5,307 research outputs found
A power consensus algorithm for DC microgrids
A novel power consensus algorithm for DC microgrids is proposed and analyzed.
DC microgrids are networks composed of DC sources, loads, and interconnecting
lines. They are represented by differential-algebraic equations connected over
an undirected weighted graph that models the electrical circuit. A second graph
represents the communication network over which the source nodes exchange
information about the instantaneous powers, which is used to adjust the
injected current accordingly. This give rise to a nonlinear consensus-like
system of differential-algebraic equations that is analyzed via Lyapunov
functions inspired by the physics of the system. We establish convergence to
the set of equilibria consisting of weighted consensus power vectors as well as
preservation of the weighted geometric mean of the source voltages. The results
apply to networks with constant impedance, constant current and constant power
loads.Comment: Abridged version submitted to the 20th IFAC World Congress, Toulouse,
Franc
Secondary Frequency and Voltage Control of Islanded Microgrids via Distributed Averaging
In this work we present new distributed controllers for secondary frequency
and voltage control in islanded microgrids. Inspired by techniques from
cooperative control, the proposed controllers use localized information and
nearest-neighbor communication to collectively perform secondary control
actions. The frequency controller rapidly regulates the microgrid frequency to
its nominal value while maintaining active power sharing among the distributed
generators. Tuning of the voltage controller provides a simple and intuitive
trade-off between the conflicting goals of voltage regulation and reactive
power sharing. Our designs require no knowledge of the microgrid topology,
impedances or loads. The distributed architecture allows for flexibility and
redundancy, and eliminates the need for a central microgrid controller. We
provide a voltage stability analysis and present extensive experimental results
validating our designs, verifying robust performance under communication
failure and during plug-and-play operation.Comment: Accepted for publication in IEEE Transactions on Industrial
Electronic
A survey on modeling of microgrids - from fundamental physics to phasors and voltage sources
Microgrids have been identified as key components of modern electrical
systems to facilitate the integration of renewable distributed generation
units. Their analysis and controller design requires the development of
advanced (typically model-based) techniques naturally posing an interesting
challenge to the control community. Although there are widely accepted reduced
order models to describe the dynamic behavior of microgrids, they are typically
presented without details about the reduction procedure---hampering the
understanding of the physical phenomena behind them. Preceded by an
introduction to basic notions and definitions in power systems, the present
survey reviews key characteristics and main components of a microgrid. We
introduce the reader to the basic functionality of DC/AC inverters, as well as
to standard operating modes and control schemes of inverter-interfaced power
sources in microgrid applications. Based on this exposition and starting from
fundamental physics, we present detailed dynamical models of the main microgrid
components. Furthermore, we clearly state the underlying assumptions which lead
to the standard reduced model with inverters represented by controllable
voltage sources, as well as static network and load representations, hence,
providing a complete modular model derivation of a three-phase inverter-based
microgrid
Coordinated Control of Energy Storage in Networked Microgrids under Unpredicted Load Demands
In this paper a nonlinear control design for power balancing in networked
microgrids using energy storage devices is presented. Each microgrid is
considered to be interfaced to the distribution feeder though a solid-state
transformer (SST). The internal duty cycle based controllers of each SST
ensures stable regulation of power commands during normal operation. But
problem arises when a sudden change in load or generation occurs in any
microgrid in a completely unpredicted way in between the time instants at which
the SSTs receive their power setpoints. In such a case, the energy storage unit
in that microgrid must produce or absorb the deficit power. The challenge lies
in designing a suitable regulator for this purpose owing to the nonlinearity of
the battery model and its coupling with the nonlinear SST dynamics. We design
an input-output linearization based controller, and show that it guarantees
closed-loop stability via a cascade connection with the SST model. The design
is also extended to the case when multiple SSTs must coordinate their
individual storage controllers to assist a given SST whose storage capacity is
insufficient to serve the unpredicted load. The design is verified using the
IEEE 34-bus distribution system with nine SST-driven microgrids.Comment: 8 pages, 10 figure
Analysis of an On-Line Stability Monitoring Approach for DC Microgrid Power Converters
An online approach to evaluate and monitor the stability margins of dc microgrid power converters is presented in this paper. The discussed online stability monitoring technique is based on the Middlebrook's loop-gain measurement technique, adapted to the digitally controlled power converters. In this approach, a perturbation is injected into a specific digital control loop of the converter and after measuring the loop gain, its crossover frequency and phase margin are continuously evaluated and monitored. The complete analytical derivation of the model, as well as detailed design aspects, are reported. In addition, the presence of multiple power converters connected to the same dc bus, all having the stability monitoring unit, is also investigated. An experimental microgrid prototype is implemented and considered to validate the theoretical analysis and simulation results, and to evaluate the effectiveness of the digital implementation of the technique for different control loops. The obtained results confirm the expected performance of the stability monitoring tool in steady-state and transient operating conditions. The proposed method can be extended to generic control loops in power converters operating in dc microgrids
Stability and Frequency Regulation of Inverters with Capacitive Inertia
In this paper, we address the problem of stability and frequency regulation
of a recently proposed inverter. In this type of inverter, the DC-side
capacitor emulates the inertia of a synchronous generator. First, we remodel
the dynamics from the electrical power perspective. Second, using this model,
we show that the system is stable if connected to a constant power load, and
the frequency can be regulated by a suitable choice of the controller. Next,
and as the main focus of this paper, we analyze the stability of a network of
these inverters, and show that frequency regulation can be achieved by using an
appropriate controller design. Finally, a numerical example is provided which
illustrates the effectiveness of the method
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