JP2002153078A - 3-level power conversion device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To achieve reduction in size of a 3-level power conversion device. SOLUTION: A group of elements consisting of four serially connected switching elements 1 to 4 and two coupling diodes 5, 6 of the 3-level power converter are disposed on a line, and the smoothing capacitors 7, 8 are disposed with the connecting terminals 9p, 11p and 10n, 11n located at the nearest position to the coupling diodes 5, 6 among these element groups. Accordingly, the lengths of two current paths before and after the turning OFF can be balanced and these current paths are laid along each other in view of reducing a wiring inductance during the turning off, controlling a surge voltage and also reducing size and weight.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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]

2. Description of the Related Art In a power converter that is constituted by a DC voltage source and a switching element and converts power between DC and AC, when a switching element is turned off, a wiring inductance between the DC voltage source and the switching element is reduced. , A surge voltage is induced and applied to the switching element. Therefore, if the wiring inductance is large, the switching element must be designed to have a high withstand voltage.

In order to reduce the wiring inductance,
The conductor that is the current path is made as wide as a flat plate,
In addition, it is known to form a so-called parallel plate that connects conductors on a forward path and a return path of a current path (hereinafter referred to as a commutation path) in which a current changes by turning off as close as possible. 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 currents flowing in the outward 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 the current is changed by the turning off of the switching element to generate a surge voltage. This is an electric circuit having an inductance that is a factor of occurrence. The details will be described later.

As means for reducing the wiring inductance, for example, Japanese Patent Application Laid-Open No. H11-89249 discloses that the positive side arm of a DC voltage source is provided with a second arm with respect to the DC voltage source.
Are closest to the first switching element, farthest to the first switching element, and the first coupling diode is connected to the first and second switching elements.
And the negative side arm section is located closest to the DC voltage source, the third switching element is farthest away from the DC voltage source, and the second coupling diode is located at the third and third switching elements. It is disclosed that each of them is arranged in the middle of the four switching elements.

[0005]

In the prior art described above, the surge voltage applied to the switching element is still large, and in order to ensure the reliability as a power conversion device, the conductor becomes large and the device is reduced in size and weight. Was insufficient.

SUMMARY OF THE INVENTION It is an object of the present invention to suppress a surge voltage at the time of turning off a switching element in a three-level power converter, and to reduce the size and weight of the power converter.

[0007]

There are two types of 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 becomes higher than the surge voltage applied to the first and fourth switching elements.

Therefore, in one aspect of the present invention, in order to reduce the wiring inductance in the commutation path of the physically long second and third switching elements, the commutation path is not only made as short as possible, but also turned off. A first current path through which a current of the switching element flows;
The second current path is configured so that the current increases along with the decrease of the current in the current path.

As will be described in detail later, one of the currents flowing through the first and second current paths decreases and the other increases with a slight temporal overlap during commutation. Alternatively, one disappears instantaneously and the other rises without overlapping in time. In order to suppress the inductance of these two current paths, it is effective to arrange the wirings of both.

According to another aspect of the present invention, the connection terminals of the DC voltage source are arranged so that the first and second current paths have substantially the same length.

As a result, the two current paths are balanced and cancel each other, so that the inductance at the time of turn-off can be further reduced.

In a preferred embodiment of the present invention,
The connection terminal of the smoothing capacitor (unit voltage source) is arranged so as to be closest to the coupling diode among the linearly arranged element group.

Thus, 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, thereby suppressing a substantial inductance at the time of turn-off. , The surge voltage is reduced.

In another embodiment of the present invention, a flat insulating layer is provided between two layers of flat conductors sandwiched between a DC voltage source and a group of elements arranged in a straight line. Provide a layer.

Thus, 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 increased, and the surge voltage can be further reduced.

[0016]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a side view of one phase of a three-level power converter according to a 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. It is. Here, an IGBT will be described as an example of a switching element for convenience, but the same effect can be obtained when another switching element such as a MOSFET or a bipolar transistor is used. Here, the positive terminal of each switching element is called a collector, and the negative terminal is called an emitter.

In FIGS. 1 to 3, one phase of the power converter constitutes the electric circuit of FIG. 2 and includes a group of elements arranged in a straight line and first and second elements constituting a DC voltage source. A smoothing capacitor as a unit voltage source is arranged so as to sandwich a flat conductor layer.

First, the structure of the element group will be described. As shown in FIGS. 1 and 3, a first switching element 1, a first coupling diode 5 for deriving an intermediate potential 5, a second switching element 2, The third switching 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.

