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Zai Jun Wu
School of Electrical Engineering, Southeast University, Nanjing 210000, China

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Journal article
Published: 12 August 2021 in IEEE Transactions on Smart Grid
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To ensure accurate active power-sharing and an improved dynamic response to DC voltages in a medium voltage DC distribution system (MVDCDS), this paper presents an adaptive master-slave (AMS) control strategy based on a novel nonlinear droop (ND) controller. This ND controller, which is based on an improved sigmoid nonlinear function, is applied to the slave converter stations. An improved sigmoid function is designed to achieve a continuous and nonlinear droop curve. Through use of the proposed ND controller, the proposed AMS strategy can achieve seamless switching between the master-slave control and droop control modes automatically. Consequently, the AMS control strategy not only guarantees precise control of the active power in the steady state but also allows a superior dynamic performance to be achieved in the transient state, during which the system suffers from both large-scale disturbances and communication failures. The effectiveness and superiority of the proposed AMS control strategy are illustrated by theoretical analyses and validated by performing hardware-in-the-loop (HIL) tests in a B110 kV MVDCDS.

ACS Style

Xingfeng Xie; Xiang Jun Quan; Zai Jun Wu; Xiaoyong Cao; Xiaobo Dou; Qinran Hu. Adaptive Master-Slave Control Strategy for Medium Voltage DC Distribution Systems Based on a Novel Nonlinear Droop Controller. IEEE Transactions on Smart Grid 2021, PP, 1 -1.

AMA Style

Xingfeng Xie, Xiang Jun Quan, Zai Jun Wu, Xiaoyong Cao, Xiaobo Dou, Qinran Hu. Adaptive Master-Slave Control Strategy for Medium Voltage DC Distribution Systems Based on a Novel Nonlinear Droop Controller. IEEE Transactions on Smart Grid. 2021; PP (99):1-1.

Chicago/Turabian Style

Xingfeng Xie; Xiang Jun Quan; Zai Jun Wu; Xiaoyong Cao; Xiaobo Dou; Qinran Hu. 2021. "Adaptive Master-Slave Control Strategy for Medium Voltage DC Distribution Systems Based on a Novel Nonlinear Droop Controller." IEEE Transactions on Smart Grid PP, no. 99: 1-1.

Journal article
Published: 19 March 2021 in IEEE Transactions on Smart Grid
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The technology of virtual synchronous machine (VSM) is attracting interest of researchers as it controls converters mimicking the synchronous machine’s response so as to provide inertial support for power electronics dominated smart grids. For the VSM based microgrid, its slow dynamics are dominated by synchronous generators (SGs) and the VSM control loops, which makes it possible to model this microgrid into an equivalent SG (EqSG) model. This paper proposes a robust secondary frequency control design method for the VSM based low voltage (LV) microgrid cluster (MGC) using equivalent modeling. The EqSG model is used to construct the MGC model so as to reduce the model order and the complexity of controller synthesis. Modeling errors caused by the EqSG model and different operating conditions are integrated into the MGC model as unstructured uncertainties. The proposed secondary frequency control strategy is based on the distributed-centralized hybrid control structure to coordinate frequency restoration among LV microgrids. Structured μ-synthesis is applied for tuning control parameters realizing H∞ robust performance against unstructured uncertainties. To reduce the communication resource consumption, an event-triggered mechanism considering communication delay is introduced in the robust secondary frequency control strategy. The triggering condition is analyzed using a Lyapunov function to guarantee H∞ robust stability. Simulation and real-time experiment results on a MGC composed of four CIGRÉ benchmark LV microgrids are presented to demonstrate the effectiveness of the proposed control strategy.

ACS Style

Wenqiang Hu; Zaijun Wu; Xinxin Lv; Venkata Dinavahi. Robust Secondary Frequency Control for Virtual Synchronous Machine-Based Microgrid Cluster Using Equivalent Modeling. IEEE Transactions on Smart Grid 2021, 12, 2879 -2889.

AMA Style

Wenqiang Hu, Zaijun Wu, Xinxin Lv, Venkata Dinavahi. Robust Secondary Frequency Control for Virtual Synchronous Machine-Based Microgrid Cluster Using Equivalent Modeling. IEEE Transactions on Smart Grid. 2021; 12 (4):2879-2889.

Chicago/Turabian Style

Wenqiang Hu; Zaijun Wu; Xinxin Lv; Venkata Dinavahi. 2021. "Robust Secondary Frequency Control for Virtual Synchronous Machine-Based Microgrid Cluster Using Equivalent Modeling." IEEE Transactions on Smart Grid 12, no. 4: 2879-2889.

