• Title, Summary, Keyword: Power sharing

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Research on the Power Sharing Control and Stability of VSGs

  • Xie, Dong;Zang, Da-Jin;Gao, Peng;Wang, Jun-Jia
    • Journal of Power Electronics
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    • v.17 no.2
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    • pp.542-550
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    • 2017
  • Aiming at the deficiencies of power sharing control performances when a traditional droop control is adopted for microgrid inverters, this paper proposes a microgrid inverter power sharing control strategy based on a virtual synchronous generator. This control method simulates the electromechanical transient characteristics of a synchronous generator in a power system by an ontology algorithm and the control laws of a synchronous generator by control over the speed governor and excitation regulator. As a result, that the microgrid system is able to effectively retain the stability of the voltage and frequency, and the power sharing precision of the microgrid inverter is improved. Based on an analysis of stability of a microgrid system controlled by a virtual synchronous generator, design thoughts are provided for further improvement of the power sharing precision of inverters. The simulation results shows that when the virtual synchronous generator based control strategy was adopted, the power sharing performances of microgrid inverters are improved more obviously than those using the droop control strategy.

An Enhanced Power Sharing Strategy for Islanded Microgrids Considering Impedance Matching for Both Real and Reactive Power

  • Lin, Liaoyuan;Guo, Qian;Bai, Zhihong;Ma, Hao
    • Journal of Power Electronics
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    • v.17 no.1
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    • pp.282-293
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    • 2017
  • There exists a strong coupling between real and reactive power owing to the complex impedances in droop based islanded microgrids (MGs). The existing virtual impedance methods consider improvements of the impedance matching for sharing of the voltage controlled power (VCP) (reactive power for Q-V droop, and real power for P-V droop), which yields a 1-DOF (degree of freedom) tunable virtual impedance. However, a weak impedance matching for sharing of the frequency controlled power (FCP) (real power for $P-{\omega}$ droop, and reactive power for $Q-{\omega}$ droop) may result in FCP overshoots and even oscillations during load transients. This in turn results in VCP oscillations due to the strong coupling. In this paper, a 2-DOF tunable adaptive virtual impedance method considering impedance matching for both real and reactive power (IM-PQ) is proposed to improve the power sharing performance of MGs. The dynamic response is promoted by suppressing the coupled power oscillations and power overshoots while realizing accurate power sharing. In addition, the proposed power sharing controller has a better parametric adaptability. The stability and dynamic performances are analyzed with a small-signal state-space model. Simulation and experimental results are presented to investigate the validity of the proposed scheme.

Accurate Power Sharing in Proportion for Parallel Connected Inverters by Reconstructing Inverter Output Impedance

  • Huang, Shengli;Luo, Jianguo
    • Journal of Power Electronics
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    • v.18 no.6
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    • pp.1751-1759
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    • 2018
  • This paper presents parallel-connected inverters to achieve accurate proportional power sharing. Due to line impedance mismatch, reactive power cannot be distributed proportionally when using the conventional $P-{\omega}$ and $\mathcal{Q}-E$ droop. In order to realize reactive proportional power sharing, the ratio of the droop coefficients should be inversely proportional to their power-sharing ratios. Meanwhile, the ratio of the line impedance should be inversely proportional to the desired power-sharing ratio, which is very difficult to be met in practice. In order to deal with this issue, a practical control strategy is presented. By measuring the PCC voltage and using the virtual impedance, the output impedance of individual inverters is reconstructed to counteract the line impedance effect. In order to guarantee system stability, a low pass filter is designed to suppress the bandwidth of the line compensation. Finally, the simulation and experimental results are given to verify the effectiveness of the proposed control strategy.

Control Strategy for Accurate Reactive Power Sharing in Islanded Microgrids

  • Pham, Xuan Hoa Thi;Le, Toi Thanh
    • Journal of Power Electronics
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    • v.19 no.4
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    • pp.1020-1033
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    • 2019
  • This paper presents a control strategy to enhance the accuracy of reactive power sharing between paralleled three-phase inverters in an islanded microgrid. In this study, the mismatch of power sharing when the line impedances have significant differences between inverters connected to a microgrid has been solved, the accuracy of the reactive power sharing in an islanded microgrid is increased, the voltage droop slope is tuned to compensate for the mismatch of voltage drops across the line impedances by using an enhanced droop controller. The proposed method ensures accurate power sharing even if the microgrid has local loads at the output of the inverters. The control model has been simulated by MATLAB/Simulink with two or three inverters connected in parallel. Simulation results demonstrate the accuracy of the implemented control method. Furthermore, in order to validate the theoretical analysis and simulation results, an experimental setup was built in the laboratory. Results obtained from the experimental setup verify the effectiveness of the proposed method.

Low-Voltage and High-Current DC Output Realized by Multiple Power Cells Based on Deadbeat and Automatic Current Sharing Control

  • Liu, Jinfeng;Zhang, Yu;Wang, Xudong;IU, Herbert Ho-Ching
    • Journal of Electrical Engineering and Technology
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    • v.12 no.4
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    • pp.1575-1585
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    • 2017
  • This paper presents a synchronous generator with a distributed system of multiple parallel three-phase power cells. This generator can immediately output high DC. Each power cell comprises three-phase windings and a three-phase synchronous rectification bridge with a deadbeat control of load power feedforward, which can improve the characteristics of dynamic response and reflect the load variance in real time. Furthermore, each power cell works well independently and modularly using the method of automatic maximum current sharing. The simulation and experimental results for the distributed controller of multiple power cells demonstrate that the deadbeat control method can respond quickly and optimize the quality of the energy. Meanwhile, automatic maximum current sharing can realize the validity of current sharing among power cells.

