JP7472768B2 - Reactor structure of power conversion device - Google Patents

Description

The present invention relates to a reactor used in a power conversion device, and to a reactor structure that can reduce the ripple of the output current.

Conventionally, for example, in a power conversion device (power converter system) described in Patent Document 1, multiple DC-DC converters are connected in series or parallel, and connecting the converters in series achieves high voltage resistance and low ripple, while connecting them in parallel achieves high capacity and low ripple.

However, a problem occurs in that ripple currents are generated through parasitic capacitance to ground that occurs in components and cables on the circuit, causing harmonics to leak into the output. This effect is particularly noticeable in the configuration shown in Figure 5 (the configuration shown in Figure 8 of Patent Document 1).

In FIG. 5, 10 is a renewable energy power plant, 14 is a converter system, and 22 is a DC-DC converter on the power distribution grid side. The output sides of multiple renewable energy sources (wind turbines) 12 are connected to one DC distribution bus 20 via multiple converter units 18 and protective switches 30 to form one converter system 14.

Each converter unit 18 of the converter system 14 has an AC-DC converter 24 that converts the AC voltage from the renewable energy source 12 to a DC voltage, and DC-DC converters 26, 28 that boost the output voltage of the AC-DC converter 24 to the desired voltage of the DC distribution bus 20.

The power grid side DC-DC converter 22 has two semiconductor switching elements 33, 34 connected in series and a reactor 35 connected to the common connection point of the semiconductor switching elements 33 and 34, and both ends of the series circuit of the semiconductor switching elements 33, 34 are connected to the DC power distribution bus 20.

The converter system 14 and the grid-side DC-DC converter 22 are provided in multiple units, and are connected to each other at the output side of each grid-side DC-DC converter 22.

The output side of each grid-side DC-DC converter 22 is connected to a load (not shown) via two DC capacitors 36, 36 connected in series between the output ends of two adjacent grid-side DC-DC converters 22 and the high-voltage DC distribution network 16.

32 is a controller that controls the AC-DC converter 24 and each of the DC-DC converters 22, 26, and 28.

JP 2017-521037 A

In the power conversion device of Figure 5, the current path through which ripple current flows through parasitic capacitance to ground caused by components on the circuit and cables, etc., is explained with reference to Figure 6.

Figure 6 shows a simplified version of part of the configuration in Figure 5, with the two adjacent grid-side DC-DC converters 22, 22 in Figure 5 depicted as DC-DC converter 22a consisting of semiconductor switching elements 33a, 34a and reactor 35a, and DC-DC converter 22b consisting of semiconductor switching elements 33b, 34b and reactor 35b.

The DC capacitors 36, 36 in FIG. 5 are represented as DC capacitors 36a, 36b, and the output sides of the two adjacent converter systems 14, 14 in FIG. 5 are represented as DC capacitors 14a, 14b. 50 is a load, and the voltage to ground is represented by the symbol for an AC voltage source.

In Figure 6, the dotted arrows indicate the paths along which the ripple current flows, and the current paths within the load 50 also have parasitic capacitance (the capacitor symbol shown to the right of the load 50 in Figure 6).

Therefore, ripple current flows through the path of voltage to ground → load 50 → parasitic capacitance in load 50 → ground, or the path of voltage to ground → DC capacitors 36a and 36b → load 50 → parasitic capacitance in load 50 → ground.

Similarly, if part of the parasitic capacitance in the load 50 is grounded, a ripple current will flow from the ground voltage to the DC capacitor 36b to the load 50 to ground.

In the example of Figure 6, since there is no reactor on the N side (negative side), the impedance from the N side to ground is low, and a large current flows due to the voltage component to ground output by the power converter (DC-DC converters 22a, 22b). If there is no reactor in the load 50, this current may have adverse effects on the load 50, such as electromagnetic interference and heat generation due to current ripple.

It is possible to address this issue by dividing the reactor into smaller parts, but in that case the current will flow in the same amount as the other reactors, so a core with the same cross-sectional area as the other reactors will be required, resulting in an increased size.

The present invention aims to solve the above problems, and its purpose is to provide a reactor structure for a power conversion device that can reduce the current ripple flowing to the output side without increasing the volume of the reactor.

