An Adaptive Switching Frequency and Conduction Loss Optimization Modulation Strategy for Single-Phase Soft-Switching Inverter

Single-phase full-bridge inverter operating in triangular current mode (TCM) can realize zero-voltage switching to achieve high efficiency. However, the TCM full-bridge inverter features a wide range of switching frequency variation, especially near the ac current zero-crossing point (ZCP), which increases the switching loss and control difficulty. In this article, an adaptive optimal quasi-trapezoidal current mode (QTCM) control strategy is proposed based on the output characteristics of the full-bridge inverter, which reduces the switching frequency and inductor current rms by adjusting the durations of the different operating modes. The relationship between the zero level ratio <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m</i> of the inverter output and the switching frequency and the peak inductor current is established. By adjusting the ratio <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m</i>, co-optimization of switching frequency and conduction loss is implemented according to the output voltage and current. The switching sequence of the power switches is improved to achieve the seamless switching of the ac current ZCP. A 1-kW prototype with Gallium nitride (GaN) devices is built to verify the effectiveness of proposed modulation strategy with a peak efficiency of 98.3%. Compared with TCM, the proposed QTCM has a higher efficiency over the whole load range with the same hardware cost.