JP3194066B2 - 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 a power converter,
In particular, the present invention relates to a power converter for an AC electric vehicle having a structure in which a semiconductor element is insulated and mounted on a cooler.

[0002]

2. Description of the Related Art FIG. 7 shows a configuration of a conventional power converter for an AC electric vehicle using AC as a power source. In FIG. 7, 1 is an AC power supply, 2 is a transformer, 3 and 4 are power converters, 5 is an induction motor, 6a and 6b are DC circuit capacitors, and are single-phase from the AC power supply 1 via the transformer 2. Is supplied to a power converter (converter) 3 and converted into a direct current by the converter 3, and the direct current is converted into a variable voltage variable frequency 3 by a power converter (inverter) 4 via capacitors 6a and 6b.
The three-phase AC is supplied to an induction motor 5 that drives an AC electric vehicle (not shown). Since the power converter of the AC electric vehicle is insulated at the transformer 2, a ground circuit is provided to determine the potential. 7-1
Numeral 0 denotes a ground circuit, which is grounded to the vehicle body (not shown) through a resistor 7, a rectifier circuit 8, and a ground switch 9 from the midpoint of the capacitor 6 of the DC circuit. The output of the rectifier circuit 8 is connected to a ground relay 10 so that a direct current flows through the ground relay 10. Normally, no current flows through the ground circuit. However, when a ground fault occurs in the circuit of the power conversion device, a ground fault current flows. Activate the device. When a withstand voltage test is performed on the power converter, the ground switch 9 is opened and a predetermined voltage is applied between the power converter and the ground.

On the other hand, FIG. 8 schematically shows a configuration and a circuit in which a semiconductor element constituting a power converter is mounted on a cooler. As an example of a power converter, a circuit for one phase of a three-level inverter is shown. Is shown. In FIG. 8, 11a
Reference numerals 11d denote semiconductor elements in which diodes are connected in anti-parallel to self-extinguishing elements such as IGBTs, and 12a and 12b are diodes to which capacitors 6a and 6b of a DC circuit are connected. 13a to 13d, 14a and 14b are semiconductor modules including semiconductor elements 11a to 11d and diodes 12a and 12b, and 15 is semiconductor modules 13 and 14.
Is a cooler for cooling. 16a to 16f are capacitances between the semiconductor modules 13, 14 and the cooler 15. One of the semiconductor modules 13 and 14 is directly attached to the cooler 15 as a cooling surface, but the semiconductor element 11, the diode 12 and the cooler 15 are insulated from each other, and the cooler 15 is normally grounded. . The semiconductor modules 13 and 14 are, for example, 1 to secure cooling performance.
Each unit has a cooling surface of about 10 cm square, and a capacitance 16 exists between the cooling unit 15 and the cooling unit 15.

[0004]

When a power converter having a capacitance 16 as shown in FIG. 8 is used in an AC electric vehicle as shown in FIG. A high-frequency current accompanying the switching flows to the vehicle body through the capacitance 16. This leakage current strays in the vehicle body casing and returns to the power converter through the ground circuit. Leakage current flowing through the housing may cause noise disturbance in railway signal communication systems such as induction radio. Also,
The ground relay 10 may malfunction by flowing through the ground circuit. An object of the present invention is to provide a power conversion device that reduces noise disturbance on a signal communication system of a railway and prevents a malfunction of a ground relay of a ground circuit.

[0005]

In order to achieve the above object, a mid point of a DC circuit of a power converter and a cooler in which a semiconductor module accommodating a semiconductor element constituting a power converter is connected by a short-circuit line. I do. In performing a withstand voltage test for confirming insulation performance between the power converter and the cooler, a switch for connecting the cooler to a middle point or a ground point of the DC circuit of the power converter is provided.

