Power conversion device

In order to reduce noise current leaking out from a frame to which semiconductor devices constituting a three-level power conversion circuit are attached to the outside of a power conversion device, the frame to which the semiconductor devices constituting the three-level power conversion circuit with which the power conversion device is equipped are attached is configured to be electrically connected to a neutral point of the three-level power conversion circuit. The noise current leaking out from the frame is thereby drawn back to the neutral point of the three-level power conversion circuit to suppress the flowing out of the noise current to the outside of the power conversion device and reduce the noise current.

TECHNICAL FIELD

The present invention relates to a power converter including a three-level power conversion circuit, and is suitable as a power converter for railway systems.

BACKGROUND ART

A three-level power converter can divide a direct current power supply voltage with two sets of smoothing capacitors, and can select and output three types of potentials, including positive, negative, and intermediate potentials, of the direct current power supply voltage. Accordingly, this is a power converter used in a case where a direct current power supply voltage is high, or in a case where a harmonic of a voltage and a current applied to an alternating current load or an alternating current power supply to be connected is desired to be reduced.

PTL 1 discloses a technique of reducing a withstand voltage of a device involved in charging and reducing the size and cost of the device by providing an initial charging circuit for a smoothing capacitor included in a power converter, which includes a three-level PWM converter and a PWM inverter.

CITATION LIST

Patent Literature

SUMMARY OF INVENTION

Technical Problem

With a switching operation of a semiconductor device constituting a main circuit, a noise current flows to a frame of a power unit via a stray capacitance between the semiconductor device and the frame. The frame of the power unit and the power converter are conducted via an attachment portion, making the noise current flow out to the power converter. In addition, since the power converter is connected to a vehicle body via a ground circuit, the noise current that flows to the outside of the power converter also flows out to the vehicle body. When this noise current flows out to the vehicle body, there is a problem that a high-frequency potential variation is caused in the vehicle body and a failure occurs in a signal device.

Solution to Problem

In order to solve the above problems, a power converter according to the invention includes a three-level power conversion circuit, in which a frame to which a semiconductor device constituting the three-level power conversion circuit is attached is electrically connected to a neutral point of the three-level power conversion circuit.

Advantageous Effect

According to the invention, the frame to which the semiconductor device constituting the three-level power conversion circuit is attached is electrically connected to the neutral point of the three-level power conversion circuit. Thereby, the noise current generated from the three-level power conversion circuit can be drawn back to the three-level power conversion circuit, and the noise current flowing out to the outside of the power converter can be reduced.

DESCRIPTION OF EMBODIMENTS

Hereinafter, first and second embodiments according to the invention will be described with reference to the drawings as modes for carrying out the invention.

First Embodiment

FIG. 1is a diagram showing an example of an overall configuration of a power converter according to the first embodiment of the invention. AlthoughFIG. 1shows a power converter to be mounted on a railway vehicle, the invention is widely applicable not only to an electric vehicle but also to a power converter used in power electronics related fields such as industrial use.

A power converter1includes a converter power unit2, which is a three-level power conversion circuit, and an inverter power unit3. The power converter1is mounted, for example, for an alternating current vehicle, and takes in a single-phase alternating current power from an alternating current overhead line via a pantograph15by passing the power through a vacuum alternating current contactor14and lowering the voltage with a main transformer13.

The alternating current power taken into the power converter1passes through an electromagnetic contactor9or10and is then rectified by the converter power unit2. The rectified direct current power is taken into the inverter power unit3, and the alternating current power obtained by conversion is supplied to a main motor4and controlled.

Further, in the power converter1, the inverter power unit3and the converter power unit2are three-level circuits, and have a configuration in which a neutral point is grounded. Regarding the grounding of the neutral point, inFIG. 1, the neutral point is configured to be grounded via a ground resistor11and a ground switch12. Here, the ground switch12is turned on in a normal state including operation, and is turned off in a special case such as a withstand voltage test.

As a semiconductor device constituting the converter power unit2and the inverter power unit3, semiconductor device5and clamp diodes6that perform a switching operation as a main circuit are attached to frames of the power units. In addition, on the other hand, it is also general that a cooler for the power unit is attached to each frame of the power units as shown in, for example,FIG. 3, which will be described later.

In addition, regarding the semiconductor device constituting the converter power unit and the inverter power unit, as the semiconductor devices that perform a switching operation as a main circuit, IGBT, hybrid SiC (a combination of IGBT and a SiC Schottky barrier diode), or full SiC is adopted.

Further, althoughFIG. 1shows a configuration of the power converter in a case of an alternating current vehicle in which a single-phase alternating current power is taken in from the alternating current overhead line, it is a matter of course that the invention can also be applied to a power converter in a case where a direct current power is taken in from a direct current overhead line. In this case, the power converter includes an inverter power unit, which is a three-level circuit.

FIG. 2is a diagram showing connection between a configuration of a part of the power conversion circuit included in the power converter according to the first embodiment and a vehicle body.

A power converter17(whose outline is in solid line shown inFIG. 2) is attached to a vehicle body16. In addition, a neutral point27of the three-level inverter is configured to be electrically connected to a frame18(whose outline is in broken line shown inFIG. 2) of the power unit to which semiconductor devices19to22and clamp diodes23and24constituting one phase of the inverter are attached. Here, as shown inFIG. 3, the frame18of the power unit also serves as a frame of the cooler for the power unit.

