PEER-TO-PEER POWER SHARING IN DC MICROGRIDS FOR RURAL ELECTRIFICATION

Remote rural regions without electricity access suffer from energy poverty and reduced opportunities for the population. Microgrid architectures with optimal planning, design, and operation strategies are essential to meet rural inhabitants’ energy demands. DC microgrids based on photovoltaic panels and batteries are used for remote rural electrification. Centralized islanded systems have shortcomings, i.e., high distribution losses, less efficiency, and are comparatively more expensive than distributed microgrids. The distributed systems comprise independent household prosumers that maywork independently or integrated.The first concept presented in this thesis is a detailed distribution loss analysis of both centralized and distributed microgrid architectures with dynamic load and generation profiles. The distribution loss modeling is extended to low-voltage, low-power islanded DC microgrids. A detailed network loss analysis of four different microgrid architectures is performed using modified Newton-Raphson power flow for DC systems. These architectures include 1) Centralized generation centralized storage (CGCS), 2) Centralized generation distributed storage (CGDS), 3) Distributed generation centralized storage (DGCS), and 4) Distributed generation distributed storage (DGDS), which are implemented with both radial and ring interconnection schemes using time-varying load demand and dynamic PV generation. A comparative distribution loss analysis with various conductor sizes and voltage levels shows that the distributed ring architecture significantly advantages based on low distribution losses, high efficiency, and low voltage drop. It offers an additional feature of scalability and lower capital cost. Secondly, a detailed distribution and conversion loss modeling and analysis is performed for centralized and distributed microgrid architectures using the bus injection method and modified Newton-Raphson power flow method. A comparative power system and power electronic loss analysis for both architectures show that distributed architectures have higher efficiency and lower losses than centralized. Third, the optimal power dispatch and power-sharing among spatially distributed nanogrids are performed to minimize distribution losses and maximize power electronic conversion efficiency in a typical islanded DC microgrid (IDCMG) for rural electrification. A branch flow model is proposed for modeling the power system with DC-DC converters. The optimal power flow is performed by relaxing the original non-convex constraints using second-order conic programming and is implemented on the modified IEEE-14 bus system. This generic framework can be used for optimal energy management in islanded microgrids using the regional solar irradiance information, climate situations, and energy requirements.The key contributions of this dissertation are: i) A comprehensive distribution loss analysis of centralized and distributed microgrid architectures, ii) Developing a mathematical framework and modeling of distribution and power electronic losses,and iii) Optimal peer-to-peer power sharing in DC microgrids for rural electrification

Assessing the Potential of Plug-in Electric Vehicles in Active Distribution Networks

A multi-objective optimization algorithm is proposed in this paper to increase the penetration level of renewable energy sources (RESs) in distribution networks by intelligent management of plug-in electric vehicle (PEV) storage. The proposed algorithm is defined to manage the reverse power flow (PF) from the distribution network to the upstream electrical system. Furthermore, a charging algorithm is proposed within the proposed optimization in order to assure PEV owner's quality of service (QoS). The method uses genetic algorithm (GA) to increase photovoltaic (PV) penetration without jeopardizing PEV owners' (QoS) and grid operating limits, such as voltage level of the grid buses. The method is applied to a part of the Danish low voltage (LV) grid to evaluate its effectiveness and capabilities. Different scenarios have been defined and tested using the proposed method. Simulation results demonstrate the capability of the algorithm in increasing solar power penetration in the grid up to 50%, depending on the PEV penetration level and the freedom of the system operator in managing the available PEV storage

A mixed-integer convex approximation for optimal load redistribution in bipolar DC networks with multiple constant power terminals

This paper proposes a mixed-integer convex model for optimal load-balancing in bipolar DC networks while considering multiple constant power terminals. The proposed convex model combines the Branch and Cut method with interior point optimization to solve the problem of optimal load balancing in bipolar DC networks. Additionally, the proposed convex model guarantees that global optimum of the problem is found, which ensures minimal power losses in the bipolar DC distribution grid branches, as the total monopolar load consumption has been balanced at the substation's terminals. In addition, an optimal load balancing improves the voltage profiles due to current redistribution between the positive and negative poles. Numerical results in the 21- and 85-bus test feeders and a comparison with three metaheuristic techniques show the effectiveness of the proposed convex model in reducing the total grid imbalance while minimizing the power losses and improving the voltage profiles

Hierarchical-power-flow-based energy management for alternative/direct current hybrid microgrids

