JP2998683B2 - Power converter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in a power converter for converting a direct current to an alternating current or an alternating current to a direct current.
In particular, the present invention relates to a technology for forming a power converter that obtains an AC output voltage having a potential of three or more levels.

[0002]

2. Description of the Related Art Conventionally, a three-level inverter is called,
In addition to the high potential point and the low potential point of the DC power supply, an intermediate potential point between the high potential point and the low potential point is provided, and by selectively turning on and off the switching element group, the high potential point and the low potential point are set. 2. Description of the Related Art An inverter is known in which a three-level potential at a point or an intermediate potential point is selectively led to an AC terminal and an AC output with a low harmonic content is obtained by apparently increasing a PWM switching frequency. is there.

Examples thereof are (1) JP-B-51-47848, (2) JP-B-53-14744, and (3) JP-A-56-7408.
No. 8, (4) JP-A-56-115182, (5) JP-A-56-115182
JP-A-121374, (6) JP-A-57-177284, (7) JP-A-63-502953, (8) JP-A-64-34182, and (9) JP-A-1-198280. Publications and the like are known.

In a relatively large-capacity inverter such as a railcar VVVF inverter, the switching arms of each phase are often arranged in a linear arrangement.

[0005]

However, in the above-mentioned conventional device, the length of the wiring from the voltage dividing capacitor to the switching element of each phase is long and non-uniform. An excessive voltage is generated in the snubber circuit of the switching element, which causes problems such as overvoltage of the switching element, an increase in snubber loss, and an increase in the size of the snubber circuit. For this reason, particularly in a large-capacity device, it is required to minimize and equalize wiring as much as possible.

As an arrangement of a DC filter capacitor, an apparatus disclosed in Japanese Patent Application Laid-Open No. 57-206279 is known. This is because, in a three-phase full-bridge inverter composed of six-arm switching elements, DC filter capacitors are arranged for each phase, and the wiring length between the DC filter capacitors and the switching elements of each phase is reduced as much as possible. Therefore, the loss of the snubber circuit is reduced and the size of the device is reduced.

However, this prior art relates to a so-called two-level inverter in which the output phase voltage of the inverter has only two voltage levels, that is, a high potential point and a low potential point of the DC power supply, and is divided and installed for each phase. The capacitors are only filter capacitors.

An object of the present invention is to obtain a multi-level AC output voltage from the voltage of a plurality of capacitors connected in series to a DC voltage source by on / off control of a switching element, and connect the output to an AC power supply. It is an object of the present invention to reduce a harmonic current flowing from an AC voltage side to an AC power supply.

[0009]

According to the present invention, a DC voltage source side is divided by two or more voltage-dividing capacitors connected in series, and an AC voltage side is turned on / off of a switching element group of a switching arm having two or more phases. By the OFF control, a potential of three or more levels is output from the DC voltage of the voltage dividing capacitor, and in a power conversion device in which an AC power supply is connected to the AC voltage side via a reactor, the voltage dividing capacitor is independent for each phase. The voltage dividing capacitors of the respective phases are arranged in the vicinity of the switching arms of the respective phases, and the series connection points of the voltage dividing capacitors of the respective phases are connected to the corresponding dividing points of the switching arms of the respective phases. Are connected in series between the respective phases.

By connecting the series connection points of the respective voltage dividing capacitors to each other, harmonics caused by switching of the switching element can be canceled between the phases, and a capacitor voltage with little voltage pulsation can be obtained. As a result, harmonics included in the AC output can be reduced.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described with reference to FIG. The present embodiment is an example of an inverter that divides the DC side into two and outputs a three-phase AC voltage that changes between three levels of potential. In FIG. 1, reference numeral 1 denotes a DC voltage source such as a DC power supply or a DC motor armature, and reference numerals 2a to 2c denote three-level switching arms of a to c phases. The phase a is a switching element group including self-extinguishing switching elements G1a to G4a, rectifying elements D1a to D4a, and auxiliary rectifying elements D5a to D6a, and outputs an AC voltage to a terminal Ta. The b-phase and c-phase have the same configuration.

Reference numerals 3a to 3c denote voltage dividing capacitors divided at intermediate points, which are connected in series (intermediate potential points).
Oca to Occ are auxiliary rectifying elements D5a, D6a to D5c,
D6c is connected to a connection point of the switching element group, that is, a division point of the switching element group or an intermediate potential input point Osa to Osc. In addition,
P indicates a high potential point of the DC power supply, and N indicates a low potential point.

Here, a-phase capacitors 31a and 32a
Are voltages Ed1 and Ed2, the switching elements G1a to G1a to
By controlling ON / OFF of G4a as shown in Table 1, a three-level voltage of the potential Ed1 at the high potential point, the potential 0 at the intermediate potential point, or the potential −Ed2 at the low potential point is applied to the output terminal Ta. ea. Spa to Sna and Sa are switching functions expressing the conduction state of each switching element by 1, 0, -1. When Ed1 = Ed2 = Ed / 2, the output voltage ea can be expressed as in equation (1).

