JP2015107021A - Power conversion device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem that for a multiple inverter, a plurality of single-phase two-level inverter cells are connected in series for each phase, but when this circuit is replaced with single-phase three-level inverter cells, the number of semiconductor elements increases and the device cost becomes expensive, although the number of control devices can be reduced.SOLUTION: To the output of a three-phase three-level inverter cell, for which two sets of a secondary windowing of an insulating transformer are inputted, is connected in series the output of a single-phase three-level inverter cell for which two sets of another secondary winding are inputted, the smoothing capacitor voltage values of the three-phase three-level inverter cell and single-phase three-level inverter cell are equalized, and the phase voltage amplitude of the three-phase three-level inverter cell is reduced to 1/2 of the phase voltage amplitude of the single-phase three-level inverter cell. Also, two forward converters of the three-phase three-level inverter cell are made to a first group, and each of three forward converters of the single-phase three-level inverter cell are made to be a second and a third group, then the converters are operated in phase within the group, and operated out of voltage phase between the groups.

Description

  The present invention is a three-phase three-level inverter that inputs a three-phase AC power source to a primary winding, is fed through one transformer having a plurality of secondary windings, and has two secondary windings as inputs. The present invention relates to a power converter that outputs three-phase alternating current by connecting in series the alternating current outputs of a plurality of single-phase three-level inverters that have other secondary windings as inputs.

  FIG. 7 shows a single-phase three-level power conversion circuit disclosed in Patent Document 1. An AC-DC conversion circuit in which a diode rectifier 21a as a forward converter is connected from a three-phase AC input A through a fuse 20a and a smoothing capacitor 22a is connected to this DC output, and a three-phase AC input B through a fuse 20b. Then, a diode rectifier 21b is connected as a forward converter, and a DC output with an AC-DC conversion circuit having a smoothing capacitor 22b connected to the DC output is connected in series, and a positive electrode P, an intermediate electrode M, and a negative electrode N are output. Configure the power supply. A DC-AC conversion is performed by a single-phase three-level inverter 23a using the DC power supply as a DC input, and a three-level AC output is obtained. In the single-phase three-level inverter 23a, a circuit in which four IGBTs having diodes connected in reverse parallel as switching elements are connected in series is connected in two circuits between the positive electrode P and the negative electrode N of the DC power supply, and further, the IGBTs are connected in series. A diode is connected between the point and the intermediate pole M of the DC power supply. The circuit configuration of FIG. 8 is called a single-phase three-level inverter cell. In the case of a three-phase three-level inverter circuit, a circuit in which four IGBTs having diodes connected in antiparallel are connected in series using three circuits, and such a circuit configuration is called a three-phase three-level inverter cell.

  FIG. 8 shows a circuit example using a single-phase three-level inverter 23b having another circuit configuration. A circuit in which two IGBTs having diodes connected in reverse parallel as switching elements are connected in series is connected between a positive electrode P and a negative electrode N of the DC power supply, and further, a series connection point of the IGBT and an intermediate pole M of the DC power supply. Are connected to bidirectional switch elements ACS1 and ACS2 capable of bidirectional current switching operation. Such a configuration is referred to as a single-phase three-level inverter cell. In the case of a three-phase three-level inverter circuit, the three-phase three-level inverter circuit is configured by using three circuits in which two IGBTs having diodes connected in reverse parallel are connected in series and three bidirectional switch elements. It is called an inverter cell.

  FIG. 9 shows a patent document 1 in which six single-phase three-level inverter cells (U1, U2, V1, V2, W1, W2) are used and the AC input of each cell is connected to the secondary winding of the transformer 12. The circuit diagram of the power converter device shown by is shown. One terminal of single-phase three-level inverter cells U1 and U2, V1 and V2, and W1 and W2 with AC outputs connected in series is connected in common, and the other terminal is connected to the motor 6, respectively. In this example, a total of twelve diode rectifiers are used. For example, four units are divided into three groups, and the voltage phase difference of the transformer secondary windings connected to their inputs is the same within the same group. As a result, a multi-rectifier equivalent to an 18-pulse rectifier circuit is provided for each group, thereby reducing low-order harmonic components contained in the input current flowing through the transformer primary winding connected to the AC power supply. It is usually done.

