inductor 231. Note that in this embodiment, since the number N of charging paths 22 is 2 as an example, the number i of charging paths 23 may be 1.

[0050] [1-4-4. Positive Side Capacitor 211 and Negative Side Capacitor 213]

[0051] Charging path 21 i ,twenty one i+1 Each positive side capacitor 211 ini , 211 i+1 and negative side capacitor 213 i , 213 i+1 Included in the charging path 23 i The positive side capacitor 211 in i and negative side capacitor 213 i+1 The capacitance is greater than that not included in the charging path 23 i The positive side capacitor 211 in i+1 and negative side capacitor 213 i For example, there are two capacitors in the charging path 21. i ,twenty one i+1 and charging path 23 i The capacitance of each capacitor on the charging path 21 can be greater than that of the capacitor only on the charging path 21 i ,twenty one i+1 Furthermore, the charging path 23 i The positive side capacitor 211 in i and negative side capacitor 213 i+1 The capacitance can be larger than that of the charging path 23 i The second diode 221 in i and inductor 231 i Discharge path 22 i Negative side capacitor 213 in i and positive side capacitor 211 i+1 In this embodiment, as an example, the capacitances of the positive capacitor 2111 and the negative capacitor 2132 in the charging path 231 are larger than the capacitances of the negative capacitor 2131 and the positive capacitor 2112 in the discharging path 222 .

[0052] [1-5. Smoothing inductor 16]

[0053] Smoothing inductor 16 is provided on positive-side wiring 103. Smoothing inductor 16 can smooth the current output from power conversion device 1. It should be noted that smoothing inductor 16 may be provided on negative-side wiring 104 instead of positive-side wiring 103, or may be provided on negative-side wiring 104 in addition to positive-side wiring 103.

[0054] [1-6. Smoothing capacitor 17]

[0055] Smoothing capacitor 17 is provided between positive-side wiring 103 and negative-side wiring 104. Smoothing capacitor 17 can smooth the current output from power converter 1. The voltage of smoothing capacitor 17, that is, output voltage Vo output from power converter 1, can be lower than the electromotive force E of the secondary coil in transformer 11.

[0056] [1-7. Operation of Power Converter 1]

[0057] In the power conversion device 1 of this embodiment, while the output current from the rectifier circuit 12 is increasing, the positive capacitor 211 and the negative capacitor 213 are charged via the charging paths 21 and 23. While the output current from the rectifier circuit 12 is decreasing, the positive capacitor 211 and the negative capacitor 213 are discharged via the discharging path 22. Furthermore, when the AC current supplied to the rectifier circuit 12 crosses zero, the direction of the current is reversed in the rectifier circuit 12, generating a surge voltage. This surge voltage can be generated significantly due to resonance between the leakage inductance 110 and the parasitic capacitance 120 and / or the reverse recovery current of the diode 12.

[0058] On the other hand, in snubber circuit 2, since positive capacitor 211 and negative capacitor 213 are discharged when a surge voltage occurs, positive capacitor 211 and negative capacitor 213 are charged via charging paths 21 and 23 to absorb the surge voltage, and then positive capacitor 211 and negative capacitor 213 are discharged. The operations in these cases will be described.

[0059] [1-7-1. Absorption of Surge Voltage via Charging Path 21]

[0060] Figure 2 2 shows the flow of current when a surge voltage is absorbed via the charging path 21. In addition, the dotted arrows in the figure indicate the flow of current.

[0061] When the direction of the current in the rectifier circuit 12 is reversed, the output current from the rectifier circuit 12 decreases and then increases. This output current flows through the positive-side capacitor 211, the first diode 212, and the negative-side capacitor 213 of each charging path 21. Thus, when the direction of the current in the rectifier circuit 12 is reversed, the energy accumulated in the inductor 110 is absorbed by charging the positive-side capacitor 211 and the negative-side capacitor 213 of the charging path 21.