Journal article
Published: 25 January 2021 in IEEE Transactions on Sustainable Energy
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Due to the intermittent and stochastic nature of solar power, solar power interval prediction is of great importance for grid management and power dispatching. A combination interval prediction model based on the lower and upper bound estimation (LUBE) is proposed to quantify the solar power prediction uncertainty efficiently. In the proposed model, the upper and lower bounds are separately predicted by two prediction engines. The Extreme Learning Machine (ELM) is selected as the basic prediction engine. The auto-encoder technique is used to initialize the input weight matrix of ELM for efficient feature learning. A novel biased convex cost function is developed for ELM to train the output weight matrix via the convex optimization technique instead of the conventional heuristic algorithm. The proposed interval prediction model can be formulated as a bi-level optimization problem. In the lower-level problem, the lower and upper ELMs are trained under different candidate hyper-parameters of the biased cost function. The optimal combination of the lower and upper prediction engines is determined by evaluating the interval prediction performance in the upper-level problem. Comprehensive experiments based on public data set are conducted to validate the superiority of the proposed interval prediction model.

ACS Style

Huan Long; Chen Zhang; Runhao Geng; Zaijun Wu; Wei Gu. A Combination Interval Prediction Model Based on Biased Convex Cost Function and Auto-Encoder in Solar Power Prediction. IEEE Transactions on Sustainable Energy 2021, 12, 1561 -1570.

AMA Style

Huan Long, Chen Zhang, Runhao Geng, Zaijun Wu, Wei Gu. A Combination Interval Prediction Model Based on Biased Convex Cost Function and Auto-Encoder in Solar Power Prediction. IEEE Transactions on Sustainable Energy. 2021; 12 (3):1561-1570.

Chicago/Turabian Style

Huan Long; Chen Zhang; Runhao Geng; Zaijun Wu; Wei Gu. 2021. "A Combination Interval Prediction Model Based on Biased Convex Cost Function and Auto-Encoder in Solar Power Prediction." IEEE Transactions on Sustainable Energy 12, no. 3: 1561-1570.

Journal article
Published: 03 December 2020 in IEEE Transactions on Industrial Electronics
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To improve the filtering capability of frequency-locked loop (FLL), the high-order bandpass filters FLL was proposed recently. This paper proposes a high-order FLL in synchronous (dq) reference frame where the high-order lowpass filter is adopted. A general analytical model is established for the high-order FLL. Based on the model, it is proven that the conventional high-order FLL exhibits no improvement in terms of filtering ability of the frequency estimation. Based on this analysis, a new frequency estimation loop is proposed to obtain an enhanced filtering capability for the FLL. Additionally, the proposed high-order FLL has the advantage of simple implementation compared to conventional high-order FLLs. A design example is then demonstrated and simulated to show the accuracy of the model and the effectiveness of the proposed FLL. Finally, the proposed high-order FLL is experimentally verified on a testbed using a 32-bit floating-point DSP TMS320F28379D at 200 MHz.

ACS Style

Xiangjun Quan; Qinran Hu; Xiaobo Dou; Zaijun Wu; Wei Li. High-Order Frequency-Locked Loop: General Modeling and Design. IEEE Transactions on Industrial Electronics 2020, PP, 1 -1.

AMA Style

Xiangjun Quan, Qinran Hu, Xiaobo Dou, Zaijun Wu, Wei Li. High-Order Frequency-Locked Loop: General Modeling and Design. IEEE Transactions on Industrial Electronics. 2020; PP (99):1-1.

Chicago/Turabian Style

Xiangjun Quan; Qinran Hu; Xiaobo Dou; Zaijun Wu; Wei Li. 2020. "High-Order Frequency-Locked Loop: General Modeling and Design." IEEE Transactions on Industrial Electronics PP, no. 99: 1-1.

Journal article
Published: 04 August 2020 in Applied Sciences
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In this paper, cross-linked polyethylene (XLPE) cables of the same batch from Factory A, which ran from 1 to 8 years in Jiangsu Province, are sampled. Some widely accepted aging characterization methods of XLPE cables such as the gel content test, differential scanning calorimetry (DSC) test, tensile test and hardness test are employed to obtain the physicochemical, mechanical and electrical properties of the samples. Then, some lifespan prediction parameters significantly correlated with operating time are obtained through correlation calculations. Finally, a prediction method is proposed to predict the operating time of XLPE cables from Factory A. The test results indicate that parameters including the gel content Cge, the crystallinity XC, tensile strength σ, ultimate elongation δ, the dielectric permittivity ε, and the dielectric loss Jtan are significantly correlated with operating time, which can be used in evaluating the aging degree of XLPE cables. Moreover, due to the high accuracy of the experimental verification, it turns out that the lifespan prediction method proposed in this paper can be used to determine the operating time of XLPE cables from Factory A in future research.

