A Variable Switching Frequency Virtual Space Vector Pulse-Width Modulation Based on the Current Ripple Prediction

Virtual space vector pulse-width modulation (VSV-PWM) is commonly used in neutral point clamped (NPC) three-level (3-L) inverters due to its intrinsic neutral point potential balancing feature. However, VSV-PWM brings higher switching loss than the traditional space-vector PWM (SV-PWM) under the same current harmonic content. To solve this problem, a variable switching frequency VSV-PWM (VSF-VSV-PWM) method based on the prediction of current ripple is proposed in this paper. Firstly, the current ripple of 3-L inverters under VSV-PWM is analyzed and a comparison of current ripple distribution under VSV-PWM and SV-PWM is presented. Based on the analytical results, a current ripple prediction method for 3-L inverters under VSV-PWM is proposed. In the proposed VSF-VSV-PWM, the current ripple is kept constant by varying the switching frequency dynamically according to the predicted current ripple. With this approach, the switching loss is reduced while the current ripple is controlled to track a given value. The distribution of current harmonics is dispersed and the electromagnetic interference (EMI) noise is mitigated using VSF-VSV-PWM. Experimental results are presented to validate the effectiveness of the proposed current ripple prediction and the VSF-VSV-PWM method.