[0062] Here, in this embodiment, as an example, the capacitance of the positive capacitor 2111 in the charging path 211 is greater than the capacitance of the negative capacitor 2131, and the capacitance of the negative capacitor 2132 in the charging path 212 is greater than the capacitance of the positive capacitor 2112. Therefore, among the positive capacitors 211 and negative capacitors 213 included in the charging paths 211 and 212, the voltage of the negative capacitor 2131 and positive capacitor 2112 not included in the charging path 231 rises earlier than the voltage of the positive capacitor 2111 and negative capacitor 2132 included in the charging path 231.

[0063] [1-7-2. Absorption of Surge Voltage via Charging Path 23]

[0064] Figure 3 This figure shows the current flow when a surge voltage is absorbed through charging path 23. Since inductor 231 is provided in charging path 23, the current in charging path 23 can be blocked immediately after a surge voltage is generated. When the voltages of negative capacitor 2131 and positive capacitor 2112 become higher than those of positive capacitor 2111 and negative capacitor 2132 due to charging through charging path 21, the output current from rectifier circuit 12 flows through positive capacitor 2111, first diode 2121, second diode 2212, inductor 231, first diode 2122, and negative capacitor 2132. Consequently, energy accumulated in inductor 110 when the direction of current in rectifier circuit 12 is reversed is also absorbed by charging positive capacitor 2111 and negative capacitor 2132 in charging path 231.

[0065] In this embodiment, the capacitances of positive capacitor 2111 and negative capacitor 2132 are larger than the capacitances of negative capacitor 2131 and positive capacitor 2112, respectively. Therefore, when a surge voltage is absorbed by positive capacitor 211 and negative capacitor 213 via charging path 21 or charging path 23 as described above, the voltage rises early due to the smaller capacitances of negative capacitor 2131 and positive capacitor 2112. This allows for both preventing further energy inflow and suppressing an excessive voltage rise caused by the larger capacitances of positive capacitor 2111 and negative capacitor 2132. As a result, the voltage of each discharge path 22 can be reduced to less than the electromotive force E on the secondary side of transformer 11. Therefore, since the energy charged in the charging paths 21 and 23 is not discharged through the discharging path 22, the energy charged in the positive capacitor 211 and the negative capacitor 213 when the direction of the current is reversed within the rectifier circuit 12 is not consumed as circuit loss by the resonant operation between the leakage inductance 110 and the positive capacitor 211 or the negative capacitor 213, but is instead accumulated in the positive capacitor 211 and the negative capacitor 213 and regenerated. This reduces the circuit loss caused by the resonant operation.

[0066] [1-7-3. Release of Surge Voltage via Discharge Path 22]

[0067] Figure 4This figure shows the current flow when a surge voltage is released via discharge path 22. When the electromotive force on the input side of the circuit, that is, the voltage between positive wiring 103 and negative wiring 104, reaches 0V or approximately 0V, smoothing inductor 16 draws a constant current through its smoothing action. Meanwhile, since the electromotive force in each discharge path 221-223 exceeds 0V due to the charge accumulated in the capacitors, the current for smoothing inductor 16 is supplied from these capacitors. As a result, each capacitor is discharged to approximately 0V. Since the discharge current is primarily determined by smoothing inductor 16 and is largely unaffected by the circuit's resistance components, the circuit loss during discharge is extremely small compared to discharge via resistance.

[0068] The snubber circuit 2 described above includes N (two, as an example, in this embodiment) parallel charging paths 21, each including a positive-side capacitor 211 and a negative-side capacitor 213. Consequently, when the direction of current is reversed within the rectifier circuit 12, the energy stored in the inductor 110 charges the positive-side capacitor 211 and the negative-side capacitor 213 through each charging path 21 to a voltage higher than the voltage between the positive-side wiring 103 and the negative-side wiring 104 (in this embodiment, as an example, the electromotive force E of the transformer 11). This prevents component damage caused by surge voltage.

