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In the present work, the problem of controlling recipe transitions in a paper-making process is addressed, in order to avoid paper breakage and reduce paper waste. A decoupling control scheme is proposed, based on the control of speed differences between contiguous motors. This guarantees smooth and fast transitions of all the motor speeds along the production line. A front-tracking scheme is also employed, in order to adapt the recipe change to the actual plant conditions. A simulation model has been constructed and validated for a real industrial paper-making plant, and the effectiveness of the proposed control algorithm has been tested by means of simulation. [Copyright &y& Elsevier]

Distributed generators have been widely used in modern power systems, and microgrids are becoming a key concept for the integration of multiple distributed generators and clusters of loads with great efficiency and high system reliability. In a microgrid, the control strategy is one of the most important issues. Various control schemes have been proposed to achieve the cooperation of distributed generators in a microgrid. This paper surveys cooperative control strategies for multiple distributed generators in DC microgrids. The three popular coordinated control strategies are presented: decentralized control, centralized control, and distributed control. The advantages and drawbacks of the control strategies are compared. Some intelligent control methods such as fuzzy logic control and neural network approaches are also briefly introduced in the context of microgrids. Further research trends and challenges in this area are also discussed. [ABSTRACT FROM AUTHOR]

Advanced microgrid (MG) is a likely model for reaching the goal of 100% renewable grid. A complete advanced MG control must steer the power flow in grid-connected mode; regulate voltage/frequency in islanded mode; and perform power sharing among distributed energy resources (DERs) in both modes. Power-based control (PBC) is a well-known centralized control capable of achieving these three targets. A serious disadvantage of usual MG structures using PBC approach is the existence of a single centralized grid-forming converter to form the islanded MG. Centralized grid-forming converter is a single point of failure, which reduces the capability of the MG expansion, and it is an expensive element for the MG. This paper proposes a MG control strategy using an improved centralized control together with a droop-based power-loop in distributed voltage-controlled mode (VCM) converters to allow the MG to operate in both modes, without a centralized grid-forming converter and critical islanding detection. Moreover, the new approach considers single- and three-phase DERs, controlled in VCM or current-controlled mode, and DERs with self-imposed limits, characterizing a heterogeneous MG. Real-time hardware-in-the-loop setup is used to test the proposed control strategy in several operating conditions considering ten heterogeneous DERs. Results show grid power flow control, power sharing, unbalance compensation, voltage/frequency restoration, and smooth transitioning between operating modes without critical islanding detection. • Precise grid power flow control. • Multiple grid-forming converters. • Proportional power sharing among heterogeneous distributed-energy resources. • Islanded operation with voltage and frequency restoration. • Smooth transitioning between operating modes without critical islanding detection. [ABSTRACT FROM AUTHOR]

Abstract: This paper addresses the problem of centralized optimization of an interconnected power system partitioned into several regions controlled by different transmission system operators (TSOs). It is assumed that those utilities have agreed to transferring some of their competencies to a centralized control center, which is in charge of setting the control variables in the entire system to satisfy every utility’s individual objective. This paper proposes an objective method for centralized optimization of such multi-TSO power systems, which relies on the assumption that each TSO has a real-valued optimization function focusing on its control area only. This method is illustrated on the IEEE 118 bus system partitioned into three TSOs. It is applied to the optimal reactive power dispatch problem, where the control variables are the voltage settings for generators and compensators. After showing that the method has some properties of fairness, namely freedom from envy, efficiency, accountability, and altruism, we emphasize its robustness with respect to certain biased behavior of the different TSOs. [Copyright &y& Elsevier]