  Further, Patent Document 1 shows a circuit configuration as shown in FIG. 10 as a single-phase two-level inverter cell. One AC input is connected to the AC input of a diode rectifier 21 as a forward converter via a fuse 20, a smoothing capacitor 22 is connected between the DC outputs PN of the diode rectifier 21, and the smoothing capacitor 22 is a single-phase two-level inverter. The output of the single-phase two-level inverter 24 becomes an AC output with a configuration connected to the DC input. The single-phase two-level inverter 24 has a circuit configuration in which a circuit in which two IGBTs having anti-parallel diodes connected in series are connected in parallel with a two-circuit capacitor 22. Such a configuration is referred to as a single-phase two-level inverter cell.

  In FIG. 11, nine single-phase two-level inverter cells (U21 to U23, V21 to V23, W21 to W23) shown in Patent Document 1 are used, and the AC input terminal of each cell is the secondary winding of the transformer. The circuit structure of the power converter connected to the line is shown. One terminal of the single-phase two-level inverter cells U21 to U23, V21 and V23, and W21 and W23 to which the AC output is connected in series is connected in common, and the other terminal is connected to the electric motor 6. Also in this example, a total of 9 diode rectifiers are divided into 3 groups, for example, 3 units each, and the voltage phase difference of the transformer secondary windings connected to their inputs is provided by 20 electrical degrees for each group, It is a common practice to reduce the low-order harmonic components contained in the input current flowing through the transformer primary winding connected to the AC power supply by using a multiple rectifier equivalent to an 18-pulse rectifier circuit.

JP 2006-254673 A

In the above-described conventional example, the AC output of the single-phase two-level inverter cell shown in FIG. 10 is connected in series for each phase as shown in FIG. 11, and the power converter is configured using a total of nine cells. In this case, the number of IGBTs to be used is as follows.
4 [pieces / cell] × 9 [cells] = 36 [pieces]
At this time, it is necessary to provide nine control devices for controlling each inverter individually, which is the same as the number of single-phase two-level inverter cells.
On the other hand, when an IGBT with the same voltage rating is applied to a single-phase three-level inverter cell, two AC outputs of the single-phase three-level inverter cell are connected in series as shown in FIG. 9 to reduce the voltage utilization rate of the IGBT. Thus, a total of six single-phase three-level inverter cells must be used. At this time, the number of IGBTs to be used is as follows.
8 [pieces / cell] × 6 [cells] = 48 [pieces]
The number of inverter control devices is the same as the number of single-phase three-level inverter cells.
As described above, the power converter configured by connecting the AC outputs of the single-phase two-level inverter cell in series for each output phase is the same in the single-phase three-level inverter cell using the same voltage rating IGBT. When configuring an output voltage rated power conversion device, there is a merit that the number of control devices that individually control inverters is reduced, but the number of IGBTs to be applied increases, and the power conversion device is expensive accordingly. There is a problem of becoming.
Therefore, the subject of this invention is providing the power converter device which can reduce the number of use of a control apparatus, and can reduce the cost of an apparatus, without increasing the number of use of IGBT.

  In order to solve the above-mentioned problem, in the first invention, a set of primary windings connected to a three-phase AC power source and each insulated (6N + 2) (where N is a positive integer) Insulating transformers having three-phase secondary windings, two forward converters each converting one set of the secondary windings as input and converting alternating current to direct current, and outputs of the respective forward converters A three-phase three-phase inverter composed of a three-phase three-level inverter that inputs a smoothing capacitor connected to a DC power source having a positive electrode, a negative electrode, and an intermediate electrode and converts the direct current into a three-phase alternating current. Two level converter cells, each of which has another set of secondary windings as an input, and two forward converters for converting alternating current into direct current, and smoothing capacitors connected to the outputs of the respective forward converters; A series circuit of the smoothing capacitor is connected to a positive electrode and a negative electrode. 3N units of single-phase three-level inverter cells comprising a single-phase three-level inverter that is input as a DC power source having an intermediate pole and converts this DC into single-phase AC, The present invention relates to a power converter in which AC outputs of N single-phase three-level inverter cells are connected in series to each phase of AC output. The forward converter is operated so that the DC voltage value of the smoothing capacitor that constitutes the three-phase three-level inverter cell is equal to the DC voltage value of the smoothing capacitor that constitutes all the single-phase three-level inverter cells. The AC output voltage amplitudes of the single-phase three-level inverter cells whose outputs are connected in series are controlled to be equal, and the AC output phase voltage amplitude of the three-phase three-level inverter cell is the same as that of the single-phase three-level inverter cell. The three-phase three-level inverter cell is controlled so as to be ½ of the AC output voltage amplitude.

