Power converter

Abstract

To provide a power conversion device that keeps energy loss low and avoids increasing size.SOLUTION: A power conversion device includes a first upper arm circuit SA, a second upper arm circuit SN, a first lower arm circuit SB, a second lower arm circuit SM, and a capacitor CF. The upper arm circuits SA and SN are configured by connecting one or more first switch circuits including a first switching element in series, and the lower arm circuits SB and SM are configured by connecting one or more second switch circuits including a second switching element in series. The power conversion device includes a first circuit that connects a first capacitor and a power storage unit in parallel via the one or more first switching elements, and a second circuit that connects a second capacitor and the power storage unit in parallel via the one or more second switching elements.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] Embodiments of the present invention relate to a power conversion device.

Background Art

[0002] In recent years, multi-level power conversion devices capable of outputting voltages of multiple levels have been proposed. According to a multi-level power conversion device, it is possible to achieve miniaturization and high efficiency compared to a general two-level power conversion device. For example, a multi-level power conversion device provided with a flying capacitor can, in principle, uniformly charge and discharge the flying capacitor, and an additional circuit for balancing the capacitor voltage is unnecessary. Further, since the flying capacitor is charged and discharged at the PWM carrier frequency, the higher the PWM carrier frequency, the smaller the voltage ripple of the flying capacitor can be made, and the capacity of the flying capacitor can be reduced to achieve miniaturization.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] On the other hand, in a multi-level power conversion device provided with a flying capacitor, when the switching frequency is increased, it is necessary to increase the size of the cooler in order to cool the heat generated by the switching loss, and there is a limit to the miniaturization of the device due to the trade-off between the switching loss and the capacity of the flying capacitor.

[0005] Embodiments of the present invention have been made in view of the above circumstances, and an object thereof is to provide a power conversion device capable of suppressing energy loss to a low level and avoiding an increase in size. [Means for solving the problem]

[0006] The power conversion device according to this embodiment comprises: an energy storage unit; an upper arm having a first upper arm circuit and a second upper arm circuit connected in series between the AC terminal and the positive DC terminal; a lower arm having a first lower arm circuit and a second lower arm circuit connected in series between the AC terminal and the negative DC terminal; and a flying capacitor electrically connected to the upper arm between the first upper arm circuit and the second upper arm circuit, and electrically connected to the lower arm between the first lower arm circuit and the second lower arm circuit, wherein each of the first upper arm circuit and the second upper arm circuit has a first switching element. The first lower arm circuit and the second lower arm circuit are configured by connecting one or more switch circuits in series, and each of the first lower arm circuit is configured by connecting one or more second switch circuits having a second switching element in series, and at least one of the first switch circuits has a first capacitor connected in parallel with the first switching element, or at least one of the second switch circuits has a second capacitor connected in parallel with the second switching element, and when at least one of the first switch circuits has a first capacitor connected in parallel with the first switching element, one or more of the first switching elements are connected via 、 Multiple first capacitors They can be connected in parallel, The first capacitor and the energy storage unit are connected in parallel. It is possible When a first regenerative rectifier circuit is present and at least one of the second switch circuits has a second capacitor connected in parallel with the second switching element, via one or more of the second switching elements 、 Multiple Configurable Capacitors They can be connected in parallel, The second capacitor and the energy storage unit are connected in parallel. It is possible It has a second-stage rectifier circuit. [Brief explanation of the drawing]

[0007] [Figure 1]Figure 1 is a schematic diagram showing one example configuration of a power conversion device according to the first embodiment. [Figure 2] Figure 2 is a diagram illustrating an example of the operation of the power converter according to the first embodiment. [Figure 3] Figure 3 is a schematic diagram showing one example configuration of the power conversion device according to the second embodiment. [Figure 4] Figure 4 is a schematic diagram showing one example configuration of the power conversion device according to the third embodiment. [Figure 5] Figure 5 is a schematic diagram showing one example configuration of the power conversion device according to the fourth embodiment. [Figure 6] Figure 6 is a diagram illustrating an example of the operation of the power converter according to the fourth embodiment. [Modes for carrying out the invention]

[0008] Several embodiments of power conversion devices will be described in detail below with reference to the drawings. Figure 1 is a schematic diagram showing one example configuration of a power conversion device according to the first embodiment. The power converter of this embodiment is, for example, a three-level flying capacitor type power converter capable of mutually converting DC power and single-phase AC power, and comprises a control circuit CTR, an inverter cell 100, an upper arm, a lower arm, n+a (where n and a are positive integers) first regenerative rectifier circuits (regenerative rectifier diodes 6UN, 6UA and first resistors 5UN, 5UA), m+b (where m and b are positive integers) second regenerative rectifier circuits (regenerative rectifier diodes 6XM, 6XB and second resistors 5XM, 5XB), a flying capacitor CF, a positive DC terminal 209, a negative DC terminal 210, and an AC terminal 211.

[0009] In the embodiments described below, N, A, M, and B are N=1 to n, A=1 to a, M=1 to m, and B=1 to b (where n, a, m, and b are 2 or greater), and the same applies hereafter unless otherwise specified. Furthermore, the first resistors 5UN and 5UA and the second resistors 5XM and 5XB may also be inductance elements. The control circuit CTR controls the operation of the inverter cell 100, the upper arm, and the lower arm based on control signals from, for example, a higher-level control device of the power converter.

[0010] The upper arm of the power converter in this embodiment includes a first upper arm circuit SA and a second upper arm circuit SN. The first upper arm circuit SA includes a number of switch circuits (voltage-type clamp-type switch circuits) 101A. The second upper arm circuit SN includes n number of switch circuits (voltage-type clamp-type switch circuits) 101N.

[0011] The lower arm of the power converter in this embodiment includes a first lower arm circuit SB and a second lower arm circuit SM. The first lower arm circuit SB includes b switch circuits (voltage-type clamp switch circuits) 102B. The second lower arm circuit SM includes m switch circuits (voltage-type clamp switch circuits) 102M.

[0012] In this embodiment, a DC capacitor (not shown) is electrically connected between the positive DC terminal 209 and the negative DC terminal 210 of the power converter. The DC capacitor may be included in the power converter or mounted externally.

[0013] The inverter cell 100 includes a switching element (upper switching element) 1U, a switching element (lower switching element) 1X, an energy storage unit 2, a positive cell terminal (high potential side end) 200, a negative cell terminal (low potential side end) 201, and a cell AC terminal (AC end) 202. The positive cell terminal 200, the negative cell terminal 201, and the cell AC terminal 202 are configured to allow electrical connection of the circuit at their respective positions; the terminals may be omitted.

[0014] The switching element 1U and the switching element 1X are, for example, MOSFETs (metal-oxide semiconductor field-effect transistors). The drain (high-potential side terminal) of the switching element 1U is electrically connected to the positive side cell terminal 200, and the source (low-potential side terminal) is electrically connected to the drain (high-potential side terminal) of the switching element 1X. The source (low-potential side terminal) of the switching element 1X is electrically connected to the negative side cell terminal 201. Between the switching element 1U and the switching element 1X, it is electrically connected to the cell AC terminal 202.

[0015] The power storage unit 2 is, for example, a floating capacitor and is connected in parallel with the switching element 1U and the switching element .....

[0016] Each of the n switching circuits (first switching circuit) 101N includes a switching element (first switching element) 1UN, a positive side terminal 203N, and a negative side terminal 204N. At least one of the n first switching circuits 101N includes a diode (first diode) 4UN, a capacitor (first capacitor) 3UN, and a snubber terminal 205N. In this embodiment, the case where all of the n first switching circuits 101N include a diode (first diode) 4UN, a capacitor (first capacitor) 3UN, and a snubber terminal 205N will be described.

[0017] Note that the snubber terminal 205N, the positive side terminal 203N, and the negative side terminal 204N may be configured such that the circuit can be electrically connected at the positions of these terminals, and the terminals may be omitted. Further, the switch circuit 101N may include a plurality of switching elements 1UN. In that case, the plurality of switching elements 1UN are connected in parallel to the capacitor 3UN and the diode 4UN between the positive terminal 203N and the negative terminal 204N. The plurality of switching elements 1UN may be connected in series with each other or in parallel with each other.

[0018] The switching element 1UN is, for example, a MOSFET. The drain (high potential side end) of the switching element 1UN is electrically connected to the positive terminal 203N, and the source (low potential side end) of the switching element 1UN is electrically connected to the negative terminal 204N.

[0019] The cathode of the diode 4UN is electrically connected to the source of the switching element 1UN and the negative terminal 204N, and the anode is electrically connected to the snubber terminal 205N. Note that the diode 4UN desirably has a fast recovery characteristic with low recovery loss. For example, it is desirable to use an element using a Schottky barrier diode (SBD) with good recovery characteristics or a wide bandgap semiconductor (such as SiC or GaN).

[0020] One end (high potential side end) of the capacitor (snubber capacitor) 3UN is electrically connected to the drain of the switching element 1UN and the positive terminal 203N, and the other end (low potential side end) is electrically connected to the anode of the diode 4UN and electrically connected to the snubber terminal 205N.

[0021] The n switch circuits 101N are connected in series. That is, the positive terminal (high potential side) 203N of switch circuit 101N is electrically connected to the negative terminal (low potential side) 204N of the adjacent switch circuit 101N on the high potential side, and the positive terminal 203N (N=n) of the switch circuit 101N with the highest potential is electrically connected to the positive DC terminal 209. The negative terminal 204N of switch circuit 101N is electrically connected to the positive terminal 203N of the adjacent switch circuit 101N on the low potential side, and the negative terminal 204N (N=1) of the switch circuit 101N with the lowest potential is electrically connected to the positive terminal 203A (A=a) of the switch circuit 101A with the highest potential.

[0022] Each of the a switch circuits (first switch circuits) 101A includes a switching element (first switching element) 1UA, a positive terminal 203A, and a negative terminal 204A. At least one of the a first switch circuits 101A includes a diode (first diode) 4UA, a capacitor (first capacitor) 3UA, and a snubber terminal 205A. In this embodiment, we will describe the case where all of the a first switch circuits 101A include a diode (first diode) 4UA, a capacitor (first capacitor) 3UA, and a snubber terminal 205A.

[0023] Note that the snubber terminal 205A, the positive terminal 203A, and the negative terminal 204A only need to be configured so that the circuit can be electrically connected at the positions of these terminals, and the terminals may be omitted. Furthermore, the switch circuit 101A may include multiple switching elements 1UA. In that case, the multiple switching elements 1UA are connected in parallel with the capacitor 3UA and the diode 4UA between the positive terminal 203A and the negative terminal 204A. The multiple switching elements 1UA may be connected in series with each other, or in parallel with each other.

[0024] The switching element 1UA is, for example, a MOSFET. The drain (high-potential side) of the switching element 1UA is electrically connected to the positive terminal 203A, and the source (low-potential side) of the switching element 1UA is electrically connected to the negative terminal 204A.

[0025] Diode 4UA has its cathode electrically connected to the source and negative terminals 204A of switching element 1UA, and its anode electrically connected to the snubber terminal 205A. Ideally, diode 4UA should have fast recovery characteristics with low recovery loss; for example, it is desirable to use an element utilizing a Schottky barrier diode (SBD) or a wide-bandgap semiconductor (SiC, GaN, etc.) with good recovery characteristics.

[0026] Capacitor 3UA has one end (high-potential side) electrically connected to the drain and positive terminal 203A of switching element 1UA, and the other end (low-potential side) electrically connected to the anode of diode 4UA and also to the snubber terminal 205A.

[0027] The a switch circuits 101A are connected in series. That is, the positive terminal (high potential side) 203A of switch circuit 101A is electrically connected to the negative terminal (low potential side) 204A of the adjacent switch circuit 101A on the high potential side, and the positive terminal 203A (N=a) of the highest potential switch circuit 101A is electrically connected to the negative terminal 204N (N=1) of the lowest potential switch circuit 101N. The negative terminal 204A of switch circuit 101A is electrically connected to the positive terminal 203A of the adjacent switch circuit 101A on the low potential side, and the negative terminal 204A (A=1) of the lowest potential switch circuit 101A is electrically connected to the positive cell terminal 200 of inverter cell 100.

