双边不对称工况下无网侧变换器型可变频率变压器的控制策略

针对可变频率变压器转子电压不可控的问题，提出一种无网侧变换器的可变频率变压器（NGSC-VFT）拓扑结构。基于该拓扑结构，建立双边对称和不对称工况下NGSC-VFT的完整数学模型，并深入研究NGSC-VFT的控制策略。定子侧串联补偿变换器以维持直流母线电压、独立控制无功功率和消除定子负序电压为目标，转子侧串联补偿变换器以消除转子负序电压为目标。仿真结果表明：采用所提NGSC-VFT拓扑结构，无需网侧变换器即可维持直流母线电压，有功功率动态跟踪效果更快，直流电容电压更低，无功功率可独立控制，双边不对称工况下转矩和功率的波动得到进一步抑制。新拓扑提高了VFT系统的不对称故障穿越能力。

Control Strategy for Non Grid Side Converter-based Variable Frequency Transformer under Dual-Side Asymmetrical Conditions

In view of the problem of uncontrollable rotor voltage of variable frequency transformer, a non grid side converter-based variable frequency transformer (NGSC-VFT) configuration is proposed. Based on this configuration, an integrated mathematical model of NGSC-VFT under dual-side symmetrical and asymmetrical grid conditions is established, and the control strategy of NGSC-VFT is further studied. The stator side series compensation converte (SCC) aims to maintain the DC-link voltage, independently control reactive power, and eliminate the stator’s negative sequence voltage, while the objective of the rotor side SCC is to eliminate the rotor’s negative sequence voltage. The simulation results show that, with the proposed NGSC-VFT configuration, the DC-link voltage can be regulated without GSC with faster dynamic tracking effect of the active power and lower DC capacitor voltage, and the reactive power can be independently controlled. In addition, the fluctuations of torque and power under dual-side asymmetrical conditions can be further suppressed. The novel configuration improves the asymmetrical fault ride-through capability of VFT system.