  According to a second invention, in the power conversion device according to the first invention, the two forward converters constituting the three-phase three-level inverter cell are grouped into one group, and the total constituting the single-phase three-level inverter cell 6N forward converters are grouped in groups of 2N, and the voltage phase of the transformer secondary winding connected to the input of the forward transformer belonging to the same group is the same, and the forward converters of different groups The voltage phases of the transformer secondary windings connected to the input are all different from each other.

  In the third invention, all the AC inputs of the forward converter constituting the three-phase three-level inverter cell and the forward converter constituting the single-phase three-level inverter cell in the first or second invention are three-phase alternating current. And the voltage phase difference of the transformer secondary windings of the total (2N + 1) group is distributed at intervals of electrical angle (60 / (2N + 1)) degrees.

In the present invention, single-phase 3 in which two sets of insulated secondary windings of the transformer are input to each phase AC output of the three-phase three-level inverter cell that inputs two sets of insulated secondary windings of the transformer. The AC output of the level inverter cell is connected in series with N units, and the DC voltage value of the smoothing capacitor constituting the three-phase three-level inverter cell and the DC voltage value of the smoothing capacitor constituting all the single-phase three-level inverters are Operate the forward converter to be equal. Further, the AC output voltage amplitude of the single-phase three-level inverter cell in which AC outputs are connected in series is controlled to be all equal, and the amplitude of the AC output phase voltage of the three-phase three-level inverter cell is the single-phase 3 The three-phase three-level inverter cell is controlled so as to be ½ of the amplitude of the AC output voltage of the level inverter cell. At this time, two forward converters constituting the three-phase three-level inverter cell are grouped into one group, and a total of 6N forward converters constituting the single-phase three-level inverter cell are grouped into two groups of three. The voltage phase of the transformer secondary winding connected to the input of the forward converter belonging to the same group is the same, and the voltage phase of the transformer secondary winding connected to the input of the forward converter of a different group is Make everything different.
As a result, it is possible to reduce the number of use of the control device without increasing the number of use of the semiconductor switch elements, and it is possible to reduce the size and cost of the power conversion device.

1 is a circuit diagram showing a first embodiment of the present invention. It is a circuit diagram which shows the 2nd Example of this invention. It is a circuit diagram which shows the 3rd Example of this invention. FIG. 1 shows an example of grouping and voltage phase difference when all forward converter inputs are three-phase. FIG. 2 shows an example of grouping and voltage phase difference when all forward converter inputs are three-phase. FIG. 3 shows an example of grouping and voltage phase difference when all forward converter inputs are three-phase. FIG. 3 is a circuit diagram example A of a single-phase three-level inverter cell. FIG. 4B is a circuit diagram example B of a single-phase three-level inverter cell. It is an example of a circuit diagram of a power converter which connected two 3 level inverter cells in series. It is an example of a circuit diagram of a 2 level inverter cell. It is an example of a circuit diagram of a power converter which connected three 2 level inverter cells in series.

The main points of the present invention are the following (1) to (3).
(1) Single-phase three-level input that inputs two sets of insulated secondary windings to each phase AC output of a three-phase three-level inverter cell that inputs two sets of insulated secondary windings of the transformer The AC outputs of the inverter cells are connected in series with N units, and the DC voltage value of the smoothing capacitor constituting the three-phase three-level inverter cell is equal to the DC voltage value of the smoothing capacitor constituting all the single-phase three-level inverters. The forward converter is operated as follows.
(2) The AC output voltage amplitude of the single-phase three-level inverter cell having AC outputs connected in series is controlled to be all equal, and the amplitude of the AC output phase voltage of the three-phase three-level inverter cell is the single-phase The three-phase three-level inverter cell is controlled so as to be ½ of the amplitude of the AC output voltage of the three-level inverter cell.
(3) Two forward converters constituting the three-phase three-level inverter cell are grouped into one group, and a total of 6N forward converters constituting the single-phase three-level inverter cell are grouped into two groups of 2N. The voltage phase of the transformer secondary winding connected to the input of the forward converter belonging to the same group is the same, and the voltage phase of the transformer secondary winding connected to the input of the forward converter of a different group To make them all different.

