Consensus-based Distributed Control Research Articles

Privacy-Preserving Robust Consensus for Distributed Microgrid Control Applications

Consensus-based distributed control has been proposed for coordinating distributed energy resources (DERs) in microgrids (MGs). As one key component, distributed average observers are used to estimate the average of a group of reference signals (e.g., voltage, current, or power). State-of-the-art distributed average observers could lead to loss of privacy due to information exchange on the communication channels. The DERs' reference signals, which contains private information, could be inferred by an eavesdropper. In this paper, a privacy-preserving distributed average observer is proposed, which is based on robust consensus and uses the state decomposition method to preserve privacy. Compared to the existing methods, the proposed observer does not require the knowledge of the reference signal's derivative and gives accurate and smooth estimation, and is thus applicable for MG distributed control applications. A detailed analysis regarding the convergence and privacy properties of the proposed observer is presented. The proposed observer is implemented on hardware controllers and validated in the context of distributed MG control applications through hardware-in-the-loop (HIL) tests.

Notice of Violation of IEEE Publication Principles:Consensus-Based Distributed Anti-Disturbance Control of DC Microgrids Over Fading Channels

This paper develops a novel consensus-based distributed anti-disturbance control scheme that can achieve current sharing of distributed generations (DG) and voltage restoration of DC bus in mean square subject to multiplicative measurement noises and communication delays over fading networks. Since the cyber channels are exposed to inherent communication delays, the measurement information exchange with noise interferences among multiple and cooperative DGs may be disturbed in fading communication networks, where fading may either be due to noises, delays, and shadowing from obstacles affecting the wave propagation. As a result, fading makes every DG receives incomplete/imprecise information from its neighbors. To dispel the adverse influences of measurement noises and time delays over fading networks, a washout filter-based distributed anti-disturbance control algorithm is developed for DC microgrids, in which only the current state variable is exchanged among DGs with the local decentralized voltage controller. By introducing stochastic theory and Lyapunov stability function, the criteria for the stability analysis and delays boundedness considering noise interferences is derived to ensure the stability operation of the whole closed-loop DC network. The obtained results show the effectiveness of the proposed strategy by a tested DC microgrid in OPAL-RT real-time simulator.

An overview on consensus-based distributed secondary control schemes in DC microgrids

An overview on consensus-based distributed secondary control schemes in DC microgrids

An enhanced consensus-based distributed secondary control for voltage regulation and proper current sharing in a DC islanded microgrid

A centralized secondary control is utilized in a DC islanded microgrid to fine-tune voltage levels following the implementation of droop control. This is done to avoid conflicts between current allocation and voltage adjustments. However, because it introduces a single point of failure, a distributed secondary control is preferred. This paper introduces a consensus-based secondary distributed control approach to restore critical bus voltages to their nominal values and properly distribute current among converters. The critical bus takes the lead in voltage adjustments, with only connected energy resources contributing to regulation. The microgrid is represented as an undirected graph to facilitate consensus building. Two adjustment terms, δv and δi, are generated to assist in returning voltage to its nominal level and correctly allocating current among energy resources. To enhance consistency and improve controller performance compared to those reported in existing literature, all buses are connected to a leader node. In the event of the failure of all converters except one, voltage can still be effectively restored. MATLAB-Simulink simulations are conducted on two medium-voltage DC (MVDC) microgrids to validate the efficiency of the proposed control method. The results confirmed that the proposed control method can effectively maintain voltage stability and enhance the precise distribution of current among agents by 8%.

Accurate consensus-based distributed secondary control with tolerance of communication delays for DC microgrids

Distributed secondary control is widely used in DC microgrids (MGs), which can achieve average voltage recovery and accurate power/current sharing among the distributed generators (DGs). In the distributed control architecture, a consensus-based average observer is usually desired to estimate the global average of the output voltage. However, the inevitable communication delay between DGs will cause the output average voltage to deviate from the rated. To tackle this problem, a novel dynamic average consensus observer based on bias compensation has been proposed in this paper, which can accurately converge to the average of the variables being tracked with tolerance of the bounded communication delay while getting rid of the harsh requirement for identical initial value of conventional distributed observer. Based on it, the proposed distributed secondary controller can ensure that the average output voltage converges to the rated without steady-state deviation and that the output currents are proportionally shared accurately. Instead of the conventional voltage and current dual secondary controller, the proposed secondary controller estimates the average of the voltage-current coupling variables and achieves the average voltage recovery and accurate current sharing simultaneously. Moreover, the communication delay margin is determined quantitatively. Finally, the performance of the proposed controller and the efficacy of the calculated communication delay margin is verified by real-time hardware-in-loop (HIL) tests.

