Hybrid modulation technique with dc-bus voltage control for multiphase NPC converters

The paper presents a novel Carrier-Based Pulse Width Modulation (CBPWM) technique for multiphase Neutral Point Clamped (NPC) converters. The technique is aimed to actively control the Neutral Point (NP) potential while supplying the desired set of line-to-line voltages to the load. Standard techniques are either based on the sole Common Mode Voltage Injection (CMI) or on the sole Multi-Step (MS) switching mode; contrarily, the proposed algorithm combines these two approaches to take advantage of their main benefits. The technique performs well for each number of phases, for each modulation index and for each type of load. It can control in closed-loop the NP voltage to any desirable value with a reduced number of switching transitions. The proposed approach has been experimentally validated and compared with other carrier-based algorithms

Analysis and Reduction of Current and Voltage Ripple in DC-Link for Three-Level NPC Inverter-Fed Dual Three-Phase Motor Drives

In this paper, switching strategies for DC-link current and voltage ripple reduction have been studied. Considered topology is a neutral-point clamped three-level (NPC-3L) inverter feeding a dual three-phase permanent-magnet synchronous motor (PMSM). The mechanisms of DC-link current and voltage ripple generation in NPC-3L inverter-fed PMSM drive are analysed in detail. Then, a two-step collaborative switching strategy is proposed, where the optimum switching sequences, including opposite small vectors, are applied in the two inverters collaboratively. Furthermore, the switching vectors of two inverters are rearranged in the sequence of their corresponding DC-link capacitor currents so that the overlapping of their peaks is avoided. Consequently, both the voltage ripple and current ripple in the DC-link capacitors are mitigated with the proposed two-step collaborative switching strategy. For the mid-point voltage of the NPC-3L inverter, the amplitude of fluctuation is reduced under low modulation index operation, while the high-frequency harmonic components are mitigated under high modulation index operation. The experimental results are given to verify the validity of the theoretical analysis and the proposed switching strategy