This article proposes a small-scale high-precision digital closed-loop modulation method for a flying-capacitor three-level inverter to eliminate the influence of dead time. The proposed method only uses a resistive voltage divider to collect the state information, without the need for a current sensor and an analog-to-digital converter, enabling a small footprint. This method does not require complex calculations, can be applied to high switching frequencies, and is independent of the original control system, so it is easy to integrate into a controller or a stand-alone IC. Finally, a 450-W/400-Hz prototype is built to verify the effectiveness of the proposed method.

Wide bandgap semiconductor devices enable inverters with higher switching and output frequencies. This poses more challenges to obtain high-quality output waveform and control performance. Dead time and switching transients can cause inverter model errors and output waveform distortion, making it difficult to effectively use a model-based high-performance controller. Classical dead-time compensation methods require additional sensing and control loops and are limited in effectiveness at high switching frequencies. Therefore, this paper proposes an advanced digital closed-loop modulation for high switching frequency inverters. By introducing the bridge arm output waveform, the effects of dead time and switching transients and model errors can be eliminated directly in the modulation part without current sensing or additional control loops, and can operate at high switching frequencies. In addition, the proposed modulation method has high integrability, flexibility and scalability. The theoretical analysis is verified by illustrative simulation and experimentally validated examples using a 1-kVA laboratory prototype with a 1000Hz fundamental frequency.

A feedforward combined with state feedback linear quadratic regulator (LQR) is proposed to reduce the output waveform distortion and load regulation of high-bandwidth inverters. However, when digital control is adopted, the additional delays introduced by each part can lead to unmodeled model errors, which not only seriously affects the stability of the system, but also complicates the design of the controller. Therefore, a method of converting the design of a digital control system into time domain pole position selection is proposed to simplify the analysis and design of the controller, and can easily convert the time domain control method into the corresponding digital control. Furthermore, to ensure system stability in the presence of parametric uncertainties in the filter components and input bus voltage, robustness to parametric uncertainties is incorporated into the proposed digital control method. The feasibility, effectiveness and superiority of this method were verified through simulation comparison and experiments.

Limited by the switching frequency of an insulated gate bipolar transistor (IGBT), the system bandwidth of high-power inverters is low. If the amplitude and phase changes of each harmonic from the reference signal to the output waveform are defined as transmission characteristics, it can be concluded that the limited bandwidth will result in nonlinear system transmission characteristics. This results in the amplitude and phase distortion of each harmonic of the asymmetric sine wave, which in turn leads to severe distortion of the output waveform. Therefore, this article proposes a method to linearize transmission characteristics. This method effectively offsets the nonlinear effect of transmission characteristics, which is caused by the limited bandwidth, by causing distortions with respect to each harmonic in the reference signal, thereby suppressing the distortion of the output waveform. In addition, an online identification method of transmission characteristics based on a state observer is proposed to achieve the online linearization of system transmission characteristics. This method does not rely on closed-loop system control, has no stability problems, and can be used for a variety of control methods. Simulation and experiments verify the effectiveness of this method.