Control Strategy For Islanded Microgrids Research Articles

Distributed fixed-time control strategy for islanded microgrids considering perturbations and switching topologies

Distributed fixed-time control strategy for islanded microgrids considering perturbations and switching topologies

Distributed fixed-time control strategy for islanded microgrids considering perturbations and switching topologies

Distributed fixed-time control strategy for islanded microgrids considering perturbations and switching topologies

Hierarchical control of island microgrid based on consensus algorithm

When the load inside the microgrid changes, droop control maintains a stable power supply cycle of the microgrid by controlling the voltage and frequency at the parallel network of the distributed generation. Since the traditional microgrid droop control usually uses a fixed droop coefficient to adjust the output active power and reactive power, the frequency and voltage of the inverter parallel network will deviate from the system frequency and voltage rating to varying degrees, so a new layer of control link is needed to restore the target value. Moreover, most of the hierarchical control methods adopt centralized control methods, which have limitations such as high dependence on communication. This paper combines a hierarchical control framework and a consistency algorithm to propose a distributed sag control strategy for islanded microgrids based on a multi-agent system. It achieves equal-to-ratio output when distributed generation responds to power changes while maintaining the stability of the microgrid’s main performance indicators. Since the distributed system with a consistency algorithm does not require a centralized control centre, it increases the system’s robustness and reduces the dependence of the system on the communication network. Finally, an islanded AC microgrid model is built by MATLAB/Simulink, and the effectiveness of the proposed islanded microgrid hierarchical control strategy is verified by simulation.

A FDI Attack-Resilient Distributed Secondary Control Strategy for Islanded Microgrids

Distributed cooperative control has been used as a preferred secondary control strategy for maintaining frequency synchronization and voltage restoration in cyber-physical AC microgrids due to its flexibility, scalability and better computational performance. However, such a control system is susceptible to potential cyber attacks, i.e., false data injection (FDI) attacks. To this end, this article introduces a hidden layer based attack-resilient distributed cooperative control algorithm to solve the problem of the secondary control of islanded microgrids under FDI attacks. In comparison to the existing attack-resilient distributed control methods, the proposed controller with sufficient large $\alpha $ can mitigate the adverse effects of time dependent FDI attacks on actuators, sensors and communication links of the control system, and is also robust to state dependent FDI attacks. Furthermore, the algorithm is applicable even when all DGs and communications are compromised. Finally, the efficiency of the proposed controller is evaluated for a test microgrid with 4 DGs under different types of attack.

Distributed cooperative control strategy for islanded microgrids

In this paper, a distributed cooperative control strategy for islanded microgrids (MGs) is proposed, to minimize the total generation cost of distributed generators (DGs), and maintain the state of charge (SoC) balancing of battery energy storage systems (BESSs). First, a consensus-based economic dispatch (ED) strategy is proposed, to achieve the minimum total generation cost of DGs, while the aggregated power output of DGs meets the power dispatch command from the supervisory control system. Further, an SoC-based droop control strategy is developed for BESSs, to maintain the SoC balancing and power balance in the islanded MG simultaneously. Compared with the centralized control schemes, the proposed cooperative control strategy is fully distributed such that it simply requires local information exchange without the necessity of a central controller. More importantly, the proposed cooperative control strategy is able to achieve multiple control objectives in a unified framework. Finally, the simulation results in an islanded MG with renewable energy and time-varying load demands are presented, to demonstrate the effectiveness of the proposed distributed cooperative control strategy.

Distributed Discrete Robust Secondary Cooperative Control for Islanded Microgrids

It is desirable to develop robust controllers for fast frequency/voltage regulation and active/reactive power sharing in an islanded microgrid with high penetration level of renewable energy sources. This paper proposes a fully distributed discrete two-level control strategy for islanded microgrids. The upper-level control determines the active/reactive power generation references to minimize the overall voltage deviations while achieving accurate active/reactive power sharing. The lower-level control enables the inverter to track the power references by adjusting inverter output voltage magnitude and angle. A flexible finite-step convergence tracking controller, which considers the uncertainties and disturbances, is introduced to improve the robustness and control accuracy. The convergence and optimality of the proposed discrete control algorithm are validated by rigorous analysis. The effectiveness of the proposed distributed control approach is verified by simulation results.

