Energy Management Of District Integrated Electric-Gas Systems With Frequency Active Supporting Ability

At present,the proportion of installed capacity and electricity generated by new energy sources in China’s power grid is increasing.Compared with traditional power sources,new energy sources is connected to the grid through power electronics and usually operates in maximum power point tracking mode,which is weakly supportive of grid frequency.The sharp increase in its access ratio will increase the risk of grid frequency instability.Therefore,it is urgent to explore flexible and reliable frequency regulation methods to enhance the frequency regulation capability of the grid.The micro-gas turbines and power-togas devices under the district integrated electric-gas systems(D-IEGS)can quickly respond to active regulation commands and are capable of supporting grid frequency.To this end,this paper investigates the energy management method of D-IEGS to support grid frequency.(1)A time-domain analytical model of power grid frequency dynamics considering D-IEGS active support is developed:based on the classical SFR model,the frequency-supported dynamic characteristics of a grid-connected DIEGS are constructed by considering the active-frequency dynamic characteristics of the micro-gas turbine and the power-to-gas,taking into account the non-linear aspects of the governor dead zone and limiter.The finite difference method is used to discretize the frequency dynamic model in the time domain,and the optimization method with variable step size strategy is further used to obtain an easily solvable linear algebraic model.The algorithm validates the advantages of the proposed model in terms of modelling accuracy and solution cost.(2)A D-IEGS energy management strategy for actively supporting the power grid frequency is proposed:considering that D-IEGS supports grid frequency by providing fast frequency response services,a method for calculating frequency regulation benefits based on the two-part pricing scheme was designed.By constructing a feasibility check sub-problem,the effect of the frequency regulation behaviour of micro-gas turbines and power-to-gas on the operational constraints of the gas distribution network is investigated.The energy management problem is modelled as a two-stage robust optimisation problem and solved by the column and constraint generation(C&CG)algorithm.The results of the algorithm verify the effectiveness of the proposed strategy in supporting the grid frequency and the need to consider the dynamic safety constraints of the gas distribution network.(3)A D-IEGS frequency support capability evaluation method based on double-layer robust optimization is proposed:the D-IEGS double-layer robust evaluation model is constructed with the admissible domain of the upper-level grid disturbance and the security constraints of the gas distribution network as assessment indicators.The upper layer of the model is the scheduling master problem,which solves for the operating points and reserve of units within the DIEGS.The lower layer of the model includes two sub-problems,the disturbance admissible domain assessment sub-problem reflects the frequency support capability of the D-IEGS;the distribution network safety operation assessment sub-problem ensures the feasibility of the D-IEGS’s participation in frequency regulation.The algorithm analyzes the safety domain of power grid disturbance and the safe operation boundary of gas distribution network with active support of frequency.