dr. S. Izadkhast

1. Design of Plug-In Electric Vehicle's Frequency-Droop Controller for Primary Frequency Control and Performance Assessment
   Izadkhast, S.; Garcia-Gonzalez, P.; Frías, P.; Bauer, P.;
   IEEE Transactions on Power Systems,
   Volume 32, Issue 6, pp. 4241--4254, November 2017. DOI: 10.1109/TPWRS.2017.2661241
   
   Abstract: ...

   This paper describes a novel strategy to design the frequency-droop controller of plug in electric vehicles (PEVs) for primary frequency control (PFC). To be able to properly compare the frequency response of control system with and without PEVs, the design is done to guarantee the same stability margin for both systems in the worst case scenario. To identify the worst case, sensitivity analyses are conducted on a large set of system parameters performing eigenvalue analysis and bode plots. Three main contributions are included in this work: 1) we demonstrate that PEVs using the well-design droop controller significantly improve the PFC response while successfully preserving the frequency stability, 2) since the fast response of PEVs may cause to mask the governor-turbine response in conventional units, a novel control scheme is developed to replace some portion of PEV's reserve after a certain time by the reserve of conventional units during PFC, and 3) a method is proposed to evaluate the positive economic impact of PEV's participation in PFC. For the latter, the system PFC cost savings mainly through the avoidance of under frequency load shedding by PEVs are calculated. A large-scale power system and an islanded network are evaluated and compared through dynamic simulations, which illustrate the validity and effectiveness of the proposed methodologies.

2. Aggregation of plug-in electric vehicles in power systems for primary frequency control
   Izadkhast, Seyedmahdi;
   PhD thesis, Delft University of Technology, Comillas University, KTH Royal Institute, Madrid, Spain, 2017.
   
   Abstract: ...

   The number of plug-in electric vehicles (PEVs) is likely to increase in the near future and these vehicles will probably be connected to the electric grid most of the day time. PEVs are interesting options to provide a wide variety of services such as primary frequency control (PFC), because they are able to quickly control their active power using electronic power converters. However, to evaluate the impact of PEVs on PFC, one should either carry out complex and time consuming simulation involving a large number of PEVs or formulate and develop aggregate models which could efficiently reduce simulation complexity and time while maintaining accuracy.This thesis proposes aggregate models of PEVs for PFC. The final aggregate model has been developed gradually through the following steps. First of all, an aggregate model of PEVs for the PFC has been developed where various technical characteristics of PEVs such as operating modes (i.e., idle, disconnected, and charging) and PEV’s state of charge have been formulated and incorporated. Secondly, some technical characteristics of distribution networks have been added to the previous aggregate model of PEVs for the PFC. For this purpose, the power consumed in the network during PFC as well as the maximum allowed current of the lines and transformers have been taken into account. Thirdly, the frequency stability margins of power systems including PEVs have been evaluated and a strategy to design the frequency-droop controller of PEVs for PFC has been described. The controller designed guaranties similar stability margins, in the worst case scenario, to those of the system without PEVs. Finally, a method to evaluate the positive economic impact of PEVs participation in PFC has been proposed
   
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3. An Aggregate Model of Plug-in Electric Vehicles Including Distribution Network Characteristics for Primary Frequency Control
   Izadkhast, S.; Garcia-Gonzalez, P.; Frìas, P.; Ramìrez-Elizondo, L.; Bauer, P.;
   IEEE Transactions on Power Systems,
   Volume 31, Issue 4, pp. 2987--2998, July 2016. DOI: 10.1109/TPWRS.2015.2471091
   
   Abstract: ...

   In the future, the number of plug-in electric vehicles (PEVs) that will participate in the primary frequency control (PFC) is likely to increase. In our previous research, the computational complexity of the PFC problem for a large number of PEVs was reduced using aggregate models of PEVs. However, in the literature on the PFC, the distribution network characteristics have not been included in the aggregate models of PEVs for the PFC, despite the fact that PEVs will be dispersedly connected to the distribution network. This paper proposes an aggregate model of PEVs for the PFC that further incorporates distribution network characteristics, i.e., the distribution network power loss (DNPL) and the maximum allowed current (MAC) of the lines and transformers. The DNPL variation is formulated according to the line and transformer impedance, spatial distribution of PEVs and loads, and active power variation of PEVs. Then, DNPL variation together with the MAC of the lines and transformers are incorporated in the proposed model of PEVs. Finally, the simulation results show an excellent agreement of 98\% between the detailed model and the proposed aggregate model of PEVs.

