  For enhancing power flow control in power transmission, a simplified new
structure of direct power flow controller with continuous full regulation range
(F-DPFC) was proposed. It has only one-stage power conversion and comprises of
a three-phase transformer in parallel and a three-phase trans-former in series
with grid, three single-phase full-bridge ac units, and a three-phase filter.
Compared with previous DPFC, the proposed one dispenses with two complex
three-phase se-lection switches which connect with high-voltage grid directly,
and has a continuous 360{\deg} adjustment range of compensation voltage by
taking place of buck-type ac unit with full-bridge type ac unit, and then
expanding the limit of its duty cycle from [0,1] to [-1,1]. Within a large
smooth zone replacing six separate zones, the proposed F-DPFC can regulate the
ampli-tude and phase angle of grid node voltage respectively and
simultaneously, and then the active and reactive power flow in grid can be
controlled smoothly and effectively. The new structure is easy to achieve
modular expansion and enables it to operate under high voltage and power
conditions. Its struc-ture and operational principle were analyzed in detail,
and a prototype was developed. The experimental results verified the
feasibility and the correctness of the theoretical analysis.