[0069] Furthermore, the buffer circuit 2 includes a positive side capacitor 211 extending from the positive side wiring 103 side. i , second diode 221 i+1 and negative side capacitor 213 i+1 There is another charging path 23 for the current to flow to the negative side wiring 104. Therefore, when the direction of the current is changed in the rectifier circuit 12, charging can also be performed through the charging path 23. i and the negative side capacitor 213 i+1 Between the second diode 221 i+1 An inductor 231 is connected in series, and the charging path 23 i The positive side capacitor 211 in i and negative side capacitor 213 i+1 The capacitance of the negative side capacitor 213 is greater than i and positive side capacitor 211 i+1 Thus, when the direction of the current is changed in the rectifier circuit 12, the charging path 21 is started. i ,twenty one i+1 The positive side capacitor 211 i , 211 i+1 and negative side capacitor 213 i , 213 i+1After charging, start charging path 23 i The positive side capacitor 211 i and negative side capacitor 213 i+1 Therefore, the negative side capacitor 213 with small capacitance i , positive side capacitor 211 i+1 The voltage due to the charging path 21 i ,twenty one i+1 After the charge of the positive side capacitor 211 increases earlier, the capacitance of the positive side capacitor 211 increases i , negative side capacitor 213 i+1 The voltage due to the charging path 23 i Since the voltage increases with the charge, the timing of the voltage increase between the positive-side wiring 103 and the negative-side wiring 104 can be dispersed, and the peak voltage can be reduced. As a result, it is possible to more reliably prevent element damage caused by surge voltage.

[0070] Furthermore, the snubber circuit 2 includes N+1 discharge paths 22, which flow current from the negative wiring 104 to the positive wiring 103 via at least one of the negative capacitor 213 and the positive capacitor 211. When the surge voltage generated by the current switching within the rectifier circuit 12 is absorbed by the charging paths 21 and 23, the voltage in each discharge path 22 is lower than the electromotive force E on the secondary side of the transformer. Therefore, the energy stored in the charging paths 21 and 23 during the application of electromotive force E is not discharged through the discharge paths 22. Consequently, recharge after discharge, or resonant operation, is not performed. The energy stored in the positive capacitor 211 and the negative capacitor 213 when the current switching within the rectifier circuit 12 occurs is retained until the secondary electromotive force reaches 0 V. Thereafter, it is regenerated to the load side through the current draining operation of the smoothing inductor 16. This reduces circuit losses caused by resonant operation.

[0071] Furthermore, since this prevents component damage caused by surge voltages when the direction of current is reversed within the rectifier circuit 12 and reduces circuit losses, it is possible to increase the allowable inductance of the wiring connected to the positive-side wiring 103 and the negative-side wiring 104. In other words, the degree of freedom in the wiring length of the positive-side wiring 103 and the negative-side wiring 104 can be increased.

[0072] Furthermore, since the inductance of each charging path 21 is smaller than the inductance of each discharging path 22, the surge voltage generated when the direction of current is reversed within the rectifier circuit 12 can be reliably reduced by the charging path 21. Furthermore, the wiring inductance of the discharging path 22 can prevent the generation of an excessive inrush current when current flows due to discharge.

[0073] Furthermore, according to the power conversion device 1 having the snubber circuit 2 as described above, even if a surge voltage increases when the direction of current is reversed in the rectifier circuit 12 due to resonance between the leakage inductance 110 of the transformer 11 and the parasitic capacitances 120a to 120d included in the diodes 12a to 12d of the rectifier circuit 12 and / or reverse recovery current of the diodes 12a to 12d, the surge voltage can be reduced to prevent damage to the components.

[0074] Furthermore, since smoothing inductor 16 is provided on at least one of positive-side wiring 103 and negative-side wiring 104, when the direction of current is switched within rectifier circuit 12, the energy charged in positive-side capacitor 211 and negative-side capacitor 213 is drained through smoothing inductor 16 and supplied to the load. Thus, when the direction of current is switched within rectifier circuit 12, all energy stored in inductor 110 is supplied to the load via smoothing inductor 16, excluding conduction losses in first diode 212 and second diode 221. Therefore, power can be supplied to the load with substantially no loss.