This paper compares traditional local voltage control strategy with coordinated, optimization-based ones in low voltage (LV) distribution systems with photovoltaics and battery energy storage systems. Optimization-based strategies are formulated within a model predictive control (MPC) framework. Three strategies based on MPC are proposed and implemented, namely, centralized, decentralized and distributed MPC. The formulated strategies for voltage control are compared in a case study using a modified CIGRÉ European 3-area low-voltage network. Results indicate that decentralized MPC gives a better voltage profile in the network when compared to local voltage control strategy, since the latter inherently fails to maintain voltages of buses in the network not connected to photovoltaics or battery storage system within limits. Centralized MPC strategy is able to provide the optimal voltage profile across the network but utilizes 13 % higher reactive power from the control devices to achieve this when compared to decentralized MPC. The latter performs well as long as the reactive power reserves within an area is sufficient but faces drawbacks similar to that of local voltage control strategy when the reactive reserves are completely exhausted. Distributed MPC utilizes 1.3 % higher amount of reactive power reserves compared to centralized MPC in order to provide a network voltage profile similar to that of the latter while also yielding architectural advantages of decentralized MPC. [ABSTRACT FROM AUTHOR]

Residential heating, ventilation and air conditioning (HVAC) systems usually employ on/off controllers to regulate the temperature. Generally, there is no supervisory controller which can use the weather forecast and electricity time of use (TOU) price information to reduce the overall operating cost of the equipment. Lack of a supervisory controller results in higher operating costs of the HVAC system. In this paper, a model predictive control (MPC) based supervisory controller is designed to shift the heating and cooling load of a house to off-peak hours. Supervisory MPC generates the temperature set-points trajectory for on/off controllers. The approach was verified through extensive experiments in an experimental archetype house. By employing the supervisory controller with variable set-points 16% cost savings were obtained when compared to the fixed zone temperature set-points at 25 °C. More significant savings of about 50% were seen when MPC-based centralized controller was compared with the fixed zone temperature set-points of 24 °C. [ABSTRACT FROM AUTHOR]

The traditional model predictive control (MPC) design strategy heavily depends on the discritization of the non-linear model of DC/DC power converters to approximate the direct current (DC) microgrid system model. The system model does not includes the whole information of the physical implementation of the system. Assumptions have been made to add the model and sensor uncertainties in the system model to form a model with fully physical information that enables its solution through the linear kalman filtering method (LKFM). Due to the unbounded of the DC bus voltage estimation error, the instability of the LKFM during transient response increases exponentially. To standardize the MPC model and ensure bounded the DC bus voltage estimation error, a centralized controller design for DC bus voltage estimation error constrained is proposed in this paper. The proposed system model is constructed from DC/DC power converters and then translated into a deterministic model. Through measurements and time updates, the LKFM has been employed to estimate the DC bus voltage. The linear quadratic regulator is used for stabilizing the DC bus voltage estimation and current sharing error between DC/DC power converters. During a transient response, an integral action is utilized to close the loop and eliminate an error in DC bus voltage. A feedback control rule of the DC bus voltage estimation and a Riccati equation have been used to develop the proposed controller. Finally, the proposed approach was validated using Simulink, the Hardware-in-the-loop laboratory, and compared with conventional control approaches. Moreover, the LKFM's stability was examined using exponential stability criteria. [ABSTRACT FROM AUTHOR]

This paper presents a feasibility study on a waste heat recovery system for heavy-duty truck engines based on organic Rankine cycle (ORC) technology. The elements of novelty of the work are: i) the proposed plant configuration, and ii) the feasibility study that encompasses the whole preliminary design workflow of the system, namely, from the thermodynamic cycle optimization and the components preliminary sizing, to dynamic modelling and the design of a PI-based control system. The conceived ORC turbogenerator employs hexamethyldisiloxane (MM) as working fluid and achieves a maximum rated mechanical power of approximately 5 kW at the design point, corresponding to a truck cruise speed and a Diesel engine power output of 85 km h -1 and 100 kW respectively. Regarding the dynamic performance, the higher response time of the ORC unit compared to that of the Diesel engine makes the adoption of an advanced control system necessary. In particular, the simulation of a PI-based control system shows that it becomes impossible to prevent the thermal decomposition of the working fluid when the engine operates continuously at high power levels. This case study demonstrates the importance for automotive ORC applications of performing the investigation of dynamic performance and control design already in the early design phase. [ABSTRACT FROM AUTHOR]

