An Efficient Loss Evaluation and Injection Method for MMC Based on AAVM With Switching Frequency Surface and Thermal Feedback

Accurate and efficient evaluation of losses in modular multilevel converters (MMC) is of great significance for the design and reliable operation of high‐voltage direct current transmission systems. In this paper, an efficient online loss evaluation method for MMC is proposed. First, a switching frequency surface is constructed based on the determined modulation and capacitor voltage balancing strategy, which enables the estimation of the switching frequency under any steady‐state operating condition. Then, an arm average value model (AAVM) is employed to estimate the upper bounds of the switching frequency and associated switching losses. Moreover, combined with the switching frequency surface, an approximate and efficient estimation of the actual switching losses is achieved, which ensures a balance between computational accuracy and efficiency. In addition, the thermal network model is employed to represent the temperature‐dependent characteristics of losses. Considering the impact of losses on simulation results, the energy absorbed by a controlled voltage source in series with the arm is used to characterize the losses. Subsequently, a switching loss injection method based on a decay function is proposed, which mitigates voltage spikes and enhances the effectiveness of loss injection. Finally, an AAVM considering loss injection is developed in PSCAD to verify the computational efficiency and accuracy of the proposed method.