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Control Strategy for Accurate Reactive Power Sharing in Islanded Microgrids
Pham, Xuan Hoa Thi,Le, Toi Thanh The Korean Institute of Power Electronics 2019 JOURNAL OF POWER ELECTRONICS Vol.19 No.4
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.
Control Strategy for Accurate Reactive Power Sharing in Islanded Microgrids
Xuan Hoa Thi Pham,Toi Thanh Le 전력전자학회 2019 JOURNAL OF POWER ELECTRONICS Vol.19 No.4
This paper presents a control strategy to enhance the accuracy of reactive power sharing between paralleled three-phaseinverters in an islanded microgrid. In this study, the mismatch of power sharing when the line impedances have significantdifferences between inverters connected to a microgrid has been solved, the accuracy of the reactive power sharing in an islandedmicrogrid is increased, the voltage droop slope is tuned to compensate for the mismatch of voltage drops across the lineimpedances by using an enhanced droop controller. The proposed method ensures accurate power sharing even if the microgridhas local loads at the output of the inverters. The control model has been simulated by MATLAB/Simulink with two or threeinverters connected in parallel. Simulation results demonstrate the accuracy of the implemented control method. Furthermore, inorder to validate the theoretical analysis and simulation results, an experimental setup was built in the laboratory. Resultsobtained from the experimental setup verify the effectiveness of the proposed method.
Effects of Corporate Governance and Earning Quality on Listed Vietnamese Firm Value
DANG, Hung Ngoc,PHAM, Cuong Duc,NGUYEN, Thang Xuan,NGUYEN, Hoa Thi Thanh Korea Distribution Science Association 2020 The Journal of Asian Finance, Economics and Busine Vol.7 No.4
The paper examines the influence of corporate governance (CG) and earning quality (EQ) on corporate value (FV) of Vietnamese enterprises. The study uses GLS regression and linear structure model using data collected from companies listing on the stock market in Vietnam during 2008-2018, with a total of 2,937 observations. The research results indicate that EQ and CG represented by the Integrated Board of Directors and the Integrated Supervisory Board have a positive effect on FV directly and indirectly. The results show that the Integrated Board of Directors has a positive effect on EQ, whereas the Integrated Supervisory Board has a negative effect on EQ. Based on the research results, we suggest that companies need to strictly comply and implement GC, so to bring down the agency cost and consequently to increase performance. The companies also should establish the Board of Director of a proper size, with financial and accounting specialty, and including women board members. The government also needs to improve the management mechanism asking for firms to prepare and publish financial statements with reliable company information, which could be provided to users. These recommendations are a useful basis to help businesses improve FV via changes in the corporate governance factors in each enterprise.
Line Impedance Estimation Based Adaptive Droop Control Method for Parallel Inverters
Le, Phuong Minh,Pham, Xuan Hoa Thi,Nguyen, Huy Minh,Hoang, Duc Duy Vo,Nguyen, Tuyen Dinh,Vo, Dieu Ngoc The Korean Institute of Power Electronics 2018 JOURNAL OF POWER ELECTRONICS Vol.18 No.1
This paper presents a new load sharing control for use between paralleled three-phase inverters in an islanded microgrid based on the online line impedance estimation by the use of a Kalman filter. In this study, the mismatch of power sharing when the line impedance changes due to temperature, frequency, significant differences in line parameters and the requirements of the Plug-and-Play mode for inverters connected to a microgrid has been solved. In addition, this paper also presents a new droop control method working with the line impedance that is different from the traditional droop algorithm when the line impedance is assumed to be pure resistance or pure inductance. In this paper, the line impedance estimation for parallel inverters uses the minimum square method combined with a Kalman filter. In addition, the secondary control loops are designed to restore the voltage amplitude and frequency of a microgrid by using a combined nominal value SOGI-PLL with a generalized integral block and phase lock loop to monitor the exact voltage magnitude and frequency phase at the PCC. A control model has been simulated in Matlab/Simulink with three voltage source inverters connected in parallel for different ratios of power sharing. The simulation results demonstrate the accuracy of the proposed control method.
Line Impedance Estimation Based Adaptive Droop Control Method for Parallel Inverters
Phuong Minh Le,Xuan Hoa Thi Pham,Huy Minh Nguyen,Duc Duy Vo Hoang,Tuyen Dinh Nguyen,Dieu Ngoc Vo 전력전자학회 2018 JOURNAL OF POWER ELECTRONICS Vol.18 No.1
This paper presents a new load sharing control for use between paralleled three-phase inverters in an islanded microgrid based on the online line impedance estimation by the use of a Kalman filter. In this study, the mismatch of power sharing when the line impedance changes due to temperature, frequency, significant differences in line parameters and the requirements of the Plug-and-Play mode for inverters connected to a microgrid has been solved. In addition, this paper also presents a new droop control method working with the line impedance that is different from the traditional droop algorithm when the line impedance is assumed to be pure resistance or pure inductance. In this paper, the line impedance estimation for parallel inverters uses the minimum square method combined with a Kalman filter. In addition, the secondary control loops are designed to restore the voltage amplitude and frequency of a microgrid by using a combined nominal value SOGI-PLL with a generalized integral block and phase lock loop to monitor the exact voltage magnitude and frequency phase at the PCC. A control model has been simulated in Matlab/Simulink with three voltage source inverters connected in parallel for different ratios of power sharing. The simulation results demonstrate the accuracy of the proposed control method.