4. An aggregate model of plug-in electric vehicles including distribution network characteristics for primary frequency control
   Izadkhast, S.; Garcia-Gonzalez, P.; Frías, P.; Ramírez-Elizondo, L.; Bauer, P.;
   In 2016 IEEE Power and Energy Society General Meeting (PESGM),
   pp. 1--1, July 2016. DOI: 10.1109/PESGM.2016.7741118
   
   Abstract: ...

   Summary form only given. In the future, the number of plug-in electric vehicles (PEVs) that will participate in the primary frequency control (PFC) is likely to increase. In our previous research, the computational complexity of the PFC problem for a large number of PEVs was reduced using aggregate models of PEVs. However, in the literature on the PFC, the distribution network characteristics have not been included in the aggregate models of PEVs for the PFC, despite the fact that PEVs will be dispersedly connected to the distribution network. This paper proposes an aggregate model of PEVs for the PFC that further incorporates distribution network characteristics, i.e., the distribution network power loss (DNPL) and the maximum allowed current (MAC) of the lines and transformers. The DNPL variation is formulated according to the line and transformer impedance, spatial distribution of PEVs and loads, and active power variation of PEVs. Then, DNPL variation together with the MAC of the lines and transformers are incorporated in the proposed model of PEVs. Finally, the simulation results show an excellent agreement of 98\% between the detailed model and the proposed aggregate model of PEVs.

5. An aggregate model of plug-in electric vehicles for primary frequency control
   Izadkhast, S.; Garcia-Gonzalez, P.; Frías, P.;
   In 2016 IEEE Power and Energy Society General Meeting (PESGM),
   pp. 1--1, July 2016. DOI: 10.1109/PESGM.2016.7741672
   
   Abstract: ...

   Summary form only given. The penetration level of plug-in electric vehicles (PEVs) has the potential to be notably increased in the near future, and as a consequence, power systems face new challenges and opportunities. In particular, PEVs are able to provide different types of power system ancillary services. The capability of storing energy and the instantaneous active power control of the fast-switching converters of PEVs are two attractive features that enable PEVs to provide various ancillary services, e.g., primary frequency control (PFC). However, concurrently, PEVs are obliged to be operated and controlled within limits, which curbs the grid support from PEVs. This paper proposes a new model for PEV using a participation factor, which facilitates the incorporation of several PEV fleets characteristics such as minimum desired state of charge (SOC) of the PEV owners, drive train power limitations, constant current and constant voltage charging modes of PEVs. In order to reduce computational complexity, an aggregate model of PEVs is provided using statistical data. In the end, the performance of PEVs for the provision of PFC is evaluated in a power system. Results show that PEV fleets can successfully improve frequency response, once all the operating constraints are respected.

6. An Aggregate Model of Plug-In Electric Vehicles for Primary Frequency Control
   Izadkhast, S.; Garcia-Gonzalez, P.; Frías, P.;
   IEEE Transactions on Power Systems,
   Volume 30, Issue 3, pp. 1475--1482, May 2015. DOI: 10.1109/TPWRS.2014.2337373
   
   Abstract: ...

   The penetration level of plug-in electric vehicles (PEVs) has the potential to be notably increased in the near future, and as a consequence, power systems face new challenges and opportunities. In particular, PEVs are able to provide different types of power system ancillary services. The capability of storing energy and the instantaneous active power control of the fast-switching converters of PEVs are two attractive features that enable PEVs to provide various ancillary services, e.g., primary frequency control (PFC). However, concurrently, PEVs are obliged to be operated and controlled within limits, which curbs the grid support from PEVs. This paper proposes a new model for PEV using a participation factor, which facilitates the incorporation of several PEV fleets characteristics such as minimum desired state of charge (SOC) of the PEV owners, drive train power limitations, constant current and constant voltage charging modes of PEVs. In order to reduce computational complexity, an aggregate model of PEVs is provided using statistical data. In the end, the performance of PEVs for the provision of PFC is evaluated in a power system. Results show that PEV fleets can successfully improve frequency response, once all the operating constraints are respected.

