Voltage Regulation In DC Microgrids Research Articles

A model predictive control based MPPT technique for novel DC-DC converter and voltage regulation in DC microgrid

A model predictive control based MPPT technique for novel DC-DC converter and voltage regulation in DC microgrid

Passivity-Based Power Sharing and Voltage Regulation in DC Microgrids With Unactuated Buses

Passivity-Based Power Sharing and Voltage Regulation in DC Microgrids With Unactuated Buses

Fixed-Time Secondary Controller for Rapid State-of-Charge Balancing and Flexible Bus Voltage Regulation in DC Microgrids

Fixed-Time Secondary Controller for Rapid State-of-Charge Balancing and Flexible Bus Voltage Regulation in DC Microgrids

Distributed Secondary Control Based on Dynamic Diffusion Algorithm for Current Sharing and Average Voltage Regulation in DC Microgrids

Distributed Secondary Control Based on Dynamic Diffusion Algorithm for Current Sharing and Average Voltage Regulation in DC Microgrids

Design of Fuzzy PI Controller for Voltage Regulation in DC Micro-Grid

Efficiency, standard and security of a micro-grid can be tested by measuring the voltage regulation in the DC bus. Photovoltaic micro-grid are prone to time invariant and non-linearity due to variation in solar irradiance. Energy storage device is incorporated to overcome such variations. Traditionally using PI controllers, we can control the charging and dis-charging of battery which only regulates voltage in the bus but it fails to control the fluctuations in the DC bus. Therefore, Fuzzy PI controller is proposed in this paper where it employs the intelligent controlling method thereby reducing the fluctuations in the DC bus. Keywords—Fuzzy, PI, Fuzzy-PI, DC-micro-grid, closed loop control, voltage regulation.

Autonomous DC-Bus Voltage Regulation in DC Microgrid Using Distributed Energy Storage Systems

A DC microgrid has many advantageous features, such as low power losses, zero reactive power, and a simple interface with renewable energy sources (RESs). A bipolar DC microgrid is also highlighted due to its high-power quality, improved reliability, and enhanced system efficiency. However, the bipolar DC microgrid has high DC bus voltage fluctuation due to the load power unbalance between the poles. Therefore, this paper analyzes the DC bus voltage fluctuation that can occur in the bipolar DC microgrid. An autonomous grid voltage regulation method is introduced to regulate the DC bus voltage of a bipolar DC microgrid using distributed energy storage systems (ESSs). The proposed grid voltage regulation scheme using the distributed ESSs could regulate DC bus voltage in real time, regardless of the structure of the DC microgrid without external communication. Lastly, experimental results using a lab-scale bipolar DC microgrid prototype verified the proposed method.

Distributed Periodic Event-Triggered Optimal Control of DC Microgrids Based on Virtual Incremental Cost

This article presents a distributed periodic event-triggered (PET) optimal control scheme to achieve generation cost minimization and average bus voltage regulation in DC microgrids. In order to accommodate the generation constraints of the distributed generators (DGs), a virtual incremental cost is firstly designed, based on which an optimality condition is derived to facilitate the control design. To meet the discrete-time (DT) nature of modern control systems, the optimal controller is directly developed in the DT domain. Afterward, to reduce the communication requirement among the controllers, a distributed event-triggered mechanism is introduced for the DT optimal controller. The event-triggered condition is detected periodically and therefore naturally avoids the Zeno phenomenon. The closed-loop system stability is proved by the Lyapunov synthesis for switched systems. The generation cost minimization and average bus voltage regulation are obtained at the equilibrium point. Finally, switch-level microgrid simulations validate the performance of the proposed optimal controller.

Distributed control for state‐of‐charge balance and load voltage regulation in DC microgrids with clustered generations

AbstractIn this paper, the issue of state‐of‐charge balance and load voltage regulation of DC microgrids used in solar‐powered vehicles is investigated. The system consists of multiple distributed generation units, each of which is equipped with photovoltaic cells and energy storage systems. Based on the information shared among the neighbors, a single‐layered distributed control strategy is proposed to solve two aspects of the problem simultaneously. Rigorous analysis of the closed‐loop system ensures stability and the effectiveness of the control strategy. The power constraints of each distributed generation unit are taken into consideration so that safety and applicability are guaranteed. To avoid the cycling of the batteries, the state‐of‐charge balance is achieved by regulating the output power feeding a common load, promoting efficiency and battery life. The proposed controller operates without any knowledge about load, line impedance, and global information of communication network, and consequently possesses the capability of plug‐and‐play. Finally, the effectiveness and applicability are illustrated by an example from the Sky‐Sailor project.

