A Unified Control and Power Management Scheme for PV-Battery-Based Hybrid Microgrids for Both Grid-Connected and Islanded Modes
quinta-feira, 11 de abril de 2024
A Unified Control and Power Management Scheme for PV-Battery-Based Hybrid Microgrids for Both Grid-Connected and Islanded Modes Zhehan Yi, Student Member, IEEE, Wanxin Dong, and Amir H. Etemadi, Member, IEEE
A Unified Control and Power Management Scheme for PV-Battery-Based Hybrid Microgrids for Both Grid-Connected and Islanded Modes
Zhehan Yi, Student Member, IEEE, Wanxin Dong, and Amir H. Etemadi, Member, IEEE
Abstract
Battery storage is usually employed in Photovoltaic (PV) system to mitigate the power fluctuations due to the characteristics of PV panels and solar irradiance. Control schemes for PV-battery systems must be able to stabilize the bus voltages as well as to control the power flows flexibly. This paper proposes a comprehensive control and power management system (CAPMS) for PV-battery-based hybrid microgrids with both AC and DC buses, for both grid-connected and islanded modes. The proposed CAPMS is successful in regulating the DC and AC bus voltages and frequency stably, controlling the voltage and power of each unit flexibly, and balancing the power flows in the systems automatically under different operating circumstances, regardless of disturbances from switching operating modes, fluctuations of irradiance and temperature, and change of loads. Both simulation and experimental case studies are carried out to verify the performance of the proposed method.
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quarta-feira, 10 de abril de 2024
Smart inverters for seamless voltage and frequency dynamics in microgrids by Mohsen Shid Pilehvar-DISSERTATION submitted in partial fulfillment of the requirements for the degree DOCTOR OF PHILOSOPHY Mike Wiegers Department of Electrical & Computer Engineering --KANSAS STATE UNIVERSITY Manhattan, Kansas 2021-
Smart inverters for seamless voltage and frequency dynamics in microgrids by Mohsen Shid Pilehvar
AN ABSTRACT OF A DISSERTATION
submitted in partial fulfillment of the
requirements for the degree
DOCTOR OF PHILOSOPHY
Mike Wiegers
Department of Electrical & Computer Engineering
Carl R. Ice College of Engineering
KANSAS STATE UNIVERSITY
Manhattan, Kansas
2021
Abstract
This dissertation focuses on improving the dynamic behavior of microgrids during the abnormal
conditions. For this purpose, novel approaches are presented to turn the conventional
inverters implemented in distributed generation (DG) units into smart inverters capable of
dealing with disturbances. In the context of microgrids, the smartness of an inverter is tied
to its ability to cope with abnormalities such as sudden load changes, loss of generation, and
transitions between different modes of operation. Founded on these principles, this dissertation
advances the state-of-the-art in enhancing the dynamic response of microgrids. To
this end, firstly, a new approach of forming smart loads in a fleet of nanogrids, which is
also referred as a grid of nanogrids (GNG), is presented in this dissertation. The proposed
smart load configuration is obtained via series connection of electric dampers (EDs) with
critical loads to cope with disturbances at the point of critical loads. A systematic approach
is presented for modeling of the proposed smart loads considering the switching states of
EDs. The stability of the smart loads is then studied using the developed state-space model.
Secondly, the conventional controllers of battery energy storage system (BESS) and photovoltaic
(PV) units are modified in this dissertation in order to enable them to participate
in dynamic-response enhancement of islanded mixed-inertia microgrids. For this purpose,
two piecewise linear-elliptic (PLE) droops are proposed and employed in BESS to improve
the voltage and frequency profiles during abnormalities. Besides, the controllers of PV units
are equipped with an adaptive piecewise droop (APD) to cope with disturbances. Lastly,
an approach is presented in this dissertation for seamless interconnection of three singlephase
feeders at distribution level for residential communities that are suffering from power
imbalance within the phases during islanded mode. To attain this, a seamless transition
algorithm is presented which monitors the system condition in real time and sends appropriate
commands to the static transfer switches (STSs) and modified controllers of single-phase
inverters. Using the proposed method for interconnecting the isolated single-phase feeders
results in forming a unified single-phase residential microgrid and maintaining the power
balance and voltage level within all three phases. Moreover, the proposed approach enables
the residential community to seamlessly reconnect to the main grid after resolving the abnormal
condition on the grid side. In this dissertation, numerous case studies are carried
out in PSCAD/EMTDC environment to validate the viability of proposed approaches in
improving the dynamic behavior of microgrids.
