JP2015104286A - Inverter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a small and inexpensive inverter.SOLUTION: An inverter comprises: a first arm 21 which generates first voltage; a second arm 22 which generates second voltage; and a third arm 23 which generates intermediate voltage between the first voltage and the second voltage, the inverter 1 by which single-phase two-line output is possible by driving switching elements (11, 12, 13, 14) of the first arm 21 and the second arm 22, and single-phase three-line output is further possible by driving switching elements (15, 16) of the third arm 23 makes inductance of a reactor 53 which is connected to an output end of the third arm 23 smaller than inductance of reactors (51, 52) which are connected to an output end of the first arm 21 and an output end of the second arm 22, respectively.

Description

  The present invention relates to an inverter, and more specifically, the present invention relates to an inverter used in a power conditioner that interconnects electric power generated by solar power generation or the like.

  Conventionally, as a power conditioner used for photovoltaic power generation, a storage battery, and the like, there is one that outputs 100 VAC by operating in conjunction with a commercial power system. In addition, there is a power conditioner that can supply electric power to a load such as a home appliance by performing independent operation as an independent power source even during a power failure. Furthermore, there is also a power conditioner that can operate a 100V or 200V load device by outputting AC100V / 200V in a single-phase three-wire system during a power failure and connecting it to a single-phase three-wire wiring in the home.

  In such a power conditioner, a technology has been proposed that includes an inverter with a single-phase three-wire output and that effectively uses the power that can be generated by the solar cell even during the independent operation, as in the case of the interconnected operation. (For example, refer to Patent Document 1).

JP 2003-18859 A

  The inverter included in the power conditioner described in Patent Document 1 includes three arms (an N-phase arm, a U-phase arm, and a V-phase arm) each composed of a pair of switching elements. . Each arm is connected to an AC reactor as an output filter. Of these three AC reactors, two can be shared with those used during interconnected operation, but the remaining one needs to be prepared separately only for autonomous operation. The AC reactor has a role of suppressing harmonics and removing noise. The inductance required for the reactor is determined by the current ripple of the switching element.

  In such a configuration, when the reactor has high inductance and low loss, the size of the reactor tends to increase and the cost tends to increase. Moreover, the reactor is generally large and heavy, and the cost is high compared to other components.

  Accordingly, an object of the present invention is to provide a small and inexpensive inverter.

The invention of the inverter according to the first aspect to achieve the above object is as follows:
A first arm by a first voltage generating switching element;
A second arm by a second voltage generating switching element;
A third arm by a switching element for generating an intermediate voltage between the first voltage and the second voltage,
Single-phase two-wire output is possible by driving the switching elements of the first arm and the second arm, and single-phase three-wire output is possible by driving the switching element of the third arm. An inverter,
The inductance of the reactor connected to the output end of the third arm is made smaller than the inductance of the reactor connected to the output end of the first arm and the output end of the second arm, respectively. To do.

  The switching frequency of the switching element of the third arm may be higher than the switching frequency of the switching element of each of the first arm and the second arm.

  The switching frequency of the switching element of the third arm is set to the inductance of the reactor connected to the output end of the third arm, the output end of the first arm, and the output end of the second arm. You may determine based on ratio with the inductance of each connected reactor.

  Moreover, this invention is good also as a power conditioner provided with the above inverters.

  According to the present invention, a small and inexpensive inverter can be provided.

It is a figure which shows schematically the structure containing the inverter which concerns on embodiment of this invention.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a diagram schematically showing a configuration including an inverter according to an embodiment of the present invention.

  As shown in FIG. 1, the inverter 1 according to the embodiment of the present invention includes a first arm 21 including switching elements 11 and 12, a second arm 22 including switching elements 13 and 14, and switching elements 15 and 16. And a third arm 23. Furthermore, the inverter 1 also includes a control unit 30, a capacitor 40, and reactors 51 to 53. In the following description, description of elements and function units well known in the art will be simplified or omitted as appropriate.

