JP3637276B2 - 3-level power converter - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a technology for mounting a three-level power converter, and more particularly to a technology for reducing inductance between a DC voltage source and a switching element.
[0002]
[Prior art]
In a power converter configured by a DC voltage source and a switching element and converting power between DC and AC, when the switching element is turned off, a surge voltage is induced in the wiring inductance between the DC voltage source and the switching element. And applied to the switching element. For this reason, when the wiring inductance is large, the switching element must be designed to have a high withstand voltage.
[0003]
In order to reduce the inductance of the wiring, the conductor that is the current path is made as wide as possible, and the forward and return conductors of the current path (hereinafter referred to as a commutation path) in which the current changes by turn-off are as close as possible It is known to form so-called parallel flat plates that are connected together. This is because the change in the apparent magnetic flux, that is, the inductance can be reduced by canceling out the magnetic fluxes generated by the current flowing in the forward path and the return path of the commutation path. The commutation path of the switching element referred to here is a current path in the converter that occurs at the moment when the switching element is turned off, and a surge voltage is generated by changing the current by turning off the switching element. It is an electric circuit with an inductance that causes generation. Details will be described later.
[0004]
As means for reducing the wiring inductance, for example, in Japanese Patent Application Laid-Open No. 11-89249, the positive side arm portion of the DC voltage source is closest to the second switching element with respect to the DC voltage source. , The first coupling diode is disposed in the middle of each of the first and second switching elements, and the negative arm portion is closest to the third switching element with respect to the DC voltage source, and the fourth switching element It is disclosed that the element is farthest and the second coupling diode is placed in between the third and fourth switching elements, respectively.
[0005]
[Problems to be solved by the invention]
In the above-described prior art, the surge voltage applied to the switching element is still large, and the conductor becomes large and the device is insufficiently reduced in size and weight in order to ensure the reliability as the power conversion device.
[0006]
An object of the present invention is to suppress a surge voltage when a switching element is turned off in a three-level power converter, and to reduce the size and weight of the power converter.
[0007]
[Means for Solving the Problems]
There are two possible commutation paths when the four switching elements are turned off. These are a commutation path of the first and fourth switching elements and a commutation path of the second and third switching elements. The commutation paths of the first and fourth switching elements are relatively short, while the commutation paths of the second and third switching elements are relatively long. Therefore, the surge voltage applied to the second and third switching elements is larger than the surge voltage applied to the first and fourth switching elements.
[0008]
Therefore, in one aspect of the present invention, in order to reduce the wiring inductance in the commutation path of the second and third switching elements that are physically long, not only the commutation path is made as short as possible but also the switching element that is turned off. The first current path through which the current flows and the wiring of the second current path in which the current increases as the current in the first current path decreases are arranged.
[0009]
As will be described in detail later, one of the currents flowing through these first and second current paths decreases and the other increases with a slight temporal overlap during commutation. Or without overlapping in time, one disappears momentarily and the other rises. In order to suppress the inductance of these two current paths, it is effective to align both wirings.
[0010]
In another aspect, the present invention is characterized in that the connection terminals of the DC voltage source are arranged so that the lengths of the first and second current paths are substantially the same.
[0011]
Thereby, both current paths balance and cancel each other, and the inductance at the time of turn-off is further suppressed.
[0012]
In a preferred embodiment of the present invention, the connection terminal of the smoothing capacitor (unit voltage source) is disposed so as to be closest to the coupling diode in the linearly arranged element group.
[0013]
As a result, the first and second current paths in the commutation paths of the second and third switching elements are balanced, and an overlapping portion of the wiring is generated, so that a substantial inductance at the time of turn-off is suppressed, and a surge voltage is reduced. Becomes smaller.
[0014]
In another embodiment of the present invention, a flat insulating layer is provided between two flat conductive layers arranged so as to be sandwiched between a DC voltage source and a linearly arranged element group. .
[0015]
As a result, the two-layer flat conductors can be arranged closer to each other, the commutation path can be shortened, and the overlapping of the wirings can be strengthened, resulting in a smaller surge voltage.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
[0017]
1 is a side view of one phase of the three-level power converter according to the first embodiment of the present invention, FIG. 2 is an electric circuit diagram of one phase, and FIG. 3 is a plan view of one phase. Here, the IGBT is described as an example of the switching element for convenience, but the same effect can be obtained when other switching elements such as a MOSFET and a bipolar transistor are used. Here, the positive terminal of each switching element is called a collector, and the negative terminal is called an emitter.
