Research On Static Voltage Stability And Active Power Loop Control Of Wind Power System

The safe and stable operation of power system is the foundation of economic and social development,but the increasingly large scale and complex structure of modern power grid bring challenges to its security and stability.With the increase of wind power,the voltage stability problem becomes more prominent.Moreover,unreasonable power grid structure or power flow controller parameters can easily cause loop flow,cause economic losses and even threaten the security of power grid,lead to voltage collapse or accelerate its process.Phase shifting transformer(PST)can optimize power flow distribution and eliminate system circulation by adjusting phase shifting angle,provided that voltage instability cannot be caused.In view of the above problems,the main research contents of this paper are as follows:(1)Taking the two-core symmetric discrete thyristor controlled phase-shifting transformer(TCSD-TCPST)as the research object,the sensitivity model of L index to the phase-shifting angle is proposed by considering the change of its impedance.Equivalent impedance is gradually updated,and the level of sensitivity is corrected by Newton method,the phase-shifting angle that achieves the largest voltage stability margin is obtained by iteration to verify the effect of the PST on the static voltage stability.(2)The sensitivities of B index are corrected,and the sensitivities of L index to node injection power and on-load tap changer are deduced.For the first time,the adverse control effects with different sites of load shedding,the optimality of local load shedding,the opposite effects of tap adjustment,and the inconsistency of L and B indices with the same control measures,are quantified.(3)Loop states are divided according to their characteristics,and then a multi-state model of active power loop based on Markov chain is established.Based on the history data of wind velocity,the probability matrix of state transition is calculated,and combined with the initial state to predict probability distribution of loop at different instants of time.The specific loop path is judged,and the proportion of loop branches is defined to reflect the loop scale and quantify the loop severity.Combining with the loop probability distribution and loop severity,the severity index of the active power loop is proposed,and calculated under different phase shifting angles to evaluate the loop risk.