Coordinated control strategy for MMC-CLCC considering AC voltage support and active power transmission

Abstract

• The hybrid HVDC transmission system employing the Modular Multilevel Converter (MMC) at the sending end and the Controllable Line-Commutated Converter (CLCC) at the receiving end offers advantages such as avoiding commutation failures and providing reactive power support to the sending end, thus holding promising application prospects. This paper analyzes the dynamic process of MMC and CLCC under receiving-end AC faults, as well as the power characteristics of the CLCC. It determines operational ranges of DC current, active power, and reactive power under fault conditions, and proposes a coordinated control strategy for MMC and CLCC that addresses both AC voltage support and DC power transmission. This strategy introduces reactive power sensitivity constraints to determine the reduction amount of the CLCC’s extinction angle. Meanwhile, the rectifier side calculates the maximum operating points of DC current and active power based on extinction angle command and the receiving-end AC voltage magnitude to control the DC current. Finally, two cases of three-phase short-circuit faults with different severities in the receiving-end AC system are simulated using PSCAD/EMTDC. The simulation results verify that the proposed coordinated control strategy can provide support for receiving-end AC system during fault period and ensure DC power transmission capability.