ACS Style

Yi Zhang; Zaijun Wu; Cheng Qian; Xiao Tan; Jinggang Yang; Linlin Zhong. Research on Lifespan Prediction of Cross-Linked Polyethylene Material for XLPE Cables. Applied Sciences 2020, 10, 5381 .

AMA Style

Yi Zhang, Zaijun Wu, Cheng Qian, Xiao Tan, Jinggang Yang, Linlin Zhong. Research on Lifespan Prediction of Cross-Linked Polyethylene Material for XLPE Cables. Applied Sciences. 2020; 10 (15):5381.

Chicago/Turabian Style

Yi Zhang; Zaijun Wu; Cheng Qian; Xiao Tan; Jinggang Yang; Linlin Zhong. 2020. "Research on Lifespan Prediction of Cross-Linked Polyethylene Material for XLPE Cables." Applied Sciences 10, no. 15: 5381.

Journal article
Published: 14 January 2020 in Energies
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In this paper, a distributed economic dispatch scheme considering power limit is proposed to minimize the total active power generation cost in a droop-based autonomous direct current (DC) microgrid. The economical dispatch of the microgrid is realized through a fully distributed hierarchical control. In the tertiary level, an incremental cost consensus-based algorithm embedded into the economical regulator is utilized to search for the optimal solution. In the secondary level, the voltage regulator estimating the average voltage of the DC microgrid is used to generate the voltage correction item and eliminate the power and voltage oscillation caused by the deviation between different items. Then, the droop controller in the primary level receives the reference values from the upper level to ensure the output power converging to the optimum while recovering the average voltage of the system. Further, the dynamic model is established and the optimal communication network topology minimizing the impact of time delay on the voltage estimation is given in this paper. Finally, a low-voltage DC microgrid simulation platform containing different types of distributed generators is built, and the effectiveness of the proposed scheme and the performance of the optimal topology are verified.

ACS Style

Zhenyu Lv; Zaijun Wu; Xiaobo Dou; Min Zhou; Wenqiang Hu. Distributed Economic Dispatch Scheme for Droop-Based Autonomous DC Microgrid. Energies 2020, 13, 404 .

AMA Style

Zhenyu Lv, Zaijun Wu, Xiaobo Dou, Min Zhou, Wenqiang Hu. Distributed Economic Dispatch Scheme for Droop-Based Autonomous DC Microgrid. Energies. 2020; 13 (2):404.

Chicago/Turabian Style

Zhenyu Lv; Zaijun Wu; Xiaobo Dou; Min Zhou; Wenqiang Hu. 2020. "Distributed Economic Dispatch Scheme for Droop-Based Autonomous DC Microgrid." Energies 13, no. 2: 404.

Journal article
Published: 08 January 2020 in IEEE Transactions on Industrial Informatics
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The increasing penetration of photovoltaic (PV) generators has led to a reduction in the effectiveness of existing strategies for restoring the power distribution network. This paper proposes a dynamic robust restoration (DRR) framework for the recovery of outage power considering uncertain PV outputs and demands. This framework is presented in two subsequent steps. In the first step, optimal decisions regarding the network configurations are generated. The second step then computes the modified dynamic Distflows and constraints under consideration of the worst operating conditions over the associated uncertainty sets with the aim of maximizing the recovery of outage power. The DRR model is formulated as a bi-level mixed-integer linear programming problem. A decomposition algorithm in a master-sub structure is used to solve the resulting system. The results of case studies show that the proposed DRR model yields obvious advantages over the existing deterministic dynamic restoration model in terms of robustness against system uncertainties.

ACS Style

Junjun Xu; Zaijun Wu; Xinghuo Yu; Sheng Cheng; Qinran Hu; Qiuwei Wu. A Dynamic Robust Restoration Framework for Unbalanced Power Distribution Networks. IEEE Transactions on Industrial Informatics 2020, 16, 6301 -6312.

AMA Style

Junjun Xu, Zaijun Wu, Xinghuo Yu, Sheng Cheng, Qinran Hu, Qiuwei Wu. A Dynamic Robust Restoration Framework for Unbalanced Power Distribution Networks. IEEE Transactions on Industrial Informatics. 2020; 16 (10):6301-6312.

Chicago/Turabian Style

Junjun Xu; Zaijun Wu; Xinghuo Yu; Sheng Cheng; Qinran Hu; Qiuwei Wu. 2020. "A Dynamic Robust Restoration Framework for Unbalanced Power Distribution Networks." IEEE Transactions on Industrial Informatics 16, no. 10: 6301-6312.

