JP3375003B2 - Three-phase power converter - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a three-phase power converter composed of three single-phase power converters. 2. Description of the Related Art FIG. 2 shows an example of the configuration of a main part of a general three-phase power converter, wherein 1 is a DC power source, 2 is a three-phase power converter, 3 is a three-phase transformer, Is the load. Here, in the three-phase power converter 2, 211 to 216 are switching elements such as IGBTs, 221 to 226 are diodes,
X, Y, and Z are AC output terminals. FIG. 3 shows a three-phase power converter according to FIG.
This figure shows operation waveforms when pulse width modulation control is performed by a well-known triangular wave comparison method, where A1 represents a triangular wave as a carrier, and B1, C1, and D1 represent sine waves as modulated waves. Also, 211 is a waveform indicating the on / off operation of the switching element 211, and X is a waveform indicating the output voltage of the AC output terminal X with reference to the midpoint of the DC power supply 1. In addition, Y phase and Z phase
It has the same waveform with a phase difference of 120 degrees. [0004] In the three-phase power converter according to FIG. 2, as shown by X in FIG. 3, the output contains a harmonic of the carrier frequency. Therefore, the three-phase transformer 3
Alternatively, noise may be generated in a filter reactor (not shown) or a reactive element such as when the load 4 is a motor. It is extremely difficult to suppress the noise. Therefore, it is desired to reduce the noise by setting the carrier frequency to a frequency higher than the audible frequency limit (15 to 20 kHz). [0005] However, at such a high frequency, the switching elements 211 to 216 generate extremely large switching losses. For example, in the case of an IGBT, a switching loss of 4 to 8 times the conduction loss occurs at a carrier frequency of 15 kHz. Therefore, there are the following problems and the like, and it has been difficult to reduce noise. (B) Reduce the efficiency of the device. (B) For large capacity, additional facilities such as air conditioning will be increased. (C) Due to the heat generation limit of the switching element, the number of used parallel devices increases in a large-capacity device, which is large and uneconomical. Next, as a conventional example in which the above-mentioned disadvantages are improved, there is a three-phase power converter shown in FIG. FIG.
Shows an example of the main configuration of a conventional three-phase power converter,
Reference numeral 5 denotes a three-phase power converter constituted by three single-phase power converters 51, 52, 53, and reference numerals 61, 62, 63 denote single-phase transformers. In the figure, components having the same reference numerals as those in FIG. 2 indicate the same components. Here, the single-phase power converters 51, 52, 53 have the same configuration,
11 to 514 are switching elements such as IGBTs, 515 to 518
Is a diode, and U, X, V, Y, W, and Z are AC output terminals. FIG. 5 shows the operation of the three-phase power converter shown in FIG. 4, where A 2 is a triangular wave serving as a carrier, and B 2
, C2 and D2 indicate sine waves which are modulated waves. 511, 513
Are the switching elements 511 of the single-phase power converter 51,
The on / off operation of the 513 is defined as (UX), (VY), (W
−Z) are W between the UX terminals of the single-phase power converter 51, VY terminals of the single-phase power converter 52, and W of the single-phase power converter 53, respectively.
3 shows an output voltage waveform between Z terminals. [0008] That is, 511, 513, shown in FIG.
As is clear from (UX), in the three-phase power converter according to FIG. 4, the pulse frequency output from each single-phase power converter is the same as the carrier frequency, but the operating frequency of the switching element is the carrier frequency. The switching loss can be halved while achieving noise reduction. However, in the configuration of FIG. 4, as is apparent from (UX), (VY) and (WZ) shown in FIG. 5, the output voltage of each single-phase power converter is The instantaneous sum does not become zero, and a so-called zero-phase voltage is generated. As is well known, a normal three-phase transformer having a tripod core provides a current path having an extremely low impedance with respect to the zero-sequence voltage, and generates an excessive current in the power converter and damages the switching element. Or, a normal three-phase transformer cannot be used due to increased switching loss. For this reason, FIG.
