JP7701835B2 - Inverter Device - Google Patents

Description

The present invention relates to an inverter device that obtains a high voltage output, and in particular to a multiple inverter device that obtains a high voltage output by using multiple inverter units.

The need to save power by operating AC motors at variable speeds is becoming widespread, especially in industrial equipment. Small capacity, low voltage AC motors in particular are operated in an energy-saving manner by combining them with general-purpose inverter devices. On the other hand, inverter devices that output high voltages have also been put into practical use with the aim of enabling large capacity, high voltage AC motors to be operated at variable speeds in an energy-saving manner.

Patent Document 1 is a background technology for an inverter device that outputs such a high voltage. Patent Document 1 discloses an inverter device that generates a predetermined variable frequency voltage from an AC power source, which has multiple inverter units with smoothing capacitors and a main transformer installed on the input side of the inverter device, with a third winding provided on the AC power source side to form part of the main transformer, and the AC power source is applied to the smoothing capacitors of each of the multiple inverter units via the third winding to perform initial charging.

JP 2002-345258 A

Patent Document 1 discloses an external initial charging method that uses a power source separate from the main power source to initially charge the smoothing capacitor in an inverter unit at low cost and with good power efficiency.

On the other hand, in an inverter device that generates a predetermined variable frequency voltage from an AC power source, there are multiple inverter units and a main transformer that is installed on the input side of the inverter device, and a third winding is provided on the AC power source side to form part of the main transformer. As a technology for suppressing excitation inrush current to the main transformer, 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.

Therefore, it is conceivable that by using the separate power supply used in the external initial charging method in combination with the external power supply used in the lap control, it would be possible to suppress the magnetizing inrush current without adding any additional components.

However, the effectiveness of overlap control in suppressing magnetizing inrush current depends on the phase difference between the external power supply and the main power supply, and there is a problem that magnetizing inrush current cannot be sufficiently suppressed if the phase difference is large. In particular, since the manufacturers of inverter equipment do not have control over the external power supplies of users who use inverter equipment, the wiring method of the transformer that generates the external power supply is not necessarily the same as the wiring method of the inverter equipment's main transformer, and depending on the combination of the wiring methods of the respective transformers, the phase difference may become large, making it possible that magnetizing inrush current cannot be suppressed.

In view of the above problems, the present invention aims to provide an inverter device capable of suppressing magnetizing inrush current for various external power sources in a wrap control method that suppresses magnetizing inrush current to the main transformer by applying a voltage from an external power source in a wrap manner when the main power source is turned on.

One example of the present invention is an inverter device that generates a predetermined three-phase variable frequency voltage from a three-phase AC power source, and includes a main transformer that applies a first voltage of an external three-phase AC power source 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, and an inverter body that is connected to the three-phase secondary winding of the main transformer and is made up of a plurality of inverter units. The main transformer has a third three-phase winding on the primary side so that when the first voltage is applied to the three-phase primary winding, a second voltage lower than the first voltage is applied in a wrapping manner to the primary side, and the main transformer has connection terminals on both ends of each of the third three-phase windings.

According to the present invention, an inverter device capable of suppressing magnetizing inrush current for various external power sources can be provided in a wrap control method that suppresses magnetizing inrush current to a main transformer by applying a voltage from an external power source in a wrap manner when the main power source is turned on.

FIG. 1 is a configuration diagram of an inverter device according to an embodiment. FIG. 2 is a configuration diagram of an inverter unit in the embodiment. FIG. 4 is a diagram for explaining the timing of voltage application to a main transformer in the embodiment. FIG. 4 is a diagram for explaining the phase of a voltage applied to a main transformer in the embodiment. FIG. 11 is an explanatory diagram of a case where the connection method of the three-phase primary winding and the third three-phase winding of the main transformer in the embodiment is YΔ1. FIG. 11 is an explanatory diagram of a case where the connection method of the three-phase primary winding and the third three-phase winding of the main transformer in the embodiment is YΔ11. FIG. 2 is a diagram illustrating connection terminals of a three-phase primary winding and a third three-phase winding of a main transformer in the embodiment. 10 is a diagram illustrating another example of the connection terminals of the three-phase primary winding and the third three-phase winding of the main transformer in the embodiment. FIG.