[0075] [2. Resonance between Leakage Inductance 110 and Snubber Circuit 2]

[0076] In the power conversion device 1 of this embodiment, when absorbing the surge voltage via the charging path 23, the negative side capacitor 213 i and the negative side capacitor 213 i+1 The voltage difference can also be obtained from the negative side capacitor 213 i The energy is drained and passes through the second diode 221 i and inductor 231 i Supplied to the negative side capacitor 213 i+1 In addition, the output current output from the rectifier circuit 12 can also be output from the positive side capacitor 211 i The current does not flow to the second diode 221 but flows to the negative side capacitor 213. i side (ie through the charging path 21 i ), to the negative side capacitor 213 i As a result, the negative side capacitor 213 i The voltage can oscillate.

[0077] Such oscillation can be adjusted by the resonance period between the leakage inductance 110 of the transformer 11 and the inductance of the inductor 231 of the snubber circuit 2 and the capacitor of the charging path 21, and the resonance period between the leakage inductance 110 and the capacitor of the charging path 23. i The positive side capacitor 211 in i and negative side capacitor 213 i+1The resonance period T2 is relative to the leakage inductance 110 and the charging path 21. i ,twenty one i+1 Each of the positive side capacitors 211 i , 211 i+1 and negative side capacitor 213 i , 213 i+1 The resonance period T1 of the positive capacitor 211 can be an even multiple (in this embodiment, as an example, it is 2 times). i , negative side capacitor 213 i+1 When the voltage on the positive side wiring 103 and the negative side wiring 104 increases due to charging through the charging path 23 and reaches its maximum, the voltage on the capacitor with the smaller capacitance in the charging path 21 reaches its minimum. This effectively reduces the peak voltage generated between the positive side wiring 103 and the negative side wiring 104, and more effectively prevents component damage caused by surge voltage. It should be noted that the resonance period T2 may not be a strictly even multiple of the resonance period T1, but rather a roughly even multiple. The resonance period T2 may be in the range of 1.5 to 2.5 times the resonance period T1.

[0078] Here, the leakage inductance 110 of the transformer 11 may be equal to the inductance of the inductor 231 in the snubber circuit 2. i Negative side capacitor 213 in i+1 With the positive side capacitor 211 i The capacitances of the diodes 221 and 222A can be equal to each other. i+1 and inductor 231 i Discharge path 22 i Negative side capacitor 213 in i With the positive side capacitor 211 i+1 The capacitances of the capacitors can be equal to each other. This makes it easier to adjust the resonance period.

[0079] That is, in this case, the negative side capacitor 213 with a smaller capacitance can be i and positive side capacitor 211 i+1 The capacitances of the capacitors are represented as Ca, and the negative side capacitor 213 on the side with the larger capacitance i+1 and positive side capacitor 211 i The capacitances of the transformers 11 and 231 are represented by Cb. Therefore, if the leakage inductance 110 of the transformer 11 is Lt and the inductance of the inductor 231 in the snubber circuit 2 is Ls (= Lt), the resonant periods T1 and T2 are as shown in equations (4) and (5). By adjusting Ca, Cb, and Lt, T2 can be easily made an even multiple of T1 (for example, 2). For example, Cb can be 5 to 6 times Ca.

[0080] T1≈2π√{Lt·2Ca·Cb / (Ca+Cb)}…(4)

[0081] T2≈2π√{(Lt+Ls)·Ca / 2}

[0082] =2π√(Lt·Ca)…(5)

[0083] Figure 5 The operating waveforms of buffer circuit 2 are shown. The upper graph in the figure shows the relationship between the voltage V1p of the positive-side capacitor 2111, the voltage V1n of the negative-side capacitor 2131, the output voltage Vs of the buffer circuit 2, and the output voltage Vs' of a conventional buffer circuit, all over time. Furthermore, the lower graph in the figure shows the relationship between the current I1p of the positive-side capacitor 2111, the current I1n of the negative-side capacitor 2131, and the output current Is of the buffer circuit 2, all over time. It should be noted that conventional buffer circuits may, for example, have a single buffer capacitor connected between the positive-side wiring 103 and the negative-side wiring 104.