[0028] The first regenerative rectifier circuit connects multiple first capacitors 3UA or the first capacitors 3UA to the energy storage unit 2 in parallel via one or more first switching elements 1UA, when at least one of the first switching circuits 101A has a first capacitor 3UA connected in parallel with a first switching element 1UA. Furthermore, the first regenerative rectifier circuit, when at least one of the first switch circuits 101N has a first capacitor 3UN connected in parallel with a first switching element 1UN, connects multiple first capacitors 3UN or the first capacitor 3UN and the energy storage unit 2 (or first capacitor 3Ua) in parallel via one or more first switching elements 1UN.

[0029] The a regenerative rectifier diodes 6UA (A=1~a) are connected in series with each other, with the forward direction being from the low potential side to the high potential side, between the low potential terminal of the switching element 1X (the low potential end of the inverter cell 100) and the low potential end of the capacitor 3U1 of the first switch circuit 101A (A=1) located at the lowest potential side, and between the low potential end of the capacitor 3UA of the adjacent first switch circuit 101A.

[0030] The n regenerative rectifier diodes 6UN (N=1~n) are connected in series with each other, with the forward direction being from the low potential to the high potential, between the low potential end of capacitor 3Ua of the first switch circuit 101A (A=a) on the highest potential side and the low potential end of capacitor 3U1 of the first switch circuit 101N (N=1) on the lowest potential side, and between the low potential end of capacitor 3UN of the adjacent first switch circuit 101N.

[0031] Each cathode of the regenerative rectifier diode (first regenerative rectifier diode) 6UA (A=1~a) is electrically connected to the snubber terminal 205A (A=1~a) of switch circuit 101A and to the anode of the adjacent regenerative rectifier diode 6UA (A=1~a) on the high-potential side. Each cathode of the regenerative rectifier diode (first regenerative rectifier diode) 6UN (N=1~n) is electrically connected to the snubber terminal 205N (N=1~n) of switch circuit 101N and to the anode of the adjacent regenerative rectifier diode 6UN (N=1~n) on the high-potential side. For example, the cathode of regenerative rectifier diode 6Uk (1≦k≦n-1) is electrically connected to the snubber terminal 205k of switch circuit 101k and to the anode of regenerative rectifier diode 6U (k+1).

[0032] Resistor 5UA is connected in series at one end to a parallel circuit of diode 4UA and capacitor 3UA. The other end of resistor 5UA is electrically connected via regenerative rectifier diode 6UA to a circuit in which capacitor 3UA and resistor 5UA are connected in series in switch circuit 101A, which is located on the low-potential side. The other end of resistor 5UA in switch circuit 101A (A=1), which is located on the lowest potential side, is electrically connected to the negative cell terminal 201 of inverter cell 100 via regenerative rectifier diode 6UA.

[0033] Resistor 5UN is connected in series at one end to a parallel circuit of diode 4UN and capacitor 3UN. The other end of resistor 5UN is electrically connected via regenerative rectifier diode 6UN to a circuit in which capacitor 3UN and resistor 5UN are connected in series in switch circuit 101N, which is connected to the low potential side. The other end of resistor 5UN in switch circuit 101N (N=1), which is located on the lowest potential side, is electrically connected to the negative cell terminal 201 of inverter cell 100 via a plurality of regenerative rectifier diodes 6UA (A=1~a).

[0034] Each of the m switch circuits (second switch circuits) 102M comprises a switching element (second switching element) 1XM, a positive terminal 206M, and a negative terminal 207M. At least one of the m switch circuits (second switch circuits) 102M comprises a diode (second diode) 4XM, a capacitor (second capacitor) 3XM, and a snubber terminal 208M. In this embodiment, we will describe the case where all of the m switch circuits (second switch circuits) 102M comprise a diode (second diode) 4XM, a capacitor (second capacitor) 3XM, and a snubber terminal 208M.

[0035] Note that the positive terminal 206M, the negative terminal 207M, and the snubber terminal 208M only need to be configured so that the circuit can be electrically connected at the positions of these terminals, and the terminals may be omitted. Also, the switch circuit 102M may have multiple switching elements 1XM. In that case, the multiple switching elements 1XM are connected in parallel with the capacitor 3XM and the diode 4XM between the positive terminal 206M and the negative terminal 207M. The multiple switching elements 1XM may be connected in series with each other, or in parallel with each other.

[0036] The switching element 1XM is, for example, a MOSFET. The drain (high-potential side) of the switching element 1XM is electrically connected to the positive terminal 206M, and the source (low-potential side) is electrically connected to the negative terminal 207M.

[0037] Diode 4XM has its anode electrically connected to the drain and positive terminal 206M of switching element 1XM, and its cathode electrically connected to the snubber terminal 208M. Ideally, diode 4XM should have fast recovery characteristics with low recovery loss; for example, it is desirable to use an element utilizing a Schottky barrier diode (SBD) or a wide-bandgap semiconductor (SiC, GaN, etc.) with good recovery characteristics.

[0038] Capacitor (snubber capacitor) 3XM has one end (low-potential side) electrically connected to the source and negative terminals 207M of switching element 1XM, and the other end (high-potential side) is electrically connected to the cathode of diode 4XM and also to the snubber terminal 208M.

[0039] The m switch circuits 102M are connected in series. That is, the positive terminal 206M of switch circuit 102M is electrically connected to the negative terminal 207M of the adjacent switch circuit 102M on the high-potential side, and the positive terminal 206M (M=1) of the switch circuit 102M on the highest potential side is electrically connected to the negative terminal 207B (B=b) of the switch circuit 102B on the lowest potential side. The negative terminal 207M of switch circuit 102M is electrically connected to the positive terminal 206M of the adjacent switch circuit 102M on the low-potential side, and the negative terminal 207M (M=m) of the switch circuit 102M on the lowest potential side is electrically connected to the negative DC terminal 210.

[0040] Each of the b switch circuits (second switch circuits) 102B comprises a switching element (second switching element) 1XB, a positive terminal 206B, and a negative terminal 207B. At least one of the b switch circuits (second switch circuits) 102B comprises a diode (second diode) 4XB, a capacitor (second capacitor) 3XB, and a snubber terminal 208B. In this embodiment, we will describe the case where all of the b switch circuits (second switch circuits) 102B comprise a diode (second diode) 4XB, a capacitor (second capacitor) 3XB, and a snubber terminal 208B.

[0041] Note that the positive terminal 206B, the negative terminal 207B, and the snubber terminal 208B only need to be configured so that the circuit can be electrically connected at the positions of these terminals, and the terminals may be omitted. Also, the switch circuit 102B may have multiple switching elements 1XB. In that case, the multiple switching elements 1XB are connected in parallel with the capacitor 3XB and the diode 4XB between the positive terminal 206B and the negative terminal 207B. The multiple switching elements 1XB may be connected in series with each other, or in parallel with each other.

[0042] The switching element 1XB is, for example, a MOSFET. The drain (high-potential side) of the switching element 1XB is electrically connected to the positive terminal 206B, and the source (low-potential side) is electrically connected to the negative terminal 207B.

[0043] Diode 4XB has its anode electrically connected to the drain and positive terminal 206B of switching element 1XB, and its cathode electrically connected to the snubber terminal 208B. Ideally, diode 4XB should have fast recovery characteristics with low recovery loss. For example, it is desirable to use a Schottky barrier diode (SBD) or a wide-bandgap semiconductor (SiC, GaN, etc.) with good recovery characteristics.

[0044] Capacitor 3XB has one end (low-potential side) electrically connected to the source and negative terminal 207B of switching element 1XB, and the other end (high-potential side) electrically connected to the cathode of diode 4XB and also to the snubber terminal 208B.

[0045] b switch circuits 102B are connected in series. That is, the positive terminal 206B of switch circuit 102B is electrically connected to the negative terminal 207B of the adjacent switch circuit 102B on the high-potential side, and the positive terminal 206B (B=1) of the switch circuit 102B with the highest potential is electrically connected to the negative cell terminal 201 of the inverter cell 100. The negative terminal 207B of switch circuit 102B is electrically connected to the positive terminal 206B of the adjacent switch circuit 102B on the low-potential side, and the negative terminal 207B (B=b) of the switch circuit 102B with the lowest potential is electrically connected to the positive terminal 206M (M=1) of the switch circuit 102M with the highest potential.

[0046] In the second regenerative rectifier circuit, when at least one of the second switch circuits 102B has a second capacitor 3XB connected in parallel with a second switching element 1XB, one or more second capacitors 3XB or the second capacitors 3XB and the energy storage unit 2 are connected in parallel via one or more second switching elements 1XB. Furthermore, in the second regenerative rectifier circuit, if at least one of the second switch circuits 102M has a second capacitor 3XM connected in parallel with a second switching element 1XM, then one or more second switching elements 1XM are used to connect multiple second capacitors 3XM or the second capacitor 3XM and the energy storage unit 2 (or second capacitor 3Xb) in parallel.

[0047] The b regenerative rectifier diodes (second regenerative rectifier diodes) 6XB (B=1~b) are connected in series with each other, with the forward direction being from the low potential side to the high potential side, between the high potential ends of the capacitors 3XB of adjacent second switch circuits 102B, and between the high potential terminal of the switching element 1U (high potential end of inverter cell 100) and the high potential end of the capacitor 3XB of the second switch circuit 102B (B=1) located on the highest potential side.

[0048] The m regenerative rectifier diodes (second regenerative rectifier diodes) 6XM (M=1~m) are connected in series with each other, with the forward direction being from the low potential to the high potential, between the high potential ends of the capacitors 3XM of adjacent second switch circuits 102M, and between the high potential end of the capacitor 3XM of the second switch circuit 102M (m=1) located on the highest potential side and the high potential end of the capacitor 3XB of the second switch circuit 102B (B=b) located on the lowest potential side.

[0049] Each anode of the regenerative rectifier diode 6XB (B=1~b) is electrically connected to the snubber terminal 208B (B=1~b) of switch circuit 102B and to the cathode of the adjacent regenerative rectifier diode 6XB (B=1~b) on the low-potential side. Each anode of the regenerative rectifier diode 6XM (M=1~m) is electrically connected to the snubber terminal 208M (M=1~m) of switch circuit 102M and to the cathode of the adjacent regenerative rectifier diode 6XM (M=1~m) on the low-potential side. For example, the anode of regenerative rectifier diode 6Xj (1≦j≦m-1) is electrically connected to the snubber terminal 208j of switch circuit 102j and to the cathode of regenerative rectifier diode 6X(j+1).

[0050] Resistor 5XM is connected in series at one end to a parallel circuit of diode 4XM and capacitor 3XM. The other end of resistor 5XM is electrically connected via regenerative rectifier diode 6XM to a circuit in which capacitor 3XM and resistor 5XM of switch circuit 102M, which is connected in series, and which is connected to the high-potential side. The other end of resistor 5XM of switch circuit 102M (M=1), which is located on the highest potential side, is electrically connected via regenerative rectifier diode 6Xb to a circuit in which capacitor 3Xb and resistor 5Xb of switch circuit 102b are connected in series.

[0051] Resistor 5XB is connected in series at one end to a parallel circuit of diode 4XB and capacitor 3XB. The other end of resistor 5XB is electrically connected via regenerative rectifier diode 6XB to a circuit in which capacitor 3XB of switch circuit 102B, which is connected in series to resistor 5XB, is connected to switch circuit 102B, which is connected to the high potential side. The other end of resistor 5XB of switch circuit 102B (B=1), which is located on the highest potential side, is electrically connected to the positive cell terminal 200 of inverter cell 100 via regenerative rectifier diode 6XB.

[0052] Furthermore, in at least one of the first switch circuits 101N and 101A, it is sufficient that at least one of the first switch circuits 101N and 101A includes a first diode 4UN and 4UA whose cathode is connected to the low-potential side end of the first switching element 1UN and 1UA, and a first capacitor 3UN and 3UA connected between the anode of the first diode 4UN and 4UA and the high-potential side end of the first switching element 1UN and 1UA. In other words, the power converter of this embodiment includes a regenerative rectifier circuit that connects the low-potential end of the inverter cell 100 and the low-potential end of the first capacitors 3UN and 3UA on the upper arm, with the direction from the low-potential side to the high-potential side being the forward direction. This is because at least one of the first switch circuits 101N and 101A includes first diodes 4UN and 4UA whose cathodes are connected to the low-potential side ends of first switching elements 1UN and 1UA, and first capacitors 3UN and 3UA connected between the anodes of the first diodes 4UN and 4UA and the high-potential side ends of the first switching elements 1UN and 1UA.