  FIG. 1 shows a first embodiment of the present invention. Each phase of the AC output of the three-phase three-level inverter cell 3 is individually set via a transformer 2a having one set of three-phase primary windings and eight sets of three-phase secondary windings connected to an AC power source. This is a circuit configuration in the case of connecting to the phase 3 level inverter cell (4u, 4v, 4w) and supplying power to the electric motor 6 as a load. The three-phase three-level inverter cell 3 uses two diode rectifiers as forward converters as in the conventional example described in FIG. A DC power source having an intermediate pole M and a negative electrode N is made, and is constituted by a three-phase three-level inverter circuit using this DC power source as an input. Further, the single-phase three-level inverter cell (4u, 4v, 4w) connected to each phase of the AC output of the three-phase three-level inverter circuit is a forward converter as in the conventional example described in FIG. 7 or FIG. Using two diode rectifiers, connecting a smoothing capacitor to the output of the two diode rectifiers, connecting them in series to create a DC power source having a positive electrode P, an intermediate electrode M, and a negative electrode N. It consists of a phase 3 level inverter circuit.

  Here, in order to control the AC output voltage according to a desired command value in the three-phase three-level inverter cell 3, the individual control device 3a is also connected to each single-phase three-level inverter cell (4u, 4v, 4w). In order to control the AC output voltage according to a desired command value, an individual control device 4a is provided. In this embodiment, a diode rectifier is used as a forward converter, but a self-excited rectifier using a self-extinguishing device may be used. In this example, all diode rectifiers are used as forward converters, and the voltages of the smoothing capacitors of all cells are made to be the same by making the voltage of the transformer secondary winding the same. . Further, an inverter output voltage command is given to the individual control devices 3a and 4a provided in each cell from the main control device 5 that controls the whole. This voltage command is a signal having the same output frequency and output voltage amplitude and a voltage phase shifted by 120 degrees in electrical angle for each single-phase three-level inverter cell (4u, 4v, 4w). The phase voltage command for each output of the three-phase three-level inverter is the same as the voltage command given to the single-phase three-level inverter cell to which the output is connected, the output frequency and the voltage phase are the same, and the output voltage amplitude is ½ The following signal is given from the main controller 5.

The output relationship between the three-phase three-level inverter and the single-phase three-level inverter when configured as described above will be described. Assuming that the DC input voltage is Ed, the maximum output voltage of the single-phase three-level inverter (during one pulse operation) is (2√2 / π) Ed. On the other hand, the maximum output phase voltage (during one pulse operation) of the three-phase three-level inverter is as follows when the DC input voltage is the same Ed.
(√6 / π) Ed / √3 = (√2 / π) Ed
As described above, the maximum output phase voltage of the three-phase three-level inverter is ½ of the maximum output voltage of the single-phase three-level inverter. For this reason, in the three-phase three-level inverter, the DC input power of the three-phase three-level inverter can be reduced by always controlling the voltage of the phase voltage to 1/2 of the amplitude of the output voltage of the single-phase three-level inverter. 3/2 times the DC input power of the phase 3 level inverter. Since the output of the single-phase three-level inverter cell is connected in series to each phase output terminal of the three-phase three-level inverter cell 3, the same current flows through the single-phase three-level inverter cell connected in series. Moreover, the output voltage of the three-phase three-level inverter cell is the same as the output frequency and voltage phase of the single-phase three-level inverter cell of the phase to which the single-phase three-level inverter cell is connected. Is ½ of the amplitude of the output voltage of the single-phase three-level inverter cell. As a result, the active power for one phase of the AC output of the three-phase three-level inverter cell is ½ of the AC output effective power of each single-phase three-level inverter cell.

