Influence of Filter Inductances and Number of Paralleled Grid-Connected Converters on the System’s Stable Region Under Weak Grid Condition

Yang Shude,Sun Yipeng,Jiang Wei,Zhang Jiyong,Wang Qianlong,Tong Xiangqian 대한전기학회 2021 Journal of Electrical Engineering & Technology Vol.16 No.2

It has been found that both the number of paralleled grid-connected converters and the fi lter inductance value will aff ect the system’s stability in weak grid condition. However, a quantitative study on this eff ect is missing in the current literature. The main contribution of this paper is to quantitatively evaluates the infl uence of the number of paralleled grid-connected converters as well as the inductance value of the L fi lters on the system’s stable region. It is fi rst revealed that, when the same controller design principles are applied for L -type grid-connected converters, the stable region of the paralleled grid-connected converter system is dependent on the ratio between the fi lter inductances and the number of paralleled converters. Specifi - cally, the stable region is proportional to the ratio. Compared to the qualitative analysis in previous work, this fi nding can provide quantitative guidelines on the fi lter inductors or control system design for grid-connected converter applications in weak grid. Finally, experimental tests are carried out using two paralleled grid-connected converters to confi rm the fi ndings.

Voltage Feedforward Control with Time-Delay Compensation for Grid-Connected Converters

Yang, Shude,Tong, Xiangqian The Korean Institute of Power Electronics 2016 JOURNAL OF POWER ELECTRONICS Vol.16 No.5

In grid-connected converter control, grid voltage feedforward is usually introduced to suppress the influence of grid voltage distortion on the converter's grid-side AC current. However, owing to the time-delay in control systems, the suppression effect of the grid voltage distortion is seriously affected. In this paper, the positive effects of the grid voltage feedforward control are analyzed in detail, and the time-delay caused by the low-pass filter (LPF) in the voltage filtering circuits and digital control are summarized. In order to reduce the time-delay effect on the performance of the feedforward control, a voltage feedforward control strategy with time-delay compensation is proposed, in which, a leading correction of the feedforward voltage is used. The optimal leading step used in this strategy is derived from analyzing the phase-frequency characteristics of a LPF and the implementation of digital control. By using the optimal leading step, the delay in the feedforward path can be further counteracted so that the performance of the feedforward control in terms of suppressing the influence of grid voltage distortion on the converter output current can be improved. The validity of the proposed method is verified through simulation and experiment results.

BPF-based Grid Voltage Feedforward Control of Grid-connected Converters for Improving Robust Stability

Yang, Shude,Tong, Xiangqian,Yin, Jun,Wang, Haiyan,Deng, Yaping,Liu, Le The Korean Institute of Power Electronics 2017 JOURNAL OF POWER ELECTRONICS Vol.17 No.2

Grid voltage feedforward is extensively used for controlling grid-connected converters. However, the conventional voltage feedforward control reduces the stability margins of the converter connected to a high-impedance grid. The effect mechanism of voltage feedforward on the grid-connected converter control under high-inductive conditions of the grid impedance is clearly explained in this study using the equivalent transformations of control block diagrams. Results show that the delay produced by the digital control is the root cause of this effect. An improved voltage feedforward strategy, in which a bandpass filter (BPF) is introduced into the feedforward path, is proposed to strengthen the converter's robust stability against grid impedance variations. The selection method of the BPF's bandwidth is also provided considering the tradeoff between the response speed to the grid voltage sag and the system's robust stability. The converter can work stably over a wide range of the grid impedance through the proposed approach. Simulation and experimental results fully verify the effectiveness of the BPF-based voltage feedforward strategy.

Voltage Feedforward Control with Time-Delay Compensation for Grid-Connected Converters

Shude Yang,Xiangqian Tong 전력전자학회 2016 JOURNAL OF POWER ELECTRONICS Vol.16 No.5

In grid-connected converter control, grid voltage feedforward is usually introduced to suppress the influence of grid voltage distortion on the converter’s grid-side AC current. However, owing to the time-delay in control systems, the suppression effect of the grid voltage distortion is seriously affected. In this paper, the positive effects of the grid voltage feedforward control are analyzed in detail, and the time-delay caused by the low-pass filter (LPF) in the voltage filtering circuits and digital control are summarized. In order to reduce the time-delay effect on the performance of the feedforward control, a voltage feedforward control strategy with time-delay compensation is proposed, in which, a leading correction of the feedforward voltage is used. The optimal leading step used in this strategy is derived from analyzing the phase-frequency characteristics of a LPF and the implementation of digital control. By using the optimal leading step, the delay in the feedforward path can be further counteracted so that the performance of the feedforward control in terms of suppressing the influence of grid voltage distortion on the converter output current can be improved. The validity of the proposed method is verified through simulation and experiment results.