[0018]
1 to 3, one phase of the power conversion device constitutes the electric circuit of FIG. 2, and a group of elements arranged in a straight line and first and second unit voltage sources constituting a DC voltage source. Are arranged so as to sandwich a flat conductor layer.
[0019]
First, in terms of the configuration of the element group, as shown in FIGS. 1 and 3, the first switching element 1, the first coupling diode 5 for deriving the intermediate potential 5, the second switching element 2, and the third switching element. The element 3, the second coupling diode 6 for deriving the intermediate potential, and the fourth switching element 4 are arranged substantially on a straight line.
[0020]
Next, two upper and lower flat conductor layers are disposed above the element group. The lower layer of the conductor layer is composed of a first intermediate potential conductor 12, an AC side conductor 13, and a second intermediate potential conductor 14, as shown in FIG. 3B, and is parallel to the element as shown in FIG. The flat plate-like portion is in the same plane on the upper side of the element layer in FIG. As shown in FIG. 3A, the upper layer of the conductor layer is composed of a positive electrode side conductor 9, a third intermediate potential conductor 11, and a negative electrode side conductor 10, and as shown in FIG. 1, is parallel to the element group. The flat plate portion is disposed above the lower layer of the conductor layer, and the upper layer and the lower layer of these conductor layers are in a parallel relationship.
[0021]
Finally, the DC voltage sources 7 and 8 are arranged so that the conductor layer is sandwiched between the DC voltage source and the element group. The DC voltage source is composed of first and second smoothing capacitors 7 and 8 which are unit voltage sources.
[0022]
In this embodiment, the negative terminal 11p of the first unit voltage source 7 is arranged so as to be closest to the first coupling diode 5 in the element group, and the second unit voltage source 8 The positive electrode terminal 11n is arranged so as to be closest to the second coupling diode 6 in the element group.
[0023]
Next, the connection relationship by conductor layer is described. In the lower layer of the conductor layer, the first intermediate potential conductor 12 connects the emitter of the first switching element 1, the collector of the second switching element 2, and the cathode of the first coupling diode 5 as shown in FIG. As shown in FIG. 6B, a hole or notch 15 for insulation with the third intermediate potential conductor 11 connected to the anode of the first coupling diode is provided. The AC side conductor 13 connects the emitter of the second switching element 2 and the collector of the third switching element, and is provided with an AC output terminal (not shown) at an arbitrary location. The second intermediate potential conductor 14 connects the emitter of the third switching element 3, the collector of the fourth switching element 4, and the anode of the second coupling diode, as shown in FIG. 3B. A hole or notch 16 is provided for insulation from the third intermediate potential conductor 11 connected to the cathode of the second coupling diode.
[0024]
On the other hand, the connection in the upper layer of the conductor layer is such that the positive conductor 9 connects the collector of the first switching element 1 and the positive terminal 9 p of the first smoothing capacitor 7. The negative conductor 10 connects the emitter of the fourth switching element 4 and the negative terminal 10 n of the second smoothing capacitor 8. The third intermediate potential conductor 11 connects the anode of the first diode 5 and the cathode of the second diode 6, and the negative terminal 11 p of the first smoothing capacitor 7 and the positive terminal 11 n of the second smoothing capacitor 8. Connected to.
[0025]
Here, one collector and one emitter of each switching element are shown, but a similar configuration is possible even with a switching element having a plurality of collectors and emitters. Further, as shown in FIG. 2, each of the switching elements 1 to 4 includes a switching function unit for turning on / off current and a freewheeling function unit for an AC circuit connected in reverse parallel to the switching function unit. In particular, as shown in FIG. 3 (c), the element group arranged in a line includes the anode terminal (the collector C of the switching element, the anode A of the diode) and the cathode terminal (the emitter E of the switching element). , Diode cathodes K) are arranged in a substantially straight line. The flat conductors 9 to 14 have a width that is sufficiently wider than the terminal groups C, E, A, and K as shown in FIGS. The DC voltage sources 7 and 8 and the element groups 1 to 6 are arranged so as to be sandwiched between them.