  As shown in FIG. 1, the inverter 1 according to this embodiment includes a first arm 21 that generates a first voltage, a second arm 22 that generates a second voltage, a first voltage, And a third arm 23 that generates an intermediate voltage of two voltages. The first arm 21 includes a pair of switching elements 11 and 12 connected in series with each other. The second arm 22 includes a pair of switching elements 13 and 14 connected in series with each other. The third arm 23 includes a pair of switching elements 15 and 16 connected in series with each other. Each of these switching elements 11 to 16 is driven by a control signal from the control unit 30. This inverter 1 functions as a single-phase three-wire output inverter having switching elements 15 and 16 for generating a neutral phase.

  Reactors 51, 52, and 53 are connected to the output ends of the first arm 21, the second arm 22, and the third arm 23, respectively. These reactors 51 to 53 use AC reactors having an inductance described later.

  As shown in FIG. 1, the first arm 21, the second arm 22, and the third arm 23 are connected in parallel. Further, the inverter 1 also includes a capacitor 40 connected in parallel to the output terminal of the rechargeable battery 60. As shown in FIG. 1, the capacitor 40 and the rechargeable battery 60 are connected in parallel to the first arm 21, the second arm 22, and the third arm 23. Although FIG. 1 shows a configuration in which a rechargeable battery 60 is connected to the converter 1, the rechargeable battery 60 may be another distributed power source such as a solar cell or a power device.

  Control unit 30 includes a U-phase drive circuit that drives switching elements 11 and 12, a W-phase drive circuit that drives switching elements 13 and 14, and an O-phase drive circuit that drives switching elements 15 and 16. . These drive circuits drive each switching element at a switching frequency described later. At this time, the control signal input to the switching elements 11 to 16 by the control unit 30 can be, for example, a PWM (Pulse Width Modulation) signal. Hereinafter, the first arm 21 will be described as a U-phase generation arm, the second arm 22 as a W-phase generation arm, and the third arm 23 as an O-phase generation arm. Therefore, as shown in FIG. 1, the inverter 1 outputs the U phase from the output end 71, the W phase from the output end 72, and the O phase from the output end 73.

  As shown in FIG. 1, a load 81 is connected between the output ends 71 and 73, and a load 82 is connected between the output ends 73 and 72. These output terminals 71, 72, and 73 are also connected to a commercial power system in order to operate in conjunction with the system, but the commercial power system is not shown in FIG.

  In the present embodiment, the control unit 30 stops the switching elements 15 and 16 of the third arm 23 during the interconnection operation, and switches the switching elements 11, 12 and 13 and 14 of the first and second arms 21 and 22. Drive. Thereby, the inverter 1 operates as a single-phase two-wire inverter, and supplies power from the first arm 21 and the second arm 22 to the loads 81 and 82 connected to the commercial power system. As described above, the inverter 1 can drive the switching elements 11, 12, 13, and 14 of the first arm 21 and the second arm 22 to perform single-phase two-wire output.

  In addition, the control unit 30 drives the first and second arms 21 and 22 and the switching elements 15 and 16 of the third arm 23 during the independent operation. As a result, the inverter 1 operates as a single-phase three-wire inverter and supplies power to the loads 81 and 82 connected between the third arm 23 and the first and second arms 21 and 22. I do. Thus, the inverter 1 drives the switching elements 11, 12 and 13, 14 of the first arm 21 and the second arm 22, and the switching elements 15, 16 of the third arm 23 to drive the single-phase 3 Line output is possible.

  In the present embodiment, the reactors 51 to 53 function as a filter that absorbs noise of a waveform when the switching elements 11 to 16 driven by the PWM signal supplied from the control unit 30 perform switching. Here, the reactor can generally increase its ability to absorb noise as the inductance increases. However, when the inductance of the reactor is increased, the size of the reactor also increases, and the cost of the component parts tends to increase. In addition, the fact that the size of the reactor is increased requires more space for installing the reactor in the inverter 1.

