Special Issue

Special Issue on Operation and Control of Power Electronics Dominated Power Systems


Guest Editors:  
Xiongfei Wang, Aalborg University, Denmark 
Ning Zhang, Tsinghua University, China 
Kai Sun, Tsinghua University, China

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Editorial for the Special Issue on Operation and Control of Power Electronics Dominated Power Systems Chinese Journal of Electrical Engineering    2021, 7 (4): 1-2.   DOI: 10.23919/CJEE.2021.000032 Abstract （308）      PDF       Knowledge map    Related Articles | Metrics

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Evaluation of High Step-up Power Conversion Systems for Large-capacity Photovoltaic Generation Integrated into Medium Voltage DC Grids* Shilei Lu, Kai Sun, Haixu Shi, Yunwei Li, Guoen Cao Chinese Journal of Electrical Engineering    2021, 7 (4): 3-14.   DOI: 10.23919/CJEE.2021.000033 Abstract （411）      PDF       Knowledge map    With the increase of dc based renewable energy generation and dc loads, the medium voltage dc (MVDC) distribution network is becoming a promising option for more efficient system integration. In particular, large-capacity photovoltaic (PV)-based power generation is growing rapidly, and a corresponding power conversion system is critical to integrate these large PV systems into MVDC power grid. Different from traditional ac grid-connected converters, the converter system for dc grid interfaced PV system requires large-capacity dc conversion over a wide range of ultra-high voltage step-up ratios. This is an important issue, yet received limited research so far. In this paper, a thorough study of dc-dc conversion system for a medium-voltage dc grid-connected PV system is conducted. The required structural features for such a conversion system are first discussed. Based on these features, the conversion system is classified into four categories by series-parallel connection scheme of power modules. Then two existing conversion system configurations as well as a proposed solution are compared in terms of input/output performance, conversion efficiency, modulation method, control complexity, power density, reliability, and hardware cost. In-depth analysis is carried out to select the most suitable conversion systems in various application scenarios. Reference | Related Articles | Metrics

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Python Supervised Co-simulation for a Day-long Harmonic Evaluation of EV Charging* Lu Wang, Zian Qin, Lucia Beloqui Larumbe, Pavol Bauer Chinese Journal of Electrical Engineering    2021, 7 (4): 15-24.   DOI: 10.23919/CJEE.2021.000034 Abstract （359）      PDF       Knowledge map    To accurately simulate electric vehicle DC fast chargers' (DCFCs') harmonic emission, a small time step, i.e., typically smaller than 10 μs, is required owing to switching dynamics. However, in practice, harmonics should be continuously assessed with a long duration, e.g., a day. A trade-off between accuracy and time efficiency thus exists. To address this issue, a multi-time scale modeling framework of fast-charging stations (FCSs) is proposed. In the presented framework, the DCFCs' input impedance and harmonic current emission in the ideal grid condition, that is, zero grid impedance and no background harmonic voltage, are obtained based on a converter switching model with a small timescale simulation. Since a DCFC's input impedance and harmonic current source are functions of the DCFC's load, the input impedance and harmonic emission at different loads are obtained. Thereafter, they are used in the fast-charging charging station modeling, where the DCFCs are simplified as Norton equivalent circuits. In the station level simulation, a large time step, i.e., one minute, is used because the DCFCs' operating power can be assumed as a constant over a minute. With this co-simulation, the FCSs' long-term power quality performance can be assessed time-efficiently, without losing much accuracy. Reference | Related Articles | Metrics

