To address the issue of simulation accuracy degradation caused by virtual power losses in traditional associated discrete circuit(ADC) models for voltage-source converters (VSCs) in real-time simulation, a dual-mode constant admittance method is proposed. Firstly, by analyzing the mechanism of equivalent energy storage mutation during switching state transitions, the accumulation law of virtual losses under high-frequency PWM modulation is revealed. Secondly, based on the characteristics of switching actions during unlocking and blocking states, a constant admittance model for the converter in the unlocked state is constructed using the proposed semi-implicit decoupling method, eliminating virtual losses while maintaining a constant admittance matrix. For the blocked state, where switching transitions are fewer, the traditional ADC model is retained. Simulation results demonstrate that the proposed converter modeling exhibits minimal virtual power dissipation and high accuracy in both unlocked and blocked conditions, with no numerical oscillations during state transitions.