A Two-Degree-of-Freedom DPWM Strategy for Loss-Harmonic Collaborative Optimization in Three-Phase VSCs

With the trend toward miniaturization and high integration in urban distribution networks, the thermal management of three-phase voltage-source converter (VSC) faces severe challenges due to high switching frequency and power loss-driven junction temperature (Tj) fluctuations. Traditional discontinuous pulse width modulation (DPWM) strategies often suffer from a misalignment between clamping windows and peak current regions under non-unity power factor conditions, leading to suboptimal cooling performance. This paper proposes an improved DPWM strategy with two-degree-of-freedom (2-DOF) adjustment characteristics. By introducing the clamping width angle ψ and the offset angle δ as independent control variables, the proposed strategy enables flexible reshaping of the power device commutation logic. An adaptive phase compensation mechanism is established to ensure the clamping window tracks the load current peaks in real-time, effectively maximizing switching loss suppression. Furthermore, the variable ψ provides a quantitative trade-off between conversion efficiency and total harmonic distortion (THD). The proposed algorithm is based on instantaneous logic judgment with low computational overhead, making it suitable for digital control platforms. Simulation results obtained from the PLECS electro-thermal coupling platform verify that the proposed strategy reduces the average junction temperature by approximately 10.3°C compared to traditional 30° DPWM while maintaining a low THD of 3.08%. The research demonstrates that the 2-DOF regulation mechanism successfully achieves collaborative optimization of thermal reliability and power quality.