[0053] Similarly, the second switch circuit 102M and the second switch circuit 102B only need to have at least one of them, which includes a second diode 4XM, 4XB whose anode is connected to the high-potential side of the second switching element 1XM, 1XB, and a second capacitor 3XM, 3XB connected between the cathode of the second diode 4XM, 4XB and the low-potential side of the second switching element 1XM, 1XB. In other words, the power converter of this embodiment includes a regenerative rectifier circuit that connects the high-potential end of the inverter cell 100 and the high-potential end of the second capacitors 3XM and 3XB on the lower arm, with the direction from the low-potential side to the high-potential side being the forward direction. This is because at least one of the second switch circuits 102M and 102B includes second diodes 4XM and 4XB whose anodes are connected to the high-potential side ends of the second switching elements 1XM and 1XB, and second capacitors 3XM and 3XB connected between the cathodes of the second diodes 4XM and 4XB and the low-potential side ends of the second switching elements 1XM and 1XB.

[0054] In the power conversion device of this embodiment, it is desirable that the number n of switch circuits 101N and the number m of switch circuits 102M be the same, but they may be different numbers. Similarly, it is desirable that the number a of switch circuits 101A and the number b of switch circuits 102B be the same, but they may be different numbers.

[0055] Furthermore, in the power conversion device of this embodiment, the switching elements 1U, 1X, 1UN, 1UA, 1XM, and 1UB are not limited to MOSFETs, but may also be IGBTs (Insulated Gate Bipolar Transistors) or mechanical switches, for example.

[0056] Furthermore, the effects of this embodiment can be obtained even when elements with different voltage ratings and current ratings are used as switching elements 1U, 1X, 1UN, 1UA, 1XM, and 1UB. However, it is preferable to use elements with the same voltage and current ratings as switching elements 1U, 1X, 1UN, 1UA, 1XM, and 1UB.

[0057] The high-potential end of the flying capacitor CF is electrically connected to the upper arm between the negative terminal 204N of the lowest-potential first switch circuit 101N (N=1) and the positive terminal 203A of the highest-potential first switch circuit 101A (A=a). The low-potential end of the flying capacitor CF is electrically connected to the lower arm between the positive terminal 206M of the highest-potential second switch circuit 102M (M=1) and the negative terminal 207B of the lowest-potential second switch circuit 102B (B=b).

[0058] Furthermore, it is desirable that capacitor 3Ua of switch circuit 101a, which is located between the positive DC terminal 209 and the AC terminal 211 and connects the flying capacitor CF to the drain (or collector) of the switching element, and capacitor 3Xb of switch circuit 102b, which is located between the negative DC terminal 210 and the AC terminal 211 and connects the flying capacitor CF to the source (or emitter) of the switching element, have larger capacitances than the other capacitors 3UN, 3UA, 3XB, and 3XM in order to temporarily buffer the absorbed energy.

[0059] Next, an example of the operation of the power converter of this embodiment will be described. The power converter of this embodiment holds multiple different voltages in a flying capacitor CF and enables multi-level output by adding and subtracting voltage values.

[0060] In this embodiment, the power converter is controlled such that the voltage of the flying capacitor CF is less than the sum of the voltages of the upper arm capacitors 3UN and 3UA, and less than the sum of the voltages of the lower arm capacitors 3XB and 3XM. The voltage of the flying capacitor CF is predetermined by the DC power supply voltage of the power converter and the voltage divider applied to the flying capacitor CF. Therefore, for example, by adjusting the specified value of the DC power supply voltage of the power converter or by adjusting the voltage command value used to control the output power of the power converter, the voltage of the flying capacitor CF can be controlled to be less than the sum of the voltages of the upper arm capacitors 3UN and 3UA, and less than the sum of the voltages of the lower arm capacitors 3XB and 3XM. Furthermore, the voltage of the flying capacitor CF may be controlled to be smaller than, for example, the minimum voltage of capacitors 3UN and 3UA multiplied by the number of series connections in the first switch circuit (=n+a), and smaller than the minimum voltage of capacitors 3XB and 3XM multiplied by the number of series connections in the second switch circuit (=m+b).

[0061] For example, if the voltage of the flying capacitor CF becomes greater than the sum of the voltages of capacitors 3UN and 3UA, an unintended current may flow from the flying capacitor CF to the regenerative rectifier circuit. In this case, the power conversion efficiency of the power converter will decrease, and it will become impossible to output the desired power. For example, if the voltage of the flying capacitor CF is lowered, when comparing the sum of the voltages of the snubber capacitors corresponding to the outer (closer to the DC terminal) capacitors 3UN and 3UA with the voltage obtained by subtracting the voltage of the flying capacitor CF from the DC voltage, the latter voltage will be larger, increasing the risk of inrush current flowing through the outer snubber capacitor. However, since the outer snubber capacitor 3UN is located far from the floating capacitor 2, its voltage is more likely to rise than that of the inner (further from the DC terminal) snubber capacitor 3UA. Therefore, it is desirable to also consider the voltage of the inner snubber capacitor 3UA. As described above, by making the voltage of the flying capacitor CF smaller than the sum of the voltages of the upper arm capacitors 3UN and 3UA, and smaller than the sum of the voltages of the lower arm capacitors 3XB and 3XM, a decrease in the power conversion efficiency of the power converter can be avoided.

[0062] Figure 2 is a diagram illustrating an example of the operation of the power converter according to the first embodiment. In this embodiment, the control circuit CTR generates control signals for the second upper arm circuit SN, the first upper arm circuit SA, the first lower arm circuit SB, the second lower arm circuit SX, and the switching elements 1U and 1X using a carrier phase shift modulation scheme with carrier waves C1 and C2 whose phases are shifted by approximately 180 degrees from each other.

[0063] The control signals for the first upper arm circuit SA and the first lower arm circuit SB are generated, for example, by comparing the carrier wave C1 with a command value. The control signals for the second upper arm circuit SN and the second lower arm circuit SM are generated, for example, by comparing the carrier wave C2 with a command value.

[0064] When all switching elements 1UN of the second upper arm circuit SN and all switching elements 1UA of the first upper arm circuit SA are ON, and all switching elements 1XB of the first lower arm circuit SB and all switching elements 1UM of the second lower arm circuit SM are OFF (first switch mode), the voltage at AC terminal 211 is equal to the DC power supply voltage (the voltage between the positive DC terminal 209 and the negative DC terminal 210).

[0065] When all switching elements 1XB of the first lower arm circuit SB and all switching elements 1XM of the second lower arm circuit SM are ON, and all switching elements 1UN of the second upper arm circuit SN and all switching elements 1UA of the first upper arm circuit SA are OFF (second switch mode), the voltage at AC terminal 211 is equal to the negative DC power supply voltage.

[0066] When all switching elements 1UN of the second upper arm circuit SN and all switching elements 1XB of the first lower arm circuit SB are ON, and all switching elements 1UA of the first upper arm circuit SA and all switching elements 1XM of the second lower arm circuit SM are OFF (third switch mode), a voltage obtained by subtracting the voltage across the flying capacitor CF from the DC power supply voltage is applied to the AC terminal 211.

[0067] When all switching elements 1UA of the first upper arm circuit SA and all switching elements 1XM of the fourth switch circuit SM are ON, and all switching elements 1UN of the second upper arm circuit SN and all switching elements 1XB of the first lower arm circuit SB are OFF (fourth switch mode), the voltage of the flying capacitor CF is applied to the AC terminal 211.

[0068] Next, an example of the operation in which the energy generated during switching is collected in the floating capacitor 2 in the power conversion device of this embodiment will be described. In the power converter of this embodiment, the control circuit CTR sequentially switches multiple switching elements 1UN, 1UA, 1UB, and 1XM in the upper arm circuits SN and SA and the lower arm circuits SB and SM at predetermined time intervals, thereby reducing losses such as turn-on losses, turn-off losses, and recovery losses.

[0069] The following describes an example of operation when the power converter is in the first switch mode. When all of the switching elements 1U and 1X of the inverter cell 100, the multiple switching elements 1UN and 1UA on the upper arm, and the multiple switching elements 1UB and 1XM on the lower arm are turned off, and current is output from the AC terminal 211, the current flows through the parasitic diode of the switching element 1X of the inverter cell 100 and the parasitic diodes of the switching elements 1XM and 1XB of the switch circuits 102M and 102B.

[0070] In this state, when the switching element 1U of the inverter cell 100 is turned on, the current flows through the parasitic diodes of the multiple switching elements 1XM of the lower arm switch circuits 102B and 102M, and also flows in the direction of discharging the floating capacitor 2 in the inverter cell 100, and then flows through the switching element 1U to the AC terminal 211.

[0071] Next, one of the switching elements 1UN in the upper arm switch circuit 101N is turned on, and one of the switching elements 1UA in the switch circuit 101A is also turned on. Here, we will explain the case where the switching element 1Un of switch circuit 101n and the switching element 1Ua of switch circuit 101a are turned on.

[0072] When the switching element 1Un is turned on, the voltage applied to one of the multiple switch circuits 101N is divided by the number of switch circuits 102M in series (=m) and applied to each of the multiple switch circuits 102M. As a result, the voltage applied during the recovery of the parasitic diodes of the switching elements 1XM in the multiple switch circuits 102M becomes smaller, and the loss that occurs during recovery (recovery loss) is reduced. Furthermore, the parasitic inductance of the switching loop increases according to the number of switch circuits 102M in series, which reduces the amount of change in the recovery current, and as a result the recovery charge decreases, and the recovery loss is reduced.

[0073] Similarly, when the switching element 1Ua is turned on, the voltage applied to one of the multiple switch circuits 101A is divided by the number of switch circuits 102B in series (=b) and applied to each of the multiple switch circuits 102B. As a result, the voltage applied during the recovery of the parasitic diodes of the switching elements 1XB in the multiple switch circuits 102B becomes smaller, and the loss that occurs during recovery (recovery loss) is reduced. Furthermore, the parasitic inductance of the switching loop, which increases according to the number of switch circuits 102B in series, reduces the amount of change in recovery current, and as a result, the recovery charge decreases and the recovery loss is reduced.

[0074] When a voltage is applied to switch circuits 102M and 102B, the current can no longer pass through the parasitic diodes of switching elements 1XM and 1XB and is commutated to switch circuits 101N and 101A. Therefore, in switch circuits 101n and 101a, current flows through the switched elements 1Un and 1Ua, which are turned on, and in the other switch circuits 101N (N=1~(n-1)) and 101A (A=1~(a-1)), current flows through capacitors 3UN (N=1~(n-1)) and 3UA (A=1~(a-1)) and diodes 4UN (N=1~(n-1)) and 4UA (A=1~(a-1)).

[0075] As the state in which the above current flows transitions, for example, the energy that would be converted into heat as switching loss in a conventional two-level inverter is stored in capacitors 3UN (N=1~(n-1)) and 3UA (A=1~(a-1)) in the power converter of this embodiment. In other words, the switching loss in the power converter of this embodiment is only the loss associated with the switching of the switching elements 1UN and 1UA of the multiple switch circuits 101N and 101A, which is significantly smaller than that of a conventional two-level inverter.

[0076] Furthermore, for example, when the switching element 1Un is turned on, the diode 4Un and capacitor 3Un of the switch circuit 101n are connected in parallel. One end of resistor 5Un is connected in series with the parallel circuit of diode 4Un and capacitor 3Un. The other end of resistor 5Un is electrically connected via regenerative rectifier diode 6Un to the circuit in which capacitor 3U(n-1) and resistor 5U(n-1) of the switch circuit 101(n-1) are connected in series. As a result, capacitor 3Un and capacitor 3U(n-1) are connected in parallel, and the energy stored in capacitor 3Un is discharged into capacitor 3U(n-1). The above discharge ends when the voltages between capacitor 3Un and capacitor 3U(n-1) become equal.

[0077] In the example above, capacitor 3Un discharges when its voltage is higher than that of capacitor 3U(n-1). Furthermore, because the difference between the voltage of capacitor 3Un and the voltage of capacitor 3U(n-1) is sufficiently small compared to the individual voltages of capacitors 3Un and 3U(n-1), the energy can be discharged efficiently even if resistors 5Un and 5U(n-1) are present in the energy discharge path.