A Novel Hierarchical Control Strategy for Low-Voltage Islanded Microgrids Based on the Concept of Cyber Physical System

Based on the concept of cyber physical system (CPS), a novel hierarchical control strategy for islanded microgrids is proposed in this paper. The control structure consists of physical and cyber layers. It’s used to improve the control effect on the output voltages and frequency by droop control of distributed energy resources (DERs), share the reactive power among DERs more reasonably and solve the problem of circumfluence in microgrids. The specific designs are as follows: to improve the control effect on voltages and frequency of DERs, an event-trigger mechanism is designed in the physical layer. When the trigger conditions in the mechanism aren’t met, only the droop control (i.e., primary control) is used in the controlled system. Otherwise, a virtual leader-following consensus control method is used in the cyber layer to accomplish the secondary control on DERs; to share the reactive power reasonably, a method of double virtual impedance is designed in the physical layer to adjust the output reactive power of DERs; to suppress circumfluence, a method combined with consensus control without leader and sliding mode control (SMC) is used in the cyber layer. Finally, the effectiveness of the proposed hierarchical control strategy is confirmed by simulation results.

Distributed Optimal Control of Reactive Power and Voltage in Islanded Microgrids

This paper presents a distributed optimal control strategy for islanded microgrids, which allows performing reactive power sharing and voltage regulation without using a communication system. To perform the twofold objectives, a small signal model is first developed to reconstruct the system input-output relationship, which is evaluated through sensitivity analysis. A state estimator is then constructed to observe reactive power distribution and system voltages by local measurement. An optimal regulator is developed to perform both reactive power sharing and system voltage restoration. And the dynamic performance of the optimal controller is analyzed, from which the guideline for choosing controller parameters is formulated. The results obtained from sensitivity analysis, simulations, and experiments show that the proposed approach provides the expected reliability and flexibility for optimizing the reactive power sharing and system voltages restoration.

Synthesizing Virtual Oscillators to Control Islanded Inverters

Virtual oscillator control (VOC) is a decentralized control strategy for islanded microgrids where inverters are regulated to emulate the dynamics of weakly nonlinear oscillators. Compared to droop control, which is only well defined in sinusoidal steady state, VOC is a time-domain controller that enables interconnected inverters to stabilize arbitrary initial conditions to a synchronized sinusoidal limit cycle. However, the nonlinear oscillators that are elemental to VOC cannot be designed with conventional linear-control design methods. We address this challenge by applying averaging- and perturbation-based nonlinear analysis methods to extract the sinusoidal steady-state and harmonic behavior of such oscillators. The averaged models reveal conclusive links between real- and reactive-power outputs and the terminal-voltage dynamics. Similarly, the perturbation methods aid in quantifying higher order harmonics. The resultant models are then leveraged to formulate a design procedure for VOC such that the inverter satisfies standard ac performance specifications related to voltage regulation, frequency regulation, dynamic response, and harmonic content. Experimental results for a single-phase 750 VA, 120 V laboratory prototype demonstrate the validity of the design approach. They also demonstrate that droop laws are, in fact, embedded within the equilibria of the nonlinear-oscillator dynamics. This establishes the backward compatibility of VOC in that, while acting on time-domain waveforms, it subsumes droop control in sinusoidal steady state.

A Control Strategy for Islanded Microgrids With DC-Link Voltage Control

New opportunities for optimally integrating the increasing number of distributed-generation (DG) units in the power system rise with the introduction of the microgrid. Most DG units are connected to the microgrid via a power-electronic inverter with dc link. Therefore, new control methods for these inverters need to be developed in order to exploit the DG units as effectively as possible in case of an islanded microgrid. In the literature, most control strategies are based on the conventional transmission grid control or depend on a communication infrastructure. In this paper, on the other hand, an alternative control strategy is proposed based on the specific characteristics of islanded low-voltage microgrids. The microgrid power is balanced by using a control strategy that modifies the set value of the rms microgrid voltage at the inverter ac side as a function of the dc-link voltage. In case a certain voltage, which is determined by a constant-power band, is surpassed, this control strategy is combined with P/V -droop control. This droop controller changes the output power of the DG unit and its possible storage devices as a function of the grid voltage. In this way, voltage-limit violation is avoided. The constant-power band depends on the characteristics of the generator to avoid frequent changes of the power of certain DG units. In this paper, it is concluded that the new control method shows good results in power sharing, transient issues, and stability. This is achieved without interunit communication, which is beneficial concerning reliability issues, and an optimized integration of the renewable energy sources in the microgrid is obtained.