Journal article
Published: 30 October 2019 in IEEE Transactions on Smart Grid
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ACS Style

Peishuai Li; Cuo Zhang; Zaijun Wu; Yan Xu; Minqiang Hu; Zhaoyang Dong. Distributed Adaptive Robust Voltage/VAR Control With Network Partition in Active Distribution Networks. IEEE Transactions on Smart Grid 2019, 11, 2245 -2256.

AMA Style

Peishuai Li, Cuo Zhang, Zaijun Wu, Yan Xu, Minqiang Hu, Zhaoyang Dong. Distributed Adaptive Robust Voltage/VAR Control With Network Partition in Active Distribution Networks. IEEE Transactions on Smart Grid. 2019; 11 (3):2245-2256.

Chicago/Turabian Style

Peishuai Li; Cuo Zhang; Zaijun Wu; Yan Xu; Minqiang Hu; Zhaoyang Dong. 2019. "Distributed Adaptive Robust Voltage/VAR Control With Network Partition in Active Distribution Networks." IEEE Transactions on Smart Grid 11, no. 3: 2245-2256.

Journal article
Published: 30 April 2019 in IEEE Transactions on Sustainable Energy
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This paper proposes an image-based algorithm for detecting and cleaning the wind turbine abnormal data based on wind power curve (WPC) images. The abnormal data are categorized into three types, negative points, scattered points and stacked points. The proposed algorithm includes three steps, data pre-cleaning, normal data extraction and data marking. The negative abnormal points, whose wind speed are greater than cut-in speed and power are below zero, are first filtered in the data pre-cleaning step. The scatter figure of the rest wind power data forms the WPC image and corresponding binary image. In the normal data extraction step, the principle part of the WPC binary image, representing the normal data, is extracted by the mathematical morphology operation (MMO). The optimal parameter setting of MMO is determined by minimizing the dissimilarity between the extracted principle part and the reference WPC image based on Hu moments. In the data mark step, the pixel points of scattered and stacked abnormal data are successively identified. The mapping relationship between the wind power points and image pixel points is built to mark the wind turbine normal and abnormal data. The proposed image-based algorithm is compared with k-means, local outlier factor (LOF), combined algorithm based on change point grouping algorithm and quartile algorithm (CA). Numerous experiments based on 33 wind turbines from two wind farms are conducted to validate the effectiveness, efficiency and universality of the proposed method.

ACS Style

Huan Long; Linwei Sang; Zaijun Wu; Wei Gu. Image-Based Abnormal Data Detection and Cleaning Algorithm via Wind Power Curve. IEEE Transactions on Sustainable Energy 2019, 11, 938 -946.

AMA Style

Huan Long, Linwei Sang, Zaijun Wu, Wei Gu. Image-Based Abnormal Data Detection and Cleaning Algorithm via Wind Power Curve. IEEE Transactions on Sustainable Energy. 2019; 11 (2):938-946.

Chicago/Turabian Style

Huan Long; Linwei Sang; Zaijun Wu; Wei Gu. 2019. "Image-Based Abnormal Data Detection and Cleaning Algorithm via Wind Power Curve." IEEE Transactions on Sustainable Energy 11, no. 2: 938-946.

Journal article
Published: 13 February 2019 in IEEE Transactions on Industrial Informatics
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Distribution networks with high penetration of distributed generation (DG) yield complicated and uncertain power flow, which make most existing faulted line identification methods not adaptable for industrial applications. Driven by this motivation, a novel single-phase-to-ground (SPTG) faulted line identification method is proposed based on hybrid state estimator (HSE). The first step of the method is to present a HSE for power distribution networks using power flow measurements (PFM) mixed phasor measurement units (PMU). Then, a SPTG fault on a power line is treated as an event that suddenly increases one virtual bus in the monitored network, so as to form the extended bus admittance matrix and augmented HSE based on the specific network topology. In this way, the faulted line identification could be obtained by computing parallel estimated results transversally. Robustness and effectiveness of the proposed HSE and the HSE-based SPTG faulted line identification method are validated by means of a cyber-physical system (a co-simulation platform), where two typical three-phase power distribution networks are considered to simulate with its hybrid measurement system.

ACS Style

Junjun Xu; Zaijun Wu; Xinghuo Yu; Chengzhi Zhu. Robust Faulted Line Identification in Power Distribution Networks via Hybrid State Estimator. IEEE Transactions on Industrial Informatics 2019, 15, 5365 -5377.

AMA Style

Junjun Xu, Zaijun Wu, Xinghuo Yu, Chengzhi Zhu. Robust Faulted Line Identification in Power Distribution Networks via Hybrid State Estimator. IEEE Transactions on Industrial Informatics. 2019; 15 (9):5365-5377.

Chicago/Turabian Style

Junjun Xu; Zaijun Wu; Xinghuo Yu; Chengzhi Zhu. 2019. "Robust Faulted Line Identification in Power Distribution Networks via Hybrid State Estimator." IEEE Transactions on Industrial Informatics 15, no. 9: 5365-5377.