Centralised and decentralised data communication scheme for voltage regulation in DC Microgrids

Voltage regulation is one of the main control issues in DC Microgrids (MGs). To achieve voltage regulation in MGs, exchange information between distributed generation units (DG) is inevitable. There are two types of data exchange proposed and discussed, centralised and decentralised data communication schemes. Many papers in the literature did not give attention to the type of data communication infrastructure that will have a significant impact on both centralised and decentralised schemes. This paper proposes centralised and decentralised data communication scheme and their impact on voltage regulation in DC MGs. The dynamic performance of a DC MG with loads fluctuations, operating with the proposed technique, is evaluated through simulation analyses, realized in MATLAB. Both the proposed centralised and decentralised methods are able to maintain the voltage within acceptable limit during loads fluctuations; however the centralised method is around five times faster than the decentralised method. The results show the superiority of the proposed method for the DC MGs operations during load demands fluctuations, loads varieties, communication delays and structures.

Enhancing Voltage Regulation in DC Microgrids Using a Price Incentive Load Management Approach

Enhancing Voltage Regulation in DC Microgrids Using a Price Incentive Load Management Approach

A Two-Layer Control Scheme Based on P – V Droop Characteristic for Accurate Power Sharing and Voltage Regulation in DC Microgrids

The increasing penetration of dc distributed energy resources (DERs) and dc loads has motivated the utilization of dc microgrids (MGs). In this paper, a new two-level control scheme is proposed for accurate power sharing and appropriate voltage regulation in dc MGs during islanded operation mode. In the primary control level, a P-· V droop method is proposed to eliminate the dependency of power sharing among DERs on line resistances. Since the P-· V droop deviates the voltage derivative to a nonzero value, a voltage derivative restoration mechanism is adopted in the secondary control level to provide voltage stability. The secondary control level also compensates the voltage deviations by cascading an outer voltage control loop with the inner voltage derivative restoration loop. The secondary control signal is broadcasted to each DER via a unidirectional low-bandwidth communication link. Small signal stability of the proposed scheme is analyzed by studying the locus of the system eigenvalues. To verify the efficacy of the proposed method and compare it with the conventional scheme, real-time simulations in OPAL-RT lab setup are provided.

Fully Distributed Discrete-Time Control of DC Microgrids With ZIP Loads

In a multibus dc microgrid, both the constant power loads (CPLs) and the discrete-time (DT) sampling of digital controllers tend to destabilize the system. To address these issues, a novel distributed DT control scheme is presented in this article to achieve proportional load current sharing and weighted average bus voltage regulation in dc microgrids with constant impedance loads, constant current loads, and CPLs (ZIP loads). First, a dc microgrid model with ZIP loads is established in the DT domain, based on which the distributed DT controller is developed. A sparse communication network is then exploited to achieve the proportional load current sharing by exchanging sampled current information between neighbors. Specifically, a distributed voltage observer utilizing the neighbors’ current information and local voltage information is designed to estimate and regulate the weighted average bus voltage. To alleviate the destabilizing effect induced by the DT sampling of digital controllers, a constrained condition on control gains is established. Additionally, a sufficient condition on CPLs that guarantees their negative impact on stability being locally counteracted is proposed. Through Lyapunov synthesis, the objectives of current sharing and voltage regulation are proved to be achieved simultaneously. Simulation studies on a detailed switch-level model validate the control scheme and demonstrate its robustness against communication network imperfections and the capability of accommodating plug-and-play operations.

Integrated control scheme for dynamic power management with improved voltage regulation in DC microgrid

This article presents an integrated control scheme to improve power sharing for power management and voltage regulation in DC microgrids. The proposed scheme considers the available power and the stochastic nature of sources to achieve adequate power sharing among them. Therefore, it achieves effective utilization of each source. In addition, the effective use of energy storage systems (ESSs) is also achieved by reducing their charging/discharging cycles. The proposed control scheme improves voltage regulation under various operating conditions. It enhances the stability of microgrids and improves their dynamic response. The proposed control scheme is adaptive to changes in the source or load. It operates without historical/previous data, which reduces the computational burden. The proposed control scheme is experimentally validated under diverse operating conditions.

Voltage-Based Distributed Optimal Control for Generation Cost Minimization and Bounded Bus Voltage Regulation in DC Microgrids

In conventional DC microgrid control schemes, optimization and real-time control are usually performed at different time scales. It is hard for such control schemes to achieve real-time optimization. Even a small disturbance can result in deviations of bus voltages and output currents from their optimal operating points. In addition, most real-time controllers cannot guarantee the satisfaction of pre-defined constraints on individual bus voltages due to the disconnection between steady-state optimization and real-time control. In this paper, a distributed optimal control scheme is presented for DC microgrid. The objectives are to simultaneously realize generation cost minimization and individual bus voltage regulation. First, the optimal control problem is formulated, based on which a necessary and sufficient optimality condition is derived that characterizes the optimal operating points. The distributed optimal controller is then proposed to dynamically drive the system to operate at the optimality condition. Convergence to the optimal operating points that minimizes generation cost under constraints is guaranteed through rigorous Lyapunov synthesis. Each individual bus voltage can also be maintained within bounds in both transient- and steady-state. The performance of the proposed controller is validated through simulations based on a switch-level microgrid model.

