Estimation Of The Minimum Inertia Demand Of Power Systems Considering Power Electronic Power Sources For Frequency Regulation

With the continuous promotion of low-carbon adjustment of the energy structure,multiple types of power electronic power sources are connected to the grid on a large scale,and the power system gradually shows a trend towards power electronics.The decoupling characteristics of grid-connected converters make the main grid frequency dip when new energy units,energy storage systems and flexible HVDC transmission are connected to the grid,and the active support interaction of diverse frequency regulation units gradually complicates the frequency characteristics of the power system.In addition,due to the high proportion of new energy units penetrating,the synchronous inertia of the traditional power system is replaced in large numbers and the immediate synchronous inertia support capacity decreases rapidly.The equivalent inertia level of the power-electronized power system can hardly meet the requirements of safe and stable operation of frequency.Therefore,in order to ensure that the grid can still operate safely and stably under low inertia critical conditions,the minimum inertia demand assessment under the frequency characteristic safety index needs to be studied urgently.This paper addresses the problem of evaluating the critical capacity of inertia support for powerelectronized power systems for safe frequency operation and develops a thesis on ‘Estimation of the minimum inertia demand of power-electronized power systems considering power electronic power sources for frequency regulation’.The main research is as follows:(1)Study of primary frequency control strategies for power electronic power source of multiple typesConsidering the participation of typical power electronic power sources in the primary frequency regulation of power systems,the mathematical models of primary frequency regulation control of wind turbines,energy storage systems and flexible high voltage direct current(HVDC)transmission are analysed from the level of transient operation mechanism.Based on the traditional power system primary frequency regulation control strategy,the characteristics of the traditional primary frequency regulation control model in which the synchronous inertia support capability is dominant are analysed.Combined with the primary frequency control mechanism of power electronic power sources,a primary frequency control strategy for power-electronized power system that takes into account the participation of wind power,energy storage and flexible HVDC transmission in frequency regulation is proposed.The strategy provides theoretical support for the analysis of the frequency characteristics of power-electronized power systems.Finally,an AC-DC power system simulation environment based on MATLAB/Simulink is established and the feasibility of the proposed frequency regulation control strategy is verified.(2)Quantitative analysis of power system frequency characteristics considering power electronic power sources involved in frequency regulationFirstly,the general idea of quantitative analysis of grid frequency characteristics under the participation of multiple frequency regulation resources is proposed,and the wind turbines-energy storage-flexible HVDC transmission frequency regulation frequency response model is established.Then,based on the frequency characteristic transfer function,the theoretical derivation of the steadystate frequency deviation,the initial rate of change of frequency,the maximum frequency deviation and the frequency safety margin of the power system is carried out.The influence of the steady-state frequency deviation,the inertia time constant and the control scale factors of the auxiliary frequency regulation unit on the frequency stability are quantified and the relationship between the steady-state frequency deviation and the power disturbance is calculated.Finally,the feasibility and effectiveness of the proposed analysis method is verified based on MATLAB/Simulink and the PSD-BPA simulation platform.The simulations show that the proposed method can effectively quantify the frequency characteristics of power systems and can provide guidance for the safe and stable frequency operation and control of power-electronized power systems.(3)Estimation of the minimum inertia demand of power-electronized power systemsWith the frequency-safe operation of power-electronized power systems as the target orientation,the inertia support capacity of power systems under the participation of wind turbines and flexible HVDC transmission in frequency regulation is analysed based on an improved system frequency response(SFR)model as influenced by the primary frequency regulation parameters.Based on the basis of quantitative analysis of the system frequency response characteristics,a mathematical model of the theoretical inertia of the power system is established in the form of rotor kinetic energy and the calculated inertia is obtained using a sliding window algorithm.For the requirements of safe frequency operation,the minimum inertia demand of power-electronized power systems are quantitatively estimated with the rate of change of frequency(RoCoF),the maximum frequency deviation and the steady-state frequency deviation as constraint indicators.Based on the rotor equation of motion and the frequency response derivation mechanism,optimisation strategies are proposed to increase the system inertia directly,reduce the size of the maximum active power disturbance,adjust the conventional primary frequency control parameters,adjust the power electronic power sources frequency control parameters and relax the frequency constraint to meet the minimum inertia demand of the power-electronized power systems.The proposed method integrates the frequency operation characteristics of power electronic power sources with the system minimum inertia demand estimation method and its optimisation measures,and proposes a minimum inertia demand estimation process for power-electronized power systems taking into account the classification of multiple types of evaluation time scales.The proposed inertia assessment method is validated in MATLAB/Simulink and PSD-BPA platforms.