A novel transient rotor current control scheme is proposed in this paper for a doubly-fed induction generator(DFIG)equipped with a superconducting magnetic energy storage(SMES) device to enhance its transient voltage and frequency support capacity during grid faults. The SMES connected to the DC-link capacitor of the DFIG is controlled to regulate the transient dc-link voltage so that the whole capacity of the grid side converter(GSC) is dedicated to injecting reactive power to the grid for the transient voltage support. However, the rotor-side converter(RSC) has different control tasks for different periods of the grid fault. Firstly, for Period I, the RSC injects the demagnetizing current to ensure the controllability of the rotor voltage. Then, since the dc stator flux degenerates rapidly in Period II, the required demagnetizing current is low in Period II and the RSC uses the spare capacity to additionally generate the reactive(priority) and active current so that the transient voltage capability is corroborated and the DFIG also positively responds to the system frequency dynamic at the earliest time. Finally, a small amount of demagnetizing current is provided after the fault clearance. Most of the RSC capacity is used to inject the active current to further support the frequency recovery of the system. Simulations are carried out on a simple power system with a wind farm. Comparisons with other commonly used control methods are performed to validate the proposed control method.
随着电网运行对电压控制和无功管理水平要求的提高,自动电压控制(automatic voltage control,AVC)日渐成为研究的热点。由于管理模式的制约,其应用性研究在北美电网仍属空白。文中设计并实现了适用于美国东北部某互联电网特殊管理模式和在线运行要求的自动电压控制系统。该系统扩展了移相器元件模型的处理,并在利用最优潮流(optimal power flow,OPF)计算控制策略的过程中考虑预想故障后的静态安全约束。长时间的在线试运行数据及其评估结果表明,文中所设计和实现的自动电压控制系统应用于该电网可显著改善该电网的无功电压水平,提高电网的安全性和经济性。
