Search for: droop-controllers
Decentralized load sharing in a low-voltage direct current microgrid with an adaptive droop approach based on a superimposed frequency, Article IEEE Journal of Emerging and Selected Topics in Power Electronics ; Volume 5, Issue 3 , 2017 , Pages 1205-1215 ; 21686777 (ISSN) ; Mokhtari, H ; Blaabjerg, F ; Sharif University of Technology
Conventional droop methods for load sharing control in low-voltage direct current microgrids suffer from poor power sharing and voltage regulation, especially in the case when operating many dc sources with long feeders. Hence, the communication-based approaches are employed to improve the load sharing accuracy and voltage regulation. To avoid using such an infrastructure and the corresponding effects on the reliability and stability, an adaptive droop controller based on a superimposed frequency is proposed in this paper. Load sharing accuracy is improved by adapting the droop gains utilizing an introduced ac power. The secondary controller locally estimates and compensates the voltage drop...
Article Energies ; Volume 9, Issue 11 , 2016 ; 19961073 (ISSN) ; Jalilvand, A ; Ehsan, M ; Sharif University of Technology
MDPI AG 2016
This paper attempted to control a hybrid DC microgrid in islanded operation mode using decentralized power management strategies. Proposed adaptive I/V characteristic for hybrid photovoltaic (PV) and battery energy storage system (BESS) and wind turbine generator (WTG) adapts the distributed energy resources (DER) behavior independently in accordance with the load demand. Hence, the PV module can spend its maximum power on load demand and spend the extra power for charging the BESS, which will regulate DC bus voltage and maintain the power balance within the microgrid. When load demand is beyond the maximum generation power of PV unit, WTG will supply the energy shortage. The proposed...
Article Microgrid: Advanced Control Methods and Renewable Energy System Integration ; 2016 , Pages 63-100 ; 9780081012628 (ISBN) ; Mokhtari, H ; Blaabjerg, F ; Sharif University of Technology
Elsevier Inc 2016
Because of the advances in power electronics, DC-based power systems, have been used in industrial applications such as data centers [. 18], space applications [. 10], aircraft [. 12], offshore wind farms, electric vehicles [. 56], DC home systems [. 5, 20], and high-voltage DC transmission systems. To provide such sensitive loads with more reliability, efficiency, and controllability for future power systems, AC microgrid and more recently DC microgrid and smart-grid technologies have been employed [. 5-9].To obtain stable and optimal operation in DC power systems (microgrids), proper load sharing among different energy units and acceptable voltage regulation across the microgrid is...
Article PEDSTC 2014 - 5th Annual International Power Electronics, Drive Systems and Technologies Conference ; December , 2014 , p. 84-89 ; Ashourloo, M ; Mokhtari, H ; Sharif University of technology
DC microgrids (MGs) are becoming popular as effective means to integrate different energy resources. Conventionally, the droop control is adopted as a decentralized control method for power sharing in DC MGs. However, current sharing accuracy or voltage regulation deteriorates due to the effects of line impedances. In this paper, a new adaptive control strategy is proposed for DC MGs. In low load conditions, the output currents of the DGs are far from their maximum acceptable limits. Therefore, current sharing accuracy is not important. As load increases, the output currents of the DGs approach their maximum acceptable limits. Therefore, at high load conditions, accurate current sharing is...
Ph.D. Dissertation Sharif University of Technology ; Mokhtari, Hossein
A microgrid is a collection of loads, sources, and power storage units that operates as a single controllable system and can operate in grid-connected or islanded mode. From the generating side, renewable energy resources such as photovoltaic system, fuel cell and power storage units are inherently DC. From the load side, electronic loads such as computers, data centers and most of the variable speed motor drives require a DC supply. Therefore, DC Microgrids have gained widespread attention in recent years. On the other hand, since existing distribution systems are mostly AC, a hybrid microgrid is more likely. The hybrid microgrid is composed of two AC and DC subgrids interlinked by power...
Article IEEE Transactions on Industrial Electronics ; Volume 62, Issue 11 , May , 2015 , Pages 6647-6657 ; 02780046 (ISSN) ; Ghazanfari, A ; Mohamed, Y. A. R. I ; Karimi, Y ; Sharif University of Technology
Institute of Electrical and Electronics Engineers Inc 2015
This paper presents an effective control scheme in dc microgrids to precisely share the load current oscillatory and dc components among distributed generation (DG) units. The proposed control strategy includes current and voltage control blocks. The current control block consists of oscillatory and dc current-sharing units. The main idea of the proposed method is to share the load current oscillatory and dc components among the DG units based on their rated power, by assigning appropriate output impedance values and droop coefficients to each DG unit. The voltage control block is a multiloop voltage control unit employed to control the microgrid voltage. The detailed model of the proposed...