  For this reason, the active power corresponding to the output three phases of the three-phase three-level inverter cell is 3/2 (three times the output phase effective power) of the output effective power of the single-phase three-level inverter. That is, ignoring the loss of the forward converter and the inverter, the input power of the forward converter of the three-phase three-level inverter cell is also 3/2 times the input power of the forward converter of the single-phase three-level inverter cell. For this reason, if all the secondary winding voltages of the transformer have the same voltage amplitude, the current flowing through the transformer secondary winding to which the forward converter of the three-phase three-level inverter cell is connected is also a single-phase three-level inverter cell. 3/2 times the current flowing in the secondary winding of the transformer to which the forward converter is connected.

Therefore, two forward converters constituting the three-phase three-level inverter cell are grouped into one group, and any three forward converters among the forward converters constituting the single-phase three-level inverter cell are separated. , The total ampere turns of the transformer secondary windings of both groups are the same. Dividing into such groups and reducing the harmonic components of a specific order of the current flowing through the transformer primary winding by providing a phase difference by a specific angle for each group in the voltage of the transformer secondary winding. Is possible.
In the case of the configuration shown in FIG. 1, the number of IGBTs used is 12 [pieces / three-phase cells] × 1 [cells] +8 [pieces / single-phase cell] × 3 [cells] = 36 [pieces]. The number is the same as when nine of the single-phase two-level inverter cells shown are used. In addition, there are four control devices that individually control the inverters. When nine single-phase two-level inverter cells shown in FIG. 11 are used, or when six single-phase three-level inverter cells shown in FIG. 9 are used. Compared to this, the cost can be reduced.

  4, in the circuit configuration of FIG. 1, when the AC power supply, the primary winding of the transformer, all the secondary windings are three-phase, and all the forward converters in the cell are three-phase diode rectifiers, The grouping is No. 1-No. 3 shows an example in which the voltage phase of each group is shifted by 20 degrees. No. 1 is a group composed of one forward converter in each of single-phase three-level inverter cells (4u, 4v, 4w), No. 1; No. 2 is a group composed of two forward converters of the three-phase three-level inverter cell 3; Reference numeral 3 denotes a group composed of the remaining one forward converter in each of the single-phase three-level inverter cells (4u, 4v, 4w). With this configuration, it is possible to reduce the low-order harmonic component of the current flowing through the three-phase primary winding of the transformer 2a.

  FIG. 2 shows a second embodiment of the present invention. This power is supplied from an AC power source to one of the three-phase three-level inverter cells 3 and six single-phase three-level inverter cells (4u1, 4u2, 4v1, 4v2, 4w1, 4w2) via the transformer 2b. Is the case. FIG. 1 shows the case where the number of series of single-phase three-level inverter cells is N = 1, but FIG. 2 shows an embodiment where the number of series of single-phase three-level inverter cells N is two.

  Since the AC outputs of two single-phase three-level inverter cells are connected in series to each phase AC output terminal of the three-phase three-level inverter cell 3, the same current flows through the inverter cells connected in series. Here, the AC output voltage of the three-phase three-level inverter cell is the same as the AC output frequency and voltage phase of the single-phase three-level inverter cell of the phase to which the single-phase three-level inverter cell is connected. The amplitude of the AC output phase voltage is set to ½ of the amplitude of the output voltage of the single-phase three-level inverter cell. The effective power for one phase of the output of the three-phase three-level inverter cell is ½ of the output power of each single-phase three-level inverter.

  For this reason, the active power for the three-phase output of the three-phase three-level inverter cell is 3/2 (three times the effective output power) of the single-phase three-level inverter cell. That is, ignoring the loss of the forward converter and the inverter, the input power of the forward converter of the three-phase three-level inverter cell is also 3/2 times the input power of the forward converter of the single-phase three-level inverter cell. For this reason, if all the secondary winding voltages of the transformer have the same voltage amplitude, the current flowing through the transformer secondary winding to which the forward converter of the three-phase three-level inverter cell is connected is also a single-phase three-level inverter cell. 3/2 times the current flowing in the secondary winding of the transformer to which the forward converter is connected.

