Distribution operation must satisfy N-1 security criterion. However

it has not been taken into account in modern optimization operation models of distributed generators (DGs)

which may not satisfy security demands. In order to solve the fundamental problem

this paper proposes a new visualization method of controlling output power of DG considering N-1 security constraint. Firstly

the distribution system security region (DSSR) theory is introduced

and the concept

the model and the meaning for the security margin and the security distance is analyzed. Secondly

wind-photovoltaic conversion factor by using coordinate transformation technique is defined to analyze output power characteristics of distributed generation combination with wind power and photovoltaic generation. Next

the method to calculate output limit of DG is analyzed with the constraint of bus voltage and N-1 power flow. Then

the visualization flow chart of output power control is introduced for DG in a feeder line unit. Finally

the modified IEEE RBTS-Bus4 distribution system is presented to prove that the controlling method of output power of DG is correct and has the characteristic of visualization under the N-1 security principle. While ensuring asset efficiency maximized

this method improves theoretical and practical credentials for real-time security monitor and assessment of distribution networks including DG. This work is supported by National High Technology Research and Development Program of China (863 Program) (No. 2014AA051901).