Voltage Stability Analysis Of The Grid With Large-scale Wind Farm

As with the development of society, energy resources and environment problemshas emerged. Wind power generation develops increasingly as a result of itsadvantages of cleanliness without any pollution, abundance and mature technology aswell. Characteristics of wind power generation in our country are developed inlarge-scale, transmitted in high-voltage and long-distance, coupled with higher andhigher grid voltage level. However, wind power is random and partly controlled,impact of wind power on the grid voltage stability of the grid is more and moreprominent as wind power capacity and voltage level is higher and higher, therefore,this paper will study on the static voltage stability and transient voltage stability of thegrid with large-scale wind farm connected to. The details are as follows:(1)Built the wind turbine model and its control system model inDIgsilent/PowerFactory. Established the steady-state and transient model of commonasynchronous wind turbine and doubly-fed induction generator; Also built the overallcontrol system of doubly-fed induction generator with pitch angle control, rotor sideinverter control and grid side inverter control.(2)Put forward the handing method of wind farm nodes in power flowcalculation, continuous flow algorithm is written in Matlab. Wind farm node will betreated as a special load node, modified the growing mode of load node in continuouspower flow calculation by taking the relationship of reactive power and voltage ofcommon asynchronous wind turbine into account not with the linear mode of reactivepower keeping constant or growing with fixed power factor when the active powerincreases.(3)Double voltage stability index was established which can consider both activepower and reactive power for static voltage stability analysis. Considering the effectsof active power and reactive power on static voltage stability, this paper coordinatedthe source and grid from wind power fluctuation and node reactive power margin bycontinuous power flow method, then distributed the weight of double voltage stabilityindex by structure entropy method. Results showed that the double voltage stabilityindex based on structure entropy method overcame the limitation of individual voltagestability index and difference between different indexes in weak nodes identification.The results derived from double voltage stability index were more comprehensive andaccurate.(4)Adopted critical fault clearing time index and transient voltage drop extent and duration time index to analyze transient voltage stability. Analyzed the transientvoltage stability of the grid with large-scale wind farm connected to after subjected tolarge disturbance by time-domain simulation method. Modified the wind turbine pitchangle control and the rotor side converter control were modified, proposing acoordinated control strategy consist of fast pitch angle control and rotor-side convertercontrol with transient voltage support to improve the transient voltage stability of thegrid with large-scale wind farm connected to. The case simulation verified the effectof modified control system on transient voltage stability of the grid after subjected tolarge disturbance.