• A high-speed data acquisition system was designed based on PXI Express. • The software adopts Visual Studio development environment and Visual C# language. • The system is integrated into the HL-2A centralized control system based on EPICS. • The Epics C# application was developed to realize the remote control under EPICS. • The system can work stably at 10KSps sampling rate. In order to meet the increasing experimental requirements of HL-2A tokamak device discharge and improve the integration of HL-2A host centralized control system, this paper designs a high-speed data acquisition system based on PXI Express. In order to enable the fast acquisition system to be integrated into the HL-2A host centralized control system under the EPICS platform for centralized control and management, it mainly describes how to realize the communication between fast acquisition signal system based on C# and the upper layer OPI through the PON network under the EPICS platform. The data acquisition system hardware adopts PXIe-based chassis, embedded controller and high-speed synchronous acquisition card, which has the advantages of good mechanical encapsulation, high modularity and high sampling rate. The software adopts a measurement and control system development platform based on Microsoft. NET platform, Visual Studio development environment and Visual C# language. In this paper, the Epics C# library was studied, the EPICS Server application was developed and the remote control of the state and parameters in HL-2A host engineering system was realized. The system runs stably in the HL-2A device 2018 experiment. The result shows that the system can work stably at 10KSps sampling rate, which can better meet the needs of the device operation. This work completed the basic framework of the HL-2A Tokamak host centralized control system. And the technology and method can provide reference for the design of the next-generation device HL-2 M host centralized control system of the, laying a good foundation. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

• A comprehensive review of secondary level control structures has been studied. • Communication network subjects and control methods of microgrids are explained and discussed. • Major challenges of communication network on microgrid control have been analysed. • Time delay has been highlighted as an effective communication disturbance. The development of distributed energy resources in distribution networks has created a new concept called microgrids. Their control is one of the main development issues that must be addressed before any implementation process. In this paper, a comprehensive literature review of the main hierarchical control algorithms such as centralized, decentralized, and distributed, with a focus on the secondary level, with an emphasis on their main strengths and weaknesses are discussed and compared. Microgrid communication infrastructures allow the use of different control schemes for the secondary control layer which is given the importance of secondary control over the stable and reliable performance of microgrids, and the lack of comprehensive reference for researchers. Also, provides a literature review on current key issues regarding microgrid secondary control strategies with respect to communication network challenges. The issue of secondary control is discussed with a focus on challenges such as time delays. Also Distributed control methods at the secondary level to reduce the use of the communication network and subsequently reduce communication network delays are discussed. [ABSTRACT FROM AUTHOR]

This article presents a new scheme to design full matrix controller for high dimensional multivariable processes based on equivalent transfer function (ETF). Differing from existing ETF method, the proposed ETF is derived directly by exploiting the relationship between the equivalent closed-loop transfer function and the inverse of open-loop transfer function. Based on the obtained ETF, the full matrix controller is designed utilizing the existing PI tuning rules. The new proposed ETF model can more accurately represent the original processes. Furthermore, the full matrix centralized controller design method proposed in this paper is applicable to high dimensional multivariable systems with satisfactory performance. Comparison with other multivariable controllers shows that the designed ETF based controller is superior with respect to design-complexity and obtained performance. [ABSTRACT FROM AUTHOR]

Abstract: This paper studies models of centralized, decentralized and distributed control of excitation in a network of interacting purposeful agents. As examples, we analyze models of threshold behavior and mob control. [Copyright &y& Elsevier]

Abstract: The progress in FPGA technology has enabled FPGA-based reconfigurable systems to target increasingly sophisticated applications, which has led to a high control design complexity, resulting in longer design cycles. In this paper, we propose a control design approach for FPGA-based reconfigurable systems aiming at increasing design productivity. This approach is based on a semi-distributed control model that splits different control concerns (monitoring, decision-making and reconfiguration) between autonomous modular controllers and makes use of formalism-oriented design, to decrease the control design complexity and facilitate design verification, reuse and scalability. This model is composed of distributed controllers handling the self-adaptivity of the system reconfigurable regions and a coordinator to respect the system global constraints. To enhance design productivity, the proposed control model is generated automatically using a high-level modeling approach. This approach is based on MDE (Model-Driven Engineering) and the MARTE (Modeling and Analysis of Real-Time and Embedded Systems) standard, allowing to make low-level technical details transparent to designers and to automate code generation from high-level models. Experiments on the generated control systems showed that the proposed semi-distributed control model is more flexible, reusable and scalable than the centralized one, at the cost of a slight increase in required hardware resources. [Copyright &y& Elsevier]

