JP2009027089A - Shield structure - Google Patents

Abstract

An object of the present invention is to suppress the external influence of a magnetic field caused by a current flowing in a power cable.
Power cables 14p and 14n through which current from a battery 10 flows are covered with shields 42p and 42n. Then, both ends of the shields 42p and 42n are connected by connecting lines 44 and 46. As a result, leakage of the magnetic field to the outside due to the current flowing through the power cable 14p is suppressed.
[Selection] Figure 1

Description

  The present invention relates to a shield structure that covers an output line from a DC power supply.

  Conventionally, many devices are mounted on a vehicle, and a signal processing circuit or the like may be adversely affected by incoming noise. Therefore, the noise generation portion is covered with a shield to prevent the noise from spreading as much as possible. For example, in an inverter or converter, noise is generated along with the switching. In particular, since a large current flows in an inverter for a drive motor of an electric vehicle, noise is likely to be generated from the power line due to the current flowing by switching.

  In view of this, it has been proposed that the power cable connected to the positive and negative buses of the inverter is covered with a cylindrical member and shielded to prevent leakage of electromagnetic waves (Patent Document 1).

JP 2005-268716 A

  However, in the above conventional example, a current flows through the shield, and a magnetic field corresponding to the current leaks to the outside, which may affect peripheral devices.

  The present invention includes a pair of positive and negative output lines from a DC power source, an inverter connected to the pair of output lines and performing power conversion, a pair of shields formed of a conductive material and covering the pair of output lines, respectively. And connecting each end of the pair of shields to form a circuit including the pair of shields.

  Moreover, it is preferable that the direct-current power source is for converting power from a battery by a DC / DC converter.

  The present invention also provides a pair of positive and negative output lines from a DC power source, a converter connected to the pair of output lines and performing power conversion, a pair of shields formed of a conductive material and covering the pair of output lines, respectively. And connecting ends of the pair of shields to form a circuit including the pair of shields.

  Further, it is preferable that the shield is connected to the ground at at least one place, and has a current detection means for detecting a current flowing in a portion connecting the ends of the pair of shields.

  Thus, according to the present invention, leakage of noise and magnetic field can be prevented by the shield covering the output line.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a diagram illustrating the overall configuration of the embodiment. The battery 10 has an output voltage of about 200V, for example. Various types of battery 100 such as a nickel metal hydride battery, a lithium ion battery, and a fuel cell can be used. A converter 12 is connected to the battery 10. The converter 12 boosts the output voltage of the battery 10 (for example, about 300 V), but can also step down depending on conditions. A positive power supply line 14p and a negative power supply line 14n are connected to the positive / negative power supply output of the converter 12. The other ends of the positive power supply line 14p and the negative power supply line 14n are connected to the positive and negative buses of the inverter 16, respectively. The inverter 16 has a three-phase output, which is connected to a three-phase AC motor 18. With such a system, the voltage of the battery 10 can be boosted by the converter 12, and the boosted DC power can be converted into a desired AC current by the inverter 16 to drive the motor 18. The motor 18 is, for example, a vehicle driving motor, and can control the output torque of the motor 18 by controlling an inverter in accordance with an output torque command or the like.

  Here, the converter 12 has a coil 20 having one end connected to the positive side of the battery 10. The other end of the coil 20 is connected to a connection point between the two switching elements 22p and 22n. That is, the collector of the positive switching element 22p is connected to the positive power supply line 14p via the diode 24, and the emitter of the negative switching element 22n is connected to the negative electrode of the battery 10 and the negative power supply line 14n. A connection point between the emitter of the switching element 22 p and the collector of the switching element 22 n is connected to the coil 20. A diode that allows current to flow from the emitter to the collector side is connected between the emitter and collector of each switching element 22p, 22n. A smoothing capacitor 26 is provided between the positive power line 14p and the negative power line 14n. Therefore, by alternately turning on the switching elements 22p and 22n, DC / DC conversion according to the duty ratio can be performed.

