Inverter device

Abstract

To provide an inverter device capable of suppressing an excitation rush current with respect to various external power supplies, according to a lap control system in which suppression of the excitation rush current into a main transformer is performed by lapping and applying a voltage from an external power supply thereto during application of a main power supply.SOLUTION: An inverter device that generates a predetermined three-phase variable frequency voltage from a three-phase AC power supply comprises a main transformer for obtaining a predetermined voltage from a three-phase secondary winding on a secondary side by applying a first voltage of the three-phase AC power supply from outside to a three-phase primary winding on a primary side, and an inverter body formed from a plurality of inverter units, that is connected to the three-phase secondary winding of the main transformer. It is so constituted that the main transformer provides a third three-phase winding on the primary side so as to apply a second voltage lower than the first voltage onto the primary side via lapping, when applying the first voltage to the three-phase primary winding; and the main transformer comprises connection terminals at both ends of each third three-phase winding.SELECTED DRAWING: Figure 7

Description

Technical Field

[0001] The present invention relates to an inverter device for obtaining a high-voltage output, and particularly to a multi-inverter device configured to obtain a high-voltage output using a plurality of inverter units.

Background Art

[0002] The need to perform variable-speed operation of an AC motor to save power has been spreading mainly in industrial equipment. In particular, small-capacity low-voltage AC motors are being operated in an energy-saving manner in combination with general-purpose inverter devices. On the other hand, inverter devices that output a high voltage have also been put into practical use for the purpose of enabling variable-speed operation and energy-saving operation of large-capacity high-voltage AC motors.

[0003] As the background art of such an inverter device that outputs a high voltage, there is Patent Document 1. In Patent Document 1, in an inverter device that generates a predetermined variable-frequency voltage from an AC power source, it has a plurality of inverter units having smoothing capacitors and a main transformer installed on the input side of the inverter device. A third winding is provided on the AC power source side so as to form a part of the main transformer, and the AC power source is applied to each smoothing capacitor of the plurality of inverter units via the third winding for initial charging. A configuration is disclosed.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] Patent Document 1 discloses an external initial charging method for performing initial charging of a smoothing capacitor in an inverter unit with low cost and good power efficiency using a power source different from the main power source.

[0006] On the other hand, in an inverter device that generates a predetermined variable frequency voltage from an AC power source, having a plurality of inverter units and a main transformer installed on the input side of the inverter device, a third winding is provided on the AC power source side so as to form a part of the main transformer, and as a technique for suppressing the inrush current to the main transformer, a wrap control is known in which when the main power source is applied to the primary winding of the main transformer, the voltage from an external power source is wrapped and applied to the third winding.

[0007] Therefore, by making the separate power source used in the external initial charging method also serve as the external power source used in the wrap control, it is conceivable to suppress the inrush current without adding components.

[0008] However, the effect of suppressing the inrush current by the wrap control depends on the phase difference between the external power source and the main power source. When the phase difference is large, there is a problem that the inrush current cannot be sufficiently suppressed. In particular, for the manufacturer of the inverter device, since the external power source used by the user of the inverter device is outside its jurisdiction, the wiring method of the transformer that generates the external power source is not necessarily the same as the wiring method of the main transformer of the inverter device. Depending on the combination of the wiring methods of the respective transformers, the phase difference may become large and the inrush current may not be suppressed.

[0009] Therefore, in view of the above problems, the present invention aims to provide an inverter device capable of suppressing the inrush current to the main transformer by wrapping and applying the voltage from the external power source when the main power source is turned on in a wrap control method.

Means for Solving the Problems

[0010] The present invention, for example, is an inverter device that generates a predetermined three-phase variable frequency voltage from a three-phase AC power supply, comprising: a main transformer that applies a first voltage of an external three-phase AC power supply to a three-phase primary winding on the primary side to obtain a predetermined voltage from a three-phase secondary winding on the secondary side; and an inverter body connected to the three-phase secondary winding of the main transformer and composed of a plurality of inverter units. The main transformer is provided with a third three-phase winding on the primary side such that when applying the first voltage to the three-phase primary winding, a second voltage lower than the first voltage is wrapped and applied to the primary side, and the main transformer has connection terminals at both ends of each of the third three-phase windings.

Advantages of the Invention

[0011] According to the present invention, in a wrap control method for suppressing the inrush current to the main transformer by wrapping and applying the voltage from the external power supply when the main power supply is turned on, an inverter device capable of suppressing the inrush current for various external power supplies can be provided.

