A power consensus algorithm for DC microgrids (original) (raw)
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A Robust Consensus Algorithm for Current Sharing and Voltage Regulation in DC Microgrids
IEEE Transactions on Control Systems Technology
In this paper a novel distributed control algorithm for current sharing and voltage regulation in Direct Current (DC) microgrids is proposed. The DC microgrid is composed of several Distributed Generation units (DGUs), including Buck converters and current loads. The considered model permits an arbitrary network topology and is affected by unknown load demand and modelling uncertainties. The proposed control strategy exploits a communication network to achieve proportional current sharing using a consensus-like algorithm. Voltage regulation is achieved by constraining the system to a suitable manifold. Two robust control strategies of Sliding Mode (SM) type are developed to reach the desired manifold in a finite time. The proposed control scheme is formally analyzed, proving the achievement of proportional current sharing, while guaranteeing that the weighted average voltage of the microgrid is identical to the weighted average of the voltage references.
A robust consensus algorithm for DC microgrids
2018
The increasing use of electrical energy influences the quality of the mains voltage and current, which can cause problems. The quality of the energy supply falls worldwide under the name power quality. A high-quality energy supply can be characterized by the ability to supply a clean and stable grid voltage. A perfect Power Quality ideally ensures low transport losses and a mains voltage that is always available, noise-free and pure sinusoidal, and always within the level and frequency tolerances. Problems with the quality of power have become important for electricity users at all usage levels. The use of non-linear loads and sensitive electronic equipment in both the industrial and commercial sectors and the domestic environment has increased considerably in recent decades. Unfortunately, the same type of equipment often generates disturbances in the energy supply, which in turn affect other devices negatively. In addition to annoying phenomena such as flicker (blinking of light),...
Distributed consensus-based control of multiple DC-microgrids clusters
IECON 2014 - 40th Annual Conference of the IEEE Industrial Electronics Society, 2014
This paper presents consensus-based distributed control strategies for voltage regulation and power flow control of dc microgrid (MG) clusters. In the proposed strategy, primary level of control is used to regulate the common bus voltage inside each MG locally. An SOC-based adaptive droop method is introduced for this level which determines droop coefficient automatically, thus equalizing SOC of batteries inside each MG. In the secondary level, a distributed consensus based voltage control strategy is proposed to eliminate the average voltage deviation while guaranteeing proper regulation of power flow among the MGs. Using the consensus protocol, the global information can be accurately shared in a distributed way. This allows the power flow control to be achieved at the same time as it can be accomplished only at the cost of having the voltage differences inside the system. Similarly, a consensus-based cooperative algorithm is employed at this stage to define appropriate reference for power flow between MGs according to their local SOCs. The effectiveness of proposed control scheme is verified through detailed hardware-in-the-loop (HIL) simulations.
IFAC-PapersOnLine
In this paper we study a distributed control scheme, achieving current sharing and average voltage regulation in Direct Current (DC) microgrids. The considered DC microgrid is composed of several Distributed Generation Units (DGUs) interconnected, through resistive-inductive power lines, with loads. Each DGU includes a generic energy source that supplies the loads through a DC-DC buck converter. Remarkably, the proposed control scheme achieves average voltage regulation without the need of voltage measurements. An experimental validation is performed to assess the capabilities of the solution in a real network. The initial results are promising and show an additional need to compensate for partly unknown resistances present at the DGUs.
Distributed Averaging Control for Voltage Regulation and Current Sharing in DC Microgrids
IEEE Control Systems Letters
In this letter we propose a new distributed control scheme, achieving current sharing and average voltage regulation in Direct Current (DC) microgrids. The considered DC microgrid is composed of several Distributed Generation Units (DGUs) interconnected through resistive-inductive power lines. Each DGU includes a generic energy source that supplies a local current load through a DC-DC buck converter. The proposed distributed control scheme achieves current sharing and average voltage regulation, independently of the initial condition of the controlled microgrid. Moreover, the proposed solution requires only measurements of the generated currents, and is independent of the microgrid parameters and the topology of the used communication network, facilitating Plug-and-Play capabilities. Global convergence to a desired steady state is proven and simulations indicate a good performance.
Stability, control, and power flow in ad hoc DC microgrids
2016 IEEE 17th Workshop on Control and Modeling for Power Electronics (COMPEL), 2016
Lack of access to electricity continues to plague more than one billion people. Microgrids which could be set up with limited planning would allow underserved communities to participate in energy markets without central oversight, but preexisting stability criteria and control techniques are illsuited to this kind of network. We focus on the stability and control of networks formed by the ad hoc interconnection of modular power sources and loads. Equilibrium point feasibilitya minimum node voltage and minimum distribution efficiencycan be guaranteed by placing upper bounds on the droop and line resistances. Small-signal stability of the equilibrium point can be guaranteed by including a minimum capacitance (often already present) at the input of each load converter. We derive closed-form expressions for each of these bounds. Additionally, we present experimental validation of a new, multipurpose, secondary microgrid control scheme. The proposed method improves voltage regulation and power sharing-eliminating the steady-state power sharing error inherent to previous methods.
