Dead-Time Compensation Based on Current Phase Estimation for High-Frequency Cascaded Transformer Multilevel Inverter

The cascaded transformer multilevel inverter (CTMI) is a promising topology for high-power electromagnetic wave amplifiers with over 17 kHz high frequency. However, due to the large number of submodules and the short period, the low-order harmonics introduced by dead-time effects are significant and severely deteriorate the waveform quality. To address the dead-time harmonic problems of CTMIs in high-frequency applications, this paper proposes a novel dead-time compensation method based on accurate current phase estimation. The CTMI is mathematically modeled using an original cascaded transformer decoupling method, which includes all the parasitic parameters. With the correction of dead-time hysteresis effects, the current phase angle is accurately estimated using the proposed model. The pulse width of each submodule is compensated according to the estimated angle. The proposed method avoids the current sampling and the communication delay. Compared with conventional methods, the proposed method has a more excellent low-order harmonic suppression effect. The 3rd and 5th harmonics are significantly suppressed and the total harmonic distortion (THD) is reduced. The proposed method has been validated by simulation and experiments in a 17-level high-frequency CTMI.