A Diesel Power Sharing Algorithm for Wind-Diesel Hybrid Electric Power Generation Systems (풍력-디젤 하이브리드 발전 시스템의 디젤 출력 배분 알고리즘 개발)

  • Nam, Yong-Youn;Lee, Geun-Ho;Han, Jeong-Woo;Park, Young-Jun;Lee, Young-Soo
    • Journal of The Korean Society of Manufacturing Technology Engineers
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    • v.20 no.5
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    • pp.673-678
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    • 2011
  • For the wind-diesel hybrid electric power generation system equiped with two diesel generators, the diesel power sharing is studied analytically and a power sharing technique of less fuel consumption is developed. Based on the technique, as example, a diesel power sharing algorithm is suggested for two diesel generators of capacity 500Kw(200Kw+300Kw).

Power Conditioning Inverter Controlled by Sinewave Tracking Boost Chopper without DC Smoothing Capacitor Stage

  • Ahmed, Nabil A.;Miyatake, Masafumi;Kang, Tae-Kyung;Lee, Hyun-Woo;Nakaoka, Mutsuo
    • 제어로봇시스템학회:학술대회논문집
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    • pp.179-185
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    • 2005
  • This paper presents a novel circuit topology of a high efficiency single-phase power conditioner. This power conditioner is composed of time-sharing sinewave absolute pulse width modulated boost chopper with a bypass diode in the first power processing stage and time-sharing sinewave pulse width modulated full-bridge inverter in the second power processing stage operated by time-sharing dual mode pulse pattern control scheme. The unique operating principle of the two power processing stage with time-sharing dual mode sinewave modulation scheme is described with a design example. This paper proposes also a sinewave tracking voltage controlled soft switching PWM boost chopper with a passive auxiliary edge-resonant snubber. The new conceptual operating principle of this novel power conditioner related to new energy utilization system is presented and discussed through the experimental results.

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Secondary Voltage Control for Reactive Power Sharing in an Islanded Microgrid

  • Guo, Qian;Wu, Hongyan;Lin, Liaoyuan;Bai, Zhihong;Ma, Hao
    • Journal of Power Electronics
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    • v.16 no.1
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    • pp.329-339
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    • 2016
  • Owing to mismatched feeder impedances in an islanded microgrid, the conventional droop control method typically results in errors in reactive power sharing among distributed generation (DG) units. In this study, an improved droop control strategy based on secondary voltage control is proposed to enhance the reactive power sharing accuracy in an islanded microgrid. In a DG local controller, an integral term is introduced into the voltage droop function, in which the voltage compensation signal from the secondary voltage control is utilized as the common reactive power reference for each DG unit. Therefore, accurate reactive power sharing can be realized without any power information exchange among DG units or between DG units and the central controller. Meanwhile, the voltage deviation in the microgrid common bus is removed. Communication in the proposed strategy is simple to implement because the information of the voltage compensation signal is broadcasted from the central controller to each DG unit. The reactive power sharing accuracy is also not sensitive to time-delay mismatch in the communication channels. Simulation and experimental results are provided to validate the effectiveness of the proposed method.

Voltage and Frequency Droop Control for Accurate Power Sharing of Parallel DG Inverters in Low Voltage Microgrid

  • Nguyen, Tien Hai;Kim, Kyeong-Hwa
    • Proceedings of the KIPE Conference
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    • pp.95-96
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    • 2016
  • This paper presents a voltage and frequency droop control for accurate power sharing of parallel distributed generation (DG) inverters in low voltage microgrid. In practice, line impedances between inverters and the point of common coupling of a microgrid are not always equal. This inequality in line impedances often results in reactive power sharing mismatch among inverters. To address this problem, intensive researches have been conducting. Although these methods can solve the unbalanced reactive power sharing, there are still problems remain unresolved, such as complicated structure or circulating current. To overcome such problems, a new droop control scheme is proposed, which not only guarantees accurate reactive power sharing but also has simple structure so that it can be easily implemented in existing systems without any hardware modification. The simulation is performed using Matlab/Simulinks to validate the proposed scheme.

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Adaptive Power Control Strategy based on Spectrum Sensing for Cognitive Relay Networks (CR 넷워크를 위한 주파수 감지에 기번한 적응적인 전력 제어 전략)

  • HU, SIYUAN;Joe, Inwhee
    • Proceedings of the Korea Information Processing Society Conference
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    • pp.82-85
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    • 2019
  • An adaptive power control scheme is proposed for the cognitive relay networks with joint overlay and underlay spectrum sharing model. The transmit power of the secondary user is adjusted adaptively according to the spectrum sensing results and the interference channel condition. The outage probability of the secondary user is compared by Monte - Carlo simulations between the fixed power control scheme and pure overlay or underlay spectrum sharing schemes. The results show that, by employing the adaptive power control strategy, the interference probability of the secondary user to the primary user is decreased by 70 % ~ 80 % under the same outage probability. Also, the outage probability of the secondary user is reduced by 1 ~ 2 orders of magnitude under the same interference probability. Thus, the performance of the spectrum sharing is improved effectively.