The following describes an embodiment of the present invention with reference to the drawings.

Figure 1 is a block 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 source. As shown in Figure 1, the inverter device 5 mainly has a main transformer 3 that applies a first voltage of an external three-phase AC power source 1 to a three-phase primary winding 31 on the primary side and obtains a predetermined voltage from a three-phase secondary winding 32 on the secondary side, and an inverter main body 4 consisting of a plurality of inverter units 41-49 connected to the three-phase secondary winding 32 of the main transformer 3.

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

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

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

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

The main transformer 3 also has a third three-phase winding 33 on the primary side, and as a technique for suppressing the excitation inrush current to the main transformer 3, when a first voltage is applied to the three-phase primary winding 31, a second voltage lower than the first voltage is applied in a wraparound manner 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 source 1 as an external power source, and is supplied to the third three-phase winding 33 via the auxiliary switch 21. For example, the three-phase AC power source 1, which is the first voltage, is three-phase AC 6600V, and the second voltage, which is lower than that, is three-phase AC 200V to 440V.

Figure 3 is a diagram explaining the timing of the voltage applied to the main transformer 3 in this embodiment. In Figure 3, when the operation command of the inverter device is turned ON, the auxiliary switch 21 is closed and turned 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 in which the auxiliary switch 21 is closed and turned ON, the main switch 11 is closed and turned ON, and the first voltage from the three-phase AC power source 1 is applied to the three-phase primary winding 31.

In addition, by applying the second voltage to the smoothing capacitor of each of the multiple inverter units via the third winding, the initial charging of the smoothing capacitor can be performed at low cost and with good power efficiency, and can also be used as an external initial charging method. In FIG. 3, the period during which the auxiliary switch 21 is closed and ON is the initial charging time of the smoothing capacitor, which is, for example, about 5 seconds.

Here, there is a technique for suppressing the magnetizing inrush current to the main transformer 3, which is a wrap control that applies a voltage from a low-voltage power supply that wraps when the high-voltage power supply, which is the main power supply to the main transformer 3, is turned on. However, due to its characteristics, the effectiveness of this control varies depending on the phase difference between the low-voltage power supply and the high-voltage power supply. For example, if the phase difference is zero, the magnetizing inrush current is about 1 time the rated current, but if the phase difference is ±30°, it is about 2 times the rated current, and if the phase difference is ±60°, it is about 5 times the rated current.

Figure 4 is a diagram explaining the phase of the voltage applied to the main transformer in this embodiment. In Figure 4, the same components as in Figure 1 are given the same reference numerals and their explanation will be omitted. In Figure 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, and for example, if the connection method is delta-delta connection (hereinafter referred to as △△), the phase shift is zero, and if it is star-delta connection (hereinafter referred to as Y△), it 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.

Figures 5 and 6 are diagrams explaining the connection method of the three-phase primary winding 31 and the third three-phase winding 33 of the main transformer 3. In Figures 5 and 6, the left diagram shows a vector diagram, and the right diagram shows a connection diagram, with the thick lines indicating the windings. Various connection methods are used depending on the difference in the connection at both ends of each winding. Figure 5 shows the case where the connection method is Y△1, and Figure 6 shows the case where the connection method is Y△11. As shown in Figure 5, if the connection method is Y△1, phase B is 30°, and as shown in Figure 6, if the connection method is Y△11, phase B is -30°. Although not shown, if the connection method is star-star connection (hereinafter referred to as YY), phase B is zero.

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

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, the manufacturer of the inverter device 5 does not have jurisdiction over the low-voltage transformer 2 on the user side that uses the inverter device 5, so depending on the combination of the connection methods of each transformer, the phase difference may become large and it may not be possible to suppress the excitation inrush current.

Therefore, in this embodiment, the main transformer on the inverter device side is configured to have connection terminals on both ends of each winding of the third three-phase winding so that multiple connection methods are possible. The details of this embodiment are described below.

Figure 7 is a diagram 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.

