Discontinuous Dual-Signal PWM for Neutral-Point Voltage Balancing in Three-Level Converters

Neutral-point voltage (NPV) imbalance presents a significant challenge in three-level converters, especially under conditions of high modulation index (MI) and low power factor (PF). This article proposes a novel discontinuous dual-signal pulsewidth modulation (DDSPWM), which can effectively balance the NPV at high MI and the full range of PF. It is implemented by injecting a simple zero-sequence signal into a carrier-based dual-signal PWM. In each switching cycle, the maximum phase is clamped to the P level to increase the NPV, or the minimum phase is clamped to the N level to decrease it, depending on the direction of the zero-sequence injection. The NPV is pushed toward the balanced potential in each switching cycle by this hysteresis control. It is robust and does not require parameter design. Moreover, the clamping mechanism also reduces switching losses, as switching actions in the maximum or minimum phase are saved. Experimental results confirm the effectiveness of the proposed method. DDSPWM exhibits consistently lower switching losses compared to traditional virtual space vector PWM in all tested conditions. The proposed method is particularly advantageous for high-power applications, such as battery energy storage systems.