A simplified consensus-based distributed secondary control for battery energy storage systems in DC microgrids

DC microgrids have become a promising solution for efficient and reliable integration of renewable energy sources (RESs), battery energy storage systems (BESSs) and loads. To simultaneously achieve average voltage regulation, accurate current-sharing and state-of-charge (SoC) balance, at least two state variables need to be transmitted between neighboring BESS nodes in conventional distributed secondary control. In this paper, a simplified consensus-based distributed secondary control for BESSs in DC microgrids is proposed with only one virtually defined state variable being transmitted, where a cascaded control framework consisting of an SoC controller and a voltage controller is used to regulate DC bus voltages. This virtual state variable combines BESS SoC and its converter output current, there is no need to change the control law when BESSs switch between charging/discharging modes. Once SoCs are balanced, SoC controller works as a current controller. With the proposed control strategy, the number of transmitted state variables and the complexity of controller design are significantly reduced. Stability and steady-state analysis are also conducted to confirm the effectiveness of the proposed control strategy. Finally, Simulink simulation and hardware-in-loop tests are presented to validate the proposed control strategy.

A Consensus-Based Distributed Secondary Control Optimization Strategy for Hybrid Microgrids

In this paper, a new consensus-based distributed secondary control (DSC) strategy is proposed for frequency control, dc-voltage regulation, and optimal dispatch (OD) in isolated hybrid ac/dc-microgrids (HMGs). At the same time, all the units are maintained within limits. The proposed control scheme dispatches the distributed generators (DGs) within the microgrid in compliance with the Karush-Kuhn-Tucker (KKT) conditions of a linear optimal power flow (OPF) formulation. Furthermore, the power through the interlinking converters (ICs) is also dispatched to help minimize the total operation cost of the microgrid. The controllers rely on local measurements and information from neighbouring devices at both sides of the microgrid (DGs and ICs). Thus, unlike conventional methods, the microgrid is considered a single entity and not as three independent systems interacting with one another, and the OD is calculated considering both the ac-DGs and dc-DGs. Extensive simulations demonstrate a good performance of the controller amid load step changes and unit congestion, driving the system to an optimal economic operation.

Distributed control for multiple hybrid energy storage systems using consensus algorithm in direct current power supply system

Multiple hybrid energy storage systems (multi-HESSs) consisting of batteries and supercapacitors (SCs) is widely used to share the requirement of system pulsating power, reducing the dependence on a single hybrid energy storage system (HESS) to improve the system reliability. The filter composed of virtual resistance droop control (VRDC) and virtual capacitance droop control (VCDC) in a HESS can achieve frequency distribution of pulsating power between a battery and SC. However, it suffers from the output voltage deviation and terminal voltage variation. Mismatched line impedances and different system parameters can cause different output voltages and inaccurate current sharing in the multi-HESSs. Meanwhile, the differences in the terminal voltages of SCs can affect the transient output capability. Therefore, this paper proposes a consensus-based distributed control strategy (CDCS) for multi-HESSs, which not only achieves global average output voltage and current sharing for batteries but also realizes restoration and consistency of SCs terminal voltage. The state variable information of adjacent converters for multi-HESSs is exchanged by the sparse communication network, and the steady-state analysis of state variables is proved. The direct current (DC) power supply system with four HESSs is established to verify the effectiveness of the proposed control strategy.

