Abstract:  ABSTRACT： A LCC-LCC+FBMMC series based hybrid HVDC system, for which the rectifier side adopts the line commutated converter （LCC）,and the inverter side is composed by LCC in series with the full bridge sub module modular multilevel converter （FBMMC）, with the technical advantages of DC fault ride-through, mitigating commutation failure, and power flexible reversal capability and so on, is a kind of hybrid dc transmission topology suitable for future long-distance high-capacity overhead transmission. Reasonable and effective selection of controller parameters is a prerequisite for ensuring good performance of the system. This paper first establishes the mathematical model of LCC-LCC+FBMMC series based hybrid HVDC system；on this basis, proposes a controller parameter optimization method based on Simplex algorithm, and constructs an objective function based on the deviation of controller input signal to optimize the controller parameters both on the rectifier and inverter sides. Finally, an EMT model of LCC-LCC+FBMMC series based hybrid HVDC system is established in PSCAD/EMTDC, and tested under four different conditions, including active power step-change, power reversal, three-phase short-circuit fault and DC ground fault. The simulation results prove the effectiveness of the proposed optimization method, which show that the controller parameters based on the proposed optimization method can improve both the steady and transient performance of LCC-LCC+FBMMC system in different operating conditions.

Key words:  KEYWORDS： hybrid HVDC system, line commutated converter, modular multilevel converter, Simplex algorithm, parameter optimization