Research On Online Voltage Feedback Control Of Distribution Network With High Proportion Of Distributed Photovoltaics

Inspired by the national "dual carbon" goal,the construction of renewable-dominated power systems is a clear direction for the transformation and development of energy and power in China,and the high penetration of renewable energy in the distribution networks has become the future development trend.The frequent voltage violations caused by the volatility of photovoltaic(PV)and other renewable energy generation threaten the secure and reliable operation of the distribution grid and thereby becoming an important factor restricting the consumption of renewable energy.In addition,dispersed renewable energy generation is mostly single-phase interfaced with grid,which makes the three-phase asymmetric phenomenon of the low-voltage distribution networks(DNs)more prominent.Therefore,investigating efficient and appropriate voltage control schemes has become an imperative task to ensure the secure operation of DNs with high penetration of renewable energy.The research work of this paper is organized as follows:A reactive power optimization model taylored for three-phase asymmetrical operation DNs is proposed to resolve the voltage violations caused by the fluctuation of renewable energy generation.The model incorporates the distributed PV inverters for reactive power regulation with the objective of minimizing the total network loss.Considering the coupling effect across different phases,the complete linearized three-phase power flow model is established,which is further converted to a linear equation between the squared nodal voltage magnitudes and the nodal power injections.Meanwhile,the multiphase loss calculation equation is derived,which is formulated as a quadratic function of nodal power injections,and then the non-convex reactive power optimization control problem is transformed into a convex quadratic programming problem.Finally,the effectiveness of the proposed model is verified by the case studies on IEEE 37-bus system and 123-bus system,which provides a theoretical foundation for the subsequent distributed online voltage control.A distributed synchronous online voltage feedback control method using distributed PV inverters is proposed to address the real-time voltage control problem of low-voltage DNs with high penetration of renewable energy.The dual ascent method is applied to derive the fast and efficient synchronous distributed algorithm with closed-form solutions for reactive power control variables.The control variables of different nodes are decoupled through the analysis of the distribution network property,which effectively reduces the communication complexity and realizes the coordinated optimization and autonomous update of the reactive power set-point of the distributed PV inverter.Then,the update of reactive power control variables is modified with the feedback of the real-time local voltage measurements to cope with the fast-varying system operating conditions,and the convergence of the distributed synchronous control method is proved theoretically and numerically.Finally,case studies on IEEE 123-node distribution system demonstrate that the proposed method can quickly eliminate voltage violation,and can quickly track the optimal control point with the goal of minimizing the network loss when the operating conditions change.A distributed asynchronous online voltage feedback control method is proposed to overcome the random communication delay in practical non-ideal communication systems which is ignored by the traditional distributed control methods.By introducing an eventtriggered mechanism,an asynchronous iterative framework is designed,which lifts the restriction of inter-dependence in the synchronous iteration method.Combined with the asynchronous iterative framework and the dual ascent method,an asynchronously updating rule for the control variables is proposed.Subsequently,a novel implementing architecture for the distributed asynchronous online voltage feedback control is developed to coordinate the PV inverters at different nodes,which achieves high control autonomy and mitigates the adverse influence of communication delay.The convergence of the proposed method in the non-ideal communication system is proved.Finally,case studies are conducted on IEEE 123-node system and validate the effectiveness,fastness and robustness of the proposed distributed asynchronous online voltage feedback control method.In summary,this paper focuses on the reactive power optimization of the three-phase unbalanced DNs,the distributed synchronous voltage online voltage feedback control and the distributed asynchronous voltage online feedback control under non-ideal communication conditions.The real-time online voltage control of the distribution network is realized to deal with the voltage violations caused by the fluctuation of renewable energy generation.The decision-making autonomy of individual controllers is preserved.The communication complexity is reduced,and the computation efficiency is improved,which is beneficial to the transformation of the low-voltage DNs towards a more economical,efficient and flexible network.