Stochastic Optimal Dispatch Of AC/DC Interconnected Power System Considering Flexibility Of Sending System

The large-scale wind power bases are mostly located in the northwest China,which are in inverse distribution with loads,and the wind power needs to be across-regional absorbed by wind-fire bundled form through the HVDC transmission.Because of the large transmission capacity,the line commutate converter-based HVDC(LCC-HVDC)becomes the main mode for the cross-regional transmission.However,due to the high proportion of wind power,the lack of hydropower,the limited regulation capacity of thermal units,and the current HVDC transmission plan is lack of regional coordination,the flexibility of the HVDC sending system is insufficient,resulting in wind power curtailment.Therefore,this paper researches the day-ahead(DA)optimal dispatch of AC/DC interconnected power system,aiming to improve the flexibility of HVDC sending system and promote the consumption of wind power.The main works of this paper are as follows:(1)The DA two-stage stochastic optimal modeling idea of AC/DC interconnected power system considering energy storages(ESs)and flexible adjustment of HVDC transmission power based on the two-stage stochastic programming theory is given.The optimal strategy of ESs to improve the flexibility of HVDC sending system is introduced,that is,the filter decomposition methods are used to decompose the net loads of HVDC sending system and the decomposed high frequency fluctuation components are suppressed by the ESs,which gives full play to the fast charge and discharge characteristics of ESs and coordinates with the regulation of thermal units.The flexible adjustment characteristics of HVDC transmission power are considered,and the static operation model of converter station is introduced which describes the reactive power characteristics of HVDC system,so as to limit the actions of reactive power equipment,realizing the limited flexible adjustment of HVDC transmission power,and ensuring the system operation safety.(2)The DA two-stage stochastic optimal dispatch model of AC/DC interconnected power system considering power fluctuation suppressed by the ESs and limited flexible adjustment of LCC-HVDC transmission power is established,which minimizes the DA dispatch cost and the real-time(RT)expected regulation cost.In the first stage,the wind power predictive output is used for modeling;and in the second stage,the wind power random scenarios are used to represent the uncertainty.(3)The optimal dispatch model of AC/DC interconnected power system is linearized.Firstly,the linearization method of AC system model is introduced;Secondly,the converter station static operation model is linearized based on the first-order Taylor expansion,and the Monte-Carlo simulation is used to simulate the linearization errors.The probability statistics of linearization errors are analyzed,verifying the linearization accuracy.(4)The wind power LCC-HVDC transmission system is used for the example tests.Firstly,the optimization results of the flexibility of HVDC sending system are analyzed,verifying the effectiveness of two flexibility regulation optimization strategies and the superiority of H-P filter decomposition method;secondly,the optimization results of HVDC system dispatch plan are analyzed,verifying the necessity of limiting the actions of reactive power equipment.