[0006]

[Function] By connecting the midpoint of the DC circuit between the cooler and the power converter with a short-circuit line, the leakage current flowing through the capacitance existing between the power converter and the cooler is reduced to the body casing and the ground. Since the signal can be bypassed directly to the power converter without flowing through the circuit, it is possible to eliminate the cause of noise disturbance in the signal communication system of the railway and malfunction of the ground relay of the ground circuit. Also, by providing a changeover switch that connects the cooler to the midpoint or ground point of the DC circuit, during normal operation, the cooler is connected to the midpoint side of the DC circuit to bypass the leakage current, and to perform the withstand voltage test. By switching to the ground point, opening the ground switch, and applying a voltage between the power converter circuit and the ground point, the insulation performance can be examined.

[0007]

Embodiments of the present invention will be described below with reference to the drawings. In the drawings, the same reference numerals indicate the same object.
FIG. 1 is a circuit configuration diagram showing one embodiment of the present invention, and shows one phase of a three-level inverter, a cooler, and a ground circuit as an example of a power converter. Reference numerals 11a to 11d denote semiconductor elements in which diodes are connected in anti-parallel to self-extinguishing elements such as IGBTs, 12a and 12b denote diodes, 6a and 6b denote DC circuit capacitors, each of which corresponds to one phase of a three-level inverter. Reference numeral 15 denotes a cooler for cooling the semiconductor element 11 and the diode 12. 7 is a resistor, 8 is a rectifier circuit, 9
Denotes a ground switch, and 10 denotes a ground relay, which is a ground circuit for grounding the middle point of the capacitor 6 of the DC circuit. A short-circuit line 17 connects between the cooler 15 and the middle point of the three-level inverter (the middle point of the capacitors 6a and 6b of the DC circuit). Here, a three-level inverter is described as an example of the power converter, but any circuit including a switching element such as a two-level inverter and a converter (rectifier circuit) may be used. Further, the semiconductor switching element is not limited to the IGBT, but may be a GTO, a transistor, a thyristor, or the like.

As shown in FIG. 8, the semiconductor element 11 and the diode 12 are attached to the cooler 15 by a semiconductor module 13 containing the semiconductor element 11 and the diode 12.
14 is directly attached to the cooler 15 with one surface as a cooling surface, and the semiconductor device 11, the diode 12, and the cooler 15 are insulated. Semiconductor module 1
Each of the cooling units 3 and 14 has, for example, a cooling surface of about 10 cm square in order to secure cooling performance.
5, there exists a capacitance such as 16a to 16f. Although the capacitance 16 is not a physically existing capacitor, a high-frequency current generated by switching of the semiconductor element 11 may flow out to the cooler 15 as a leakage current through the capacitance 16. Also,
A grounding circuit is connected to the midpoint of the capacitors 6a and 6b of the DC circuit so that DC flows to a ground relay 10 connected to the output of the rectifier circuit 8. In the grounding circuit,
Normally, current does not flow, but when the circuit of the power conversion device grounds, a ground fault current flows, and the ground relay 10
Detecting that the ground fault current has flowed, the protection device (not shown) is activated. When performing a withstand voltage test of the power converter, the ground switch 9 is opened, a predetermined voltage is applied between the power converter and the ground side, and insulation performance is examined.

In a normal mode for operating the power converter, the semiconductor elements 11a to 11d of the power converter perform a switching operation, and generate a high-frequency current in accordance with the switching. This high-frequency current flows out to the cooler 15 side as a leakage current through the capacitance 16, passes through the short-circuit line 17, flows like a current path 18, and directly flows into the semiconductor element 11 a
Return to 11d. As described above, in the present embodiment, the leakage current passing through the capacitances 16a to 16f between the semiconductor elements 11a to 11d and the diodes 12a and 12b and the cooler 15 is:
Since it flows through the short-circuit line 17 and like the current path 18,
By bypassing the vehicle body casing and the ground circuit, it is possible to prevent noise disturbance to the signal communication system and malfunction of the ground relay 10.

