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A solid state transformer (SST), as a kind of energy router in the Energy Internet, provides a unified access point for AC or DC distributed power subjects. However, the DC-link capacitors inside the SST will suffer huge voltage fluctuations when the output power of the microgrid changes dramatically. With respect to this problem, caused by the random and intermittent characteristics of distributed generation (DG), a hierarchical coordinative control strategy is proposed. Compared with the common independent control, the proposed method not only makes full use of the regulation capacity of super capacitors, but also enhances the dynamic power tracking speed and reduces the speed difference between different stages of an SST. The dynamic voltage response under the proposed method is analyzed in frequency domain and compared with the independent control. To validate the effectiveness of the coordinative control strategy, a simulation model of an SST-based grid-connected DC microgrid system is established, and the topology of the SST is improved. The voltage stability of the DC bus is compared under different control strategies, and the coordinative control strategy is also verified, effectively under transition conditions.
Zheng Li; Tao Zheng; Yani Wang; Chang Yang. A Hierarchical Coordinative Control Strategy for Solid State Transformer Based DC Microgrids. Applied Sciences 2020, 10, 6853 .
AMA StyleZheng Li, Tao Zheng, Yani Wang, Chang Yang. A Hierarchical Coordinative Control Strategy for Solid State Transformer Based DC Microgrids. Applied Sciences. 2020; 10 (19):6853.
Chicago/Turabian StyleZheng Li; Tao Zheng; Yani Wang; Chang Yang. 2020. "A Hierarchical Coordinative Control Strategy for Solid State Transformer Based DC Microgrids." Applied Sciences 10, no. 19: 6853.
This paper presents a multi-terminal traveling-wave-based fault location method for phase-to-ground fault in non-effectively earthed distribution systems. To improve the accuracy of fault location, a two-terminal approach is used to identify the faulty branch and a single-ended approach is followed to determine the fault distance based on the arrival time of reflected traveling waves. Wavelet decomposition is employed to extract the time-frequency component of the aerial-mode traveling waves. Magnitude and polarity of the wavelet coefficients are used to estimate the fault distance starting from the propagation fault point to the branch terminal. In addition, the network is divided into several sub-networks in order to reduce the number of measurement units. The effectiveness of this approach is demonstrated by simulations considering the phase-to-ground fault that happens at different positions in the distribution network.
Yani Wang; Tao Zheng; Chang Yang; Li Yu. Traveling-Wave Based Fault Location for Phase-to-Ground Fault in Non-Effectively Earthed Distribution Networks. Energies 2020, 13, 5028 .
AMA StyleYani Wang, Tao Zheng, Chang Yang, Li Yu. Traveling-Wave Based Fault Location for Phase-to-Ground Fault in Non-Effectively Earthed Distribution Networks. Energies. 2020; 13 (19):5028.
Chicago/Turabian StyleYani Wang; Tao Zheng; Chang Yang; Li Yu. 2020. "Traveling-Wave Based Fault Location for Phase-to-Ground Fault in Non-Effectively Earthed Distribution Networks." Energies 13, no. 19: 5028.
Traveling wave (TW)-based fault-location methods have been used to determine single-phase-to-ground fault distance in power-distribution networks. The previous approaches detected the arrival time of the initial traveling wave via single ended or multi-terminal measurements. Regarding the multi-branch effect, this paper utilized the reflected waves to obtain multiple arriving times through single ended measurement. Potential fault sections were estimated by searching for the possible traveling wave propagation paths in accordance with the structure of the distribution network. This approach used the entire propagation of a traveling wave measured at a single end without any prerequisite of synchronization, which is a must in multi-terminal measurements. The uniqueness of the fault section was guaranteed by several independent single-ended measurements. Traveling waves obtained in a real 10 kV distribution network were used to determine the fault section, and the results demonstrate the significant effectiveness of the proposed method.
Yangang Shi; Tao Zheng; Chang Yang. Reflected Traveling Wave Based Single-Ended Fault Location in Distribution Networks. Energies 2020, 13, 3917 .
AMA StyleYangang Shi, Tao Zheng, Chang Yang. Reflected Traveling Wave Based Single-Ended Fault Location in Distribution Networks. Energies. 2020; 13 (15):3917.
Chicago/Turabian StyleYangang Shi; Tao Zheng; Chang Yang. 2020. "Reflected Traveling Wave Based Single-Ended Fault Location in Distribution Networks." Energies 13, no. 15: 3917.
Smooth transition is one of the most important issues of micro-grids. The resulting transition is much impacted by the state step of the regulator. To suppress this mutation, this paper proposes a smooth transition control based on an islanding signal, which updates the state of the regulators by detecting the change of islanding signal. Pre-synchronization control is applied during the transition from islanding mode to grid-connected mode. In comparison, the proposed approach is superior over direct transition control and state follower-based transition control, with both easier regulator parameter configuration and better performance during transition time.
Zhenghong Chen; Tao Zheng; Chang Liu. An Islanding Signal-Based Smooth Transition Control in AC/DC Hybrid Micro-Grids. Applied Sciences 2019, 9, 2804 .
AMA StyleZhenghong Chen, Tao Zheng, Chang Liu. An Islanding Signal-Based Smooth Transition Control in AC/DC Hybrid Micro-Grids. Applied Sciences. 2019; 9 (14):2804.
Chicago/Turabian StyleZhenghong Chen; Tao Zheng; Chang Liu. 2019. "An Islanding Signal-Based Smooth Transition Control in AC/DC Hybrid Micro-Grids." Applied Sciences 9, no. 14: 2804.
Power transformer rupture and fire resulting from an arcing fault inside the tank usually leads to significant security risks and serious economic loss. In order to reveal the essence of tank deformation or explosion, this paper presents a 3-D numerical computational tool to simulate the structural dynamic behavior due to overpressure inside transformer tank. To illustrate the effectiveness of the proposed method, a 17.3MJ and a 6.3MJ arcing fault were simulated on a real full-scale 360MVA/220kV oil-immersed transformer model, respectively. By employing the finite element method, the transformer internal overpressure distribution, wave propagation and von-Mises stress were solved. The numerical results indicate that the increase of pressure and mechanical stress distribution are non-uniform and the stress tends to concentrate on connecting parts of the tank as the fault time evolves. Given this feature, it becomes possible to reduce the risk of transformer tank rupture through limiting the fault energy and enhancing the mechanical strength of the local stress concentrative areas. The theoretical model and numerical simulation method proposed in this paper can be used as a substitute for risky and costly field tests in fault overpressure analysis and tank mitigation design of transformers.
Chenguang Yan; Zhiguo Hao; Song Zhang; Baohui Zhang; Tao Zheng. Numerical Methods for the Analysis of Power Transformer Tank Deformation and Rupture Due to Internal Arcing Faults. PLoS ONE 2015, 10, e0133851 .
AMA StyleChenguang Yan, Zhiguo Hao, Song Zhang, Baohui Zhang, Tao Zheng. Numerical Methods for the Analysis of Power Transformer Tank Deformation and Rupture Due to Internal Arcing Faults. PLoS ONE. 2015; 10 (7):e0133851.
Chicago/Turabian StyleChenguang Yan; Zhiguo Hao; Song Zhang; Baohui Zhang; Tao Zheng. 2015. "Numerical Methods for the Analysis of Power Transformer Tank Deformation and Rupture Due to Internal Arcing Faults." PLoS ONE 10, no. 7: e0133851.