Microgrid optimization, modelling and control

2014 Fall.To view the abstract, please see the full text of the document

Design of control tools for use in microgrid simulations

2018 Summer.Includes bibliographical references.New technologies are transforming the way electricity is delivered and consumed. In the past two decades, a large amount of research has been done on smart grids and microgrids. This can be attributed to two factors. First is the poliferation of internet. Internet today is as ubiquitous as electricity. This has spawned a new area of technology called the internet of things (IoT). It gives us the ability to connect almost any device to the internet and harness the data. IoT finds use in smart grids that allow utiliy companies to deliver electricity efficiently. The other factor is the advancement in renewable sources of electricty and high power semiconductors coupled with their decreasing cost. These new sources disrupt the traditional way of electicity production and delivery, putting an increased focus on distributed power generation and microgrids. A microgrid is different from a utility grid. The difference is in the size of the grid, power level, a variety of possible sources and the way these are tied together. These characteristics lead to some unique control challenges. Today's appliances and consumer goods are powered using a standardized AC power. Thus a microrid must deliver uninterrupted and high quality power while at the same time taking into account the vastly different nature of the microsurces that produce the power. This work describes control system tools for different power converters that will be used in simulating microgrids.\ Simulations are important tool for any researcher. It allows researchers to test their research and theories at a greatly reduced cost. The process of design, testing and verification is an iterative process. Simulations allow a cost effective method of doing research, substituting the actual process of building experimental systems. This greatly reduces the amount of manpower and capital investment. A microgrid consists of several building blocks. These building blocks can be categorized into microsources, energy stores, converters and the loads. Microsources are devices that produce electric power. For example, a photovoltaic panel is a mirosource that produces DC power. Converters act as an interface between microsources and the grid. The constituent chapters in the document describe microsources and converters. The chapters describe the underlying control system and the simulation model of the system designed in Simulink. Some of the tools described are derived from the MATLAB/Simulink Examples library. Original authors of the simulation models and systems have been duly credited. Colorado State University has a vibrant research community. The tools described in this thesis are geared to be used for research into microgrids. The tools are developed in a simulation software called Simulink. The tools would allow future researchers to rapidly build microgrid simulations and test new control system implementations etc. The research described in the thesis builds upon the research by Han on natural gas engine based microgrid. The control tools described here are used to construct a microgrid simulation. The microgrid is built around a natural gas engine. Due to the transport lag in delivering fuel, a natural gas engine exhibits significant deviation in the AC grid frequency when subjected to step load. The microgrid setup along with the control system described here, minimizes the frequency deviation, thus stabilizing the microgrid. Simulation results verify the working of the tools

Modeling, Simulation and Decentralized Control of Islanded Microgrids

Modeling, Simulation and Decentralized Control of Islanded Microgrids by Farideh Doost Mohammadi This thesis develops a comprehensive modular state-space model of microgrids containing inverter-based Distributed Energy Resources (DERs). The model is validated and then used for small signal stability enhancement and voltage and frequency control. State space models of various microgrid elements are first derived, which allow for the inclusion of any possible elements such as current controlled inverters that are missing in the literature. Then a complete state space model is obtained to complement the models that are available in the literature and whose objectives are system analysis only as compared to the purpose of this work which is stability enhancement and control design. Specifically,;1. Small signal stability is enhanced by adding current controlled inverters to the microgrid. 2. Decentralized secondary frequency and voltage control techniques are proposed.;For secondary frequency control purposes, at first, the control strategies of different kinds of inverters and storage devices are described. Then, a novel solution is introduced for islanded microgrids by decomposing the system into virtual control areas.;For the secondary voltage control an Average Consensus Algorithm (ACA) is used and applied on a network of agents which has been chosen optimally based on the required connectivity. The main purpose of the ACA is to keep the average voltage of all the buses at a desired level during islanding. Then another control strategy is proposed to improve the voltage profile. While the average voltage is kept fixed by the voltage controlled inverters, this voltage profile smoothness is obtained by dedicating zones to current controlled inverters and defining their responsibilities based on the location of the loads

Hybrid ac/dc microgrids. Part II : Review and classification of control strategies