[0014]

Ea = SpaEd1-SnaEd2 = SaEd / 2 (1) ea is Ed / 2 (high potential), 0 (intermediate potential),
-Ed / 2 (low potential) is a waveform obtained by combining pulse-like voltages. Generally, Sd is set so that ea approaches a sine wave.
a is controlled by pulse width modulation (PWM).

[0015]

[Table 1]

In this embodiment, since the DC side voltage dividing capacitors are divided and arranged for each phase, these capacitors can be arranged near the switching element group, and the wiring length can be minimized. It becomes possible. As a result, the wiring inductance between the voltage dividing capacitor and the switching element can be reduced, so that the withstand voltage of the switching element can be reduced and the size of the snubber circuit (not shown in FIG. 1) can be reduced.

Although the present embodiment is an example in the case of three phases, naturally, the same effect can be obtained even in the case of two phases or three or more phases.

FIG. 2 shows another embodiment of the present invention. Connection points Oca to O of voltage dividing capacitors arranged in each phase
It is the same as the embodiment of FIG. 1 except that cc is connected between the phases. Hereinafter, the circuit operation when the connection points of the voltage dividing capacitors are not connected and when they are connected will be described.

Assuming that the voltage of the DC voltage source is Ed, the current supplied from the DC voltage source is is, and the capacitance of the individual voltage dividing capacitor of each phase is C, the relationship of equation (2) is obtained.

[0020]

(Equation 2)

Here, Ct: total voltage dividing capacitor capacity (=
3C / 2) isp: Sum of currents ispa-ispc flowing through G1a-G1c io: Current ioa-i flowing into the connection point of the voltage dividing capacitor
Sum of oc The current icpa flowing into the upper phase voltage dividing capacitor of the a-phase is
From equation (3),

[0022]

## EQU3 ## icpa = (is-isp-io / 2) / 3 + ioa / 2 (3) The voltage vcpa of the a-phase upper voltage dividing capacitor is expressed by the following equation (4).

[0023]

(Equation 4)

As is apparent from the above equation, vcpa pulsates with ioa. PWM so that the output voltage becomes a sine wave
When performing control, ioa mainly contains a large number of inverter output frequency components (fundamental wave components) and third harmonic components.
The node voltage of the voltage dividing capacitor will pulsate at these frequencies.

On the other hand, when the intermediate point between the voltage dividing capacitors of each phase is connected, the voltage v
cpa can be expressed as in equation (5).

[0026]

(Equation 5)

Therefore, in this case, vcpa depends on io. Since io is the sum of the currents ioa to ioc flowing into the intermediate point of the voltage dividing capacitor, components other than the zero-phase currents of ioa to ioc are not included in io. Therefore, the pulsation due to the fundamental wave component is removed.

As described above, according to this embodiment, in addition to the effects of the embodiment of FIG. 1, a stable voltage of the dividing capacitor can be obtained, so that the withstand voltage of the element can be reduced and the harmonic component of the AC output can be reduced. There is a feature that can be reduced. Further, by setting the connection impedance of each intermediate potential point to be equal, it is possible to surely cancel the harmonic.

FIG. 3 shows an embodiment in which the DC voltage is divided into three in the embodiment of FIG. As described above, by increasing the number of divisions of the DC side voltage, it is possible to obtain a multi-level AC output voltage from a stable voltage dividing capacitor voltage.

Further, when there are a plurality of independent DC voltage sources such as the individual power supplies 101 and 102 in the DC voltage source 1 of the embodiment of FIG. By connecting the connection points of the capacitors, the voltage sharing of the upper and lower voltage dividing capacitors can be surely equalized.

As shown in FIG. 5, by connecting the intermediate connection points of the voltage dividing capacitors of the respective phases via impedance elements 41 to 43, the voltage of the voltage dividing capacitor more stable than in the embodiment of FIG. Obtainable. For example, when a capacitor (capacitance Co, star connection in this example) is used as the impedance element, the voltage vcpa of the upper phase voltage dividing capacitor of the a-phase can be expressed as in equation (6).

[0032]

(Equation 6)

In this case, the fundamental component contained in the current flowing into the intermediate connection point of the voltage dividing capacitor is 2C / (2C +
Co) times. In the embodiment of FIG. 5, the impedance element is a star connection, but may be a delta connection.

Further, as in the embodiment shown in FIG. 6, a stable DC voltage can be established by disposing the filter capacitor 5 in parallel on the DC voltage source side. In particular, it is effective when the DC voltage source 1 is a DC voltage source including harmonics in the DC output, such as the AC power supply 11 and the rectifier circuit 12. In the figure, 121 to 124 are GTO thyristors, 1
Reference numerals 25 to 128 denote diodes, which schematically represent known PWM converters. FIG. 7 is an external perspective view of a vehicle fitting device for the phase switching arms 2a to 2c and the voltage dividing capacitors 3a to 3c common to the embodiments of FIGS.

FIG. 8 shows a unit inverter (power conversion device) unit 6 for each phase.