[0078] When the switching elements 1UN of multiple switch circuits 101N are sequentially turned on and all switching elements 1UN are turned on, the energy stored in capacitor 3UN is sequentially discharged, and the discharged energy is stored in capacitor 3Ua. The energy discharged from capacitor 3UN is temporarily stored in capacitor 3Ua, and then finally discharged to the AC terminal 211 via floating capacitor 2.

[0079] Furthermore, when the switching elements 1UA of multiple switch circuits 101A are sequentially turned on and all switching elements 1UA are turned on, the energy stored in capacitor 3UA is sequentially discharged, and when all switching elements 1UA are turned on, the discharged energy is stored in floating capacitor 2. In this state, the switching element on the upper arm of the power converter is turned on, entering the first switch mode.

[0080] Subsequently, the multiple switching elements 1UN and 1UA are sequentially turned off. When all of the multiple switching elements 1UN and 1UA are turned off, the floating capacitor 2 is discharged, making it possible to efficiently regenerate the energy generated by the switching. After that, the switching element 1U is turned off, and the upper arm of the power converter is turned off.

[0081] Similarly, when switching the switching element of the lower arm of the power converter, the energy generated by the switching can be stored in the floating capacitor 2 via multiple capacitors 3XM and 3XB, and the energy generated by the switching can be efficiently regenerated by discharging the floating capacitor 2.

[0082] As described above, in the power conversion device of this embodiment, for example, most of the energy during switching, which would otherwise be lost in a conventional inverter, can be stored in the floating capacitor 2 via capacitors 3UN, 3UA, 3XM, and 3XB. By discharging the floating capacitor 2, switching losses can be reduced without increasing the switching speed. Furthermore, recovery losses can be reduced by applying a low voltage to the switching elements 1UN, 1UA, 1XM, and 1XB during the recovery of the parasitic diodes of the switching elements 1UN, 1UA, 1XM, and 1XB. In other words, the power conversion device of this embodiment can improve the trade-off between switching losses and the capacity of the flying capacitor CF.

[0083] In this embodiment of the power conversion device, all switching elements switch during one cycle of the carrier wave. Therefore, capacitors 3UN, 3UA, 3XM, and 3XB can collect energy in the floating capacitor 2 without accumulating the absorbed energy for multiple cycles. In other words, in this embodiment, there are no switching modes in which capacitors 3UN, 3UA, 3XM, and 3XB become larger, thus avoiding an increase in the size of the power conversion device.

[0084] As described above, according to this embodiment, it is possible to provide a power conversion device that can keep energy loss low while avoiding increasing size. Furthermore, the upper arm of the inverter cell 100 may be a voltage-type clamp switch circuit with a configuration similar to that of switch circuit 101N, and the lower arm of the inverter cell 100 may be a voltage-type clamp switch circuit with a configuration similar to that of switch circuit 102M. In this case, the regenerative rectifier circuit further comprises a circuit connected between the low-potential end of the inverter cell 100 and the low-potential end of the snubber capacitor of the upper arm, with the direction from the low-potential side to the high-potential side being the forward direction, and circuits connected between the high-potential end of the inverter cell 100 and the high-potential end of the snubber capacitor of the lower arm, respectively. The upper and lower arms of the inverter cell 100 can use a common circuit as a switch circuit similar to that of switch circuits 101N and 102M.

[0085] Next, the power conversion device of the second embodiment will be described in detail with reference to the drawings. In the following embodiments, components similar to those in the first embodiment described above are denoted by the same reference numerals and their descriptions are omitted.

[0086] Figure 3 is a schematic diagram showing one example configuration of the power conversion device according to the second embodiment. The power converter of this embodiment is, for example, a three-level flying capacitor type power converter capable of mutually converting DC power and single-phase AC power, and comprises a control circuit CTR, an inverter cell 100, an upper arm, a lower arm, n+a (where n and a are positive integers) first regenerative rectifier circuits (regenerative rectifier diodes 6UN, 6UA and first resistors 5UN, 5UA), m+b (where m and b are positive integers) second regenerative rectifier circuits (regenerative rectifier diodes 6XM, 6XB and second resistors 5XM, 5XB), a flying capacitor CF, a positive DC terminal 209, a negative DC terminal 210, and an AC terminal 211.

[0087] Here, N, A, M, and B are N=1~n, A=1~a, M=1~m, and B=1~b (n, a, m, and b are 2 or greater), and the same applies hereafter unless otherwise specified. Also, the first resistors 5UN and 5UA and the second resistors 5XM and 5XB may be inductance elements.

[0088] The power conversion device of this embodiment differs from the power conversion device of the first embodiment described above in the configuration of the first regenerative rectifier circuit and the second regenerative rectifier circuit. The multiple first regenerative rectifier circuits include multiple first circuits and multiple second circuits. Each of the multiple first circuits comprises a regenerative rectifier diode 6UA and a resistor 5UA. Each of the multiple second circuits comprises a regenerative rectifier diode 6UN and a resistor 5UN.

[0089] The regenerative rectifier diode 6UA is connected between the negative cell terminal 201 of the inverter cell 100 and the snubber terminal 205A of the switch circuit 101A, with the forward direction being from the negative cell terminal 201 to the snubber terminal 205A. Resistor 5UA is connected in series with the regenerative rectifier diode 6UA in the path that electrically connects the cathode of the regenerative rectifier diode 6UA to the snubber terminal 205A. In other words, the anodes of multiple regenerative rectifier diodes 6UA are electrically connected to the negative cell terminal 201 of the inverter cell 100 without going through other regenerative rectifier diodes 6UA.

[0090] In other words, in this embodiment, the multiple first circuits are connected between the low-potential terminal of the lower switching element (the low-potential end of the inverter cell 100) and the low-potential end of the first capacitor of the multiple first switch circuits, with the forward direction being from the low-potential side to the high-potential side.

[0091] The regenerative rectifier diode 6UN is connected between snubber terminal 205a and snubber terminal 205N, with the forward direction being from snubber terminal 205a to snubber terminal 205N of the switch circuit 101N. Resistor 5UN is connected in series with the regenerative rectifier diode 6UN in the path that electrically connects the cathode of the regenerative rectifier diode 6UN to snubber terminal 205N. In other words, the anodes of multiple regenerative rectifier diodes 6UN are electrically connected to snubber terminal 205a without going through other regenerative rectifier diodes 6UN.

[0092] In other words, in this embodiment, the multiple second circuits are connected, with the forward direction being from the low-potential side to the high-potential side, between the low-potential end of the capacitor 3Ua of the switch circuit 101a located on the highest-potential side of the first upper arm circuit SA adjacent to the low-potential side and the low-potential end of the first capacitors of the multiple first switch circuits.

[0093] The multiple second regenerative rectifier circuits include multiple third circuits and multiple fourth circuits. Each of the multiple third circuits comprises a regenerative rectifier diode 6XB and a resistor 5XB. Each of the multiple fourth circuits comprises a regenerative rectifier diode 6XM and a resistor 5XM.

[0094] The regenerative rectifier diode 6XB is connected between the snubber terminal 208B of the switch circuit 102B and the positive cell terminal 200 of the inverter cell 100, with the forward direction being from the snubber terminal 208B of the switch circuit 102B to the positive cell terminal 200 of the inverter cell 100. Resistor 5XB is connected in series with the regenerative rectifier diode 6XB in the path that electrically connects the anode of the regenerative rectifier diode 6XB to the snubber terminal 208B. In other words, the cathodes of multiple regenerative rectifier diodes 6XB are electrically connected to the positive cell terminal 200 of the inverter cell 100 without going through other regenerative rectifier diodes 6XB.

[0095] In other words, in this embodiment, the multiple third circuits are connected between the high-potential terminal of the upper switching element (the high-potential end of the inverter cell 100) and the high-potential end of the second capacitor of the multiple second switch circuits, with the forward direction being from the low-potential side to the high-potential side.

[0096] The regenerative rectifier diode 6XM is connected between snubber terminals 208B and 208b, with the forward direction being from the snubber terminal 208M of the switch circuit 102M towards the positive cell terminal 200 of the inverter cell 100. Resistor 5XM is connected in series with the regenerative rectifier diode 6XM in the path that electrically connects the anode of the regenerative rectifier diode 6XM to the snubber terminal 208M. In other words, the cathodes of multiple regenerative rectifier diodes 6XM are electrically connected to snubber terminal 208b (the high-potential side of capacitor 3Xb) without going through other regenerative rectifier diodes 6XM.

[0097] In other words, in this embodiment, the multiple fourth circuits are connected, with the forward direction being from the low potential side to the high potential side, between the high potential side end of the capacitor 3Xb of the switch circuit 102b located on the lowest potential side of the first lower arm circuit SB adjacent to the high potential side and the high potential side end of the second capacitors of the multiple second switch circuits.

[0098] As described above, the power converter of this embodiment includes a regenerative rectifier circuit that connects the low-potential end of the inverter cell 100 and the low-potential end of the first capacitor 3UN on the upper arm, with the direction from the low-potential side to the high-potential side being the forward direction.

[0099] Furthermore, in this embodiment, the power converter includes a regenerative rectifier circuit that connects the high-potential end of the inverter cell 100 and the high-potential end of the second capacitor 3XM on the lower arm, with the direction from the low-potential side to the high-potential side being the forward direction. This is achieved when at least one of the second switch circuits 102X includes a second diode 4XM whose anode is connected to the high-potential side of the second switching element 1XM, and a second capacitor 3XM connected between the cathode of the second diode 4XM and the low-potential side of the second switching element 1XM.

[0100] In the power conversion device of this embodiment, the switching operation of the switching elements 1U, 1X, the plurality of switching elements 1UN, 1UA, and the plurality of switching elements 1XM, 1XB is the same as in the first embodiment described above. That is, the control circuit CTR sequentially switches the plurality of switching elements 1UN, 1UA on the upper arm and the plurality of switching elements 1XM, 1XB on the lower arm at predetermined time intervals.

[0101] In this embodiment, due to the switching operation and the configuration of the regenerative rectifier diodes 6UN, 6UA, 6XM, and 6XB, the energy stored in the capacitors 3UN, 3UA, 3XM, and 3XB of the switch circuits 101N, 101A, 102M, and 102B is charged into the floating capacitor 2 without passing through the multiple regenerative rectifier diodes 6UN, 6UA, 6XM, and 6XB.

[0102] Therefore, the power conversion device of this embodiment makes it possible to reduce losses such as turn-on losses, turn-off losses, and recovery losses, and also reduces energy loss in the energy discharge path from capacitors 3UN, 3UA, 3XM, and 3XB to the floating capacitor 2, enabling more efficient energy recovery.

[0103] In this embodiment of the power converter, the voltage applied to the regenerative rectifier diodes 6UN, 6UA, 6XM, and 6XB is higher compared to the circuit configuration of the power converter of the first embodiment described above. Therefore, it is desirable to use elements with higher voltage ratings than those in the first embodiment for the regenerative rectifier diodes 6UN, 6UA, 6XM, and 6XB. Furthermore, the multiple second circuits may be connected between the low-potential terminal of the lower switching element (the low-potential end of the inverter cell 100) and the low-potential end of the first capacitor of the multiple first switch circuits, with the forward direction being from the low-potential side to the high-potential side. The multiple fourth circuits may be connected between the high-potential terminal of the upper switching element (the high-potential end of the inverter cell 100) and the high-potential end of the second capacitor of the multiple second switch circuits, with the forward direction being from the low-potential side to the high-potential side. In this case, the energy generated by the switching elements 1UN and 1XM is stored in the floating capacitor 2 without going through the capacitors 3Ua and 3Xb.

[0104] As described above, the power converter of this embodiment can achieve the same effects as the first embodiment described above. That is, the power converter of this embodiment can keep energy loss low and avoid increasing the size of the device.

[0105] Next, the power conversion device of the third embodiment will be described in detail with reference to the drawings. Figure 4 is a schematic diagram showing one example configuration of the power conversion device according to the third embodiment. The power converter of this embodiment is, for example, a 3-level flying capacitor type power converter capable of mutually converting DC power and single-phase AC power, and comprises a control circuit CTR, an upper arm, a lower arm, n+a (where n and a are integers of 2 or more) first regenerative rectifier circuits (regenerative rectifier diodes 6UN, 6UA and first resistors 5UN, 5UA), m+b (where m and b are integers of 2 or more) second regenerative rectifier circuits (regenerative rectifier diodes 6XM, 6XB and second resistors 5XM, 5XB), a flying capacitor CF, a positive DC terminal 209, a negative DC terminal 210, an AC terminal 211, and energy storage units CU and CX.

