2,416 research outputs found
A Dual-loop Model Predictive Voltage Control/Sliding-mode Current Control for Voltage Source Inverter Operation in Smart Microgrids
The design of a robust controller for the voltage source inverter
is essential for reliable operation of distributed energy resources
in future smart microgrids. The design problem is challenging in the
case of autonomous operation subsequent to an islanding situation.
In this article, a dual-loop controller is proposed for voltage source
inverter control. The outer loop is designed for microgrid voltage and
frequency regulation based on the model predictive control strategy.
This outer loop generates reference inverter currents for the inner
loop. The inner loop is designed using a sliding-mode control strategy,
and it generates the pulse-width modulation voltage commands
to regulate the inverter currents. A standard space vector algorithm
is used to realize the pulse-width modulation voltage commands.
Performance evaluation of the proposed controller is carried out for
different loading scenarios. It is shown that the proposed dual-loop
controller provides the specified performance characteristics of an
islanded microgrid with different loading conditions.http://www.tandfonline.com/loi/uemp20hb201
A dual-loop model predictive voltage control/sliding-mode current control for voltage source inverter operation in smart microgrids
The design of a robust controller for the voltage source inverter
is essential for reliable operation of distributed energy resources
in future smart microgrids. The design problem is challenging in the
case of autonomous operation subsequent to an islanding situation.
In this article, a dual-loop controller is proposed for voltage source
inverter control. The outer loop is designed for microgrid voltage and
frequency regulation based on the model predictive control strategy.
This outer loop generates reference inverter currents for the inner
loop. The inner loop is designed using a sliding-mode control strategy,
and it generates the pulse-width modulation voltage commands
to regulate the inverter currents. A standard space vector algorithm
is used to realize the pulse-width modulation voltage commands.
Performance evaluation of the proposed controller is carried out for
different loading scenarios. It is shown that the proposed dual-loop
controller provides the specified performance characteristics of an
islanded microgrid with different loading conditions.http://www.tandfonline.com/loi/uemp20hb201
Microgrid Control Strategy Study and Controller Design Based on Model Predictive Control
In the 21st century, because of the exhausting of oil, coal and other non-renewable energy, human beings enter a period of large-scale exploitation and utilization of renewable energy. Renewable energy generation become an important way for new energy utilization, however, as more and more distributed generation connect to power distribution network, the traditional distribution network structure will be changed. A large number of distributed generation applications of modern power electronic technology, have also produced a lot of harmonics to impact the power quality. It will threaten the safe operation of the distribution network and obstruct the utilization of renewable energy. The concept of microgrid provides a new thinking for the application of renewable energy. Microgrid can make full use of the characteristics of the renewable energy and it is the key of the future resources and environment for human beings. We can predict that, microgrid construction will be rapidly developed in 21st century, based on the utilization of renewable energy.
In order to coordinate the contradiction between power grid and distributed generation, the concept of microgrid arises at the historic moment. Microgrid has two operation modes: islanded mode and grid-connected mode. By theoretically analyzing, simulation model construction and result analyzing, the microgrid coordinated control strategies will be studied in this paper.
Firstly, this paper starts from the microgrid operation control mode, respectively establishing the traditional control strategy of simulation for the isolated and connected microgrid. The isolated grid control strategies is V/f control strategy based on droop characteristic and the connected grid control strategies is P/Q control strategy.
Second, the model predictive control is introduced in chapter three including its principle and application. In the case study, the traditional PI controller is compared with model predictive control controller in single distributed generation system to introduce advantages of model predictive control method.
Last, the model of microgrid with multiple distributed generations is built in MATLAB/Simulink. There are three cases in this model: working model switches between grid-connected and islanded mode; increase and decrease load in islanded mode; disconnect one PV system at certain time in islanded mode. By analyzing results of three cases, the MPC controller can achieve desirable efficiency of power control. Meanwhile, the voltage and frequency are working in the required range of the system. That proves the effectiveness of MPC controller
CONTROL STRATEGIES OF DC MICROGRID TO ENABLE A MORE WIDE-SCALE ADOPTION
Microgrids are gaining popularity in part for their ability to support increased penetration
of distributed renewable energy sources, aiming to meet energy demand and overcome global
warming concerns. DC microgrid, though appears promising, introduces many challenges in the
design of control systems in order to ensure a reliable, secure and economical operation. To enable
a wider adoption of DC microgrid, this dissertation examines to combine the characteristics and
advantages of model predictive control (MPC) and distributed droop control into a hierarchy and
fully autonomous control of the DC microgrid. In addition, new maximum power point tracking
technique (MPPT) for solar power and active power decoupling technique for the inverter are
presented to improve the efficiency and reliability of the DC microgrid.