• A new structure is presented for the centralized control of hybrid microgrids. • Improve system stability by modeling and analysis of all system state variables. • Recovery of voltage and frequency system in islanded condition and load changes. • Using bidirectional interface converter to improve voltage and frequency stability. • Comparison of centralized and decentralized control to reduce system fluctuations. In this paper, based on the nonlinear controller, a new structure is presented for centralized control of hybrid microgrids. In the proposed model, AC and DC buses are used to connect AC and DC sources and loads respectively. A bidirectional interface converter (BIC) is provided for the electrical and control connection of these two buses. Here, based on the generalized backstepping method (GBM), a new method is presented for integrated and simultaneous controlling of AC bus frequency and DC bus voltage. The advantages of this method are the centralized control of the hybrid microgrid, taking into account the dynamics of the whole system and the interaction of its state variables with each other. Harmonized and optimal exchange of power and precise regulation of control signals in this structure has led to improved stability and thus improved system performance. The comparative results of centralized and decentralized control show the efficiency of the proposed model to reduce fluctuations and improve the stability of the system. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents a method to decrease the number of inputs needed to control a system comprised of a large set of subsystems. The method couples the inputs of the subsystems using a row–column structure, thus reducing the number of inputs from to . The resulting underactuated system is shown to maintain complete controllability if the subsystems are decoupled. Feedback for the entire system is performed by reducing the dimension of the subspace of the control inputs from a high dimension to one dimension using singular value decomposition. A stability condition for this feedback loop is presented based on the small gain theorem. In addition, the effect of the dimension reduction is explained using a simulation example. [Copyright &y& Elsevier]

Abstract: In recent years, distributed generations based on natural energy or co-generation systems are increasing due to global warming and reduction of fossil fuels. Many of the distributed generations are set up in the vicinity of customers, with the advantage that this decreases transmission losses and transmission capacity. However, output power generated from renewable energy such as wind power and photovoltaics, is influenced by weather conditions. Therefore if the distributed generation increases with conventional control schemes, the voltage variation in a distribution system becomes a serious problem. In this paper, an optimal control method of distribution voltage with coordination of distributed installations, such as On Load Tap Changer (OLTC), Step Voltage Regulator (SVR), Shunt Capacitor (SC), Shunt Reactor (ShR), and Static Var Compensator (SVC), is proposed. In this research, the communication infrastructure is assumed to be widespread in the distribution network. The proposed technique combines genetic algorithm (GA) and Tabu search (TS) to determine the control operation. In order to confirm the validity of the proposed method, simulation results are presented for a distribution network model with distributed (photovoltaic) generation. [Copyright &y& Elsevier]

This paper describes a controller hardware-in-the loop (C-HIL) approach for testing centralized and distributed secondary frequency control schemes of AC microgrids operating in islanded mode. We describe the formulation of the secondary frequency control problem and the theory behind the centralized and distributed implementations of the control schemes. Then, we describe the testbed utilized for C-HIL testing activities. Finally, we provide the testing results that compare the performance (in terms of the system response time), and resilience (in terms of withstanding the failure of a control device), of both schemes. [ABSTRACT FROM AUTHOR]

Microgrids based on renewable energy require energy storage systems to mitigate the power imbalances that arise due to variable and intermittent nature of renewable sources. Battery energy storage system (BESS) has been widely used to provide the necessary support. However, higher cost and limited life depending on number of charging and discharging cycles, restricts its application. The calendar life of the BESS can be improved by optimizing the control operation of the battery. This paper presents a control strategy for distributed BESS in a centrally controlled microgrid to enhance the calendar life of BESS. The proposed strategy controls the charging and discharging of individual batteries based on state of charge (SOC), state of health (SOH) and maximum capacity. The controller selects the BESS with better health and higher capacity for operation on priority resulting in better calendar life of the energy storage system. The simulations results for the test system indicates an overall improvement in calendar life of BESS by 57%. [ABSTRACT FROM AUTHOR]

