Electromagnetic compatibility filter
View Patent ↗The variable speed drive system is arranged to receive input power at fixed input voltage magnitude and frequency and provide power at a variable voltage and variable frequency. The variable speed drive includes a converter connected to an AC source to convert the input voltage to a boosted DC voltage. A DC link connected to the converter filters the DC voltage from the converter stage. An inverter converts the DC link voltage into variable voltage and the variable frequency AC power. An electromagnetic compatibility (EMC) filter includes a series RC circuit from phase-to-ground circuit for each input phase of the converter. The RC circuit includes a resistor connected in series with a capacitor between the converter phase and ground. The EMC filter is connected to the line side of the converter. An inductor is connected between the input source and the EMC filter.
1. A variable speed drive system configured to receive as an input AC power at a fixed AC input voltage magnitude and frequency and provide an output AC power at a variable voltage and a variable frequency, the variable speed drive comprising:
a converter adapted to be coupled to an AC power source providing the input AC voltage, the converter being configured to convert the input AC voltage to a DC voltage;
a DC link connected to the converter, the DC link being configured to filter the DC voltage and to store energy from the converter;
an inverter connected to the DC link, the inverter being configured to convert the DC voltage from the DC link into the output AC power having the variable voltage and the variable frequency;
an input filter comprising a three phase inductor having three windings, each winding having a first end adapted to be coupled to a phase of the input AC power and a second end coupled to the inverter; and
an electromagnetic compatible filter having a resistor-capacitor circuit between at least one of the second ends of the input filter winding and a ground point, wherein the electromagnetic compatible filter is not required to carry all of the current of the variable speed drive system and wherein the electromagnetic compatible filter is configured to substantially reduce the gain of noise over a frequency range at which the converter generates noise by parallel resonance thereby preventing the noise from the parallel resonance from passing through the input filter to a source of the input AC power.
2. The variable speed drive system of claim 1 , the electromagnetic compatible filter further comprising first filter ends connected to respective second ends of the input filter winding, and a second filter end connected to a common ground point.
3. The variable speed drive system of claim 2 , the electromagnetic compatible filter further comprising a resistor-capacitor filter bank, the first filter ends connected to the respective second ends of the input filter winding forming a WYE configuration.
4. The variable speed drive system of claim 1 , further comprising the common ground point being a ground point on the converter.
5. The variable speed drive system of claim 1 , further comprising a converter having a passive front end.
6. The variable speed drive system of claim 1 , further comprising each winding of the three-phase inductor having a center tap dividing each winding into a pair of inductor sections.
7. The variable speed drive system of claim 6 , further comprising a converter having an active front end.
8. A method of operating a variable speed drive system, the method comprising:
receiving input AC power at a fixed AC input voltage magnitude and frequency;
converting the input AC voltage to a DC voltage in a converter;
filtering the DC voltage and storing energy from the converter in a DC link;
inverting the DC voltage from the DC link into AC power;
providing an output AC power at a variable voltage and a variable frequency; and
attenuating the gain of noise caused by parallel resonance in the converter thereby preventing the noise from passing through the input filter to a source of the input AC power.
9. The method of claim 8 , wherein the step of attenuating the gain of noise caused by parallel resonance in the converter is achieved by an electromagnetic compatible filter.
10. An electromagnetic compatible filter for use with a variable speed drive, the variable speed drive comprising an input adapted to be coupled to an input AC Power source, an input filter coupled between the input and a converter, the electromagnetic compatible filter coupled at a first end to the juncture of the input filter and the converter, and at a second end to a ground, the electromagnetic compatible filter capable of attenuating the gain of noise caused by parallel resonance in the converter thereby preventing the noise from passing through the input filter to the AC power source.
11. The electromagnetic compatible filter of claim 10 , further comprising the ground to which the second end is coupled is a ground point on the converter.