Stability Analysis And Its Predictive Control Of Power Systems With Time-Delay

With the increasing of scale and complexity of the interconnected power system, the local controllers, in which the local measurements are employed as the feedback signals, are increasingly difficult to maintain the stability of the interconnected power system. The rapid development of the synchronized phasor technology and wide-area measurement system (WAMS) provides an opportunity to apply global signals to monitor and control the power system. The signals transmit from WAMS via communication networks will inevitably introduce time delays into the control loop. Those time delays will degrade the dynamic performance of the power system and may even cause the instability of the whole power systems.The main objective of this thesis is to investigate the the delay-dependent stability analysis and control of the power systems with time delays. Power system exsiting communication delays, and the current research backgrounds and results in the field of time-delay power system stability analysis and control are presented. Then, the main difficulties of the stability analysis and control the time-delay power system have been identified. Two time-varying delay-dependent stability criterions and the networked predictive control (NPC) have been applied for the stability analysis, compensation the network communication delays and control of the time-delay power system, respectively. The structure of the whole thesis is listed as follows:Firstly, two novel free-weighting matrices based stability criterions with small conservative for the single time-varying delays and multiple time delays linear systems are recalled, two methods, which use the linear matrix inequalities (LMI) to calculate the delay margin of the linear time-delay system, are proposed. After giving the basic principle and structure of the NPC system, two NPC control strategies, based on the controlled auto-regressive moving average (CARMA) model and the controlled auto-regressive integrated moving average (CARIMA) model, are stated, respectively. These NPC methods, based on the modified generalized predictive control (MGPC), increase networked delay compensator (NDC) to compensate the communication delays. Compared with the traditional GPC, which is only use one step predictive control signal, the NPC uses all of the predictive control sequence to compensate the communication delays.Secondly, the delay-dependent stability of the power systems with a wide-area damping controller (WADC) embedded is analyzed. The stability criterion of the linear system with single time-varying delay is applied to calculate its delay margin. Calculated results show the delay margin can be used to tune the parameters of the WADC to ensure the power system have both large enough delay margin and good damping performances.Thirdly, the delay-dependent stability criterions with single and multiple delays are employed to analyze one-area and two-area load frequency control (LFC) system with the conventional PI controllers. The relationships between the delay margin and the PI controller parameters are studied. Moreover, time-domain simulation method is used to verify the effectiveness of calculated delay margin.Fourthly, a decentralized LFC controller is designed based on NPC considering the communication delays. Then, this decentralized LFC controller is applied in three-area LFC system for the case study. The generation rate constraints are considered in the simulation. The simulation results validate the effectiveness of the proposed decentralized LFC controller. Furthermore, this proposed controller is relatively simple and easy to implement online.Fifthly, a WADC based on NPC is designed. CARMA model is used as predictive model is identified online by using the recursive least-squares (RLS) with a variable forgetting factor algorithm. The design of the proposed WADC is carried out and verified based on the two-area four-machine benchmark power system. The simulation results show that the proposed WADC can improve the damping performances of the inter-area oscillation and effectively compensate both the constant and random communication delays. In addition, the structure and algorithm of the proposed WADC are simple and easy for online implementation.Finally, the conventional wide-area supplementary damping controller (WSDC) of static Var compensator (SVC) has been investigated. The New England test power system (NETPS) equipped with a SVC is used as the test system. At first, the input wide-area signal of the WSDC is selected by analyzing the controllability/observability of linear model of the NETPS. Then, the residue method is used to determine the parameters of the conventional WSDC. The delay-dependent stability of the closed-loop power system is analyzed. The gain of the conventional WSDC is determined by using the analysis results. Simulation results are presented to show that the designed conventional WSDC of the SVC can improve the damping performances and handle a relative large communication delays.