[0106] Here, N, A, M, and B are N=1~n, A=1~a, M=1~m, and B=1~b (n, a, m, and b are 2 or greater), and the same applies hereafter unless otherwise specified. Also, the first resistors 5UN and 5UA and the second resistors 5XM and 5XB may be inductance elements.

[0107] The energy storage units CU and CX can be, for example, capacitors or batteries. In this embodiment, the case in which the energy storage units CU and CX are capacitors will be described. The high-potential energy storage unit (first energy storage unit) CU has one end electrically connected to the positive DC terminal 209 and the other end connected to the first regenerative rectifier circuit. The low-potential energy storage unit (second energy storage unit) CX has one end electrically connected to the negative DC terminal 210 and the other end connected to the second regenerative rectifier circuit.

[0108] The power conversion device of this embodiment may include a DC / DC converter that converts the energy stored in the energy storage units CU and CX into a predetermined voltage and discharges it. The output terminal of the DC / DC converter may be connected to, for example, a control power supply (not shown), a DC power supply for the power conversion device, or other circuits. The power conversion device of this embodiment may also include a DC / AC converter that converts the energy stored in the energy storage units CU and CX into AC power and discharges it. The operation of the DC / DC converter and DC / AC converter is controlled by the control circuit CTR.

[0109] The upper arm is equipped with n+a switch circuits (voltage-type clamp-type switch circuits) 101N, 101A. Each of the n+a switch circuits (first switch circuits) 101N, 101A is equipped with a switching element (first switching element) 1UN, 1UA, a diode (first diode) 4UN, 4UA, a capacitor (first capacitor) 3UN, 3UA, snubber terminals 205N, 205A, positive terminals 203N, 203A, and negative terminals 204N, 204A.

[0110] Note that the positive terminals 203N, 203A, the negative terminals 204N, 204A, and the snubber terminals 205N, 205A only need to be configured so that the circuit can be electrically connected at the positions of these terminals, and the terminals may be omitted. Also, each of the switch circuits 101N, 101A may be equipped with multiple switching elements 1UN, 1UA. In that case, the multiple switching elements 1UN, 1UA are connected in parallel with the capacitors 3UN, 3UA and diodes 4UN, 4UA between the positive terminals 203N, 203A and the negative terminals 204N, 204A. The multiple switching elements 1UN, 1UA may be connected in series with each other, or in parallel with each other.

[0111] Switching elements 1UN and 1UA are, for example, MOSFETs (Metal-Oxide Semiconductor Field-Effect Transistors). The drains (high-potential terminals) of switching elements 1UN and 1UA are electrically connected to the positive terminals 203N and 203A, and the sources (low-potential terminals) are electrically connected to the negative terminals 204N and 204A.

[0112] Diodes 4UN and 4UA have their anodes electrically connected to the drain and positive terminals 203N and 203A of switching elements 1UN and 1UA, respectively, and their cathodes electrically connected to the snubber terminals 205N and 205A. Diodes 4UN and 4UA should preferably have fast recovery characteristics with low recovery losses. For example, it is desirable to use elements utilizing Schottky barrier diodes (SBDs) or wide-bandgap semiconductors (SiC, GaN, etc.) that have good recovery characteristics.

[0113] Capacitors 3UN and 3UA have one end (low-potential side) electrically connected to the source and negative terminals 204N and 204A of switching elements 1UN and 1UA, and the other end (high-potential side) electrically connected to the cathode of diodes 4UN and 4UA, as well as to the snubber terminals 205N and 205A.

[0114] n+a switch circuits 101N and 101A are connected in series. That is, the positive terminals 203N and 203A of switch circuits 101N and 101A are electrically connected to the negative terminals 204N and 204A of adjacent switch circuits 101N and 101A on the high-potential side. On the other hand, the negative terminals 204N and 204A of switch circuits 101N and 101A are electrically connected to the positive terminals 203N and 203A of adjacent switch circuits 101N and 101A on the low-potential side.

[0115] Furthermore, the positive terminal 203N of the highest potential switch circuit 101N is electrically connected to the positive DC terminal 209. The positive terminal 203A of the highest potential switch circuit 101A is electrically connected to the negative terminal 204N of the lowest potential switch circuit 101N. Also, the negative terminal 204A (A=1) of the lowest potential switch circuit 101A is electrically connected to the AC terminal 211 and the lower arm.

[0116] n regenerative rectifier diodes (first regenerative rectifier diodes) 6UN (N=1~n) are connected between the snubber terminal 205N (N=1~n) of the first switch circuit 101N and the other end (low-potential side end) of the high-potential energy storage unit CU, with the forward direction being from the low-potential side to the high-potential side. In other words, the snubber terminal 205N of the first switch circuit 101N is electrically connected to the anode of the corresponding regenerative rectifier diode 6UN. The other end of the energy storage unit CU is electrically connected to the cathodes of the multiple regenerative rectifier diodes 6U1~6Un.

[0117] Resistor 5UN is electrically connected at one end to the connection point between diode 4UN and capacitor 3UN (part of a configuration that electrically connects the other end (high-potential side) of capacitor 3UN to the cathode of diode 4UN). The other end of resistor 5UN is electrically connected to the anode of regenerative rectifier diode 6UN.

[0118] The a regenerative rectifier diodes (first regenerative rectifier diodes) 6UA (A=1~a) are connected between the snubber terminals 205A (A=1~a) and 205N (N=1) of the first switch circuit 101A, with the forward direction being from the low potential side to the high potential side. In other words, the snubber terminal 205A of the first switch circuit 101A is electrically connected to the anode of the corresponding regenerative rectifier diode 6UA. The snubber terminal 205N (N=1) is electrically connected to the cathodes of the multiple regenerative rectifier diodes 6UA (A=1~a) and to the anode of the regenerative rectifier diode 6UN (N=1).

[0119] Resistor 5UA is connected in series at one end to the connection point between diode 4UA and capacitor 3UA (part of a configuration that electrically connects the other end (high-potential side) of capacitor 3UA to the cathode of diode 4UA). The other end of resistor 5UN is electrically connected to the anode of regenerative rectifier diode 6UA.

[0120] The lower arm is equipped with m+b switch circuits (voltage-type clamp-type switch circuits) 102M, 102B. Each of the m+b switch circuits (second switch circuits) 102M, 102B is equipped with a switching element (first switching element) 1XM, 1XB, a diode (second diode) 4XM, 4XB, a capacitor (second capacitor) 3XM, 3XB, snubber terminals 208M, 208B, positive terminals 206M, 206B, and negative terminals 207M, 207B.

[0121] Note that the positive terminals 206M, 206B, the negative terminals 207M, 207B, and the snubber terminals 208M, 208B only need to be configured so that the circuit can be electrically connected at the location of these terminals, and the terminals may be omitted. Also, each of the switch circuits 102M and 102B may be equipped with multiple switching elements 1XM, 1XB. In that case, the multiple switching elements 1XM, 1XB are connected in parallel with the capacitors 3XM, 3XB and diodes 4XM, 4XB between the positive terminals 206M, 206B and the negative terminals 207M, 207B. The multiple switching elements 1XM, 1XB may be connected in series with each other, or in parallel with each other.

[0122] The switching elements 1XM and 1XB are, for example, MOSFETs (Metal-Oxide Semiconductor Field-Effect Transistors). The drains (high-potential ends) of the switching elements 1XM and 1XB are electrically connected to the positive terminals 206M and 206B, and the sources (low-potential ends) are electrically connected to the negative terminals 207M and 207B.

[0123] Diodes 4XM and 4XB have their cathodes electrically connected to the source and negative terminals 207M and 207B of switching elements 1XM and 1XB, respectively, and their anodes electrically connected to the snubber terminals 208M and 208B. Diodes 4XM and 4XB should preferably have fast recovery characteristics with low recovery losses. For example, it is desirable to use elements utilizing Schottky barrier diodes (SBDs) or wide-bandgap semiconductors (SiC, GaN, etc.) that have good recovery characteristics.

[0124] Capacitors 3XM and 3XB have one end (low-potential side) electrically connected to the anode of diodes 4XM and 4XB, as well as to snubber terminals 208M and 208B, and the other end (high-potential side) electrically connected to the drain and positive terminals 206M and 206B of switching elements 1XM and 1XB.

[0125] The m+b switch circuits 102M and 102B are connected in series. That is, the positive terminals 206M and 206B of switch circuits 102M and 102B are electrically connected to the negative terminals 207M and 207B of adjacent switch circuits 102M and 102B on the high-potential side. On the other hand, the negative terminals 207M and 207B of switch circuits 102M and 102B are electrically connected to the positive terminals 206M and 206B of adjacent switch circuits 102M and 102B on the low-potential side.

[0126] Furthermore, the positive terminal 206B of the highest potential switch circuit 102B (B=1) is electrically connected to the AC terminal 211 and the upper arm. The positive terminal 206M of the highest potential switch circuit 102M (M=1) is electrically connected to the negative terminal 207B of the lowest potential switch circuit 102B (B=b). Also, the negative terminal 207M (M=m) of the lowest potential switch circuit 102M (M=m) is electrically connected to the negative DC terminal 210.

[0127] m regenerative rectifier diodes (second regenerative rectifier diodes) 6XM (M=1~m) are connected between one end (high-potential side end) of the low-potential energy storage unit CX and the snubber terminal 208M (M=1~m) of the second switch circuit 102M, with the forward direction being from the low-potential side to the high-potential side. In other words, the snubber terminal 208M of the second switch circuit 102M is electrically connected to the cathode of the corresponding regenerative rectifier diode 6XM. One end of the energy storage unit CX is electrically connected to the cathodes of multiple regenerative rectifier diodes 6X1~6Xm.

[0128] Resistor 5XM is electrically connected at one end to the connection point between diode 4XM and capacitor 3XM (part of a configuration that electrically connects one end (low-potential side) of capacitor 3XM to the anode of diode 4XM). The other end of resistor 5XM is electrically connected to the cathode of regenerative rectifier diode 6XM.

[0129] b regenerative rectifier diodes (second regenerative rectifier diodes) 6XB (B=1~b) are connected between the snubber terminal 208M (M=1) and the snubber terminal 208B (B=1~b) of the second switch circuit 102B, with the forward direction being from the low potential side to the high potential side. In other words, the snubber terminal 208B of the second switch circuit 102B is electrically connected to the cathode of the corresponding regenerative rectifier diode 6XB. The snubber terminal 208M (M=1) is electrically connected to the anodes of the multiple regenerative rectifier diodes 6XB (B=1~b) and the cathode of the regenerative rectifier diode 6XM (M=1).

[0130] Resistor 5XB is connected in series at one end to the connection point between diode 4XB and capacitor 3XB (part of a configuration that electrically connects one end (low-potential side) of capacitor 3XB to the anode of diode 4XB). The other end of resistor 5XB is electrically connected to the cathode of regenerative rectifier diode 6XB.

[0131] The power converter of this embodiment includes a first regenerative rectifier circuit that connects the cathodes of each first diode 4UN to the other end (low potential side) of the high potential side energy storage unit CU, with the direction toward the high potential side energy storage unit CU being the forward direction.

[0132] Furthermore, in this embodiment, the power converter includes a second regenerative rectifier circuit that connects the anodes of the second diodes 4XM and 4XB to the other end (high potential side) of the low potential side energy storage unit CX, with the direction from the low potential side energy storage unit CX to the second switch circuits 102M and 102B being the forward direction.

[0133] Furthermore, in the power conversion device of this embodiment, the switching elements 1UN, 1UA, 1XM, and 1XB are not limited to MOSFETs, but may also be IGBTs (Insulated Gate Bipolar Transistors), contactors, mechanical switches, etc.

[0134] Furthermore, the effects of this embodiment can be obtained even when elements with different voltage ratings and current ratings are used as switching elements 1UN, 1UA, 1XM, and 1XB; however, it is preferable to use elements with the same voltage and current ratings as switching elements 1UN, 1UA, 1XM, and 1XB.

