Hybrid Multiterminal HVDC System Based on Line-Commutated and Alternate Arm Converters

Challenges in long distance power transmission and large-scale integration of renewable energy systems drive the development of high-voltage direct current (HVDC) systems. HVDC systems can be configured as combinations of line-commutated converters (LCCs), voltage source converters (VSCs) and hybrid systems. However, each hybrid configuration poses its own challenges and requires unique control. Thus, it is necessary to explore other possible configurations, especially different configurations in more complex hybrid multiterminal DC (MTDC) systems and future dc grids. This article develops the steps for integration of alternate arm converters (AACs) in hybrid MTDCs and demonstrates the operation of AACs in a hybrid MTDC system. The detailed system structure and control hierarchy are developed. The performance of the hybrid MTDC system under multiple operating scenarios including ac and dc faults are demonstrated, verifying the feasibility of an LCC and AAC-based hybrid MTDC system.