Stability Analysis And Load Frequency Control For Delayed Power Systems

The emergence of large-scale interconnected power grid accelerates the construction of China's modern power system and makes great contribution to the development of China's power industry.At the same time,the dimension of modern power system and the control difficulty of safe and stable operation are also increasing.Although the wide area measurement technology based on phasor measurement unit provides information guarantee for the safe and stable operation of modern power system,when the wide area measurement technology uses open communication network for information transmission,there will inevitably be transmission delay.The emergence of time delay often deteriorates the operation performance of power system,and sometimes endangers the safety and stability of the whole system.Therefore,the problem of stability analysis and control of high-dimensional power system with time delay has become an important topic.Based on the research methods of time delay system and sampled-data control system,this paper studies the stability and load frequency control of time delay power system.The research results are as follows:(1)Stability and load frequency control analysis method of power system with time delay based on model reconstruction technologyIn order to reduce the computational complexity of the existing methods for stability analysis and load frequency control of time delay power system,this paper uses model reconstruction technology to reduce the dimension of the stability analysis and load frequency control model of time delay power system,so as to achieve the purpose of reducing the computational complexity.Because the state matrix of power system is mostly sparse matrix,and the number of delayed states is far less than the number of all states in power system,the matrix dimension involving the delayed state is far less than that of the whole power system.The key point of model reconstruction is to separate the delayrelated and delay-free terms in the system,so as to construct a new system equation.Based on the new system equation,by combining Lyapunov theory and free-matrix-based integral inequality method,the stability conditions of delayed power system described by linear matrix inequalities are obtained.The obtained stability conditions,the computational complexity of them is greatly reduced,which provides an effective means to analyze the stability and load frequency control of high-dimensional time delay power system.(2)Stability and load frequency control analysis method of time-varying delay power system based on improved free-matrix-based integral inequalityIn view of the problem that too many state variables are used in the existing analysis methods for stability and load frequency control of time-varying delay power system,which leads to too high dimension and calculation complexity of linear matrix inequalities,in this paper,based on Lyapunov direct method,a stability and load frequency control analysis method for power systems with time delay based on improved free-matrix-based integral inequality is proposed,and linear time-varying delay dependent stability criterion is obtained.In order to obtain the stability criteria related to the linear time-varying delay,the existing stability analysis methods based on the second-order Bessel-Legendre integral inequality need to introduce additional state variables,including the first-order and second-order state integral variables with time-varying delay in the upper and lower limits of the integral.Therefore,the stability criterion has the problems of too many state variables,which lead to too high dimension and computational complexity of linear matrix inequalities.In this paper,a stability analysis method based on improved free-matrix-based integral inequality is proposed,which can effectively avoid the introduction of additional state variables.Therefore,there are fewer variables in the stability criteria,and the dimension sum and calculation complexity of linear matrix inequality are smaller.Compared with the existing articles,the analysis method in this paper not only has lower computational complexity,but also has lower conservatism.Therefore,the analysis method in this paper is more effective in analyzing the stability and load frequency control of high-dimensional time delay power system.(3)Stability analysis and controller design based on sampled-data control system and its application in load frequency controlIn order to solve the problem that the existing stability analysis and controller design method based on Lyapunov direct method are over conservative,a new two-sided looped-functional is proposed in this paper.The stability analysis and controller design method of load frequency control with lower conservatism are obtained by combining the free-matrix-based integral inequality method.Because the new two-sided looped-functional has fewer constraints and the free-matrix-based integral inequality method has lower conservatism(than other integral inequality methods),the proposed analysis and synthesis method has lower conservatism.In the existing stability criteria of sampled-data control system with communication delay,the occurrence of delay always leads to the degradation of system performance,sometimes even to the instability of the system,specifically,the emergence of delay will reduce the maximum sampling period to keep the system stable.However,in this paper,for some sampled-data control systems with constant communication delay,the research proves that the effect of the delay is positive,such as increasing the maximum sampling period to keep the system stable and accelerating the convergence speed of the system.For the sampled-data control system,the positive effect of time delay has very important practical significance and further research value.