Research On Three-Phase Power Flow And Optimal Power Flow Method Of Isolated Microgrid Considering Randomness Of Wind Power

As an important method to promote new energy consumption and the reliability of power supply,microgrid has a wide prospect of development.To meet the needs of isolated operation,microgrid not only contains new energy which has the characteristics of random and intermittent,such as wind power and photovoltaic,but also the controllable source of gas turbine and diesel generator.When the penetration of new energy is high,the stochastic fluctuation of power generation will have a significant impact on the power flow and frequency of the microgrid.The microgrid mainly connects to the middle and low voltage distribution network,and its three-phase load power and even the power grid often have asymmetry.Compared with symmetric system,the micro source under asymmetric condition has more complex control objective.The influence of different control modes and control objectives on three-phase power flow of microgrid is quite different.How to accurately simulate the three-phase control mode of the micro-source and the characteristics of control the random disturbance,establish the appropriate power flow and the optimal power flow model,so as to realize the accurate quantitative evaluation and optimal control of the power flow and frequency fluctuation of the microgrid is the key problem to ensure the safe and economic operation of the microgrid.For this reason,this paper takes the accurate simulation of frequency and three-phase flow control as the starting point,and studies the deterministic and probabilistic methods for the power flow and optimal power flow of the microgrid.The main research results are as follows:In view of the diversity of control modes and control objectives of different inverter sources,a three-phase power flow calculation and analysis method for microgrid is proposed.Based on the symmetrical control charateristics of voltage-controlled and current-controlled inverter,the model of voltage-controlled PQ and PV node,current-controlled droop and PI node mode are proposed.It provides a wider range of theoretical methods for the three-phase power flow simulation of microgrid.The Newton Raphson method is used to solve the power flow model in this paper.The effectiveness of the proposed model is verified by a large number of simulations of IEEE 13 bus system.The random fluctuation of high permeability wind power will bring a significant influence on the three-phase flow and frequency of the isolated microgrid,and how to quantify the distribution probability of random fluctuation is rarely reported.Therefore,an online three-phase probabilistic power flow model for island microgrid considering frequency fluctuation is established in this paper.The models integrated used the primary frequency characteristic and the secondary frequency characteristic to balance the random prediction error components and prediction components of source and load power and the system current unbalanced power.Also,the model not only considers the characteristics of the three-phase symmetry control and the static frequency voltage regulation of the micro source,but also adds the two frequency modulation forward control equations of the controllable micro source.The model realistic simulates the disturbance power balance of the isolated microgrid and the control characteristics of the three-phase power flow,so it can realize the accurate quantitative evaluation of the probability distribution of the power flow and frequency of the microgrid,which plays an important role in the security analysis of the operation of the isolated microgrid.In this paper,three-point estimation method is applied to realize the probabilistic evaluation of the proposed model,and the effectiveness of the model is verified by a large number of simulations of the IEEE 33 bus system.In order to cope with the influence of random disturbance of high permeability wind power on the three-phase flow and frequency of the isolated microgrid,and ensure the security and optimization of the power flow in the isolated microgrid,an online optimization model of three-phase power flow in islanded microgrid is established,which takes into account the influence of extreme disturbance of source and load power.The model not only considers the three-phase symmetry control characteristics of the micro source,the static frequency voltage regulation of the system and the power loss as objective which is the same as the conventional optimal power flow,but also takes into account the power flow and frequency security constraints of the normal state and extreme disturbance state of the system at the next time,and the secondary and primary adjustment characteristic are used to deal with the different conditions.The proposed model takes into account the influence of the extreme disturbance power and the corresponding countermearsures,thus providing an effective sheme for the online optimization control of the three-phase power flow of the high permeability wind power connected to isolated microgrid.The prediction-correction primal-dual interior point method is used to solve the model.The validity of the model is verified through the simulation analysis of IEEE 33 bus system.In order to take into account the security and optimality of online power flow control for islanded microgrid,an online optimal probability decision-making method based on chance constrained programming for three-phase power flow in islanded microgrid is proposed.In the model,the random disturbance of source and load power is represented by the predictive component and the predictive error component of the normal distribution.The objective function is the expected minimum of the active power loss of the microgrid.The constraint conditions mainly consider the satisfaction degree of the three-phase power flow and the frequency safety constraint of the microgrid,and the decision variable is the secondary adjustment of the active and reactive power of the micro source.In this paper,a stochastic optimization method based on the combination of point estimation method and immune genetic algorithm is applied to solve the model.The effectiveness of the model is verified by a large number of simulations of the IEEE 33 bus system.