Hybrid Railway Power Quality Conditioner (HPQC) is newly proposed for its effective reduction in dc-link operation voltage while providing similar power quality compensation in cophase traction power supply compared to conventional railway power quality conditioner. However, reduction in HPQC operation voltage limits its power quality compensation capability. For instance, the previously proposed HPQC design based on minimum operation voltage under fixed rated load has minimum power quality compensation capability. Under practical conditions when load varies, the required HPQC active and reactive compensation power also changes. The dc-link operation voltage of HPQC may therefore need to be enhanced to increase its power quality compensation capability. Therefore in this paper, the relationship between dc-link voltage of HPQC and its power quality compensation capability, as well as its limitations, are being analyzed. Simulation and experimental results are also presented to verify the mentioned relationship via investigations of system performance under different loading conditions. The research can provide a guideline for determination of HPQC operation voltage when load varies.