Laboratorial Microgrid Emulation Based on Distributed Control Architecture

Power systems worldwide are complex and challenging environments. The increasing necessity for an adequate integration of renewable energy sources is resulting in a rising complexity in power systems operation. Multiagent based simulation platforms have proven to be a good option to study the several issues related to these systems. This paper presents an emulation of a laboratorial microgrid based on distributed control architecture. The proposed model contains real consumption and generation resources, including consumer load, photovoltaic, and wind turbine emulator. Also, a web-based graphical interface has been designed in order to monitor and control the microgrid. In this system, there are four main agents, which are connected by means of a communication network capable of sharing and exchanging information to achieve the overall system’s goal. The performance of the distributed architecture is demonstrated in order to observe the applicability of the agents and their collaboration abilities. The results of the paper show in practice that how a distributed control based microgrid manages its resources, and how it reacts if there is a fault or no activity on them.This work has received funding from the European Union's Horizon 2020 research and innovation program under the Marie Sklodowska-Curie grant agreement No 641794 (project DREAMGO) and from FEDER Funds through COMPETE program and from National Funds through FCT, under the project UID/EEA/00760/2013.info:eu-repo/semantics/publishedVersio

ENERGY MANAGEMENT AND HARMONIC MITIGATION OF HYBRID RENEWABLE ENERGY MICROGRID USING COORDINATED CONTROL OF MULTI-AGENT SYSTEM

In this paper, a novel energy management method that is based on a Multi-Agent System (MAS) is presented for hybrid Distributed Energy Sources (DES) in a microgrid. These DESs include Photovoltaic (PV), wind energy systems, and Fuel Cell (FC) in the Microgrid (MG). The MG is responsible for supplying both active and reactive powers, allowing it to serve variable linear and non-linear loads. The MAS that has been proposed and is based on a decentralized control structure offers control not only for the energy management of the Distributed Generation (DG) but also for the management of power flow between the MG and the power grid that is connected to the MG. This control is offered by the MAS. The main objective of the control strategy is to manage the amount of energy that is transferred between the power grid and the MG concerning the supply conditions of the required internal energy via DES, which will ultimately result in a reduction in the dependence on the MG on the grid. For current harmonic compensation, a Static Compensator (STATCOM) with a Fuzzy Logic (FL) based Instantaneous Reactive Power control scheme is used. On the other hand, a discrete controller is utilized to manage the energy of the MG. The findings of the simulation and the experiments demonstrated that the implementation of the suggested Energy Management System (EMS) has good performance as a novel energy management solution for a hybrid distributed power generating system and harmonic compensation

Design and Implementation of a True Decentralized Autonomous Control Architecture for Microgrids

Microgrids can serve as an integral part of the future power distribution systems. Most microgrids are currently managed by centralized controllers. There are two major concerns associated with the centralized controllers. One is that the single controller can become performance and reliability bottleneck for the entire system and its failure can bring the entire system down. The second concern is the communication delays that can degrade the system performance. As a solution, a true decentralized control architecture for microgrids is developed and presented. Distributing the control functions to local agents decreases the possibility of network congestion, and leads to the mitigation of long distance transmission of critical commands. Decentralization will also enhance the reliability of the system since the single point of failure is eliminated. In the proposed architecture, primary and secondary microgrid controls layers are combined into one physical layer. Tertiary control is performed by the controller located at the grid point of connection. Each decentralized controller is responsible of multicasting its status and local measurements, creating a general awareness of the microgrid status among all decentralized controllers. The proof-of concept implementation provides a practical evidence of the successful mitigation of the drawback of control command transmission over the network. A Failure Management Unit comprises failure detection mechanisms and a recovery algorithm is proposed and applied to a microgrid case study. Coordination between controllers during the recovery period requires low-bandwidth communications, which has no significant overhead on the communication infrastructure. The proof-of-concept of the true decentralization of microgrid control architecture is implemented using Hardware-in-the-Loop platform. The test results show a robust detection and recovery outcome during a system failure. System test results show the robustness of the proposed architecture for microgrid energy management and control scenarios

Real-time modelling and simulation of distribution system protection with and without renewable distribution generation.

