This paper evaluates mitigation of motor shaft voltage in 3-Level neutral point clamped (NPC) inverters by comparing approaches based on modulation strategies and an LCCR output filter. Analytical expressions of inverter common mode voltage are derived for carrier-based modulation strategies and mapped to shaft voltage using a frequency dependent shaft voltage model. A filter transfer function and Bode analysis quantify attenuation of common mode components by the LCCR and contrast it with a conventional LC filter Measurements of common mode and shaft voltages validate the analysis. The study shows how operating conditions and spectral distribution govern effectiveness and offers guidance for selecting modulation or filtering to reduce shaft voltage.
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