FIG. 2 shows another embodiment of the present invention. FIG.
3 shows an example of a three-level inverter. The difference from FIG. 1 is that a switch 19 is provided on the short-circuit line 17 connected to the cooler 15, and the short-circuit line 17 is connected to the middle point of the three-level inverter (the middle point of the capacitors 6 a and 6 b of the DC circuit) and the ground switch 9. Be able to switch to the ground side. In the normal mode for operating the power converter, the switch 19 is switched to the middle point of the three-level inverter (the middle point of the capacitors 6a and 6b of the DC circuit), and the switching of the semiconductor elements 11a to 11d of the power converter is performed. The generated high-frequency current flows out to the cooler 15 side as a leakage current through the capacitance 16, passes through the short-circuit line 17, and
Return to the semiconductor elements 11a to 11d directly in the same manner as described above. Also,
When performing the withstand voltage test, the switch 19 is switched to the ground side, the ground switch 9 is opened to disconnect the power converter from the ground side, and a voltage for the withstand voltage test is applied. By switching the switch 19 to the ground side and opening the ground switch 9 in this way, it is possible to check the insulation between the power converter and the cooler 15 and whether the power converter is grounded. Also, the ground switch 9
If the switch 19 is connected to the ground side when the ground switch 9 is opened by interlocking the switch 19 with the
There is no need to increase the trouble of switching the switch 19 when performing the withstand voltage test.

FIG. 3 shows another embodiment of the present invention. 1 and 2 show only one phase, such as an inverter and a converter, as a power converter, but an actual power converter is configured by connecting a plurality of units 3a to 3c. FIG. 3 shows a configuration in which the cooler 15 is divided into a plurality of coolers 15a to 15c, for example, one cooler for each phase. Even in this case, the short-circuit line 17 is provided for each of the coolers 15a to 15c.
And the short-circuit line 17 connected to each of the coolers 15a to 15c is connected to the switch 19, and the capacitor 6 of the DC circuit is connected.
The configuration may be such that the midpoint between a and 6b and the ground side of the ground switch 9 are switched.

Another embodiment in which the present invention is applied to various power converters is shown in FIGS. FIG. 4 shows one cooler 15a to 15g for each phase for a power converter composed of two-level converters 3a and 3b and a two-level inverter 4.
This is an example in which is provided. The transformer 2a is a two-level converter 3.
a, the transformer 2b is connected to the two-level converter 3b, respectively, the two-level converters 3a, 3b are connected in parallel to the capacitors 6a, 6b of the DC circuit, and the two-level inverter 4 is connected to the capacitors 6a, 6b of the DC circuit. Connecting. Also in this case, the short-circuit line 17 is provided for each of the coolers 15a to 15g, the short-circuit line 17 connected to each of the coolers 15a to 15g is connected to the switch 19, and It is configured to switch between the ground switch 9 and the ground side.

FIG. 5 shows, for a power converter composed of three-level converters 3a and 3b and a three-level inverter 4, a configuration having one cooler 15a for four phases of the converter and one cooler 15b for three phases of the inverter. This is an example. The transformer 2a is connected to a three-level converter 3a,
b is connected to the three-level converter 3b, respectively, and the three-level converters 3a, 3b are connected to the capacitors 6a,
6b, and a three-level inverter 4 is connected to the capacitors 6a and 6b of the DC circuit. Also in this case, a short-circuit line 17 is provided for each of the coolers 15a and 15b, and the short-circuit line 17 connected to each of the coolers 15a and 15b is switched to a switch 19.
, And switches between the middle point of the three-level inverter (the middle point of the capacitors 6a and 6b of the DC circuit) and the ground side of the ground switch 9.

FIG. 6 shows converters 3a and 3b and a two-level inverter 4 using a thyristor bridge circuit.
In this example, one cooler 15a, 15b is provided for each thyristor bridge circuit 3a, 3b, and one cooler 15c to 15e is provided for one phase of the inverter. Transformer 2a
Is connected to the converter 3a by a thyristor bridge circuit, the transformer 2b is connected to the converter 3b by the thyristor bridge circuit, respectively, the converters 3a and 3b are connected in series, and the converters 3a and 3b connected in series are connected to the capacitor 6 of the DC circuit. , The two-level inverter 4 is connected to the capacitor 6 of the DC circuit. In this case, the grounding circuit is connected to the midpoint of two thyristor bridge circuits connected in series, provided with a short-circuit line 17 for each of the coolers 15a to 15e, and connected to the short-circuit line 1 connected to each of the coolers 15a to 15e.
7 is connected to a switch 19, and a midpoint between two thyristor bridge circuits connected in series and the ground side of the ground switch 9 are switched. If the thyristor bridge is not connected in series, the connection point of the ground circuit may be the middle point of the secondary winding of the transformer 2. When a ground relay that can be used for alternating current is used, it can be used without a rectifier circuit as shown in FIG. As described above, the present invention can be applied to power converters having various configurations, similarly to FIGS.

