The authors have proposed a three-phase SR-SAB converter with a star-delta connected transformer. The proposed SR-SAB converter is a buck converter for high-power applications. In the proposed circuit, the improved total-power-factor of the star-delta connected transformer reduces the reactive power, thereby reducing the volume and loss of the high-frequency transformer. This paper presents the detailed analysis and wide-range output power characteristics of the proposed circuit. The proposed circuit achieves a wide-range output power characteristics adjusting the frequency of the transformer voltage. The operating range of the proposed output power characteristics is approximately one-fifth of the rated output power to the rated output power. The proposed analysis method using an equivalent input voltage derives the proposed output power characteristics including wiring resistance. The proposed analysis enables the accurate circuit design and modeling of the proposed circuit. The effectiveness of the proposed output power characteristics is verified by experiments using a 2.9-kW laboratory prototype.
This paper presents a Power Balance Control Technique (PBCT) for multi-converter DC systems operating under constant power load (CPL) conditions. The proposed PBCT is derived from an explicit input-output power balance principle, where instantaneous power mismatch is compensated through the inductor current. This PBCT coordinates with a conventional PI controller to improve dynamic performance control complexity. Experimental validation was conducted on two representative platforms: a low-power DC distribution system with multiple interconnected converters and a high-power in-house-designed electric-vehicle DC powertrain exhibiting severe CPL behavior and negative incremental impedance. By enforcing coordinated power regulation across cascaded converters, the proposed PBCT effectively mitigates DC bus oscillations, voltage deviations, and prolonged settling times. Experimental results under bidirectional operation, wide-range CPL step changes, and simultaneous CRL conditions demonstrate superior transient performance. Comparative results with a linear PI controller and a nonlinear sliding-mode controller (SMC) confirm faster settling times, reduced voltage drop, and enhanced DC bus stability, establishing the PBCT as a practical and robust solution for advanced DC distribution and electric-vehicle (EV) power systems.
In nonelectrified railway lines, advancements are underway for the electrification of vehicles to reduce their environmental impact, along with research and development for the practical application of electric vehicles powered by diesel generators and battery. A series-resonant permanent magnet synchronous generator (PMSG) system, consisting of a permanent magnet synchronous generator, full-wave rectifier, and resonant capacitor, is expected to be highly efficient and cost-effective, making it well-suited for applications in electric vehicles. However, the generation characteristics of series-resonant PMSG systems have not been evaluated in terms of total harmonic distortion. Therefore, this study experimentally investigated these characteristics. The experimental results revealed that the output can be enhanced by connecting a resonant capacitor, even in the presence of harmonics.
Conventional phase-shifted full-bridge (PSFB) converters employ fixed dead-time settings to guarantee zero-voltage switching (ZVS) under light-load conditions, which leads to excessive dead time and increased body-diode conduction losses at higher loads. Prior approaches either rely on additional ZVS detection circuits or use simplified models that neglect nonlinear device characteristics, limiting practical applicability. This paper proposes a load-current-based closed-loop dead-time regulation method that updates the dead time on a cycle-by-cycle basis using only output current feedback. By incorporating a nonlinear MOSFET capacitance model and resonant current behavior into a discrete-time control framework, the proposed method minimizes excess dead time while maintaining sufficient ZVS margin. The implementation requires no auxiliary sensing circuits and is compatible with standard digital controllers. A 1 kW, 100 kHz PSFB prototype is developed for validation. Experimental results show that the proposed method significantly reduces excess dead time and body-diode conduction losses, achieving up to 0.2% efficiency improvement over a 300 W-1 kW range. The method provides a practical and hardware-efficient solution for high-power-density PSFB converters.
This paper presents the advantages of a unidirectional three-phase isolated Secondary-Resonant Single-Active-Bridge (SR-SAB) DC-DC converter, wherein a resonant capacitor is connected in parallel to each diode of a three-phase Single-Active-Bridge (SAB) DC-DC converter. The SR-SAB converter can reduce the peak value of the transformer secondary voltage, allowing the use of switching devices with low breakdown voltage. This advantage of the SR-SAB converter is experimentally verified using a prototype with an output voltage of 250 V and output power of 3.3 kW.
This paper presents a unidirectional three-phase AC/DC power converter based on a single-delta bridge-cell (SDBC) converter integrated with a single-phase diode rectifier through a medium-frequency transformer. The proposed configuration targets applications requiring circuit simplicity, robustness, and reactive power control capability, such as a substation auxiliary load supply. The circuit structure is simplified by employing a diode rectifier instead of a conventional single-phase pulse width modulation converter; however, conventional circulating-current-based cluster balancing becomes difficult because the AC-side current cannot be actively controlled. To address this issue, a cluster balancing control method based on negative-sequence current injection is applied. Experimental verification using a 100 V, 5 kVA downscaled model confirmed that the proposed converter supplies active power to the DC-side loads while simultaneously controlling the reactive power on the grid side, with stable regulation of the cluster capacitor voltages. Steady-state operation and operation under a single-phase 50% voltage sag are experimentally demonstrated. In addition, the RMS current increase caused by the diode rectifier was quantitatively evaluated.
