Cost mitigation strategy for microgrid using an advanced energy management system with an intelligent controller

Context: This paper proposes an energy management system (EMS) for battery energy storage systems (BESS) to reduce operating costs in AC microgrids (MGs) operating in grid-connected (GON) and islanded (GOFF) mode, considering energy purchase, conventional generation, and maintenance costs while accounting for all the operational constraints of the system and its components. Method: A master-slave methodology based on particle swarm optimization (PSO) and an hourly power flow based on the successive approximations method (SAM) is used as a smart BESS operation strategy. This proposal is validated in a 33-bus AC-MG operating in GON and GOFF modes, in comparison with two methods utilizing the vortex search algorithm (VSA) and conitnuos version of the Chu & Beasley genetic algorithm (CBGA) and the same power flow. Results: The PSO-based EMS achieved the lowest costs i.e., 6897.59 USD/day (GON) and 17 527.42 USD/day (GOFF), with cost reductions of 1.45 and 0.13 %, and low standard deviation values (0.067 and 0.014 %), which confirms its efficiency, robustness, and constraint compliance. Conclusions: The EMS based on PSO/SAM delivers superior solution quality and processing times in both modes of operation. In GON mode, it reduces the mean costs by 0.0287%compared to the VSA and 0.2252%vs. the CBGA, whereas, in GOFF mode, the reductions are 0.0191 and 0.0355 %, respectively. These results reflect a more effective cost reduction than exact methods, which constitutes this paper’s main contribution.

Microgrids are energy systems that can work independently from the main grid in a stable and self-sustainable way. They rely on energy management systems to schedule optimally the distributed energy resources. Conventionally, the main research in this field is focused on scheduling problems applicable for specific case studies rather than in generic architectures that can deal with the uncertainties of the renewable energy sources. This paper contributes a design and experimental validation of an adaptable energy management system implemented in an online scheme, as well as an evaluation framework to quantitatively assess the enhancement attained by different online energy management strategies. The proposed architecture allows the interaction of measurement, forecasting and optimization modules, in which a generic generation-side mathematical problem is modeled, aiming to minimize operating costs and load disconnections. The whole energy management system has been tested experimentally in a test bench under both grid-connected and islanded mode. Also, its performance has been proved considering severe mismatches in forecast generation and load. Several experimental results have demonstrated the effectiveness of the proposed EMS, assessed by the corresponding average gap with respect to a selected benchmark strategy and ideal boundaries of the best and worst known solutions.

This paper presents a seamless transition method for a droop-controlled inverter. The droop control is suitable to make the inverter work as a voltage source in both islanded and grid-connected modes, however, the transfer between theses modes can result in a big inrush current that may damage the system. The proposed method allows the droop-controlled inverter to improve the transient response when transferring between modes, by detecting the inrush current, activating a current control loop during transients, and then transferring back to droop-controlled mode smoothly by using a virtual inductance loop. In addition, a local phase-locked-loop (PLL) is proposed to align the inverter voltage with the grid in order to reduce the transient current during the transition. Therefore, the droop-controlled inverter is able to operate in both grid-connected and islanded modes, providing as well a smooth transition between them, requiring neither synchronization signals nor grid-side information. The control algorithm and design procedure are presented. Experimental results from a laboratory prototype validate the effectiveness of the proposed method.

