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With the development of modern industrial high and new technology, users have higher and higher requirements for power supply quality. Therefore, the power quality problem of micro grid cannot be ignored. In this paper, the power quality of micro grid is taken as the research object. Through understanding the basic structure of micro grid, the power quality of micro grid is analyzed, and the impact of voltage sag on micro grid is obtained. Based on the characteristics of power transmission, the difference between droop control in micro grid and that in traditional large power grid is analyzed. Because the droop control has the problem of voltage and frequency offset, especially in the isolated operation of micro grid, over migration directly affects the stability of the system. In this paper, the restoration control of voltage and frequency is adopted to guarantee the stability of the whole system. Then, the simulation of the control strategy studied in this paper was completed based on MATLAB/Simulink simulation software, which verified the feasibility of the control method studied.

Existing personal and network encryption application modes are summarized, and a new kind of offline team confidential document application mode is defined and analyzed for satisfying special confidential demand in practical. In this mode, confidential electronic documents are classified by team’s role. Team is the smallest unit of key distribution, and access authority is allowed to be delivered between teams. PKI system dependable on Intranet or Internet is forbidden to use in this mode. In response, a cross-access method based on offline key management for this new mode is proposed, algorithms for authorization, encryption, authentication, and decryption in this method are described in detail through an implement example of transparent encryption system using Microsoft Office plug-in technology.

Existing personal and network encryption application modes are summarized, and a new kind of offline team confidential document application mode is defined and analyzed for satisfying special confidential demand in practical. In this mode, confidential electronic documents are classified by team's role. Team is the smallest unit of key distribution, and access authority is allowed to be delivered between teams. PKI system dependable on Intranet or Internet is forbidden to use in this mode. In response, a cross-access method based on offline key management for this new mode is proposed, algorithms for authorization, encryption, authentication, and decryption in this method are described in detail through an implement example of transparent encryption system using Microsoft Office plug-in technology.