Master of Science in Electrical Engineering. University of KwaZulu-Natal. Durban, 2017.The conventional radial power distribution systems were initially not designed to accommodate distribution generation (DG). As DG penetration is being considered by many distribution utilities, there is a rising need to address many incompatibility issues that put a big emphasis on the need to review and implement suitable protection schemes. For a significant greenhouse gas reduction using photovoltaic systems, numerous generators ought to be embedded in the distribution system. For an effective penetration of PV systems on a large-scale into the current distribution network, considerable work to investigate the nature of incompatibility problems has been done and research is being carried out to develop successful integration strategies. The main objectives of the thesis are; to model and simulate a distribution system protection scheme, to study radial networks’ protection system challenges after embedding distributed generation sources, investigation on the impacts of high PV penetrations on protection systems of distribution networks and lastly make modification recommendations and essential review process of existing protection equipment settings. To accomplish the above-mentioned objectives, a radial distribution network is modelled, simulated and protection settings validated. The PV generation system is designed and added to specific distribution feeders and steady steady-state results obtained. The results show that addition of DGs cause the system to lose its radial power flow. There is an increase in fault contribution hence causing maloperation such as protection coordination mismatch. An overall protection scheme is then proposed based on the addition of DG’s and an efficient adaptive protection system for the distribution networks with a considerable penetration of dispersed generations implemented. The impact study is performed which is compared with the existing protection scheme and necessary modifications done. The entire analysis is simulated on a real-time digital simulator (RTDS) and results displayed in a MATLAB environment. For the islanded mode, relaying considerations are provided and implementation of anti-islanding techniques achieved

Coordinated Control of Distributed Energy Resources in Islanded Microgrids

As the penetration of the distributed energy resources (DERs) in the power grid increases,new challenges are revealed, including: stability issues, frequency fluctuations, voltage control, protection system coordination, etc. A systematic approach for dealing with those issues is to view the DERs and associated loads as a subsystem or a microgrid (MG). MGs can operate either in the grid connected or islanded modes. As opposed to the grid connected mode, the voltage and frequency regulation and load/generation balancing during islanded mode is solely dependent on the local generation units. Therefore, stable and reliable operation of islanded MGs requires a real time coordinated control scheme. Conventionally, such coordination is achieved by means of the active power-frequency and reactive powervoltage droop control schemes. The conventional droop method, which is based on P-f droop concept in power systems, lacks compatibility with the resistive nature of networks as well as the low inertia of electronically interfaced DER units in MGs. As a result, it features a slow dynamic response but also a low power quality due to frequency and voltage fluctuations. This PhD research proposes a novel droop concept based on the global positioning system (GPS) and voltage-current (V-I) droop characteristics for coordination of inverter-based DER units in islanded MGs. The concept of V-I droop control is introduced in Chapter 2. In this control approach, each DER is equipped with a GPS receiver, which produces a pulse at frequency of 1Hz (1PPS). Since all GPS receivers are locked to atomic clocks of the GPS satellites, the 1PPS signal can be utilized to synchronize the time reference of the DER units. Using the common time reference and fixing the frequency at the nominal value, all of the units can share a common synchronous rotating reference frame (SRRF). Furthermore, proportional load sharing is achieved by drooping the d and q axis components of the reference voltage with respect to the d and q axis components of current, respectively. The proposed scheme not only circumvents the issue of frequency fluctuations but also is in accordance with the fast dynamics of inverter-based DER units and resistive nature of the networks in islanded MGs. The V-I droop scheme, in its basic form, relies on availability of GPS signals at each of the DER units. With the intention of improving the MG robustness with respect to GPS signal failure, a new control strategy based on V-I droop concept is presented Chapter 3. In this method, an adaptive reactive power-frequency droop scheme is used as a backup for the V-I droop controller to ensure synchronization in case of a GPS signal failure. Droop control schemes in general, and the proposed V-I droop strategy in particular are characterized by non-ideal sharing of current among the DER units due to the variations of voltage along the MGs. In order to improve the sharing accuracy of the V-I droop scheme iv while regulating the average voltage at the nominal value, a new distributed secondary control method based on consensus protocol is proposed in Chapter 4. In this method, the daxis droop characteristics is altered so as to regulate the average microgrid voltage to the rated value but also guarantee proper sharing of active power among the DERs. Additionally, the q-axis component of voltage is adjusted to perform proper sharing of current. Generally, DERs might be supplied from different energy sources, including renewables and storage systems. The intermittency of renewable energy resources on one hand and the limited capacity of the energy storage systems on the other hand, necessitate modification of droop characteristics based on an energy management plan. In Chapter 5, a novel distributed secondary control strategy is introduced for power management of integrated photovoltaicbattery DER units in islanded MGs. The distributed secondary controllers are coordinated based on a leader-follower framework, where the leader restores the MG voltage to the rated value and the followers pursue energy management. Unbalanced and nonlinear loads, which are quite common in MGs, adversely affect the power quality and sharing accuracy. In order to mitigate those issues, two new solutions are proposed in this thesis. In the first approach (Chapter 6), a new supplementary droop control scheme is added to the V-I droop controller to reduce the voltage unbalance while preventing current and power overload under unbalanced loading conditions. In the second approach (Chapter 7), a hierarchical control scheme, consisting of primary (modified V-I droop) and distributed secondary control levels is introduced to mitigate harmonic distortions and prevent overcurrent stresses under nonlinear and unbalanced loading conditions. Finally, the conclusions and possible future work are addressed in Chapter 8