Power-synchronization control is particularly applicable to voltage-source converters based high-voltage direct-current (HVDC) transmission connected to weak ac systems. In this paper, the multivariable feedback design aspect of the power-synchronization control is investigated by two design approaches: internal model control (IMC) and H_infin control. The paper shows that both of the methods can meet the design requirements and show good robustness with different model uncertainties and load disturbances. The advantage of the IMC approach is that it provides a transparent framework for control-system design and tuning. The algorithm used for the IMC design in this paper is simple, yet it achieves similar or even better performance and robustness compared to the more advanced optimization-based H_infin controller.