A decentralized self-adjusting control strategy for reactive power management in an islanded multi-bus MV microgrid, Article Canadian Journal of Electrical and Computer Engineering ; Volume 36, Issue 1 , 2013 , Pages 18-25 ; 08408688 (ISSN) ; Mokhtari, H ; Karimi, H ; Sharif University of Technology
This paper presents a decentralized self-adjusting reactive power controller for the autonomous operation of a multi-bus medium voltage (MV) microgrid. The main objective of the proposed control strategy of each distributed generation (DG) unit is to compensate the reactive power of its local loads and to share the reactive power of the nonlocal loads among itself and other DG units. The proposed control strategy includes an improved droop controller whose parameters are adjusted according to the reactive power of the local loads. A virtual inductive impedance loop is augmented to the voltage controller to enhance the steady state and transient responses of the proposed reactive power...
Prevention of distribution network overvoltage by adaptive droop-based active and reactive power control of PV systems, Article Electric Power Systems Research ; Volume 133 , 2016 , Pages 313-327 ; 03787796 (ISSN) ; Parniani, M ; Sharif University of Technology
Proliferation of grid-connected photovoltaic systems (PVSs) causes technical problems due to their variable and non-dispatchable generated power. High penetration of PVS in distribution networks can result in overvoltage in some operating conditions. Although this situation occurs rarely, it limits the installed capacity of PVS. In this paper, adaptive droop-based control algorithms are presented to regulate active and reactive power of PVS, with the objectives of loss minimization and increasing the PVS capacity installation without unallowable overvoltage. Operating voltage range of the PVS is divided into several intervals, and a specific control algorithm is presented for each of them....
Article IEEE Transactions on Energy Conversion ; Vol. 29, issue. 4 , Dec , 2014 , p. 793-801 ; 08858969 ; Ashourloo, M ; Mokhtari, H ; Sharif University of Technology
DC microgrids (DC-MGs) are becoming popular as an effective means to integrate various renewable energy resources. Conventionally, the droop control is adopted as a decentralized control strategy for proper power sharing without using any communication link. However, the conventional droop control often deteriorates due to the effects of unequal line resistances. In this paper, a control strategy is proposed for a DC-MG to achieve perfect power sharing considering the effects of line resistances. The DC-MG under study consists of a photovoltaic system, two energy storage systems, a grid-connected converter system, and dc loads. The control strategy of the converters is addressed under...
Article 7th Power Electronics, Drive Systems and Technologies Conference, PEDSTC 2016, 16 February 2016 through 18 February 2016 ; 2016 , Pages 641-645 ; 9781509003754 (ISBN) ; Blaabjerg, F ; Peyghami Akhuleh, S ; Mokhtari, H ; Sharif University of Technology
Institute of Electrical and Electronics Engineers Inc 2016
In this paper, a distributed secondary power sharing approach with low bandwidth communication network is proposed for low voltage direct current (LVDC) microgrids. Conventional droop control causes voltage drop in the grid and also a mismatch on the current of converters in the case of consideration of the line resistances. Proposed control system carry out the current value of the other converters to reach the accurate current sharing and suitable voltage regulation as well. Voltage and current controllers locally regulate the voltage and current of converters as a secondary controller. Secondary controller is realized locally and the communication network is only used to transfer the data...
Article IEEE Transactions on Industry Applications ; Volume 53, Issue 5 , 2017 , Pages 4855-4862 ; 00939994 (ISSN) ; Mokhtari, H ; Davari, P ; Loh, P. C ; Blaabjerg, F ; Sharif University of Technology
Centralized or decentralized secondary controller is commonly employed to regulate the voltage drop raised by the primary controller. However, in the case of high capacity microgrids (MGs) and long feeders with much voltage drop on the line resistances, the conventional methods may not guarantee the voltage regulation on the load busses within a suitable range. Therefore, in addition to compensate the voltage drop of the primary controller, it is necessary to regulate the voltage of critical loads. In this paper, a new voltage regulation strategy is proposed to regulate the voltage of MG by employing the average voltage of identified critical busses, which are determined by the proposed...
Distributed Primary and secondary power sharing in a droop-controlled lvdc microgrid with merged AC and DC characteristics, Article IEEE Transactions on Smart Grid ; Volume 9, Issue 3 , 2018 , Pages 2284-2294 ; 19493053 (ISSN) ; Mokhtari, H ; Loh, P. C ; Davari, P ; Blaabjerg, F ; Sharif University of Technology
Institute of Electrical and Electronics Engineers Inc 2018
In an ac microgrid, a common frequency exists for coordinating active power sharing among droop-controlled sources. A common frequency is absent in a dc microgrid, leaving only the dc source voltages for coordinating active power sharing. That causes sharing error and poorer voltage regulation in dc microgrids, which in most cases, are solved by a secondary control layer reinforced by an extensive communication network. To avoid such an infrastructure and its accompanied complications, this paper proposes an alternative droop scheme for low-voltage dc microgrid with both primary power sharing and secondary voltage regulation merged. The main idea is to introduce a non-zero unifying frequency...
