Using a Passive Sinewave Filter to Eliminate Common Mode and Differential Mode

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An integrated output filter that eliminates motor problems due to the PWM waveforms in both common mode and differential mode operation is proposed. The filter includes a three phase inductor constructed with tricore laminations with six mutually coupled windings. The windings possess differential mode inductance and proportionally very large common mode inductance characteristics. The single integrated inductor with the capacitors creates a low pass filter with additional band stop
attenuation near the switching frequency in both common mode and differential mode operation. The filter voltage transfer functions are derived. A prototype was constructed and test results presented. Simulation results correlated well with the prototype test data. The prototype filter reduced the differential mode THVD to 4.6% while the common mode voltage near the PWM switching frequency was reduced by 90%.

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An Integrated Inverter Output Passive Sinewave Filter for Eliminating Both Common and Differential Mode PWM Motor Drive Problems