RFI filter for a frequency converter
First Claim
1. A filter for avoiding mains retro-action in the form of electrical noise transmitted via a supply conductor, comprising the supply conductor being connected on one end to a voltage source and on another end to an electronic circuit which generates the electrical noise;
- the filter in the direction from the voltage source incorporating a coil inserted serially in the supply conductor, and, branching from the supply conductor, an earthed serial connection including a noise-decoupling capacitor and a resistor, and wherein a switch is connected in parallel to the resistor, the switch being movable between an open and closed position in response to a control signal issued from a controller.
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Accused Products
Abstract
The invention relates to an RFI filter used for avoidance of mains retro-action in the form of radio noise. RFI filters are connected to frequency converters in order to reduce radio noise transmitted via conductors. These filters comprise large noise-decoupling capacitors which are connected to earth, and during start up of the frequency converter the capacitors cause leakage currents to earth. This gives rise to problems in those circumstances, where a circuit breaker is connected to a frequency converter and an RFI filter, because the leakage current is higher than the trigger current for the circuit breaker. The solution to this problem is to place a resistor in series with the noise-decoupling capacitor and parallel with the resistor to place a switch, which can be opened or closed with a control signal from a controller. The invention also concerns a method for activation of an RFI filter.
102 Citations
12 Claims
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1. A filter for avoiding mains retro-action in the form of electrical noise transmitted via a supply conductor, comprising the supply conductor being connected on one end to a voltage source and on another end to an electronic circuit which generates the electrical noise;
- the filter in the direction from the voltage source incorporating a coil inserted serially in the supply conductor, and, branching from the supply conductor, an earthed serial connection including a noise-decoupling capacitor and a resistor, and wherein a switch is connected in parallel to the resistor, the switch being movable between an open and closed position in response to a control signal issued from a controller.
- View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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10. A method of activating at least one RFI filter which is connected to a frequency converter, where the at least one RFI filter comprises a serial connection connected to earth and where the serial connection comprises a noise-decoupling capacitor in series with a resistor, the method including the steps of:
- connecting a switch in parallel across the resistor and maintaining the switch in an open position until the noise-reducing capacitor is approximately fully charged, and closing the switch in response to signals generated by a controller, thereby short circuiting the resistor.
- View Dependent Claims (11)
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12. A frequency converter for controlling an electric motor comprising:
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a first filter placed on a mains side of the frequency converter, a second filter placed in a d.c. intermediate circuit of the frequency converter, and a controller communicating with the first and second filters, each filter comprising a supply conductor having a coil inserted serially therein, and, branching from the supply conductor, an earthed serial connection including a noise-decoupling capacitor and a resistor, and wherein a switch is connected in parallel to the resistor, the switch being movable between an open and closed position in response to a control signal issued from the controller, and wherein the controller simultaneously closes the switches of the first and second filters.
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Specification