Journal article
Published: 08 January 2019 in IEEE Transactions on Industrial Electronics
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An enormous challenge for state estimation (SE) in power distribution networks with high penetration of photovoltaic (PV) generators lies in how to deal with measurement uncertainty. Driven by this motivation, an interval arithmetic (IA) based SE is proposed in this paper, which considers interval modeling for measurement uncertainty. The proposed SE is formulated as two interval optimization models based on the unknown-but-bounded (UBB) theory, and solution bounds of state variables are obtained using a two-stage linear programming approach. In particular, the proposed SE is extended to realistic power distribution networks with mixed micro-phasor measurement units (μPMU), voltage magnitude (VM), smart meters (SM) and feeder terminal units (FTU). Case studies and results are illustrated and discussed to demonstrate the performance of the proposed IA-based SE. It could provide the operators intuitive and effective bounds of system states for advanced power industrial applications under consideration of uncertainty.

ACS Style

Junjun Xu; Zaijun Wu; Xinghuo Yu; Qinran Hu; Xiaobo Dou. An Interval Arithmetic-Based State Estimation Framework for Power Distribution Networks. IEEE Transactions on Industrial Electronics 2019, 66, 8509 -8520.

AMA Style

Junjun Xu, Zaijun Wu, Xinghuo Yu, Qinran Hu, Xiaobo Dou. An Interval Arithmetic-Based State Estimation Framework for Power Distribution Networks. IEEE Transactions on Industrial Electronics. 2019; 66 (11):8509-8520.

Chicago/Turabian Style

Junjun Xu; Zaijun Wu; Xinghuo Yu; Qinran Hu; Xiaobo Dou. 2019. "An Interval Arithmetic-Based State Estimation Framework for Power Distribution Networks." IEEE Transactions on Industrial Electronics 66, no. 11: 8509-8520.

Journal article
Published: 18 December 2018 in IEEE Transactions on Sustainable Energy
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ACS Style

Pudong Ge; Xiaobo Dou; Xiangjun Quan; Qinran Hu; Wanxing Sheng; Zaijun Wu; Wei Gu. Extended-State-Observer-Based Distributed Robust Secondary Voltage and Frequency Control for an Autonomous Microgrid. IEEE Transactions on Sustainable Energy 2018, 11, 195 -205.

AMA Style

Pudong Ge, Xiaobo Dou, Xiangjun Quan, Qinran Hu, Wanxing Sheng, Zaijun Wu, Wei Gu. Extended-State-Observer-Based Distributed Robust Secondary Voltage and Frequency Control for an Autonomous Microgrid. IEEE Transactions on Sustainable Energy. 2018; 11 (1):195-205.

Chicago/Turabian Style

Pudong Ge; Xiaobo Dou; Xiangjun Quan; Qinran Hu; Wanxing Sheng; Zaijun Wu; Wei Gu. 2018. "Extended-State-Observer-Based Distributed Robust Secondary Voltage and Frequency Control for an Autonomous Microgrid." IEEE Transactions on Sustainable Energy 11, no. 1: 195-205.

Article
Published: 20 November 2017 in Science China Technological Sciences
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Modern distribution network with high penetration of intermittent renewable sources and the so-called prosumers requires more reliable distribution automation (DA) system for safe operation and control. The design of optimal feeder terminal units (FTU) placement is critical and economical for the effective DA application. Previously proposed solutions of optimal FTU placement aiming to ensure the accuracy of state estimation (SE), typically include the following two main shortcomings: 1) only to obtain the optimal FTU placement in quantity, and the analysis of FTU location is not considered yet; 2) few consider the uncertainty of intermittent power injections in the analysis of state estimation. In this paper, a modified methodology of FTU placement is proposed not only aiming to ensure the accuracy of state estimation with the minimum number of meters, but also finding those specific FTU locations to guarantee the power service reliability. Moreover, the uncertainty models of those intermittent power injections are also considered by using probability density function (PDF). The resultant optimization problem is addressed by using the covariance matrix adaptation evolution strategy (CMA-ES). Case studies demonstrate the feasibility and effectiveness of the proposed methodology.

ACS Style

Junjun Xu; Zaijun Wu; Xinghuo Yu; Qinran Hu; Chengzhi Zhu; Xiaobo Dou; Wei Gu; Zhi Wu. A new method for optimal FTU placement in distribution network under consideration of power service reliability. Science China Technological Sciences 2017, 60, 1885 -1896.

