Research On Phase Sequence Exchange Technology Applied To Stability Control

Stability is the biggest problem of AC transmission system.With the expansion of power grid and the increase of regional interconnection.various uncertain operation variables and complex disturbance factors in the system interfere with each other.Power swing of tie-line occurs frequently,which significantly increases the probability of transient instability of the system,and brings great risks to the safe and stable operation of the system.In order to solve this problem,a new exploratory solution-phase sequence exchange technology is proposed.The basic connotation of this measure is:when the power angle of the system swings to a suitable value.the primary side phase of the tie line is rapidly reversed,and the power angle mutating 120 degrees is realized by"staggered connection(phase sequence exchange)".which brings the continuously increasing power angle back to a smaller state and restrains the occurrence of instability.Focusing on the basic subject of phase sequence exchange.this paper makes the following preliminary studies:1.Firstly,by means of the classical equal area rule,the reasons why the system can be stable after phase sequence exchange are briefly explained.Secondly,the process of energy changing after phase sequence exchange is analyzed,and the quantitative expression is given.According to the expression of system energy variation,the basic conditions of phase sequence exchange technology are defined,and the optimal angle of phase sequence exchange technology operation is deduced.Finally,the corresponding validation is given by numerical examples and simulation,which proves that the phase sequence exchange technology can greatly improve the stability margin of the system.2.Phase sequence exchange technology belongs to discontinuous control,so it is necessary to check the impact produced during the operation.In this paper,the impulse current and the impulse electromagnetic torque produced during the operation of phase sequence exchange are deduced,and the relevant preconditions for the system to withstand the impulse of phase sequence exchange are determined through analysis.The conclusion shows that when the ratio of the system connection reactance to the generator sub-transient reactance is greater than 0.543(Xs/X"d>0.543),the impact of phase sequence exchange on the system is tolerable.3.The core basis of phase sequence exchange technology is power angle,and real-time measurement of power angle is the precondition for this technology.In this paper,the limitations of current power angle measurement schemes are analyzed,and a new power angle measurement scheme based on port electrical quantity and PMU is proposed.The theoretical error of this scheme is analyzed.Through simulation,it is concluded that the power angle measurement scheme proposed in this paper can achieve high precision measurement at the optimal sequence exchange angle,so it is suitable for"phase sequence exchange" technology.