JP2002136153A - Power converter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent malfunctions of the control devices in an electric vehicle or signaling apparatuses on ground due to leakage current produced in an inverter device for driving the car. SOLUTION: A heat-receiving plate 5, against which switching elements 21 and 22 are abutted and one end of a filter capacitor 8 are connected with each other with a resistor 7 in-between using a conductor 6. As the result of the insertion of the resistor 7, resonance of the stray capacitance possessed by the switching elements and the leakage current produced in a bypass path returning to the one end of the filter capacitor via the heat receiving plate, is suppressed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power converter for converting a direct current to an alternating current or a reverse conversion by a plurality of switching elements, and more particularly to a technique for reducing an induction failure caused by the switching elements.

[0002]

2. Description of the Related Art Conventionally, in a railway electric vehicle in which an induction motor is driven by a power converter that converts direct current into alternating current using a plurality of switching elements, a leakage current generated from the power converter (to the switching frequency of the inverter). (Equivalent harmonic current) reaches the induction motor, flows through the body of the electric vehicle via the stray capacitance between the armature windings of the induction motor and the motor frame, and causes adverse effects such as erroneous operation of the signal equipment on the ground was there. An example that solves this problem is disclosed in Japanese Patent Laid-Open No. 7-1.
No. 5976. In this technique, the leakage current generated from the power converter is focused on flowing into the cooling unit via a stray capacitance included in a switching element that is a component of the power converter, and the cooling unit and the power converter are connected to each other. By electrically connecting one end of the filter capacitor connected to the DC input terminal, the leakage current is directly bypassed to the filter capacitor so that the leakage current generated from the power converter does not flow out of the power converter. By doing so, induction failure due to leakage current is reduced.

[0003]

However, in the above prior art, the switching element has a stray capacitance therein and a wiring inductance of a conductive line returning from the cooling means to one end of the filter capacitor. It has been found that a resonance current flows in a closed loop path for returning the leakage current from the cooling means directly to the filter capacitor during the switching operation of the switching element. Thus, in the closed loop path, a current in which the resonance current is superimposed on the leakage current generated from the power conversion device flows. Most of the superimposed current flows in a closed loop having a low impedance, and only a small amount flows out of the power converter having a higher impedance than the closed loop path. However, when the resonance current increases, the leakage current flows into the control device in the vehicle and the signal device on the ground, and there is a problem that an induction failure due to a malfunction or the like occurs.

[0004] It is an object of the present invention to reduce an induction failure caused by malfunction of a control device in a vehicle and a signal device on the ground by suppressing a resonance current flowing through a closed loop path.

[0005]

In order to solve the above-mentioned problem, a cooling wire in a closed loop and one end of a filter capacitor are connected by a conductive line via a resistor.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As an embodiment to which a power converter according to the present invention is applied, a case where the present invention is applied to a two-level inverter of an electric vehicle will be described.

FIG. 9 shows an example of a main circuit configuration of a well-known two-level inverter device in a DC-fed inverter electric vehicle. A DC voltage is supplied from the overhead line 51 to each phase arm 20, 30, 40 via a filter circuit including a pantograph 52, a filter reactor 53, and a filter capacitor 8. Switching element 21 of each phase
The DC voltage is converted into a two-level phase voltage by the selective on / off operation of 2, 31, 32, 41, and 42, and the induction motor 54 is rotated.

FIG. 1 is a cross-sectional view in which one phase 20 is mounted. The switching element has a module structure. For example, the switching element 21 is a gate insulating bipolar transistor (IGB
T), a self-turn-off switching element 21 such as a gate turn-off thyristor (GTO) or a bipolar transistor
1 and the free wheel diode 212 are anti-parallel. Other switching elements 22, 31, 3
2, 41 and 42 have the same configuration.