Worldwide, the current energy system increasingly shows economic, social and environmental drawbacks and it does not appear to be sustainable. Among the most pressing problems are climate change due to CO2 emissions, the depletion of fossil resources, the security of energy supply, and threats to economic development. These problems can be addressed by moving towards energy systems that increasingly rely on renewable and sustainable energy sources. At the same time, the rapid progress in renewable energy harvesting and information and telecommunication technologies offer unprecedented opportunities for energy generation, distribution and management, and to more strongly involve people in the process of energy generation and management, which is needed to further enhance the sustainable energy systems. Indeed, renewable and sustainable energy sources are likely to be produced and distributed in a decentralised manner, and require energy management systems that differ greatly from the current centralised system. Hence, the integration of renewable sources has major implications for the design and management of energy systems, relying on innovative ICT solutions and stronger user involvement that facilitate supply and demand matching. Effective energy management requires the active participation and support of end users, who should accept the energy management systems, and adapt their energy use to the available demand as to enhance the efficiency and stability of the energy system. Hence, the design of future smart grids should be based on sound behavioural models, which should be integrated in ICT centred solutions that facilitate supply and demand matching. More specifically, we need to understand how truly complex information on energy production, use and storage can be effectively communicated among relevant actors, and what type of information and incentives should be provided to realise effective supply and demand matching. In addition, we need to understand how to take into account cultural specifics in the design of energy management systems, to enhance effective energy management across the world. The active and aware involvement of the end-user can only be achieved if a scalable and reliable ICT infrastructure is in place, which naturally interfaces the energy flows with the decision autonomy of the people. Hence, the design of effective energy management systems should be take into account key behavioural as well as ICT requirements in an integrated way. Our proposal is thus to investigate (1) ICT based solutions for monitoring and controlling the power grid focusing on the distribution networks (medium-low voltage) and buildings (offices and residential complexes) specific to the Qatar context; (2) behavioural models on effective and acceptable incentives to match energy supply and demand; (3) cultural specificities in the design of energy management systems by comparing results from research in Qatar to similar research in other parts of the world, in particular Europe. Together, these will provide important insights in how to promote efficient and stable renewable energy systems that meet Qatar's sustainability goals.

This article proposes a unified controller for Cuk converter assisted variable speed wind turbine driven self-excited induction generator (SEIG) in dc nanogrid configuration for rural electrification. Cuk converter assisted SEIG based wind energy conversion system (WECS) is considered as a master source in the proposed nanogrid, which operates in both grid-connected and islanded mode of operation. In grid connected mode, the system operates in maximum power point tracking (MPPT) under varying wind velocity. A single sensor, modified perturb and observe (P&O) MPPT algorithm, which is independent of the generator parameter is developed and implemented through Cuk converter. During a fault, the WECS necessitates to operate in islanded mode with voltage regulation to supply the local loads continuously. The unified control strategy is developed for selecting the mode of operation, which are MPPT and voltage regulation in grid-connected and islanded mode, respectively. Harmonic spectrum analysis is carried to justify the selection of diode bridge rectifier over semicontrolled/controlled rectifier. The effectiveness and feasibility of the proposed system is verified by means of MATLAB/Simulink. To demonstrate the operational capability, a laboratory scaled prototype is fabricated and tested under various dynamic scenarios.

The existing distributed operation schemes for microgrids lack the ability to determine the power selling to the grid during normal operation mode and are unable to provide service reliability to critical loads, during islanded operation mode. In order to overcome these issues, in this study, we have proposed a distributed operation method for both grid-connected and islanded modes of microgrids. Unlike the existing studies, where the utility grid is considered as a dispatchable generator, the bi-directional flow of power with the grid is considered in this study. Similarly, different load agents are considered for different priority loads to assure the service reliability to the critical loads during islanding. A two-step operation method is proposed for both grid-connected and islanded mode operations. During the first step, each agent in the network shares information with its neighboring agents to determine the total load and available renewable power in the network. Whereas, in the second step, each agent in the network determines the optimal operation points based on the local information received from the neighboring agents. Moreover, a modified cost function for the battery is also proposed in this study, which utilizes the information of market price and load to enhance the battery operation. A comparison is made between the centralized method, conventional distributed method, and the proposed distributed operation method. Simulation results have proved the effectiveness of the proposed method for realizing distributed operation for microgrids in both grid-connected and islanded modes.

There are a lot of nonlinear loads in real low voltage microgrid system. It will cause serious output voltage and grid current harmonic distortions problems in island and grid-connected modes, respectively. To solve this problem, this paper proposes a droop control scheme with quasi-proportion and resonant (quasi-PR) controller based on αβ stationary reference frame to make microgrid smoothly switch between grid-connected and island modes without changing control method. Moreover, in island mode, not only stable output voltage and frequency, but also reduced output voltage harmonics with added nonlinear loads can be achieved; In grid-connected mode, not only constant power, but also reduced grid current harmonics can be achieved. Simulation results verify the effectiveness of the proposed control scheme.

