Impedance-based stability criterion is widely used in small-signal stability analysis of converter-interfaced power systems. However, this criterion faces challenges in some multiterminal scenarios. For example, when a new connection is added to form a ring network, the criterion may yield erroneous results because the two ports are not independent. Moreover, its application becomes very complex in multi-terminal system with both impedance-stable (IS) and admittance-stable (AS) devices. To address these challenges, this paper develops an irreducible general port model based on transfer function matrix theory. This model offers a rigorous theoretical framework to revisit the fundamental principles of impedance-based criteria, clarifying their equivalence and sufficiency in high-dimensional cases. We further classify subsystems and analyze their relationships from both mathematical and physical perspectives, summarizing the rules for applying these criteria. Building on this theoretical foundation, a method based on constructing virtual subsystems is proposed for ring network formation scenarios, which accurately predicts stability. For systems with both IS and AS devices, the impedance-based criterion is extended via a rearranged port model, significantly simplifying modeling and analysis. Case studies on diverse multi-terminal systems demonstrate the effectiveness and applicability of the proposed methods.

Power electronic systems demand high reliability, yet process defects within direct bonded copper (DBC) substrates significantly compromise insulation integrity under coupled electro-thermal stress. This paper introduces a novel visual intelligent detection method based on the electroluminescence (EL) effect that employs a “working condition separation strategy” to quantitatively assess this risk. First, the electric field distribution is mapped under no-load/room temperature conditions to identify static stress concentrations caused by geometric features and defects. Subsequently, the surface temperature distribution is characterized under a representative operational load (0.8 kV DC bus, 100 Ω load resistance), where our EL-based thermometry model achieves a Mean Absolute Error (MAE) of approximately ±3.2°C, with peak module temperatures reaching 90°C. By integrating these distinct electro-thermal datasets, a fuzzy logic-based model generates a quantitative, 2D insulation risk map. Experimental validation on a commercial 1.2 kV/600 A Insulated-Gate Bipolar Transistor (IGBT) module demonstrates the framework's efficacy. The results precisely identify and differentiate high-risk locations, such as a 63% probability of insulation weakness at sharp corners versus a 23% probability along straight trace edges, and quantify their combined stress state. This visual, spatially resolved approach offers a powerful tool for refined quality control, in-depth reliability analysis, and design validation for power modules.

Grid-forming (GFM) inverters with priority current limiter suffer the fault recovery issue, commonly manifested as the failure to exit from current limitation after fault clearance. To overcome this issue, this paper proposes a virtual power <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">P_IVS</i>-feedback method. This method employs the virtual power of the internal voltage source <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">P_IVS</i> as power feedback, rather than relying on the actual output power <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">P</i><sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">e</sub>. The inherent fault recovery issue of priority current limiters can be well-solved in this simple yet efficient way. Furthermore, the proposed universal virtual power <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">P_IVS</i>-feedback framework can be expanded from a specific case of <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d</i>-axis priority current limiter to other cases of circular current limiters. Besides, a comparative study of typical virtual power feedback methods shows the feasibility and superior applicability of the proposed method. Compared to existing methods, the proposed method eliminates the necessity for complex control design, additional line or grid information, and control structure reconfiguration. Comprehensive theorical analysis and hardware-in-loop experiments verify the effectiveness of the proposed method.

On-board chargers (OBCs) with conventional two-stage architecture, consisting of an active front-end (AFE) converter and an isolated dc-dc stage, require bulky line filters and dc-link capacitors, resulting in low volumetric efficiency. Active third-harmonic injection and current unfolding methods offer significant improvement in terms of efficiency and power density in power factor correction (PFC) applications. However, existing unfolding-based topologies require two isolated dc-dc converters capable of handling the rated power for PFC and output voltage regulation. This article presents a three-phase ac-dc converter with a third-harmonic current injection circuit that processes a fraction of the total power and a single isolated dc-dc converter for galvanic isolation. Line frequency switching in the rectifier produces varying dc-link voltages, eliminating the requirement of bulky electrolytic capacitors. The article discusses detailed operation and design procedures along with an elaborate comparative analysis between the proposed topology and the conventional two-stage and Swiss rectifier-based isolated topologies. A 6.6 kW prototype is developed and tested for experimental validation of the system in both balanced and unbalanced grid conditions. The experimental results demonstrate unity power factor (upf) operation throughout the operating range, achieving a peak efficiency above 97%.

Grid-forming converters (GFMCs) receive increasing adoption in modern power systems due to their salient advantages, such as grid formulation and improved stability in weak grids. In GFMCs, inertia and damping play an essential role on the frequency regulation of modern grids. As such, the accurate estimation of these parameters is of great value for ensuring system stability, advancing ancillary service markets, and supporting grid-forming standardization. However, existing estimation methods rarely target at GFMCs' inertia and damping, rely on large amounts of data, and lack validations through experiments. In view of this, this article proposes a simple and effective model-based testing method that exploits the inherent relationship between frequency and power. By decoupling inertial power and damping power, the estimation accuracy is greatly improved. Building on this method, we further developed the first grid-forming testing equipment. As verified by experiments, inertia and damping coefficients estimation errors are within 5% and 2%, respectively.