Modern microgrids are systems comprising both Alternative Current (AC) and Direct Current (DC) subgrids, integrated with Distributed Generations (DGs), storage systems, and Electric Vehicles (EVs) parking facilities. Achieving stable and reliable load flow control amidst varying load, generation, and charging/discharging strategies requires a hierarchical control scheme. This paper proposes an hourly power flow (PF) analysis within an Energy Management System (EMS) for AC/DC Hybrid Microgrids interconnected via an Interlinking Converter (IC) in both grid-connected and islanded modes. The framework operates within a two-level hierarchically controlled platform. Tertiary control at the top level optimizes DGs' reference power for generation and consumption, minimizing power purchase costs and load shedding in grid-connected and islanded modes, respectively. DG converters employ current control mode to share their power references as the primary controller. While no secondary controller is adopted in this scheme, the Battery Energy Storage System (BESS) in islanded mode utilizes P/Q droop control to maintain voltage and frequency in the AC subsystem. Power sharing between AC and DC subgrids through IC is determined by the difference between AC grid frequency and DC link voltage. Integration of controlled converters’ buses into PF equations enables solving the unified system using the traditional Newton-Raphson (NR) method. A segment of a real distribution grid planned for installation in Italy under the HYPERRIDE project serves as a case study. Comparison with MATLAB/Simulink results confirms the effectiveness, precision, and convergence speed of the proposed model and control schemes, demonstrating efficient load distribution and voltage/frequency restoration in islanded mode

Ancillary services analysis of an offshore wind farm cluster-technical integration steps of a simulation tool

In this publication, the authors present methodology and example results for the analysis of ancillary services of an offshore wind farm cluster and its electrical power system. Thereby the operation tool Wind Cluster Management System (WCMS) is used as simulation tool to evaluate certain planning scenarios. Emphasis is made on two topics: 1) the integration of high voltage direct current (HVDC) technology to the WCMS, 2) the ancillary service analysis. As examples, voltage source converter based HVDC (VSC-HVDC) and the provision of reserve respectively balancing power are discussed in detail. The analyzed study case considers the Kriegers Flak area while the associated power system connects wind farms to Sweden, Denmark and Germany.EC/FP7/ENERGY-2011-1/ 28279

Parameter Identification of Micro-Grid Control System

Micro-grid provides an effective means of integrating distributed energy resource (DER) units into the power systems. A micro-grid is defined as an independent low- or medium-voltage distribution network comprising various DER units, power-electronic interfaces, controllable loads, and monitoring and protection devices. Following the development of the renewable energy, micro-grid has attracted much attention. This thesis emphasizes on the parameter identification of the control system of the micro-grid. The control system plays an important role in the stable operation of the micro-grid. The micro-grid has two operation modes, which are grid-connected operation mode and islanded operation mode. The transition between two operation modes of the micro-grid often occurs according to the condition of the entire grid. In order to make this process smooth, the control system is crucial, and the parameters of the control system is critical to the disturbance suppression during the process of transition. In the thesis, a method combining least square method with Newton-Raphson algorithm is proposed. In order to prove the utility of the method, the parameter identification of a typical control system and its several separated elements are simulated in MATLAB. This method can identify multiple parameters at the same time and have fast convergence

Storage coordination of photovoltaic injection for loss reduction purpose

Tese de mestrado integrado. Engenharia Electrotécnica e de Computadores (Energia). Universidade do Porto. Faculdade de Engenharia. 201

Optimal allocation of distributed generation for power loss reduction and voltage profile improvement

Distributed generation (DG) integration in a distribution system has increased to high penetration levels. There is a need to improve technical benefits of DG integration by optimal allocation in a power system network. These benefits include electrical power losses reduction and voltage profile improvement. Optimal DG location and sizing in a power system distribution network with the aim of reducing system power losses and improving the voltage profile still remain a major problem. Though much research has been done on optimal DG location and sizing in a power system distribution network with the aim of reducing system power losses and improving the voltage profile, most of the existing works in the literature use several techniques such as computation, artificial intelligence and an analytical approach, but they still suffer from several drawbacks. As a result, much can still be done in coming up with new algorithms to improve the already existing ones so as to address this important issue more efficiently and effectively. The majority of the proposed algorithms emphasize real power losses only in their formulations. They ignore the reactive power losses which are the key to the operation of the power systems. Hence, there is an urgent need for an approach that will incorporate reactive power and voltage profile in the optimization process, such that the effect of high power losses and poor voltage profile can be mitigated. This research used Genetic Algorithm and Improved Particle Swarm Optimization (GA-IPSO) for optimal placement and sizing of DG for power loss reduction and improvement of voltage profile. GA-IPSO is used to optimize DG location and size while considering both real and reactive power losses. The real and reactive power as well as power loss sensitivity factors were utilized in identifying the candidate buses for DG allocation. The GA-IPSO algorithm was programmed in Matlab. This algorithm reduces the search space for the search process, increases its rate of convergence and also eliminates the possibility of being trapped in local minima. Also, the new approach will help in reducing power loss and improve the voltage profile via placement and sizing