• Renewable asset management in long-term planning and short-term operation. • Asset profitability maximization, as long as ensuring technical and market compliance. • Energy storage degradation models from experimental and semi-empirical testing. • Novel state of charge equalization technique thanks to renewable complementarity. • Impact of centralized asset control on storage lifetime enhancement. On the path to increase the renewable penetration level in power systems, energy storage systems are increasingly considered a key flexible technology to support renewable operation. Despite the reduction of ESS capital costs and their progressive inclusion in electricity markets, the major challenge is to develop new cost-effective business cases for renewable sources and electrical storage devices, which operate in aggregation and participate reliably in electricity markets as well as provide additional ancillary services. The main goal of the paper is to propose a centralized energy management strategy focused on portfolio scheme maximization including favorable market opportunities, such as continuous intraday market and frequency restoration reserve. Besides conventional cost function maximization, the consideration of technical aspects in the optimization allows high reliability of reserve requirements and reduction of energy imbalances. The main research contribution is the novel centralized supervisory control in real-time operation compared to a decentralized approach. This centralized control re-allocates reserve energy to achieve full market compliance and takes advantage of renewable complementarity to apply an innovative state of charge technique which minimizes battery stress and enhances their lifetimes. Therefore, in addition to the optimal storage sizing analysis, storage capacity fade and expected lifetime are accurately estimated according to the operation by means of experimental cycling and calendar aging models to calculate investment and replacement costs. Finally, a techno-economic evaluation of the cost-effectiveness of storage integration is provided. [ABSTRACT FROM AUTHOR]

• A robust centralized controller is designed for an islanded DC microgrid. • The DGs of microgrid have parametric uncertainties and are exposed to input–output disturbances. • LMI approach is used to design the controller. • The proposed controller is robust against the disturbances and uncertainties. In this paper, a new robust centralized controller for a DC islanded microgrid is proposed. The proposed controller is designed to be robust against parametric uncertainties of the distributed generation units and to attenuate exogenous disturbances. In order to design the controller, a multi-input–multi-output, linear time-varying model of the DC microgrid is obtained. The upper and lower bounds of the uncertainties are determined by a Lebesque-measurable matrix, and a norm reduction criterion is applied for disturbance rejection. Moreover, it is assumed that all states of the system are measurable; thus, the state-feedback scheme is considered. The system stability is guaranteed by the Lyapunov theory. Linear matrix inequality constraints are formulated for the system and are solved for sub-optimal controller gains. The robustness of the proposed controller is verified via simulations, and the proposed control method is compared with existing schemes. [ABSTRACT FROM AUTHOR]

• A centralized control strategy for an AC meshed MG is presented. • The strategy facilitates the management of power systems including several MGs. • The MG can be operated as a Virtual Synchronous Machine (VSM). • An extended load flow model is used to identify the PQ production of each DG source. This paper proposes a centralized control strategy for distributed generation (DG) sources connected to an AC meshed microgrid (MG). Through the proposed strategy, power production of distributed generators is managed such that the injected active and reactive powers at the point of common coupling are equal to predefined set-points. Thus, the MG is able to provide the main ancillary services including frequency and voltage control. An extended load flow model is used to identify active and reactive power production of each DG unit such that the total power injected to the utility grid satisfies the required setpoints. Hence, from the point of view of the transmission system operator (TSO), the whole MG can be seen as a single entity that behaves as a «PQ» generator. This control is intended to facilitate the management of power systems including a large number of microgrids and DG sources in terms of stability analysis, optimal reactive power dispatch, optimal power flow, etc. Furthermore, since the centralized control allows to set «PQ» power production to any predefined value, it was proposed to operate the whole MG using the concept of Virtual Synchronous Machine (VSM). It has been shown that, through the proposed control, the MG can reproduce the behavior of conventional synchronous generators during normal conditions and during faults. [ABSTRACT FROM AUTHOR]