AMA Style

Junjun Xu, Zaijun Wu, Xinghuo Yu, Qinran Hu, Chengzhi Zhu, Xiaobo Dou, Wei Gu, Zhi Wu. A new method for optimal FTU placement in distribution network under consideration of power service reliability. Science China Technological Sciences. 2017; 60 (12):1885-1896.

Chicago/Turabian Style

Junjun Xu; Zaijun Wu; Xinghuo Yu; Qinran Hu; Chengzhi Zhu; Xiaobo Dou; Wei Gu; Zhi Wu. 2017. "A new method for optimal FTU placement in distribution network under consideration of power service reliability." Science China Technological Sciences 60, no. 12: 1885-1896.

Journal article
Published: 07 September 2017 in Energies
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To achieve accurate reactive power sharing and voltage frequency and amplitude restoration in low-voltage microgrids, a control strategy combining an improved droop control with distributed secondary power optimization control is proposed. The active and reactive power that each distributed generator (DG) shares is calculated by extracting load information and utilizing a power sharing ratio, and is reset to be the nominal power to recalculate droop gains. The droop control curves are reconstructed according to the nominal active and reactive power and the recalculated droop gains. The reconstructed active power-frequency droop control can regulate active power adaptively and keep frequency at a nominal value. Meanwhile, the reconstructed reactive power voltage droop control can reduce voltage amplitude deviation to a certain extent. A distributed secondary power optimization control is added to the reconstructed reactive power voltage droop control by using average system voltage. The average system voltage is obtained by using a consensus algorithm in a distributed, sparse communication network which is constituted by all controllers of DGs. As a result, accurate reactive power sharing is realized, average system voltage is kept at a nominal value, and all voltage amplitude deviations are further reduced. Due to the absence of a microgrid central controller, the reliability of the strategy is enhanced. Finally, the simulation results validate the proposed method.

ACS Style

Demin Li; Bo Zhao; Zaijun Wu; Xuesong Zhang; Leiqi Zhang. An Improved Droop Control Strategy for Low-Voltage Microgrids Based on Distributed Secondary Power Optimization Control. Energies 2017, 10, 1347 .

AMA Style

Demin Li, Bo Zhao, Zaijun Wu, Xuesong Zhang, Leiqi Zhang. An Improved Droop Control Strategy for Low-Voltage Microgrids Based on Distributed Secondary Power Optimization Control. Energies. 2017; 10 (9):1347.

Chicago/Turabian Style

Demin Li; Bo Zhao; Zaijun Wu; Xuesong Zhang; Leiqi Zhang. 2017. "An Improved Droop Control Strategy for Low-Voltage Microgrids Based on Distributed Secondary Power Optimization Control." Energies 10, no. 9: 1347.

Journal article
Published: 24 July 2015 in Energies
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Inverter voltage control is an important task in the operation of a DC/AC microgrid system. To improve the inverter voltage control dynamics, traditional approaches attempt to measure and feedforward the load current, which, however, needs remote measurement with communications in a microgrid system with distributed loads. In this paper, a load current observer (LCO) based control strategy, which does not need remote measurement, is proposed for sinusoidal signals tracking control of a three-phase inverter of the microgrid. With LCO, the load current is estimated precisely, acting as the feedforward of the dual-loop control, which can effectively enlarge the stability margin of the control system and improve the dynamic response to load disturbance. Furthermore, multiple PR regulators are applied in this strategy conducted in a stationary frame to suppress the transient fluctuations and the total harmonic distortion (THD) of the output voltage and achieve faster transient performance compared with traditional dual-loop control in a rotating dq0 frame under instantaneous change of various types of load (i.e., balanced load, unbalanced load, and nonlinear load). The parameters of multiple PR regulators are analyzed and selected through the root locus method and the stability of the whole control system is evaluated and analyzed. Finally, the validity of the proposed approach is verified through simulations and a three-phase prototype test system with a TMS320F28335 DSP.

ACS Style

Xiaobo Dou; Kang Yang; Xiangjun Quan; Qinran Hu; Zaijun Wu; Bo Zhao; Peng Li; Shizhan Zhang; Yang Jiao. An Optimal PR Control Strategy with Load Current Observer for a Three-Phase Voltage Source Inverter. Energies 2015, 8, 7542 -7562.

AMA Style

Xiaobo Dou, Kang Yang, Xiangjun Quan, Qinran Hu, Zaijun Wu, Bo Zhao, Peng Li, Shizhan Zhang, Yang Jiao. An Optimal PR Control Strategy with Load Current Observer for a Three-Phase Voltage Source Inverter. Energies. 2015; 8 (8):7542-7562.

Chicago/Turabian Style

Xiaobo Dou; Kang Yang; Xiangjun Quan; Qinran Hu; Zaijun Wu; Bo Zhao; Peng Li; Shizhan Zhang; Yang Jiao. 2015. "An Optimal PR Control Strategy with Load Current Observer for a Three-Phase Voltage Source Inverter." Energies 8, no. 8: 7542-7562.

