LEAKAGE CURRENT REDUCING APPARATUS

• US 20130147419A1
• Filed: 06/16/2011
• Published: 06/13/2013
• Est. Priority Date: 08/26/2010
• Status: Active Grant

• Current Assignee: Mitsubishi Electric Corporation
• Original Assignee: Mitsubishi Electric Corporation
• Inventors: Sakai, Takuya, Azuma, Satoshi
• Granted Patent: US 9,099,945 B2
• Time in Patent Office: Days
• US Class Current: 318/722
• CPC Class Codes: H02M 1/12 Arrangements for reducing harmonics from ac input or output
• CPC Class Codes: H02M 1/123 Suppression of common mode voltage or current
• CPC Class Codes: H02M 1/44 Circuits or arrangements for compensating for electromagnetic interference in converters or inverters
• CPC Class Codes: H02M 5/4585 having a rectifier with controlled elements
• CPC Class Codes: H02P 27/04 using variable-frequency supply voltage, e.g. inverter or converter supply voltage

Abstract

In a system supplying power from an AC power supply to a three-phase motor via a converter and an inverter, a leakage current reducing apparatus is connected to a connection line between the AC power supply and the converter. A common mode transformer detects, as common mode voltage, common mode current flowing from the AC power supply to the connection line. The common mode voltage is inputted to a voltage amplifier via a filter apparatus. Output voltage obtained by voltage amplification passes through a capacitor and then is applied as an AC component to a neutral point of capacitors connected in a Y-connection fashion, so as to have the same phase as that of the common mode voltage. Thus, current having the same phase as that of the common mode current is supplied via the capacitors to the converter through the connection line, thereby reducing the common mode current.

Claims

1. A leakage current reducing apparatus which is provided between a first electric apparatus and a second electric apparatus, via a plurality of connection lines connected between the first and the second electric apparatuses, and reduces leakage current flowing from the first electric apparatus to the connection lines, the leakage current reducing apparatus comprising:

a voltage detection section having main windings connected in series to the connection lines, and a winding for leakage current detection, and detecting, as detected voltage, the leakage current flowing from the first electric apparatus to the connection lines by the winding for leakage current detection;

a filter apparatus receiving the detected voltage;

a voltage amplifier amplifying the output of the filter apparatus and outputting the amplified voltage as output voltage; and

a current supply section provided, on the second electric apparatus side with respect to the voltage detection section, between the first and the second electric apparatuses, and supplying current having substantially the same phase as the phase of the leakage current, to the connection lines, wherein

the current supply section has a plurality of injection capacitors whose terminals on one side are connected to the connection lines and whose terminals on the other side are commonly connected to a common connection point grounded via an impedance device, and applies the output voltage to the common connection point, thereby supplying the current having substantially the same phase as the phase of the leakage current from the injection capacitors to the connection lines.

4. The leakage current reducing apparatus according to claim 1, wherein the output voltage is controlled by the voltage amplifier so as to make the leakage current approach zero.

5. The leakage current reducing apparatus according to claim 4, wherein a power supply for driving the voltage amplifier is generated by power reception from the connection lines, and a power reception point on the connection lines is on the first electric apparatus side with respect to the current supply section.

6. The leakage current reducing apparatus according to claim 1, wherein the filter apparatus adjusts the amplitude and the phase of the detected voltage for each frequency.

7. The leakage current reducing apparatus according to claim 1, wherein the filter apparatus is composed of one filter whose pass frequency range can be adjusted or a plurality of filter circuits whose pass frequency ranges can be adjusted and which are connected in parallel or in series or connected in series and parallel in a multistage fashion.

8. The leakage current reducing apparatus according to claim 1, wherein the filter apparatus is set so as to restrict pass of, among frequency components of the detected voltage, a frequency component at which the phase of current outputted from the voltage amplifier inverts from the phase of the leakage current.

9. The leakage current reducing apparatus according to claim 8, wherein the filter apparatus is configured such that the constant thereof can be adjusted and the phase inverting frequency can be adjusted by adjustment of the constant.

10. The leakage current reducing apparatus according to claim 1, wherein

the filter apparatus has a plurality of filter circuits which respectively restrict pass of different frequency components of the detected voltage that is inputted,

the voltage amplifier has a plurality of voltage amplifier circuits which respectively receive and amplify the outputs of the filter circuits, and an output filter which reduces mutual interference among the voltage amplifier circuits, and

the current supply section applies output voltage outputted via the output filter from each of the voltage amplifier circuits, to the common connection point.

11. The leakage current reducing apparatus according to claim 10, wherein the output filter is set so as to pass a frequency component only in a pass frequency band of the filter circuit on the voltage amplifier circuit input side that is connected to the output filter.

12. The leakage current reducing apparatus according to claim 10, wherein the filter apparatus has two filter circuits as the plurality of filter circuits, and the constant of each of the filter circuits is adjusted such that one of the filter circuits passes only a high-frequency component higher than a frequency at which the phase of the output voltage of each of the voltage amplifier circuits inverts from the phase of the detected voltage, and the other one of the filter circuits passes only a low-frequency component lower than the frequency.

13. The leakage current reducing apparatus according to claim 1, wherein in the current supply section, a phase inverting frequency at which the phase of the output voltage inverts from the phase of the detected voltage can be adjusted by adjustment of the capacitances of the injection capacitors.

14. The leakage current reducing apparatus according to claim 1, wherein

one of the first and the second electric apparatuses is an inverter of a pulse width modulation type, and

the filter apparatus restricts pass of, among frequency components of the detected voltage;

a frequency component equal to or lower than a carrier frequency of the inverter.

15. The leakage current reducing apparatus according to claim 1, wherein the first electric apparatus is an AC power supply, and the second electric apparatus is a converter which converts AC power of the AC power supply to DC power.

16. The leakage current reducing apparatus according to claim 1, wherein the first electric apparatus is a converter which converts AC power to DC power, and the second electric apparatus is an inverter which converts the DC power from the converter to AC power.

2-3. -3. (canceled)

17-19. -19. (canceled)