Multi-time Scale Voltage Control Methods For Distribution Networks Based On Active And Reactive Power Coordinated Optimization

To achieve the goal of carbon peak and carbon neutrality,China is accelerating the construction of a new type of power system with new energy as the main body.With the rapid development and large-scale application of renewable energy power generation technologies,the installed capacity of the distributed generation(DG)such as photovoltaic(PV)and wind power in distribution networks is continuously increasing.However,power fluctuations of DGs and loads can result in frequent nodal voltage fluctuations of distribution networks,and nodal voltages may even exceed the safe operating range,which will not only seriously affect the power quality and power supply reliability of distribution networks,but also is not conducive to the consumption of renewable energy.Therefore,the research on the voltage control method of distribution networks with high penetrations of DGs has important theoretical value and practical significance.Regarding the the problem of the active and reactive power coordination based multi-time scale voltage control for distribution networks with high levels of DGs,the specific research contents of this dissertation are as follows:(1)The voltage profile model of distribution network feeders is established firstly,followed by the theoretical analysis regarding the impact of power variations of DGs and loads on nodal voltages of distribution networks.Meanwhile,we discuss the importance of coordinated optimization of active and reactive power to reduce nodal voltage fluctuations of distribution networks.Then,a second-order cone programming based solution method of voltage control for distribution networks is presented.The second-order cone programming model can be converted from the fundamental voltage control model by using linearization and conic relaxation technologies,and then can be quickly solved.Simulations are implemented to verify the effectiveness and correctness of the above method in solving the fundamental voltage control model of distribution networks,providing a theoretical support for the following research.(2)Regarding the application of soft open points(SOPs)to participate in voltage control of distribution networks,the usage of the fixed parameter based voltage-var droop control for SOPs has the limitation of low utilization rate of available reactive power capacities and reduced regulating capabilities,and the active power at both sides of the SOPs cannot be controlled independently.To this end,this dissertation develops a voltage control method for distribution networks considering the dynamic optimization of SOPs’ voltage-var droop parameters,including three stages: long time-scale optimization,short-time scale optimization,and real-time control.In the long time-scale optimization stage,with the goal of minimizing the adjustments of the on-load tap changer(OLTC)and capacitor banks as well as the nodal voltage deviations of distribution networks,a rolling optimization based coordinated optimization model for the OLTC and capacitor banks is established.In the short time-scale optimization stage,to reduce operating losses and nodal voltage deviations of distribution networks,the active and reactive power coordinated optimization strategy among multiple SOPs and the dynamic optimization strategy of voltage-var droop control parameters of each SOP are proposed.Meanwhile,we utilize the second-order cone programming to solve the optimization models established in above two stages.In the real-time control stage,a voltage-var droop control based real-time reactive power control strategy for both sides of SOPs is given.Simulation results show that the proposed method can not only effectively deal with the problem of nodal voltage violations,but also significantly reduce the operating losses of distribution networks and the adjustments of the OLTC and capacitor banks.(3)Regarding the distribution network voltage control schemes using the traditional voltage regulation devices such as the OLTC and capacitor banks,as well as the fast-responding voltage regulation devices such as DGs,SOPs,and battery energy storage systems(BESSs),the insufficient coordination between different voltage regulation devices may lead to high operating losses of distribution networks,as well as high active power curtailments of DGs.Therefore,this dissertation proposes an active and reactive power coordination based centralized-distributed voltage control method for distribution networks.In the centralized optimization stage,a multi-objective coordinated optimization model for the OLTC,capacitor banks,SOPs and DGs is established,aiming to reduce nodal voltage fluctuations,operating losses of distribution networks,active power curtailments of DGs,and adjustments of the OLTC and capacitor banks.Meanwhile,a fast decision-making strategy is developed to find the most feasible solution from the Pareto optimal set.In the distributed optimization stage,a leader-follower consensus algorithm(LFCA)based active and reactive power coordinated control model for DGs and BESSs is established,and an adaptive adjustment scheme for the state of sharge(SOC)of BESSs is proposed.Simulation results show that the proposed method can take into account multiple optimization objectives,reasonably adjust the operation status of the OLTC,capacitor banks,SOP,BESSs and DGs according to the voltage distribution of all feeders,and finally realize the real-time voltage control of distribution networks.(4)Regarding the usage of the energy storage integrated soft open point(E-SOP)to control voltages of distribution networks,the problem of the coordinated active and reactive power optimization among multiple E-SOPs,the coordinated active and reactive power optimization between the SOP and BESS in each E-SOP,as well as the SOC control in each E-SOP should be solved.Therefore,this dissertation proposes an interval optimization based two-stage coordinated optimization method for distribution networks.In the day-ahead optimization stage,to reduce comprehensive operating costs,voltage deviations,and load balancing indexes of distribution networks,as well as to deal with the uncertainty of the DG and load power,the interval optimization model for the OLTC,capacitor banks,and E-SOPs considering the day-ahead SOC proactive planning is established.This mixed-integer nonlinear programming model can coordinate and optimize the tap position of the OLTC,switching groups of capacitor banks,the active and reactive power of each E-SOP,as well as the SOC fluctuation range of the BESS in each E-SOP.Also,this model is solved by using the column-and-constraint generation and second-order cone programming algorithms.To reduce the comprehensive operating cost of distribution networks,the intra-day optimization stage develops a rolling optimization based coordinated optimization model to optimize the active and reactive power at both sides of each E-SOP and the charging and discharging power of the BESS in each E-SOP.Simulation results show that the proposed method can effectively deal with the uncertainty of the DG and load power,not only can control the nodal voltage of distribution network within the ideal voltage range,but also can reasonably plan the allowable SOC fluctuation range of the BESS in each E-SOP.