The reactor structure of a power converter according to claim 1 for solving the above problem comprises:
A reactor structure of a power conversion device including a plurality of power converters,
a DC output side of a power conversion unit in which a plurality of power converters are connected in series or parallel is connected to a load via a reactor configured by windings connected to a positive output terminal and a negative output terminal of the power conversion unit, the windings being wound around the same iron core ;
The power conversion unit is characterized by comprising a first power converter having first and second semiconductor switching elements connected in series between the positive and negative terminals of a first DC power source, and a second power converter having third and fourth semiconductor switching elements connected in series between the positive and negative terminals of a second DC power source or between the positive and negative terminals of the first DC power source .

The reactor structure of the power conversion device according to claim 2 is the reactor structure according to claim 1,
a series circuit of capacitors connected in series across the load and having a midpoint grounded;
the power conversion unit includes a capacitor connected between the positive and negative terminals of the first DC power supply and a capacitor connected between the positive and negative terminals of the second DC power supply, and third and fourth semiconductor switching elements of the second power converter are connected in series between the positive and negative terminals of the second DC power supply,
The reactor includes a first core portion and a second core portion formed by dividing a rectangular core into halves at approximately the center of each of a pair of opposite sides,
a first winding wound around one end of the first core portion, one end of the first winding being connected to a common connection point of first and second semiconductor switching elements of the first power converter, and the other end of the first winding being connected to one end of the load and one end of a series circuit of a capacitor;
a second winding wound around the other end of the first core portion in a direction that generates a magnetic flux in a direction opposite to the direction of the magnetic flux generated by the first winding, one end of which is connected to a negative terminal of a second power converter and the other end of which is connected to the other end of the load and the other end of the series circuit of a capacitor;
a third winding wound around one end of the second core portion facing the first winding in a direction that generates a magnetic flux that strengthens the magnetic flux generated by the first winding, and having one end connected to a negative pole terminal of the first power converter;
the second core portion is provided with a fourth winding wound on the other end side opposite to the second winding in a direction that generates a magnetic flux that strengthens the magnetic flux generated in the second winding and is opposite to the magnetic flux generated in the third winding, one end of which is connected to a common connection point of the third and fourth semiconductor switching elements of the second power converter and the other end of which is connected to the other end of the third winding.

The reactor structure of the power conversion device according to claim 3 is the reactor structure according to claim 1,
the power conversion unit includes a capacitor connected between a positive terminal and a negative terminal of the first DC power supply, a capacitor connected between a positive terminal and a negative terminal of the second DC power supply, a first output terminal formed in the first power converter, and a second output terminal formed in the second power converter;
a capacitor series circuit in which a capacitor is connected in series between a first output terminal and a second output terminal of the power conversion unit,
The reactor includes a first core portion and a second core portion formed by dividing a rectangular core into halves at approximately the center of each of a pair of opposite sides,
a first winding wound around a central portion of the first core portion, one end of the first winding being connected to a first output terminal of the power conversion unit and the other end being connected to one end of a load;
The second core portion is provided with a second winding wound in a central portion facing the first winding in a direction that generates a magnetic flux that strengthens the magnetic flux generated in the first winding, one end of which is connected to the other end of the load and the other end of which is connected to a second output terminal of the power conversion unit.

The reactor structure of the power conversion device according to claim 4 is the reactor structure according to claim 2 or 3,
The core is characterized in that a gap is formed at a boundary between the divided first core portion and second core portion.

(1) According to the inventions recited in claims 1 to 4, the reactor between the output side of the power conversion unit and the load is constructed by winding separate windings around the same iron core. This makes it possible to equalize the impedance of the circuit to ground and reduce the current ripple flowing out to the output side without increasing the volume of the reactor.
(2) According to the invention as set forth in claim 4, the leakage inductance caused by the gap can also have a suppressing effect on the ground current caused by the common mode voltage.