Article IEEE Transactions on Smart Grid ; Volume 10, Issue 6 , 2019 , Pages 6782-6791 ; 19493053 (ISSN) ; Davari, P ; Mokhtari, H ; Blaabjerg, F ; Sharif University of Technology
Institute of Electrical and Electronics Engineers Inc 2019
Power sharing control among grid forming dc sources employing a conventional voltage droop approach meets inaccurate load sharing and unacceptable voltage regulation performance. Thereby, communication-based secondary and supervisory controllers have been presented to overcome the aforementioned issues. Furthermore, with the aim of eliminating communication system, frequency-based droop approaches have been introduced for low-voltage dc grids where the frequency of the superimposed ac signal onto the dc voltage is proportional to the output power. However, in reality, dc grid structures can be applied to medium and high voltage applications with different X/R ratios. This paper generalizes...
Article IEEE Transactions on Power Systems ; Volume 27, Issue 4 , 2012 , Pages 2225-2232 ; 08858950 (ISSN) ; Karimi, H ; Mokhtari, H ; Sharif University of Technology
This paper proposes a new control strategy for the islanded operation of a multi-bus medium voltage (MV) microgrid. The microgrid consists of several dispatchable electronically-coupled distributed generation (DG) units. Each DG unit supplies a local load which can be unbalanced due to the inclusion of single-phase loads. The proposed control strategy of each DG comprises a proportional resonance (PR) controller with an adjustable resonance frequency, a droop control strategy, and a negative-sequence impedance controller (NSIC). The PR and droop controllers are, respectively, used to regulate the load voltage and share the average power components among the DG units. The NSIC is used to...
An Improved Voltage and Frequency Droop Control Method for Microgrids having Inverter Based Resources, Realizing the Effect of Lines R/X, M.Sc. Thesis Sharif University of Technology ; Vakilian, Mehdi
The centralized and decentralized control approaches are the most effective control approaches to be applied in micro grids. However, practically to rerduce the cost and improve the reliability, decentralized control is usually employed. Initially, this thesis discusses the components and dynamic model of the micro grid in order to evaluate the stability. Then, it introduces the decentralized control methods which can be used in a micro grid. In the next step, a sample micro gird is studied (with high ratio of lines R/X). This microgrid has three DG plants having DC voltage sources, inverter, and LCL filter. The performance of AVR controls is evaluated by combining the PQ and droop control...
A proportional-resonant controller-based wireless control strategy with a reduced number of sensors for parallel-operated UPSs, Article IEEE Transactions on Power Delivery ; Volume 25, Issue 1 , 2010 , Pages 468-478 ; 08858977 (ISSN) ; Caglar Onar, O ; Mokhtari, H ; Khaligh, A ; Sharif University of Technology
In this paper, a novel droop method to control the power sharing of parallel uninterruptible-power-supply (UPS) systems is presented. In a clear-cut contrast to the previously reported works, the controller is a proportional-resonant controller which ensures good transient response and steady-state objectives. Furthermore, the need for sensing the output current for the power-sharing control is removed by implementing it in a software routine. This brings a less complicated and less expensive structure in which the number of feedback sensors is reduced from three to two. The droop paralleling strategy is based on the drop in the inverter output frequency and amplitude. The application of...
Active power management of multihybrid fuel cell/supercapacitor power conversion system in a medium voltage microgrid, Article IEEE Transactions on Smart Grid ; Volume 3, Issue 4 , 2012 , Pages 1903-1910 ; 19493053 (ISSN) ; Hamzeh, M ; Mokhtari, H ; Karimi, H ; Sharif University of Technology
This paper proposes a hierarchical active power management strategy for a medium voltage (MV) islanded microgrid including a multihybrid power conversion system (MHPCS). To guarantee excellent power management, a modular power conversion system is realized by parallel connection of small MHPCS units. The hybrid system includes fuel cells (FC) as main and supercapacitors (SC) as complementary power sources. The SC energy storage compensates the slow transient response of the FC stack and supports the FC to meet the grid power demand. The proposed control strategy of the MHPCS comprises three control loops; dc-link voltage controller, power management controller, and load current sharing...
A simplified droop method implementation in parallel UPS inverters with Proportional-Resonant controller, Article Iranian Journal of Science and Technology, Transaction B: Engineering ; Volume 33, Issue 2 , 2009 , Pages 163-178 ; 10286284 (ISSN) ; Mokhtari, H ; Sharif University of Technology
In this paper, a simpler implementation of the well-known droop method for the control of parallel Uninterruptible Power Supply (UPS) systems is presented. In this method, in the power-sharing control scheme, the output current is calculated by software without the need for a current sensor, resulting in a simpler and cheaper structure. By doing so, the number of feedback sensors is reduced from three to two. The paralleling strategy uses the droop method in which the control strategy is based on the drop in the inverter output frequency and amplitude. The application of Proportional-Resonant (PR) controllers is also extended to parallel inverter and its superior performance over the...