  As described above, the third arm 23 does not operate during normal interconnection operation, but operates only during an independent operation in an emergency such as a power failure. Therefore, the reactor 53 connected to the third arm 23 does not operate at the time of normal interconnection operation, but operates only at the time of an autonomous operation in an emergency, and the usage frequency is relatively low. Therefore, in the present embodiment, the inverter 1 has the inductance of the reactor 53 connected to the output end of the third arm 23 connected to the output end of the first arm 21 and the output end of the second arm 22, respectively. This is smaller than the inductance of the reactors 51 and 52. For example, in FIG. 1, when the inductance of the reactor 51 and the reactor 52 is set to 500 μH, the inductance of the reactor 53 can be set to 250 μH instead of 500 μH. By reducing the inductance of the reactor 53, the reactor 53 can be made relatively small and inexpensive.

  Thus, the inverter 1 according to the present embodiment can reduce the size and cost of the reactor used only during the self-sustained operation, as compared with the conventional inverter. Moreover, since the space for installing the reactor 53 in the inverter 1 can be reduced by downsizing the reactor, the size of the inverter 1 itself can also be reduced.

  By the way, as described above, the reactor tends to increase the ability to absorb noise as the inductance is increased. For this reason, when the inductance of the reactor 53 is reduced, the ability to absorb switching noise by the third arm 23 is also somewhat reduced. However, during the self-sustained operation of driving the switching elements 15 and 16 of the third arm 23, the current flowing from the third arm 23 to the neutral line (that is, the current flowing to the reactor 53) by balancing the loads 81 and 82. ) Can be made small. Therefore, by reducing the inductance of the reactor 53, even if the ability to absorb switching noise by the third arm 23 is reduced to some extent, the influence on the efficiency of the entire inverter 1 can be suppressed in this way.

  Next, a configuration will be described in which even if the inductance of the reactor 53 is reduced as described above, the influence of noise caused by switching performed by the switching elements 15 and 16 of the third arm 23 is not increased.

  When the switching frequency of the switching elements 11 to 16 constituting each of the arms 21 to 23 is increased, the number of times of switching per unit time increases, so that the peak per switching becomes smaller. That is, by increasing the switching frequency of the switching element, the peak of the output from the arm by the switching element is reduced, so that the noise can be reduced. For example, when the switching frequency of the switching elements 11, 12 and 13, 14 is 20 kHz, the switching frequency of the switching elements 15, 16 can be set to 40 kHz instead of 20 kHz. Thus, by setting the switching frequency of the switching elements 15 and 16 of the third arm 23 to be relatively high, the inductance of the reactor 53 can be made smaller than the inductances of the reactors 51 and 52 as described above. .

  Here, in addition to the third arm 23, the switching elements 11, 12, 13 and 14 of the first and second arms 21 and 22 also reduce the inductance of the reactors 51 and 52 by increasing the switching frequency. Seems to be able to. However, in general, in switching, a switching loss occurs for each switching. For this reason, if the number of times of switching is increased, the loss will increase accordingly, and the efficiency will deteriorate. Therefore, switching elements that are frequently used such as switching elements 11, 12, 13, and 14 of the first and second arms 21 and 22 during normal interconnection operation do not increase the switching frequency. It is desirable to do.

  Thus, in this embodiment, the switching frequency of the switching elements 15 and 16 of the third arm 23 is set to the switching frequency of the switching elements 11, 12 and 13 and 14 of the first arm 21 and the second arm 22, respectively. It is preferable to make it higher.