Journal article
Published: 16 July 2015 in Energies
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The Voltage Source Converter-HVDC (VSC-HVDC) system applied to wind power generation can solve large scale wind farm grid-connection and long distance transmission problems. However, the low voltage ride through (LVRT) of the VSC-HVDC connected wind farm is a key technology issue that must be solved, and it is currently lacking an economic and effective solution. In this paper, a LVRT coordinated control strategy is proposed for the VSC-HVDC-based wind power system. In this strategy, the operation and control of VSC-HVDC and wind farm during the grid fault period is improved. The VSC-HVDC system not only provides reactive power support to the grid, but also effectively maintains the power balance and DC voltage stability by reducing wind-farm power output, without increasing the equipment investment. Correspondingly, to eliminate the influence on permanent magnet synchronous generator (PMSG)-based wind turbine (WT) systems, a hierarchical control strategy is designed. The speed and validity of the proposed LVRT coordinated control strategy and hierarchical control strategy were verified by MATLAB/Simulink simulations.

ACS Style

Xinyin Zhang; Zaijun Wu; Minqiang Hu; Xianyun Li; Ganyun Lv. Coordinated Control Strategies of VSC-HVDC-Based Wind Power Systems for Low Voltage Ride Through. Energies 2015, 8, 7224 -7242.

AMA Style

Xinyin Zhang, Zaijun Wu, Minqiang Hu, Xianyun Li, Ganyun Lv. Coordinated Control Strategies of VSC-HVDC-Based Wind Power Systems for Low Voltage Ride Through. Energies. 2015; 8 (7):7224-7242.

Chicago/Turabian Style

Xinyin Zhang; Zaijun Wu; Minqiang Hu; Xianyun Li; Ganyun Lv. 2015. "Coordinated Control Strategies of VSC-HVDC-Based Wind Power Systems for Low Voltage Ride Through." Energies 8, no. 7: 7224-7242.

Journal article
Published: 24 December 2014 in Energies
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Operation control is a vital and complex issue for microgrids. The objective of this paper is to explore the practical means of applying decentralized control by using a multi agent system in actual microgrids and devices. This paper presents a hierarchical control framework (HCF) consisting of local reaction control (LRC) level, local decision control (LDC) level, horizontal cooperation control (HCC) level and vertical cooperation control (VCC) level to meet different control requirements of a microgrid. Then, a hybrid multi-agent control model (HAM) is proposed to implement HCF, and the properties, functionalities and operating rules of HAM are described. Furthermore, the paper elaborates on the implementation of HAM based on the IEC 61850 Standard, and proposes some new implementation methods, such as extended information models of IEC 61850 with agent communication language and bidirectional interaction mechanism of generic object oriented substation event (GOOSE) communication. A hardware design and software system are proposed and the results of simulation and laboratory tests verify the effectiveness of the proposed strategies, models and implementations.

ACS Style

Xiaobo Dou; Xiangjun Quan; Zaijun Wu; Minqiang Hu; Kang Yang; Jian Yuan; Mengmeng Wang. Hybrid Multi-Agent Control in Microgrids: Framework, Models and Implementations Based on IEC 61850. Energies 2014, 8, 31 -58.

AMA Style

Xiaobo Dou, Xiangjun Quan, Zaijun Wu, Minqiang Hu, Kang Yang, Jian Yuan, Mengmeng Wang. Hybrid Multi-Agent Control in Microgrids: Framework, Models and Implementations Based on IEC 61850. Energies. 2014; 8 (1):31-58.

Chicago/Turabian Style

Xiaobo Dou; Xiangjun Quan; Zaijun Wu; Minqiang Hu; Kang Yang; Jian Yuan; Mengmeng Wang. 2014. "Hybrid Multi-Agent Control in Microgrids: Framework, Models and Implementations Based on IEC 61850." Energies 8, no. 1: 31-58.

Journal article
Published: 02 December 2014 in Energies
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Ultracapacitors (UCs), with their features of high power density and high current charge-discharge, have become the best choice for dynamic power compensation to improve the stability of microgrids and are increasingly being applied in microgrids. This paper presents the control of an energy storage system (ESS) based on ultracapacitors in the context of grid-connected microgrids. The ESS is composed of DC/AC and DC/DC converters tied by a dc link. An improved dynamic model for the ESS is proposed. Based on the proposed model a Proportional-Integral-Resonant (PIR) DC link voltage controller is proposed to maintain the DC link voltage through the charging-discharging control of ultracapacitors, capable of working properly under all operating conditions. An extra double frequency component is injected into the UC current by a R controller to dynamically compensate for DC instantaneous power and double frequency AC instantaneous power due to unbalanced grid conditions and disturbances. This feature maintains the DC link voltage constant under unbalanced conditions and increases the degrees of freedom of the DC/AC converter and thus facilitates the application of UCs in microgrids. Simulation and experimental results verify the effectiveness of the proposed control strategy.

