Ehsan Pashajavid

Development of a Self-Healing Strategy to Enhance the Overloading Resilience of Islanded Microgrids

This paper proposes a self-healing strategy for two neighboring islanded microgrids (MGs) that are connected together through a normally open interconnecting static switch (ISS). Each MG is expected to support the other during power deficiencies, which is facilitated by the developed self-healing agent. This agent operates based on either a centralized approach, when data communication system is available, or a decentralized approach, when data communication system does not exist or is temporarily unavailable. The necessity and possibility of the MGs interconnection or isolation is determined based on instantaneous power generation of the distributed energy resources in both MGs (in the centralized approach) and local frequency measurements at either side of ISS (in the decentralized approach). The dynamic performance of the MGs with the proposed strategies is evaluated by PSCAD simulation studies. Furthermore, the stability of the system of coupled MGs is investigated through small-signal stability and modal analyses in MATLAB.

Overload management of autonomous microgrids

Load-shedding is a mechanism to prevent overloading of the autonomous microgrids (MG). To minimize load-shedding, extra support can be provided by the embedded floating batteries in the autonomous MG. Furthermore, two islanded neighboring MGs can be interconnected to support each other. For this, the state of charge (SOC) of the floating batteries should be above the minimum SOC and extra generation capacity needs to be available in the distributed energy resources (DER) of the neighboring MG. In this paper an overload management strategy based on these two options is presented. This strategy needs to decide the connection time of the floating batteries as well as the interconnection time of the two neighboring MGs. It should also decide when the battery to be disconnected or the two interconnected MGs to be isolated. This paper focuses on a decentralized approach based on monitoring the frequencies of the MGs. The proposed strategy is validated by PSCAD/EMTDC simulations.

Interconnection of two neighboring autonomous microgrids based on small signal analysis

Load-shedding is a mechanism to prevent overloading of an islanded microgrid (MG). To minimize load-shedding, extra support can be provided by interconnecting the overloaded MG to another islanded neighboring MG to support each other. For this, extra generation capacity needs to be available in the distributed energy resources of the neighboring MG. This paper proposes a decision making criterion for interconnection of two neighboring islanded MGs based on small signal stability analysis. The closed-loop control system of an MG is expressed in statespace domain and used for the stability analysis of the individual MGs as well as the system of coupled MGs. The results of this analysis are applied as a stability criterion to allow interconnection of two islanded MGs. Additionally, if it is revealed that interconnection of MGs will cause instability, the analysis yields the proper range for the droop control coefficients which need to be updated in the DERs, before they MGs are interconnected. MATLAB-based simulation studies are provided to evaluate the developed small signal stability analysis.

Overloading conditions management in remote networks by coupling neighboring microgrids

Remote area microgrids (MG) can experience overloading or power deficiency throughout their dynamic operations due to load and generation uncertainties. Under such conditions, load-shedding is traditionally considered as the first successful mechanism to prevent system instability. To minimize load-shedding, islanded neighboring MGs can be connected to each other in remote areas to provide a self-healing capability. For this, extra generation capacity needs to be available in the distributed energy resources (DER) of one of the MGs to supply the extra demand in the other MG. In this way, the total load in the system of interconnected MGs will be shared by all the DERs within those MGs. This process falls within the network tertiary controller functions. Therefore, the tertiary controller should have a self-healing algorithm that needs to be carefully designed to initiate the command for interconnection of the MGs. The self-healing strategy needs to consider the required criteria to prevent system instability. The MGs will then be interconnected through an interconnecting static switch (ISS). This strategy also needs to decide when two interconnected MGs should be isolated. This paper focuses on the self-healing strategy, its criteria and features. The efficacy of the developed strategy in interconnecting and isolating the neighboring MGs is validated through PSCAD/EMTDC simulations.

A Multimode Supervisory Control Scheme for Coupling Remote Droop-Regulated Microgrids

This paper proposes a supervisory control scheme to facilitate coupling of remote droop-regulated microgrids (MGs) during power shortfalls. In this scheme, instead of power converters, an instantaneous static switch is incorporated for the interconnection. Therefore a supervisory controller is essential to cope with the associated challenges, which are: 1) the level of supporting power provided by the neighboring MG and 2) isolation procedure of the coupled MGs (CMG) when the power deficiency condition is removed. Droop coefficients of distributed generators of the overloaded MG are dynamically updated by the controller according to the three operating modes defined to address the aforementioned challenges. The transit criteria, as well as the controlling signals, are accurately formulated based only on the local measurements to decrease the dependency on the communication systems. This enhances the reliability level of the coupled system. Effectiveness of the proposed strategy is validated through the results obtained from PSCAD/EMTDC simulations. Also, small-signal stability of the CMG operated by the proposed controller is examined using a developed model in MATLAB.

