A Dynamic Model and Modified One-Cycle Control of Three-Level Front-End Rectifier for Neutral Point Voltage Balance

This paper presents a dynamic phasor-based model for three-level front-end VIENNA rectifiers. The proposed model comprehensively predicts the behavior of the ac- and dc-side variables of the rectifier on which the issue of neutral point (NP) voltage is studied. The nonzero NP current causes an imbalance of dc-link voltages and the occurrence of low-frequency ripples (LFRs). By employing the offset voltage injection method, a mathematical relationship is derived between the NP current and the dominant components of the injected offset voltage. A distribution parameter is introduced to optimize the dc-link voltages balance and LFRs reduction. A modified one-cycle control (OCC) combined with offset voltage injection is proposed, and the closed-loop voltage regulator is analyzed. The modified OCC scheme proposed in this paper is capable of balancing the dc-link voltages and eliminating the LFRs. It also provides good performance both in transient and steady states. The proposed approach is verified by simulations in MATLAB/Simulink and experimental results.