In FIG. 1, a heat receiving plate (heat block)
Switching elements 21 and 22 are fixed and attached to 5 by bolts or the like (not shown). Naturally, each switching element is insulated from the heat receiving plate. Also,
The heat receiving plate 5 is attached to the housing 1 by bolts 2 via a sufficiently thick insulator 3 and electrically connected to the negative side (ground point in FIG. 1) of the filter capacitor 8 by a conductive wire 6 via a resistor 7. Connected. Here, since the heat receiving plate 5 is attached to the housing 1 via the insulator 3, a leakage current flows through the stray capacitance of the switching element to the heat receiving plate and does not flow to the housing 1, but the conductive wires 6 and the resistance A current path returning to the negative side of the filter capacitor 8 through 7 is formed.

Next, the operation at the time of switching in the circuit of FIG. 2 will be described. FIG. 2 shows the switching element 21 shown in FIG.
Is an equivalent circuit in consideration of the stray capacitance 11a of the switching element 22, the stray capacitance 11b of the switching element 22, and the wiring inductance 12 of the conductive line 6.

For example, when the switching element 22 is turned off and the switching element 21 is turned on, the switching element 22 is turned off.
A DC power supply voltage applied to the filter capacitor 8 is applied to both ends of the filter element 8, and a leakage current il flows out to the heat receiving plate 5 via the floating capacitance 11b due to a change in the collector potential of the switching element 22. This leakage current passes through the freewheel diode 222, the stray capacitance 11b, the resistor 7, and the wiring inductance 12 of the conductive line 6 and returns to the negative side of the filter capacitor 8, thereby forming a path of the leakage current il shown in the drawing. In the next mode, the switching element 21 is turned on, and at the moment when the switching element 22 is turned on, the switching element 21 is turned on.
Is applied to the filter capacitor 8, the collector potential of the switching element 22 fluctuates, and a leakage current il flows in the current path shown by the arrow in the direction opposite to the arrow.

Since the collector side of the switching element 21 is connected to the positive side of the filter capacitor 8 connected to the positive side of the DC power supply, the collector potential does not fluctuate due to turning on and off of the switching element 21. Therefore, the heat receiving plate 5 is connected through the floating capacitance 11a.
Has a negligible value compared to the leakage current flowing through the stray capacitance 11b.

Thus, the leakage current il flowing through the heat receiving plate flows through the path shown by the solid line of the arrow in FIG. However, in the path through which the leakage current shown by the solid line of the arrow flows, a resonance circuit formed by the stray capacitance 11b and the wiring inductance 12 is also formed, so that the resonance current ir1 superimposed on the leakage current il flows. Therefore, the current flowing through the path indicated by the arrow in FIG. 2 is il + ir1.

Here, the path through which the resonance current ir1 flows can be equivalently shown by the circuit of FIG. 11b
Is a stray capacitance of the switching element 22, and 13a schematically represents a collector potential of the switching element 22 at the moment when the switching element 22 is turned off and turned on. Since the path through which ir1 flows is equivalently represented by an RLC series circuit, ir1 can be easily calculated. FIG.
, The resistance value of the resistor 7 is R, the capacitance value of the stray capacitance 11b is C, the inductance of the wiring inductance 12 is L,
The collector potential of the switching element 22 becomes 0 at the moment when the switching element 22 is turned off and 21 is turned on.
Ir1 is expressed by the following equation (1).

[0015]

(Equation 1) Here, α and f are values represented by the following equations (2) and (3).

[0016]

(Equation 2)

[0017]

(Equation 3) Thus, ir1 flowing in the path of FIG. 3 has a resonance frequency determined by R, L, and C.

In the prior art disclosed in Japanese Patent Application Laid-Open No. 7-15976, the resistor 7 does not exist as shown in FIG. Therefore, an equivalent circuit when the switching element 22 is turned off and the switching element 21 is turned on is shown in FIG. 13b schematically shows the collector potential of the switching element 22 at the moment when the switching element 22 is turned off and turned on. The resonance current ir1 'is expressed by the following equation (4).