Next, two upper and lower flat conductor layers are arranged above the element group. Figure 3 shows the lower layer of the conductor layer.
As shown in FIG. 2B, the first intermediate potential conductor 12, the AC side conductor 13, and the second intermediate potential conductor 14 are arranged. As shown in FIG. (C)
In the same plane on the upper side of the element layer. The upper layer of the conductor layer is
As shown in FIG. 3A, a plate-shaped portion composed of a positive conductor 9, a third intermediate potential conductor 11, and a negative conductor 10 is parallel to the element group as is apparent from FIG. The upper and lower layers of these conductor layers are arranged in a parallel relationship.

Finally, DC voltage sources 7 and 8 are arranged so as to sandwich the conductor layer between the DC voltage source and the element group. The DC voltage source includes first and second smoothing capacitors 7 and 8 which are unit voltage sources.

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 The positive terminal 11n of the source 8 is arranged so as to be closest to the second coupling diode 6 in the group of elements.

Next, the connection relationship by the conductor layer will be described. Starting from the lower 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 (b), a hole or cut 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 has 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. And a hole or cut 16 for insulation with the third intermediate potential conductor 11 connected to the cathode of the second coupling diode.

On the other hand, in the connection in the upper layer of the conductor layer, 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 connects the negative terminal 11p of the first smoothing capacitor 7 and the positive terminal 11n of the second smoothing capacitor 8. Connected to

Here, the collector of each switching element,
Although each of the emitters is illustrated one by one, a similar configuration is possible even with a switching element having a plurality of collectors and emitters. As shown in FIG. 2, each of the switching elements 1 to 4 includes a switching function unit for turning on and off a current, and a free-wheeling function unit for an AC circuit, that is, a freewheeling diode connected in anti-parallel to the switching function unit.

The commutation paths when each switching element is turned off are the four paths shown in FIGS. 4 (a) to 4 (d). 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 in the electric circuit, and if they are arranged in a similar physical relationship in terms of physical space, the inductance is reduced. Is also equivalent. Therefore,
The types of commutation paths are (a), (d) and (b),
(C) can be considered. Here, the commutation paths (a) and (b) will be described, and (c) and (d) will be omitted, but the same can be understood.

First, the commutation path (a) is a current path in the converter that has been generated at the moment when the switching element 1 is turned off. This is an electric circuit having an inductance that causes the occurrence of When the switching element 1 is turned on, the switching element 2 is always turned on. "Positive electrode of the second smoothing capacitor 8 → coupling diode 5 → second switching element 2 → AC terminal → AC (load) circuit → Other phase switching elements 3, 4 → 2nd
The diode 5 flows through the path of “the negative electrode of the smoothing capacitor 8”. Therefore, within the range of the magnitude of the current, the diode 5 can flow in the reverse direction.
As shown by the thick line in (a), the commutation path at the time of turning off the switching element 1 is “the positive electrode of the first smoothing capacitor 7 → the first switching element 1 → the diode 5 (reverse direction) → the first smoothing path”. The negative electrode of the capacitor 7,
When the switching element 1 is turned off, the current in this commutation path is interrupted, and a surge voltage is generated by the inductance of this path and applied to the switching element 1.

Since the commutation path (a) is relatively short and the wiring inductance is relatively small, the surge voltage applied to the first switching element 1 is small and poses no problem. In particular, in the present embodiment, the commutation path (a) is shortened as shown by the broken line in FIG.

Next, the commutation path (b) is a current path in the converter which occurs at the moment when the switching element 2 is turned off (a short time before and after), and the current is changed by the turning off of the switching element 2. This is an electric circuit having an inductance which causes a surge voltage to be generated when the electric circuit is operated. When the switching element 2 is turned off, the free wheel diodes in the third and fourth switching elements 3 and 4 are switched to an “AC (load) circuit → switching element 4”.
Since the circuit is in a state in which conduction is possible in the path of the anti-parallel diode 3 → AC terminal → AC (load) circuit 3 as shown by the bold line in FIG. 4B, “the positive electrode of the second smoothing capacitor 8 →
Coupling diode 5 → second switching element 2 → third third
A current can flow through a path of “freewheel diodes of the fourth switching elements 3 and 4 (reverse direction) → 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.
It is a side view which shows this commutation route (b) with a broken line.