[0135] Next, an example of the operation of the power converter of this embodiment will be described. In both the upper and lower arms, the operation of the multiple switching elements 1UN, 1UA, 1XM, and 1XB is controlled by the control circuit CTR, similar to the first embodiment described above. Specifically, the control circuit CTR controls the multiple switching elements 1UN, 1UA, 1XM, and 1XB to switch sequentially with a predetermined time interval between them in both the upper arm circuit and the lower arm circuit, so that the multiple elements do not switch simultaneously.

[0136] At this time, load current flows within the arm during the time (delay time) between the on-turn of one of the multiple switching elements 1UN, 1UA, 1XM, and 1XB and the on-turn of the next one. In switch circuits 101N, 101A, 102M, and 102B where switching elements 1UN, 1UA, 1XM, and 1XB are off, the load current flows through the diodes (rectifier devices) 4UN, 4UA, 4XM, and 4XB connected in parallel with the switching elements 1UN, 1UA, 1XM, and 1XB, or through the regenerative rectifier circuit. The current flowing through the regenerative rectifier circuit is stored as energy in the energy storage units CU and CX.

[0137] In the upper arm, when one switching element 1UA and all of the switching elements 1UA connected to a higher potential side than that element are turned on, capacitors 3UA and 3UN(N=1), which are connected in parallel to that element, are connected in parallel. As energy is stored due to the load current, the voltage of capacitor 3UA increases, causing current to flow from capacitor 3UA to capacitor 3UN(N=1), and energy is discharged (regenerated) into capacitor 3UN(N=1). The energy regeneration efficiency at this time depends on the voltage difference between capacitor 3UA and capacitor 3UN(N=1), and the smaller the voltage difference, the higher the efficiency.

[0138] Furthermore, in the upper arm, when one element of switching element 1UN and all of the switching elements 1UN connected to a higher potential than that element are turned on, the capacitor 3UN and the energy storage unit CU, which are connected in parallel to that element, are connected in parallel. As the voltage of capacitor 3UN increases due to the storage of energy from the load current, current flows from capacitor 3UN to energy storage unit CU, and energy is discharged (regenerated) into energy storage unit CU. The energy regeneration efficiency at this time depends on the voltage difference between capacitor 3UN and energy storage unit CU, and the smaller the voltage difference, the higher the efficiency.

[0139] As described above, the energy storage unit CU collects energy from all capacitors 3UN and 3UA on the upper arm. The energy stored in the energy storage unit CU can be discharged, for example, by a DC / DC converter (not shown) and used as a DC power supply or control power supply. Furthermore, by discharging the energy stored in the energy storage unit CU using a DC / DC converter, it is possible to avoid the voltage of the energy storage unit CU becoming too high.

[0140] In the lower arm, when one switching element 1XB and all other switching elements 1XB connected to a lower potential than that element are turned on, capacitors 3XB and 3XM (M=1), which are connected in parallel to that element, are connected in parallel. As energy is stored due to the load current, the voltage of capacitor 3XB increases, causing current to flow from capacitor 3XB to capacitor 3XM (M=1), and energy is discharged (regenerated) into capacitor 3XM (M=1). The energy regeneration efficiency at this time depends on the voltage difference between capacitor 3XB and capacitor 3XM (M=1), and the smaller the voltage difference, the higher the efficiency.

[0141] Furthermore, in the lower arm, when one switching element 1XM and all of the switching elements 1XM connected to a lower potential than that element are turned on, the capacitor 3XM and the energy storage unit CX, which are connected in parallel to that element, are connected in parallel. As energy is stored due to the load current, the voltage of the capacitor 3XM increases, causing current to flow from the capacitor 3XM to the energy storage unit CX, and energy is discharged (regenerated) into the energy storage unit CX. The energy regeneration efficiency at this time depends on the voltage difference between the capacitor 3XM and the energy storage unit CX; the smaller the voltage difference, the higher the efficiency.

[0142] As described above, energy is collected in the energy storage unit CX from all capacitors 3XM and 3XB on the lower arm. The energy stored in the energy storage unit CX can be discharged, for example, by a DC / DC converter (not shown) and used as a DC power supply or control power supply. Furthermore, by discharging the energy stored in the energy storage unit CX using a DC / DC converter, it is possible to avoid the voltage of the energy storage unit CX becoming too high.

[0143] Next, the energy loss improvement effect of the power conversion device of this embodiment will be explained. For example, in a conventional power conversion device, at the timing when the switching element turns on, the current flowing through the switching element increases and the voltage applied to the switching element decreases. The energy generated in the switching element by the current flowing through it and the voltage applied to it is not absorbed by other elements and is converted into heat, resulting in switching loss.

[0144] In contrast, in the power conversion device of this embodiment, while energy is generated when each switching element is turned on, as in the conventional method, when viewed as a whole arm, the energy generated during switching is absorbed by the energy storage units CU and CX via capacitors 3UN, 3UA, 3XM, and 3XB. The energy stored in the energy storage units CU and CX can be discharged and regenerated, for example, by a DC / DC converter. Therefore, only a portion of the energy generated when the switching elements 1UN, 1UA, 1XM, and 1XB are turned on becomes a loss for the whole arm, resulting in improved energy efficiency.

[0145] Furthermore, in conventional power converters, for example, when a switching element turns off, the voltage applied to the switching element increases and the current flowing through the switching element decreases. The energy generated in the switching element by the current flowing through it and the voltage applied to it is not absorbed by other elements but is converted into heat, resulting in switching losses.

[0146] In contrast, in the power conversion device of this embodiment, while energy is generated during turn-off for each switching element, as in the conventional method, when viewed as a whole arm, the energy generated during switching is absorbed by the energy storage units CU and CX via capacitors 3UN, 3UA, 3XM, and 3XB. The energy stored in the energy storage units CU and CX can be discharged and regenerated, for example, by a DC / DC converter. Therefore, only a portion of the energy generated when the switching elements 1UN, 1UA, 1XM, and 1XB turn off is lost to the whole arm, resulting in improved energy efficiency.

[0147] Furthermore, in a conventional power converter, for example, when the switching element of the lower arm is turned on, recovery losses occur due to the current flowing through the parasitic diode and the applied voltage during the recovery of the parasitic diode of the switching element of the upper arm.

[0148] In contrast, in the power conversion device of this embodiment, when, for example, one of the switching elements 1XM is turned on by the control circuit CTR, the voltage applied to one of the multiple switch circuits 102M is divided by the number of series-connected switch circuits 101N (=n) and applied to each of the multiple switch circuits 101N. As a result, the voltage applied during the recovery of the parasitic diodes of the switching elements 1UN in the multiple switch circuits 101N becomes smaller, and the loss that occurs during recovery (recovery loss) is reduced.

[0149] As described above, the power converter of this embodiment achieves highly efficient switching by recovering and utilizing energy that would otherwise be lost in conventional power converters. Furthermore, in the power converter of this embodiment, the switching speed of the switching elements 1UN, 1UA, 1XM, and 1XB controlled by the control circuit CTR is the same as that of conventional power converters, thus reducing losses without increasing the switching speed.

[0150] Furthermore, for example, when a power converter has multiple legs, it is not necessary to provide energy storage units CU and CX and DC / DC converters for each phase. Even if the power converter is multiphase (two or more phases), it can be implemented by using one energy storage unit and one DC / DC converter for both the high-potential and low-potential sides. This makes it possible to miniaturize and reduce the cost of the power converter. In other words, according to this embodiment, it is possible to provide a power conversion device and a switching device that can keep energy loss low and avoid increasing size.

[0151] In the power conversion device of this embodiment, the capacitor 3UN(N=1) connected between the flying capacitor CF and the source (or emitter) of the switching element 1UN(N=1) between the positive DC terminal 209 and the AC terminal 211 is preferably provided with a larger capacitance than the other capacitors 3UN and 3UA, in order to temporarily store the energy absorbed from the multiple capacitors 3UA of the first upper arm circuit SA.

[0152] Furthermore, between the negative DC terminal 210 and the AC terminal 211, the capacitor 3XM (M=1) connected between the flying capacitor CF and the drain (or collector) of the switching element 1XM (M=1) is desirable to have a larger capacitance than the other capacitors 3XM and 3XB, in order to temporarily store the energy absorbed from the multiple capacitors 3XB of the first lower arm circuit SB.

[0153] In the power converter shown in Figure 4, the energy generated in the upper arm switch circuit is absorbed by the energy storage unit CU, and the energy generated in the lower arm switch circuit is absorbed by the energy storage unit CX. However, the regenerative rectifier circuit may be configured so that the energy generated in the upper and lower arm switch circuits is absorbed by either the energy storage unit CU or CX. Even in this case, the same effect as the power converter shown in Figure 4 can be obtained. Furthermore, in the above case, the switch circuits 101N, 101A, 102M, and 102B can be configured in the same way, and the other of the energy storage units CU and CX can be omitted.

[0154] Next, the power conversion device of the fourth embodiment will be described in detail with reference to the drawings. Figure 5 is a schematic diagram showing one example configuration of the power conversion device according to the fourth embodiment. The power converter of this embodiment is, for example, a 4-level flying capacitor type power converter capable of mutually converting DC power and single-phase AC power, and comprises a control circuit CTR, an inverter cell 100, an upper arm, a lower arm, n+a+c (where n, a, and c are integers of 2 or more) first regenerative rectifier circuits (regenerative rectifier diodes 6UN, 6UA, 6UC and first resistors 5UN, 5UA, 5UC), m+b+d (where m, b, and d are integers of 2 or more) second regenerative rectifier circuits (regenerative rectifier diodes 6XM, 6XB, 6XD and second resistors 5XM, 5XB, 5XD), flying capacitors CF, CF2, a positive DC terminal 209, a negative DC terminal 210, and an AC terminal 211.

[0155] Here, N, A, C, M, B, and D are N=1~n, A=1~a, C=1~c, M=1~m, B=1~b, and D=1~d, respectively (n, a, c, m, b, and d are 2 or greater), and the same applies hereafter unless otherwise specified. Also, the first resistors 5UN, 5UA, and 5UC and the second resistors 5XM, 5XB, and 5XD may be inductance elements.

[0156] The upper arm of the power converter in this embodiment includes a first upper arm circuit SA, a second upper arm circuit SN, and a third upper arm circuit SC. The first upper arm circuit SA includes a number of switch circuits (voltage-type clamp-type switch circuits) 101A. The second upper arm circuit SN includes n number of switch circuits (voltage-type clamp-type switch circuits) 101N. The third upper arm circuit SC includes c number of switch circuits (voltage-type clamp-type switch circuits) 101C.

[0157] The lower arm of the power converter in this embodiment includes a first lower arm circuit SB, a second lower arm circuit SM, and a third lower arm circuit SD. The first lower arm circuit SB includes b switch circuits (voltage-type clamp switch circuits) 102B. The second lower arm circuit SM includes m switch circuits (voltage-type clamp switch circuits) 102M. The third lower arm circuit SD includes d switch circuits (voltage-type clamp switch circuits) 102D.

[0158] Each of the c switch circuits (first switch circuits) 101C has the same configuration as switch circuits 101N and 101A. That is, switch circuit 101C includes a switching element (first switching element) 1UC, a diode (first diode) 4UC, a capacitor (first capacitor) 3UC, a snubber terminal 205C, a positive terminal 203C, and a negative terminal 204C.

[0159] Note that the snubber terminal 205C, the positive terminal 203C, and the negative terminal 204C only need to be configured so that the circuit can be electrically connected at the positions of these terminals, and the terminals may be omitted. Also, the switch circuit 101C may have multiple switching elements 1UC. In that case, the multiple switching elements 1UC are connected in parallel with the capacitor 3UC and the diode 4UC between the positive terminal 203C and the negative terminal 204C. The multiple switching elements 1UC may be connected in series with each other, or in parallel with each other.

[0160] The switching element 1UC is, for example, a MOSFET. The drain (high potential side) of the switching element 1UC is electrically connected to the positive terminal 203C, and the source (low potential side) of the switching element 1UC is electrically connected to the negative terminal 204C.

[0161] Diode 4UC has its cathode electrically connected to the source and negative terminals 204C of switching element 1UC, and its anode electrically connected to the snubber terminal 205C. Ideally, diode 4UC should have fast recovery characteristics with low recovery loss. For example, it is desirable to use a Schottky barrier diode (SBD) or a wide-bandgap semiconductor (SiC, GaN, etc.) with good recovery characteristics.

