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The grid forming (GFM) converter may undesirably output a higher current during the recovery stage than fault duration due to its transient angle swing, which would cause the power devices to face the risk of overcurrent or even damage in both the fault stage and the recovery stage. In this letter, the current power angle plane is presented for the current trajectory description and the mechanism of the recovery overcurrent (ROC) issue is revealed through the proposed concept of critical recovery angle (CRA). On top of that, the power angle relationship in the critical ROC state is described in detail and the ROC boundary is further characterized accurately. Moreover, an analytical calculation method of CRA is proposed to identify whether the ROC phenomenon occurs, which is well validated by a series of experiments. The proposed method depicts the inherent relationship between the current behavior and power angle motion of GFM converters quantitatively and intuitively, and it may provide some new insights into the transient analysis and control optimization of GFM converters.

The dual active bridge converter using series-connected SiC mosfets (S-SiC) has attracted considerable interest in medium voltage power conversion. However, under certain operating conditions, S-SiC tends to lose zero voltage switching-on (ZVS-on), which severely impacts the converter's efficiency and S-SiC's reliability. This article proposes an enhanced phase shift segmentation modulation (EPSS) to achieve ZVS-on of S-SiC over a wide range of voltage ratio and transmission power. The foundation of this work lies in the analysis of the soft-switching boundary, which uncovers the auxiliary soft-switching effect linked to the magnetizing current and voltage ratio. This insight facilitates the derivation of an equivalent voltage ratio, simplifying parameter design. Furthermore, phase shift ratio combinations are expanded based on soft-switching boundaries to propose EPSS. A rigorous analysis of operational modes and characteristics reveals that EPSS can achieve a significant reduction in S-SiC loss with limited low voltage (LV) side arm loss incurred. Finally, experiments validate EPSS's effectiveness in achieving soft-switching and enhancing overall efficiency.

With the increasing penetration of virtual synchronous generator (VSG)-controlled inverters in the renewable power system, the transient stability analysis of the paralleled VSG system with the interactions between inverters is urgently needed. However, the large damping effect brought by VSGs on the relative motion between inverters is still unclear, which impedes the accurate transient stability evaluation of the paralleled system. In this article, the damping effect in the paralleled VSG system is explored with the recognition of the uniform and the nonuniform damping effects, and it is found that the large damping in VSGs may also destabilize the system under some nonuniform damping configurations. To figure out the influential mechanism of the damping terms in the paralleled VSGs, two customized phase portraits are presented to visualize the uniform and the nonuniform damping energies with the respective areas. On top of that, a damping energy approximation method is further proposed to quantitatively depict damping energy, and thus, the critical clearing time can be analytically solved. The effectiveness of the proposed method is validated by both simulation results and control hardware-in-loop experimental results. The results demonstrate that the proposed method can clearly characterize the large damping effects and accurately solve the critical fault clearing point, which may provide some new insights for the transient stability analysis of the paralleled VSG system.

Talkative power conversion (TPC) is a promising communication solution for the dc distributed power system (DPS). It involves embedding data into the output power ripple of a converter by using the power and signal dual modulation (PSDM) method. This article proposes a frequency shift keying (FSK)-based method for active rectified LLC (ARLLC) resonant converters. The method integrates the communication function into the power conversion by modulating data into the switching carrier. The phase control of the secondary active rectified switching devices is employed to suppress the input–output voltage gain fluctuations caused by frequency modulation, thereby avoiding communication’s influence on power conversion. For data transmission, no additional hardware or cabling is required, reducing the complexity and costs. In addition, a detailed design guideline considering both communication and power conversion is provided, facilitating the general TPC-ARLLC system design. Finally, a 500 W prototype with a resonant frequency of 120 kHz is constructed, and the experiment achieves a 10-kb/s bitrate with a 0.33% maximum output voltage fluctuation ratio, demonstrating the correctness of the proposed modulation method.

In a photovoltaic (PV) system equipped with dc power optimizers (DCPOs), communication is a critical function for ensuring reliability. This article presents a talkative power conversion (TPC) method for DCPOs using power/signal dual modulation (PSDM) to achieve integrated dc power line communication (PLC). The method integrates modulated data signal into the power control loop of a DCPO, so no transmission circuit is added for communication. The proposed PV system consists of several series-connected DCPOs and a communication hub. A communication model of the system is built, based on which the modulation/demodulation method and noise distribution are discussed. Furthermore, the cross effects between communication and power transfer are analyzed in detail, especially in pass-through mode. At last, a 2.2 kW practical system including 12 PV panels is implemented with a 3.75 kb/s data rate. The communication performance is verified in long-term running under various environments.

Due to ultrafast switching speed and high-frequency switching of silicon carbide (SiC) metal-oxide-semiconductor field-effect transistor (mosfets), crosstalk effect, high turn-on losses and electromagnetic interference are becoming constraints to the efficient and safe applications of SiC mosfets. The split-output structure has attracted widespread attention due to its advantages of overcoming the above constraints by integrating decoupling inductors. Thereby, it fully exploits the potential benefits of SiC mosfets. In this article, the effects of the split inductors on short-circuit characteristics of split-output power module are analyzed. An analytical model of the split-output power module is established to compare the electrical characteristics of the split inductors under normal operation and short-circuit faults. A dedicated short-circuit protection method is proposed based on the detection of the voltage pulse duration across the split inductors. The protection method is validated by hard switching fault and fault under load experiments. The results show that the short-circuit power device can be shut down when the short-circuit current is much lower than the continuous drain current. Besides, the short-circuit energy of the power device has the same order of magnitude as the dissipated energy under normal switching, which avoids degradation and even destruction of SiC mosfets under short-circuit faults.

In this paper, a sub-module capacitor voltage control (SCVC) is proposed to alleviate the energy balance restriction in the alternate arm converter (AAC). Considering that the arm inductor has a great impact on the energy exchange in AAC, the current commutation modulation is demonstrated firstly in this paper to extend the operating range. Then, the current commutation process for the alternate arms is further explored and derived by analytical expressions. During the commutation process, the current through the turning-on arm is rising, while the contralateral arm current is reversely freewheeling through the diodes of director switches (DSs). Moreover, the mechanism of the capacitor voltage sag caused by commutation process is clarified, which provides the fundamental to design the controller. In this manner, the sub-module capacitor voltage control (SCVC) strategy is further provided to compensate the capacitor voltage sag and achieve the normal operating in the four quadrants. Finally, the simulation and experimental results are both performed to verify the effectiveness of the presented modulation and control strategy in the different conditions.