BPF-based Grid Voltage Feedforward Control of Grid-connected Converters for Improving Robust Stability

Shude Yang,Xiangqian Tong,Jun Yin,Haiyan Wang,Yaping Deng,Le Liu 전력전자학회 2017 JOURNAL OF POWER ELECTRONICS Vol.17 No.2

Grid voltage feedforward is extensively used for controlling grid-connected converters. However, the conventional voltage feedforward control reduces the stability margins of the converter connected to a high-impedance grid. The effect mechanism of voltage feedforward on the grid-connected converter control under high-inductive conditions of the grid impedance is clearly explained in this study using the equivalent transformations of control block diagrams. Results show that the delay produced by the digital control is the root cause of this effect. An improved voltage feedforward strategy, in which a bandpass filter (BPF) is introduced into the feedforward path, is proposed to strengthen the converter’s robust stability against grid impedance variations. The selection method of the BPF’s bandwidth is also provided considering the tradeoff between the response speed to the grid voltage sag and the system’s robust stability. The converter can work stably over a wide range of the grid impedance through the proposed approach. Simulation and experimental results fully verify the effectiveness of the BPF-based voltage feedforward strategy.

Grain-Refinement and Mechanical Properties Optimisation of A356 Casting Al by Ultrasonic-Assisted Friction Stir Processing

Lin Ma,Changzhuang Zhou,Yao Shi,Qinghe Cui,Shude Ji,Kang Yang 대한금속·재료학회 2021 METALS AND MATERIALS International Vol.27 No.12

Conventional friction stir processing (FSP) and ultrasonic-assisted friction stir processing (Ua-FSP) were applied to modifythe microstructure and enhance the mechanical properties of as-cast A356 aluminium alloy. A series of experiments withdifferent processing parameters were conducted in these two processing methods. Forming characteristics, grain-refinement,and mechanical properties in FSP and Ua-FSP were compared to determine the effect of ultrasound. The results revealed thatultrasound improved the grain-refinement level in both grain size and grain uniformity. Further, the effect of ultrasound onmicrostructural evolution was more significant with relatively high processing heat-input. Ultrasonic vibration also positivelyaffected the hardness, tensile strength, and elongation.

Comparative analysis of metabolites and in vitro hypoglycemic activity of Taiwanofungus camphoratus cultured using various methods

Ming YongFei,Li Yin,Chu JianZhi,Zhou XiaoShuang,Huang YuXuan,Yang ShuDe,Mu YueJun,Wang Lin,Zhang Rui,Cheng XianHao 한국응용생명화학회 2024 Applied Biological Chemistry (Appl Biol Chem) Vol.67 No.-

Taiwanofungus camphoratus has attracted much attention because it can abundantly produce various active substances that exhibit blood-sugar lowering, immunity improving, and antioxidant properties. Currently, T. camphoratus is cultured using four main methods: cutting wood culture, solid-state fermentation, submerged fermentation, and dish culture. T. camphoratus produces different metabolites under different culture methods. In this study, nontargeted metabolomics was used to compare the metabolites of T. camphoratus produced under these four culture methods. Principal component analysis and supervised partial least squares-discriminant analysis were used to analyze the differences in the metabolites. Moreover, in vitro hypoglycemic activity of T. camphoratus extracts produced under four culture methods was compared by assessing their ability to inhibit the activity of α-glucosidase, α-amylase, and sucrase. A total of 186 metabolites were identified. In total, 127 metabolites were common under the four culture methods. Under solid-state fermentation, submerged fermentation, and cutting wood culture, 12, 1, and 4 metabolites were unique, respectively. The differential metabolites produced by T. camphoratus under four culture methods were mainly triterpenoids, phenolic compounds, and fatty acid compounds. α-glucosidase, α-amylase, and sucrase activity inhibition was the best using T. camphoratus extract obtained under cutting wood culture; the inhibition rates were 55.97%, 51.96%, and 78.02%, respectively, which were comparable to those exhibited by 0.001, 3, and 12 mg/mL acarbose (positive control). The metabolites produced by T. camphoratus and α-glucosidase, α-amylase, and sucrase inhibitory activities were different under the four culture methods. Cutting wood culture exhibited the best enzyme inhibitory activity. This study provided a theoretical basis for further use and development of various culture methods for the rational production of active metabolites of T. camphoratus.