  Therefore, two forward converters of three-phase three-level inverter cells are grouped into one group, and any three forward converters of the forward converters constituting the single-phase three-level inverter cell are grouped into another group. The total ampere turns of the transformer secondary windings of both groups will be the same. Dividing into such groups and reducing the harmonic components of a specific order of the current flowing through the transformer primary winding by providing a phase difference by a specific angle for each group in the voltage of the transformer secondary winding. Is possible.

  FIG. 5 shows an example of how to divide groups and assign phase differences when the embodiment of FIG. 2 is divided into five groups (No. 1 to No. 5). When the AC power supply and the primary winding and all secondary windings of the transformer 2b are three-phase, and all the forward converters in the cell are three-phase diode rectifiers, the voltage phase is divided into 12 groups. This is an example shifted by degrees. Group No. 1 is a group constituted by one forward converter in each of single-phase three-level inverter cells (4u1, 4v1, 4w1), group No. 2 is a group composed of two forward converters in the three-phase three-level inverter cell 3; 3 is a group composed of one forward converter in each of single-phase three-level inverter cells (4u2, 4v2, 4w2), group No. 4 is a group consisting of the remaining one forward converter in the single-phase three-level inverter cell (4u1, 4v1, 4w1), group No. Reference numeral 5 denotes an embodiment in which a group consisting of the remaining one forward converter in the single-phase three-level inverter cell (4u2, 4v2, 4w2) is formed. By doing in this way, it can be set as the multiple rectifier equivalent to 30 pulse rectification, and it is possible to reduce the low order harmonic component of the electric current which flows through the primary winding of a transformer.

FIG. 3 shows a third embodiment of the present invention. This is because one three-phase three-level inverter cell 3 and four single-phase three-level inverter cells 3N (4u1 to 4uN, 4v1 to 4vN, 4w1 to 4wN) are fed from an AC power supply via a transformer 2n. Is the case.
The operation principle is the same as in the first and second embodiments. Since the AC outputs of N single-phase three-level inverter cells are connected in series to each phase output terminal of the three-phase three-level inverter cell 3, the same current flows through the inverter cells connected in series. Here, the output voltage of the three-phase three-level inverter cell is the same as the output frequency and voltage phase of the single-phase three-level inverter cell of the phase to which the single-phase three-level inverter cell is connected. The amplitude of the voltage is ½ of the amplitude of the output voltage of the single-phase three-level inverter cell.

  When two forward converters of three-phase three-level inverter cells are combined into one group and any three forward converters of single-phase three-level inverter cells are combined into another group, the transformer secondary winding of both groups The total ampere turn of the line is the same. Dividing into such groups and reducing the harmonic components of a specific order of the current flowing through the transformer primary winding by providing a phase difference by a specific angle for each group in the voltage of the transformer secondary winding. Is possible.

6 shows an example of how to divide a group and add a phase difference when the embodiment shown in FIG. 3 is divided into (2N + 1) groups (No. 1 to No. (2N + 1)).
All inputs of the forward converter constituting the three-phase three-level inverter cell and the forward converter constituting the single-phase three-level inverter cell, that is, all transformer secondary windings are set to three-phase alternating current, When the forward converter is a three-phase diode rectifier, it is divided into (2N + 1) groups and the voltage phase is shifted by (60 / (2N + 1)) degrees. By doing in this way, it can be set as the multiple rectifier equivalent to a (6 * (2N + 1)) pulse rectification, and it is possible to reduce the low order harmonic component of the electric current which flows through the primary winding of a transformer.

  For example, in the case of Example 1 in which one single-phase three-level inverter cell is connected to each AC output phase of a three-phase three-level inverter cell, one group is composed of two forward converters of the three-phase three-level inverter cell. Can constitute two groups of three out of a total of six forward converters constituting a single-phase three-level inverter cell, and a total of three groups can be provided. When the phase difference of electrical angle 20 degrees (= 60 degrees / 3 groups) is provided for the voltage of the transformer secondary winding for each of these three groups, nine single-phase two-level inverter cells described in the prior art are used. The lower harmonic component of the input current can be reduced to the equivalent of 18 pulse rectification equivalent to the case of FIG.

