This book includes original, peer-reviewed research papers from the 2021 International Top-Level Forum on Engineering Science and Technology Development Strategy -- the 6th PURPLE MOUNTAIN FORUM on Smart Grid Protection and Control (PMF2021), held in Nanjing, China, on August 14-22, 2021. The accepted papers cover the following topics:  1. Advanced power transmission technology 2. AC/DC hybrid power grid technology 3. Power Internet of Things Technology and Application 4. Operation, control and protection of smart grid 5. Active distribution network technology 6. Power electronic technology and application 7. New technology of substation automation 8. Energy storage technology and application 9. Application of new technologies such as artificial intelligence, blockchain, and big data 10. Application of Information and Communication Technology 11. Low-carbon energy planning and security 12. Low-carbon operation of the power system 13. Low-carbon energy comprehensive utilization technology 14. Carbon trading and power market 15. Carbon emission stream and carbon capture technology 16. Energy saving and smart energy technology 17. Analysis and evaluation of low-carbon efficiency of power system 18. Carbon flow modelling in power system operation The papers included in this proceeding share the latest research results and practical application examples on the methodologies and algorithms in these areas, which makes the book a valuable reference for researchers, engineers, and university students.