Browsing by Author "Tamimi, Behnam"

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An Effective Controllable Grid Interface for Microgrids
(Institute of Electrical and Electronics Engineers (IEEE), 2022-08-31) Tamimi, Behnam; Gu, Hanwen; Canizares, Claudio A.
The interest in the integration of distributed power generation and microgrids into power grids has significantly increased. In this context, interfacing microgrids with a host grid is of significant relevance, and therefore, in this paper, a cost-effective controllable grid interface for microgrids is proposed, modeled, and studied under various conditions, including smooth and abrupt power fluctuations, faults, and interface tripping. The proposed interface, named Microgrid Connector Controller (MGC), is an adequate and affordable alternative to the existing Back-to-Back (B2B) microgrid-grid interface, at a fraction of its capital costs. Thus, the proposed MGC’s performance is compared a B2B interface through detailed time-domain simulations in a realistic benchmark test system to demonstrate the controller’s capabilities. Compared with B2B, MGC’s direct frequency synchronization and power and voltage control capabilities makes it easier for microgrid operators to satisfy required standards and reduce wear and tear in grid equipment and customer loads. Finally, the MGC’s lower voltage ratings may translate into significantly smaller size and thus easier logistics and lower costs.
Effect of Reactive Power Limit Modeling on Maximum System Loading and Active and Reactive Power Markets
(Institute of Electrical and Electronics Engineers (IEEE), 2010-02-05) Tamimi, Behnam; Canizares, Claudio A.; Vaez-Zadeh, Sadegh
This paper presents a comparative investigation of various representations of reactive power limits in maximum loadability and active and reactive power market studies. Previously proposed optimal power flow (OPF) models for these types of analyses are first reviewed and briefly discussed. Different models for representing reactive power limits in these optimization problems are then presented, concentrating in particular on the proper modeling of the generators' capability curves as terminal voltages change, which has been identified as a shortcoming of previous studies. Comparative numerical analyses of the effect of various reactive power limit models in maximum loading and active and reactive power dispatch and pricing levels are presented and discussed, to thus quantify the effect these various limit representations have on the corresponding results. Two test systems, namely, the CIGRE-32 benchmark system and a 1211-bus dispatch model of a European network, are used for numerical studies. The presented results show that in most OPF applications, the improvement on the reactive power limits representation lead to subtle differences at the cost of increased computational complexity, which in some cases may be difficult to justify in practice.
Effect of Reactive Power Limit Modeling on Maximum System Loading and Active and Reactive Power Markets
(Institute of Electrical and Electronics Engineers (IEEE), 2010-02-05) Tamimi, Behnam; Canizares, Claudio A.; Vaez-Zadeh, Sadegh
This paper presents a comparative investigation of various representations of reactive power limits in maximum loadability and active and reactive power market studies. Previously proposed optimal power flow (OPF) models for these types of analyses are first reviewed and briefly discussed. Different models for representing reactive power limits in these optimization problems are then presented, concentrating in particular on the proper modeling of the generators' capability curves as terminal voltages change, which has been identified as a shortcoming of previous studies. Comparative numerical analyses of the effect of various reactive power limit models in maximum loading and active and reactive power dispatch and pricing levels are presented and discussed, to thus quantify the effect these various limit representations have on the corresponding results. Two test systems, namely, the CIGRE-32 benchmark system and a 1211-bus dispatch model of a European network, are used for numerical studies. The presented results show that in most OPF applications, the improvement on the reactive power limits representation lead to subtle differences at the cost of increased computational complexity, which in some cases may be difficult to justify in practice.