[0162] Capacitor (snubber capacitor) 3UC has one end (high potential side) electrically connected to the drain and positive terminal 203C of switching element 1UN, and the other end (low potential side) electrically connected to the anode of diode 4UC and also to the snubber terminal 205C.

[0163] The c switch circuits 101C are connected in series. That is, the positive terminal (high potential side) 203C of switch circuit 101C is electrically connected to the negative terminal (low potential side) 204C of the adjacent switch circuit 101C on the high potential side, and the positive terminal 203C (C=c) of the switch circuit 101C with the highest potential is electrically connected to the positive DC terminal 209. The negative terminal 204C of switch circuit 101C is electrically connected to the positive terminal 203C of the adjacent switch circuit 101C on the low potential side, and the negative terminal 204C (C=1) of the switch circuit 101C with the lowest potential is electrically connected to the positive terminal 203N (N=n) of the switch circuit 101N with the highest potential.

[0164] In the power converter of this embodiment, the first regenerative rectifier circuit has the same configuration as the first regenerative rectifier circuit in the power converter of the second embodiment. The c regenerative rectifier diodes 6UC (C=1~c) are connected between the low-potential end of capacitor 3Un of the first switch circuit 101N (N=n), which is on the highest potential side, and the low-potential end of capacitor 3UC of the first switch circuit 101C (C=1), with the forward direction being from the low-potential side to the high-potential side.

[0165] Each cathode of the regenerative rectifier diode (first regenerative rectifier diode) 6UC (C=1~c) is electrically connected to the snubber terminal 205C (C=1~c) of the switch circuit 101C. The anode of the regenerative rectifier diode 6UC (C=1~c) is electrically connected to the low-potential side of capacitor 3UN (N=n) of the switch circuit 101N (N=n). In other words, the low-potential side of capacitor 3UN (N=n) is electrically connected to the anodes of multiple regenerative rectifier diodes 6UC (C=1~c).

[0166] Resistor 5UC is connected in series at one end to the connection point between the anode of diode 4UC and capacitor 3UC (part of a configuration that electrically connects one end of capacitor 3UC (the low-potential side) and the anode of diode 4UC). The other end of resistor 5UC is electrically connected to the cathode of regenerative rectifier diode 6UC. The other end of resistor 5UC of switch circuit 101C (C=1), which is located on the lowest potential side, is electrically connected via regenerative rectifier diode 6UC (C=1) to the circuit in which capacitor 3Un and resistor 5Un of switch circuit 101n are connected in series.

[0167] Each of the d switch circuits (second switch circuits) 102D has the same configuration as switch circuits 102M and 102B. That is, switch circuit 102D includes a switching element (second switching element) 1XD, a diode (second diode) 4XD, a capacitor (second capacitor) 3XD, a snubber terminal 208D, a positive terminal 206D, and a negative terminal 207D.

[0168] Note that the positive terminal 206D, the negative terminal 207D, and the snubber terminal 208D only need to be configured so that the circuit can be electrically connected at the positions of these terminals, and the terminals may be omitted. Also, the switch circuit 102D may have multiple switching elements 1XD. In that case, the multiple switching elements 1XD are connected in parallel with the capacitor 3XD and the diode 4XD between the positive terminal 206D and the negative terminal 207D. The multiple switching elements 1XD may be connected in series with each other, or in parallel with each other.

[0169] The switching element 1XD is, for example, a MOSFET. The drain (high-potential side) of the switching element 1XD is electrically connected to the positive terminal 206D, and the source (low-potential side) is electrically connected to the negative terminal 207D.

[0170] Diode 4XD has its anode electrically connected to the drain and positive terminal 206D of switching element 1XD, and its cathode electrically connected to the snubber terminal 208D. Ideally, diode 4XD should have fast recovery characteristics with low recovery loss. For example, it is desirable to use a Schottky barrier diode (SBD) or a wide-bandgap semiconductor (SiC, GaN, etc.) with good recovery characteristics.

[0171] Capacitor (snubber capacitor) 3XD has one end (low-potential side) electrically connected to the source and negative terminals 207D of switching element 1XM, and the other end (high-potential side) is electrically connected to the cathode of diode 4XD and also to the snubber terminal 208D.

[0172] The d switch circuits 102D are connected in series. That is, the positive terminal 206D of switch circuit 102D is electrically connected to the negative terminal 207D of the adjacent switch circuit 102D on the high-potential side, and the positive terminal 206D (D=1) of the switch circuit 102D with the highest potential is electrically connected to the negative terminal 207M (M=m) of the switch circuit 102M with the lowest potential. The negative terminal 207D of switch circuit 102D is electrically connected to the positive terminal 206D of the adjacent switch circuit 102D on the low-potential side, and the negative terminal 207D (D=d) of the switch circuit 102D with the lowest potential is electrically connected to the negative DC terminal 210.

[0173] In the power converter of this embodiment, the second regenerative rectifier circuit has the same configuration as the second regenerative rectifier circuit in the power converter of the second embodiment. d regenerative rectifier diodes (second regenerative rectifier diodes) 6XD (D=1~d) are connected, with the forward direction being from the low potential side to the high potential side, between the high potential side terminal of capacitor 3Xm of the second switch circuit 102M (M=m) on the lowest potential side and the low potential side terminal of capacitor 3XD of the second switch circuit 102D.

[0174] Each cathode of the regenerative rectifier diode 6XD (D=1~d) is connected to the snubber terminal 208D (D=1~d) of the switch circuit 102D. Each cathode of the regenerative rectifier diode 6XD (D=1~d) is electrically connected to the high-potential terminal of capacitor 3Xm of the second switch circuit 102M (M=m), which is on the lowest potential side. In other words, the high-potential terminal of capacitor 3UM (M=m) is electrically connected to the anodes of the multiple regenerative rectifier diodes 6XD (D=1~d).

[0175] Resistor 5XD is connected in series at one end to the connection point between the cathode of diode 4XD and capacitor 3XD (part of a configuration that electrically connects one end of capacitor 3XD (the high-potential side) and the anode of diode 4XD). The other end of resistor 5XD is electrically connected to the anode of regenerative rectifier diode 6UC. The other end of resistor 5XD in switch circuit 102D (D=1), which is located on the highest potential side, is electrically connected via regenerative rectifier diode 6XD (D=1) to the circuit in which capacitor 3Xm and resistor 5Xm of switch circuit 102m are connected in series.

[0176] In other words, the power converter of this embodiment includes a regenerative rectifier circuit that connects the low-potential end of the inverter cell 100 and the low-potential end of the first capacitors 3UN, 3UA, 3UC on the upper arm, with the direction from the low-potential side to the high-potential side being the forward direction, when at least one of the first switch circuits 101N, 101A, 101C comprises first diodes 4UN, 4UA, 4UC whose cathodes are connected to the low-potential side ends of the first switching elements 1UN, 1UA, 1UC, and first capacitors 3UN, 3UA, 3UC connected between the anodes of the first diodes 4UN, 4UA, 4UC and the high-potential side ends of the first switching elements 1UN, 1UA, 1UC.

[0177] Furthermore, the power converter of this embodiment includes a regenerative rectifier circuit that connects the high-potential end of the inverter cell 100 and the high-potential end of the second capacitors 3XM, 3XB, 3XD on the lower arm, with the direction from the low-potential side to the high-potential side being the forward direction, when at least one of the second switch circuits 102M, 102B, 102D comprises a second diode 4XM, 4XB, 4XD whose anode is connected to the high-potential side end of the second switching element 1XM, 1XB, 1XD, and a second capacitor 3XM, 3XB, 3XD connected between the cathode of the second diode 4XM, 4XB, 4XD and the low-potential side end of the second switching element 1XM, 1XB, 1XD.

[0178] In the power conversion device of this embodiment, it is desirable that the number c of switch circuit 101C and the number d of switch circuit 102D be the same, but they may be different numbers. Furthermore, in the power conversion device of this embodiment, the switching elements 1UC and 1XD are not limited to MOSFETs, but may also be IGBTs (Insulated Gate Bipolar Transistors) or mechanical switches, for example.

[0179] Furthermore, even when elements with different voltage and current ratings are used as switching elements 1U, 1X, 1UN, 1UA, 1UC, 1XM, 1UB, and 1XD, the effects of this embodiment can still be obtained. However, it is preferable to use elements with the same voltage and current ratings as switching elements 1U, 1X, 1UN, 1UA, 1UC, 1XM, 1UB, and 1XD.

[0180] The high-potential end of the flying capacitor CF2 is electrically connected to the upper arm between the negative terminal 204C of the lowest-potential first switch circuit 101C (C=1) and the positive terminal 203N of the highest-potential first switch circuit 101N (N=n). The low-potential end of the flying capacitor CF2 is electrically connected to the lower arm between the positive terminal 206D of the highest-potential second switch circuit 102D (D=1) and the negative terminal 207M of the lowest-potential second switch circuit 102M (M=m).

[0181] Furthermore, the capacitors 3Ua and 3Un of switch circuits 101a and 101n, which are located between the positive DC terminal 209 and the AC terminal 211 and to which the flying capacitors CF and CF2 are connected to the drain (or collector) of the switching element, and the capacitors 3Xb and 3Xm of switch circuits 102b and 102m, which are located between the negative DC terminal 210 and the AC terminal 211 and to which the flying capacitors CF and CF2 are connected to the source (or emitter) of the switching element, should preferably have a larger capacitance than the other capacitors 3UN, 3UA, 3UC, 3XB, 3XM, and 3XD in order to temporarily buffer the absorbed energy.

[0182] Next, an example of the operation of the power converter of this embodiment will be described. The power converter of this embodiment holds multiple different voltages in flying capacitors CF and CF2, and enables multi-level output by adding and subtracting voltage values. Figure 6 is a diagram illustrating an example of the operation of the power converter according to the fourth embodiment.

[0183] In this embodiment, the control circuit CTR generates control signals for the first upper arm circuit SA, the second upper arm circuit SN, the third upper arm circuit SC, the first lower arm circuit SB, the second lower arm circuit SX, the third lower arm circuit SD, and the switching elements 1U and 1X using a carrier phase shift modulation scheme with carrier waves C3, C4, and C5 whose phases are shifted by approximately 120 degrees from each other.

[0184] The control signals for the third upper arm circuit SC and the third lower arm circuit SD are generated, for example, by comparing the carrier wave C3 with a command value. The control signals for the second upper arm circuit SN and the second lower arm circuit SM are generated, for example, by comparing the carrier wave C4 with a command value. The control signals for the first upper arm circuit SA and the first lower arm circuit SB are generated, for example, by comparing the carrier wave C5 with a command value.

[0185] In a 4-level flying capacitor type power converter, the control circuit CTR can selectively output four levels of voltage (Ed, 2Ed / 3, Ed / 3, -Ed) to the AC terminals of the power converter by, for example, setting the voltage of the flying capacitor CF2 to 2 / 3 times the DC power supply voltage (Ed) and the voltage of the flying capacitor CF to 1 / 3 times the DC power supply voltage.

[0186] In the power conversion device of this embodiment, similar to the second embodiment described above, the control circuit CTR can collect the energy generated during switching into the floating capacitor 2. In other words, in the power conversion device of this embodiment, the control circuit CTR can reduce losses such as turn-on losses, turn-off losses, and recovery losses by sequentially switching multiple switching elements 1UN, 1UA, 1UC, 1UB, 1XM, and 1XD in each of the upper arm circuits SN, SA, SC and lower arm circuits SB, SM, and SD at predetermined time intervals.

[0187] As described above, in the power conversion device of this embodiment, for example, most of the energy during switching, which was lost in conventional inverters, can be stored in the floating capacitor 2 via capacitors 3UN, 3UA, 3UC, 3XM, 3XB, and 3XD. By discharging the floating capacitor 2, it is possible to reduce switching losses without increasing the switching speed. Furthermore, recovery losses can be reduced by applying a low voltage to the switching elements 1UN, 1UA, 1UC, 1XM, 1XB, and 1XD during the recovery of the parasitic diodes of the switching elements 1UN, 1UA, 1UC, 1XM, 1XB, and 1XD. In other words, the power conversion device of this embodiment can improve the trade-off between switching losses and the capacitance of the flying capacitors CF and CF2.