FIG. 1 is a circuit diagram showing an example of a circuit configuration using a first embodiment of the present invention. FIG. 1 is a configuration diagram of a reactor according to a first embodiment of the present invention. 5A is a circuit diagram showing a circuit configuration using a second embodiment of the present invention, FIG. 5B is a circuit diagram showing a first example of a power converter configuration, and FIG. 5C is a circuit diagram showing a second example of a power converter configuration. FIG. 6 is a configuration diagram of a reactor according to a second embodiment of the present invention. FIG. 1 is a circuit diagram showing a circuit configuration in the prior art. FIG. 13 is an explanatory diagram showing an example of current ripple flowing out in the prior art.

The following describes an embodiment of the present invention with reference to the drawings, but the present invention is not limited to the following embodiment. In the embodiment of the present invention, a reactor connection method and structure are proposed that can reduce the current ripple flowing to the output side without increasing the volume of the reactor by dividing and magnetically coupling the windings.

Figure 1 shows a circuit configuration using Example 1, and Figure 2 shows an example of a reactor configuration for achieving Figure 1. In Figure 1, 100 is a power conversion unit equipped with a first power converter 101 and a second power converter 102.

The first power converter 101 has a DC capacitor 14a connected between the positive and negative terminals of a first DC power source (not shown), and first and second semiconductor switching elements 33a, 34a connected in series between both ends of the capacitor 14a.

The second power converter 102 has a DC capacitor 14b connected between the positive and negative terminals of a second DC power source (not shown), and third and fourth semiconductor switching elements 33b, 34b connected in series between both ends of the capacitor 14b.

The output side of the power conversion unit 100 is connected to one end of each of the windings 81 to 84 of a reactor formed by winding four separate windings around a core 60 (iron core) as shown in FIG. 2.

A series circuit of DC capacitors 36a and 36b is connected between the other end of the first winding 81 and the other end of the second winding 82. The midpoint of the series circuit of DC capacitors 36a and 36b is grounded, and a load (not shown) is connected between both ends.

The symbols a, b, c, d, e, f, g, and h for each terminal of the first to fourth windings 81 to 84 in Figure 1 correspond to the symbols in Figure 2.

In FIG. 2, which shows the reactor configuration, 60 is a rectangular core (iron core), which is divided in half at approximately the center of each pair of opposing sides to form a first core portion 61 (first iron core portion) and a second core portion 62 (second iron core portion).

70a and 70b are gaps formed between the first core portion 61 and the second core portion 62. Note that the configuration may be such that the gaps 70a and 70b are not provided.

A first winding 81 is wound around one end of the first core portion 61, one end a of the first winding 81 is connected to the common connection point of the first and second semiconductor switching elements 33a, 34a, and the other end b is connected to the DC capacitor 36a and one end of a load not shown.

A second winding 82 is wound around the other end of the first core 61 in a direction that generates a magnetic flux in the opposite direction to the magnetic flux generated by the first winding 81. One end g of the second winding 82 is connected to the negative terminal of the second power converter 102 (the common connection point of the fourth semiconductor switching element 34b and the DC capacitor 14b), and the other end h is connected to the DC capacitor 36b and the other end of the illustrated power-saving load.

A third winding 83 is wound around one end of the second core portion 62 facing the first winding 81 in a direction that generates a magnetic flux that strengthens the magnetic flux generated by the first winding 81, and one end c of the third winding 83 is connected to the negative terminal of the first power converter 101 (the common connection point of the second semiconductor switching element 34a and the DC capacitor 14a).

A fourth winding 84 is wound on the other end of the second core portion 62 facing the second winding 82 in a direction that generates a magnetic flux that strengthens the magnetic flux generated by the second winding 82 and is opposite to the magnetic flux generated by the third winding 83. One end e of the fourth winding 84 is connected to the common connection point of the third and fourth semiconductor switching elements 33b, 34b, and the other end f is connected to the other end d of the third winding 83.

As described above, by connecting a reactor formed by winding the divided first to fourth windings 81 to 84 around a single core 60 to the circuit in FIG. 1, it is possible to equalize the impedance to ground, thereby preventing the flow of ripple current as in the prior art. In this case, the currents flowing through the four windings 81 to 84 are equal, so the cross-sectional area of the core 60 can be the same as that of the prior art.

Furthermore, by providing gaps 70a and 70b in the reactor core 60, leakage inductance is generated, but this leakage inductance can also have a suppressing effect on the ground current generated by the common mode voltage.

