This work presents a variable frequency phase-shift modulation quasi-steady-state observer-based control (VFPSM-QSSOBC) strategy for series parallel resonant converters (LCC) employed in grid-friendly repetitive bipolar pulse generator (RBPG), which has advantages of high efficiency and low interharmonics injection. To reduce interharmonics, constant power (CP) charging is well achieved by using quasi-steady-state observer to accurately obtain the averaged charging power. The VFPSM strategy is applied to improve the efficiency and narrow down the switching frequency range. In order to validate the feasibility of the proposed design, a 2.8 kW/1.2 kV prototype is constructed. Experimental results show that the prototype has an efficiency of 95.4% and a lower total interharmonic distortion (TIHD) under the rated operation, which proves that VFPSM-QSSOBC has advantages over conventional variable frequency modulation proportion-integration control (VFM-PIC) and frequency trajectory control (VFM-FTC) in the efficiency and the input current quality.

A novel multimode constant power (CP) charging strategy is proposed for full-bridge (FB) and half-bridge (HB) topology morphing (TPM) LCC resonant capacitor charging power supply (CCPS) in this paper. Firstly, the virtual voltage method is used to simplify the modelling difficulty of the state plane analysis (SPA) for the HB LCC resonant converter, upon which its current output characteristics are derived. Second, a multimode constant power (CP) control strategy is proposed. The strategy utilizes the HB LCC resonant converter operating in continuous current mode (CCM) in the low-gain range, which exhibits a lower switching frequency and fewer switching devices, thereby minimizing switching losses and enhancing initial charging efficiency. Furthermore, an adaptive optimization control (AOC) strategy is proposed to make full use of the current capacity of power devices, which can reduce the duration time of the power ramp-up phase and enhance the initial charging speed. In the high-gain range, the LCC resonant converter morphs to the FB topology under DCM operation, achieving low switching losses and EMI. In addition, the optimal trajectory control (OTC) strategy is proposed to solve the large current stress at the startup stage of the HB LCC resonant converter and the seamless morphing between HB and FB topologies. Finally, the model of the HB LCC resonant converter, multimode CP charging strategy, and OTC strategy are validated by both simulation and a 3.9 kW CCPS experimental platform.

Transcranial magnetic stimulation (TMS) is a noninvasive technique that stimulates the brain via electric fields induced by pulsed currents in a coil. Beyond coil design, the pulse waveform also affects neuronal activation, though specific mechanisms remain unclear. A waveform optimization method is presented to improve stimulation selectivity, in which a multiscale model with realistic neuronal morphology quantifies the selectivity index, the induced electric field is parameterized for a pulse parameter controllable TMS discharge circuit, and particle swarm optimization is applied to refine the waveform parameters. Optimized waveforms show the potential to achieve higher selectivity than monophasic waveforms, which are known for relatively high selectivity. The results further show that waveform polarity, defined as the ratio of the positive to negative integrated areas of the induced electric field waveform, plays a key role in selectivity across cortical layers. Other waveform parameters, such as the relative order and amplitude of induced electric field levels, may also affect selectivity, with their influence varying according to neuronal morphology and the local electric field distribution. The neuronal time constant also influences how waveform parameters affect stimulation selectivity. Furthermore, stronger polarity-selectivity correlations are often associated with greater alignment between selectivity and coil heating. The proposed method can enhance TMS selectivity by optimizing stimulation waveforms. The identified patterns may help explain variability in TMS outcomes across different waveforms and between individuals, and support the development of personalized designs that enhance stimulation efficacy while minimizing coil heating.

