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State-of-charge (SoC) consistency and bus voltage regulation are two major control objectives of shipboard DC microgrids. To achieve these objectives, this paper presents a novel distributed model predictive control (DMPC) strategy with multiple cost functions. Firstly, based on the bus voltage derivative and SoC dynamic model, the voltage and SoC control equations in discrete form are established. Subsequently, considering the safe operation of battery energy storage systems (BESSs), a DMPC taking the energy storage current as the control set is designed. Finally, the average voltage compensation is taken to achieve precise control of the average voltage. The proposed method can avoid the complex process of adjusting weight coefficients, thereby simplifying controller design. Furthermore, the robustness and practicality of the proposed DMPC method are verified through MATLAB/Simulink 2021a simulations and hardware-in-the-loop (HiL) experiments. [ABSTRACT FROM AUTHOR]

As an effective method to improve the reliability, the advanced communication infrastructure also exposes the islanded AC microgrid (MG) to potential privacy threats. Although the existing differential-privacy based secondary controls provide the privacy protection through adding noise, the noise would bring about large harmonic components thereby degrading the power quality. To tackle with this problem, a novel integrated privacy-preserving distributed fixed-time (PDF) secondary control of the islanded AC MG is proposed for the accurate frequency restoration and active power sharing. The state decomposition strategy and the additional virtual proportional (AVP) coefficient are innovatively designed to achieve the privacy preservation, where the active power ratio of each DG is decomposed into several sub-states. The integrated PDF secondary control only requires each DG to transmit the first sub-state of active power ratio through communication network, which would not increase the communication burden. The designed privacy-preserving mechanism can protect the initial value and real-time running values simultaneously when the AVP coefficient is not disclosed to the external eavesdropper. The real-time simulations based on the NI-PXI real-time simulator are conducted to validate the effectiveness and advantages of the integrated PDF secondary control. [ABSTRACT FROM AUTHOR]

In AC microgrids (MGs), the required high control gain for dealing with control faults would reduce the robustness of the secondary control to communication constraints. To tackle with this problem, the subarea physical infrastructure of AC MGs and the two-layer secondary control framework are designed. For the physical infrastructure, the whole AC MG is divided into several areas, where each area is composed of a distributed generator (DG) and several geographical-close loads. Furthermore, by utilizing the advanced metering infrastructure (AMI), loads transmit the local load change information to the DG in the same area. Based on this physical infrastructure, a distributed event-triggered fixed-time fault-tolerant (ET-FTFT) secondary control framework is proposed in this paper to improve the resilience of the secondary control to sensor and actuator faults/attacks, and communication constraints, simultaneously. The adopted two-layer control framework is to decouple the communication constraints and control faults. The event-based strategy is adopted in the upper layer to reduce the communication burden and Zeno behavior can be evaded. Real-time simulations based on the NI-PXI real-time simulator validate the advantages of the distributed ET-FTFT secondary control framework, which are the better robustness to control faults, and the fixed-time convergence to improve the power quality. [ABSTRACT FROM AUTHOR]

Energy storage systems (ESSs) are being utilized to improve wind farms’ (WF) frequency support capability due to their high reliability, fast response and the dual role of energy users and suppliers. Nevertheless, the problem of how much capacity should each ESS possesses in order to better serve the WFs has never been investigated. With this perspective, this paper proposes an optimal ESS allocation (OEA) scheme for doubly fed induction generator (DFIG) based WFs to mitigate the impact of wake effect in frequency support. Firstly, the synchronous stability of wind turbines under frequency dips is analyzed with the concept of frequency support margin (FSM), and the detrimental impact of the wake effect is also investigated. Subsequently, the role of ESSs to improve wind turbines’ synchronous stability is demonstrated. To make the OEA scheme practical, the wind turbines in a WF are segmented into different clusters based on the received wind speed. Afterwards, the OEA problem is formulated, where the objective is to optimize the coherency of the wind turbine clusters’ FSM level. The simulation results show that ESS can provide secondary frequency support under major grid frequency drops, and the proposed OEA scheme can reduce the risk of loss of synchronous stability. [ABSTRACT FROM AUTHOR]

