This paper presents a harmonic domain single-input single-output (SISO) equivalent modeling technique for the impedance modeling and stability analysis of a single-phase grid-connected voltage-source-converter (VSC). The basis is a conversion technique that transforms a harmonic-transfer-function (HTF)-based model into a SISO equivalent model while preserving all the information of frequency couplings. The proposed SISO modeling concept is useful for understanding the meaning and consequence of SISO impedance measurement of an interconnected system with frequency couplings and can be applied to impedance measurement-based analysis. Applications of this method for analyzing model reduction and stability characteristics of the VSC are presented, from which some useful conclusions regarding the accuracy of three reduced-order VSC models and the stability effects of the VSC controls with and without compensation for dc voltage variation are obtained. These examples of applications also demonstrate how the presented SISO modeling technique facilitates a simpler application of impedance-based analysis. Finally, experimental results verify the proposed VSC-SISO admittance and corresponding analyses.

Low-power grid-tied inverters can be designed to operate in discontinuous current mode (DCM) with a model-based feed-forward control, which can be advantageous for further increasing the switching frequency to achieve high power density. However, current distortions can be generated due to the parasitic capacitance of the devices. To address the issue, an improved modulation for the DCM is proposed in this study. We describe the proposed modulation, and then demonstrate its improved performance by a time-domain simulation. We also discuss the proposed modulation in comparison with another method that has been proposed previously. The proposed method is also verified by experiments using a 400 W laboratory prototype. A significant improvement in the current harmonics by the improved modulation has been confirmed.

The magnetic energy recovery switch (MERS) has been proposed as a new reactive power compensator. It has been proven by some series compensation applications. In terms of shunt compensation, however, research on MERS is still at its early stage. In this study, the characteristics of MERS that operates as a static Var compensator (SVC‐MERS) technology are clarified. First, the operating principles of SVC‐MERS are described. The proposed device achieves continuously controllable capacitive power compensation with a simple control. Its unique characteristics include line frequency switching and wide‐range impedance control by a small capacitor, which lead to a wide operating range. Second, the electrical model of SVC‐MERS is described using analytical equations, and then followed by a detailed performance analysis. In particular, the optimal parameter design and the optimal combination of control variables are established from the perspectives of low peak capacitor voltage and current harmonics. Simulation and experimental results are presented to verify the characteristics of SVC‐MERS. Finally, SVC‐MERS is compared with other existing SVC technologies. In conclusion, SVC‐MERS is determined to be an attractive alternative shunt compensator.

This article proposes to apply an improved modulation based on a discontinuous current mode (DCM) to grid-tied inverters for efficiency improvement. The losses caused by the parasitic capacitance of the devices can be nonnegligible in MHz-operated converters even with Gallium Nitride high-electron-mobility transistors (GaN-HEMTs). The proposed off-time discrete control can achieve ZVS by discretely adjusting the oscillation period. This article reviews the principles of the proposed modulation, and the mechanism of the losses caused by the parasitic capacitance of semiconductor devices and printed circuit board. This article also reports some experimental verification with a 400-W fabricated converter, which consists of GaN-HEMT devices and is operated at 1 MHz. The loss reduction by the proposed off-time discrete control was verified in the experiments, and it was confirmed that the experimentally measured loss reduction agreed with the estimated loss reduction based on the model and device characteristics.

This paper presents a meta-parameterized approach for the evaluation of Power Switch Modules (PSMs) in power converters. General models and parameters for the evaluation of power losses and volume of a PSM are presented. Then, meta-parameterization is performed for two semiconductor devices that have been successfully commercialized for low/medium power converters, Si-IGBTs, and SiC-MOSFETs. A comparative analysis based on the efficiency and power density of the considered technologies is presented. A bidirectional non-isolated DC-DC converter topology is considered as application example in order to show how meta-parameters can be used in comparative studies to optimize device selection.