A survey on power management strategies of hybrid energy systems in microgrid

The power generation through renewable energy resources is increasing vastly, Solar energy and Wind Energy are the most abundantly available renewable energy resources. The growth of small scale distributed grid networks increasing rapidly in the modern power systems and Distributed Generation (DG) plays a predominant role. Microgrid is one among the emerging techniques in power systems. Power Management is mainly required to have control over the real and reactive power of individual DG and for smooth operation, maintaining stability and reliability. This paper presents a survey of the research works already reported focusing on power management of hybrid energy systems such as mainly solar and wind systems in microgrid. Six different approaches have been studied in detail for AC,DC and hybrid AC/DC microgrid

DC Microgrid Protection in the Presence of the Photovoltaic and Energy Storage Systems

In recent years, most of the loads and distributed generations are connected to the AC grid through the power electronic converters. Using the DC grid beside the AC grid can reduce the conversion stages and power losses. Protection of the DC grids is a challenging issue because of the new structures of DC grids and fast transients of the DC faults. This paper studies the protection of the low voltage DC (LVDC) system in the presence of the photovoltaic (PV) and energy storage systems (ESS). An LVDC system consisting of a DC microgrid is considered and Different operating modes are analyzed. DC faults behavior and protection challenges are discussed for each mode through simulations employing MATLAB software. Finally, some methods are presented to solve the protection challenges. The results show that changing the protection arrangement of the system and choosing suitable control logics for the ESS and the PV prevent the unwanted outage of the loads and provide the possibility of the microgrid operation in islanded mode

Planning and Operation of Hybrid AC-DC Microgird with High Penetration of Renewable Energy Sources

A hybrid ac/dc microgrid is a more complex but practical network that combines the advantages of an AC and a DC system. The main advantage of this network is that it connects both alternating current and direct current networks via an interlinking converter (IC) to form a unified distribution grid. The hybrid microgrid (HMG) will enable the direct integration of both alternating current (AC) and direct current (DC) distributed generators (DGs), energy storage systems (ESS), and alternating current and direct current (DC) loads into the grid. The alternating current and direct current sources, loads, and ESS are separated and connected to their respective subgrids primarily to reduce power conversion and thus increase overall system efficiency. As a result, the HMG architecture improves power quality and system reliability. Planning a hybrid microgrid entails estimating the capacities of DGs while taking technical, economic, and environmental factors into account. The hybrid ac-dc microgrid is regarded as the distribution network of the future, as it will benefit from both ac and dc microgrids. This thesis presents a general architecture of a hybrid ac-dc microgrid, which includes both planning and design. The goal of the Hybrid ac-dc microgrid planning problem is to maximise social welfare while minimising total planning costs such as investment, maintenance, and operation costs. This configuration will assist Hybrid microgrid planners in estimating planning costs while allowing them to consider any type of load ac/dc and DER type. Finally, this thesis identifies the research questions and proposes a future research plan

Robust adaptive nonlinear control of microgrid frequency and voltage in the presence of renewable energy sources

Global warming of the planet and air pollution have prompted an increased use of renewable energy sources for power generation. These new sources of clean energy are now very much in demand for setting up microgrids that provide energy independence to communities far from major urban centers. These microgrids should be able to operate either in isolated mode or to be connected to the main power grid. These requirements pose significant challenges. Indeed, in isolated mode, small and medium power grids are very sensitive to fluctuations in consumer power use as well as changes in the power produced by generators. In gridconnected mode, renewable energy sources do not contribute to the grid's stability and robustness as well as conventional generators do. Photovoltaic power plants pose some challenges when integrated with the power grid. The PV plants always focus on extracting the maximum power from the arrays. This makes the PV system unavailable for helping in regulating the grid frequency as compared to conventional generators. One of the main objectives of this research is to develop a robust adaptive nonlinear control technique which provides frequency regulation functionality to PV systems as well as voltage regulation. A small-scale power microgrid incorporating photovoltaic generators, synchronous generator and load is considered in our study. Dynamic models of the proposed microgrid were determined. The final model highlights the interactions between the sources of renewable energy and the rest of the network. A new robust adaptive nonlinear (exact input-output feedback linearization) control strategy was developed in order to meet the requirement of frequency regulation as well as voltage regulation. The new control strategy allows the PV system to have a similar response to changes in microgrid frequency as that of a conventional generator. The controller is also self-adjusting (adaptive) as well as robust in order to compensate the perturbation due to the changes in users’ power consumption, or any defects in the MG electrical network. The performance of the proposed solutions was evaluated in simulation using the Matlab/Simulink. For further verification, a small-scale laboratory experimental prototype of proposed microgrid was developed in laboratory to implement the proposed technique. This research may be regarded as an important basis for the development of microgrid power station for remote communities isolated from the main power system or large-scale power network with higher penetration of renewable energy sources