Combining Data-Driven and Model-Driven Approaches for Optimal Distributed Control of Standalone Microgrid

This paper focuses on the comprehensive restoration of both voltage and frequency in a standalone microgrid (SAMG). In a SAMG, the power balance is achieved through traditional methods such as droop control for power sharing among distributed generators (DGs). However, when such microgrids (MGs) are subjected to perturbations coming from stochastic renewables, the frequency and voltage parameters deviate from their specified values. In this paper, a novel hybrid-type consensus-based distributed controller is proposed for voltage and frequency restoration. Data-based communication is ensured among the DGs for controlling voltage and frequency parameters. Different parameters such as voltage, frequency, and active and reactive power converge successfully to their nominal values using the proposed algorithms, thereby ensuring smooth operation of inverter-dominated DGs. Additionally, the machine-learning-based long short-term memory (LSTM) algorithm is implemented for renewable power forecasting using historical data from the proposed location for visualising the insolation profile. The effectiveness of our approach is demonstrated through a SAMG, which consists of four inverters, showing that the proposed approach can improve system stability, increase efficiency and reliability, and reduce costs compared to traditional methods. The complete study is performed in Python and MATLAB environments. Our results highlight the potential of data-driven approaches to revolutionise power system operation and control.

Consensus-based distributed formation control for coordinated battle system of manned/unmanned aerial vehicles

In this paper, a consensus-based distributed formation control method is proposed for improving the coordinated battle efficiency of coordinated battle system for manned/unmanned aerial vehicles (MAV/UAVs). The method proposed is designed based on consensus protocol, which contains three parts. First, the distributed structure with limited centralized strategy for MAV/UAVs cooperative system is designed. Second, a second-order dynamic model is built up to describe the distributed formation system, which is further simplified using feedback linearization method. Third, the information exchange topology of MAV/UAV-coordinated battle system is established on the basis of graph theory and leader–follower mechanism. Finally, the effectiveness of the proposed formation strategy for MAV/UAVs cooperative system is proved asymptotic convergence by constructing a reasonable Lyapunov function which guarantees the accurate formation maintenance. Simulation results are presented to demonstrate the effectiveness of the proposed method. And comparative simulation results reveal that the method proposed in this paper is superior to traditional algorithms in the aspects of accuracy and stability.

Distributed dual objective control of an energy storage system under jointly connected switching networks

This paper studies a dual objective control problem for an energy storage system (ESS) consisting of multiple independently-controlled energy storage units (ESUs). The power output of the entire ESS is designed to meet its reference, and meanwhile the state-of-energy (SOE) of all the ESUs maintains to be balanced. In practice, the communication among ESUs might be unreliable and thus is modeled by jointly connected switching networks. By making use of the so-called Generalized Krasovskii–LaSalle Theorem together with a novel two-step recursive analysis method, it is rigorously proven that the dual objective control problem subject to jointly connected switching networks can be solved by a consensus-based distributed control algorithm.

Privacy-Informed Consensus-Based Secondary Control in Cyber-Physical DC Microgrids

This letter proposes a privacy-informed consensus-based distributed secondary control strategy for cyber-physical dc microgrids. The proposed secondary control approach relies on output masks that transform the physical states of distributed generation (DG) units to some auxiliary states by adding local perturbation signals, whose functional form and parameters are local and chosen independently by each DG unit. The proposed privacy-preserving secondary control scheme ensures voltage balancing and proportional current sharing in dc microgrids without disclosing the physical states of distributed generation units to their neighbors. Simulation case studies confirm the theoretical results of this letter.

A Robust Cooperative Distributed Secondary Control Strategy for DC Microgrids With Fewer Communication Requirements

This article proposes a robust cooperative distributed secondary control strategy for dc microgrids, with the main focus on reducing communication burdens. To this end, we adopt a sparsity-promoting consensus-based distributed secondary control framework for converter-interfaced dc microgrids consisting of multiple distributed generation (DG) units. The proposed control strategy relies on less (sparse) information exchange over a communication network and does not require exchanging voltage signals or their estimated values amongst neighboring DG units. Rigorous Lyapunov-based stability certificates for dc microgrids are derived. The stability conditions can be verified without the knowledge of distribution lines connecting different DG units. The effectiveness of the proposed secondary control approach is verified by experimental results and a comparative simulation case study on a multiple-DG dc microgrid.