[0188] In this embodiment of the power conversion device, all switching elements switch during one cycle of the carrier wave. Therefore, capacitors 3UN, 3UA, 3UC, 3XM, 3XB, and 3XD can collect energy in the floating capacitor 2 without accumulating the absorbed energy for multiple cycles. In other words, in this embodiment, there are no switching modes in which capacitors 3UN, 3UA, 3UC, 3XM, 3XB, and 3XD become larger, thus avoiding an increase in the size of the power conversion device.

[0189] In the fourth embodiment described above, the power converter was equipped with an inverter cell 100, but similar effects can be obtained by, for example, using a 4-level flying capacitor type power converter as the power converter of the third embodiment. Furthermore, similar effects can be obtained by using a 5-level or more multi-level flying capacitor type power converter as the power converter of the first to fourth embodiments.

[0190] As described above, according to this embodiment, it is possible to provide a power conversion device that can keep energy loss low while avoiding increasing size. While several embodiments of the present invention have been described, these embodiments are presented as examples only and are not intended to limit the scope of the invention. These novel embodiments can be carried out in a variety of other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their variations are included in the scope and spirit of the invention, as well as in the claims of the invention and its equivalents. For example, in the above-described embodiments, it is not necessary for all first switch circuits to include a first diode and a first capacitor, nor for all second switch circuits to include a second diode and a second capacitor. At least one of the first switch circuits in the upper arm may include a first diode and a first capacitor, and at least one of the second switch circuits in the lower arm may include a second diode and a second capacitor. Even in this case, the same effects as in the embodiments described above can be obtained. [Note 1] The energy storage unit, An upper arm comprising a first upper arm circuit and a second upper arm circuit connected in series between the AC terminal and the positive DC terminal, A lower arm comprising a first lower arm circuit and a second lower arm circuit connected in series between the AC terminal and the negative DC terminal, A flying capacitor electrically connected to the upper arm between the first upper arm circuit and the second upper arm circuit, and electrically connected to the lower arm between the first lower arm circuit and the second lower arm circuit, Equipped with, Each of the first upper arm circuit and the second upper arm circuit is configured by connecting one or more first switch circuits having a first switching element in series, Each of the first lower arm circuit and the second lower arm circuit is configured by connecting one or more second switch circuits having a second switching element in series. At least one of the first switch circuits has a first capacitor connected in parallel with the first switching element, or at least one of the second switch circuits has a second capacitor connected in parallel with the second switching element. When at least one of the first switch circuits has a first capacitor connected in parallel with the first switching element, it has a first regenerative rectifier circuit that connects a plurality of the first capacitors or the first capacitor and the energy storage unit in parallel via one or more of the first switching elements. When at least one of the second switch circuits has a second capacitor connected in parallel with the second switching element, it has a second regenerative rectifier circuit that connects a plurality of the second capacitors or the second capacitor and the energy storage unit in parallel via one or more of the second switching elements. Power converter. [Note 2] The first regenerative rectifier circuit is a circuit that connects the low-potential side of the energy storage unit and the low-potential side of the first capacitor when at least one of the first switch circuits has a first diode whose cathode is connected to the low-potential side of the first switching element, and a first capacitor connected between the anode of the first diode and the high-potential side of the first switching element, The power conversion device according to Appendix 1, wherein the second regenerative rectifier circuit is a circuit that connects the high-potential side of the energy storage unit to the high-potential side of the second capacitor when at least one of the second switch circuits has a second diode whose anode is connected to the high-potential side of the second switching element and a second capacitor connected between the cathode of the second diode and the low-potential side of the second switching element. [Note 3] The aforementioned energy storage unit is a floating capacitor, An upper switching element connected between the AC terminal and the high-potential terminal, a lower switching element connected between the AC terminal and the low-potential terminal, a floating capacitor connected in parallel to the upper switching element and the lower switching element between the high-potential terminal and the low-potential terminal, and the power conversion device as described in Appendix 1. [Note 4] The first regenerative rectifier circuit is a circuit having one or more first regenerative rectifier diodes connected in series and a first resistor connected between the cathode of one of the first regenerative rectifier diodes and the low-potential side terminal of the first capacitor, or a circuit having multiple first regenerative rectifier diodes and multiple first resistors connected between the cathodes of each of the first regenerative rectifier diodes and the corresponding low-potential side terminal of the first capacitor, The power conversion device according to Appendix 1, wherein the second regenerative rectifier circuit is a circuit having one or more second regenerative rectifier diodes connected in series and a second resistor connected between the anode of one of the second regenerative rectifier diodes and the high-potential side of the second capacitor, or a circuit having multiple second regenerative rectifier diodes and multiple second resistors connected between the anodes of each of the second regenerative rectifier diodes and the corresponding high-potential side of the second capacitor. [Note 5] The capacitance of the first capacitor included in the first switch circuit connected to the lowest potential side of the first upper arm circuit and the second upper arm circuit is greater than the capacitance of the other first capacitors. The power conversion device as described in Appendix 1, wherein the capacitance of the second capacitor included in the second switch circuit connected to the highest potential side of the first lower arm circuit and the second lower arm circuit is greater than the capacitance of the other second capacitors. [Note 6] The energy storage unit comprises a first energy storage unit with one end electrically connected to the positive DC terminal, and a second energy storage unit with one end electrically connected to the negative DC terminal. The first regenerative rectifier circuit is electrically connected to the other end of the first energy storage unit, and when at least one of the first switch circuits has the first capacitor connected in parallel with the first switching element, one or more of the first capacitors or the first capacitor and the first energy storage unit are connected in parallel via the first switching element. The power conversion device according to Appendix 1, wherein the second regenerative rectifier circuit is electrically connected to the other end of the second energy storage unit, and when at least one of the second switch circuits has the second capacitor connected in parallel with the second switching element, a plurality of the second capacitors or the second capacitors are connected in parallel with the first energy storage unit via one or more of the second switching elements. [Note 7] The first switch circuit comprises the first switching element, a first diode whose anode is connected to the high-potential side of the first switching element, and the first capacitor connected between the cathode of the first diode and the low-potential side of the first switching element. The second switch circuit comprises the second switching element, a second diode whose cathode is connected to the low-potential side of the second switching element, and the second capacitor connected between the anode of the second diode and the high-potential side of the second switching element. The first regenerative rectifier circuit connects the high-potential end of the first capacitor to the other end of the first energy storage unit, with the direction from the low-potential side to the high-potential side being the forward direction. The power conversion device described in Appendix 6, wherein the second regenerative rectifier circuit connects the low-potential end of the second capacitor of the lower arm to the other end of the second energy storage unit, with the direction from the low-potential side to the high-potential side being the forward direction. [Explanation of symbols]

[0191] 1U, 1X, 1UN, 1UA, 1UC, 1XM, 1XB, 1XD... Switching elements, 2... Floating capacitors, 3UN, 3UA, 3UC, 3XM, 3XB, 3XD... Capacitors, 4UN, 4UA, 4UC, 4XM, 4XB, 4XD... Diodes, 5UN, 5UA, 5UC, 5XM, 5XB, 5XD... Resistors, 6UN, 6UA, 6UC, 6XM, 6XB, 6XD... Regenerative rectifier diodes, 100... Inverter cells, 101N, 101A, 101C, 102M, 102B, 102D... Switch circuits, 209... Positive DC terminal, 210... Negative DC terminal, 211... AC terminal (AC end), CF, CF2... Flying capacitors, CU, CX... Energy storage section, CTR... Control circuit.

Claims

1. The energy storage unit, An upper arm comprising a first upper arm circuit and a second upper arm circuit connected in series between the AC terminal and the positive DC terminal, A lower arm comprising a first lower arm circuit and a second lower arm circuit connected in series between the AC terminal and the negative DC terminal, A flying capacitor electrically connected to the upper arm between the first upper arm circuit and the second upper arm circuit, and electrically connected to the lower arm between the first lower arm circuit and the second lower arm circuit, Equipped with, Each of the first upper arm circuit and the second upper arm circuit is configured by connecting one or more first switch circuits having a first switching element in series. Each of the first lower arm circuit and the second lower arm circuit is configured by connecting one or more second switch circuits having a second switching element in series. At least one of the first switch circuits has a first capacitor connected in parallel with the first switching element, or at least one of the second switch circuits has a second capacitor connected in parallel with the second switching element. When at least one of the first switch circuits has a first capacitor connected in parallel with the first switching element, there is a first regenerative rectifier circuit that can connect a plurality of the first capacitors in parallel via one or more of the first switching elements, and can connect the first capacitor and the energy storage unit in parallel. When at least one of the second switch circuits has a second capacitor connected in parallel with the second switching element, the second regenerative rectifier circuit has the ability to connect a plurality of the second capacitors in parallel via one or more of the second switching elements, and to connect the second capacitor and the energy storage unit in parallel. Power converter.

2. The first regenerative rectifier circuit is a circuit that connects the low-potential side of the energy storage unit and the low-potential side of the first capacitor when at least one of the first switch circuits has a first diode whose cathode is connected to the low-potential side of the first switching element, and a first capacitor connected between the anode of the first diode and the high-potential side of the first switching element, The power conversion device according to claim 1, wherein the second regenerative rectifier circuit is a circuit that connects the high-potential side of the energy storage unit and the high-potential side of the second capacitor when at least one of the second switch circuits has a second diode whose anode is connected to the high-potential side of the second switching element and a second capacitor connected between the cathode of the second diode and the low-potential side of the second switching element.

3. The aforementioned energy storage unit is a floating capacitor, The power conversion device according to claim 1, wherein an upper switching element connected between the AC terminal and the high-potential side terminal and a lower switching element connected between the AC terminal and the low-potential side terminal are connected in parallel.

4. The first regenerative rectifier circuit is a circuit having one or more first regenerative rectifier diodes connected in series and a first resistor connected between the cathode of one of the first regenerative rectifier diodes and the low-potential side terminal of the first capacitor, or a circuit having multiple first regenerative rectifier diodes and multiple first resistors connected between the cathodes of each of the first regenerative rectifier diodes and the corresponding low-potential side terminal of the first capacitor, The power conversion device according to claim 1, wherein the second regenerative rectifier circuit is a circuit having one or more second regenerative rectifier diodes connected in series and a second resistor connected between the anode of one of the second regenerative rectifier diodes and the high-potential side of the second capacitor, or a circuit having a plurality of the second regenerative rectifier diodes and a plurality of second resistors connected between the anodes of each of the second regenerative rectifier diodes and the corresponding high-potential side of the second capacitor.

5. The capacitance of the first capacitor included in the first switch circuit connected to the lowest potential side of the first upper arm circuit and the second upper arm circuit is greater than the capacitance of the other first capacitors. The power conversion device according to claim 1, wherein the capacitance of the second capacitor included in the second switch circuit connected to the highest potential side of the first lower arm circuit and the second lower arm circuit is greater than the capacitance of the other second capacitors.

6. The energy storage unit comprises a first energy storage unit with one end electrically connected to the positive DC terminal, and a second energy storage unit with one end electrically connected to the negative DC terminal. The first regenerative rectifier circuit is electrically connected to the other end of the first energy storage unit, and when at least one of the first switch circuits has the first capacitor connected in parallel with the first switching element, it is possible to connect a plurality of the first capacitors in parallel via one or more of the first switching elements, and it is also possible to connect the first capacitor and the first energy storage unit in parallel. The power conversion device according to claim 1, wherein the second regenerative rectifier circuit is electrically connected to the other end of the second energy storage unit, and when at least one of the second switch circuits has the second capacitor connected in parallel with the second switching element, a plurality of the second capacitors can be connected in parallel via one or more of the second switching elements, and the second capacitor and the second energy storage unit can be connected in parallel.

7. The first switch circuit comprises the first switching element, a first diode whose anode is connected to the high-potential side of the first switching element, and the first capacitor connected between the cathode of the first diode and the low-potential side of the first switching element. The second switch circuit comprises the second switching element, a second diode whose cathode is connected to the low-potential side of the second switching element, and the second capacitor connected between the anode of the second diode and the high-potential side of the second switching element. The first regenerative rectifier circuit connects the high-potential end of the first capacitor to the other end of the first energy storage unit, with the direction from the low-potential side to the high-potential side being the forward direction. The power conversion device according to claim 6, wherein the second regenerative rectifier circuit connects the low-potential end of the second capacitor of the lower arm to the other end of the second energy storage unit, with the direction from the low-potential side to the high-potential side being the forward direction.

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