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Single-phase Grid-connected PV System with Golden Section Search-based MPPT Algorithm* Shuang Xu, Riming Shao, Bo Cao, Liuchen Chang Chinese Journal of Electrical Engineering    2021, 7 (4): 25-36.   DOI: 10.23919/CJEE.2021.000035 Abstract （450）      PDF       Knowledge map    Maximum power point tracking (MPPT) is a technique employed for with variable-power sources, such as solar, wind, and ocean, to maximize energy extraction under all conditions. The commonly used perturb and observe (P&O) and incremental conductance (INC) methods have advantages such as ease of implementation, but they also have the challenge of selecting the most optimized perturbation step or increment size while considering the trade-off between convergence time and oscillation. To address these issues, an MPPT solution for grid-connected photovoltaic (PV) systems is proposed that combines the golden section search (GSS), P&O, and INC methods to simultaneously achieve faster convergence and smaller oscillation, converging to the MPP by repeatedly narrowing the width of the interval at the rate of the golden ratio. The proposed MPPT technique was applied to a PV system consisting of a PV array, boost chopper, and inverter. Simulation and experimental results verify the feasibility and effectiveness of the proposed MPPT technique, by which the system is able to locate the MPP in 36 ms and regain a drifting MPP in approximately 30 ms under transient performance. The overall MPPT efficiency is 98.99%. Reference | Related Articles | Metrics

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Controller Design-oriented Analysis of Grid-forming Converters for Stability Robustness Enhancement Yicheng Liao, Xiongfei Wang Chinese Journal of Electrical Engineering    2021, 7 (4): 37-48.   DOI: 10.23919/CJEE.2021.000036 Abstract （294）      PDF       Knowledge map    Grid-forming converters can suffer from control interaction problems in grid connections that can result in small-signal instability. Their inner-loop voltage controller tends to interact with the outer-loop power controller, rendering the controller design more difficult. To conduct a design-oriented analysis, a control-loop decomposition approach for grid-forming converters is proposed. Combined with impedance-based stability analysis, the control-loop decomposition approach can reveal how different control loops affect the converter-grid interaction. This results in a robust controller design enabling grid-forming converters to operate within a wider range of grid short-circuit ratios. Finally, simulation and experimental results, which validate the approach, are presented. Reference | Related Articles | Metrics

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Distributed Control Framework and Scalable Small-signal Stability Analysis for Dynamic Microgrids Yuxi Men, Yuhua Du, Xiaonan Lu Chinese Journal of Electrical Engineering    2021, 7 (4): 49-59.   DOI: 10.23919/CJEE.2021.000037 Abstract （305）      PDF       Knowledge map    As a growing number of microgrids (MGs) has been integrated into the modern power grids, the interconnection and applicable cooperation among multiple MGs motivate the development of networked MGs. Dynamic MGs, as an advanced networked MGs structure, can not only integrate multiple MGs into the distribution system but also fulfill the requested system network reconfiguration with improved flexibility. A general distributed control approach for networked MGs is reviewed. A distributed control framework for dynamic MGs operation is developed, along with an extensible architecture with considerations of large-scale distributed energy resources (DERs) integration. A scalable small-signal stability analysis is conducted per the proposed distributed control strategies and the conditions under which the system is exponentially stable are derived. At last, the effectiveness of the proposed control framework and stability analysis are verified using a 6-bus test feeder. Reference | Related Articles | Metrics

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Stability and Robustness of a Coupled Microgrid Cluster Formed by Various Coupling Structures S.M.Ferdous, Farhad Shahnia, GM Shafiullah Chinese Journal of Electrical Engineering    2021, 7 (4): 60-77.   DOI: 10.23919/CJEE.2021.000038 Abstract （257）      PDF       Knowledge map    A standalone microgrid (MG) may frequently experience overloading owing to insufficient power generation or excessive renewable-based generation, which can cause unacceptable voltage and frequency deviations. Such problems are conventionally alleviated by load-shedding or renewable curtailment. Alternatively, autonomously operating MGs can be provisionally connected to facilitate temporary power exchange. The power-exchange link among the MGs can be of different types, e.g., three-phase ac, single-phase ac, or dc-link and power electronic converter-interfaced. All these topologies can facilitate power exchange, but they differ with regard to stability and robustness. In the present study, the stability and robustness of such structures are investigated, and the effects of factors such as the length of the interconnecting line among the MGs, the amount of power supplied to the troubled MGs, and the number of coupled MGs are compared. The stability and robustness of the structures are evaluated in Matlab. Reference | Related Articles | Metrics