  In the present embodiment, for the third arm 23, the correlation between the degree of increasing the switching frequency of the switching elements 15 and 16 and the degree of reducing the inductance of the reactor 53 is based on various conditions. Can be set. For example, for the third arm 23, when the inductance of the reactor 53 is halved, the switching frequency of the switching elements 15, 16 can be doubled, and so on. Such a correlation is preferably determined in consideration of the relationship with other components and peripheral circuits. As a general tendency, it is assumed that the inductance of the reactor 53 can be lowered as the switching frequency of the switching elements 15 and 16 is increased. Therefore, the switching frequency of the switching elements 15 and 16 can be determined according to how much the inductance of the reactor 53 is made smaller than the inductance of the reactors 51 and 52 (for example, the ratio of the inductance).

  Thus, in the present embodiment, the switching frequency of the switching elements 15 and 16 of the third arm 23 may be determined based on the ratio between the inductance of the reactor 53 and the inductances of the reactors 51 and 52.

  As described above, in the present embodiment, in the inverter that performs single-phase three-wire output using a switching element having a three-arm configuration during the self-sustaining operation, the inductance of the reactor connected to the neutral wire is reduced during the interconnection operation. The inductance is made smaller than the inductance of the U-phase and W-phase reactors used. With such a configuration, according to the present embodiment, out of the three reactors necessary for each arm as an output filter in the three-arm inverter, the reactor used only during the self-sustained operation that is less frequently used can be downsized. High-inductance and low-loss reactors are often increased in size, and in general, reactors tend to be larger and heavier than other components, and more expensive. According to the present embodiment, it is possible to reduce the number of such reactors used, reduce the size of the inverter, and reduce the cost.

  Moreover, in this embodiment, you may use a small reactor by making the switching frequency of the arm used only at the time of self-sustained operation higher than other two arms. In this case, the switching frequency of the arm that generates the neutral line voltage is set higher than that of the other two phases. Thus, according to the present embodiment, a small and inexpensive power control device can be realized.

  Although the present invention has been described based on the drawings and examples, it should be noted that those skilled in the art can easily make various variations and modifications based on the present disclosure. Therefore, it should be noted that these variations and modifications are included in the scope of the present invention. For example, the functions included in each functional unit, each means, each step, etc. can be rearranged so that there is no logical contradiction, and a plurality of functional units, steps, etc. are combined or divided into one. It is possible. Further, each of the above-described embodiments of the present invention is not limited to being performed faithfully to each of the embodiments described above, and can be implemented by appropriately combining each feature.

  Moreover, this invention can also be implement | achieved as a power conditioner provided with the inverter 1 which concerns on this embodiment mentioned above. Moreover, although embodiment mentioned above was demonstrated as invention of an inverter, this invention can also be set as the electric power control method by the inverter 1. FIG.

DESCRIPTION OF SYMBOLS 1 Inverter 11, 12 1st voltage generation switching element 13, 14 2nd voltage generation switching element 15, 16 Intermediate voltage generation switching element 21 1st arm 22 2nd arm 23 3rd arm 30 Control Part 40 Capacitor 51, 52, 53 Reactor 60 Rechargeable battery 71 U-phase output end 72 W-phase output end 73 O-phase output end 81, 82 Load

Claims (4)

A first arm by a first voltage generating switching element;
A second arm by a second voltage generating switching element;
A third arm by a switching element for generating an intermediate voltage between the first voltage and the second voltage,
Single-phase two-wire output is possible by driving the switching elements of the first arm and the second arm, and single-phase three-wire output is possible by driving the switching element of the third arm. An inverter,
The inductance of the reactor connected to the output end of the third arm is made smaller than the inductance of the reactor connected to the output end of the first arm and the output end of the second arm, respectively. An inverter.   The inverter according to claim 1, wherein a switching frequency of the switching element of the third arm is set higher than a switching frequency of each of the switching elements of the first arm and the second arm.   The switching frequency of the switching element of the third arm is connected to the inductance of the reactor connected to the output end of the third arm, and to the output end of the first arm and the output end of the second arm, respectively. The inverter according to claim 2, wherein the inverter is determined based on a ratio to an inductance of a reactor to be operated. A power conditioner comprising the inverter according to claim 1.

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