The use of IGCT-based current source converters (CSC) as the transmission solution for offshore wind farms can significantly reduce the construction costs of offshore converter stations compared to traditional solutions

making it a more economical choice. However

the existing modulation methods for CSCs use either pulse width modulation (PWM) or fundamental frequency modulation. The former suffers from high switching losses

while the latter

due to having only one control parameter (namely

the triggering angle)

cannot achieve flexible control of active and reactive power. To address these issues

this paper proposes a current-source converter station with integrated S7 bridge arms and its control strategy. First

the S7CSC DC transmission topology is introduced

and its operating model is analyzed in detail. The coordination between the switching control of the S7 bridge arms and the fundamental frequency modulation strategy is discussed

and a mathematical model is developed. An offshore AC voltage/frequency control strategy is then proposed. The fault characteristics of offshore AC faults are analyzed

and a low-voltage ride-through strategy under AC faults is introduced. Finally

a PSCAD simulation model of the S7CSC is built to simulate and analyze the system structure and control strategy. The results verify that the S7CSC has two degrees of freedom

can stably control the offshore AC voltage

and demonstrates good fault response characteristics

making it capable of adapting to fluctuations in wind power output.