There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

DC and AC Microgrids are key elements to integrate renewable and distributed energy resources as well as distributed energy storage systems. In the last years, efforts toward the standardization of these Microgrids have been made. In this sense, this paper present the hierarchical control derived from ISA-95 and electrical dispatching standards to endow smartness and flexibility to microgrids. The hierarchical control proposed consist of three levels: i) the primary control is based on the droop method, including an output impedance virtual loop; ii) the secondary control allows restoring the deviations produced by the primary control; and iii) the tertiary control manage the power flow between the microgrid and the external electrical distribution system. Results from a hierarchical-controlled microgrid are provided to show the feasibility of the proposed approach.

/pdf/hierarchical-control-of-droop-controlled-dc-and-ac-26q2w9lpco.pdf

Hierarchical control of droop-controlled DC and AC microgrids — a general approach towards standardization

Energy management means to optimize one of the most complex and important technical creations that we know: the energy system. While there is plenty of experience in optimizing energy generation and distribution, it is the demand side that receives increasing attention by research and industry. Demand Side Management (DSM) is a portfolio of measures to improve the energy system at the side of consumption. It ranges from improving energy efficiency by using better materials, over smart energy tariffs with incentives for certain consumption patterns, up to sophisticated real-time control of distributed energy resources. This paper gives an overview and a taxonomy for DSM, analyzes the various types of DSM, and gives an outlook on the latest demonstration projects in this domain.

/pdf/demand-side-management-demand-response-intelligent-energy-27yx5jmy0a.pdf

Demand Side Management: Demand Response, Intelligent Energy Systems, and Smart Loads

The enabling of ac microgrids in distribution networks allows delivering distributed power and providing grid support services during regular operation of the grid, as well as powering isolated islands in case of faults and contingencies, thus increasing the performance and reliability of the electrical system. The high penetration of distributed generators, linked to the grid through highly controllable power processors based on power electronics, together with the incorporation of electrical energy storage systems, communication technologies, and controllable loads, opens new horizons to the effective expansion of microgrid applications integrated into electrical power systems. This paper carries out an overview about microgrid structures and control techniques at different hierarchical levels. At the power converter level, a detailed analysis of the main operation modes and control structures for power converters belonging to microgrids is carried out, focusing mainly on grid-forming, grid-feeding, and grid-supporting configurations. This analysis is extended as well toward the hierarchical control scheme of microgrids, which, based on the primary, secondary, and tertiary control layer division, is devoted to minimize the operation cost, coordinating support services, meanwhile maximizing the reliability and the controllability of microgrids. Finally, the main grid services that microgrids can offer to the main network, as well as the future trends in the development of their operation and control for the next future, are presented and discussed.

Control of Power Converters in AC Microgrids

The increasing interest in integrating intermittent renewable energy sources into microgrids presents major challenges from the viewpoints of reliable operation and control. In this paper, the major issues and challenges in microgrid control are discussed, and a review of state-of-the-art control strategies and trends is presented; a general overview of the main control principles (e.g., droop control, model predictive control, multi-agent systems) is also included. The paper classifies microgrid control strategies into three levels: primary, secondary, and tertiary, where primary and secondary levels are associated with the operation of the microgrid itself, and tertiary level pertains to the coordinated operation of the microgrid and the host grid. Each control level is discussed in detail in view of the relevant existing technical literature.

Trends in Microgrid Control

This paper presents a linear active disturbance rejection control (LADRC) for grid-connected converter with LCL filter. The high rejection performance for external disturbance, internal decoupling, parameter variation is achieved by adopting extended state observer(ESO) and designing controller with direct pole placement. Robustness of parameter uncertainty and sensitivity of input disturbance are analyzed in frequency domain to demonstrate the superior characteristic in disturbance rejection. The theoretical analysis is verified in Matlab/Simulink. The simulation results show the excellent capability of rejection in grid voltage disturbance.

