Power Flow Computing Model And Operation Optimization Of AC&DC Hybrid Network Considering Energy Routers

Energy router(ER),based on the modern power electronics technology,is the key to expanding the scale interconnection of AC&DC grid in the future,which is regarded as the new development trend for the next generation smart transformer.Therefore,a common steady-state model of the ER is conducive to scientific designing of AC&DC system and reasonable analyzing of its operational status.In this paper,the steady-state modeling of ER,the establishment and the feasible solution of the AC&DC power flow calculation model considering ERs and the status optimization of the hybrid system are carried out as follows:(1)The representative functional features of ER have been generalized in this paper.Then,the modularization method is employed to model the individual parts of the ER based on a highly expandable structure.A generic steady-state model,therefore,is developed after adequate consideration of the internal and external control strategies of the ER.The steady-state values of this model are guaranteed to accurate versus a simulation model,which shows the evident superiority in minimizing the time of simulation modeling and operational computing.(2)Focus on the approaching age of power system including ERs,a power flow computation model for the AC&DC mixing system taking account of the control strategies of ER is formed.An improved solution strategy based on Newton method is proposed to solve the possible divergence problem arises in the results caused by the low-resistance of DC lines and the initial voltage values in a hybrid system.The Jacobian matrix during the joint iteration solution at first is simplified by changing the actual value of the variable to the given value of the control variable of the ER at the initial calculation.Then we correct the step-length of AC&DC variables separately in the next step by combining the method of step-length correction coefficient with the feature of solving the status variables of AC&DC network independently.The comparison strategy is adopted simultaneously in the end to obtain the optimal step-length so that the optimum control of the iteration step size can be accomplished.We also propose a feasible solution search strategy considering the operation constraints of hybrid systems,which is the ER's capability of power regulation is given priority.This reformative algorithm of the joint solution proves the superiority in reducing iterations and strong anti-jamming through some typical examples.The AC&DC hybrid grid embedded ERs established in our work,which takes into account the power adjustment of the ERs,can be applied in various operating scenarios and cover the shortcoming of merely one balance node exists in the conventional power flow calculation,which means it can be employed in planning and analyzing complex grids.(3)Supposing the original power output of generators in a system is constant,a hybrid system operation optimization model employed multiple ERs is formed on the synthetical optimization target index composed of loss,voltage deviation,and stability margin.Assuming the port control strategies of energy router are set,the PSO is utilized to optimize and adjust the variables of the individual port to ameliorate the operation of the system.The cases verify the optimization model employed the comprehensive target index has a certain superiority against a single index in enhancing the general status of the system.The PSO shows desirable convergence features and stable optimization results in solving the status optimization problem of system considering ERs.