This chapter examines the All-DC collection and transmission system for large-scale new energy bases. It covers the following topics: three phases and characteristics of new energy base power transmission development; structure of the All-DC collection system; photovoltaic array and outlet boost converter topology; medium-voltage DC collection system design and voltage level selection; medium-voltage DC transformer schemes; high-voltage and ultra-high-voltage DC systems for power transmission; modular multilevel HVDC transformers; UHVDC transformers; grounding schemes; and DC voltage control strategies for the All-DC collection and transmission system.