| dc.description.abstract | Current harmonic suppression and DC-link voltage ripple mitigation under three-phase grid unbalance have become crucial research topics in rectifier studies in recent years. The three-phase Vienna rectifier has emerged as a widely recognized three-level topology due to its high efficiency and low-cost characteristics. However, due to its current polari-ty-dependent conduction mechanism, current distortion occurs at zero-crossing, and this phenomenon becomes more pronounced under output neutral point unbalance. Furthermore, under grid unbalance conditions, the injection of active and reactive power ripple commands is required to suppress DC-link second-order ripple disturbances. This compensation mecha-nism leads to phase shifts between current and voltage, and this phase difference between current and grid voltage can cause the Vienna rectifier to enter non-synthesizable regions at high modulation indices, where reference voltage vectors cannot be effectively synthesized, resulting in severe current distortion and voltage disturbance issues. To reduce the impact of non-synthesizable regions on the three-phase Vienna rectifier, this paper proposes a Non-Unity Power Factor Current Optimization (NUPF-CO) strategy, effectively mitigating the negative effects of non-synthesizable regions on system performance. This strategy ena-bles the three-phase Vienna rectifier to achieve DC-link second-order ripple suppression while avoiding current zero-crossing distortion under both grid unbalance and output neutral point active unbalance conditions, ensuring excellent neutral point current disturbance sup-pression and power factor correction effects. Moreover, through theoretical analysis and nu-merical calculations, this paper provides detailed comparisons of operating ranges (non-overmodulation ranges) between the proposed and conventional strategies, and further derives optimal operating ranges for ensuring proper current polarity transition, providing comprehensive theoretical foundations for system design.
Furthermore, with the proliferation of renewable energy and electric vehicle charging equipment, power conversion devices are increasingly facing grid unbalance and load un-balance issues. Particularly in three-phase Vienna rectifiers, output neutral point unbalance leads to current zero-crossing distortion and DC-side voltage disturbances, affecting overall system performance. Addressing this issue, this paper proposes a Reduced Zero-Crossing In-terval (RZCI) compensation strategy, effectively reducing the clamping interval range of three-phase Vienna rectifiers under output neutral point unbalance conditions, thereby de-creasing DC-side voltage disturbances. Considering potential current harmonic issues intro-duced by the RZCI strategy, upper and lower limits for compensation ranges are established to ensure the compensated three-phase Vienna rectifier still complies with individual current harmonic limits set by international standards.
This paper also combines the proposed NUPF-CO strategy, RZCI strategy, and virtual capacitor feedforward current method, with dynamic compensation weight adjustment, ena-bling the Vienna rectifier to simultaneously suppress DC-link second-order ripple disturb-ances caused by grid unbalance and DC-side voltage disturbances caused by output neutral point unbalance, while maintaining excellent power factor correction effects and eliminating zero-crossing distortion.
Finally, experimental validation is conducted on a 2.5 kW three-phase Vienna rectifier, systematically comparing the performance of traditional SCIS, VJCIS strategies with the proposed NUPF-CO strategy under various unbalance conditions. Experimental results demonstrate that the solution combining RZCI strategy and virtual capacitor technology not only effectively compensates for DC-side voltage disturbances but also ensures system oper-ation current harmonics meet relevant regulatory requirements, showcasing superior com-prehensive performance. | en_US |