Similarly, in the case of Example 2 in which two single-phase three-level inverter cells are connected to each AC output phase of the three-phase three-level inverter cell, two forward converters of the three-phase three-level inverter cell are used. One group can be composed of four groups of three out of a total of twelve forward converters constituting a single-phase three-level inverter cell, and a total of five groups can be provided. By providing a phase difference of 12 electrical degrees (= 60 degrees / 5 groups) to the voltage of the transformer secondary winding for each of these five groups, a multiple rectifier equivalent to 30 pulse rectification can be obtained. It is possible to reduce the low-order harmonic component of the current flowing through the primary winding.
In the above embodiment, the description has been made centering on the case where the input of the forward converter is a three-phase AC input. However, the AC input of the forward converter is not limited to three phases, but is a single-phase AC input insulated from each other. This can also be realized in the case of an AC power source that can provide a phase difference of.
In the embodiment, the three-level inverter circuit is described as an example using the circuit configuration described with reference to FIG. 7, but the same can be realized when the circuit configuration described with reference to FIG. 8 is used.

  The present invention is a configuration technology of a multiple inverter in which an AC output of a single-phase three-level inverter cell is connected in series to each phase AC output of a three-phase three-level inverter cell, such as a high-voltage motor drive device, a grid interconnection power conversion device, etc. Application to is possible.

2a, 2b, 2c, 2n, 12 ... transformers 3a, 4a ... individual control devices 5 ... main control devices 20, 20a, 20b ... fuses 21, 21a, 21b ... rectifier 22, 22a, 22b ... smoothing capacitors 23a, 23b ... single phase three level inverter circuit 24 ... single phase two level inverter circuit ACS1, ACS2 ... bidirectional switches U21-U23, V21-V23, W21-W23 ... Single-phase two-level inverter cells U1, U2, V1, V2, W1, W2 ... Single-phase three-level inverter cells

Claims (3)

An isolation transformer having a set of primary windings connected to a three-phase AC power source and a (6N + 2) set of three-phase secondary windings, each of which is insulated (where N is a positive integer), Two sets of forward converters that take one set of the secondary windings as input and convert alternating current into direct current, a smoothing capacitor connected to the output of each of the forward converters, and a series circuit of the smoothing capacitors as a positive electrode A three-phase three-level inverter cell composed of a three-phase three-level inverter that inputs as a DC power source having a negative electrode and an intermediate electrode and converts this direct current into a three-phase alternating current, and each of the other secondary windings Two forward converters for converting alternating current into direct current with one set as input, and a smoothing capacitor connected to the output of each forward converter, a series circuit of the smoothing capacitors, provided with a positive electrode, a negative electrode, and an intermediate electrode Input as a DC power supply and this DC is single phase 3N single-phase three-level inverter cells each comprising a single-phase three-level inverter for converting into a current, and N single-phase three-level inverter cells for each phase of the AC output of the three-phase three-level inverter cell In the power conversion device in which the AC outputs are connected in series,
The forward converter is operated so that the DC voltage value of the smoothing capacitor that constitutes the three-phase three-level inverter cell is equal to the DC voltage value of the smoothing capacitor that constitutes all the single-phase three-level inverter cells. The AC output voltage amplitudes of the single-phase three-level inverter cells whose outputs are connected in series are controlled to be equal, and the AC output phase voltage amplitude of the three-phase three-level inverter cell is the same as that of the single-phase three-level inverter cell. The power conversion device, wherein the three-phase three-level inverter cell is controlled so as to be ½ of an AC output voltage amplitude.   2. The power converter according to claim 1, wherein two forward converters constituting the three-phase three-level inverter cell are grouped, and a total of 6N forward converters constituting a single-phase three-level inverter cell. The transformer is connected to the input of the forward converter belonging to the same group with the same voltage phase of the secondary winding connected to the input of the forward converter belonging to the same group. A power conversion device characterized in that the voltage phases of the secondary windings are all different.   The power converter according to claim 1 or 2, wherein all inputs of the forward converter constituting the three-phase three-level inverter cell and the forward converter constituting the single-phase three-level inverter cell are three-phase alternating current, and the total ( 2N + 1) A power converter characterized by distributing the voltage phase difference of the secondary windings of the transformer at an electrical angle (60 / (2N + 1)) degree interval.