Special Issue

    Not found
    Special Issue on Grid Power Electronics Technology

    Guest EditorsYong Li (Hunan University, China)
                             Qianyi Liu (Hunan University, China)
                             Zhengming Zhao (Tsinghua University, China)
                             Fred Wang (The University of Tennessee, USA)
    Please wait a minute...
    For Selected: Toggle Thumbnails
    Benefits of High-voltage SiC-based Power Electronics in Medium-voltage Power-distribution Grids*
    Fred Wang, Shiqi Ji
    Chinese Journal of Electrical Engineering    2021, 7 (1): 1-26.   DOI: 10.23919/CJEE.2021.000001
    Abstract457)      PDF      
    Medium-voltage (MV) power electronics equipment has been increasingly applied in distribution grids, and high-voltage (HV) silicon carbide (SiC) power semiconductors have attracted considerable attention in recent years. This paper first overviews the development and status of HV SiC power semiconductors. Then, MV power-converter applications in distribution grids are summarized and the benefits of HV SiC in these applications are presented. Microgrids, including conventional and asynchronous microgrids, that can fully demonstrate the benefits of HV SiC power semiconductors are selected to investigate the benefits of HV SiC in detail, including converter-level benefits and system-level benefits. Finally, an asynchronous microgrid power-conditioning system (PCS) prototype using a 10 kV SiC MOSFET is presented.
    Reference | Related Articles | Metrics
    Review of General Modeling Approaches of Power Converters*
    Dong Yan, Chenglin Yang, Lijun Hang, Yuanbin He, Ping Luo, Lei Shen, Pingliang Zeng
    Chinese Journal of Electrical Engineering    2021, 7 (1): 27-36.   DOI: 10.23919/CJEE.2021.000002
    Abstract389)      PDF      
    The modeling approaches of power converters occupy an important position in power electronic systems and have made considerable progress over the past years. Continuous modeling approaches and linearization techniques are reviewed, including the state-space average model, generalized average model, averaged small-signal model, and describing function method. A Buck converter with PWM modulation and voltage-mode control is taken as an example to compare the advantages and disadvantages of different methods through simulation analysis. Moreover, the corresponding equivalent circuit with an intuitive physical meaning of state-space average model, generalized average model, and averaged small-signal model is given. The results point out that the generalized average model can improve the modeling accuracy based on the state-space average model. In the linearization techniques, the averaged small-signal model reflects accuracy at low frequencies, but introduces phase lag in the high-frequency region. The describing function method is derived from harmonic linearization, which takes into account the sideband effect and improves the modeling accuracy at high frequencies.
    Reference | Related Articles | Metrics
    Comparative Analysis on the Stability Mechanism of Droop Control and VID Control in DC Microgrid*
    Gang Lin, Wei Zuo, Yong Li, Jiayan Liu, Shaoyang Wang, Pengcheng Wang
    Chinese Journal of Electrical Engineering    2021, 7 (1): 37-46.   DOI: 10.23919/CJEE.2021.000003
    Abstract388)      PDF      
    Voltage resonance and fluctuation deteriorate the stability of DC microgrids (DC-MGs) and restrict their popularization. Conventional droop control cannot suppress voltage fluctuation and damp oscillations. Therefore, new control methods, namely, droop+filter control and virtual inertia and damping control, are proposed. These methods differ owing to the addition of low pass filter (LPF) and virtual inertia loop. In this study, the stability of these control methods is investigated comprehensively to understand their differences arising from the use of LPF and inertia loop as well as the underlying dynamic stability mechanism. The leading causes of voltage instability in DC-MGs regulated by droop control are first presented. Subsequently, control methods for solving this issue are compared and their simplified small-signal models are constructed. Based on eigenvalue analysis, the DC-MG is equivalent to a third-order system. Different control effects can be acquired by changing the control parameters and the location of the eigenvalues; furthermore, they can be used to understand the dynamic stability. Eigenvalue analysis can provide parameter design guidelines. Finally, the simulation results verify the validity of the theoretical analysis.
    Reference | Related Articles | Metrics
    Resonance Mechanism Analysis of Large-scale Photovoltaic Power Plant*
    Jinjie Lin, Yong Li, Sijia Hu, Qianyi Liu, Jing Zhang, Shaoyang Wang, Lihong Dong, Juan Ni
    Chinese Journal of Electrical Engineering    2021, 7 (1): 47-54.   DOI: 10.23919/CJEE.2021.000004
    Abstract376)      PDF      
    To analyze the resonance mechanism of a photovoltaic (PV) power plant, a simplified impedance model of the PV power plant is first established. The structure of the PV power plant is then introduced, and the reason for the resonance is obtained by analyzing the on-site situation and measured data of the PV power plant. Finally, a simple and effective solution is proposed based on the structure of the PV power plant and its existing facilities. The results of the engineering experiments and the stable operation of the PV power plant verify the effectiveness of the proposed method.
    Reference | Related Articles | Metrics
    A Novel Soft-start Method for SVG Based on D-axis Orientation*
    Shicheng Zheng, Ying Shu, Mengmeng Qi, Jiahong Lang, Xuefeng Hu
    Chinese Journal of Electrical Engineering    2021, 7 (1): 55-62.   DOI: 10.23919/CJEE.2021.000005
    Abstract262)      PDF      
    In this paper, a novel method for shock-free soft-start is proposed. The novel method can realize the aim of no-overshoot and inrush of current during the entire soft-start process, thus the start process is safe, stable, and reliable. When the uncontrolled rectification stage ends, a sinusoidal signal synchronized with the grid voltage is generated through dq coordinate transformation and D-axis orientation, then the signal is transmitted to the three-phase inverter bridge. The AC voltage output of the inverter bridge is superimposed on both ends of the soft-start resistor along with the grid. The open-loop control method is adopted to gradually reduce the modulation ratio of the sinusoidal PWM wave until the capacitor voltage on the DC side reaches the rated voltage value, then the soft-start resistor is removed, which means the shock-free soft-start process is completed. Experimental results prove the effectiveness and feasibility of the control strategy proposed in this paper.
    Reference | Related Articles | Metrics
    Multi-objective Model Predictive Control of Grid-connected Three-level Inverter Based on Hierarchical Optimization*
    Ting Liu, Yong Li, Li Jiang, Jianghu Wan, Jiaqi Yu, Chao Ding, Yijia Cao
    Chinese Journal of Electrical Engineering    2021, 7 (1): 63-72.   DOI: 10.23919/CJEE.2021.000006
    Abstract322)      PDF      
    In order to solve the problem of weighting factors selection in the conventional finite-control-set model predictive control for a grid-connected three-level inverter, an improved multi-objective model predictive control without weighting factors based on hierarchical optimization is proposed. Four control objectives are considered in this strategy. The grid current and neutral-point voltage of the DC-link are taken as the objectives in the first optimization hierarchy, and by using fuzzy satisfaction decision, several feasible candidates of voltage vectors are determined. Then, the average switching frequency and common-mode voltage are optimized in the second hierarchy. The average ranking criterion is introduced to sort the objective functions, and the best voltage vector is obtained to realize the coordinated control of multiple objectives. At last, the effectiveness of the proposed strategy is verified by simulation results.
    Reference | Related Articles | Metrics