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In this letter, we propose an optimal voltage feedback control algorithm for wind farms where the voltage set-point of wind-farm-side voltage source converter (WFVSC) and reactive powers of wind turbines (WTs) are coordinated. The proposed control establishes on the gradient descent and operates in an online fashion. Each WT updates its reactive power based on the local instantaneous terminal voltage and therefore, the proposed control can be implemented in a decentralized manner. Besides, we also address its asynchronous counterpart to enhance the practical applicability in real world. [ABSTRACT FROM AUTHOR]

Faults on the alternating current (AC) transmission lines could cause commutation failures of nearby line-commutated converter-based high-voltage direct-current (LCC-HVDC) systems, which in turn, may challenge the fault detection of AC systems. To address this issue, this paper proposes a fast fault detection method based on instantaneous active power and fault variation component to alleviate the impacts of commutation failures and reactive power compensation while mitigating the dead zone problem. Upon that, an integral-based differential protection algorithm is presented to enhance reliability. Simulations are carried out on a real hybrid AC/DC system in North China with different fault locations and resistances to verify the effectiveness of the proposed method. Finally, we further validate the proposed method by leveraging on-site recorded fault data. [ABSTRACT FROM AUTHOR]

This paper considers the voltage control problem in wind farms, with the goals of maintaining feasible voltage profile and adequate reactive power (VAR) reserves by coordinating the reactive power outputs of wind turbines (WTs) and static synchronous compensators (STATCOMs). Rather than a conventional centralized and offline fashion, we propose a distributed online voltage control scheme based on dual decomposition. First, the optimal voltage control problem is formulated based on the branch flow model. Then, thanks to the sparsity of the constraints in this problem, a distributed solution framework is developed based on the dual decomposition and its online implementation is achieved through voltage feedback. To pursue fast convergence of the distributed algorithm and consequently facilitate the online implementation, the fast gradient method is generalized and then applied to solve the dual problem. The effectiveness of the proposed voltage control scheme is numerically validated under both static and dynamic cases. [ABSTRACT FROM AUTHOR]

This letter considers the closed-loop stability issue of droop-based voltage control for wind power plants (WPPs) under varying grid strength. We first propose a data-driven online system equivalent/identification method (DOnSE) for WPPs using the weighted least-squares estimation (WLSE). Then, upon the analysis of link between stability boundary of droop gain and external grid strength, a self-adaptive gain-scheduling droop voltage control scheme for WPPs based on the DOnSE is developed to enhance the closed-loop stability and reactive power utilization of wind turbines (WTs). [ABSTRACT FROM AUTHOR]

This paper proposes a double-time-scale coordinated voltage control scheme for distribution networks with distributed generators (DGs) based on model predictive control (MPC) to regulate the voltage profile across a network. The slow-time-scale control scheme is designed to correct long-term voltage deviations while reducing the number of actions of the on-load tap changer, step voltage regulators, and capacitor banks. The MPC problem is formulated as a mixed-integer quadratic programming (MIQP). A tailored exaction solution method based on the branch-and-bound algorithm embedded with an alternating direction method of multiplier-based QP solver is developed to efficiently solve the MIQP problem. In the fast-time-scale control, the active and reactive power outputs of DGs are optimally coordinated to handle the fast voltage fluctuations as well as capture more renewable energy. An efficient analytical sensitivity calculation method is used to update the voltage sensitivities online. The effectiveness of the proposed control scheme along with the exact solution method is verified on a modified real 20 kV distribution system. [ABSTRACT FROM AUTHOR]

This paper presents a model predictive control (MPC)-based coordinated voltage control scheme for distribution networks with high penetration of distributed generation (DG) and energy storage. In this scheme, the DG units, energy storage devices, and on-load tap changer are optimally coordinated to maintain all bus voltages in the network within a permissible range. To better coordinate the economical operation and voltage regulation, two control modes are designed according to the operating conditions. In the preventive mode, the DG units operate in the maximum power point tracking mode. State-of-charge of energy storage system (ESS) units and power outputs of DG and ESS units are optimized while maintaining the voltages within the feasible range. In the corrective mode, active power curtailment of DG units is also used as a necessary method to correct the severe voltage deviations. The voltage sensitivity coefficients with respect to the power injections and tap changes are updated in real time using an analytical sensitivity calculation method to improve the computation efficiency. A test system consisting of two 20-kV feeders fed from the same substation based on a real distribution network was used to validate the proposed coordinated voltage control scheme under both normal and large-disturbance conditions. [ABSTRACT FROM AUTHOR]