Hybrid Power Flow Controller Steady-state Modeling, Control, and Practical Application
(Institute of Electrical and Electronics Engineers (IEEE), 2016-07-07) Tamimi, Behnam; Canizares, Claudio; Battistelli, Claudia
Steady-state models of the hybrid power flow controller (HPFC) for power flow and optimal power flow (OPF) studies are presented in this paper, considering the multiple control modes of the device. A strategy for control mode switching and limit handling in power flow calculations is proposed. The OPF model of the HPFC represents all the device control and physical limits as constraints in the mathematical formulation, so that the HPFC can be optimally dispatched as a part of the transmission system control assets. The power flow model is demonstrated and validated through loadability studies on a two-area benchmark test system, where the OPF model is used to determine the optimal ratings of the device based on a cost-benefit analysis. A study is also presented of the HPFC application to Ontario-Canada's grid, to address particular congestion problems in this network; an HPFC cost analysis is also shown for this system. The presented studies demonstrate the application of the proposed models for planning and operation studies, illustrating the performance, effectiveness, and feasibility of the controller to solve congestion issues in a real grid.
Improved Control and Stability Analysis of a Microgrid Connector Controller Under Unbalanced Network Conditions
(Institute of Electrical and Electronics Engineers (IEEE), 2025-03-19) Gu, Hanwen; Tamimi, Behnam; Cañizares, Claudio A.
The microgrid connector controller has been shown to be a more cost-effective alternative for a microgrid-grid interface than a back-to-back connector. This paper proposes an improved control system for this controller under unbalanced operation, as distribution feeder and microgrid loads are normally unbalanced. The controller regulates the utility interface while minimizing the impact of load unbalancing on both the utility feeder and the microgrid. An improved reference current generation strategy is designed to suppress the fluctuations of the dc link voltage, thereby preventing them from being introduced into the control system and affecting the controller operation. Furthermore, a four-stage start-up strategy is proposed to avoid an external dc source for charging the controller’s dc link capacitor, making the interface more practical and cost-effective. The paper also presents a comprehensive investigation of the effects of the controller parameters and microgrid load unbalance on the small-perturbation stability of grid-connected microgrids. The performance of the presented controller is compared with its original controls, a back-to-back with existing unbalance control techniques, and a switch interface through detailed simulations in a benchmark test system. The results illustrate that the proposed controls can minimize the impact of feeder and microgrid unbalancing by eliminating the negative-sequence components and reducing the fluctuations in the transferred powers and dc link voltage, showing similar overall performance to a back-to-back interface.
Modeling and Application of Hybrid Power Flow Controller in Distribution Systems
(Institute of Electrical and Electronics Engineers (IEEE), 2018-08-01) Tamimi, Behnam; Canizares, Claudio A.
The smartening of distribution systems with distributed generation, storage devices, and intelligent loads have created challenges for the operation of distribution feeders, which can be addressed with power-electronics based controllers. However, the capital-intensive nature of these controllers is an obstacle for their wide use. The Hybrid Power Flow Controller (HPFC) is shown here to provide an adequate solution to the application of flexible ac transmission systems controllers to distribution systems and hence the merits and the added value of this controller are discussed here through detailed modeling and simulations, examining its impact on a distribution system under different conditions. Thus, in this paper, a detailed dynamic model of the HPFC is developed and implemented in PSCAD, describing and proposing control strategies to properly operate this controller in distribution-system applications, such as an effective and simple procedure for starting up the device. The developed model is used to demonstrate the effectiveness of the controller for solving problems in distribution systems, such as voltage sags associated with feeder faults and power flow fluctuations due to intermittent renewable generation using a benchmark network as an illustrative example.
System Stability Impact of Large-Scale and Distributed Solar Photovoltaic Generation: The Case of Ontario, Canada
(Institute of Electrical and Electronics Engineers (IEEE), 2013-02-15) Tamimi, Behnam; Canizares, Claudio; Bhattacharya, Kankar
This paper presents a comparative investigation of (PV) effect on system stability at different penetration levels. Three different scenarios with their relevant dynamic models are considered, namely, distributed units, and centralized farms with and without voltage regulation capabilities. Based on these models, the impact is examined through eigenvalue, voltage stability and transient stability analyses using real network data pertaining to Ontario and its neighboring systems. This impact is quantized in monetary terms based on the long run marginal cost of electricity production in Ontario. It is demonstrated that distributed solar PV generators are significantly more advantageous, from the stability point of view, than solar farms.