Nowadays, power production, reliability, quality, efficiency and penetration of renewable energy sources are amongst the most important topics in the power systems analysis. The need to obtain optimal power management and economical dispatch are expressed at the same time. The interest in extracting an optimum performance minimizing market clearing price (MCP) for the consumers and provide better utilization of renewable energy sources has been increasing in recent years. Due to necessity of providing energy balance while having the fluctuations in the load demand and non-dispatchable nature of renewable sources, implementing an energy management system (EMS) is of great importance in Microgrids (MG). The appearance of new technologies such as energy storage (ES) has caused increase in the effort to present new and modified optimization methods for power management. Precise prediction of renewable energy sources power generation can only be provided with small anticipation. Hence, for increasing the efficiency of the presented optimization algorithm in large-dimension problems, new methods should be proposed, especially for short-term scheduling. Powerful optimization methods are needed to be applied in such a way to achieve maximum efficiency, enhance the economic dispatch as well as provide the best performance for these systems. Thus, real-time energy management within MG is an important factor for the operators to guarantee optimal and safe operation of the system. The proposed EMS should be able to schedule the MG generation with minimum information shares sent by generation units. To achieve this ability, the present thesis proposes an operational architecture for real time operation (RTO) of a MG operating in both islanding and grid-connected modes. The presented architecture is flexible and could be used for different configurations of MGs in different scenarios. A general formula is also presented to estimate optimum operation strategy, cost optimization plan and the reduction of the consumed electricity combined with applying demand response (DR). The proposed problem is formulated as an optimization problem with nonlinear constraints to minimize the cost related to generation sources and responsive load as well as reducing MCP. Several optimization methods including mixed linear programming, pivot source, imperialist competition, artificial bee colony, particle swarm, ant colony, and gravitational search algorithms are utilized to achieve the specified objectives. The main goal of the thesis is to validate experimentally the design of the real-time energy management system for MGs in both operating modes which is suitable for different size and types of generation resources and storage devices with plug-and-play structure. As a result, this system is capable of adapting itself to changes in the generation and storage assets in real-time, and delivering optimal operation commands to the assets quickly, using a local energy market (LEM) structure based on single side or double side auction. The study is aimed to figure the optimum operation of micro-sources out as well as to decrease the electricity production cost by hourly day-ahead and real time scheduling. Experimental results show the effectiveness of the proposed methods for optimal operation with minimum cost and plug-and-play capability in a MG. Moreover, these algorithms are feasible from computational viewpoints while having many advantages such as reducing the peak consumption, optimal operation and scheduling the generation unit as well as minimizing the electricity generation cost. Furthermore, capabilities such as the system development, reliability and flexibility are also considered in the proposed algorithms. The plug and play capability in real time applications is investigated by using different scenarios.

This paper proposes a predictive control of the fixed switching frequency model of the AC microgrid (MG). The MG comprises a solar photovoltaic array, a battery energy storage system (BESS), a voltage source inverter (VSI), a bidirectional converter (BDC), and a static transfer switch. The proposed control algorithm enables the fixed switching frequency operation of both the VSI and the BDC. The VSI in grid-connected (GC) mode not only injects the generated solar power but also provides power quality improvement features through load compensation. However, the BDC charges the BESS up to its capacity. In islanded (IS) mode, the VSI maintains a stiff AC voltage at the point of the common coupling terminals. Whereas, the BDC meets both the power balance and the DC-bus voltage regulation. The synchronised sequential triggering of converters enables a seamless transition between IS and GC modes and vice versa. The performance of the MG in GC and IS modes is tested experimentally on a hardware prototype under step changes in solar irradiance and load. Furthermore, the transition performances of the MG from GC to IS mode under grid fault and reconnection to the grid after voltage recovery are tested.