In this paper, a distributed predefined-time fractional-order sliding mode controller (DPTFOSMC) is proposed for performance improvement of power system. The proposed DPTFOSMC is designed based on the multi-agent framework and distributed control theory, which can reduce the pressure of central controller in communication and calculation, thus obtaining fast and coordinated response. The DPTFOSMC can achieve the advantages of sliding mode control (SMC) with fast response and strong robustness for the power system. In addition, the power system under the proposed DPTFOSMC can be stabilized in stable range within a predefined time which is directly equal to the tunable parameter, thus meeting the high requirement for convergence time of the power system. The prescribed performance function (PPF) is carried out to design the DPTFOSMC, which can ensure that the power system can achieve the expected transient and steady responses. Meanwhile, fractional calculus is implemented to devise the DPTFOSMC to eliminate the chattering phenomenon of conventional SMC. The Lyapunov function is adopted to analysis the predefined-time stability of the power system under the proposed DPTFOSMC. Simulations are taken to validate the effectiveness and superior performance of the proposed DPTFOSMC for the power system. The results show that the DPTFOSMC can ensure the power system to achieve superior performances than the existing control methods. [ABSTRACT FROM AUTHOR]

During frequency controller design, the system frequency dynamic behavior is normally assessed by a system frequency response (SFR) model, which is a linearized low-order model that can be efficiently handled. Existing SFR models for a system with wind turbines cannot precisely characterize the nonlinear dynamic of fast frequency controllers in these turbines, causing inaccurate evaluation of the system frequency behavior that may lead to undesired design of fast frequency control parameters. To deal with this issue, the linearization error of the SFR model is formally analyzed. A compensation strategy is proposed to guarantee the accuracy of the frequency behavior assessment. Further considering that fast frequency controllers potentially degrade the small-signal rotor angle stability, this paper presents a coordinated parameter optimization model of fast frequency controllers, which guarantees the system frequency behavior while meeting the small-signal rotor angle stability requirement. Case studies validate the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

This paper proposes a fractional-order sliding mode controller (FOSMC) for fixed-time stability of multimachine power systems. Fractional calculus has been applied in sliding mode control (SMC) to design FOSMC which can better suppress the chattering phenomenon than the traditional integer-order SMC. Hence, a FOSMC is proposed to regulate the excitation of synchronous generators to improve the transient stability of the power system. In addition, the FOSMC can maintain the multimachine power systems stabilization in an upper bound and measurable convergence time independent of the initial operating conditions of the power system. The Lyapunov function is implemented to demonstrate the stability of multimachine power systems under the FOSMC, and the upper bound convergence time of the power system is generally estimated. The New England 10-machine 39-bus power system is taken into simulation to test the effectiveness and superior performances of the FOSMC than the existing control methods under different operating conditions. Meanwhile, the FOSMC with different orders are presented to verify that the FOSMC can better restrain the chattering phenomenon than traditional integer-order SMC. Simulation results show that the FOSMC can effectively reduce the chattering phenomenon and ensure the power system stabilization in an upper bound time, thus enhancing the dynamic performances of the power system. [ABSTRACT FROM AUTHOR]

Increasing use of series compensation in doubly-fed induction generator (DFIG)-based wind farms has led to subsynchronous control interaction (SSCI) incidents. The irregular exchange of energy between the network side and generator side is considered responsible for SSCI. Therefore, an energy-shaping controller (ESC) is proposed in this paper to mitigate SSCI from the energy perspective. Firstly, based on energy relationship and physical nature, Hamiltonian model is established to describe the system structure. Secondly, the controller is obtained by solving the energy equation. Damping is then injected into the controller dynamics and it is back-propagated to the system, ensuring the global asymptotical stability. Thirdly, the controller is further improved to make gamma-dissipation inequality hold, thereby enhancing the robustness. Time-domain simulation and impedance model (IM)-based stability analysis are conducted to evaluate the damping performance of ESC. Simulation results demonstrate the effectiveness of ESC under a wide range of operating conditions. Moreover, ESC also improves system robustness against external disturbance and parameter uncertainty. [ABSTRACT FROM AUTHOR]