This paper presents an anti-windup composite adaptive speed controller (AW-CASC) for permanent-magnet synchronous motors (PMSMs) operating under parameter uncertainties, external load torque, and input saturation. The proposed AW-CASC integrates three components, an adaptive compensation control (ACC) term, an adaptive proportional-integral (API) controller, and an anti-windup (AW) mechanism, and is therefore referred to as AW[API-ACC]. The ACC compensates for unknown disturbances using an adaptive law that relies only on measurable feedback signals, ensuring robust operation of the composite controller without requiring disturbance observers. The API employs a nonlinear adaptive gain algorithm based on exponential and fractional functions of the velocity error, enabling fast transient response and improved tracking accuracy without the need for fuzzy logic or gain scheduling. To suppress overshoot caused by integrator windup under large step-speed commands, a lightweight AW strategy is integrated directly into the Lyapunov-based control framework. Stability analysis confirms that all closed-loop signals are uniformly ultimately bounded. The proposed AW[API-ACC] method is implemented and experimentally validated under various speed profiles, incorporating parameter uncertainties, external load torque, and current saturation conditions. Compared with a conventional PI controller with disturbance observer (PI-OB), an adaptive optimal control (AOC) strategy, and adaptive sliding mode control combined with an extended state observer (ASMC-ESO), the AW[API-ACC] method achieves up to a 61% reduction in RMS speed error (sinusoidal), 33% and 31% reductions in overshoot and maximum tracking error (ramp), a 70% faster recovery under load torque disturbances, and an 8.8% improvement in settling time (step). These results highlight the improved robustness and tracking performance of the proposed method.

The symmetrical phase-shift modulation of the three-to-two-level neutral-point-clamped dual-active-bridge (3/2LNPC-DAB) DC-DC converter has more controllable control variables than the conventional two-level DAB converter. The increase in control variables leads to an increase in the number of operating modes and inequality constraints, significantly complicating the modulation optimization process. To enhance the efficiency of the converter, this paper proposes an optimized quadruple phase-shift (OQPS) modulation considering both conduction losses and switching losses. Five effective operating modes that have the potential to achieve zero-voltage-switching (ZVS) for all switching devices are screened based on the ZVS inequality constraints. The inductor peak current is used as an optimization objective to minimize the conduction losses while satisfying the ZVS inequality constraints. The boundary of the feasible region satisfied by the optimal solution is derived by numerical optimization. Based on this, an improved Lagrange function and Karush-Kuhn-Tucker (KKT) conditions are proposed to solve the analytical solution of OQPS modulation. Finally, the proposed OQPS modulation is applied to a 1.6kW prototype to verify the improvement of efficiency. The designed prototype can achieve 96.9% peak efficiency at 300V input and 150V output voltages. Compared with previous modulations, the proposed OQPS modulation can achieve the highest efficiency in the full power range.

Transverse flux PM linear generator (TF-PMLG) enables a higher power density under low-speed wave characteristics. However, thrust pulsation and magnetic leakage are major issues in these generators. To address the foregoing problems, a hybrid excitation TF-PMLG is proposed. However, it presents significant control challenges due to large phase inductance and non-negligible internal resistance, particularly under conditions of insufficient bus voltage. Additionally, the necessity for electromagnetic thrust to adapt in real time to wave variations further intensifies the demands on the dynamic performance of the control system. To this end, this paper proposes a model predictive thrust control (MPTC) strategy based on optimal flux linkage vector selection. It can effectively mitigate thrust fluctuations of the generator in response to wave action. Furthermore, a dynamic flux-enhancing strategy is developed, which can reduce the dependence on bus voltage magnitude, thus increasing the peak thrust of the generator. Finally, simulations and experimental results are provided to validate the effectiveness of the proposed MPTC methods in direct-drive wave energy converter (DDWEC) system.

Ion pumps operate under drastically varying load conditions, where maintaining stable high-voltage output during the extremely light-load stage (ultra-high vacuum maintenance) is particularly challenging for conventional resonant converters due to frequency runaway and gain nonlinearity. To address this, a hybrid PFM-PWM control strategy is proposed to ensure precise regulation and robust stability across the entire wide load range. The proposed method employs Pulse Frequency Modulation (PFM) with a fixed conduction time under heavy loads to ensure sufficient energy delivery, and seamlessly transitions to Pulse Width Modulation (PWM) under light-load conditions. This dual-mode approach effectively eliminates the voltage drift and instability issues inherent to traditional PFM at light loads, enabling smooth, monotonic regulation down to near-open-circuit conditions. Experimental validation on a digitally controlled 7 kV, 200 W prototype demonstrates superior performance across the complete operational spectrum. The system achieves a stable 7 kV constant voltage output even under complete open-circuit conditions, maintains rated Voltage-Current (UI) curve characteristics through constant current (100 mA), constant power (200 W), and constant voltage (7 kV) regions, and exhibits excellent dynamic response during load step transitions. Arcing simulation tests confirm robust operation under periodic short-circuit conditions with 110 ms cycles, while actual ion pump driving experiments validate reliable vacuum pumping performance from initial pump-down through ultra-high vacuum maintenance, with small and large ion pumps requiring 6.7 and 16 minutes, respectively, to complete the pumping process.

This paper presents an integrated on-board charging solution for electric vehicles (EVs) driven by switched reluctance motors (SRMs). By reusing the SRM windings and the existing asymmetric half bridge (AHB), three-phase charging can be realized with only minimal modifications to the original SRM driving system, and without incurring any additional hardware costs. A mathematical model of the instantaneous resultant torque during three-phase charging is developed, which identifies two types of rotor positions with zero average resultant torque and quantifies their phase inductance asymmetry. To tackle the intrinsic inductance asymmetry of SRM, a control strategy that combines hybrid static-dynamic feedforward decoupling with quasi-resonant controller is proposed. This method reduces the unbalance factor of the three-phase input current by 90%, which also benefits the battery due to the well mitigated double-frequency fluctuation of the output DC voltage. Experiments are conducted to validate the effectiveness of the proposed charging topology and control method.