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Your search keyword '"Wen, Huiqing"' showing total 225 results
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225 results on '"Wen, Huiqing"'

2. Analyzing Spatio-Temporal Dynamics of Grassland Resilience and Influencing Factors in the West Songnen Plain, China, for Eco-Restoration.

Author

Wang, Gefei, Shi, Zhenyu, Wen, Huiqing, Bo, Yansu, Li, Haoming, and Li, Xiaoyan

Subjects
LEAF area index, ALKALI lands, SODIC soils, SPATIO-temporal variation, ECOLOGICAL resilience, LAND cover
Abstract

Grassland plays an indispensable role in the stability and development of terrestrial ecosystems. Quantitatively assessing grassland resilience is of great significance for conducting research on grassland ecosystems. However, the quantitative measurement of resilience is difficult, and research on the spatio-temporal variation of grassland resilience remains incomplete. Utilizing the Global Land Surface Satellite (GLASS) leaf area index (LAI) product derived from MODIS remote sensing data, along with land cover and meteorological data, this paper constructed the grassland resilience index (GRI) in the west Songnen Plain, China, a typical region with salt and alkali soils. This paper analyzed the spatio-temporal changes of the GRI and explored the contribution of climate factors, human activities, and geographical factors to the GRI. The results revealed that from 2000 to 2021, the GRI in the study area ranged from 0.1 to 0.22, with a multi-year average of 0.14. The average GRI exhibited a pattern of high-value aggregations in the north and low-value distributions in the south. Trend analysis indicated that areas with an improved GRI accounted for 59.09% of the total grassland area, but there were still some areas with serious degradation. From 2000 to 2015, the latitude and mean annual temperature (MAT) were principal factors to control the distribution of the GRI. In 2020, the mean annual precipitation (MAP) and MAT played important roles in the distribution of the GRI. From 2000 to 2021, the influence of human activities was consistently less significant compared to geographical location and climate variables. [ABSTRACT FROM AUTHOR]

Published
2024
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3. Mapping Topsoil Carbon Storage Dynamics of Croplands Based on Temporal Mosaicking Images of Landsat and Machine Learning Approach.

Author

Li, Xiaoyan, Wen, Huiqing, Xing, Zihan, Cheng, Lina, Wang, Dongyan, and Wang, Mingchang

Subjects
*FARMS, *LANDSAT satellites, *SUSTAINABLE agriculture, *MACHINE learning, *BLACK cotton soil, *PLATEAUS
Abstract

Understanding changes of soil organic carbon (SOC) in top layers of croplands and their driving factors is a vital prerequisite in decision-making for maintaining sustainable agriculture. However, high-precision estimation of SOC of croplands at regional scale is still an issue to be solved. Based on soil samples, synthetic image of bare soil and geographical data, this paper predicted SOC density of croplands using Random Forest model in the Black Soil Region of Jilin Province, China in 2005 and 2020, and analyzed its influencing factors. Results showed that random forest model that integrates bare soil composite images improve the accuracy and robustness of SOC density prediction. From 2005 to 2020, the total SOC storage in croplands decreased from 89.96 to 82.79 Tg C with an annual decrease of 0.48 Tg C yr−1. The mean value of SOC density of croplands decreased from 3.42 to 3.32 kg/m2, and high values are distributed in middle parts. Changes of SOC represented significant heterogeneity spatially. 62.14% of croplands with SOC density greater than 4.0 kg/m2 decreased significantly, and 38.60% of croplands with SOC density between 2.5 and 3.0 kg/m2 significantly increased. Climatic factors made great contributions to SOC density, however, their relative importance (RI) to SOC density decreased from 44.65% to 37.26% during the study period. Synthetic images of bare soil constituted 23.54% and 26.29% of RI in the SOC density prediction, respectively, and the contribution of each band was quite different. The RIs of topographic and vegetation factors were low but increased significantly from 2005 to 2020. This study can aid local land managers and governmental agencies in assessing carbon sequestration potential and carbon credits, thus contributing to the protection and sustainable use of black soils. [ABSTRACT FROM AUTHOR]

Published
2024
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19. A Fast and Low-Cost Open-Circuit Fault Detection and Isolation Technique for Three-Phase Dual-Active-Bridge Converters Based on Finite State Machines

Author

Khan, Shahamat Shahzad and Wen, Huiqing

Abstract

As one of popular high-power power interface topologies between the energy storage devices and the dc link, the three-phase dual-active-bridge (3$\Phi$-DAB) dc–dc converter has received increasing attention. However, due to high number of semiconductor devices and multiple possible operation modes in the 3$\Phi$-DAB converters, the reliability and healthy operation become increasingly challenging compared with traditional single-phase DAB converters. This study presents detailed waveform analyses for 3$\Phi$-DAB converters under the normal and open-circuit faulty mode operation. Based on the analysis, a fast, cost-effective, reliable and sensor-less fault detection (FD) and fault isolation (FI) mechanism based on finite state machines for 3$\Phi$-DAB converters is presented in this article. Specifically, switch node voltages between the primary and secondary bridges of 3$\Phi$-DAB converters are adopted as the open-circuit fault (OCF) diagnostic signature and a low-cost OCF diagnostic circuit is utilized to perform the required signal processing. Using this technique, the open-circuit FD was achieved within 1/25th of the switching frequency and the open-circuit FI was performed within 1/6th of the switching frequency, which is the fastest FD and FI time for 3$\Phi$-DAB converters reported so far. Experimental results were acquired from a built prototype under various OCF scenarios to validate the effectiveness of the proposed technique.

