Electric power conversion systems – Current conversion – With means to introduce or eliminate frequency components
Patent
1985-09-17
1987-03-17
Salce, Patrick R.
Electric power conversion systems
Current conversion
With means to introduce or eliminate frequency components
363 35, 363 37, 363 51, 363126, H02M 112
Patent
active
046512667
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to a high-frequency noise absorbing circuit and, more particularly, to a high-frequency noise absorbing circuit suitable for reducing high-frequency noise that propagates through an AC power supply line of a drive unit during variable speed drive of an induction motor.
BACKGROUND ART
In an induction motor control circuit or the like for performing a DC.fwdarw.AC conversion by utilizing the switching of a transistor in a switching regulator, transistor inverter or the like, voltage undergoes a sudden change owing to the switching of the transistor and a high-frequency current is generated by the integrated component (dv/dt) of the voltage. This high-frequency current flows through the stray capacitance of the loading device (namely the capacitance between the device and earth) and through the capacitance between a power supply cable and earth, so that the power supply cable acts as an antenna and emits radio waves. These radio waves have an influence upon the carrier waves (500 KHz-2 MHz) of an AM radio and are a source of such noise as radio noise. It is desired that radio wave trouble caused by such transistor switching be prevented.
If an insulating transformer serving as means for countering radio wave trouble is provided on the side of the loading device, the emission of radio waves from the power supply cable can be prevented since the high-frequency current is not transmitted to the exterior of the loading device. However, an insulating transformer is disadvantageous in that it is costly, complicates the construction of the apparatus and results in an apparatus of larger size.
There has recently been proposed a noise absorbing circuit in which a low-pass filter comprising a capacitor and an AC reactor (inductance component) is arranged on the input side to cut the high-frequency current from a load circuit inside the apparatus so that this current is not transmitted to the power supply cable side.
According to such an arrangement, cutting of the high-frequency current caused by transistor switching can be achieved without using a transformer. Installation of a leakage current breaker is mandatory from the viewpoint of safety and prevention of fire caused by leakage current. The leakage current breaker is actuated when current exceeds 30 mA.
Consequently, when the low-pass filter is provided, there is the danger that a leakage current at the power supply frequency will be produced, thereby actuating the leakage current breaker. Further, though there is little risk of erroneous operation in a case where one apparatus is connected to one leakage current breaker, ordinarily a plurality of apparatus are connected to a single leakage current breaker. In such case, a problem arises wherein the leakage current breaker malfunctions due to a low-pass filter leakage current having a power supply frequency component. Thus, the state of the art is such that technical difficulties are encountered in fabricating a satisfactory high-frequency noise absorbing circuit.
DISCLOSURE OF THE INVENTION
In view of the foregoing, an object of the present invention is to provide an inexpensive high-frequency noise absorbing circuit in a control circuit of a loading device, which noise absorbing circuit does not employ an insulating transformer while suppressing an increase in leakage current caused by a low-pass filter, thereby enabling absorption of high-frequency noise to be satisfactorily performed.
According to the present invention, there is provided a high-frequency noise absorbing circuit in which capacitors are connected between ground and respective positive and negative terminals of a DC link section in a control circuit of a loading device having a power supply section, converter circuit section, the DC link section and an inverter circuit section.
Further, according to the present invention, there is provided a high-frequency noise absorbing circuit in which a zero-phase reactor is arranged in the power supply section.
Further, according to the present invention, there
REFERENCES:
patent: 3683271 (1972-08-01), Kobayashi
Fujioka Yoshiki
Shinohara Tatsuo
Ault Anita M.
Fanuc Ltd
Salce Patrick R.
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