[0084] First, when the direction of the current is reversed in the rectifier circuit 12, the positive side capacitor 2111 and the negative side capacitor 2131 of the charging path 211 are charged, and the voltage of the negative side capacitor 2131 with smaller capacitance rises first, thereby suppressing the increase of the current Is (time T1).

[0085] Next, due to the self-inductance of leakage inductor 110, the current output from rectifier circuit 12 flows through charging path 23, charging negative capacitor 2132. This suppresses the rise in voltage V1n of negative capacitor 2131. Furthermore, current flows from negative capacitor 2131 through inductor 231 of charging path 23, resulting in a decrease in voltage V1n (time T2).

[0086] Next, the negative capacitor 2131 is recharged by the current further output from the rectifier circuit 12 due to the self-inductance of the leakage inductor 110 (time T3). Since only the voltage V1P of the positive capacitor 2111 is lower than the electromotive force E on the secondary side of the transformer 11, no discharge occurs through the discharge path 221. Similarly, since the combined voltage V1n+V2P of the voltage V1n of the negative capacitor 2131 and the voltage V2P of the positive capacitor 2112 is lower than the electromotive force E, no discharge occurs through the discharge path 222. Similarly, since only the voltage V2n of the negative capacitor 2112 is lower than the electromotive force E on the secondary side of the transformer 11, no discharge occurs through the discharge path 223. Therefore, the energy charged to the positive capacitor 211 and the negative capacitor 213 is not dissipated as circuit loss through charging and discharging due to the resonant operation of the leakage inductor 110 with the positive capacitor 211 or the negative capacitor 213.

[0087] [3. Modifications]

[0088] Figure 6 This figure shows a power conversion device 1A according to a modified example. The power conversion device 1A includes an inverter 3 that outputs a DC voltage between a positive-side wiring 103 and a negative-side wiring 104, and a buffer circuit 2. Multiple loads 4 can be connected in parallel to the power conversion device 1A. The inverter 3 can generate a DC voltage from an AC voltage. The inverter 3 can also be a chopper.

[0089] According to the above-described power conversion device 1A, since the snubber circuit 2 is connected between the positive-side wiring 103 and the negative-side wiring 104 that receive the DC voltage, when current is interrupted in any of the multiple loads 4 connected in parallel to the positive-side wiring 103 and the negative-side wiring 104, a surge voltage can be reduced. This prevents other loads 4 from being damaged by the surge voltage.

[0090] [4. Other Modifications]

[0091] While the above-described embodiments and modifications illustrate a case where the power conversion devices 1 and 1A include a single snubber circuit 2 between the positive-side wiring 103 and the negative-side wiring 104, multiple snubber circuits 2 connected in parallel may also be provided. This more reliably prevents component damage due to surge voltage. For example, if the power conversion device 1 includes two snubber circuits 2, one snubber circuit 2 can be physically located close to the series circuit of diodes 12a and 12b in the rectifier circuit 12, while the other snubber circuit 2 can be physically located close to the series circuit of diodes 12c and 12d.

[0092] Furthermore, although the inductance of the wiring connected to the positive-side wiring 103 or the negative-side wiring 104 is described as the leakage inductance 110 of the transformer 11 , the wiring inductance of the wiring or an inductor provided in the wiring may be used.

[0093] Furthermore, although the number N of the charging paths 21 is described as 2, the number N may be 3 or more. In this case, the number of the additional charging paths 23 may be 1 or 2 or more.

[0094] While the present invention has been described above using embodiments, the technical scope of the present invention is not limited to the scope described in the above embodiments. It will be apparent to those skilled in the art that various modifications or improvements can be made to the above embodiments. As will be apparent from the claims, such modifications or improvements are also encompassed within the technical scope of the present invention.

[0095] It should be noted that as long as the order of execution of the operations, sequences, steps, and stages of the apparatus, system, program, and method described in the claims, specifications, and drawings is not specifically specified as "before...", "prior to...", etc., and as long as the results of the previous process are not used in the subsequent process, they may be implemented in any order. Even if the workflow in the claims, specifications, and drawings is described using the phrases "first" or "next" for convenience, it does not mean that it must be executed in that order.

