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Dynamic voltage support is a type of critical ancillary service in electric power networks. With the increasing penetration of inverter-based renewable energy resources, utilizing their idle capacity to provide dynamic voltage support is becoming essential. However, the performance of traditional control methods is ofter limited due to the frequently changing operating point and network parameters, which are tuned only in a specific condition and suffer performance deterioration in others. This article presents a model-free dynamic voltage control method for inverter-based energy resources to supply dynamic voltage support. This method can dynamically estimate the system with pseudo gradients, in which a continuous parameter function is proposed to adaptively approximate the optimal intermediate parameters. It guarantees the performance when the host system operating states vary without tuning the controller's parameters, while in comparison the PID controllers require the parameters being tuned repeatedly. Both numerical simulation and field tests demonstrate that the proposed method significantly outperforms the classic PI and adaptive PI controllers, especially in the case when the host system varies over time. [ABSTRACT FROM AUTHOR]

Conventional loss of excitation (LOE) detection methods for synchronous generators may misoperate during power swings. In this paper, a novel method based on measured slip frequency at the terminal of synchronous generators is proposed to differentiate power swing conditions from LOE conditions. To enhance performance of the proposed method for noisy measured signals, a modified Prony method based on a combination of generalized total least-squares method and conventional Prony method is implemented to estimate slip frequency and an energy sorting technique is applied to distinguish the dominant frequency components of measured signals. Performance of the proposed method is evaluated under various operating conditions of a test system that is simulated in a co-simulation platform by linking CAPE and PSS/E software. Case study results illustrate that the proposed method can accurately differentiate power swing conditions from LOE conditions. [ABSTRACT FROM AUTHOR]

With the increasing applications of VSC-HVDC technologies in power grids, the importance of incorporating DC grids and converter stations into the optimal power flow (OPF) problem is increasing. The modeling of a converter station involves highly nonlinear operational constraints and integer variables representing the tap settings of LTC transformers. In this paper, an efficient OPF algorithm for hybrid AC–DC grids with discrete control devices is presented. A successive linear approximation method for the power flow equations in both AC and DC grids is introduced. The operational constraints of the converter station are thoroughly investigated. The proposed linearization of the power flow equations facilitates the convexity of the VSC modeling. A fictitious branch is added to the AC grid to handle the highly nonlinear converter losses. The discrete nature of the LTC transformer in the converter station is accurately modeled. An iterative solving algorithm is proposed for the OPF model. The strict satisfaction of the power flow equations is enabled through the application of an AC feasibility recovery process based on the power flow calculation in hybrid AC–DC grids. Case studies demonstrate that the proposed algorithm outperforms several selected commercial solvers. [ABSTRACT FROM PUBLISHER]

In this study, a linearized and convergence-guaranteed optimal power flow (OPF) model with reactive power (Q ) and voltage magnitude (v) is proposed. Based on a linearized network model, a fully linearly-constrained OPF model is formulated with constraints on Q and v and limits on the apparent branch flow. Compared with the commonly used DC OPF method, the proposed method narrows the deviation from the AC OPF solution without requiring any additional information of the power grid. The locational marginal price (LMP) of the proposed method is closer to the AC OPF solution than the DC OPF method. The marginal price of the reactive power (Q-LMP) is provided, which offers the opportunity to price the reactive power. Case studies on several IEEE and Polish benchmark systems show that the proposed OPF method substantially enhances the performance of the prevalent DC OPF method. In addition, it is shown that if the accuracy of the linearized network model needs to be further improved, such as that during the iterative quasi-optimization process that reconstitutes the AC feasibility, a solution that is notably close to the optimum of the AC OPF model can be obtained by taking only one more iteration. [ABSTRACT FROM AUTHOR]

In this paper, the concept of locational marginal price (LMP) is revisited by analyzing the Karush–Kuhn–Tucker (KKT) condition of a general optimal power flow (OPF) problem. The impact of losses on LMP is investigated. Several well-known properties and formulations of the LMP are illustrated from a novel perspective. In particular, the special case of the lossless DC OPF model is discussed. Based on this theoretical analysis, a linear model for the loss-embedded LMP is proposed. The influence of losses on the LMP is recovered by solving a system of linear equations. The proposed method does not rely on strong subjective assumptions, such as the selection of reference buses or the determination of the “loss factor.” Case studies show that the proposed method has distinct advantages compared with the method currently practiced in major electricity markets. [ABSTRACT FROM PUBLISHER]