[0017]

As described above, according to the present invention,
Even if there is a capacitance between the power converter and its cooler, and a harmonic current generated by the switching of the power converter flows through the capacitance, the harmonic current flows through the body casing. To bypass directly to the power converter side without flowing to the power circuit or the ground circuit, and to obtain the effect of not giving noise disturbance to the signal communication system of the railway or causing the ground relay of the ground circuit to malfunction. Can be. Also, by providing a changeover switch that connects the cooler to the midpoint or ground point of the DC circuit, during normal operation, the cooler is connected to the midpoint side of the DC circuit to bypass the leakage current, and to perform the withstand voltage test. By switching to the ground point, opening the ground switch, and applying a voltage between the circuit of the power converter and the ground point, it is possible to obtain an effect that the insulation performance can be easily checked.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention.

FIG. 2 is a circuit diagram showing another embodiment of the present invention.

FIG. 3 is a circuit diagram showing another embodiment of the present invention.

FIG. 4 is a circuit diagram showing another embodiment of the present invention.

FIG. 5 is a circuit diagram showing another embodiment of the present invention.

FIG. 6 is a circuit diagram showing another embodiment of the present invention.

FIG. 7 is a diagram showing a configuration of a conventional power conversion device for an AC electric vehicle.

FIG. 8 is a diagram showing a configuration in which a semiconductor element constituting a power converter is attached to a cooler;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 AC power supply 2 Transformer 3,4 Power converter 5 Induction motor 6 Capacitor of DC circuit 7 Resistor 8 Rectifier circuit 9 Ground switch 10 Ground relay 11 Semiconductor element 12 Diode 13,14 Semiconductor module 15 Cooler 16 Electrostatic capacity 17 Short-circuit line 18 Current path 19 Switch

Continuation of the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H02M 7/5387 H02M 7/04

Claims (3)

(57) [Claims] 1. A DC circuit having a midpoint at a dividing point of a divided capacitor and connected in series as one phase to both ends of the DC circuit.
Both ends of a serial connection of the first to fourth semiconductor elements are connected to the connection point of the first and second semiconductor elements and the connection point of the third and fourth semiconductor elements of the series connection. A midpoint of the DC circuit is connected, an AC output terminal is connected to a connection point of the second and third semiconductor elements of the series connection body, and the operation of the series connection body causes a DC connection between the DC circuit and the AC terminal. And a three-level power converter for performing AC power conversion and a cooler having the semiconductor element insulated and installed in an electric vehicle, wherein a midpoint of the cooler and the DC circuit is provided. And a power converter, wherein the power converter is connected by a short-circuit line. 2. A DC circuit having a midpoint at a dividing point of a divided capacitor and connected in series as one phase to both ends of the DC circuit.
The two ends of a series connection of semiconductor elements are connected, an AC output terminal is connected to a series connection point of the series connection, and the operation of the series connection allows direct current and alternating current between the DC circuit and the AC terminal. In a power converter in which a two-level power converter for performing power conversion and a cooler having the semiconductor element insulated and mounted are installed in an electric vehicle, a short circuit between the cooler and a midpoint of the DC circuit is provided. A power converter characterized by being connected by a wire. 3. The power converter according to claim 1 or 2, wherein the power converter detects a ground circuit that grounds a middle point of the DC circuit to a ground point, and detects that a ground fault current flows in the ground circuit. A relay, comprising: a switching unit that connects the cooler and the midpoint of the DC circuit during normal operation of the power converter, and a switching unit that connects the cooler and the ground point during a withstand voltage test. Conversion device.