Key Technology And Application Of The Inertia-Stiffness-Compensator For Improving The Dynamic Of Grid Frequency And Voltage

Recently the large-sacle power-electronic-based facilities e.g.wind power generations,solar power generations and high voltage direct transmission are integrated into grid with different control structure and dynamic characteristics from traditional synchronous generators.On the one hand,the inertia characteristic of the divices with typical control structures and paramters is very low,which will reduce the inertia of the power system and deteriorate the dynamic performance of grid frequency.On the other hand,in the studies of traditional power system the studies and understanding on the dynamic process of grid voltage are less.The voltage deviation(?U)is used as the input to control the voltage level in the existing voltage control technology,whereas the voltage change rate(d?U/dt)is less considered as well as lack of awareness and effective control means.Rapid Voltage change and limited voltage control response lead to the voltage flicker,fluctuation and overvoltage problems.Most of power-electronic equipments are based on the vector current control technology.In front of the ac voltage controller works,these equipment behaves as current source characteristic without dynamic support for grid voltage,which may lead to the rapid voltage change before the action of the voltage control and further deteriorate the voltage dynamic.Moreover,Over-voltage and over-current tolerance of power-electronic devices is weak,thus it is more strict to the requirement of dynamic voltage and voltage levels.Based on the understanding the dynamic process of grid frequency and voltage,this paper proposes a power-electronic compensating device—Inertia-Stiffness-Compensator to improve the dynamic of grid frequency and voltage in the power system with large-sacle wind power generations.The inertia characteristics of the compensator's internal votage is used to reduce the change rate of grid frequency and the stiffness of the compensator's internal votage is used to reduce the change rate of grid voltage.Combining the theory and experimental practice,this paper studies the control and protection method,dynamic characteristics and the influecnes on the dynamic of the grid voltage and voltage,which can summarized as follow:1.This paper studies the control methods based on the deviation of active and reactive powers of the inertia-stiffness compensator,which is used to achieve the inertia and stiffness characteristics.The inertial voltage motion equation is established and used to analyze the inertia and stiffness characteristics of the inertia-stiffness compensator.2.This paper proposes the analysis model and method for the dynamic of grid frequency and voltage with the inertia characteristics and stiffness of the inertia-stiffness compensator.The application of the inertia-stiffness compensator for improving the dynamic of grid frequency and voltage is discussed in an example of the power system with large-scale wind power generations.3.The paper analyzes the major challenges of the inertia-stiffness compensator under symmetrical and asymmetrical grid fault conditions,and proposes corrensponding fault ride through strategy and continuous operations strategy,which is the important guarantee of actual project application.4.This paper designs and develops an experimental prototype to validate the control methods as well as influences on the dynamic of grid frequency and voltage of the inertia-stiffness-compensator.The proposed fault ride through operation and control methods are also verified.The experimental test in lab gives some certain reference value to the actual work.