低电压穿越控制诱导的陆上风电场电压振荡的分岔分析及其判据研究

Bifurcation Analysis and Criteria of Voltage Oscillation Induced by Low Voltage Ride Through Control in Onshore Wind Farms

集中送出的陆上风电场电压支撑能力弱,且有功送电距离大多较长,随着其有功出力的增加,其电压稳定问题不可忽视。在实际电网中,曾出现过陆上风电场在高出力、无故障下、低电压穿越控制方式导致的电压振荡失稳现象,该文基于简化模型,针对该现象进行机理分析,并引申出适用于多机系统的判据。在机理分析方面,说明其对应一种高出力下低电压穿越控制诱导的非光滑分岔(high output excited low voltage ride through control induced non-smooth bifurcation,HLINB),并分析了HLINB与鞍结分岔(saddle node bifurcation,SNB)发生的边界条件;在判据方面,给出了发生HLINB的判据,并结合二阶锥算法给出判据的阈值计算方法。具体地,首先,基于实际案例,对陆上风电场无故障、高出力下,由低穿控制方式导致的电压振荡现象进行分析,说明该振荡现象对应于HLINB,进一步,推导HLINB与SNB发生的边界条件,结果表明,在风电场的典型低穿控制方式下,陆上风电场在高出力时更容易发生HLINB而非SNB;其次,分析了其他风电场无功控制方式对于待评估风电场的最大输出功率的影响,并基于二阶锥算法,给出考虑风电场无功控制方式及无功约束下,计及HLINB约束的风电场的最大输出功率的计算方法;最后,3机9节点和10机39节点的仿真算例表明,所提方法考虑风电场的控制方式,能够更加有效的评估系统的电压稳定性。

The voltage support capacity of the centralized onshore wind farms is weak,and the active power transmission distance is often long.With the increase of their active power generation,the voltage stability of the system cannot be ignored.For the voltage oscillation instability phenomenon caused by the low voltage ride through(LVRT)control mode in the actual power grid under no fault condition,this paper analyzes the mechanism of the phenomenon based on a simplified model and extends criteria applicable to multi-machine systems.In theory,the phenomenon corresponds to high output excited low voltage ride through control induced non-smooth Bifurcation(HLINB),and the boundary conditions of HLINB and Saddle node bifurcation(SNB)is analyzed.In criterion,based on the second-order cone algorithm,the critical criterion of HLINB is given.Specifically,based on actual cases,the onshore wind farm voltage oscillation phenomenon caused by the LVRT control under no fault is analyzed,which indicates that the oscillation phenomenon corresponds to HLINB.Further,the boundary conditions of HLINB and SNB are derived.The results show that under the typical LVRT control mode of the onshore wind farms,wind farms with high active power output are more prone to experiencing HLINB rather than SNB in the actual power grid.Secondly,the influence of other wind farm reactive power control methods on the maximum active power output of the wind farm to be evaluated is analyzed.Also,based on the second-order cone algorithm,considering the reactive power control methods and reactive power constraints of the wind farms,the calculation method of the maximum active power output of the wind farm with HLINB constraints is given.Finally,the simulation examples of 3 machines 9 buses and 10 machines 39 buses show that as the proposed method considers the control mode of the wind farms,it can more effectively evaluate the voltage stability of the system.