Loss Imbalance and Transient DC-Bias Mitigation in Dual-Active-Bridge DC/DC Converters

The triple-phase shift (TPS) modulation has been widely used in dual-active-bridge (DAB) converters to improve system efficiency but still has much greater potentials to be explored. Specifically, pulsewidth modulation (PWM) generation techniques are often not discussed, which, however, are found to be crucial to enhance the converter performances. First, in conventional TPS modulations, switches in the same H-bridge turn on and off under different currents, which leads to imbalances in switching losses and, thus, different temperature rises. This will result in different heat stresses on the switches and eventually impact reliability. Second, transient dc biases occur when phase shifts are updated, which is hard to be addressed by dc-blocking capacitors. The abovementioned two issues can be simultaneously resolved by properly utilizing PWM generation techniques, without any extra components or sensors. To this end, this article presents a comprehensive analysis of loss imbalances and transient dc biases and then proposes mitigation methods. To fully exploit the proposed methods, a generalized PWM generation technique that combines the advantages of switching loss balance and transient dc-bias mitigation is proposed for enhanced performances and fast dynamic responses of DAB converters. The proposed modulation and the PWM generation strategy were verified with a laboratory prototype.