Energy management system (EMS) design has traditionally been a top-down process, in which a single vector provides the algorithms, software, and hardware to meet the utility's functional specifications. Trends in power systems, such as the move by utilities to open systems architectures, and the development of distributed computing systems indicate that this process must be changed to incorporate the new expertise required in EMS design. An open design approach is proposed to accomplish this. The design approach is based on decomposing the EMS design problem according to different levels of abstraction. The authors define the components of this decomposition and discuss their relationships. These components form the conceptual design for a CAD simulation package which is being developed at UC Berkeley to evaluate and compare the performance of alternative designs. >

RETRACTED: Robust-based risk assessment of buildings in resiliency and self-scheduling operations for coordinated vehicle-to-home and renewable resources

The DC microgrid plays an essential role in realizing smart power supply systems for the DC loads. It combines various distributed generations and transmits the power to the loads or the utility grid through the DC bus. It attaches great importance to energy management because of the load and photovoltaic power fluctuations. This paper proposes an improved coordinated control based on the characteristics of various distributed generations and utility grids. The proposed method can realize the stabilization of bus voltage when the system switches between multiple operating modes in grid-connected and island mode due to the change of energy. Compared with the present ways, the proposed method provides a further optimization on the design of charging for energy storage units in the grid-connected mode and the current sharing with the backup storage units in the islanded mode which is conducted by SoC balancing droop control. Finally, the DC microgrid simulation platform is built to verify the correctness and feasibility of the proposed method.

As a single controllable unit, microgrid can be grid-connected with utility grid and detached from grid to become a controllable autonomous system. When microgrid is switching between grid-connected mode and islanding mode, it will cause fluctuation of voltage, current and frequency, which will have a certain impact on the load. The stable control in both modes is the basic condition to ensure the reliable operation of microgrid. In this paper, control strategy of grid-connected and islanding mode switching based on the master-slave structure of microgrid system is mainly researched. The proposed method of PQ outer loop controller, V/f outer loop controller and current inner loop controller of the master inverter of microgrid is given. Based on the analysis of the structure of the controller, a mathematic model of the master inverter of the microgrid is established, and a current inner loop controller based on the LADRC (Linear Active Disturbance Rejection Control) technique is designed. The presented smooth switching control strategy makes the outer loop controller running in parallel, and the inner loop controller share the improved current inner loop controller. LADRC control structure has strong anti-interference ability, it can effectively inhibit the fluctuations of various parameters, has a good inhibitory effect on the uncertainty of the power grid. The design method is simple and feasible. The simulation results show that the switching range of voltage, current and frequency is small, and the switching process time is less than 20ms, which can achieve stable and smooth switching between microgrid and utility grid.

DC microgrids with energy storage units are becoming attractive solutions for absorbing and transmitting renewable energy. The energy storage unit can be charged or discharged as a current source according to system commands when connected to the DC grid, and can act as a voltage source to maintain the power balance of renewable energy and local loads in the island mode. However, during the island detection, the DC bus voltage is uncontrollable, and the transition between modes of operation may cause DC bus voltage fluctuations and even make the system unstable. Therefore, a smooth transition between grid-connected and island mode is necessary. In this paper, combined with the advantages of peer-to-peer control, an improved master-slave control strategy based on I-ΔV droop is proposed to control the smooth transition between grid-connected and island mode. It enables the energy storage unit to operate under current control like conventional master-slave control during grid connection, and adaptive smooth transition to voltage control based on I-ΔV droop during island detection and islanding. Analysis and experimental results show that smooth transition between grid-connected and island mode can be easily achieved, especially in the case of non-intention islanding.

In this paper, a DC microgrid based on solar PV array and battery storage is simulated and a dual-mode control system is developed for grid-connected and islanded modes. The developed dual-mode control approach is based on model predictive control (MPC). The control system is flexible to allow operating the microgrid under different modes that include islanded and grid-connected modes. The considered microgrid is modeled and simulated using MATLAB/Simulink software and different scenarios have been tested to verify the proposed principle.