Three-level Generalized Discontinuous Pulse-width Modulation Strategy Considering Neutral Point Potential Balance

Abstract

Traditional discontinuous pulse width modulation (DPWM) cannot be efficiently used in some inverters like active power filters (APFs) whose currents are difficult to predict. Therefore, this paper proposes a new generalized discontinuous pulse width modulation (GDPWM) strategy considering neutral point potential balance for neutral-point clamped (NPC) three-level inverters. The core of the proposed strategy is the optimal efficiency modulation strategy. The optimal efficiency modulation strategy determines the clamp mode in real time based on the current flowing through the converter. This strategy minimizes switching losses by clamping the converter to the phase with the largest absolute value of current. At the same time, according to the neutral point potential shift, the neutral point balance strategy and the optimal efficiency modulation strategy are switched to achieve the balance between the switching loss and the neutral point potential. The proposed strategy can be efficiently applied in NPC three-level APFs to minimize the switching losses without the need of predicting the currents and to make neutral point potential balance. In this paper, the proposed modulation strategy is theoretically analyzed, and simulation and experimental verification are carried out.