[0019]

(Equation 4)

[0020]

(Equation 5) As a result, in the prior art, the amplitude of the resonance current ir1 'returning from the heat receiving plate 5 to the negative side of the filter capacitor 8 through the floating capacitance of the switching element 22 does not attenuate, and the resonance frequency f' is expressed by Expression (5). For example, if the stray capacitance of the switching element 22 is 5 nF and the wiring inductance of the conductive line 6 is 3 μH, the resonance frequency f ′ of ir1 ′ is 1.3 MHz. Here, in FIG.
In the path where 1 'flows, there is a resistance component (not shown) of the conductive line 6. Accordingly, the resistance component of the conductive wire 6 and the resistance component 541 of the armature winding of the induction motor 54
Inverter and induction motor 54 by the amount determined by the ratio of
A resonance current ir2 'having a resonance frequency f' also flows through the conductive wire connecting the control signal and the inverter, and the resonance current ir2 'superimposed on the leakage current generated from the inverter causes malfunction of a control device in the vehicle and a signal device on the ground. Induction failure occurs.

In the embodiment shown in FIG. 1, a damping resistor 7 is inserted between the heat receiving plate 5 and the negative side of the filter capacitor 8 to suppress the resonance current ir1. From equation (1), the ir1 by inserting a resistance attenuation term e ^- due to the presence of ^{alpha t,} resonance generated from the heat receiving plate 5 through the stray capacitance of the switching element 22 on the negative side returns to the path of the filter capacitor 8 The current ir1 can be suppressed. Further, the resonance current ir2 flowing through the conductive line connecting the inverter and the induction motor 54 is also suppressed by the amount determined by the resistance component and the resistance 7 of the conductive line 6 and the resistance component 541 of the armature winding of the induction motor 54. Can
Resonant current i superimposed on leakage current generated from inverter
Induction disturbance due to r2 can be reduced.

The damping effect of the resistor 7 will be described with reference to specific measurement results. FIG.
FIG. 8 shows a spectrum analysis result of a leakage current flowing through the conductive wire 6 when the technology of Japanese Patent No. 976 is used.
Shows the result of spectrum analysis of the leakage current flowing through the conductive wire 6 when the resistance 7 is set to 10Ω in the present embodiment. The resonance frequency due to the stray capacitance 11b of the switching element and the wiring inductance 12 of the conductive line 6 is 1.1 MHz.
It is near. In the prior art, 1.
While the current spectrum around 1 MHz is about 800 mA, the current spectrum around 1.1 MHz is about 100 mA in this embodiment, and it can be seen that the effect of the resonance current can be suppressed to 1/8 or less by the resistor 7. .

Although the description has been given of one phase 20, the same applies to the other phases 30 and 40.

Next, another embodiment of the present invention will be described with reference to FIG. The difference from the embodiment shown in FIG. 1 is that a ground switch 9 of the housing is provided, and the ground side of the ground switch 9 and the heat receiving plate 5 are connected by a conductive wire 6 via a resistor 7. is there. The ground switch 9 is for performing an insulation test between the charged part of the main circuit and the housing. During the insulation test, the ground switch 9 is opened to apply a predetermined voltage between the charged part of the main circuit and the housing. You. At this time, the conductive wires 6 from the heat receiving plate 5
Is separated from the main circuit charging section by the ground switch, so that there is no problem in the insulation test between the charging section of the main circuit and the housing.

According to the present embodiment, a simple structure in which the heat receiving plate and the negative side of the filter capacitor are connected via a resistor reduces induction troubles such as malfunctions of control equipment in the vehicle and signal equipment on the ground. can do.

In the above description, a two-level inverter has been described as an example of the power converter, but the same effect can be obtained by applying the present invention to a multi-level inverter of three or more levels, a converter, and the like. In the above description, the electric vehicle is described as an example. However, the present invention is not limited to the electric vehicle, and any power conversion device in which a heat receiving plate in contact with a switching element and one end of a power supply are connected by a conductive wire may be used. By applying the method, it is possible to suppress a resonance current in a path returning from one end of the switching element to one end of the power supply through the heat receiving plate.