Voltage Regulation of DC-Microgrid With PV and Battery

This paper studies voltage regulation and maximum power point tracking (MPPT) control for a DC-microgrid that includes a photovoltaic (PV) panel, battery, constant resistance and constant power loads. A dynamic model of the DC-microgrid system described by a multi-input and multi-output nonlinear system with non-affine inputs is derived. Based on this nonlinear dynamic model, we use output regulation theory to design a local state feedback controller that regulates voltages to prescribe set points and maximizes PV power output. Global set point regulation is also studied using passive system theory for non-affine systems and Lyapunov stability theory. The effectiveness of the proposed control schemes is investigated using simulations when changes in both illumination and load occur.

A Consensus-Based Algorithm for Power Sharing and Voltage Regulation in DC Microgrids

In dc microgrids, load power sharing and bus voltage regulation are two common control objectives. In this article, a consensus-based algorithm is presented to achieve proportional power sharing and regulation of weighted geometric mean of bus voltages in dc microgrids with ZIP (constant impedance, constant current, and constant power) loads simultaneously. By using the virtue of the Laplacian matrices of undirected connected graphs, a lemma is derived to assist the stability analysis of the dc microgrids. Thus, a sufficient condition that stabilizes the system with ZIP loads is established. In addition, with the help of a distributed voltage regulation error estimator, the tuning of the bus voltages can be realized without the requirement on initial voltage conditions. Through the Lyapunov synthesis, the large-signal stability of the closed-loop system is theoretically ensured for a wide range of load conditions. Finally, simulation studies are performed to validate the merits of the proposed consensus-based algorithm.

Distributed Periodic Event-Triggered Algorithm for Current Sharing and Voltage Regulation in DC Microgrids

In modern control systems, most control algorithms, especially system-level ones, are implemented in discretetime (DT) with digital controllers and digital communications. In this paper, a distributed DT algorithm is developed to achieve proportional load current sharing and average bus voltage regulation in DC microgrids. In order to reduce the communication requirement among the controllers, a periodic event-triggered (PET) DT algorithm is proposed by introducing a novel PET condition. Since the PET condition is detected periodically, the Zeno phenomenon existing in continuous-time (CT) event-triggered algorithms can be avoided. The communication burden for detecting the PET condition is also relieved since only the local and neighbors' triggered information is required. Through the Lyapunov synthesis, the current sharing error is proved to converge to zero asymptotically. Finally, comparative results among different algorithms, based on a detailed switchlevel microgrid model, are given to validate the effectiveness of the proposed PET control design.

Compromised Controller Design for Current Sharing and Voltage Regulation in DC Microgrid

Since a DC micro-grid consists of power converters connected through different line impedances, tuning of the voltage controller provides a simple and intuitive tradeoff between the conflicting goals of voltage regulation and current sharing. A highly flexible distributed control strategy is proposed to achieve the balanced control between the two control objectives, which includes the containment-based voltage controller and consensus-based current controller. The terminal voltage can be bounded within a prescriptive range which means each terminal voltage is controllable instead of only controlling the average voltage; meanwhile, the current-sharing performance can be regulated among converters. The two objectives, including either bounding voltages tightly or decreasing current sharing errors, can be compromised between each other by tuning the weightings of controllers. The large-signal model is developed to analyze the tuning principle about different control parameters. The proposed strategy can provide flexible control performance according to various control requirements. Experimental results and comparisons are illustrated to verify the effectiveness of the proposed method and compromised tuning under resistive loads and constant power loads, dynamic voltage boundary conditions.

Voltage Regulation of DC-Microgrid with PV and Battery: A Passivity Method

This paper presents voltage regulation and maximum power point tracking (MPPT) control schemes for a class of DC-microgrids. The DC-microgrid under consideration consists of a photovoltaic (PV) panel, battery, along with constant resistance and constant power loads. In this study, a dynamic model of the DC-microgrid system is derived and described by a multi-input and multi-output nonlinear system with non-affine inputs. Based on the nonlinear model thus built, we design nonlinear controllers that globally regulate voltages to prescribe set points and maximize the power output from PV by virtue of passivity and Lyapunov stability. The effectiveness of the proposed control schemes is validated by simulations.

A Robust Consensus Algorithm for Current Sharing and Voltage Regulation in DC Microgrids

In this paper, a novel distributed control algorithm for current sharing and voltage regulation in DC microgrids is proposed. The DC microgrid is composed of several distributed generation units, including buck converters and current loads. The considered model permits an arbitrary network topology and is affected by an unknown load demand and modeling 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 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.