7. Evaluating the determinants of the scalability and replicability of islanded operation in medium voltage networks with cogeneration
   Rodriguez-Calvo, A.; Izadkhast, S.; Cossent, R.; Frías, P.;
   In 2015 International Symposium on Smart Electric Distribution Systems and Technologies (EDST),
   pp. 80--87, September 2015. DOI: 10.1109/SEDST.2015.7315187
   
   Abstract: ...

   The development of smart grid solution concepts, such as islanding, make it possible to improve the security of supply in networks. The results experimented in real-life test systems must be extrapolated to wider areas and in other locations, which is not straightforward. The scalability and replicability analysis (SRA) aims to identify the relevant factors that affect smart grid implementations and understand the effects of their variation on the results achieved by smart grid solutions. This paper presents the SRA of an islanding use case in a medium voltage network using cogeneration. Furthermore, the results obtained have been used to obtain a set of scalability and replicability rules for islanding use cases that can be applied in other cases.

8. Aggregation of plug-in electric vehicles in distribution networks for primary frequency control
   Izadkhast, S.; Garcia-Gonzalez, P.; Frías, P.; Ramirez-Elizondo, L.; Bauer, P.;
   In 2014 IEEE International Electric Vehicle Conference (IEVC),
   pp. 1--7, December 2014. DOI: 10.1109/IEVC.2014.7056225
   
   Abstract: ...

   Plug-in electric vehicles (PEVs) have great potential in the near future to be connected in a large number to the power systems. This will lead to influence the overall dynamic behavior of power systems, specifically when PEVs participate in the primary frequency control (PFC). Modeling a large number of PEVs for PFC can be a complex and time consuming task. In order to reduce computational complexity, in [1], we proposed that a large number of PEVs was represented by an aggregate model which was connected to the transmission system. In [1], in the aggregate model of PEVs for the frequency stability analysis, the distribution network has been neglected, although in reality PEVs will be dispersedly connected to the distribution network. This paper proposes an aggregate model of PEVs that incorporates distribution network characteristics, i.e. the power losses. Thus, the proposed aggregate model represents the active power response of PEVs taking into consideration distribution network power losses (DNPL). To achieve this goal, the DNPL increment, which is caused by the participation of PEVs in the PFC, is mathematically formulated with respect to the active power variation of PEVs following a disturbance. Then, the proposed aggregate model of PEVs is obtained according to the PEV fleet behavior and also the calculated power loss variation. In order to compare the detailed model and the proposed aggregate model, the simulations are carried out in Matlab / Simulink. Finally, the simulation results show high level of correspondence between the detailed and the proposed aggregate model of PEVs following a disturbance in the power system.

9. A framework for the energy aggregator model
   Moreno, R.; Chamorro, H. R.; Izadkhast, S. M.;
   In 2013 Workshop on Power Electronics and Power Quality Applications (PEPQA),
   pp. 1--5, July 2013. DOI: 10.1109/PEPQA.2013.6614965
   
   Abstract: ...

   The new resources available in power system require a new agent to manage these resources in the most efficient way. Resources provided by the supply side or the demand side can be managed together in order to provide some services to the grid. New resources such as massive electric vehicle and distributed generation have been being gradually integrated to the grid and for the next years the integration tendency will follow increasing. These resources require a different approach to be managed adequately. The integration of intermittent resources into the grid is a challenging area but these issues can be addressed by an aggregator agent. On the other hand, the demand of power required by electric vehicle integration can impact the load curve of different distribution system far from its capability. An aggregator agent also can be useful to manage adequately the demand required by Electric Vehicles. This paper proposes an energy aggregator model (EAM) to manage power transactions between the grid and the demand side resources.

10. Modeling and control of a grid-connected BDFM under unbalanced grid voltage conditions
    Sotoodeh, P.; Izadkhast, Seyed Mahdi; Khosravi, H.; Oraee, H.;
    In 2011 IEEE International Electric Machines Drives Conference (IEMDC),
    pp. 1647--1651, May 2011. DOI: 10.1109/IEMDC.2011.5994609
    
    Abstract: ...

    This paper presents a mathematical model for Brushless Doubly-Fed Machine (BDFM) based on Stator Flux Orientation (SFO) in positive and negative reference frames under unbalanced grid voltage conditions. A negative controller is designed to eliminate the effects of unbalanced conditions on electrical torque. The model and controller performance during unbalanced conditions is validated by time domain simulation in MATLAB/Simulink.

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