With the purpose of eliminating the oscillation around the maximum power point (MPP),
an improved MPPT technique was proposed by adding a steady state MPP determination algorithm
after the adaptive perturb and observe method. This control method is proved independent with
the environmental conditions and has much smaller oscillations around the MPP compared to
existing ones. Therefore, it helps increase the energy harvest efficiency of the DC microgrid with
less continuous DC power ripple.
A novel hierarchy strategy consisting of two control loops is proposed to the DC microgrid
in study, which is composed of two PV boost converters, two battery bi-directional converters and
one multi-level packed-u-cell inverter with grid connected. The primary loop task is the control of
each energy unit in the DC microgrid based on model predictive current control. Compared with
traditional PI controllers, MPC speeds up the control loop since it predicts error before the
switching signal is applied to the converter. It is also free of tuning through the minimization of a
flexible user-defined cost function. Thus, the proposed primary loop enables the system to be
expandable by adding additional energy generation units without affecting the existing ones.
Moreover, the maximum power point tracking and battery energy management of each energy unit
are included in this loop. The proposed MPC also achieves unity power factor, low grid current
total harmonics distortion. The secondary loop based on the proposed autonomous droop control
identifies the operation modes for each converter: current source converter (CSC) or voltage source
converter (VSC). To reduce the dependence on the high bandwidth communication line, the DC
bus voltage is utilized as the trigger signal to the change of operation modes. With the sacrifice of
small variations of bus voltage, a fully autonomous control can be realized. The proposed
distributed droop control of different unit converters also eliminates the potential conflicts when
more than two converters compete for the VSC mode.
Single-phase inverter systems in the DC microgrid have low frequency power ripple, which
adversely affects the system reliability and performance. A power decoupling circuit based on the
proposed dual buck converters are proposed to address the challenges. The topology is free of
shoot-through and deadtime concern and the control is independent with that of the main power
stage circuit, which makes the design simpler and more reliable. Moreover, the design of both PI
and MPC controllers are discussed and compared. While, both methods present satisfied
decoupling performances on the system, the proposed MPC is simpler to be implemented.
In conclusion, the DC microgrid may be more widely adopted in the future with the
proposed control strategies to address the current challenges that hinder its further development
Plug-and-play and coordinated control for bus-connected AC islanded microgrids
This paper presents a distributed control architecture for voltage and
frequency stabilization in AC islanded microgrids. In the primary control
layer, each generation unit is equipped with a local controller acting on the
corresponding voltage-source converter. Following the plug-and-play design
approach previously proposed by some of the authors, whenever the
addition/removal of a distributed generation unit is required, feasibility of
the operation is automatically checked by designing local controllers through
convex optimization. The update of the voltage-control layer, when units plug
-in/-out, is therefore automatized and stability of the microgrid is always
preserved. Moreover, local control design is based only on the knowledge of
parameters of power lines and it does not require to store a global microgrid
model. In this work, we focus on bus-connected microgrid topologies and enhance
the primary plug-and-play layer with local virtual impedance loops and
secondary coordinated controllers ensuring bus voltage tracking and reactive
power sharing. In particular, the secondary control architecture is
distributed, hence mirroring the modularity of the primary control layer. We
validate primary and secondary controllers by performing experiments with
balanced, unbalanced and nonlinear loads, on a setup composed of three
bus-connected distributed generation units. Most importantly, the stability of
the microgrid after the addition/removal of distributed generation units is
assessed. Overall, the experimental results show the feasibility of the
proposed modular control design framework, where generation units can be
added/removed on the fly, thus enabling the deployment of virtual power plants
that can be resized over time
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
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