With the increasing penetration of renewable energy and the low-inertia characteristics of the external power grids, traditional traction power supply systems lack effective inertia response capability, posing significant challenge to frequency stability. To address this issue, this paper proposes a control strategy for an energy storage-based virtual synchronous generator railway power conditioner (ES-VSG-RPC). First, the basic principle of dynamic compensation for negative-sequence and harmonic currents using the ES-RPC is analyzed, and the corresponding current compensation control strategy is developed. Subsequently, a weighted system frequency considering the load powers and frequencies of the left and right power supply arms is proposed, through which the traction power supply system is equivalently modeled as a single-area power system. By combining the synchronous generator swing equation with the supercapacitor power equation, the active power output of the energy storage device is regulated according to system frequency, thereby emulating the inertia response characteristics of a synchronous generator. Based on this framework, a DC-DC converter control strategy for the ES-VSG is proposed. Finally, a time-domain simulation model is built in MATLAB/Simulink to verify the effectiveness of the proposed ES-VSG-RPC control strategy under typical operating conditions of traction power supply systems. The results show that, in low inertia traction power supply systems, the proposed ES-VSG-RPC not only achieves dynamic compensation of power quality disturbances, but also dynamically regulates the charging and discharging power of the energy storage system, thereby improving traction network frequency stability and supporting stable dynamic operation.