Grid-Friendly Integration of Photovoltaic Systems Design and Control

Yongheng YANG 전력전자학회 2019 ICPE(ISPE)논문집 Vol.2019 No.5

Benchmarking of Phase Locked Loop based Synchronization Techniques for Grid-Connected Inverter Systems

Yongheng Yang,Lenos Hadjidemetriou,Frede Blaabjerg,Elias Kyriakides 전력전자학회 2015 ICPE(ISPE)논문집 Vol.2015 No.6

Grid-connected renewables are increasingly developed in recent years, e.g. wind turbine systems and photovoltaic systems. Synchronization of the injected current with the grid is mandatory. However, grid disturbances like voltage sags, harmonics, and frequency deviations may occur during operation, becoming inevitable challenges to the synchronization of the grid-connected renewable energy systems. In order to ensure the quality of the power generation from the renewables, robust and reliable synchronization methods are in demand. Among the prior-art solutions, Phase Locked Loop (PLL) based synchronization methods have gained much popularity in grid-connected applications. However, an appropriate selection and thus a proper design of the selected PLL synchronization remain of interest in practice, especially for single-phase systems. Therefore, in this paper, a benchmarking of the main PLL synchronization methods for single-phase grid-connected inverter systems in terms of accuracy, dynamic response, harmonic immunity, etc., has been conducted. Experiments on a 1-kW single-phase gridconnected system, suffering from different grid disturbances, are performed for the benchmarking. The experimental results have verified the discussions.

Effects of dexmedetomidine on pulmonary function in patients receiving one-lung ventilation: a meta-analysis of randomized controlled trial

Yang Lin,Cai Yongheng,Dan Lin,Huang He,Chen Bing 대한마취통증의학회 2023 Korean Journal of Anesthesiology Vol.76 No.6

Background: Mechanical ventilation, particularly one-lung ventilation (OLV), can cause pulmonary dysfunction. This meta-analysis assessed the effects of dexmedetomidine on the pulmonary function of patients receiving OLV. Methods: The Embase, PubMed, MEDLINE, Cochrane Library, ClinicalTrials.gov, and Chinese Clinical Trial Registry databases were systematically searched. The primary outcome was oxygenation index (OI). Other outcomes including the incidence of postoperative complications were assessed. Results: Fourteen randomized controlled trials involving 845 patients were included in this meta-analysis. Dexmedetomidine improved the OI at 30 (mean difference [MD]: 40.49, 95% CI [10.21, 70.78]), 60 (MD: 60.86, 95% CI [35.81, 85.92]), and 90 min (MD: 55, 95% CI [34.89, 75.11]) after OLV and after surgery (MD: 28.98, 95% CI [17.94, 40.0]) and improved lung compliance 90 min after OLV (MD: 3.62, 95% CI [1.7, 5.53]). Additionally, dexmedetomidine reduced the incidence of postoperative pulmonary complications (odds ratio: 0.44, 95% CI [0.24, 0.82]) and length of hospital stay (MD: −0.99, 95% CI [−1.25, −0.73]); decreased tumor necrosis factor-α, interleukin (IL)-6, IL-8, and malondialdehyde levels; and increased superoxide dismutase levels. However, only the results for the OI and IL-6 levels were confirmed by the sensitivity and trial sequential analyses.Conclusions: Dexmedetomidine improves oxygenation in patients receiving OLV and may additionally decrease the incidence of postoperative pulmonary complications and shorten the length of hospital stay, which may be related to associated improvements in lung compliance, anti-inflammatory effects, and regulation of oxidative stress reactions. However, robust evidence is required to confirm these conclusions.

A Switched Quasi-Z-Source Inverter with Continuous Input Currents

Jing Yuan,Yongheng Yang,Frede Blaabjerg 전력전자학회 2019 ICPE(ISPE)논문집 Vol.2019 No.5

This paper proposes a modified Switched quasi-ZSource Inverter (Sq-ZSI). The proposed Sq-ZSI achieves continuous input currents with a larger conversion ratio by replacing one diode of the Diode-assisted Switched Boost Inverter (DASBI) with a capacitor. Moreover, the voltage stress of the power switches in the proposed Sq-ZSI is lower and the voltage stress of the capacitors remains the same. The proposed topology is benchmarked with other Z-source inverters using active switches in terms of conversion ratio, voltage gain, and stresses on the power switches and capacitors. Simulation and experimental tests are provided to validate the analysis.