This study proposes a novel high-frequency flat-top longitudinal magnetic field-assisted tungsten inert gas (HF-FTLMF TIG) welding method to improve arc constriction and weld penetration. The effects of magnetic field intensity and frequency on arc morphology, weld appearance, and microstructure were systematically investigated. The results show that, compared with conventional TIG welding, when the frequency of the FTLMF exceeds 1000 Hz, the arc becomes noticeably constricted, the conical angle decreases, and the heat input becomes more concentrated. Under appropriate magnetic field conditions, the arc pressure increases from 251.3 Pa for the free arc to 452.9 Pa, and the weld penetration depth increases from 0.84 mm to 1.09 mm. In addition, HF-FTLMF reduces surface unevenness and improves weld uniformity. Compared with low-frequency FTLMF (<1000 Hz), HF-FTLMF exhibits more stable arc behavior and better weld formation. SEM and EDS results further indicate that the application of HF-FTLMF affects the fusion-zone microstructure and elemental redistribution, and a relatively finer microstructure was observed under the 2000 Hz condition. These findings suggest that HF-FTLMF provides an effective approach for regulating TIG arc behavior and improving weld formation through magnetic field assistance.

The central adjustment coil of a gasdynamic Electron Cyclotron Resonance (ECR) ion source requires wide-range bipolar current regulation over ±100 A with flat-top stability within 0.1% (1000 ppm) and a current rise time below 4 ms. Conventional fully controlled H-bridge converters operating under hard-switching conditions are unable to satisfy these requirements simultaneously, as the switching loss penalty restricts the control bandwidth and degrades flat-top stability. This paper presents an Asymmetrical Half-Bridge Flyback (AHB-Flyback) converter specifically designed for this application. By incorporating a dedicated resonant branch $L_r$–$C_r$ on the primary side, the converter achieves primary-side Zero-Voltage Switching (ZVS) and secondary-side Zero-Current Switching (ZCS) over the full operating range, enabling 100 kHz operation without incurring the switching losses that would otherwise limit control bandwidth. A decoupled energy management architecture is adopted in which the primary circuit pre-charges an energy storage capacitor during idle intervals, and the coil current is subsequently established through an autonomous capacitor-to-coil discharge, effectively decoupling the peak power demand from the upstream supply network. The operating modes of the flat-top maintenance stage are analyzed through time-domain state equations, yielding an explicit closed-form expression for the Mode 3 duty cycle $D_{T3}$. This expression demonstrates that $D_{T3}$ is determined solely by the switching frequency and circuit parameters, independent of the load current setpoint, which is the fundamental mechanism enabling stable wide-range current regulation without parameter re-tuning. Parameter selection guidelines are derived from this result. Simulation results across the 20–100 A operating range and experimental validation on a scaled prototype confirm flat-top current stability within 1000 ppm and a current rise time of 4 ms, demonstrating the suitability of the proposed converter for precision ECR ion source power supply applications.

Objective. Pulse parameter controllable transcranial magnetic stimulation (cTMS) devices with fully-controlled semiconductor switches are increasingly being developed, but the primary waveform they generate is often accompanied by ringing, which is due to the resonance between the stimulation coil inductance and the snubber capacitors paired with the switches at the end of the pulse. This study provides a ringing suppression design method to effectively suppress it and reduce its impact on stimulation efficacy. Methods. A three-pronged design method is developed to suppress the ringing at its source. Firstly, laminated busbars are designed to connect main components, reducing parasitic inductance and thus decreasing the snubber energy requirement and the energy stored in the snubber capacitors, which is the main source of ringing energy. Secondly, the snubber circuit structure is improved by employing unidirectional snubber circuits to cut off the ringing loop. Lastly, a specially designed converter is used to transfer the energy stored in the snubber circuit, which to some extent represents the energy of the ringing, back to the cTMS storage capacitor. Results. The suppressed ringing duration has been significantly reduced from around 1000μs to within 30μs. Conclusion. The proposed method effectively suppresses ringing, making the realized waveform much closer to the ideal waveform, which minimizes the impact of ringing on the stimulation effect and reduces the uncontrollable deviation between the actual activated region and the ideal target activation region. Significance. The method can be easily transferred to other cTMS devices, enhancing the controllability of stimulation efficacy.