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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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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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.

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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.