[0026]
Now, the commutation paths when each switching element is turned off are the four paths shown in FIGS. The commutation path (a) of the first switching element 1 of the positive arm, the commutation path (d) of the fourth switching element 4 of the negative arm, and the commutation path of the second switching element 2 of the positive arm. (B) and the commutation path (c) of the third switching element 3 of the negative arm have a similar relationship on the electric circuit, and if arranged in a similar positional relationship in physical space, inductance Is equivalent. Therefore, two types of commutation paths (a), (d) and (b), (c) may be considered. Here, the commutation paths (a) and (b) will be described, and (c) and (d) will be omitted, but they can be understood in exactly the same way.
[0027]
First, the commutation path (a) is a current path in the converter that has occurred at the moment when the switching element 1 is turned off, and generates a high voltage when the current is interrupted by the turn-off of the switching element 1. It is an electric circuit with inductance that becomes a factor. When the switching element 1 is turned on, the switching element 2 is also turned on, and “the positive electrode of the second smoothing capacitor 8 → the coupling diode 5 → the second switching element 2 → the AC terminal → the AC (load) circuit → The diode 5 flows through the path of the other phase switching elements 3, 4 → the negative electrode of the second smoothing capacitor 8. Therefore, the diode 5 can also flow in the reverse direction within the range of the magnitude of the current. Therefore, as shown by the bold line in FIG. The positive electrode of the smoothing capacitor 7 → the first switching element 1 → the diode 5 (reverse direction) → the negative electrode of the first smoothing capacitor 7 ”. When the switching element 1 is turned off, the current in the commutation path is This is interrupted, and a surge voltage is generated by the inductance of this path, and is applied to the switching element 1.
[0028]
Since the commutation path (a) is relatively short and the wiring inductance is also relatively small, the surge voltage applied to the first switching element 1 is small and causes no problem. In particular, in this embodiment, the commutation path (a) is shortened as shown by a broken line in FIG.
[0029]
Next, the commutation path (b) is a current path in the converter that occurs at the moment when the switching element 2 is turned off (short time before and after), and the current is changed by turning off the switching element 2. This is an electric circuit having an inductance that causes a surge voltage. When the switching element 2 is turned off, the free wheel diodes in the third and fourth switching elements 3 and 4 are “AC (load) circuit → an antiparallel diode of the switching elements 4 and 3 → AC terminal → AC (load ) Circuit ”, it is in a state where it can be conducted. Therefore, as shown by a thick line in FIG. 4B,“ the positive electrode of the second smoothing capacitor 8 → the coupling diode 5 → the second switching element 2 → the third, Current can flow through a path of “freewheel diodes (reverse direction) of the fourth switching elements 3, 4 → negative electrode of the second smoothing capacitor 8”. When the switching element 2 is turned off, a high voltage is generated by the inductance of the commutation path and applied to the switching element 2. FIG. 6 is a side view showing the commutation path (b) with a broken line.
[0030]
Here, the wiring inductance of the commutation path (b) is considered. This commutation path (b) must be relatively longer than the commutation path (a), as is apparent from the figure. Since the wiring inductance increases with the length of the path, the commutation path must be designed as short as possible. Further, it is also important how the current paths immediately before and after the switching element 2 is turned off are arranged (overlapped). The three-level power conversion device switches the voltage to an AC terminal and outputs the voltage to three levels of DC in a short time by PWM control. On the other hand, the AC load current uses the inductance of the load as a current source, and hardly changes during a very short event of PWM control such as the turn-off time of each switching element. A free wheel diode is provided to continue the AC load current. The current I1 to the AC load immediately before the switching element 2 is turned off is expressed as “positive electrode of capacitor 8 → diode 5 → switching element 2 → AC load → switching elements 3 and 4 of other phases → negative electrode of capacitor 8”. On the other hand, the current I2 of the AC load immediately after the switching element 2 is turned off is “AC load → switching elements 3 and 4 of other phases → freewheel diodes of switching elements 4 and 3 → AC load”. It flows in the route. FIG. 7 is a side view obtained by adding these currents I1 and I2 in this embodiment. The current I2 increases as the current I1 decreases, or the current I2 rises at the same time as the current I1 disappears. Since these currents overlap in the part (e) of FIG. 7 and flow in the same direction, a substantial inductance at the moment of turn-off can be reduced. That is, in this portion, one increase (rise) and the other decrease (disappearance) overlap, and the total current change dI / dt becomes small, and the substantial inductance becomes small. As a result, the surge voltage applied to the switching element 2 can be suppressed small. The same applies to the switching element 3. According to the experiment, the magnitude of the surge voltage to the switching elements 2 and 3 can be reduced by 20% compared to the prior art described in the above-mentioned publication.