Development of a self-healing strategy to enhance the overloading resilience of islanded microgrids

Summary form only given: This paper proposes a self-healing strategy for two neighboring islanded microgrids (MGs) that are connected together through a normally open interconnecting static switch (ISS). Each MG is expected to support the other during power deficiencies, which is facilitated by the developed self-healing agent. This agent operates based on either a centralized approach, when data communication system is available, or a decentralized approach, when data communication system does not exist or is temporarily unavailable. The necessity and possibility of the MGs interconnection or isolation is determined based on instantaneous power generation of the distributed energy resources in both MGs (in the centralized approach) and local frequency measurements at either side of ISS (in the decentralized approach). The dynamic performance of the MGs with the proposed strategies is evaluated by PSCAD simulation studies. Furthermore, the stability of the system of coupled MGs is investigated through small-signal stability and modal analyses in MATLAB.

A decentralized strategy to remedy the power deficiency in remote area microgrids

Power deficiency management is an important factor in the operation of remote microgrids (MG). Load-shedding is traditionally considered as the main mechanism to manage the network under power deficiency conditions. To minimize load-shedding, islanded neighboring MGs can be connected to each other in remote areas to provide a self-healing capability. For this, extra generation capacity needs to be available in the distributed energy resources (DER) of one of the MGs to supply the extra demand in the other MG. In this way, the total load in the system of interconnected MGs will be shared by all the DERs within those MGs. This paper presents a strategy which aims to interconnect two neighboring microgrids in remote areas to minimize the necessity of load-shedding. This strategy also needs to decide when two interconnected MGs should be isolated. This paper focuses on the self-healing strategy, its criteria and features. The presented algorithm in this paper does not need any data communication system for its operation. The performance of the developed technique is validated by PSCAD/EMTDC simulations.

Sensitivity of Electric Vehicles Demand Profile to the Batteries Departure State-of-Charge

This paper focuses on the impacts of considering batteries state-of-charge (SOC) at the departure time on the demand modeling of plug-in electric vehicles (PEVs). Almost all of the previous researches assumed that PEVs batteries at the departure time are fully charged; however, this assumption is highly questionable because it is probable for a PEV to not be charged every day. The probability density function of a vehicle owners willingness to fulfill the daily charging is extracted according to the initial SOC of a PEV and the estimated distance of its next trip. Afterwards, with the aim of considering the uncertainties with the associated random variables as well as properly adjusting vehicles SOC at the departure time, a Monte Carlo based multi loop (MCML) algorithm is developed which is composed of two loops, namely the inner loop and the outer loop. In order to implement the proposed stochastic method, a case study has been conducted employing the gathered datasets related to the ICE vehicles in Tehran. Appropriate Students t copula functions have been fitted to the datasets in order to take into account the correlation structure among them as well as to generate the required random samples.

A fully decentralized approach for mitigating destructive disturbances in isolating process of remote coupled microgrids

Coupling remote microgrids (MGs) is a promising technique to handle power deficiency in such systems. However, once the shortfall is removed, the coupled MGs (CMG) should isolate to carry on their operation autonomously. Due to the non-zero power still flowing through the tie-line, however, considerable voltage spikes may be imposed on the interconnecting static switch (ISS) during the isolation that may damage the device. This paper proposes a practical decentralized approach to efficiently alleviate the mentioned transients, facilitating a successful MG isolation procedure. Two auxiliary controllable loads (ACL) are to be considered at two sides of the ISS. When the necessity of applying the isolation action is detected, the ISS controller commands the ACL on the supporting MG side to connect. A droop-based scheme is formulated to derive the load should be demanded by the ACL such that the power passing through the ISS drops to zero, preventing any spikes across it at the opening moment. Once the isolation action is accomplished, the controller disconnects the ACL. Efficiency of the proposed algorithm is validated through various cases simulated using PSCAD/EMTDC.

Frequency Support for Remote Microgrid Systems With Intermittent Distributed Energy Resources—A Two-Level Hierarchical Strategy

A two-level decentralized hierarchical control strategy is developed to cope with active power deficiencies in remote microgrid (MG) systems containing intermittent energy resources. The primary level consists of a multilayer droop-based scheme designed to dispatch the required loads to be shed amongst controllable loads (CLs). The dispatch is proportionally fulfilled through the appropriate assignment of each layer of the droop curves to its corresponding priority type of the CLs. If the primary level is unable to handle the shortfall, the secondary level of the scheme is invoked by coupling of the overloaded MG with a neighboring one. Appropriate criteria are accurately formulated to assure desirable interconnections and proper isolations of the MGs. By detecting an overloading condition, the primary level attempts to raise the frequency by managing the CLs, whereas the secondary level assesses the possibility of forming a system of coupled MGs (CMG). Depending on the level of support provided by the neighboring MG, the shed loads can be restored completely or partially once the system of CMG is formed. Implementation of the two levels is coordinated such that the power shortfall can be relieved with very low bandwidth communication systems. Validity of the proposed strategy is demonstrated through several PSCAD/EMTDC studies.