That is, in the embodiments shown in FIGS. 1 to 6, the configuration of the unit inverters of the a to c phases is completely the same, including the voltage dividing capacitor. Therefore, these are unitized, and the DC terminals P, N, and Oc, and the AC terminal T are provided and mass-produced, so that a power converter having an arbitrary number of phases can be configured by a combination thereof.

FIG. 9 shows still another embodiment of the present invention.
The difference from the embodiment of FIG. 2 is that the voltage dividing capacitor is divided into only two sets, 3b and 3c, for the three-phase three-level inverter. Then, the intermediate connection points Occ and Occ of the voltage dividing capacitors and the switching arms 2
The intermediate voltage input points asa to 2c (division points of the switching element group) Osa, Osb and Osc are all connected.

FIG. 10 shows the switching arms 2a to 2c and the voltage dividing capacitors 3b and 3c in the embodiment of FIG.
1 is an external perspective view of an outfitting device for a vehicle.

That is, each phase switching arm 2a-
2c are arranged in a linear arrangement, and the voltage dividing capacitors 3b and 3c are connected to the two-phase switching arm 2a.
2b and 2b and 2b and 2c.

FIG. 11 is also an external perspective view of a different arrangement example of the outfitting device for the vehicle, with the switching arms 2a to 2c and the voltage dividing capacitors 3b and 3c in the embodiment of FIG.

That is, each phase switching arm 2a-
2c are arranged in a linear arrangement, and 2
Divided voltage dividing capacitors 3b and 3c are arranged respectively.

With the configuration shown in FIGS. 10 and 11, the conditions of the switching element groups of all three phases are not completely the same, but the effect of miniaturization is remarkable as compared with the prior art.

Although all of the embodiments have been described above with respect to inverters, the output terminals of these inverters can be connected to an AC power supply via a reactance element to operate as a self-excited converter for converting AC to DC. is there. In this case, the same effect as that of the inverter can be expected.

[0044]

According to the present invention, even if the voltage dividing capacitor is divided for each phase switching arm, the harmonic component contained in the AC output can be reduced by electrically connecting the intermediate potential points of each phase. Since it is possible to reduce the harmonic current flowing to the power supply even if the AC side of the power converter is connected to the AC power supply, the effect of reducing the harmonic current is obtained.

[Brief description of the drawings]

FIG. 1 is a connection diagram of a three-phase power converter showing one embodiment of the present invention.

FIG. 2 is a connection diagram of a three-phase power converter showing another embodiment of the present invention.

FIG. 3 is a connection diagram of a three-phase power converter showing another embodiment of the present invention.

FIG. 4 is a connection diagram of a three-phase power converter showing another embodiment of the present invention.

FIG. 5 is a connection diagram of a three-phase power converter showing another embodiment of the present invention.

FIG. 6 is a connection diagram of a three-phase power converter showing another embodiment of the present invention.

FIG. 7 is an external perspective view showing an arrangement example of a switching arm and a voltage dividing capacitor common to FIGS. 1 to 6;

FIG. 8 is a connection diagram of a unit inverter unit having a switching arm and a voltage dividing capacitor common to FIGS. 1 to 6;

FIG. 9 is a connection diagram of a three-phase power converter showing another embodiment of the present invention.

FIG. 10 is an external perspective view showing different arrangement examples of the switching arm and the voltage dividing capacitor of FIG. 9;

FIG. 11 is an external perspective view showing different arrangement examples of the switching arm and the voltage dividing capacitor in FIG. 9;

[Description of Signs] 1 ... DC voltage source, 2a-2c ... a-c phase switching arm, 3a-3c ... voltage dividing capacitor, 5 ... filter capacitor, 6 ... unit inverter unit (parts), 41-
43: impedance element, P: high potential point of DC voltage source, N: low potential point, Oc: intermediate potential point, Os: intermediate potential input point (division point), T: AC terminal.

──────────────────────────────────────────────────の Continued on the front page (72) Inventor Yoshio Tsutsui 4026 Kuji-cho, Hitachi City, Ibaraki Prefecture Within Hitachi Research Laboratory, Hitachi, Ltd. (56) References JP-A-57-206279 (JP, A) JP-A-3-164070 (JP, A) JP-A-63-283470 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H02M ⁷ /42-7/98

Claims (1)

(57) [Claims] A DC voltage source is divided by two or more voltage-dividing capacitors connected in series, and an AC voltage is turned on / off of a switching element group of a switching arm of two or more phases.
By the off control, the DC voltage of the voltage dividing capacitor is
In the power converter in which the potential of the above level is output and an AC power supply is connected to the AC voltage side via a reactor, the voltage dividing capacitors are provided independently for each phase, and the voltage dividing capacitors of the respective phases are It is arranged in the vicinity of the switching arm of each phase, and connects the series connection point of the voltage dividing capacitor of each phase and the corresponding division point of the switching arm of each phase, and connects the series connection point of the voltage dividing capacitor of each phase. Are connected between the respective phases.