[0031]
Thus, in this embodiment, among the two types of commutation paths (a) and (b) when the switching element is turned off, the commutation path (in which the commutation path is long and the wiring inductance is large) In order to reduce the wiring inductance of b), the smoothing capacitor 7 as the first DC voltage source is arranged so that the negative electrode terminal 11p is closest to the first coupling diode 5, while the second DC voltage is applied. The smoothing capacitor 8 as a voltage source is arranged so that the positive electrode terminal 11 n is closest to the second coupling diode 6. That is, there is a positional relationship in which one side of the conductor layer has the negative terminal 11p of the first DC voltage source on one side and the anode terminal of the first coupling diode 5 on the other side. Similarly, on the other side of the conductor layer, the positive terminal 11n of the second DC voltage source is on one side and the cathode terminal of the second coupling diode 6 is on the other side.
[0032]
In this way, the first current path through which the current I1 flows toward the AC terminal immediately before the second switching element 2 is turned off, and the current toward the AC terminal immediately after the second switching element 2 is turned off. Connection of the first and second unit voltage sources 7 and 8 to a position where the second current path through which I2 flows is substantially the same length (position close to the coupling diodes 5 and 6 in this embodiment), respectively. Terminals 9p, 11p and 10n, 11n are arranged, and the first and second current paths are arranged along each other in the portion (e).
[0033]
FIG. 8 is a side view showing a second embodiment of the present invention. In addition to the configurations of FIGS. 1 to 7, an insulating layer 17 is provided between the upper layer and the lower layer of the conductor layer. The insulating layer 17 is a flat plate made of an insulating material, for example, and is provided with holes or cuts in accordance with holes or cuts for ensuring insulation of the first and second intermediate potential conductors. By providing the insulating layer, the distance between the upper layer and the lower layer of the conductor layer can be reduced and the mutual induction can be further increased, so that the inductance can be further reduced. The insulating layer may be in contact with one or both of the upper layer and the lower layer.
[0034]
FIG. 9 is a plan view of a third embodiment of the present invention, showing an upper layer, a lower conductor layer, and an element layer. In this embodiment, in the first embodiment, each switching element 1 to 4 and two diodes 5 and 6 are connected in parallel, and the current capacity is doubled. In this case as well, the same effects as in the above embodiment are achieved. The main circuit configuration is the same as that shown in FIG. 18 of JP-A-11-89249.
[0035]
【The invention's effect】
ADVANTAGE OF THE INVENTION According to this invention, the surge voltage at the time of turn-off of a switching element can be suppressed, and the three-level power converter device reduced in size and weight can be provided.
[Brief description of the drawings]
FIG. 1 is a side view of one phase of a three-level power converter according to an embodiment of the present invention.
FIG. 2 is an electric circuit diagram for one phase of a three-level power converter according to an embodiment of the present invention.
FIG. 3 is a plan view of one phase of the three-level power converter according to one embodiment of the present invention.
FIG. 4 is an electric circuit diagram showing four types of commutation paths according to an embodiment of the present invention.
FIG. 5 is a side view of a commutation path (a) according to an embodiment of the present invention.
FIG. 6 is a side view of a commutation path (b) according to an embodiment of the present invention.
FIG. 7 is a side view in which a current path of a commutation path (b) is added according to an embodiment of the present invention.
FIG. 8 is a side view of another embodiment of the present invention in which an insulating layer is added.
FIG. 9 is a plan view of another embodiment of the present invention connected in parallel.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... 1st switching element, 2 ... 2nd switching element, 3 ... 3rd switching element, 4 ... 4th switching element, 5 ... 1st coupling diode, 6 ... 2nd coupling diode, 7, 8 ... first and second unit voltage sources (smoothing capacitors), 9 to 14 ... flat conductors, 17 ... insulating layers, 9p, 11p ... connection terminals of the first unit voltage source, 10n, 11n ... second Unit voltage source connection terminal.

