【作者】 魏晓云；

【导师】 孙辉；

【作者基本信息】 大连理工大学 ， 电力系统及其自动化， 2013， 博士

【摘要】 VSC-HVDC作为交直流混合电网的重要组成部分,应能够长期安全、稳定地运行,尤其在交流系统发生故障时,不仅要保障自身的安全性和可靠性,还能为故障电网提供支持,提高电网运行稳定性和可靠性,改善电网电能质量。本文针对交流电网故障条件下的VSC-HVDC系统,开展VSC-HVDC系统动态特性及改善交直流特性的VSC-HVDC控制策略研究。研究了交流电网故障、特别是相位跳变条件下的VSC-HVDC系统动态特性。以抑制直流电压脉动和负序电流为控制目标,建立了VSC-HVDC系统dq坐标正负序数学模型及两种不平衡控制系统；对比研究了抑制直流电压脉动和抑制负序电流控制系统与常规矢量控制系统的动态特性及其相位跳变控制特性。针对双序dq矢量电流控制中相序分解环节带来的系统动态性能降低和电流控制质量下降问题,提出一种基于静止αβ坐标的矢量电流控制策略和谐波补偿方法,实现了在交流系统不平衡条件下抑制直流电压脉动与提高交流电网电流质量控制的双重目标。建立VSC-HVDC统一动态模型,提出了基于有功功率/直流电压和无功功率调节的统一矢量控制方案。基于谐振积分器和谐振滤波器的外环控制可简便生成无谐波畸变的正负序电流指令,结合静止αp坐标下的内环矢量电流控制,无须附加谐波补偿措施,在PCC有功和无功功率调节基础上,能有效抑制直流电压脉动或者负序电流,同时降低VSC-HVDC不平衡运行时的低频谐波水平。在上述研究基础上,设计基于交流母线电压有差调节的VSC-HVDC统一矢量控制系统,研究了VSC-HVDC在供电系统应用中的相关电能质量控制问题。基于IEEE12-bus benchmark系统的VSC-HVDC仿真研究表明所设计的统一矢量控制系统可减缓电网电压跌落,快速恢复故障后电压,抑制系统低频谐波,提高了电网电压及电流质量。针对大连市区南部电网缺少大型电源,重要负荷所占比例高,存在供电可靠性和稳定性方面的问题,研究大连城市电网的VSC-HVDC供电方案。结果表明,采用统一矢量控制策略的VSC-HVDC方案可有效解决南部电网稳定性和可靠性问题,并提高电网供电质量。更多还原

【Abstract】 As an important part of the ac/dc hybrid power grid, VSC-HVDC should be able to run safely and stably for a long time, especially when the ac system occurs faults. VSC-HVDC is expected to not only ensure its safety and reliability, but also provide support for the faulted power grid, enhance the system stability and reliability, and improve the power quality. This thesis researches on the dynamic characteristics of VSC-HVDC system and control strategy to improve the ac/dc system performance under ac faults.Dynamic characteristics of VSC-HVDC system are studied under the ac faults, especially coupled with the phase angle jump. To restrain the dc-link voltage ripple or negative-sequence currents, the positive-and negative-sequence models of VSC-HVDC and two stratiges applicable to the unbalanced faults are investigated. The dynamics of VSC-HVDC with the control systems for the restraint of dc-link voltage ripple or the negative-sequence current are investigated as compared with that of the conventional strategy, furthermore the system performance considering phase angle jump is analysed.To improve the dynamic performance and mitigate the ac current deterioration presented in the conventional dual vector current control due to the sequence component decomposition, a new vector current control strategy and harmonic compensation controller in the stationary αβ reference frame are proposed. It can restrain the2nd harmonic ripple on the dc link and decrease the harmonic level in the ac currents under unbalanced ac grid conditions.Based on the unified dynamic models, a novel unified control scheme for active power/dc-link voltage and reactive power regulation is proposed. The resonant integrator and filter based scheme in the outer loop enables the simple acquision of the positive-and negative-sequence current references without harmonic component. Combined with the inner vector current control in the stationary αβ frame, besides the active power and reactive power regulation at PCC, the proposed scheme can restrain the dc-link voltage ripple or the negative currents along with the restraint of low-order harmonics without additional harmonics compensation.The unified control system based on the ac voltage regulation with droop control is designed, and its application in power supply related to power quality issue is investigated. The simulation studies with the IEEE12-bus benchmark show that it can mitigate the voltage dip, restore the system voltage quickly after the fault, retain a rather low level harmonics and then improve the system operating voltage and current quality.Considering the problems that the south Dalian grid lacks of large internal power supplies and has a higer proportion of important load, which will make reliability and stability issues, VSC-HVDC for the south Dalian grid is studied. The results show that the introduction of VSC-HVDC based on the unified control scheme can effectively ehance the stability and reliability and impove the quality of power supply in the south Dalian grid.更多还原