Current Issue : April-June Volume : 2026 Issue Number : 2 Articles : 5 Articles
This paper proposes a sub-sampling phase-locked loop (SSPLL) that combines a time-todigital converter (TDC)-free digital coarse loop with a high-gain analog SSPD fine loop. The coarse loop follows a counter-assisted, frequency-domain DPLL framework with an auxiliary FLL, enabling wide capture range and fast initial acquisition. Precise fractional-N operation without a TDC is achieved by reusing the fine loop delta–sigma modulator (DSM) and digital-to-time converter (DTC) in the coarse loop: the DSM maps the frequency control word (FCW) fraction to a variable integer sequence for integer-domain fractional synthesis, while the DTC aligns reference clock to the nearest oscillator edge to cancel DSM-induced quantization error. An LMS-based DTC gain calibration is enabled in the coarse loop, and its calibrated gain is handed off to the fine loop, stabilizing loop switching despite the narrow locking range of the SSPD. Constraining arithmetic to the integer path eliminates a need of TDC and simplifies hardware, improving area efficiency while preserving accurate frequency/phase alignment. Simulations in 28 nm CMOS over 4–5 GHz with a 104 MHz reference demonstrate 177-fs RMS jitter, −245.6 dB FoM, 0.146-mm2 active area, and 8.94 mW power, validating wide capture, low in-band phase noise, and robust coarse-to-fine handover....
This study proposes an unsupervised anomaly detection method to identify the performance degradation in grid-connected photovoltaic (PV) inverters under multitask operation. Principal Component Analysis (PCA) and One-Class Support Vector Machine (OCSVM) were integrated to build a detection model using routine operational data. The key features include DC input, AC output, AC/DC ratio, and AC power variation, which are reduced to two principal components for anomaly boundary construction. The inverters were flagged as degraded if the AC/DC ratio was <0.96, the power fluctuation exceeded 20%, or the data fell outside the OCSVM-defined boundary. Compared with the Isolation Forest, the proposed method showed higher sensitivity. When applied to a 120 MW PV plant in Taiwan with 1292 inverters, including 55 PV-STATCOM units at night, the framework detected degradation in 5.4% of them. These results support their use in intelligent monitoring and predictive maintenance. In addition, through early fault detection and maintenance prioritization, the proposed framework contributes to enhancing reliability, reducing maintenance costs, and promoting the sustainable operation of utility- scale photovoltaic power plants....
The virtual synchronous generator (VSG) strategy has good application prospects as an effective measure to improve the grid inertia level. However, VSG strategy cannot stabilize DC voltage and may even affect the stability of DC voltage. To address this issue, this paper proposes an AC and DC inertia enhancement strategy for a bidirectional gridconnected converter (BGC) in a DC microgrid, which is simple and easy to implement, and highly similar to the traditional VSG strategy in terms of control structure. When the load fluctuates, the strategy can better improve DC voltage stability, slow down AC frequency variations, and adjust the active power of the BGC more smoothly. Firstly, the integration of the virtual inertia equations on both sides of the AC and DC is achieved without using the differentiator. Secondly, the proportional relationship between DC voltage and frequency is utilized to simplify the AC virtual inertia equation and improve the control dynamic response speed. Finally, simulation and experimental results validate the effectiveness of the proposed strategy....
This study comparatively investigates the effects of vacuum sintering and traditional sintering on the structure and electrical properties of lead zirconate titanate (PZT) 5H (PZT- 5H) piezoelectric ceramics. The density of the vacuum-sintered ceramics increases from 7.67 g/cm3 (for traditionally sintered ceramics) to 7.98 g/cm3. Importantly, the dielectric constant (εr), remnant polarization (Pr), planar electromechanical coupling coefficient (kp), and piezoelectric coefficient (d33) for the PZT-5H ceramics increase by 35%, 20%, 9%, and 12%, respectively, when vacuum sintering is employed instead of traditional sintering. Over a temperature range from room temperature to 180 ◦C, the d33 variation measured by the resonant method is only about 4% for the vacuum-sintered PZT-5H ceramics. Hightemperature impedance spectroscopy analysis reveals that vacuum sintering reduces the hole concentration in PZT-5H ceramics, leading to significant improvements in their dielectric and piezoelectric performance. This research demonstrates that vacuum sintering is a simple and effective method to enhance the density, dielectric, and piezoelectric properties of PZT-5H ceramics....
This paper proposes a super-twisting sliding mode observer-based model-free current controller (ST-MFCC) for permanent-magnet synchronous motor (PMSM). First, the mathematical model of the PMSM is established, and the model dependence of the deadbeat predictive current controller which serves as the foundation for the proposed ST-MFCC is analyzed, along with the stability impact of parameter variations on deadbeat predictive current control. Subsequently, the ST-MFCC is designed based on an ultralocal model and the super-twisting algorithm, eliminating dependence on the current model. Additionally, an adaptive method for tuning the key coefficients of the ultralocal model is introduced, enabling controller parameters to be rapidly optimized when deviations from actual system parameters occur. This approach reduces dependency on inductance parameters and aims to achieve high-performance PMSM current control with deadbeat characteristics. Finally, the effectiveness of the ST-MFCC is verified on a 400 W experimental platform....
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