Distributed control strategy for voltage and frequency restoration and accurate reactive power-sharing for islanded microgrid

For a conventional droop-controlled islanded microgrid, the poor reactive power-sharing and drop of bus voltage and frequency caused by line impedance mismatch and droop characteristics are inevitable. So far, consensus-based distributed control algorithms, in which a secondary control layer with the integration of voltage and frequency restoration and reactive power-sharing compensation mechanisms, has been treated as a promising solution. However, for most of the currently available distributed algorithms, it is the active power-sharing rather than the reactive power-sharing that was made the control goal, which is opposite to the fact that accurate power-sharing could always hold considering the integration effect in the active power control loop. Although a few recently published distributed algorithms added the reactive power-sharing goal in the second control layer, the system efficiency and reliability may deteriorate because a large circulating current could be induced at the malfunction of the communication network since there is no virtual impedance injected at the bottom control layer to limit that. This paper proposes a voltage and frequency restoration method based on the dynamic average consensus algorithm and an accurate reactive power-sharing method based on a first-order consensus algorithm and virtual impedance method. A simple pseudo-unidirectional communication network with a narrow communication band is adopted for the proposed distributed control to lower the communication burden and system complexity. The operational principle is first analyzed in detail. The proposed strategy is easily implementable and features not breaking droop characteristics. Then simulations and hardware-in-the-loop (HIL) real-time experiments verify the proposed approach.

Cyber-Attacks in Modular Multilevel Converters

Distributed control of modular multilevel converter (MMC) submodules (SMs) offers several potential benefits such as flexibility, scalability, and modularity. In this approach, low-level control tasks, such as capacitor voltage balancing, can be distributed amongst controllers placed in the SMs. This decreases the computational burden for the central control system that performs high-level control tasks; also, a single point of failure is avoided. Distributed control architecture requires a cyber-physical network (CFN) through which local controllers share all the information necessary to perform their respective control loops. To date, none of the reported works in this field have paid attention to potential imperfections in the CFN. Indeed, previous works are based on the assumption that the network always provides correct information to the local controllers. However, erroneous measurements in the CFN may degrade the distributed control scheme operation, leading to suboptimal or even unstable operation. These events can occur in the presence of cyberattacks, for example, which can be created through illegitimate data intrusion into the distributed control architectures. This article is the first to investigate the impacts of cyberattacks on distributed control schemes used in MMCs. The effects of a specific cyberattack, named false data injection attack (FDIA), on a consensus-based distributed control strategy are studied in this article. Additionally, a method for detecting FDIAs is proposed, along with a countermeasure strategy, to ensure the safe operation of the MMC, while the attack is cleared. The proposals reported in this article are validated using simulation and experimental results.

Cyber-Resilient Sliding-Mode Consensus Secondary Control Scheme for Islanded AC Microgrids

In this article, a cyber-resilient consensus-based distributed control scheme is proposed for islanded ac microgrids. Considering the impacts of false data injection (FDI) attacks on the conventional consensus algorithms, a hybrid solution is presented based on the combination of multiobjective sliding-mode control and communication link quality observer to provide a reliable performance against different types of FDIs. Unlike the commonly developed distributed observer-based cyber-resilient algorithms, this approach aims to form a complete localized solution without the requirements for transmission of extra distributed signals in the secondary layer. Using the proposed method, the system reliability will not be impacted by the cyber intrusions on the distributed observer terms, and the system's dynamic performance is not deteriorated by the counteracting operation resulted from adaptive distributed observers under other system-transient conditions such as load dynamics, which can be even worsened under communication delays. Using cyber-resilient offset compensation terms, performance of the proposed sliding-mode control scheme is enhanced for multiobjective regulation. Integrating the sliding-mode control with communication link observer also ensures effective isolation of the unbounded and extreme cyberattacks. Unlike the former indirect local observers, the proposed scheme operates directly based on monitoring the affected distributed signals rather than only power terms, which enhances its reliability on detection. The effectiveness of the proposed scheme is validated through a real-time model developed in Typhoon HIL-402 real-time simulator as well as the experimental tests.