/pdf/linear-active-disturbance-rejection-control-for-lcl-type-57f666qvnu.pdf

Linear active disturbance rejection control for LCL type grid-connected converter

This paper describes a theoretical and simulation study on a control strategy for the parallel operation of three-phase current source inverters (CSI), to be applied to uninterruptible power systems (UPS). A circulating current suppression strategy for parallel CSIs is proposed in this paper based on an auxiliary current control loop used to modify the reference currents by compensating the error currents between parallel inverters. The proposed method is coordinated together with droop and virtual impedance control. In this paper, droop control is used to generate the reference voltage of each inverter, and the virtual impedance is used to fix the output impedance of the inverters. In addition, a secondary control is used in order to recover the voltage deviation caused by the virtual impedance. and the auxiliary current control loop is added to acquire a better average current sharing performance among parallel CSIs, which can effectively suppress the circulating current. Simulation results are presented in order to verify the effectiveness of the proposed control methodology.

/pdf/control-architecture-for-paralleled-current-source-inverter-2c04761ap3.pdf

Control architecture for paralleled current-source-inverter (CSI) based uninterruptible power systems (UPS)

Advanced metering infrastructures (AMI) are required for the future smart grid operation by providing useful information about users' behavior as well as grid performance such as the consumption and power quality. This paper is focused on the development of a LabVIEW application for user-interface and implementation of a Home Energy Management System (HEMS) based on AMI.

/pdf/development-and-integration-of-a-hems-with-an-advanced-smart-2ospb6tqyo.pdf

Development and integration of a HEMS with an advanced smart metering infrastructure

In this paper, a decentralized strategy based on fuzzy logic is proposed for balancing the state of charge of the energy storage units for distributed PV-based active generators. The proposed method, weights the action of conventional droop control loops for privileging the charge of the energy storage unit with the smallest state of charge or force a faster discharge of the energy storage system with the biggest state of charge. The units are self-controlled by using local variables, hence, the microgrid can operate without relying on communication systems. The proposed strategy is completely expandable and can be applied to a several number of power generators interconnected in a microgrid. Frequency and voltage bus signaling is used in order to coordinate the control operation mode between units. Simulation results in a low-voltage, three-phase, islanded AC microgrid show the feasibility of the proposed method and its applicability even for several active generators.

/pdf/stored-energy-balance-for-distributed-pv-based-active-2oz9q6vr1e.pdf

Stored energy balance for distributed PV-based active generators in an AC microgrid

Electric vehicles (EVs) are becoming a key feature of smart grids. EVs will be embedded in the smart grids as a mobile load-storage with probabilistic behavior. In order to manage EVs as flexible loads, charging stations (CSs) have essential roles. In this paper, a new method for optimal sitting and sizing of solar CSs using energy storage (ES) options is presented. Also, behavior of EVs in the presence of other loads, electricity price and solar power generation uncertainties are considered. The proposed optimization model maximizes the distribution company (DisCo) benefit by appropriate use of CSs, maximizes the benefit of CSs owners and minimizes the power loss, load demand and voltage sags during peak times considering different technical constraints. The optimization variables are the location and capacity of solar units and energy storage systems. In this paper, charge-discharge process of EVs are considered based on time-of-use (TOU) demand response programs (DRPs). In order to solve the optimization problem considering uncertainty of load growth, electricity price, initial state of charge of batteries and solar power generation, genetic algorithm method using Monte-Carlo simulation is used. The simulation results show that the proposed method has advantages for DisCo and owners of CSs.

/pdf/combined-solar-charging-stations-and-energy-storage-units-42utslupje.pdf

Juan C. Vasquez

Papers

Linear active disturbance rejection control for LCL type grid-connected converter

Control architecture for paralleled current-source-inverter (CSI) based uninterruptible power systems (UPS)

Development and integration of a HEMS with an advanced smart metering infrastructure

Stored energy balance for distributed PV-based active generators in an AC microgrid

Combined solar charging stations and energy storage units allocation for electric vehicles by considering uncertainties