Brief Description of the Drawings

[0012]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Embodiment for Carrying Out the Invention

[0013] Hereinafter, embodiments of the present invention will be described with reference to the drawings.

Example

[0014] FIG. 1 is a configuration diagram of an inverter device in this embodiment. The inverter device in this embodiment generates a predetermined three-phase variable frequency voltage from a three-phase AC power supply. As shown in FIG. 1, the inverter device 5 mainly includes a main transformer 3 that applies the first voltage of the external three-phase AC power supply 1 to the three-phase primary winding 31 on the primary side and obtains a predetermined voltage from the three-phase secondary winding 32 on the secondary side, and an inverter main body 4 composed of a plurality of inverter units 41 - 49 connected to the three-phase secondary winding 32 of the main transformer 3.

[0015] In FIG. 1, the three-phase AC power supply 1 is a commercial AC power supply, and its power is supplied to the three-phase primary winding 31 of the main transformer 3 via the main switch 11. The three-phase secondary winding 32 of the main transformer 3 is composed of a plurality of three-phase windings, and each three-phase secondary winding 32 is connected to the AC input terminals of the plurality of inverter units 41 - 49 of the inverter main body 4. In the inverter main body 4, the AC power supplied from the three-phase AC power supply 1 is converted into three-phase AC power with a variable frequency, and power is supplied to the AC motor 9 as a load. Note that FIG. 1 shows the case of a three-fold multiple inverter, but this embodiment is not limited to three-fold and may be any n-fold.

[0016] Figure 2 is a configuration diagram of the inverter units 41 - 49 in this embodiment. In Figure 2, for each of the inverter units 41 - 49, the three-phase secondary winding 32 is connected to the AC input terminals u, v, w, and the three-phase AC power supply 103 from the three-phase secondary winding 32 is converted into a DC voltage Vdc105 by a three-phase full-wave diode rectifier 61 within each inverter unit, and the DC voltage Vdc105 is smoothed by a smoothing capacitor 62. The smoothed DC voltage Vdc105 is further converted into a single-phase variable frequency voltage 106 by each transistor inverter 63. Terminals a and b serve as the terminals for connecting the respective inverter units.

[0017] In Figure 1, for the inverter units 41 - 43, the respective terminals a and b are connected, and the respective single-phase variable frequency voltages 106 are connected in series and added to generate a variable AC voltage for the u phase. For the inverter units 44 - 46, the respective terminals a and b are connected, and the respective single-phase variable frequency voltages 106 are connected in series and added to generate a variable AC voltage for the v phase. For the inverter units 47 - 49, the respective terminals a and b are connected, and the respective single-phase variable frequency voltages 106 are connected in series and added to generate a variable AC voltage for the w phase, which is output as a three-phase variable AC voltage 104 to drive, for example, an AC motor 9.

[0018] In Figure 1, the current transformers CT and potential transformers PT installed in each layer detect the layer current and the inter-layer voltage of each layer. The control circuit 52 generates gate pulses 53 for driving each transistor inverter 63 of the inverter units 41 - 49 based on the detected layer current and inter-layer voltage. Note that 51 is a ground fault detection circuit.

[0019] In addition, the main transformer 3 is provided with a third three-phase winding 33 on the primary side. As a technique for suppressing the inrush current into the main transformer 3, when applying the first voltage to the three-phase primary winding 31, a second voltage lower than the first voltage is wrapped around and applied to the third three-phase winding 33. Here, the second voltage is generated by the low-voltage transformer 2 from the three-phase AC power supply 1 as an external power supply, and is supplied to the third three-phase winding 33 via the auxiliary switch 21. For example, the three-phase AC power supply 1, which is the first voltage, is 6600V three-phase AC, and the second voltage lower than that is 200V - 440V three-phase AC.

[0020] Figure 3 is a diagram for explaining the timing of the applied voltage to the main transformer 3 in this embodiment. In Figure 3, when the operation command of the inverter device becomes ON, the auxiliary switch 21 closes and becomes ON, and a second voltage lower than the first voltage generated by the low-voltage transformer 2 is applied to the third three-phase winding 33. Then, overlapping with the period when the auxiliary switch 21 is closed and ON, the main switch 11 closes and becomes ON, and the first voltage from the three-phase AC power supply 1 is applied to the three-phase primary winding 31.