As described above, it is possible to provide a reactor that can reduce the current ripple flowing to the ground or load without increasing the core dimensions.

When the load is a voltage source such as a battery and the power converter is operated as a current source, a reactor for controlling the current must be installed on the load side.

Figure 3 shows Example 2 in which the present invention is applied to a power conversion device configured with a reactor installed on the load side, where (a) is an overall circuit diagram, (b) is a circuit diagram of power converter configuration example 1, and (c) is a circuit diagram of power converter configuration example 2, and parts that are the same as those in Figure 1 are indicated with the same reference numerals.

In FIG. 3(a), a series circuit of DC capacitors 36a and 36b is connected between the first output terminal 201 and the second output terminal 202 on the DC output side of the power conversion unit 200.

The common connection point of the first output terminal 201 and the DC capacitor 36a is connected to the positive terminal of the load 150 as a voltage source via the first winding 91 constituting the reactor of the present invention.

The common connection point of the second output terminal 202 and the DC capacitor 36b is connected to the negative terminal of the load 150 via the second winding 92 constituting the reactor of the present invention.

The midpoint of the series circuit of DC capacitors 36a and 36b is connected to load 150 and is grounded within load 150.

In FIG. 3(b) showing a configuration example 1 of the power conversion unit 200, the common connection point of the first and second semiconductor switching elements 33a, 34a of the first power converter 101 is connected to the first output terminal 201 via a reactor 211, and the common connection point of the fourth semiconductor switching element 34b and the DC capacitor 14b of the second power converter 102 is connected to the second output terminal 202 via a reactor 212.

The common connection point of the second semiconductor switching element 34a and the DC capacitor 14a is connected to the common connection point of the third and fourth semiconductor switching elements 33b, 34b via reactors 213 and 214.

In FIG. 3(c), which shows a configuration example 2 of the power conversion unit 200, the input side of the second power converter 102 is connected to the input side of the first power converter 101 (between both ends of the DC capacitor 14a).

The common connection point of the first and second semiconductor switching elements 33a, 34a of the first power converter 101 is connected to the first output terminal 201 via a reactor 221, and the common connection point of the third and fourth semiconductor switching elements 33b, 34b of the second power converter 102 is connected to the second output terminal 202 via a reactor 222.

In the case of a configuration like that shown in Figure 3(a), the inductance components can be made equal by dividing the reactor into two units, but in that case, the amount of current flowing through each unit does not change even if it is divided, so the cross-sectional area of the required core does not change either. Therefore, dividing the reactor into two units creates the problem of the device becoming larger.

Furthermore, because the reactor is divided, the capacitance component to ground and the inductance component to ground differ depending on the installation state (wiring path, etc.), which causes an imbalance in the current flow due to the common mode voltage applied from the power converter. This current flows to ground through the voltage source, which is the load (150), and there is a risk of causing abnormal heating of the load.

In this second embodiment, a reactor that can solve the above problems is configured as shown in Figure 4.

The symbols a, b, c, and d of the terminals of the first winding 91 and the second winding 92 in Fig. 3(a) correspond to the symbols in Fig. 4. In Fig. 4, 60 is a rectangular core (iron core), which is divided in half at approximately the center of each pair of opposing sides to form a first core portion 61 (first iron core portion) and a second core portion 62 (second iron core portion).

70a and 70b are gaps formed between the first core portion 61 and the second core portion 62. Note that the configuration may be such that the gaps 70a and 70b are not provided.

A first winding 91 is wound around the center of the first core section 61, and one end a of the first winding 91 is connected to the first output terminal 201 of the power conversion section 200 and the DC capacitor 36a, and the other end b is connected to one end (positive terminal) of the load 150.

A second winding 92 is wound around the center of the second core 62, facing the first winding 91, in a direction that generates a magnetic flux that strengthens the magnetic flux generated by the first winding 91. One end c of the second winding 92 is connected to the other end (negative end) of the load 150, and the other end d is connected to the second output end 202 of the power conversion unit 200 and the DC capacitor 36b.