Published
2024
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20. Decoupled Continuous Control Set Model Predictive Control for T-Type Three-Phase Four-Leg Three-Level Inverters Driving Constant Power Loads

Author

Zhu, Yi, Wen, Huiqing, Yang, Yong, Mao, Jianliang, Wang, Pan, Huang, Weiguo, and Rodriguez, Jose

Abstract

The control coupling and stability of three-phase photovoltaic systems with constant power loads (CPLs) are two key technical issues that urgently need to be addressed. However, current methods are difficult to solve both technical challenges simultaneously. To address these issues, this article proposes a novel decoupled continuous control set model predictive control (CCS-MPC) strategy for LC-filter T-type three-phase four-leg three-level voltage source inverters (3P4L-3L-VSIs) driving CPLs. The control strategy is developed in αβγ frame. The model of 3P4L-3L-VSIs is first transformed from abc frame to the αβγ frame to remove the coupling effects in the abc frame. Then based on the decoupled model in the αβγ frame, a novel CCS-MPC strategy is proposed to provide balanced sinusoidal voltages. The α and β components are regulated by the A, B, and C legs, while the zero-sequence component is regulated by the N leg. To confirm the effectiveness of the proposed strategy, both simulation and experimental results are presented to verify the proposed decoupled CCS-MPC strategy. The results show that the proposed control achieves low computational burden and total harmonic distortion and can increase the stability margin especially for CPLs compared with the commonly used PI-based control, PR-based control, and deadbeat control.

Published
2024
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21. Performance Quantization and Comparative Assessment of Voltage Equalizers in Mismatched Photovoltaic Differential Power Processing Systems

Author

Wang, Xue, Wen, Huiqing, Chu, Guanying, Zhu, Yinxiao, Yang, Yong, Wang, Yiwang, and Jiang, Lin

Abstract

Voltage equalizers (VEs) are essential for partially shaded photovoltaic (PV) modules by equalizing the voltage of PV modules and preventing anti-paralleled diodes from bypassing the shaded PV modules, resulting in improved power yield under partial shading conditions (PSCs). Recently, different topologies for VEs have been discussed based on the distributed maximum power point tracking (DMPPT) principle at the module level. Considering that the power flow distribution, operation modes, and actual performance of these VEs show distinct differences, it becomes increasingly important for the performance quantification and comparative assessment of various topologies both theoretically and experimentally. Here, three typical differential-power-processing-based VEs are selected, including series-resonant-voltage-multiplier (SRVM), flyback-based PV-to-IP (Flyback-PV-IP), and flyback-based PV-to-Bus (Flyback-PV-Bus). Key performance indexes for VEs have been defined, including the processed power, power losses, and overall system efficiency. To quantify the performance of different topologies of VEs, an algorithm is developed in MATLAB with daily irradiation and temperature under various PSCs. Moreover, three experimental prototypes for the selected topologies have been built and main tests under different mismatching conditions have been conducted. With a systematic performance quantification and a fair comparison of typical VEs, this article will propose a systematic evaluation method for VE schemes. Meanwhile, the optimal VE topology with its control for typical PSC cases will be identified.

Published
2024
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27. An Improved Photovoltaic Power Reserve Control With Rapid Real-Time Available Power Estimation and Drift Avoidance

Author

Zhu, Yinxiao, Wen, Huiqing, Bu, Qinglei, Wang, Xue, Hu, Yihua, and Chen, Guipeng

Abstract

The main challenges in designing the power reserve control (PRC) lie in the rapid estimation of the maximum available power ($P_\mathrm{avi}$) in real time and effective drift avoidance under the condition of fast-changing irradiation. Conventional PRC strategies utilize direct measurement or curve-fitting-based estimation to determine the $P_\mathrm{avi}$, which shows obvious limitations, such as extra hardware, implementation complexity, and slow estimation speed. Meanwhile, the drifted reserved power ($\Delta P$) may deteriorate the dynamic response performance, bring high dc-link overvoltage risk, and affect the system operation stability due to the voltage-step-$\Delta P$ regulation mechanism in conventional PRC methods. To address these issues, an improved PRC strategy with a fast $\Delta P$ transient mechanism is proposed with the rapid estimation of $P_\mathrm{avi}$ through just one pair of photovoltaic (PV) voltage and current sampling. Thus, the proposed algorithm is cost-effective, easy to implement, and compatible with existing PV systems since no additional hardware components are required. Moreover, the proposed PRC breaks through the inherent limitation of the voltage-step-$\Delta P$ mechanism, which can ensure the $\Delta P$ drift mitigation even under fast-changing weather conditions. Main experimental comparisons with other advanced PRC strategies were conducted to verify the advantages of the proposed algorithm in terms of rapid real-time available power estimation and drift avoidance.

Published
2023
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45. Review of Pulse Test Setup for the Switching Characterization of GaN Power Devices.

Author

Zu, Guangze, Wen, Huiqing, Zhu, Yinxiao, Zhong, Rui, Bu, Qinglei, Liu, Wen, Zhao, Yinchao, and Cui, Miao

Subjects
*GALLIUM nitride, *SEMICONDUCTOR devices, *POWER density, *CLAMPING circuits, *SWITCHING circuits
Abstract

Pulse test techniques are widely adopted in characterizing both the static and dynamic performances of semiconductor devices considering various device structures and operating conditions. For gallium nitride (GaN) devices, due to the current collapse phenomenon, fast and accurate measurement of their key electrical parameters, such as dynamic ON-state resistance ${R}_{\text {ds}, \mathrm{\scriptscriptstyle ON}}$ , switching rising time, fall time, switching losses, and short-circuit (SC) robustness, becomes essential. This article presents a comprehensive review of state-of-the-art pulse test setup methods such as the double-pulse test (DPT), multiple-pulse test (MPT), and SC test (SCT) for the first time, which facilitates the GaN device structure design and practical applications in high efficiency and power density power converters. [ABSTRACT FROM AUTHOR]

Published
2022
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