State-Space Modeling of Grid-Connected Power Converters Considering Power-Internal Voltage Characteristics

Qiao Peng,Yongheng Yang,Frede Blaabjerg 전력전자학회 2019 ICPE(ISPE)논문집 Vol.2019 No.5

To analyze the stability of power electronicsdominated systems, this paper develops a state-space model of power converters including the DC-link voltage control, where the power-internal voltage (PIV) characteristics of the power converters are considered. The PIV concept comes from the inertia characteristic and swing equation of synchronous generators. It reflects the relationship between the output power and converter internal voltage, the converter response to grid disturbances, and finally, the impact of power converters on the grid stability. In the proposed model, the inputs are the outer controller references and the converter output power, i.e., the power at the point of common coupling (PCC). The output of the model is the internal voltage that determines the grid power distribution, including the power at the PCC. The power will be fed back to the converters as an input, and thinks the closed-loop model of the converterbased system is obtained. Importantly, the parameters of the proposed model are independent of the power grid, but related to the converter operation points and parameters. This makes the model more general and can be employed to analyze multiple converter-based systems. Furthermore, a case study is conducted in this paper to demonstrate the model and the stability analysis.

Modified Quasi-Z-Source Inverter with Model Predictive Control for Constant Common-Mode Voltage

Wenjie Liu,Yongheng Yang,Tamas Kerekes 전력전자학회 2019 ICPE(ISPE)논문집 Vol.2019 No.5

The common-mode voltage (CMV) of transformerless inverters in photovoltaic system should be properly addressed. The conventional CMV reduction methods for voltage source inverters should be modified when applied to the quasi-Z-source inverters with shoot-through states. The shoot-through states in a quasi-Z-source inverter may lead to high-frequency harmonics in the CMV, thus inducing severe leakage currents. Hence, this paper analyzes the CMV in the quasi-Z-source inverter. More importantly, a modified quasi-Z-source inverter that can achieve a constant CMV through model predictive control is discussed. Furthermore, redundant switching vectors are added to reduce the computation burden when the model predictive control is adopted. Simulations are presented to validate the CMV reduction methods.

Thermal Stress Model of Transversal Forced Air-Cooled Capacitor Banks for MWPower Converters

Zhijian Yin,Rui Wu,Morten Hygum,Yongheng Yang,Huai Wang 전력전자학회 2019 ICPE(ISPE)논문집 Vol.2019 No.5

Capacitor banks are key components in high power applications, the reliability of which affects the overall system lifetime. It is known that the thermal stress in each capacitor can affect the lifetime performance of the entire capacitor bank. In this paper, an analytical thermal model is presented to estimate the average capacitor thermal stress in a transversal forced air-cooled three-phase AC-filter capacitor bank for MW-level power converters. The proposed model calculates the thermal resistance of a capacitor bank considering power losses, geometry, cooling conditions and physical arrangement. With a conventional Foster thermal network, the hot-spot temperature and case temperature for each capacitor can be obtained. The experimental results on a full-scale three-phase filter capacitor bank consisting of 27 film sub-capacitors have demonstrated the effectiveness of this model.

Research on the Scheduling of Legal Operating Vehicles based on NFC

Jiyan Lin,Peini Shang,Fei Yang,Yongheng Zhang 보안공학연구지원센터 2016 International Journal of Grid and Distributed Comp Vol.9 No.11

In the study of reasons that cause the flush illegal operating vehicles, we found out that the insufficient legal operating vehicles were the main cause. In order to efficiently solve the illegal operating, the paper brings out the research of scheduling algorithm about the legal operating vehicles based on NFC. The research uses the NFC technology to realize the intelligent and fast identification and the scheduling algorithm to realize the problem of insufficient legal operating vehicles. The scheduling can be divided into two stages--the multi-level queues high response ratio first scheduling and the multi-level queues earliest available time first scheduling. The algorithm can choose the user whose response ratio is the highest from the users’scheduling list and allocate the user who has the highest ratio to the legal operating vehicle who has the earliest available time that in the same area. Experiment indicates that the scheduling success ratio, throughput, average waiting time of the scheduling algorithm are superior to random travel of the drivers and can efficiently resolve the insufficient of legal operating vehicles.