In recent years, high-power medium-voltage converters have attracted more and more attention. In order to ensure the health of the converters, how to achieve low-cost and high-precision condition monitoring(CM) is of great significance. In this paper, a digital twin of a converter is proposed, which provides a solution for high-power converter condition monitoring. Through the dynamically updated real-time circuit model of the converter, the voltage and current of each node during the operation of the high-power converter are estimated. By using the particle swarm optimization algorithm, combined with a small amount of real-time measured data, parameters such as capacitors and inductors can be dynamically identified. Finally, the proposed method is verified in hardware in the loop(HIL) built in Simulink and a Beckhoff industrial controller.