[0021] Note that by applying the second voltage to the smoothing capacitor of each of the plurality of inverter units via the third winding, it is possible to combine with an external initial charging method that can perform the initial charging of the smoothing capacitor at low cost and with good power efficiency. In Figure 3, the period when the auxiliary switch 21 is closed and ON becomes the initial charging time of the smoothing capacitor, for example, about 5 seconds.

[0022] Here, as a technique for suppressing the inrush current into the main transformer 3, the wrap control that wraps and applies the voltage from the low-voltage power supply when the high-voltage power supply, which is the main power supply to the main transformer 3, is turned on, shows a difference in effect depending on the phase difference between the low-voltage power supply and the high-voltage power supply due to its characteristics. For example, if the phase difference is zero, the inrush current is about 1 times the rated current, but when the phase difference is ±30°, it is about 2 times the rated current, and when the phase difference is ±60°, it is about 5 times the rated current.

[0023] FIG. 4 is a diagram for explaining the phase of the voltage applied to the main transformer in this embodiment. In FIG. 4, the same components as those in FIG. 1 are denoted by the same reference numerals and their descriptions are omitted. In FIG. 4, phase A, which is the phase of the low-voltage power supply, is the phase from the primary to the secondary of the low-voltage transformer 2. For example, if the connection method is delta-delta connection (hereinafter denoted as ΔΔ), the phase shift is zero, and if it is star-delta connection (hereinafter denoted as YΔ), the phase shift is 30°. On the other hand, phase B, which is the phase of the high-voltage power supply, is the phase from the three-phase primary winding 31 to the third three-phase winding 33 of the main transformer 3.

[0024] FIGS. 5 and 6 are diagrams for explaining the connection method of the three-phase primary winding 31 and the third three-phase winding 33 of the main transformer 3. In FIGS. 5 and 6, the left figure shows the vector diagram and the right figure shows the connection diagram. The thick lines indicate the windings, and different connection methods are adopted according to the differences in the connections at both ends of each winding. FIG. 5 shows the case where the connection method is YΔ1, and FIG. 6 shows the case where the connection method is YΔ11. As shown in FIG. 5, if the connection method is YΔ1, phase B is 30°, and as shown in FIG. 6, if the connection method is YΔ11, phase B is -30°. Although not shown, if the connection method is star-star connection (hereinafter denoted as YY), phase B is zero.

[0025] Therefore, the phase difference between the low-voltage power supply and the high-voltage power supply is phase A - phase B. In FIG. 4, R22 is a current-limiting resistor when the external initial charging method is applied.

[0026] Here, the connection method of the low-voltage transformer 2 that generates the low-voltage power supply is not necessarily the same as the connection method of the three-phase primary winding 31 and the third three-phase winding 33 of the main transformer of the inverter device. In particular, since the manufacturer of the inverter device 5 has no jurisdiction over the low-voltage transformer 2 on the user side that uses the inverter device 5, depending on the combination of the connection methods of the respective transformers, the phase difference may become large and the inrush current may not be suppressed.

[0027] Therefore, in this embodiment, the main transformer on the inverter device side is configured to have connection terminals at both ends of each winding of the third three-phase winding so that a plurality of connection methods are possible. Hereinafter, the details of this embodiment will be described.

[0028] FIG. 7 is a diagram for explaining the connection terminals of the three-phase primary winding 31 and the third three-phase winding 33 of the main transformer in this embodiment.

[0029] In FIG. 7, the connection terminals of the main transformer are indicated by white circles. For the three-phase primary winding 31, for example, 1U, 1V, and 1W for Y connection, and for the third three-phase winding 33, 3U1, 3V1, 3W1 and 3U2, 3V2, 3W2 are provided. Note that the connection terminals for the three-phase secondary winding 32 are omitted. That is, for the three-phase primary winding 31, three three-phase terminals after connecting the three-phase windings are provided, and for the third three-phase winding 33, the three-phase winding is not connected, and six connection terminals at both ends of each three-phase winding are provided.

[0030] Thereby, when a user using the inverter device 5 introduces the inverter device 5, by connecting the connection terminals of the third three-phase winding 33 of the main transformer with an external connection wire corresponding to the connection method of the low-voltage transformer 2, it is possible to connect to a predetermined connection method. For example, in FIG. 7, by connecting as shown by the dotted line, the three-phase primary winding 31 and the third three-phase winding 33 can be connected in YΔ1 connection. Also, by connecting as shown by the broken line, the three-phase primary winding 31 and the third three-phase winding 33 can be connected in YΔ11 connection. Also, by connecting as shown by the dashed-dotted line, the three-phase primary winding 31 and the third three-phase winding 33 can be connected in YY connection. Note that in FIG. 7, the Y connection is used for the three-phase primary winding 31, but the Δ connection may also be used.