Claims (8)

  A DC voltage source including first and second unit voltage sources connected in series and having three terminals of three DC voltage levels, and a series connection between a positive terminal and an AC terminal of the first unit voltage source The first and second switching elements, the first coupling diode connected between the series connection point thereof and the series connection point of the first and second unit voltage sources, the AC terminal, and the The third and fourth switching elements connected in series between the negative terminal of the second unit voltage source and the series connection point between the series connection point of the first and second unit voltage sources. The connected second coupling diode and the first switching element, the first coupling diode, the second switching element, the third switching element, the second coupling diode, and the fourth switching element in a line in this order. The arranged element group and this element group In a three-level power conversion device that is disposed so as to be sandwiched between DC voltage sources and that has a flat conductor for carrying out the electrical connection and outputs three voltage levels to the AC terminal, the conductor layers are substantially identical. The negative terminal of the first unit voltage source is arranged on one of the front and back sides of the location, the anode terminal of the first coupling diode is arranged on the other side, and the second is placed on the other side of the substantially identical location of the conductor layer A three-level power converter characterized in that the positive terminal of the unit voltage source is arranged and the cathode terminal of the second coupling diode is arranged on the other side. 2. The element group arranged in a row according to claim 1, wherein the anode terminal and the cathode terminal of all of these elements are arranged substantially in a straight line, and the flat conductor is sufficiently wider than these terminal groups. The three-level power converter is arranged so as to be sandwiched between the DC voltage source and the element group arranged in the front and back direction. In claim 1 or 2 , the flat conductor through which the current immediately before the turn-off of the second switching element flows and the flat conductor through which the current immediately after the turn-off of the second switching element flows are arranged alongside, A three-level power conversion comprising: a flat conductor through which a current immediately before turning off the third switching element; and a flat conductor through which a current immediately after turning off the third switching element are arranged. apparatus. A DC voltage source including first and second unit voltage sources connected in series and having three terminals of three DC voltage levels, and a series connection between a positive terminal and an AC terminal of the first unit voltage source The first and second switching elements, the first coupling diode connected between the series connection point thereof and the series connection point of the first and second unit voltage sources, the AC terminal, and the The third and fourth switching elements connected in series between the negative terminal of the second unit voltage source and the series connection point between the series connection point of the first and second unit voltage sources. The second coupling diode connected, the element group in which the first to fourth switching elements are arranged in a line, and the element group and the DC voltage source are arranged so as to be sandwiched between the electric connection and the electric connection. A plate-shaped conductor that provides three voltage levels to the AC terminal. To the three-level power converter, wherein the element group arranged in a line, the anode terminal and the cathode terminal of all these elements are arranged substantially in a straight line, the flat conductor is sufficiently than these terminal groups A current path through which the current flows toward the AC terminal immediately before the second switching element is turned off , and is arranged so as to be sandwiched between the DC voltage source and the element group arranged in the front and back direction. And the connection terminals of the first and second unit voltage sources are arranged at positions where the current paths through which current flows toward the AC terminal immediately after turn-off of the second switching element are substantially the same length. A three-level power converter characterized by the above. In claim 4, a current flows toward the first current path a current flows toward the AC terminal to turn off immediately before the second switching element, the AC terminals immediately after turn-off of the second switching element The connection terminals of the first and second unit voltage sources are arranged at positions where the second current path has substantially the same length, and parts of the first and second current paths are arranged along each other. A three-level power converter characterized by being arranged. 6. The three-level power converter according to claim 1, wherein a flat insulating layer is provided so as to be sandwiched between the following (1) and (2).
(1) A flat conductor that connects the positive terminal of the first unit voltage source and the first switching element, and a flat conductor that connects the negative terminal of the second unit voltage source and the fourth switching element. And a flat conductor connecting the first and second unit voltage sources.
(2) A flat conductor connecting the first and second switching elements, a flat conductor connecting the second and third switching elements, and a flat conductor connecting the third and fourth switching elements . The three-level power according to any one of claims 1 to 6, wherein the first to fourth switching elements and the first and second diodes are each composed of a plurality of switching elements and diodes connected in parallel. Conversion device.   8. The three-level power conversion device according to claim 1, wherein the first and second unit voltage sources include first and second capacitors, respectively.

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