Summary: This paper proposes an optimization approach for the participation of wind turbines in large scale power systems. The wind turbine participation optimization aims to regulate the droop slopes and the synthetic inertia of the aggregated wind turbines to command the power contribution of wind turbines proportional to their power ratings in the primary frequency response schemes. A reduced second order model of power system is firstly presented to simplify the analysis of large scale power system. Meanwhile, the internal dynamics of general wind turbines are analyzed and the concept of stability margin is proposed to describe the wind turbines' capability of enduring frequency dips at the bus node. A convex optimization based approach is then presented to regulate the droop slopes and synthetic inertia of the wind turbines incorporating their stability margin. Five case studies are conducted in New England 39‐bus system, IEEE 118‐bus power system and the Polish 3375‐bus system. The simulation results indicate that the proposed approach is capable of transiting the bus frequency to the new steady state in a smoother and more stable manner. [ABSTRACT FROM AUTHOR]

To mitigate subsynchronous control interaction (SSCI) in doubly fed induction generator (DFIG)‐based wind farm, this paper proposes a robust controller for rotor‐side converter (RSC) using fractional‐order sliding mode controller (FOSMC). The proposed FOSMC can improve robustness and convergence properties of the controlled system, thus achieving SSCI damping under various operating conditions. Impedance‐based analysis and time‐domain simulation are performed to check the capability of the designed FOSMC as compared with conventional sliding mode control (SMC) and subsynchronous damping control (SSDC). Simulation results demonstrate that FOSMC can mitigate SSCI within shorter time and effectively reduce the fluctuation range of system transient responses under various operating conditions of wind speeds and compensation levels. Moreover, FOSMC also improves system robustness against parameter uncertainties and external disturbances, which is important for safe operation of realistic wind farms. [ABSTRACT FROM AUTHOR]

This study proposes a robust sub‐synchronous damping controller based on fractional‐order sliding mode control (FOSMC) method to mitigate sub‐synchronous control interaction (SSCI) induced by DFIG‐based wind park connected to series‐compensated transmissions. Firstly, the nonlinearity of DFIG is cancelled through feedback linearisation. Secondly, FOSMC is designed and applied to the control loop of the DFIG rotor‐side converter. During the design process, the extra degree of freedom, provided by the fractional operator, is employed to achieve fast SSCI‐damping. Thirdly, a genetic algorithm is used for parameter optimisation with the aim of making system eigenvalues approach the left plane. The effectiveness of the proposed damping controller is evaluated based on the adapted IEEE first benchmark model, non‐aggregated wind system model with a realistic configuration, and experimental platform. Simulation and experiment results demonstrate the superior damping performance of FOSMC under different wind speeds, compensation levels, and the number of online wind turbines. Moreover, FOSMC also shows the robustness under parameter uncertainty, control parameter perturbation, and symmetric (three‐phase short circuit) fault. [ABSTRACT FROM AUTHOR]

This paper proposes a fractional‐order sliding mode control (FOSMC) based on feedback linearization (FL) technique to mitigate subsynchronous control interaction (SSCI) in doubly fed induction generator (DFIG)–based wind farms connected to series‐compensated transmission lines. A linearized form of the studied system is obtained with the use of FL, which leads to reduced system order and small computational burden. Then the FOSMC is designed for grid‐side converter (GSC) to stabilize SSCI and to provide a considerable robustness against external disturbances and parameter uncertainties. For FOSMC parameter tuning, genetic algorithm (GA) is performed through MATLAB/SIMULINK. Time‐domain simulation are carried out to evaluate the effectiveness of the FOSMC in mitigating SSCI at varied operating conditions, and the superior performance of the proposed control is demonstrated as compared with conventional vector control (VC), feedback linearization sliding mode control (FLSMC), high‐order sliding mode control (HOSMC). [ABSTRACT FROM AUTHOR]

