Coordinated Control of Multi-Type Embedded HVDC Systems for Prevention of Subsequent Commutation Failure

The increase of renewable energy integration is constrained by transmission congestion in a provincial power grid with limited transmission corridors. To address the congestion, the embedded high voltage direct current (HVDC) technology is proposed and being developed with anticipation, which will greatly expand transmission capacity of the grid. Multi-type embedded HVDC systems combine advantages of different HVDC technologies and are being discussed and planned, but the line-commutated converter (LCC) is still susceptible to commutation failure and even subsequent commutation failure (SCF). To prevent SCF and consequent repetitive power shocks in the hybrid AC/DC power system, a novel control scheme is proposed by coordinated regulation of multi-type embedded HVDC systems. Coupling interactions among electrical quantities between AC/DC transmission lines are constructed to illustrate the operation mechanism in the system. The feasible operation region of multi-type embedded HVDC is presented, providing a quantification of security constraints and reactive power compensation capability under certain voltage drops. A coordinated control method is then devised to collectively adjust controller settings of multi-type embedded HVDC systems according to the severity of AC faults and expected bus voltage through reactive power transfer. SCF can be effectively prevented, avoiding repetitive power shocks within the interconnected hybrid AC/DC power system. The effectiveness of the proposed control is verified in a hybrid system with multi-type embedded HVDC.