Frequency Support Control Method for Interconnected Power Systems Using VSC-MTDC

Using VSC-MTDC to provide frequency support for interconnected power systems is an attractive solution. Considering the disadvantages of traditional methods in power shortage or surplus absorption into the VSC-MTDC from AC systems requiring active power support (RAPS system) as well as flexible and effective power balance in AC systems providing active power support (PAPS system), this paper proposes a novel frequency support control method for interconnected power systems using VSC-MTDC. The main principle of the proposed frequency support control method is firstly to make the active power shortage or surplus of the RAPS system be fully and naturally absorbed into the DC grid with the AC slack bus mode control proposed for RAPS converters; in addition, the smooth switching control and the power limiting control are further proposed to realize smooth and safe power shortage or surplus absorption. Secondly, according to the proposed flexible PAPS systems matching strategy, one or more appropriate PAPS systems with adequate capacity are selected to effectively and accurately balance the unbalanced power via the corresponding PAPS converters using the active balancing power control. The theoretical analysis and simulation results using PSCAD/EMTDC have verified the validity, flexibility and universality of the proposed frequency support control method.