Here, the wiring inductance of the commutation path (b) will be considered. The 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 immediately after the switching element 2 is turned off follow (overlap). The three-level power converter uses the PWM control to connect the AC terminal to the AC terminal in a short time.
The voltage is switched to the level and output. 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 period of the PWM control such as the turn-off time of each switching element. A free wheel diode is provided to maintain the AC load current. By the way, the current I1 to the AC load immediately before the switching element 2 is turned off is "the positive electrode of the capacitor 8 →
Diode 5 → switching element 2 → AC load → switching elements 3 and 4 of other phases → negative electrode of capacitor 8 ”, while current I2 of the AC load immediately after switching element 2 is turned off is“ AC load → other phase switching elements 3, 4 → switching elements 4, 3
Of the free wheel diode → AC load. FIG. 7 shows these currents I1, I2 in this embodiment.
FIG. The current I2 increases as the current I1 decreases, or the current I2 rises simultaneously with the disappearance of the current I1. These currents overlap in the part (e) of FIG. 7 and flow in the same direction.
The substantial inductance at the moment of turn-off can be reduced. That is, in this portion, one increase (rise) and the other decrease (extinction) overlap, and the total current change dI / dt decreases, and the substantial inductance decreases. As a result, the surge voltage applied to the switching element 2 can be reduced. The same applies to the switching element 3. According to the experiment, the switching elements 2, 3 were compared with the prior art described in the above-mentioned publication.
The magnitude of the surge voltage to the power supply was reduced by 20%.

As described above, according to the present embodiment, two times (a) and (b) when the switching element is turned off.
In order to reduce the wiring inductance of the commutation path (b) in which the commutation path is long and the wiring inductance is large, the smoothing capacitor 7 as the first DC voltage source has a negative terminal. 11p is arranged closest to the first coupling diode 5, while the second
The smoothing capacitor 8 as the DC voltage source is arranged such that the positive terminal 11n is closest to the second coupling diode 6. That is, on one side of the conductor layer,
One of them is a negative terminal 11p of the first DC voltage source,
The positional relationship is that the anode terminal of the first coupling diode 5 exists on the other side. Similarly, on the other side of the conductor layer, there is a positive terminal 11n of the second DC voltage source on one side and a cathode terminal of the second coupling diode 6 on the other side.

In this manner, 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 second switching element 2
The second current path through which the current I2 flows toward the AC terminal immediately after the turn-off of the first and second current paths is located at a position having substantially the same length (in this embodiment, a position close to the coupling diodes 5 and 6). The connection terminals 9p, 11p and 10n, 11n of the second unit voltage sources 7 and 8 are arranged, and the first and second current paths are arranged along the part (e).

FIG. 8 is a side view showing a second embodiment of the present invention. In addition to the configuration shown in FIGS. 1 to 7, an insulating layer 17 is provided between an upper layer and a lower layer of a conductor layer. Insulating layer 17
Is a flat plate made of, for example, an insulating material, and is provided with holes or cuts corresponding to holes or cuts for securing 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 enhanced, 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.

FIG. 9 is a plan view of the third embodiment of the present invention, showing the upper and lower conductor layers and element layers.
This embodiment differs from the first embodiment in that two switching elements 1 to 4 and two diodes 5 and 6 are connected in parallel to double the current capacity.
In this case, the same effects as in the above embodiment can be obtained. The main circuit configuration is the same as that shown in FIG. 1 of JP-A-11-89249.
8 and the same.

[0035]

According to the present invention, a surge voltage at the time of turning off a switching element can be suppressed, and a small and lightweight three-level power converter 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 of one phase of a three-level power converter according to one embodiment of the present invention.

FIG. 3 is a plan view of one phase of a 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 in which a commutation path (a) according to an embodiment of the present invention is added.

FIG. 6 is a side view in which a commutation path (b) according to an embodiment of the present invention is added.

FIG. 7 is a side view in which a current path of a commutation path (b) according to one embodiment of the present invention is added.

FIG. 8 is a side view of another embodiment of the present invention to 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 layer,
9p, 11p... Connection terminals of the first unit voltage source, 10n,
11n: Connection terminal of the second unit voltage source.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Kiyoshi Nakata 1070 Ma, Hitachinaka-shi, Ibaraki Pref. Mito Traffic Systems Division, Transportation Systems Division, Hitachi, Ltd. (72) Inventor Asako Koyanagi Omikamachi, Hitachi, Ibaraki, Japan F-term (reference) in Hitachi, Ltd. Electric Power and Electric Power Development Laboratory 5H007 AA06 CA01 CB05 CC04 CC06 CC14 FA01 FA13 HA03

Claims (8)

