| In the past decades of China’s power system,large capacity and long-distance UHV DC transmission technology has been vigorously developed and widely used.The HVDC power is flexible and controllable,which provides favorable conditions for implementing wide-area control and solving the problem of power grid stability.In this thesis,the basic problems of multi-DC coordinated damping control are studied,including the random time delay and parameter uncertainty of multi-DC coordinated controller.A new power flow calculation algorithm,state-space model identification method,and multi DC coordinated damping control method for AC/DC hybrid system are proposed.Multi-DC coordinated control is used to improve the small disturbance stability of power angle in power system.（1）In order to provide accurate initial values for the state space modeling of AC/DC hybrid system,using the alternating iteration method,a power flow calculation method for AC/DC hybrid system is proposed,which takes into account the adjustment of converter taps,reactive power control management of converter station,converter control mode and its conversion.The parallel computing ability of multi-core CPU is used to improve the calculation speed,which improves the accuracy and efficiency of power flow calculation of AC/DC hybrid system;A 5-bus,2-circuit DC hybrid system example verifies the correctness of the proposed algorithm,and a 9241 bus,60 circuit DC hybrid system example verifies the good convergence and computational efficiency of the proposed algorithm.In order to achieve accurate identification modeling,the deterministic and stochastic hybrid system identification method DSR is applied to the state space model identification of AC/DC hybrid system.A system order determination method based on singular entropy and tanh-sigmoid saturation function is proposed.A fully automatic determination method of DSR input parameters such as order,past horizon and future horizon is proposed,which realizes the state space model identification of AC/DC hybrid system with high-dimensional,multi-input and multi-output,dense pole distribution and noise disturbance.Through three examples,the improved DSR algorithm is compared with the popular PEM,N4SID,SSREGEST and PBSID identification algorithms.The results show that the identification accuracy,anti-noise ability,closed-loop identification applicability and large-scale system identification efficiency of the proposed algorithm are significantly better than those of the compared methods.（2）A controller synthesis method is proposed to transforms the controller synthesis problem of multi-DC coordinated dynamic output feedback system into the static output feedback problem,and the orthogonal differential evolution algorithm is applied to realize multi-objective optimization.To solve the bilinear matrix inequality（BMI）problem with multi-objective optimization of H2,H∞and damping ratio,an orthogonal design method is used to generate a feedback controller,and the BMI problem is converted into the linear matrix inequality（LMI）form.The constraints such as H2,H∞and damping ratio can be expressed directly without solving multiple Lyapunov matrices constrained by multiple LMI conditions.Then the orthogonal differential evolution algorithm is used to search the optimal value of the objective function.In order to improve the search efficiency,a locally enhanced orthogonal crossover operator is introduced.Based on the above ideas,multi-objective SOF synthesis problems such as regional pole assignment,H2 and H∞minimization are realized.The efficiency and performance of the proposed algorithm are verified by the COMPLEIB test set and multi DC coordinated control example of Can Grid system.（3）In order to suppress the adverse effect of time delay on HVDC supplemental control,a delay dependent wide area damping control strategy based on Jensen integral inequality is proposed.Firstly,the state space model of AC/DC hybrid system considering time delay is derived;Secondly,based on Jensen integral inequality,the delay stability criterion of the closed-loop system is given;Aiming at the difficulty of solving the nonlinear matrix inequality in the criterion,a method of randomly generating initial solution is proposed;Finally,the delay stability upper bound of the controller is optimized by differential evolution algorithm.Compared with the popular time-delay stable controller design methods such as free weight matrix,the merits of the proposed method are based on output feedback and requires less decision variables,so it can be used in large-scale systems,and it is more practical in large-scale AC/DC hybrid systems.Three numerical examples verify the effectiveness of the proposed method.（4）In order to solve the problem that the performance of multi DC coordination controller deteriorated easily due to multi-operation modes and parameter changes of the system,a relaxed variable LMI for mixed optimization of H2,H∞,decay rate and damping ratio is derived by using convex polytopic uncertainties description,The BMI is transformed into LMI,and the differential evolution algorithm is used to provide the search direction.The hybrid optimization of H2,H∞and multiple objectives,such as decay rate and damping ratio,is realized.Compared with the method based on quadratic stability theory,the proposed method improves the solution success rate and reduces the conservatism of the controller.The simulation based on multi DC coordinated control verifies the correctness of the algorithm.（5）Aiming at the problem of ultra-low frequency oscillation system with high proportion of hydropower,the centralized or decentralized multi DC coordinated controller with specified order and the corresponding closed-loop system state space equation are derived.The performance optimization method of multi-DC coordinated controller based on orthogonal differential evolution algorithm is proposed,which can optimized the controllers’performance of given order and given structure（centralized,decentralized,include lead-lag based decentralized）in a unified framework.The proposed method is applied to CIGRE Nordic and China Southern Power Grid.The results show that the system damping is greatly improved with the three kinds of controllers designed by the purposed method. |
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