The Smart Lander for Investigating Moon (SLIM), which was developed by the Japan Aerospace Exploration Agency (JAXA) and launched in September 2023, successfully landed on the Moon on January 20, 2024. Postlanding evaluation confirmed that its precision landing performance was better than 10 m, making it the world's first lunar lander to achieve high-precision landing. Furthermore, the mass at landing was approximately 200 kg, making it one of the lightest landers ever to succeed in a lunar landing. This lightweightness was the result of the development and application of various new technologies for weight reduction. These technologies are expected to be applied to the weight reduction of future lunar and planetary probes, thereby contributing to more frequent lunar and planetary exploration missions. This review article aims to provide an overview of SLIM's achievements by citing or referring to previously published papers.
This letter proposes a non-resonant AC-AC converter applicable to induction heating (IH) systems. The proposed converter directly converts commercial-frequency AC power into high-frequency AC power without a resonant capacitor. The proposed topology achieves voltage control using a load inductance of the IH load and adjusting the duty ratio of the half-bridge switches. As a result, the proposed converter requires neither a dedicated boost inductor nor a resonant capacitor, and it can achieve power control at a fixed switching frequency. The voltage control characteristics and power control capability are experimentally verified using a 100-V, 1-kW prototype experimental setup.
The detection of inter-turn short circuits (ITSC) in transformer windings is critical, because these faults are among the most common failures encountered during transformer operation. Although conventional offline diagnostic methods have been widely applied for ITSC detection, recent research has increasingly focused on real-time monitoring approaches. In this context, this paper proposes a fault diagnosis algorithm based on Gaussian Process model to estimate the differential current of each phase under healthy operating conditions. The proposed model is trained using data from a fault-free transformer and subsequently employed to estimate the differential currents during operation. Fault detection is then performed by analyzing the error between the measured and estimated currents. When the estimated error exceeds a predefined threshold, the presence of an ITSC fault is detected. Experimental validation was conducted using a 5 kVA laboratory transformer. The results demonstrate the feasibility of the proposed approach for continuous transformer condition monitoring and real-time ITSC fault detection.
The mover operating frequency of a free-piston engine generator (FPEG) relies on its natural frequency, which is determined by the mass of the mover and engine specifications. Increasing this frequency is crucial for improving power density. Further, variable frequency operation can effectively enhance efficiency under partial load conditions. To meet these demands, this paper proposes a novel FPEG configuration with opposing air springs to realize a controllable operating frequency. A control method that adjusts the generating load coefficient using the top-dead-center (TDC) position feedback is introduced to maintain operational stability during frequency transitions. The feasibility of the proposed configuration was initially evaluated through numerical simulations, which included a comparison with a conventional configuration. Subsequently, the proposed control method was experimentally validated using a test device that simulates the dynamics of the FPEG. Results confirmed that the operating frequency could be actively varied by adjusting the air spring pressure, and the proposed control method successfully maintained the TDC position with high accuracy during these transitions.
This paper presents a coil-switching method for a multi-coil transmitter optimal control (MTOC) system applied to a planar wireless power transfer system. The MTOC system achieves constant power transmission with maximum efficiency independent of the position and orientation of the receiver. MTOC requires the simultaneous operation of multiple transmitter coils, and therefore, the number of inverter legs must match the number of activated coils, increasing system cost. To address this issue, the proposed method employs changeover switches between the transmitter and receiver, enabling a transmitter with many coils to be driven by an inverter with only a few legs while realizing MTOC operation. The coil-switching strategy operates in the search and transmission & tracking modes. In the search mode, the system detects the receiver coil and identifies the coil-combination of the transmitter coils near the receiver coil. In the transmission & tracking mode, the system performs MTOC-based power transmission while continuously tracking the position of the receiver. The effectiveness of the proposed method is experimentally demonstrated using a hexagonal honeycomb-arrayed transmitter coil configuration.
In this paper, the authors develop a collision alert system using the wide angle fovea (WAF) sensor as a safer driving support technology for the autonomous driving assistance system. The proposed system leverages the wide field of view (FOV) and high spatial resolution at the central FOV of the WAF sensor to detect vehicles farther away from the ego vehicle within the central FOV compared to the conventional system. Furthermore, it can simultaneously detect multiple vehicles by utilizing the wide FOV. The authors focus on the time to collision (TTC), issuing alerts based on time instead of distance; this implies that it can estimate the TTC independently of the speed of the vehicle. Further, the authors propose an algorithm using the mean Manhattan distance to improve the accuracy and robustness of the estimated TTC values for forward vehicles. In addition, the algorithm determines if the detected vehicle is traveling in the same lane. Evaluation results from computer simulations showed that the proposed system estimated more accurate TTC values in the high-resolution central FOV and correctly performed lane detection. Furthermore, consistent results were obtained in verification tests conducted on actual highways.
This study uses the global perturbation method to investigate global bifurcation and chaotic dynamics in a doublefed induction generator (DFIG) system with H. control. Analysis shows that the H. control law has the potential to induce dangerous homoclinic bifurcations and chaotic motions in the dynamic behavior of the rotor. These phenomena, which are particularly likely under turbulent wind conditions or weak grid connections, lead to chaotic torque pulsations, inducing mechanical stress and voltage instability, can saturate the rotor - side converter and risk controller failure. To mitigate this inherent instability, an augmented H. control strategy with wind- speed - dependent parameters is proposed. A subsequent dynamic analysis of the perturbation parameters guides their tuning to ensure stable operation. Computer simulations validate the model and verify the theoretical analysis, demonstrating that the proposed augmented control a very good fit for the experimental data.
