A high voltage direct current (HVDC) system with conventional line commutated converter (LCC) and multiple paralleled modular multilevel converters (MMCs) in hybrid cascaded connection at the inverter side

known as a hybrid LCC/VSC cascaded HVDC (HC-HVDC) system

effectively integrates the advantages of LCC

as well as MMC technologies. However

due to the master-slave control mode adopted in the project of paralleled MMC stations

current imbalance issues would inevitably occur among paralleled MMCs in the case of power change

DC voltage drop and short-circuit fault conditions

which could result in overcurrent in MMCs or even slow down the fault recovery process. To realize current of MMC group distributed evenly

a power-based compensation control is proposed in this paper. First

imbalanced current between power-controlled and voltage-controlled MMCs is deduced

then the imbalanced current is transformed into active power

and finally

obtained active power is compensated to the active power outer loop control. By compensating the active power reference value

the proposed control approach can achieve current balancing of paralleled MMCs under different conditions. The HC-HVDC system

based on the Baihetan-Jiangsu project

which is currently under construction

is developed in PSCAD/EMTDC to validate effectiveness of the proposed control approach. Results show that

power-based compensation control can effectively balance currents of paralleled MMCs

accelerate system recovery process

and improve system dynamics.