A new modulation strategy for capacitor voltage balancing in three-level NPC inverters based on matrix converter theory

This paper presents a new modulation strategy for capacitor voltage balancing in three-level neutral-point-clamped inverters by applying the matrix converter theory to eliminate the low frequency oscillation of the neutralpoint voltage and current. The proposed modulation method controls the neutral-point current without affecting the averaged output voltage and current. The behavior of the new modulation technique turns out to be a combination of two-phase unipolar PWM and one-phase dipolar PWM. The proposed PWM method yields a linear capacitor-voltage control loop, based on which the response time of capacitor voltage balancing can be precisely designed.