In this case, a plurality of single-phase transformers 61, 62, 63 as shown in (1) or a special transformer having iron cores having the number of phases or more must be used. SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned drawbacks of the conventional device, and comprises a three-phase power converter constituted by a plurality of single-phase power converters. A three-phase transformer in which the primary windings are insulated from each other is provided, and one of the connections between the pair of AC output terminals of each single-phase power converter and the corresponding primary winding of the three-phase transformer is insulated from each other. The three windings are wound around the same iron core with the same phase polarity, and each winding of the reactor is inserted. As described above, the switching frequency of the switching element with respect to the carrier frequency is reduced by forming the three-phase power converter with three single-phase power converters. By adding each winding of the reactor between the AC output terminal of the three-phase transformer and the corresponding primary winding of the three-phase transformer, the zero-sequence voltage and current are suppressed, thus enabling the use of a normal three-phase transformer. Things. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in more detail with reference to the drawings. FIG. 1 shows a main part of an embodiment of the present invention. Reference numeral 7 denotes primary windings 71, 72, 73 insulated from each other.
And a three-phase transformer 8 having a secondary winding. Reference numeral 8 denotes a reactor formed by winding three windings 81, 82, 83 insulated from each other on the same core 84 with the same polarity. u, x, v,
y, w and z indicate the terminals of the primary windings 71, 72 and 73, respectively. In the drawing, the same reference numerals as those in FIGS. 2 and 4 indicate the same components. That is, in FIG. 1, the AC output terminals U, V, W of the single-phase power converters 51, 52, 53 and one end of the corresponding primary windings 71, 72, 73 of the three-phase transformer 7 are shown. Terminals u, v,
w, the windings 81, 82, 83 of the reactor 8 are inserted. In such a configuration, the operation of the three-phase power converter 5 is as described with reference to FIG. 5, and the above-described reactor insertion can be used as follows. Since the three windings 81, 82, 83 of the reactor 8 are wound on the same iron core 84 with in-phase polarity,
Reactor 8 shows high impedance only for the instantaneous sum of output voltages of single-phase power converters 51, 52, 53, that is, only for zero-phase current, and does not show impedance for other voltage components. As a result, it is possible to effectively suppress the excessive current of the three-phase power converter based on the zero-phase voltage. Although FIG. 1 shows a single-phase power converter in a form generally referred to as a full-bridge power converter, the present invention is not limited to this and can take any form as is apparent from the above description. As described above, according to the present invention, 3
It is possible to use any single-phase power converter with a switching frequency half that of the output pulse frequency, and to achieve practical effects such as noise reduction, loss reduction, and reduction of incidental equipment. Is remarkable. In addition, the reactor can be used as a high impedance with respect to the zero-phase voltage, and the single-phase power converter can be used in any form, and even if a normal three-phase power converter is adopted, it will not hinder the use of a large-sized device. There is no. Since the reactor may be any one that can hold a zero-phase voltage at the carrier frequency level, the reactor may be extremely small.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a system diagram showing a main configuration of an embodiment according to the present invention. FIG. 2 is a system diagram showing a main configuration of a general three-phase power converter. FIG. 3 is a diagram showing operation waveforms according to FIG. 2; FIG. 4 is a system diagram showing a configuration example of a conventional main part. FIG. 5 is a diagram showing waveforms of respective parts of a three-phase power converter having a configuration of three single-phase power converters. [Description of Signs] 1 DC power supply 2 Three-phase power converter 3 Three-phase transformer 4 Load A1 Triangle wave B1 Sine wave C1 Sine wave D1 Sine wave 5 Three-phase power converter 51 Single-phase power converter 52 Single-phase power converter 53 Single-phase power converter 61 Single-phase transformer 62 Single-phase transformer 63 Single-phase transformer A2 Triangular wave B2 Sine wave C2 Sine wave D2 Sine wave 7 Three-phase transformer 8 Reactor

Claims (1)

(57) Claims 1. A three-phase transformer having three single-phase power converters each having a pair of AC output terminals and a three-phase transformer having primary windings in which each phase is insulated from each other. A three-phase power converter in which an AC output terminal of each of the single-phase power converters is connected to a primary winding of a corresponding phase of the three-phase transformer. At one end of the connection between the terminal and the corresponding primary winding of the three-phase transformer, the fact that three windings insulated from each other were wound around the same iron core with the same phase polarity and the respective windings of the reactor were inserted. Characteristic three-phase power converter.