This paper proposes a decentralized coordinated voltage control scheme (DCVCS) for voltage-source-converter high-voltage dc (VSC-HVdc) connected wind farms based on the Model Predictive Control (MPC), which regulates the voltage profile across the wind farm network within the feasible range by optimally coordinating the VSC and wind turbines (WTs). First, the centralized optimal control problem based on the MPC is formulated to minimize voltage deviations and reactive power output fluctuations of WTs. Second, the decentralized solution methodology based on Alternating Direction Method of Multipliers (ADMM) with fast convergency is used to solve the MPC problem in a decentralized manner without loss of optimality of the primal problem. A wind farm with 64 WTs was used to validate the effectiveness and superiority of the proposed DCVCS. [ABSTRACT FROM AUTHOR]

The increasing penetration level of wind power brings a number of challenges to power system operations. Voltage/reactive power control is an important task of a wind farm to fulfill the grid requirements and avoid the cascading trip faults of wind turbines (WTs). To address this issue, a distributed cooperative voltage control strategy is proposed for wind farms based on the consensus protocol in this paper. In the proposed voltage control scheme, a droop-based local controller is adopted for the primary voltage control based on the local measurements. A consensus-based distributed secondary voltage controller is proposed, aiming to regulate the voltages within the feasible range while optimizing reactive power sharing among the reactive power sources using the local and neighboring information. The controller parameters are determined by the closed-loop system stability analysis using a linearized model. A wind farm with 20 WTs was used for the case study to validate the proposed control scheme under both steady-state and fault-ride-through (FRT) conditions. Moreover, the robustness against a communication link failure and plug-and-play capability of the proposed voltage controller were tested. [ABSTRACT FROM AUTHOR]

This paper proposes an enhanced voltage control strategy (EVCS) based on model predictive control (MPC) for voltage-source-converter-based high-voltage direct-current (VSC-HVDC)-connected offshore wind farms (OWFs). In the proposed MPC-based EVCS, all wind turbine generators (WTGs) and the wind-farm-side VSCs are optimally coordinated to keep voltages within the feasible range and reduce system power losses. Considering the high R\rm/X ratio of the OWF collector system, the effects of active power outputs of WTGs on voltage control are also taken into consideration. The predictive model of the VSC with a typical cascaded control structure is derived in detail. The sensitivity coefficients are calculated by an analytical method to improve the computational efficiency. A VSC-HVDC-connected OWF with 64 WTGs was used to validate the proposed voltage control strategy. [ABSTRACT FROM PUBLISHER]

• A distributed voltage control scheme is proposed to optimally regulate voltages in distribution networks. • Distributed information synchronization is realized based on consensus protocols. • Distributed model predictive control is used to coordinate regulation of DGs and OLTC. • Two control modes are designed for both normal and dynamic conditions. This paper proposes a distributed voltage control (DVC) scheme for smart distribution networks with high penetration of inverter-based distributed generators (DGs), aiming to optimally coordinate DG units and on load tap changer (OLTC) transformer to regulate the voltages within the feasible range. The proposed scheme consists of two important parts: (1) distributed information synchronization (DIS) framework and (2) distributed model predictive control (DMPC)-based voltage control scheme. The DIS framework is established based on the consensus protocols to synchronize the specific information about the critical bus voltages and potential OLTC actions. The DMPC-based voltage control scheme is presented, in which each DG unit only exchanges information with its immediate neighbors and solves the local optimal control problem. Two control modes are designed to better deal with different operating conditions. In the normal mode, only the reactive power outputs of DG units are optimized to mitigate the voltage deviations. In the corrective mode, both of the active and reactive power outputs of DG units are optimally controlled to correct the severe voltage deviations. To mitigate the mutual interaction between the DGs and OLTC, the potential actions of OLTC are predicted and considered in the optimization problem of each units. The control performance of the proposed scheme was demonstrated using a real medium-voltage (MV) distribution network with two feeders under both normal and large-disturbance conditions. [ABSTRACT FROM AUTHOR]