In FIG. 7, the connection terminals of the main transformer are indicated by white circles, and for example, for the three-phase primary winding 31, there are 1U, 1V, and 1W in a Y connection, and for the third three-phase winding 33, there are 3U1, 3V1, and 3W1, and 3U2, 3V2, and 3W2. Note that the connection terminals for the three-phase secondary winding 32 are omitted. That is, for the three-phase primary winding 31, there are three three-phase terminals after the three-phase winding is connected, and for the third three-phase winding 33, there are six connection terminals at both ends of each of the three-phase windings, with the three-phase winding left unconnected.

This allows the user of the inverter device 5 to connect the connection terminals of the third three-phase winding 33 of the main transformer with an external connection line to a predetermined connection method when the inverter device 5 is introduced, in accordance with the connection method of the low-voltage transformer 2. For example, in FIG. 7, the three-phase primary winding 31 and the third three-phase winding 33 can be connected in a YΔ1 configuration by connecting as shown by the dotted lines. Also, the three-phase primary winding 31 and the third three-phase winding 33 can be connected in a YΔ11 configuration by connecting as shown by the dashed lines. Also, the three-phase primary winding 31 and the third three-phase winding 33 can be connected in a YY configuration by connecting as shown by the dashed lines. Note that, although a Y connection is used for the three-phase primary winding 31 in FIG. 7, a Δ connection may also be used.

In this way, 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, so that the phase of the three-phase primary winding 31 and the third three-phase winding 33 can be adjusted as desired, and the phase difference between the low-voltage power supply and the high-voltage power supply can be kept within 30°. This allows the excitation inrush current to be kept within approximately twice the rated current.

The manufacturer of the inverter device 5 may check the wiring method of the low-voltage transformer 2 of the user who will install 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 wiring method.

Figure 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 Figure 8, the same components as in Figure 7 are given the same reference numerals and their explanations are omitted. In Figure 8, the arrangement of the connection terminals 3W1 and 3W2 at both ends of one winding in Figure 7 is upside down.

In FIG. 8, when connecting the connection terminals of the third three-phase winding 33 with an external connection wire, the external connection wire can be made shorter than in the case of FIG. 7. In addition, by devising the arrangement and shape of the connection terminals for each of the U, V, and W windings, it is possible to arrange them in a way that prevents incorrect wiring.

As described above, according to this embodiment, an inverter device capable of suppressing magnetizing inrush currents for various external power sources can be provided in a wrap control method that suppresses magnetizing inrush currents to the main transformer by applying a voltage from an external power source that is wrapped when the main power source is turned on.

Although the above describes the embodiments, the present invention is not limited to the above embodiments and includes various modified examples. For example, in the above embodiments, the external power source used in the lap control is described as being used in combination with another power source used in the external initial charging method, but the present invention is not limited to this. Also, the above embodiments are described in detail to explain the present invention in an easy-to-understand manner, and the present invention is not necessarily limited to having all of the configurations described.

1: Three-phase AC power supply, 2: Low-voltage transformer, 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 (3)

An inverter device for generating a predetermined three-phase variable frequency voltage from a three-phase AC power source, the inverter device comprising: a main transformer that applies a first voltage of an external three-phase AC power source to a three-phase primary winding on a primary side and obtains a predetermined voltage from a three-phase secondary winding on a secondary side;
an inverter main body including a plurality of inverter units connected to the three-phase secondary winding of the main transformer;
the main transformer has a third three-phase winding on the primary side so as to apply a second voltage lower than the first voltage to the primary side in a wrapped manner when the first voltage is applied to the three-phase primary winding;
The inverter device is characterized in that the main transformer has connection terminals at both ends of the third three-phase winding, 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 into a predetermined connection method among a star-star connection, a star-delta 1 connection, and a star-delta 11 connection . 2. The inverter device according to claim 1,
An inverter device comprising: a current transformer for detecting layer currents of outputs from the plurality of inverter units; and a potential transformer for detecting interlayer voltages, and generating gate pulses for driving the inverter units based on the detected layer currents and interlayer voltages . 2. The inverter device according to claim 1,
the second voltage is applied to a smoothing capacitor included in each of the plurality of inverter units via the third three-phase winding to perform initial charging.

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