Virtual inertia has been extensively implemented in power systems with distributed energy resources, especially wind energy conversion systems. This paper proposes an optimal virtual inertia planning strategy for stability enhancement of power system, which is penetrated with large volume of renewable resources provided by doubly fed induction generators (DFIGs). The stability of DFIG is first analyzed and the concept of critical frequency drop is proposed. Moreover, the intersection area between the two predefined operation curves of DFIG is defined as the stability margin and it is calculated in the form of a function of local virtual inertia. Subsequently, a virtual inertia planning strategy is proposed, wherein a coherency index that considers the homogeneity of the stability margin at each node is presented, followed by a nonconvex optimization problem. The problem is simplified with the Lyapunov function method and resolved. Two case studies are conducted to verify the effectiveness and performance of the proposed approach: a 12-bus system and the IEEE-118 bus system. Both cases show that with the proposed approach, the system stability margin coherency level is enhanced and the general stability is promoted. [ABSTRACT FROM AUTHOR]

This paper proposes a fractional order sliding mode control (FOSMC) strategy for grid-connected doubly fed induction generator (DFIG). The novel approach aims to directly control the active/reactive power output of a DFIG-based wind energy conversion system with FOSMC, which has never been utilized in the control of DFIG. The fractional order sliding mode control with disturbance is introduced and the Caputo derivative is employed in constructing the sliding surface. Meanwhile, an enhanced exponential reaching law is utilized in order to mitigate the chattering phenomenon in the sliding stage and accelerate the reaching progress in the meantime. A comparative study is conducted subsequently to verify the superior performance of the proposed FOSMC control scheme over that of the conventional sliding mode control and the vector control approach. A steady state simulation is first conducted to tune the parameters of the FOSMC. A variable wind condition is subsequently simulated to compare the performance of those methods. After that, simulations with background harmonics of the grid voltage and parameter perturbation are considered. Ultimately, an experimental test is conducted to further validate the proposed method. The superior performance and the effectiveness of the FOSMC are fully validated with the above four comparative tests. [ABSTRACT FROM PUBLISHER]

This paper proposes an adaptive droop gain-based consensus approach for reactive power sharing in microgrids (MGs) with the event triggered communication protocol (ETCP). A multi-agent system-based network is constructed to establish the communication with distributed generators (DGs) in MGs. An ETCP is proposed to reduce the communication among agents to save resources and improve system reliability, as the communication is only needed when the event triggered condition is fulfilled. A stability analysis is conducted to guarantee the existence of the equilibrium point and the freeness of the Zeno solution. Moreover, an adaptive droop gain is designed to reduce the impact of imbalanced feeder impedances. Four case studies are conducted to verify the effectiveness and performance of the proposed method. The simulation results show that the ETCP-based approach is capable of achieving power sharing consensus, communication reduction and shifting the information exchange mode based on the operation scenarios. [ABSTRACT FROM AUTHOR]

A sliding mode control (SMC) scheme of doubly fed induction generator (DFIG) wind turbine with a novel exponential reaching law (NERL) is proposed in this paper. The DFIG wind turbine is running under variable wind speed. The NERL based SMC proves to be capable of reducing the system chattering phenomenon as well as accelerating the approaching process. A nonlinear case numerical simulation test is employed to verify the superior performance of the ERL method over traditional power rate reaching strategy. The NERL based SMC is employed to control the DFIG wind turbine generator under variable wind speed subsequently and the simulation results evidence the remarkable performance of the NERL based SMC control scheme. [ABSTRACT FROM AUTHOR]