By winding the first and second windings 91, 92 around one core 60 as shown in Figure 4, the capacitance and inductance components to the ground during installation can be made equal, thereby avoiding the above-mentioned problems.

In addition, because the iron core (core 60) can be made common, the reactor can be constructed without increasing its volume, and the leakage inductance created by providing gaps 70a, 70b in the reactor core (60) can also have a suppressing effect on the ground current caused by the common mode voltage.

As described above, it is possible to provide a reactor that can reduce the current ripple flowing to the ground or load without increasing the core dimensions.

Reference Signs List 14a, 14b, 36a, 36b... DC capacitor 33a, 33b, 34a, 34b... Semiconductor switching element 50, 150... Load 60... Core 61... First core portion 62... Second core portion 70a, 70b... Gap 81, 91... First winding 82, 92... Second winding 83... Third winding 84... Fourth winding 100, 200... Power conversion portion 101... First power converter 102... Second power converter 201... First output terminal 202... Second output terminal

Claims (4)

A reactor structure of a power conversion device including a plurality of power converters,
a DC output side of a power conversion unit in which a plurality of power converters are connected in series or parallel is connected to a load via a reactor configured by windings connected to a positive output terminal and a negative output terminal of the power conversion unit, the windings being wound around the same iron core ;
The power conversion unit includes a first power converter having first and second semiconductor switching elements connected in series between positive and negative terminals of a first DC power source, and a second power converter having third and fourth semiconductor switching elements connected in series between the positive and negative terminals of a second DC power source or between the positive and negative terminals of the first DC power source . a series circuit of capacitors connected in series across the load and having a midpoint grounded;
the power conversion unit includes a capacitor connected between the positive and negative terminals of the first DC power supply and a capacitor connected between the positive and negative terminals of the second DC power supply, and third and fourth semiconductor switching elements of the second power converter are connected in series between the positive and negative terminals of the second DC power supply,
The reactor includes a first core portion and a second core portion formed by dividing a rectangular core into halves at approximately the center of each of a pair of opposite sides,
a first winding wound around one end of the first core portion, one end of the first winding being connected to a common connection point of first and second semiconductor switching elements of the first power converter, and the other end of the first winding being connected to one end of the load and one end of a series circuit of a capacitor;
a second winding wound around the other end of the first core portion in a direction that generates a magnetic flux in a direction opposite to the direction of the magnetic flux generated by the first winding, one end of which is connected to a negative terminal of a second power converter and the other end of which is connected to the other end of the load and the other end of the series circuit of a capacitor;
a third winding wound around one end of the second core portion facing the first winding in a direction that generates a magnetic flux that strengthens the magnetic flux generated by the first winding, and one end of the third winding connected to a negative pole terminal of the first power converter;
2. The reactor structure of the power conversion device according to claim 1, further comprising: a fourth winding wound on the other end side of the second core portion facing the second winding in a direction to generate a magnetic flux that strengthens the magnetic flux generated in the second winding and is opposite to the magnetic flux generated in the third winding, one end of which is connected to a common connection point of third and fourth semiconductor switching elements of the second power converter and the other end of which is connected to the other end of the third winding. the power conversion unit includes a capacitor connected between a positive terminal and a negative terminal of the first DC power supply, a capacitor connected between a positive terminal and a negative terminal of the second DC power supply, a first output terminal formed in the first power converter, and a second output terminal formed in the second power converter;
a capacitor series circuit in which a capacitor is connected in series between a first output terminal and a second output terminal of the power conversion unit,
The reactor includes a first core portion and a second core portion formed by dividing a rectangular core into halves at approximately the center of each of a pair of opposite sides,
a first winding wound around a central portion of the first core portion, one end of the first winding being connected to a first output terminal of the power conversion unit and the other end being connected to one end of a load;
2. The reactor structure of the power conversion device according to claim 1, further comprising: a second winding wound in a central portion of the second core portion facing the first winding in a direction in which a magnetic flux is generated that strengthens the magnetic flux generated in the first winding, one end of which is connected to the other end of a load and the other end of which is connected to a second output terminal of the power conversion unit. 4. The reactor structure for a power converter according to claim 2, wherein a gap is formed at a boundary between the divided first core portion and second core portion of the core.

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