Specifically, as shown inFIG. 2, the neutral point27of the three-level inverter is configured to be connected to the vehicle body16(that is, ground) via the ground resistor11and a noise absorbing core29via the ground switch12, and the frame18of the power unit (and the cooler) is configured to be connected to the vehicle body16via the noise absorbing core29passing through the ground switch12.

Here, in the invention, by adopting a configuration in which the frame to which the semiconductor devices constituting the three-level power conversion circuit are attached is electrically connected to the neutral point of the three-level power conversion circuit, a noise current generated from the three-level power conversion circuit is drawn back to the three-level power conversion circuit, and the noise current can be prevented from flowing out to the outside of the power converter. The configuration shown inFIG. 2can be said to be a configuration in which the above basic configuration according to the invention is added to an existing ground circuit (grounding via a ground resistor and a ground switch). In addition, the noise absorbing core29is provided to further reduce the noise current to enhance the effect.

With the above configuration, the noise current, which flows to the frame18of the power unit (and the cooler) along with a potential variation caused by the switching operation of the semiconductor devices19to22constituting the main circuit, passes through the noise absorbing core29back and forth and then flows to the neutral point27of the three-level inverter via the ground resistor11, as indicated by the dotted line of the arrows inFIG. 2. Accordingly, the noise current can be prevented from positively flowing to the power converter17and the vehicle body16, the noise current to the vehicle body can be reduced, and the communication failure to the signal device can be reduced.

The noise absorbing core29is a ferrite core, and by flowing a current into the core, the magnetic energy generated by the noise current is converted into heat by the core for consumption, and the noise current is reduced.

As described above, flowing the noise current flowing to the frame18of the power unit (and the cooler) to the neutral point27of the three-level inverter by using the noise absorbing core29is effective means for reducing the noise current. However, the noise absorbing core29is not an essential constituent element, and as long as, at a minimum, a configuration in which the frame18of the power unit (and the cooler) is connected to the neutral point27of the three-level inverter is adopted, it is possible to prevent the noise current from flowing to the power converter17and the vehicle body16.

FIG. 3is a diagram showing the semiconductor devices (the semiconductor devices constituting the main circuit and the clamp diode) of the power converter according to the first embodiment and the frame of the power unit on which the semiconductor devices are attached.

When configuring the power unit, semiconductor devices32are attached to one side of a frame34of the power unit, and power unit coolers33are attached to the other side. In the invention, along with the potential variation caused by the switching operation of the semiconductor devices constituting the main circuit, the noise current flows to the frame of the power unit via the stray capacitance between the semiconductor devices and the frame. However, by connecting the frame of the power unit to the neutral point of the three-level inverter, the noise current can be positively prevented from flowing out to the vehicle body.

FIG. 4shows diagrams showing an example of a wiring and an example of a component of the noise absorbing core used in the power converter according to the first embodiment.

FIG. 4(a)shows an example of a wiring between the noise absorbing core29and a wiring that electrically connects the neutral point27of the three-level inverter to the frame18of the power unit (and the cooler) to which the semiconductor devices are attached, as shown inFIG. 2. A wiring28(shown by a solid line) electrically connected to the neutral point27of the three-level inverter and a wiring30(shown by a broken line) electrically connected to the frame18of the power unit (and the cooler) to which the semiconductor devices are attached are wound around the noise absorbing core29for a plurality of times and then directly connected to each other. That is, the connection configuration other than winding the wiring28and the wiring30around the noise absorbing core29for a plurality of times is the same as the connection configuration shown inFIG. 2.

In this way, the wiring30electrically connected to the frame18and the wiring28electrically connected to the neutral point27of the three-level inverter are wound around the noise absorbing core29for a plurality of times, so that the attenuation effect for the noise current flowing to the frame18by the noise absorbing core29can be enhanced, and the noise can be further reduced.

FIG. 4(b)shows a perspective view of an example of a component adopted as the noise absorbing core.

Second Embodiment

FIG. 5is a diagram showing connection between a configuration of a part of a power conversion circuit according to the second embodiment and a vehicle body. The same reference numerals are denoted by the same elements as the configuration shown inFIG. 2.

As a difference in configuration from the first embodiment, a core is used for reducing the noise in the first embodiment, while a capacitor is used in the second embodiment instead of the core. That is, as shown inFIG. 5, one end of a noise absorbing capacitor31is connected to the neutral point27side of the three-level inverter, and the other end of the noise absorbing capacitor31is connected to the frame18side of the power unit (and the cooler).

With the above configuration, the noise current flowing to the frame18of the power unit (and the cooler) passes through the noise absorbing capacitor31and then flows to the neutral point27of the three-level inverter via the ground resistor11, as shown by the dotted line of arrows inFIG. 5. Accordingly, the noise current can be prevented from positively flowing to the power converter17and the vehicle body16, the noise current to the vehicle body can be reduced, and the communication failure to the signal device can be reduced. That is, when the configuration according to the second embodiment is adopted, the same effect as the first embodiment can also be obtained.

REFERENCE SIGN LIST