In this paper, an input-series flyback converter with the coupled-inductor-based passive snubber is proposed, where the input-series converter is based on transformer-integration, and the passive snubber is composed of inductors, capacitors and diodes. The inductors of the snubber in various series-modules are made on a common magnetic core, and the coupled-inductor scheme is adopted. With the help of the coupled-inductor, active input voltage sharing (IVS) of the input-series converter can also be achieved after the switches are turned off, and voltage sharing of the switch in each series-module can be ensured, which overcome the shortcomings of the existing input-series flyback converter. Active voltage sharing processes caused by the coupled-inductor are analyzed in detail. Furthermore, design guideline of the passive snubber is discussed. Finally, experimental study has been done on a 1500Vdc/60W laboratory-made prototype composed of three flyback series-modules, and the feasibility of the proposed method and the theoretical analysis are verified by the experimental results.

In this paper, the source converter (Voltage Source Rectifier, VSR) of a cascaded system is modeled based on small signal analysis, and the closed-loop transfer functions of the converter are obtained. Then the output impedance of the source converter is calculated. The analysis of the output impedance indicates that the smaller bus capacitance is, the worse stability of the cascaded system will be, and the smaller power can be converted by the cascaded system. Three kinds of virtual impedance control methods are proposed to reduce the output impedance of the source converter, all of them improve the stability and increase the maximum power of the cascaded system. The parameters of the three kinds of methods are designed respectively and their effects are compared. Simulation and experimental results show a good agreement with the theoretical analysis, which proves the validity of the virtual impedance control methods.

The input-series converters based on transformer-integration have the advantages of active input voltage sharing (IVS) and simplicity of the whole systems, which are suitable for the high-input voltage multiple-output applications. However, due to the parameters error in each series-module, the circulating current occurs among the series-modules during the active IVS process. Aiming at this type input-series two-transistor flyback converter, mechanism and influence of the circulating current in each series-module are analyzed. On this basis, according to the characteristics of the peak current mode control scheme adopted in this converter, a suppression strategy is proposed, by which influence of the circulating current on the operational stability of the converter under the light load conditions can be eliminated. Finally, based on the simulating results, the experimental study has been done on a 60W experimental prototype composed of three series-modules, and the theoretical analysis and the proposed suppression strategy have been verified by the experimental results.

This paper proposes a simple 36-pulse diode rectifier with an unconventional interphase reactor (IPR) and single-phase full-wave rectifier (SFR). The primary winding of the unconventional IPR is double tapped and the secondary winding is connected with SFR. The operation mode of the unconventional IPR is analyzed, and the optimal tap ratio and turn ratio of the unconventional IPR are designed from both viewpoints of input line current and load voltage. With the optimal parameters of the unconventional IPR, the proposed rectifier extends the conventional 24-pulse rectifier operation to 36-pulse operation and draws near sinusoidal input line currents, the total harmonic distortion (THD) of which is about 5.035%. The kVA rating of the unconventional IPR is about 2.6% of the output power. Compared with the conventional 36-pulse rectifier with triple-tapped IPR, the proposed 36-pulse rectifier is easy and simple to implement instead of using control circuits. Experiment results are provided to verify the theoretical analysis.

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.