Wide-Area Control Of Generation Side And Demand Side In Power Systems Integrating Wind Power

With high penetration of wind power generations(WPGs)integrated into power systems,new challenges inevitably arise with respect to electromechanical stability and control.Primary characteristics of WPGs include: the stochasticity and fluctuation of wind power,the difference between the inter-area utilization and local utilization,and the structure of power electronics.Apparently,traditional power system control has hardly adapted to the above revolution.For example,some actual power systems of China,Australia and the United States always suffer the risk of electromechanical instability due to the integration of large-scale WPGs.Therefore,on the basis of the above foundation,this thesis strives to make further contribution to exploring new control technologies and improving the dynamic performance for modern power systems.The thesis firstly investigates the emerging mechanism of electromechanical stability when large-scale WPGs are integrated into power systems.Specifically,multiple-mode interarea oscillations and tie-line power fluctuation of grid-connected microgrids are two key issues in this thesis.Furthermore,in order to effectively address two issues,the general framework of wide-area closed-loop control is synthesized.Finally,detailed control strategies,including generation side control and demand side control,are proposed for improving the dynamic performance of power systems respectively.Main contributions of this thesis are as follows:(1)A comprehensive wide-area closed-loop control architecture is proposed.It can be divided into five parts: quasi-decentralized control,model reduction,time delays,wide-area signal selection and wide-area controllers.In terms of wide-area control in power systems,the emerging difficulties of coordination among multiple controllers are also clarified,including the sensitivity of equilibrium point,phase difference among multiple inter-area modes,coherent control efforts of controllers,and time-varying wind power fluctuation.(2)A design method to coordinate power system stabilizers(PSSs)and dual-channel supplementary damping controllers(SDCs)of doubly-fed induction generators(DFIGs)is proposed for suppression of inter-area power oscillations.A dynamic performance index is introduced to measure the dynamics of the conventional synchronous generator and DFIG during the damping control process.Hence,the proposed method designing the PSS and SDC is formulated as an optimization problem with the objective function being the sum of weighted performance indexes and the constraints indicating the requirements on the damping of the inter-area modes.Solving the optimization problem can obtain the optimal SDC and PSS which can meet the required damping results as well as optimize dynamics of the controlled plants.Moreover,by adjusting weights in the objective function,the damping control burden can be flexibly and feasibly allocated between active and reactive power channels of DFIGs or among the damping controllers.(3)A novel load damping control architecture is proposed to dynamically modulate the power consumption of controlled loads so as to eliminate inter-area oscillations in power systems.To uncover the mechanism by which voltage-dependent loads(VDLs)influence electromechanical dynamics,the damping torque induced by VDLs is mathematically deduced based on a single machine infinite bus system.Moreover,the basic principle of proposed control strategy is to regulate the terminal voltage and power consumption of a typical largescale VDL,i.e.,the aluminum electrolysis load.Specifically,the quasi-decentralized load damping controllers used in this architecture are designed by a proposed multi-stage mixed H2/H? control approach to guarantee robustness against uncertainties(e.g.,tie-line outages,wind generation fluctuations)as well as to ensure reasonable control efforts of controlled VDLs.(4)A wide-area closed loop control architecture is proposed to smooth the short-term tieline power fluctuations for grid-connected microgrids from demand side.To optimally design the load smoothing controllers,an output regulation approach combined with linear quadratic optimal control is developed.In particular,dominant frequencies of wind power fluctuations are analyzed and incorporated into the exogenous system that models time-varying disturbances.The demand side control based on output regulation is able to achieve not only zero steady error in rejecting the time-varying wind power disturbance but also guarantee the satisfactory dynamic performance of modulated loads for the grid-connected microgrids.