T型三电平VSC-HVDC系统模型预测灵活功率控制策略

Model predictive flexible power control strategy for T-type three-level converter based on VSC-HVDC

建立了基于T型三电平基于电压源型换流器的高压直流输电(VSC-HVDC)系统功率模型,并据此提出了基于两步预测的有限控制集模型预测直接功率控制策略,其可实现功率指令值的精确跟踪、直流侧电容电压平衡和降低平均开关频率3个控制目标。但该控制策略在电网电压不对称时会产生谐波电流,为了解决该问题,通常增加功率补偿策略。然而当采用传统的功率补偿策略时,只有3种可选的控制目标:抑制负序电流、抑制有功波动和抑制无功波动。上述3种控制目标难以在各种类型的交流故障下同时满足换流器自身的限制条件和电网对换流器故障穿越的要求。为此,提出了灵活功率控制方法,其可在各控制目标之间实现折中控制,控制方式灵活。搭建了T型三电平VSC-HVDC系统仿真模型,仿真结果验证了所提策略的正确性。

Power model of T-type three-level based on VSC-HVDC（Voltage Source Converter based HVDC）system is formulated,based on which the finite control set model predictive direct power control strategy with two-step prediction is proposed.The proposed control strategy can achieve three control targets simultaneously,i.e.,accurate power reference tracking,DC-side capacitor voltage balancing and average switching frequency decreasing.However,the proposed control strategy may cause harmonic currents under unbalanced grid voltages.To solve the above problem,power compensation strategy is usually adopted,which,however,provides only three alternative control objectives,i.e.,eliminating negative current,suppressing active power ripples and removing reactive power ripples.It is difficult for the aforementioned three control objectives satisfying the constraints of converter and the requirements for converter fault ride-through under diverse AC grid faults.In this regard,flexible power control strategy is proposed,which can achieve a compromise and flexible power control between the control targets.A simulation model of T-type three-level VSC-HVDC system is performed and the simulative results verify the correctness of the proposed control strategy.