Control Scheme For DC Microgrids Research Articles

A Novel Scalable and Reliable Control for DC Microgrids With Varying Number of Agents.

Existing scalable control methods mainly rely on a fixed block-diagonal structure for the Lyapunov matrix, potentially resulting in numerical infeasibility issues. To overcome this limitation, this article proposes a novel scalable and reliable control scheme for dc microgrids. Initially, a general model for dc microgrids is established to enhance reliability, considering scenarios involving loss of control effectiveness (LoCE) and offset faults. Subsequently, a structured free-weight matrix technique is introduced to mitigate negative coupling effects of power lines, and to address numerical infeasibility by avoiding the assumption about the Lyapunov matrix. Furthermore, the stability of the entire dc microgrid is guaranteed by checking local agent conditions, independently of power line couplings. Therefore, the proposed control scheme ensures plug-and-play scalability with varying number of agents. Finally, theoretical results are validated through numerical simulations using the MATLAB/SimPowerSystems toolbox.

A Decentralized Resilient Control Scheme for DC Microgrids Against Faults on Sensor and Actuator

A Decentralized Resilient Control Scheme for DC Microgrids Against Faults on Sensor and Actuator

Distributed economic nonlinear MPC for DC Micro-Grids with inherent bounded dynamics and coupled constraints

This paper proposes a hierarchical control scheme for DC Micro-Grids (MGs) composed of distributed energy resource (DER) units, active loads, and coupled constraints, that incorporates different control levels to achieve economic operation and coupled constraint satisfaction at all times. All loads are considered as constant power loads (CPLs), which are known to lead to instability due to the negative impedance characteristics. To this end, firstly an improved version of the recently developed sl-PI controller is introduced in the primary level to provide boundedness and local stability of the dynamics. The supervisory controller solves an economic optimisation problem to compute voltage setpoints and at a lower control layer the system is driven to those setpoints, by utilising a distributed nonlinear MPC setup with non-iterative, neighbour-to-neighbour communication framework. A rigorous analysis on the system robustness to uncertainties in the exchanged information and bounded load variations is provided, and recursive feasibility and stability of each subsystem is analytically proven for the first time, according to the authors’ knowledge. Finally, we demonstrate the proposed controller with the aid of simulated scenarios for a DC MG with multiple DER units and CPLs.

An Adaptive Droop Control Scheme for DC Microgrids Integrating Sliding Mode Voltage and Current Controlled Boost Converters

One of the most widely used techniques for controlling the dc microgrid is the droop control method. The associated problems of the droop-based systems, such as the current sharing errors and the voltage deviation are solved using current sharing loops and secondary control loop, respectively. This paper presents an adaptive droop scheme for dc microgrids to overcome the non-linearity of the system. The droop resistance is adjusted using the adaptive PI controller to eliminate the current sharing error of each unit in the microgrid. In addition, another adaptive PI controller is dedicated for the secondary loop to regulate the dc bus voltage of the microgrid by shifting the droop lines. In the proposed scheme, only the current and voltage at the dc bus of the microgrid need to transmit through low-bandwidth communication channels to individual units. Moreover, the sliding mode control, which is distinguished by robustness and fast dynamic response, is utilized to manipulate the output voltage and the input current of each converter, instantaneously. The dynamic performance of the proposed adaptive droop scheme is evaluated using the PSCAD/EMTDC simulation package.

Event-Triggered Communication Based Distributed Control Scheme for DC Microgrid

Development of microgrids and wide spread deployment of renewable generation and energy storage systems have highlighted the need for distributed control schemes to achieve maximum utilization and coordination among all the connected resources. In DC microgrids, the key goals of system-wide control are droop-based current sharing and network dc-voltage regulation. These may be achieved using a consensus algorithm secondary control that a) averages all the node voltages dynamically and maintains them at a nominal value and b) based on information from neighboring source currents to converge to a consensus in current sharing. Achieving the dynamic consensus may impose significant communication burden when implemented using conventional periodic communication methods. In this paper, an event-triggered communication based dynamic consensus algorithm is proposed that helps achieve both the stated goals of proportional current sharing along with average DC voltage regulation in a DC microgrid. The convergence and stability of the modified dynamic consensus algorithm and event triggering condition is proven using Lyapunov's stability criterion. The proposed control is applied to a DC microgrid system for secondary control of voltage and current regulation, and the performance of the proposed technique is validated under various operating conditions and disturbance in the communication system in both simulation and hardware environment.

Robust distributed cooperative control for DC mircogrids with time delays, noise disturbances, and switching topologies

This paper develops a robust consensus-based distributed cooperative control scheme for DC microgrids with asymmetric time delays and switching topologies in noisy environments. The proposed distributed cooperative control scheme, consisting of a leader-following consensus-based distributed voltage controller and a consensus-based distributed load current controller, is to respectively regulate the voltage of DC microgrids to the desired value and achieve the cost-based load current sharing through a sparse communication network (i.e., a distributed low bandwidth communication network) with asymmetric communication delays, switching topologies and noise disturbances. Moreover, the proposed controllers are implemented through sparse communication networks and thus meet the plug-and-play feature of microgrid power systems. Based on the Lyapunov–Krasovskii functional method and stochastic differential equation theory, the criteria for the stability analysis and delays boundedness to maintain the system stable are derived. The effectiveness of the proposed control methods are verified by the simulation of a DC microgrid system in MATLAB/SimPowerSystems.

An Improved Distributed Secondary Control Method for DC Microgrids With Enhanced Dynamic Current Sharing Performance

This paper proposes an improved distributed secondary control scheme for dc microgrids (MGs), aiming at overcoming the drawbacks of conventional droop control method. The proposed secondary control scheme can remove the dc voltage deviation and improve the current sharing accuracy by using voltage-shifting and slope-adjusting approaches simultaneously. Meanwhile, the average value of droop coefficients is calculated, and then it is controlled by an additional controller included in the distributed secondary control layer to ensure that each droop coefficient converges at a reasonable value. Hence, by adjusting the droop coefficient, each participating converter has equal output impedance, and the accurate proportional load current sharing can be achieved with different line resistances. Furthermore, the current sharing performance in steady and transient states can be enhanced by using the proposed method. The effectiveness of the proposed method is verified by detailed experimental tests based on a 3 × 1 kW prototype with three interface converters.

An Enhanced Droop Control Method for Accurate Load Sharing and Voltage Improvement of Isolated and Interconnected DC Microgrids

In this paper, a distributed local control scheme for dc microgrid is proposed along with the basic droop control. It eliminates the limitations of droop control when the distributed generators are geographically distributed, for which, the line resistances cannot be neglected. Effects of line inductance and constant power loading (CPL) are investigated by analyzing the voltage tracking transfer function for single source system. Stability of two sources single load microgrid with proposed controller is investigated. Simulated responses are presented for two sources single load microgrid (for the sake of simplicity) to depict the proper load sharing and voltage improvement capability of the proposed control method with the consideration of line resistances. However, this can be extended to multiple-source multiple-load configuration connected to the dc bus. A comparison of the result is presented to show the better performance of the proposed control scheme as compared to the conventional droop control and hierarchical secondary control. The interconnected operation of the microgrid is also investigated to show the applicability of the proposed control in the interconnected mode. A centralized controller in each area is used to make the tie-line power flow zero at steady state.