[0031] In this way, since the connection method of the third three-phase winding 33 of the main transformer can be changed according to the connection method of the low-voltage transformer 2, the phases of the three-phase primary winding 31 and the third three-phase winding 33 can be arbitrarily adjusted, and the phase difference between the low-voltage power supply and the high-voltage power supply can be kept within 30°. Thereby, the inrush current can be suppressed within about twice the rated current.

[0032] In addition, the manufacturer of the inverter device 5 may check the connection method of the low-voltage transformer 2 of the user who installs the inverter device 5, and connect the connection terminals of the third three-phase winding 33 of the main transformer with an external connection wire according to the connection method.

[0033] FIG. 8 is a diagram for explaining another example of the connection terminals of the three-phase primary winding 31 and the third three-phase winding 33 of the main transformer in this embodiment. In FIG. 8, the same components as those in FIG. 7 are denoted by the same reference numerals and their description is omitted. In FIG. 8, the arrangement of the connection terminals 3W1 and 3W2 at both ends of one winding in FIG. 7 is arranged upside down.

[0034] In FIG. 8, compared with the case of FIG. 7, when connecting the connection terminals of the third three-phase winding 33 with an external connection wire, the external connection wire can be shortened. In addition, by devising the arrangement and shape of the connection terminals for each of the U, V, and W windings, it is also possible to arrange them so as not to cause miswiring.

[0035] As described above, according to this embodiment, in the wrap control method for suppressing the inrush current to the main transformer by wrapping and applying the voltage from the external power supply when the main power supply is turned on, an inverter device capable of suppressing the inrush current for various external power supplies can be provided.

[0036] Although the above embodiments have been described, the present invention is not limited to the above-described embodiments and includes various modifications. For example, in the above-described embodiments, the external power supply used in the wrap control is described as being shared with another power supply used in the external initial charging method, but the present invention is not limited to this. Further, in the above-described embodiments, the present invention has been described in detail for easy understanding, and the present invention is not necessarily limited to those having all the configurations described.

Explanation of Reference Numerals

[0037] 1: Three-phase AC power supply, 2: Transformer for low voltage, 3: Main transformer, 4: Inverter body, 5: Inverter device, 9: AC motor, 11: Main switch, 21: Auxiliary switch, 22: Current limiting resistor, 31: Three-phase primary winding, 32: Three-phase secondary winding, 33: Third three-phase winding, 41 - 49: Inverter unit, 52: Control circuit, 53: Gate pulse, 61: Three-phase full-wave diode rectifier, 62: Smoothing capacitor, 63: Transistor inverter, 103: Three-phase AC power supply, 105: DC voltage Vdc, 106: Single-phase variable frequency voltage

Claims

1. An inverter device that generates a predetermined three-phase variable frequency voltage from a three-phase AC power supply, comprising: a main transformer that applies a first voltage of an external three-phase AC power supply to a three-phase primary winding on the primary side and obtains a predetermined voltage from a three-phase secondary winding on the secondary side; an inverter body comprising a plurality of inverter units connected to the three-phase secondary winding of the main transformer; the main transformer is provided with a third three-phase winding on the primary side so that when applying the first voltage to the three-phase primary winding, a second voltage lower than the first voltage is wrapped and applied to the primary side; the main transformer has connection terminals at both ends of each of the third three-phase windings, the three-phase primary winding is star-connected, and by connecting the connection terminals, the three-phase primary winding and the third three-phase winding can be configured in a predetermined connection method among star-star connection, star-delta 1 connection, and star-delta 11 connection. The inverter device is characterized by this.

2. The inverter device according to claim 1, comprising a current transformer that detects the layer current of the output from the plurality of inverter units and an instrument transformer that detects the interlayer voltage, and generating a gate pulse for driving the inverter unit based on the detected layer current and the interlayer voltage. The inverter device is characterized by this.

3. The inverter device according to claim 1, characterized in that the second voltage is applied via the third three-phase winding to a smoothing capacitor of each of the plurality of inverter units for initial charging.

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