[Claims] 1. A DC voltage source including first and second unit voltage sources connected in series and having three terminals of three DC voltage levels; a positive terminal and an AC terminal of the first unit voltage source; First and second switching elements connected in series between
A first coupling diode connected between the series connection point and the series connection point of the first and second unit voltage sources, and between the AC terminal and the negative terminal of the second unit voltage source; Third and fourth switching elements connected in series with each other, a second coupling diode connected between the series connection point and the series connection point of the first and second unit voltage sources, A switching element, a first coupling diode, a second switching element, a third switching element, a second coupling diode, and a fourth switching element. A three-level power converter that is arranged to be sandwiched between a voltage source and a flat conductor that carries out the electrical connection and that outputs three voltage levels to the AC terminal. The negative terminal of The second unit voltage source is disposed so as to be closest to the second coupling diode in the element group, while being arranged so as to be closest to the first coupling diode in the element group. A three-level power conversion device characterized by the above-mentioned. 2. 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 positive terminal and an AC terminal of the first unit voltage source. First and second switching elements connected in series between
A first coupling diode connected between the series connection point and the series connection point of the first and second unit voltage sources, and between the AC terminal and the negative terminal of the second unit voltage source; Third and fourth switching elements connected in series with each other, a second coupling diode connected between the series connection point and the series connection point of the first and second unit voltage sources, A switching element, a first coupling diode, a second switching element, a third switching element, a second coupling diode, and a fourth switching element. A three-level power converter that is disposed so as to be sandwiched by a voltage source and that carries out the electrical connection, and that outputs three voltage levels to the AC terminal. On one side A negative terminal of the first unit voltage source is disposed, an anode terminal of the first coupling diode is disposed on the other side, and a positive terminal of the second unit voltage source is disposed on one of the front and back of another substantially identical portion of the conductor layer. And a cathode terminal of a second coupling diode is disposed on the other side. 3. 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 positive terminal and an AC terminal of the first unit voltage source. First and second switching elements connected in series between
A third and fourth switching elements connected in series between the AC terminal and a negative terminal of the second unit voltage source, and an element group in which the first to fourth switching elements are arranged in a line. In the three-level power conversion device, which is provided so as to be sandwiched between the element group and the DC voltage source and has a plate-shaped conductor that carries out the electrical connection, and outputs three voltage levels to the AC terminal, A plate-shaped conductor through which a current flows immediately before the second switching element is turned off and a plate-shaped conductor through which a current flows immediately after the second switching element is turned off are arranged along with the turn-off of the third switching element. A flat plate conductor in which current flows immediately before and a flat conductor in which current flows immediately after the third switching element is turned off are arranged along with each other. Power converter. 4. 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 positive terminal and an AC terminal of the first unit voltage source. First and second switching elements connected in series between
A third and fourth switching elements connected in series between the AC terminal and a negative terminal of the second unit voltage source, and an element group in which the first to fourth switching elements are arranged in a line. In the three-level power conversion device, which is provided so as to be sandwiched between the element group and the DC voltage source and has a plate-shaped conductor that carries out the electrical connection, and outputs three voltage levels to the AC terminal, A current path through which current flows toward the AC terminal immediately before the second switching element is turned off and a current path through which current flows toward the AC terminal immediately after the second switching element is turned off have substantially the same length. A three-level power converter, wherein connection terminals of the first and second unit voltage sources are arranged at positions to be determined. 5. A DC voltage source including first and second unit voltage sources connected in series and having three terminals of three DC voltage levels, a positive terminal and an AC terminal of the first unit voltage source. First and second switching elements connected in series between
A third and fourth switching elements connected in series between the AC terminal and a negative terminal of the second unit voltage source, and an element group in which the first to fourth switching elements are arranged in a line. In the three-level power conversion device, which is provided so as to be sandwiched between the element group and the DC voltage source and has a plate-shaped conductor that carries out the electrical connection, and outputs three voltage levels to the AC terminal, A first current path through which a current flows toward the AC terminal immediately before the second switching element is turned off, and a second current path through which a current flows toward the AC terminal immediately after the second switching element is turned off. Are placed at positions having substantially the same length.
A three-level power converter, wherein the connection terminals of the unit voltage source are arranged and a part of the first and second current paths are arranged along with each other. 6. The method according to claim 1, wherein
A three-level power converter, wherein a flat insulating layer is provided between (1) and (2) below. (1) A plate-shaped conductor connecting the positive terminal of the first unit voltage source and the first switching element, and a plate-shaped conductor connecting the negative terminal of the second unit voltage source and the fourth switching element And a flat conductor for 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 . 7. The method according to claim 1, wherein
A three-level power converter, wherein the first to fourth switching elements and the first and second diodes are respectively constituted by a plurality of switching elements and diodes connected in parallel. 8. A three-level power converter according to claim 1, wherein said first and second unit voltage sources include first and second capacitors, respectively.