Microgrids are envisioned as one of the most suitable alternatives for the integration of distributed generation units in the utility grid, as they efficiently combine generation, energy storage and loads in the same distribution network. In this context, hybrid ac/dc microgrids are arising as an interesting approach as they combine the advantages of ac and dc networks and do not require excessive modifications in the distribution network. However, they require more complex control strategies as they need to control the ac and dc networks and the interface power converter simultaneously. This paper identifies and analyses the control strategies that can be implemented in hybrid microgrids for an adequate power management in grid-tied and islanded modes of operation. The review is focused on hierarchical controls as they are the most extended approach in the literature. A classification has been elaborated, which covers the three main levels of hierarchical control strategies (primary, secondary and tertiary). Each of the levels has been independently studied in order to provide a comprehensive analysis of the alternatives found in the literature. The future trends related to this topic show that a higher research effort is required regarding the control of the interface device and the ancillary services that the management strategy must provide—e.g. blackstart, transition between islanded and grid-connected modes of operation, interconnection of microgrids, etc

Microgrid, Its Control and Stability: The State of The Art

Some of the challenges facing the power industries globally include power quality and stability, diminishing fossil fuel, climate change amongst others. The use of distributed generators however is growing at a steady pace to address these challenges. When interconnected and integrated with storage devices and controllable load, these generators operate together in a grid, which has incidental stability and control issues. The focus of this paper, therefore, is on the review and discussion of the different control approaches and the hierarchical control on a microgrid, the current practice in the literature concerning stability and the control techniques deployed for microgrid control; the weakness and strength of the different control strategies were discussed in this work and some of the areas that require further research are highlighted

Applicability of Droop Regulation Technique in Microgrid - A Survey

Currently, the worth of power generation on the basis of renewable sources is rapidly growing. Correspondingly the microgrids and the DG units are impressed the researchers for their peculiar features. Power sharing is the major concern when various DGs are connected to the microgrid via power electronic converters. It is mandatory to achieve an appropriate power sharing when the manifold DGs are activated in parallel. For that, the two ultimate quantities - power angle δ and voltage magnitude V are regulated to acquire the real and reactive power sharing correspondingly. Many innovative control techniques have been used for load sharing. The most common method of local load sharing is the droop characteristics. Subsequently, there is a swift momentum in the advancement of researchers to meet the challenges of the droop control techniques in the power sharing concerns, an extensive literature review on active and reactive power sharing, voltage and frequency control in microgrid has been emphasized. The various conventional and modified droop control techniques/strategies that relates to power sharing issues have been highlighted in this work

Wind Power Frequency Control in Doubly FED Induction Generator Using CFMPC-FOPID Controller Scheme

Because the majority of wind turbines operate in maximum output power tracking mode, power system frequency cannot be supported. However, if the penetration rate of wind power increases, the system inertia related to frequency modulation may decrease. In addition, frequency stability will be severely affected in the event of significant disturbances to the system load. Due to the high penetration of wind power in isolated power systems, this study suggests a coordinated frequency management approach for emergency frequency regulation. In order to prevent the phenomenon of load frequency control in doubly fed induction generators (DFIGs), a unique efficient control scheme is developed. The Cascaded Fractional Model Predictive Controller coupled with Fractional-Order PID controller (CFMPC-FOPID) is developed to provide the DFIG system with an efficient reaction to changes in load and system parameters. The proposed controller must have a robust tendency to respond quickly in terms of minimum settling time, undershoot, and overshoot. Nonlinear feedback controllers are designed using frequency deviations and power imbalances to achieve the reserve power distribution between generators and DFIGs in a variety of wind speed conditions. It makes upgrading quick and easy. In Matlab/Simulink, a simulation model is built to test the viability of the suggested approach

Frequency robust control in stand-alone microgrids with PV sources : design and sensitivity analysis

International audienceIn this paper, a robust H-infinity control strategy for frequency regulation is proposed in isolated microgrids (MGs) composed of diesel engine generators, photovoltaic (PV) sources, and storage units. First, the linear matrix inequalities (LMI) method is adopted to design a multi-variable H-infinity controller which ensures given specifications. In a second step, uncertainties in the storage device state of charge (SoC) are considered and a sensitivity analysis is carried out in order to determine the maximum variation range of SoC for which the dynamic performances are respected. The controller's robustness and performance in the presence of various load disturbances, PV output power variations, and the SoC uncertainty are validated through a series of nonlinear time-domain simulations performed with MATLAB/Simulink.</p