A consensus-based privacy-preserving energy management strategy for microgrids with event-triggered scheme

In terms of the distributed energy management (DEM) in microgrids, increasing distributed generators and users will bring tremendous data transmitted in the communication network. Considering the data security and the computation efficiency, protecting the participants’ privacy and saving the communication network resources are essential. This paper proposes a consensus-based distributed privacy-preserving energy management strategy with the event-triggered scheme to achieve privacy-preserving and network resource-saving simultaneously. Firstly, the DEM in microgrids is formulated as a social welfare maximization problem. Then the privacy disclosure of both generators and consumers under the consensus-based distributed control strategy is analyzed. Next, a consensus-based privacy-preserving algorithm using differential privacy is designed to protect private information. An event-triggered scheme is applied to the strategy to save network resources. Besides, theoretical analysis, including convergence, accuracy and differential privacy, is presented to guarantee the algorithm’s sufficiency. The trade-off between the accuracy and privacy level is also investigated. Finally, simulation results demonstrate the effectiveness of the proposed algorithm.

Learning Assisted Demand Charge Mitigation for Workplace Electric Vehicle Charging

Uncontrolled electric vehicle (EV) charging loads at a workplace could result in hefty demand charges. Several studies in the literature have focused on mitigating these demand charges at workplaces using aggregator-based centralized control and consensus-based distributed control. Though each model has successfully mitigated the demand charges they all show some limitations. Aggregator-based centralized solver is computation and time intensive while consensus-based distributed control is communication intensive. Other works with algorithms exploring demand charge mitigation also often rely on large amounts communications. These algorithms include water filling algorithms, multiobjective optimization, and a fuzzy logic controller. The machine learning-based (ML) approach investigated in this study seeks to eliminate both drawbacks using the model trained on optimization results obtained with existing methods. The investigation of ML-based controller in this study is not only found to be superior in performance due to speed and accuracy metrics compared to existing control approaches but has also provided the promising resilient approach to deal with communication failure and cybersecurity threats.

Distributed event-triggered multi-timer synchronization scheme for secondary control in islanded microgrids

Consensus-based distributed control has been widely applied in the secondary control for microgrids (MGs) with the assumption that the control actions of each distributed generations (DGs) are triggered at the same time as others in the state-of-art literature. However, in the absence of centralized timer synchronization, the asynchrony resulting from the independent timer localized in each DG would inevitably undermine the system performance or even cause instability. This paper proposes a distributed time synchronization strategy to guarantee the update actions of individual DGs to be triggered at the same discrete instants. First, the asynchrony problem in the distributed secondary control due to the essential distributed characteristic is elaborated and the resultant convergence deviation is deduced. Then, the distributed time synchronization strategy based on pinning consensus is described, with the optimal pinning timer selected to achieve superior propagation performance. Further, the event-triggered mechanism is introduced, which reduces the communication burden significantly compared to the time-driven mode and maintains the global clock synchronization efficiently. The selection of event triggering threshold is formulated for the tradeoff between the trigger frequency and convergence accuracy. The effectiveness as well as flexibility of the proposed control strategy is demonstrated by simulations.

A Finite-Time Robust Distributed Cooperative Secondary Control Protocol for Droop-Based Islanded AC Microgrids

In this research work, a resilient finite-time consensus-based distributed secondary control protocol is presented for droop-based distributed generating (DG) units of an islanded AC microgrid (MG). Through a multi-agent control structure, the DG units of the microgrid adjust their active power outputs so that they reach an agreed-upon value in a finite time. Concurrently, all the DG units are forced to operate with their frequencies regulated to the reference MG frequency in a finite time, despite time-varying load perturbations. Each DG unit is provided with a hierarchical control architecture, where the primary control is achieved using the droop control method, while the secondary control is established through the proposed distributed control protocol. The communication between DG units takes place over a sparse communication network. The proposed control protocol is robust to both small and sufficiently large communication latencies and it supports the plug-and-play feature of DG units. Different time-domain-based numerical simulations are carried out on a small as well as large microgrid testbenches in Matlab/Simulink and demonstrate the correctness and effectiveness of the proposed distributed control protocol. A comparative study is also presented with the existing distributed control protocol, and it is found that the proposed strategy is superior in its performance.