Claims

1. A buffer circuit, characterized in that: have: N parallel charging paths, each having a positive-side capacitor, a first diode, and a negative-side capacitor connected in series between a positive-side wiring and a negative-side wiring, and allowing current to flow from the positive-side wiring side to the negative-side wiring side, where N is an integer greater than or equal to 2; N+1 discharge paths connected in parallel, each of the N+1 discharge paths having a second diode, the second diode being connected between the negative-side wiring or the negative-side capacitor in the k-th charging path among the N charging paths and the positive-side capacitor in the k+1-th charging path among the N charging paths or the positive-side wiring, the N+1 discharge paths flowing current from the negative-side wiring side through at least one of the negative-side capacitor and the positive-side capacitor to the positive-side wiring side, where k is an integer of 0≤k<N; as well as Another charging path includes an inductor connected in series with the second diode between the positive-side capacitor in the i-th charging path and the negative-side capacitor in the (i+1)-th charging path among the N charging paths, and flows current from the positive-side wiring side to the negative-side wiring side via the positive-side capacitor in the i-th charging path, the second diode, the inductor, and the negative-side capacitor in the (i+1)-th charging path, where i is an integer of 1≤i≤N-1. The capacitance of the positive-side capacitor and the negative-side capacitor included in the other charging path among the positive-side capacitor and the negative-side capacitor in the i-th charging path and the i+1-th charging path is respectively greater than the capacitance of each of the positive-side capacitor and the negative-side capacitor not included in the other charging path among the positive-side capacitor and the negative-side capacitor in the i-th charging path and the i+1-th charging path.

2. The buffer circuit according to claim 1, wherein: The capacitances of the negative side capacitor and the positive side capacitor in the other charging path are equal to each other, The capacitances of the negative side capacitor and the positive side capacitor in the discharge path passing through the second diode and the inductor are equal to each other.

3. The buffer circuit according to claim 1, wherein: N is 2.

4. The buffer circuit according to claim 2, wherein: N is 2.

5. The buffer circuit according to any one of claims 1 to 4, wherein: The inductance of each charging path is smaller than the inductance of each discharging path.

6. A power conversion device, characterized in that: have: a transformer, the primary side of which is connected to an AC power source; a rectifier circuit connected to the secondary side of the transformer and outputting a DC voltage corresponding to the output from the secondary side of the transformer between the positive side wiring and the negative side wiring; as well as The buffer circuit according to any one of claims 1 to 5, wherein the buffer circuit is connected between the positive-side wiring and the negative-side wiring.

7. A power conversion device, characterized in that: have: an inverter or a chopper that outputs a DC voltage between the positive-side wiring and the negative-side wiring; and The buffer circuit according to any one of claims 1 to 5, wherein the buffer circuit is connected between the positive-side wiring and the negative-side wiring.

8. The power conversion device according to claim 6 or 7, characterized in that: At least one of the positive side wiring and the negative side wiring has inductance, A resonance period between the inductance of the wiring and the inductance of the inductor in the snubber circuit and the positive-side capacitor and the negative-side capacitor in the other charging path is an even multiple of a resonance period between the inductance of the wiring and the positive-side capacitor and the negative-side capacitor in each of the i-th charging path and the (i+1)-th charging path.

9. The power conversion device according to claim 8, characterized in that A resonance period between the inductance of the wiring and the inductance of the inductor in the snubber circuit and the positive-side capacitor and the negative-side capacitor in the other charging path is twice a resonance period between the inductance of the wiring and the positive-side capacitor and the negative-side capacitor in each of the i-th charging path and the (i+1)-th charging path.

10. The power conversion device according to claim 8, wherein: The inductance of the wiring is equal to the inductance of the inductor in the snubber circuit.

11. The power conversion device according to claim 9, characterized in that The inductance of the wiring is equal to the inductance of the inductor in the snubber circuit.

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