Carrier‐based generalised discontinuous pulse‐width modulation strategy with flexible neutral‐point voltage control and optimal losses for a three‐level converter

Abstract

Owing to their capability to reduce switching losses, discontinuous pulse-width modulations (DPWMs) have been widely discussed in the last decades. However, when using the classical DPWMs in three-level (3L) converters, neutral-point (NP) voltage balancing may not be efficiently achieved, because the reference signals are clamped and saturated at regular intervals, and consequently it is difficult to inject the desired zero-sequence component (ZSC). In this study, as the foundation, the general implementation method of 3L carrier-based DPWM (CBDPWM) by injecting discontinuous ZSC (DZSC) is introduced. Following this, a corresponding NP voltage control method is presented and discussed. Finally, on the basis of output prediction and roll optimising method, a novel 3L generalised CBDPWM strategy is proposed which selects and injects the optimal DZSC. With this adjustment, the NP potential can be quickly and flexibly controlled within the given range, while the switching losses can be minimised. The proposed strategy is general and simple. It is applicable to any operating condition without complex calculation and extra efforts. The performance of the proposed strategy is comprehensively evaluated and compared with the traditional DPWMs, and the feasibility and effectiveness of the proposed strategy are validated by the experimental results.

A Simplified Virtual Vector PWM Algorithm to Balance the Capacitor Voltages of Four-Level Diode-Clamped Converter

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