ACS Style

Xiaobo Dou; Xiangjun Quan; Zaijun Wu; Minqiang Hu; Jianlong Sun; Kang Yang; Minhui Xu. Improved Control Strategy for Microgrid Ultracapacitor Energy Storage Systems. Energies 2014, 7, 8095 -8115.

AMA Style

Xiaobo Dou, Xiangjun Quan, Zaijun Wu, Minqiang Hu, Jianlong Sun, Kang Yang, Minhui Xu. Improved Control Strategy for Microgrid Ultracapacitor Energy Storage Systems. Energies. 2014; 7 (12):8095-8115.

Chicago/Turabian Style

Xiaobo Dou; Xiangjun Quan; Zaijun Wu; Minqiang Hu; Jianlong Sun; Kang Yang; Minhui Xu. 2014. "Improved Control Strategy for Microgrid Ultracapacitor Energy Storage Systems." Energies 7, no. 12: 8095-8115.

Journal article
Published: 12 July 2013 in Energies
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In this paper, based on the similarity, in structure and principle, between a grid-connected converter for a direct-driven permanent magnet synchronous generator (D-PMSG) and an active power filter (APF), a new D-PMSG-based wind turbine (WT) system configuration that includes not only an auxiliary converter in parallel with the grid-side converter, but also a coordinated control strategy, is proposed to enhance the low voltage ride through (LVRT) capability and improve power quality. During normal operation, the main grid-side converter maintains the DC-link voltage constant, whereas the auxiliary grid-side converter functions as an APF with harmonic suppression and reactive power compensation to improve the power quality. During grid faults, a hierarchical coordinated control scheme for the generator-side converter, main grid-side converter and auxiliary grid-side converter, depending on the grid voltage sags, is presented to enhance the LVRT capability of the direct-driven PMSG WT. The feasibility and the effectiveness of the proposed system’s topology and hierarchical coordinated control strategy were verified using MATLAB/Simulink simulations.

ACS Style

Zaijun Wu; Xiaobo Dou; Jiawei Chu; Minqiang Hu. Operation and Control of a Direct-Driven PMSG-Based Wind Turbine System with an Auxiliary Parallel Grid-Side Converter. Energies 2013, 6, 3405 -3421.

AMA Style

Zaijun Wu, Xiaobo Dou, Jiawei Chu, Minqiang Hu. Operation and Control of a Direct-Driven PMSG-Based Wind Turbine System with an Auxiliary Parallel Grid-Side Converter. Energies. 2013; 6 (7):3405-3421.

Chicago/Turabian Style

Zaijun Wu; Xiaobo Dou; Jiawei Chu; Minqiang Hu. 2013. "Operation and Control of a Direct-Driven PMSG-Based Wind Turbine System with an Auxiliary Parallel Grid-Side Converter." Energies 6, no. 7: 3405-3421.

Journal article
Published: 25 February 2013 in Energies
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This paper presents an improved control strategy for both the rotor side converter (RSC) and grid side converter (GSC) of a doubly fed induction generator (DFIG)-based wind turbine (WT) system to enhance the low voltage ride through (LVRT) capability. Within the proposed control strategy, the RSC control introduces transient feed-forward compensation terms to mitigate the high frequency harmonic components and reduce the surge in the rotor currents. The proposed GSC control scheme also introduces a compensation term reflecting the instantaneous variation of the output power of the rotor side converter with consideration of the instantaneous power of grid filter impendence to keep the dc-link voltage nearly constant during the grid faults. To provide precise control, non-ideal proportional resonant (PR) controllers for both the RSC and GSC current regulation are employed to further improve dynamic performance. Simulations performed in Matlab/Simulink verify the effectiveness of the proposed control strategy.

ACS Style

Zaijun Wu; Chanxia Zhu; Minqiang Hu. Improved Control Strategy for DFIG Wind Turbines for Low Voltage Ride Through. Energies 2013, 6, 1181 -1197.

AMA Style

Zaijun Wu, Chanxia Zhu, Minqiang Hu. Improved Control Strategy for DFIG Wind Turbines for Low Voltage Ride Through. Energies. 2013; 6 (3):1181-1197.

Chicago/Turabian Style

Zaijun Wu; Chanxia Zhu; Minqiang Hu. 2013. "Improved Control Strategy for DFIG Wind Turbines for Low Voltage Ride Through." Energies 6, no. 3: 1181-1197.