  The inverter has a configuration in which three arms in which two switching elements are connected in series between the positive and negative buses are arranged in parallel, and the midpoint of each arm is connected to the three-phase input of the motor 18. Each switching element is provided with a diode as described above.

  In the present embodiment, the positive and negative power supply lines 14p and 14n are covered with cylindrical shields 42p and 42n, respectively. The converter side ends and the inverter side ends of the shields 42p and 42n are connected by connecting lines 44 and 46, respectively.

  That is, the high-voltage power supply lines 14p, 14n connecting the converter 12 and the inverter 16 are shielded by coaxial shields 42p, 42n, and the shields 42p, 42n are connected to each other by connecting lines 44, 46. Therefore, a circuit that is electrically connected as a whole is formed.

  A coaxial cable can be used for the power supply lines 14p and 14n and the shields 42p and 42n, but it is desirable that they are in close contact with each other as long as they are insulated. The allowable currents of the shields 42p and 42n are preferably equal to or slightly smaller than the power supply lines 14p and 14n serving as the core wires.

  With such a configuration, the induced current I2 corresponding to the current I1 flowing through the power supply lines 14p and 14n flows in the opposite direction to the shields 42p and 42n, whereby the magnetic field generated by the current I1 is canceled by the current I2, and the magnetic field is Can be shielded. Therefore, noise that adversely affects other electronic devices can be reduced.

  In addition, by generating the induction current in this way, the high-frequency current itself flowing in the power supply lines 14p and 14n can be suppressed. Furthermore, although the shields 42p and 42n generate heat, it is also preferable to use this heat for heating or the like.

  In addition, as shown by a broken line in FIG. 1, it is also preferable to connect one or both of the connecting lines 44 and 46 to the ground. Thereby, a high frequency current can be reduced and a sufficient shielding effect can be obtained.

  In addition, as shown in FIG. 3, it is also preferable to provide shields 42p and 42n on the positive power supply line 34p connecting the converter 12 and the battery 10 and the negative power supply line 34n. As a result, the shielding effect by the shields 42p and 42n is obtained as described above.

  Further, FIG. 4 shows an example in which a branch line 36p, 36n is provided on the positive power supply line 34p for connecting the converter 12 and the battery 10, and the negative power supply line 34n is connected to another converter 48. Yes. In this example, shields 42p and 42n are provided on the pair of branch lines 36p and 36n. Converter 48 may be a DC / DC converter or an AC converter.

  FIG. 5 shows another embodiment. In this example, the shields 42p and 42n are arranged on the power supply lines 34p and 34n between the battery 10 and the converter 12 in the same manner as in FIG. 3, but the shields 42p and 42n are arranged at the positions shown in FIGS. You may arrange.

  A positive power supply line 34p and a negative power supply line 34n are connected to the positive electrode and the negative electrode of the battery 10, respectively. These positive and negative power supply lines 34p are shielded by shields 42p and 42n, but the positive power supply line 34p and the negative power supply line 34n are shielded. A system main relay SMR is arranged on the battery 10 side of the line 34n. Therefore, the battery 10 is disconnected from the converter 12 by turning off the system main relay SMR. The negative shield 42n is connected to the ground.

  The ends of the shields 42p and 42n are connected by connecting lines 44 and 46. The connecting line 44 is provided with a resistor 50, and both ends of the resistor 50 are connected to the detecting unit 52. . Therefore, the detection unit 52 can measure the current flowing through the connection line 44 by detecting the voltage across the resistor 50. In addition, it is preferable that the part connected to the ground of the negative shield 42n is the same as or close to the part to which the connecting line 44 provided with the resistor 50 is connected. The detection unit 52 is configured by an operational amplifier that amplifies the voltage across the resistor 50, for example.

  Here, the current flowing through the connection lines 44 and 46 is equal to the current flowing through the positive shield 42p. The current flowing through the positive shield 42p is generated based on a magnetic field generated based on the current flowing through the positive power supply line 34p, and is inversely proportional to the current flowing through the positive power supply line 34p. Therefore, the current flowing through the positive power supply line 34p can be detected by the voltage detected by the detection unit 52.