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segunda-feira, 8 de abril de 2024
Comparison Between Different Droop Based Control Techniques and a Virtual Control Oscillator Carlos G. C. Branco1,*, Jordi El Mariachet Carreno1, Mingshen Li1, Francisco Kleber de A. Lima2, José Matas1, Josep M. Guerrero3
Comparison Between Different Droop Based Control Techniques and a Virtual Control Oscillator Carlos G. C. Branco1,*, Jordi El Mariachet Carreno1, Mingshen Li1, Francisco Kleber de A. Lima2, José Matas1, Josep M. Guerrero Abstract: This work presents a literature review about control techniques for parallel connected power inverters under microgrid applications. Some control strategies, based on droop control for parallel inverters of distributed generation units in an ac distribution system will be presented in this work. Finally, an important method called Virtual Oscillating Control (VOC) is suggested for connecting voltage source inverters. Inverters are able to work in parallel with a constant-voltage constant frequency system, as well as with other inverters and also in standalone operation. The different power sources can share the load also under unbalanced conditions. Throughout this work several simulation results are presented in order to demonstrate the behaviour.
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Compensation of Voltage Sags and Swells Using Dynamic Voltage Restorer Based on Bi-Directional H-Bridge AC/AC Converter Yu-KChen , Xian-Zhi Qiu , Yung-Chun Wu , and Chau-Chung Song Citation: Chen, Y.-K.; Qiu, X.-Z.; Wu, Y.-C.; Song, C.-C. Compensation of Voltage Sags and Swells Using Dynamic Voltage Restorer Based on Bi-Directional H-Bridge AC/AC Converter. Academic Editors: Chang-Hua Lin and Jahangir Hossain Received: Published: 30 August 2021 Department of Aeronautical Engineering, National Formosa University, Hu-Wei 632, Taiwan
Abstract: In this paper, the compensation of voltage sags and swells using a dynamic voltage restorer (DVR) based on a bi-directional AC/AC converter is presented for stabilizing single-phase AC line voltage. The H-bridge AC/AC converter with bi-directional switches and without bulk capacitor is adopted as the power topology of the proposed system. The proposed novel topology of DVR is adopted to compensate both voltage sag and swell conditions. Additionally, the power factor is closed to unity because a bulk capacitor is not required. The inner and outer loop control is proposed to improve the response with gain scaling; gain control is adopted to reduce the overshoot. Finally, a 2 kVA prototype has been implemented to verify the performance and accuracy of the control method for the DVR system. The peak efficiency of the system is up to 94%, and it can compensate 50% voltage swells and 25% voltage sags.
VIEW FULL TEXT: https://www.mdpi.com/2227-9717/9/9/1541
domingo, 7 de abril de 2024
A Study of Control Technique in Stationary Reference Frame for Improving the Disturbance Rejection Performance in Parallel Operation of Multi-Modular UPS--Hyo-Jun Ryu-- Department of Automotive Engineering (Automotive-Computer Convergence) Graduate School of Hanyang University
A Study of Control Technique in Stationary Reference Frame for Improving the Disturbance Rejection Performance in Parallel Operation of Multi-Modular UPS--Hyo-Jun Ryu-- Department of Automotive Engineering (Automotive-Computer Convergence) Graduate School of Hanyang University
ABSTRACT
This paper proposes a control technique for improving the disturbance rejection
performance of a voltage controller during the parallel operation of multi modular
UPS. In a single operation of the modular UPS, it is possible to improve disturbance
rejection performance by conducting the feed-forward compensation for the load
current, which is the disturbance of the voltage controller. However, a circulating
current may occur when the modular UPS operates in parallel with the feed-forward
control compensates for the load current. As a result, load sharing between UPS
modules becomes uneven, and in severe cases, the parallel operation may not be
possible. In this paper, the circulating current impedance model according to the
load current feed-forward compensation gain explains the circulating current
occurrence during the modular UPS parallel operation. In addition, a control
technique, which is the feed-forward compensation for a portion of the load current
considering a decrease of circulating current impedance, is proposed. However, the
load current feed-forward compensation technique that considers circulating
current impedance deteriorates disturbance rejection performance compared to a
single operation of modular UPS, which is possible to apply for the load current feedforward
compensation regardless of circulating current impedance. Therefore, this
paper proposes another feed-forward compensation technique with a 2-DOF voltage
controller structure to improve the reduced disturbance rejection performance. This
technique ensures the cascade control performance of the structure of the voltagecurrent
controller by maintaining the voltage controller's reference tracking
performance and improving the disturbance rejection performance of the voltage
controller. The effectiveness of the proposed feed-forward compensation technique
is demonstrated by experimental results obtained through the operation of the fourparallel
connected the 500 W modular double conversion UPS.
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