[0027]

As described above, according to the present invention, when switching is performed with a simple configuration in which the heat receiving plate and one end of the filter capacitor are connected via a resistor, the switching is formed between the heat receiving plate and the filter capacitor. It is possible to suppress a resonance current due to a wiring inductance of a conductive line that connects the stray capacitance, the heat receiving plate, and one end of the filter capacitor via a resistor, and to reduce an induction failure generated by switching of the power conversion device.

[Brief description of the drawings]

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

FIG. 2 is a diagram illustrating a path of a resonance current flowing due to a stray capacitance between a collector and a base of a switching element and a wiring inductance of a ground line.

FIG. 3 is a diagram for explaining an equivalent circuit when a switching element is turned off from 22 to 21;

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

FIG. 5 is a diagram showing an embodiment of the related art.

FIG. 6 shows a conventional technology in which a switching element 22 is turned off →
The figure explaining the equivalent circuit at the time of 21 turn-on.

FIG. 7 is a diagram showing a result of frequency analysis of a leakage current flowing through a conductive wire 6 according to a conventional technique.

FIG. 8 is a diagram showing a result of frequency analysis of a leakage current flowing through the conductive wire 6 according to one embodiment of the present invention.

FIG. 9 is a diagram illustrating an example of a main circuit configuration of a two-level inverter.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Inverter housing, 2 ... Bolt, 3 ... Insulator, 4 ... Heat sink, 5 ... Heat receiving plate, 6 ... Conductive wire, 7 ... Resistor, 8 ... Filter capacitor, 9 ... Grounding switch, 11a, 11b ... Switching element Collector-base stray capacitance of 12
Wiring inductance of the conductive wire, 20, 30, 40... Each phase arm of the inverter, 21, 22, 31, 32, 41,
42: switching element (module configuration), 51: overhead wire, 52: pantograph, 53: filter reactor,
54: induction motor, 541: resistance component of armature winding, 5
42: Inductance component of armature winding, 55: Wheel.

 ──────────────────────────────────────────────────の Continuing on the front page (72) Inventor Shoichi Hisada 1070 Ma, Hitachinaka-shi, Ibaraki Prefecture Within Mito Transport Systems Division, Transportation Systems Division, Hitachi, Ltd. (72) Inventor Kiyoshi Nakata Ichige, Hitachinaka-shi, Ibaraki 1070 F-term (reference) Mito Transport Systems Division, Transportation Systems Division, Hitachi, Ltd. 5H007 AA01 BB06 CA01 CB04 CB05 HA02 HA03 HA05 5H115 PA03 PC01 PG01 PI03 PU09 PV07 PV09 PV23 UI27

Claims (4)

[Claims] A cooling means is connected from one end of a filter capacitor connected to both ends of a DC power supply to one end of each phase arm for performing a switching operation, and is in contact with a switching element constituting each phase arm. In the power converter in which the other end of the filter capacitor and the other end of each of the phase arms are connected, the power conversion device further includes means for connecting the cooling means and the other end of the filter capacitor with a conductive wire via a resistor. A power converter characterized by the above-mentioned. 2. A cooling means connected from one end of a filter capacitor connected to both ends of a DC power supply to one end of each phase arm for performing a switching operation, and being in contact with a switching element constituting each phase arm. In the power converter in which the other end of the filter capacitor is connected to the other end of each of the phase arms, a housing in which the power converter is housed is insulated from the cooling unit, and the cooling unit and the cooling unit are connected to each other. A power converter comprising: means for connecting the other end of the filter capacitor with a conductive line via a resistor. 3. An electric vehicle power converter for converting a DC stored in a filter capacitor into an AC by a switching operation of a plurality of switching elements and supplying the converted AC to a motor for driving an electric vehicle. A power converter for an electric vehicle, comprising: means for connecting a cooling means contacting a switching element and the other end of the filter capacitor with a conductive wire via a resistor. 4. A power converter having a configuration in which a switching element and a cooling means are in contact with each other via an insulator, further comprising a ground switch between a power supply of the switching element and a ground point, wherein the cooling means and the power A power converter, wherein the power converter is insulated from a housing in which the converter is housed, and the cooling means and the ground point side of the ground switch are connected by a conductive wire via a resistor.