Research On Stable Operation And Active Defense Of High Permeability Wind Power System In DC Outward Mode

The reverse distribution of energy resources and load demand in China presents a new challenge to the development pattern of power grid.High-voltage direct current transmission technology(HVDC)has natural advantages in the field of large-scale and long-distance transmission,and it has become the only way for the development of China’s electric power industry.After the operation of ± 800 k V Zalute-Guanggu UHVDC transmission project,northeast power grid will centrally send thermal power,wind power,nuclear power and other types of energy to shandong power grid through HVDC/UHVDC channel,providing a channel for the transmission and consumption of power resources.However,with the continuous increase of wind power permeability and UHVDC transmission capacity,northeast power grid,as an UHVDC transmission system,will face severe frequency and voltage stability problems.This dissertation aim at the frequency and voltage stability of AC/DC hybrid power network in high permeability wind power system,starting from the mathematical model construction of transient stability analysis of multi-energy AC-DC hybrid system,frequency characteristic analysis and control method of UHVDC transmission network,active defense strategy research based on improved model predictive control frequency,voltage characteristic analysis and reactive power optimization method,analyse the characteristics of system frequency and voltage stability under typical characteristics of northeast power grid,the optimization control method and active defense strategy for the stable operation of power grid frequency and voltage are proposed,which provide theoretical reference for the safe and stable operation of power grid in the DC outsourcing mode of high-permeability wind power system,and provide new ideas for the formulation of power grid safety and stability control strategy.The main research contents and achievements include:(1)Building the multi-energy AC-DC hybrid system model architecture is built,including multi-energy system model,AC-DC hybrid system model,comprehensive frequency response model and voltage stability analysis model,by means of coordinate equation transformation,the correlation relationship among the models is established,and the simultaneous solution of algebra and differential equation of AC-DC hybrid system with multiple energy sources is realized.The model architecture can reflect the same frequency and voltage stability characteristics as the actual system,as well as the response characteristics of the system after different control strategies and parameter optimization,which lays the theoretical and model foundation for the future research on the stable operation and active defense strategy of high-proportion wind power grid DC transmission.(2)Studying the frequency characteristic and control method of UHVDC transmission network.The object of this dissertation--northeast power grid only transmits power through HVDC/UHVDC channels,and there is no matching power supply near the converter station at the transmission end,the system has certain unique frequency stability characteristics.The difference characteristics of frequency stability of northeast power grid in different scenarios are simulated and analyzed,and the physical nature of frequency stability characteristics of UHVDC transmission power grid is revealed through theoretical analysis,and the frequency stability evaluation system of UHVDC transmission power grid is proposed to comprehensively measure the frequency stability level of northeast power grid;Studying the integrated frequency stability control method,which suitable for the typical characteristics of northeast power grid,and the frequency optimization control method of "wind-fire-nuclear-DC" coupling mode is proposed,which provides a new method for improving the frequency stability level of UHVDC power grid,the adaptability and rationality of this method are verified by simulation.(3)Studying the frequency active defense strategy based on Model Predictive Control(MPC).On the basis of traditional MPC control theory,an improved MPC control architecture based on feed-forward and feedback control was proposed,the frequency stability constraints and multiple optimization objectives of the power system were taken as inputs,and the frequency modulation parameters of the wind power/thermal power participating system were continuously optimized to carry out active defense control for the frequency stability of the target control system.Based on this framework,proposing an active defense control strategy of combined wind and fire frequency modulation with virtual weight,and analyzing the frequency modulation characteristics of doubly-fed fan running in parallel with synchronous generator.According to the spatiotemporal distribution characteristics of the system frequency and the real-time variation of the current wind speed,defined and adjusted the virtual weight coefficients representing the participation of the combined wind/fire frequency modulation,in order to coordinate and control the FM output power of wind power and thermal power participating systems,on the basis of ensuring that the frequency deviation of the system meets the requirements,the frequency modulation capacity of wind turbines is maximized to share the frequency modulation pressure of thermal power units,so as to provide active defense and support for the stability of the power grid frequency.(4)Studying the voltage characteristic and control method of UHVDC transmission network.Aiming at the problems of transient reactive power imbalance of AC-DC hybrid system caused by UHVDC system faults and the decrease of system voltage stability caused by wind power sources with high permeability,makes a deep analysis to the transient and static voltage stability characteristics of northeast power grid under the above typical scenarios;defined the voltage stability control domain of the UHVDC power supply network,and the voltage stability defense control architecture is constructed from the system level,which lays the foundation for the research of reactive voltage optimization control in the following paper;proposed a power flow decoupling method considering AC-DC interaction and a sensitivity decoupling calculation method for static voltage stability,and established a multi-objective reactive power optimization model considering sensitivity matrix,developed a comprehensive reactive power optimal control strategy which is in line with the voltage stability characteristics of northeast power network,and its effectiveness is verified by simulation.The study of this dissertation reveals the influence mechanism of the wind power grid connection,the interaction of power electronic devices and AC/DC system on the system frequency and voltage stability of the wind power grid with high permeability under the DC outgoing mode,developed the active defense strategy of frequency and voltage stability applicable to UHVDC power grid,which improves the safe and stable operation level of high permeability wind power grid under DC power transmission mode,and provides technical support for China’s energy base to realize large-scale power transmission.