电网电压故障下向无源网络供电的MMC电力电子变压器的控制策略

电力电子变压器（PET）具有瞬时功率调节、谐波抑制等优点,输电线路经过PET向无源网络供电是柔性输电的一个重要应用领域。将模块化多电平变换器（MMC）技术与PET相结合,使得PET应用于高电压、大容量的输电和配电系统成为了可能。首先,本文针对MMC-PET输入级在电网故障时产生的正负序电流,推导出基于欧拉-拉格朗日（EL）模型的内环正负序电流的无源控制器（PBC）;接着,将MMC技术应用于MMC-PET中间隔离级高压侧,提高其中间隔离级的供电可靠性,并采用移相调压的控制策略;再后,针对MMC-PET输出级,设计了基于EL模型的内环电流无源控制器。最后,在Matlab/Simulink中建立一个向无源网络供电的MMC-PET系统,在电网电压出现故障时,对向无源网络供电的MMC-PET系统进行了软件仿真实验验证,实验结果表明MMC-PET系统的控制策略具有良好的动态控制性能。

CONTROL STRATEGY OF MMC POWER ELECTRONIC TRANSFORMER POWERED TO PASSIVE NETWORK UNDER GRID VOLTAGE FAULT

Power electronic transformers（PET） have the advantages of instantaneous power regulation and harmonic suppression. Power transmission line to passive networks through PET is an important application field of flexible power transmission. At the same time, the combination of modular multilevel converter（MMC） technology and PET makes it possible to apply PET to high-voltage, large-capacity power transmission and power distribution systems. First of all, under the positive and negative sequences system when the grid fails, this paper derives the passive controller（PBC） of the inner loop positive and negative sequence current based on the Euler-Lagrange（EL） model; Next, applies the MMC technology to the high-voltage side of the MMC-PET isolation stage to improve the power supply reliability of the isolation stage, and adopts a PI-based phase-shift control strategy; then, for the MMC-PET output stage, this paper designs an inner loop current passive controller based on the EL model. Finally, an MMC-PET system that supplies power to the passive network is established in Matlab/Simulink. When the grid voltage fails, software simulation experiments are performed to verify the MMC-PET system that supplies power to the passive network. The experimental results show that the control strategy of the MMC-PET system has good dynamic control performance.