A new common-mode sinusoidal inverter output filter

Long cables between a PWM inverter and a motor will result in over-voltage at motor terminals. PWM voltage source inverter generates high d/spl nu//dt and high frequency common-mode voltage, which leads to shaft voltage and bearing current. Conventional inverter output filter may eliminate over-voltage when using very longer cable, but cannot achieve better filtering effects under all kinds of operation conditions for its parameter values are fixed and is useless for decreasing the common-mode voltage. A new common-mode sinusoidal inverter output filter with variable inductors is proposed in this paper to achieve a motor-friendly performance of the PWM voltage source inverter, which can automatically adjust cutoff frequency of the filter and achieve optimizing sinusoidal waveforms when operation conditions are varying, and due to the common-mode connection, common-mode voltage is also reduced significantly. Common-mode and differential-mode problems are solved with the same filter configuration. Simulation and experimental results identify the effectiveness of the proposed filter.