For the power network with infeed HVDC system, problems occur around the receiving point of HVDC that the voltage magnitudes are difficult to control, the reactive power is hard to balance, and serious high voltage limit violations may arise during light-load periods. A concept of quasi synchronous condenser (QSC) is proposed in this paper to reduce the active power output and increase the range of reactive power output and voltage control capability. The QSC and infeed HVDC systems in the power network are modeled and an optimization model for QSC planning is built based on formulation of simplified AC power flow. The optimization model runs under different operational scenarios to consider different operational states of QSCs. Simulation results on modified IEEE 39-bus and 118-bus test system demonstrate applicability and effectiveness of the proposed method.