Common mode & differential mode filter for variable speed drive

An input filter for filtering common mode and differential mode currents, comprising:

• a three-phase inductor having three windings, wherein each winding of the three-phase inductor having a center tap dividing each winding into a pair of inductor sections;
• and
• a three-phase input capacitor bank having three capacitors connected in a wye configuration to the three center taps at one end, and to a common point at the opposite end;
• wherein the three-phase input capacitor bank is configured to substantially provide a short circuit for frequencies above a predetermined fundamental frequency for shunting frequencies above a predetermined fundamental frequency through the three phase capacitor bank, while passing the predetermined fundamental frequency to an input AC power source.

An output filter for filtering common mode and differential mode currents associated with a variable speed drive comprising:

• a first output capacitor bank of three capacitors, each of the three capacitors of the first output capacitor bank connected in a wye configuration to an output phase of the inductor;
• and
• each of the three capacitors of the first output capacitor bank being connected in common at an end opposite the output phase connection;
• the common capacitor connection also being connected to earth.

A chiller system comprising:

• a refrigerant circuit comprising compressor, a condenser, and an evaporator connected in a closed refrigerant loop;
• a motor connected to the compressor to power the compressor;
• a variable speed drive connected to the motor, the variable speed drive being configured to receive an input AC power at a fixed AC input voltage magnitude and frequency and provide an output AC power at a variable voltage and variable frequency, the variable speed drive comprising:
• a converter stage connected to an AC power source providing the input AC voltage, the converter stage being configured to convert the input AC voltage to a boosted DC voltage;
• a DC link connected to the converter stage, the DC link being configured to filter and store the boosted DC voltage from the converter stage;
• an inverter stage connected to the DC link, the inverter stage being configured to convert the boosted DC voltage from the DC link into the output AC power having the variable voltage and the variable frequency;
• and
• an input filter for filtering common mode and differential mode currents, the input filter comprising:
• a three-phase inductor having three windings, wherein each winding of the three-phase inductor having a center tap dividing each winding into a pair of inductor sections;
• and
• a three-phase input capacitor bank having three capacitors connected in a wye configuration to the three center taps at one end, and to a common point at the opposite end;
• wherein the three-phase input capacitor bank is configured to substantially provide a short circuit for frequencies above a predetermined fundamental frequency for shunting frequencies above a predetermined fundamental frequency through the three phase capacitor bank, while passing the predetermined fundamental frequency to the converter stage.