Lixia Tong

Bound states in the continuum (BIC) have recently attracted extensive research interest, owing to their exceptional capability for light confinement and high quality-factor (Q-factor) resonances. In this work, we design an all-dielectric terahertz metasurface based on the symmetry-breaking properties of silicon rectangular pillars. Numerical simulations demonstrate that breaking the in-plane inversion (C₂) symmetry transforms the BIC into a quasi-BIC (q-BIC), which features a high Q-factor and a narrow resonance linewidth. Through far-field multipole decomposition and near-field electromagnetic field distribution analysis, the excitation mechanism of the q-BIC mode is elucidated, revealing that the magnetic dipole (MD) contribution remains predominant over a certain range of asymmetry. Furthermore, the q-BIC resonance exhibits high sensitivity to the change in refractive index, achieving a theoretical sensitivity of 110 GHz/RIU even with an analyte thickness of only 15 μm. When MS2 and PRD1 bacteriophages are employed as model analytes with distinct effective refractive indices, the sensor produces a larger resonance frequency shift for MS2 than for PRD1, demonstrating its capability for theoretical dielectric discrimination based on refractive index differences. These findings provide a valuable reference for the development of all-dielectric terahertz metasurface platforms for label-free refractive index sensing and model virus differentiation.

Circulating current suppression can effectively improve the reliability and redundancy of parallel inverter systems. The mechanism and influencing factors of the low- and high-frequency zero-sequence circulating current (ZSCC) are analyzed in this study. Based on a mechanism analysis and the built mathematical model, the composite control strategy of zero-sequence voltage difference (ZSVD) compensation and virtual inductance is proposed to suppress the low- and high-frequency ZSCC. In the composite control strategy, the low-frequency ZCSS (LF-ZCSS) is suppressed by the ZSVD compensation method, and the HF-ZCSS is suppressed by the virtual inductance method. The ZSVD compensation is incorporated into the SVPWM as an input to regulate the modulation and suppress the LF-ZCSS, and virtual inductance is introduced into the current control loop to suppress the HF-ZCSS. A parallel system prototype composed of two 6 kW inverters is constructed. The experiments show that the ZSCC of the parallel system is reduced by 45%, which verifies the effectiveness of the proposed composite control strategy.

With the development of power conversion systems or bidirectional grid-connected inverters characterized by high DC voltage, high efficiency, and high-power density, high-switching-frequency SiC power switches are being widely used, and these require a short computational time of control algorithm. Based on the sector judgment of a space voltage vector and the midpoint potential control balancing of a DC bus, an improved finite control set method prediction control (FCS-MPC) method was proposed for a T-type three-level PCS. This improved FCS-MPC first judges the sector of the space voltage vector and locates the position of the corresponding large sector according to phase lock information; then, it analyzes the sampled voltage of the upper and lower bus capacitors to obtain the midpoint potential situation and selects appropriate small vectors based on the midpoint potential situation. This simple improved strategy can reduce the computational complexity of traditional MPC for rolling optimization, resulting in a reduction in the vectors from 27 to 8. A SiC-based 10 kW bidirectional PCS prototype verified the improved FCS-MPC, and the computational time was reduced about by 56% in comparison to traditional FCS-MPC.