抑制直流送端过电压的进相水电机组功角稳定分析

Power Angle Stability Analysis of Leading Phase Hydropower Units for Restraining Overvoltage at HVDC Sending End

我国西北地区的水电与新能源打捆经电网换相高压直流(line-commutated converter HVDC,LCC-HVDC)输电系统送出,直流发生单极闭锁故障时送端系统将承受严重的过电压冲击。送端水电机组具有进相运行能力,可进一步发掘其动态无功容量用于抑制系统过电压,但水电机组进相协调的相关研究几近空白。此外,进相协调控制下水电机组的功角稳定特性尚不明确,亟需开展研究。为此,首先针对送端系统不同程度的过电压工况,提出水电机组进相协调策略,包括水电与直流换流站协调、水电机组间协调两部分;其次,基于电磁功率解析表达式和等面积准则(equal area criterion,EAC),研究直流单极闭锁前后水电机组的功角稳定特性;然后,以保障系统功角稳定为目标,分析直流单极闭锁前后水电机组最大进相深度的变化规律,并由此提出与进相协调策略相适配的低励限制曲线改进方法;最后,基于西北地区某实际风光水送端系统的PSCAD/EMTDC模型进行验证,结果表明:提出的水电机组进相协调策略及低励限制曲线改进方法,在保障功角稳定的前提下,进一步提高了送端系统抑制过电压能力,对实际工程具有一定指导意义。

Hydropower and new energy in Northwest China are bundled and sent out through line-commutated converter HVDC(LCC-HVDC)transmission system.When the monopole blocking fault occurs in LCC-HVDC,the sending end system will bear severe overvoltage impact.Due to the leading phase operation ability of the sending end hydropower unit,its dynamic reactive power capacity can be further explored to restrain the system overvoltage,but the research on the leading phase coordination of hydropower unit is almost blank.In addition,the power angle stability characteristics of the hydropower unit under the leading phase coordination control are not clear,so it is urgent to carry out research.For this reason,firstly,according to different degrees of overvoltage conditions of the sending end system,the leading phase coordination strategy of hydropower units was proposed,including the coordination of hydropower and HVDC converter station,and the coordination between hydropower units.Secondly,based on the analytical expression of electromagnetic power and equal area criterion(EAC),the power angle stability characteristics of hydropower units before and after LCC-HVDC monopole blocking were studied.Then,in order to ensure the power angle stability of the system,the variation law of the maximum leading phase depth of the hydropower unit before and after line-commutated converter hydropower unit before and after LCC-HVDC monopole blocking was analyzed,and an improved method of low excitation limit curve was proposed to adapt to the leading phase coordination strategy.Finally,the verification test was carried out based on the PSCAD/EMTDC model of an actual wind-solar-hydro sending end system in Northwest China.The results show that the leading phase coordination strategy and the improved method of low excitation limit curve proposed in this paper can further improve the overvoltage suppression ability of the sending end system on the premise of ensuring the power angle stability,which has guiding significance for practical engineering.