Research On Optimal Dispatching And Control Strategy Of DC Distribution Network

With the rapid development of the national economy,users have requirement of higher electricity demand.For the existing AC power distribution network,du e to the access of distributed power sources and a large number of power electronic converters,the power quality,power flow control,and the like are complicated,and it is difficult to meet the increasing power demand.Compared with the AC distribution network,the DC distribution network is gradually applied according to its advantages in power supply capacity,power quality,line loss and power supply reliability.However,since the connection between the DC distribution network and the AC load still needs to be realized through the converter station,the calculation and control of the power flow including the AC part remains to be studied.Therefore,scheduling optimization and related control strategies in DC distribution networks are mainly discussed.For the dispatching optimization of the distribution network,it is mainly aimed at the optimal power flow distribution strategy in the DC distribution network.Based on the traditional optimal power flow distribution calculation,the load margin is optimized to alleviate the voltage instability caused by the load margin.Aiming at the problem of solving the optimal power flow distribution under the condition of considering the lowest cost and load margin,the convex optimization method can effectively reduce the difficulty of solving the optimal power flow distribution.Therefore,the original constraints of the system under non-convex conditions is discussed.Based on this situation,the original optimal power flow distribution problem is transformed into convex optimization by adding a convex extension set to the non-convex feasible set in the optimal power flow problem.Then,the semi-definite programming method is used to solve and verify the rank of the matrix in the semi-determined space,and finally the obtained optimization result is restored to the original space to obtain the current scheduling result.In the study of the control strategy of the converter station level,the droop control strategy applicable to the DC distribution network is discus sed first.Based on the traditional control strategy,referring to the secondary regulation of the frequency in the AC microgrid,it is discussed here that the steady state error inherent in the conventional droop control is eliminated by adding the integr al term to complete the secondary adjustment.However,this method may make the power distribution of each converter station uneven and the adjustment speed is slow.Therefore,based on the drooping algorithm,an improved droop control combined with the distribution averaging algorithm and integral action is proposed.Through this control,the power can be effectively distributed between the converter stations,and the steady-state error is eliminated,and the instructions issued by the upper-level scheduling are followed.Finally,this paper analyzes and verifies the above-mentioned scheduling optimization and control methods through a DC instance in a certain area.Through the analysis of the current situation of the region,the relevant system scheme,the parameters of the converter station and the selection of related components are designed according to the requirements.Through the relevant design,the relevant model is built in the simulation software according to the designed scheme and the corresponding simulation is carried out,which verifies the effectiveness of the scheduling optimization and control strategy in this example.