Structural Improvements in Consensus-Based Cooperative Control of DC Microgrids
Electronics
This study is dedicated to establishing a comparative analysis of the performance ofdifferent local controllers on the cooperative control of DC microgrids. One of the elementary andchallenging issues in DC microgrids is the assurance of fairness in proportional current sharingwhile accomplishing voltage regulation in parallelly connected distributed energy sources. In thiswork, structural improvements are proposed to enhance the system stability and controlperformance. A finite-gain controller was employed in the outer voltage control loop with a simpleproportional (P) controller in the inner current control loop of a converter. Due to the finite-gaincontroller, droop-like power sharing was achieved without droop coefficient. In order to furtherenhance the power-sharing accuracy and DC voltage regulation, a different method was adopted inconsensus-based cooperative control to estimate the average current and average voltage difference.Moreover, small signal analysis was used to scr...
IEEE Transactions on Smart Grid, 2015
Distributed control methods based on consensus algorithms have become popular in recent years for microgrid (MG) systems. These kinds of algorithms can be applied to share information in order to coordinate multiple distributed generators within a MG. However, stability analysis becomes a challenging issue when these kinds of algorithms are used, since the dynamics of the electrical and the communication systems interact with each other. Moreover, the transmission rate and topology of the communication network also affect the system dynamics. Due to discrete nature of the information exchange in the communication network, continuous-time methods can be inaccurate for this kind of dynamic study. Therefore, this paper aims at modeling a complete DC MG using a discrete-time approach in order to perform a sensitivity analysis taking into account the effects of the consensus algorithm. To this end, a generalized modeling method is proposed and the influence of key control parameters, the communication topology and the communication speed are studied in detail. The theoretical results obtained with the proposed model are verified by comparing them with the results obtained with a detailed switching simulator developed in Simulink/Plecs. usually in this control level and it is a fashionable way to achieve distributed power sharing in the short-term without communications. The secondary controller can help improving the power quality of a MG and it can also provide ancillary services. This kind of control hierarchy can be implemented in centralized [2], [5], [6] or distributed fashion [7]-[9]. In the top level, a tertiary controller manages the power flow of the MG and optimizes economic issues. A method to optimize the efficiency is proposed in [10]. Here, a genetic algorithm is implemented in the tertiary controller to minimize the losses of the whole system. Other types of centralized energy management controllers are studied in the literature [11]-[14]. On the other hand, several attempts have been made to achieve distributed management [15]-[17]. For that matter, consensus algorithm [18] is often used since it facilitates the information synthesis and aggregation among a set of distributed agents.
Distributed Cooperative Control of DC Microgrids
IEEE Transactions on Power Electronics, 2015
A cooperative control paradigm is used to establish a distributed secondary/primary control framework for dc Microgrids. The conventional secondary control, that adjusts the voltage set point for the local droop mechanism, is replaced by a voltage regulator and a current regulator. A noise-resilient voltage observer is introduced that uses neighbors' data to estimate the average voltage across the Microgrid. The voltage regulator processes this estimation and generates a voltage correction term to adjust the local voltage set point. This adjustment maintains the Microgrid voltage level as desired by the tertiary control. The current regulator compares the local per-unit current of each converter with the neighbors' and, accordingly, provides a second voltage correction term to synchronize per-unit currents and, thus, provide proportional load sharing. The proposed controller precisely handles the transmission line impedances. The controller on each converter communicates with only its neighbor converters on a communication graph. The graph is a sparse network of communication links spanned across the Microgrid to facilitate data exchange. The global dynamic model of the Microgrid is derived, and design guidelines are provided to tune the system's dynamic response. A low-voltage dc Microgrid prototype is set up, where the controller performance, noise resiliency, linkfailure resiliency, and the plug-and-play capability features are successfully verified.
Stability and control of ad hoc dc microgrids
2016 IEEE 55th Conference on Decision and Control (CDC), 2016
Ad hoc electrical networks are formed by connecting power sources and loads without predetermining the network topology. These systems are well-suited to addressing the lack of electricity in rural areas because they can be assembled and modified by non-expert users without central oversight. There are two core aspects to ad hoc system design: 1) designing source and load units such that the microgrid formed from the arbitrary interconnection of many units is always stable and 2) developing control strategies to autonomously manage the microgrid (i.e., perform power dispatch and voltage regulation) in a decentralized manner and under large uncertainty. To address these challenges we apply a number of nonlinear control techniques-including Brayton-Moser potential theory and primal-dual dynamics-to obtain conditions under which an ad hoc dc microgrid will have a suitable and asymptotically stable equilibrium point. Further, we propose a new decentralized control scheme that coordinates many sources to achieve a specified power dispatch from each. A simulated comparison to previous research is included.