  The detection voltage V1 of the detection unit 52 is supplied to the comparator 54. The comparator 54 compares it with a preset reference voltage V2. This reference voltage V2 is set according to the maximum current allowable in this circuit. Therefore, the fact that V1 is larger than V2 means that the current flowing through the positive power supply line 34p exceeds the allowable maximum current (overcurrent flows).

  When the comparator 54 detects that an overcurrent flows, the comparator 54 outputs a signal to that effect, for example, an H level signal. The output of the comparator 54 is sent to the SMR control unit 56. When the SMR control unit 56 detects an overcurrent, the system main relay SMR is turned off. This can protect the system from overcurrent. The comparator 54 can be configured with a normal operational amplifier.

  In particular, in the present embodiment, the current flowing through the connection line 44 is detected instead of directly detecting the current flowing through the positive power supply line 34p. Therefore, effective detection can be performed.

  When detecting the current flowing through the positive power supply line 34p, it is conceivable to arrange a resistor in the positive power supply line 34p and detect the voltage across the resistor. However, when the voltage of the battery 10 is 200V, the positive power supply line 34p is also 200V, and this high voltage is applied to the voltage detection circuit that is in direct contact, and protection measures for the high voltage portion must be taken. . On the other hand, it is conceivable to detect the current flowing in the positive power supply line 34p using a Hall element or a transformer, but in this case, there is a problem that the detection circuit becomes large or expensive.

  According to this embodiment, the current flowing through the shield 42p is detected at the connecting line 44 in accordance with the current flowing through the positive power supply line 34p. Therefore, according to the present embodiment, it is possible to shield the electromagnetic wave and the magnetic field by the shields 42p and 42n, and to obtain an effect that the current flowing through the high-voltage power supply line can be detected while being insulated from the high-voltage power supply line.

  FIG. 6 shows an example of the current I1 flowing through the positive power supply line 34p, the current I2 flowing through the shield 42p, the voltage V1 detected by the detector 52, and the reference voltage V2. As described above, the current I2 flows through the shield 42p according to the change of the current I1 flowing through the positive power supply line 34p, and this is detected by the detector 52.

  In the case of the present embodiment, the current I2 flows through the circuit of the shield 42p, the connection line 44, the shield 42n, and the connection line 46. Therefore, the current flowing through the connection line 46 may be detected. Therefore, it is possible to perform overcurrent protection based on a sudden current change such as a ground fault of the positive power supply line 34p or a short circuit of the positive and negative power supply lines 34p and 34n.

It is a figure which shows the whole structure of embodiment. It is a figure explaining the electric current which flows into a shield. It is a figure which shows the other example about the location which attaches a shield. It is a figure which shows the further another example about the location which attaches a shield. It is a figure which shows the example which added the structure of the electric current detection. It is a figure which shows the electric current which flows through each part, and the voltage to detect.

Explanation of symbols

  10 battery, 12 converter, 14p, 34p positive power line, 14n, 34n negative power line, 16 inverter, 18 motor, 20 coils, 22p, 22n switching element, 24 diode, 26 capacitor, 36p, 36n branch line, 42p , 42n shield, 44, 46 connecting line, 48 converter, 50 resistor, 54 comparator, 56 control unit.

Claims (4)

A pair of positive and negative output lines from a DC power supply;
An inverter connected to the pair of output lines and performing power conversion;
A pair of shields formed of a conductive material and covering each of the pair of output lines;
Including
A shield structure characterized in that each end of the pair of shields is connected to form a circuit including the pair of shields. The shield structure according to claim 1,
The direct current power source is a shield structure characterized in that the battery converts power by a DC / DC converter. A pair of positive and negative output lines from a DC power supply;
A converter connected to the pair of output lines and performing power conversion;
A pair of shields formed of a conductive material and covering each of the pair of output lines;
Including
A shield structure comprising a pair of shields connected to each end of the pair of shields to form a circuit including the pair of shields. In the shield structure according to any one of claims 1 to 3,
The shield is connected to ground in at least one place;
A shield structure comprising current detection means for detecting a current flowing in a portion connecting the ends of the pair of shields.

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