In this paper, a novel solution to the optimal reactive power dispatch (ORPD) problem is proposed. The nonlinearity of the power flow equations is handled by a new successive linear approximation approach. For the voltage magnitude terms, a mathematical transformation that improves the accuracy and facilitates the linear modeling of shunt capacitors is used. Without loss of accuracy, the load tap changers and shunt capacitors are both modeled by linear constraints using discrete variables, which facilitates the linearly constrained mixed-integer formulation of the proposed ORPD model. An efficient iterative solving algorithm is introduced. The obtained solution strictly satisfies the power flow equations. Case studies on several IEEE benchmark systems show that the proposed algorithm can efficiently provide near-optimal solutions with the error of the objective functions of less than 0.1%. Compared with several commercial solvers, the proposed method shows distinct advantages in terms of both robustness and efficiency. Moreover, based on the round-off results, a heuristic method that reduces the optimization ranges of the discrete control variables is proposed. This method can further improve the computational efficiency with small losses in accuracy. [ABSTRACT FROM AUTHOR]

This study presents a comprehensive optimisation model that combines reactive power (VAR) optimisation and network reconfiguration to minimise power losses and eliminate voltage violations. In this model, the reactive power of distributed generators (DGs), VAR compensators, the position of tap‐changer and the states of branches are formulated as continuous and discrete decision variables. The original non‐convex three‐phase optimisation model was converted to a mixed‐integer second‐order cone programming model using the second‐order cone relaxation, big‐M method and piecewise linearisation. The results of numerical tests showed that the proposed model can achieve significant additional gains in network loss reduction and voltage violation mitigation. This developed method can be used as a basic analysis tool for active distribution networks operation schedule or planning. [ABSTRACT FROM AUTHOR]

As the power demand becomes higher all over the world, transmission lines are often carrying electric power near their limits, which can cause power systems to be operated under serious stress. Voltage collapse is one of the more critical problems that impacts power system operational security and many of the recent major blackouts were caused, at least partially, by voltage collapse. Therefore, a fast and accurate voltage stability monitor is necessary for the modern system, together with a fast calculation of possible remedial actions. The development and application of wide-area measurement systems established the foundation of online assessment of voltage stability in large-scale power systems. In this paper, a voltage stability (QV) index based on phasor measurements is used to identify the weak buses and a new parallel optimization method that increases this voltage stability margin is introduced. Results on the IEEE standard systems show the accuracy and efficiency of the methods. [ABSTRACT FROM PUBLISHER]

Smart grid technologies are expected to increase system efficiency and reliability using advancement in automation, communication, computation, and optimization. Several control algorithms have been developed or enhanced for operation and control of smart distribution grid. In recent years, volt/var control (VVC) algorithms have been proposed for energy saving in distribution systems due to advancement provided by smart grid automation and control. VVC helps to lower distribution feeder voltage to decrease energy consumption. However, quantification of this impact is hard due to several external factors such as weather and end users' behavior. On the other hand, existing evaluation methods of VVC algorithms are either not suitable for long-term study or intrusive. This paper addresses these issues by proposing a new technique to estimate “distribution system demand without smart grid implementation” utilizing “data measured from system with smart grid implementation.” Interdependence of voltage and load is considered based on estimated load characteristic. Our key contribution is developing a method for quantifying the real-time energy saving of smart grid automation and control focused on VVC and implementing in an electric utility in eastern Washington, USA. The algorithm is developed using both commercial and open-source software. [ABSTRACT FROM AUTHOR]

In this paper, we present the design ofa localized competitive market for reactive power ancillary services at the level of individual voltage-control areas. The concept of electrical distance has been used to identify the different voltage-control areas within a power system. The proposed reactive power market is settled on uniform price auction, using a modified optimal power-flow model. Uniform prices for various components of reactive power service are obtained for each voltage-control area. In the study cases described in the paper, we examine whether such a localized reactive power market is more desirable than a common system-wide reactive power market. [ABSTRACT FROM AUTHOR]