The stability of the grid-connected voltge source converter (VSC) with limits of phase locked loop (PLL) is investigated in this letter. The studied system is a nonlinear switched system that consists of three subsystems and a switching rule that connects switching between these subsystems. It is proved that the three subsystems share one common Lyapunov function, and the derivation of the constructed

Uninterruptible power supply (UPS) storage facilities deployed on the demand side have spare capacity that could be used to participate in power system operation. However, their capacity contributions to a power system's load-carrying capability have not been appropriately recognized. This letter exhibits the insight that UPS storage can serve loads during power shortages and therefore has a capacity

A bus impedance matrix ( Zbus ) is primarily used for power system analysis. Zbus is typically obtained from prior information on power systems (topology and line impedance) or from the measurement data of phasor measurement units (PMUs). However, the prior power system information may be inaccurate, missing, or inaccessible, and PMUs are difficult to install for all measurements due to the high cost

This letter proposes a physics-informed action network (PIAN) for power system transient stability preventive control (TSPC). The network firstly renders deep learning to reduce the TSPC complexity. Unlike common data-driven methods that superficially imitate control experience, TSPC is then analytically embedded into the proposed PIAN network, so that to enforce the network to learn in-depth physical

Grid-following voltage source converter (GFL-VSC) does not establish frequency like synchronous generator (SG), but follows the frequency of the terminal bus using phase-looked loop (PLL). This letter demonstrates that GFL-VSC also affects the terminal frequency, rather than simply follows it, due to the dynamics of the PLL and outer control loops. The relationship between PLL frequency, d-axis current

Frequency-Domain (FD) modal method is a useful tool for oscillation analysis of converters-dominated systems. In this regard, the nodal admittance and loop-gain models are often applied, and both have their respective eigen-sensitivity-based Participation Factor (PF) analysis methods. Therefore, a question on how are they related or differed naturally arises, to this end, this letter uncovers and establishes

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This paper presents necessary and sufficient conditions for a linear three-phase circuit to have a linear and time-invariant $dq0$ model. More specifically, we show that a circuit with state and input matrices that can be partitioned into three-by-three circulant matrices at the $abc$ frame of reference, can be transformed into a linear and time-invariant model in the $dq0$ frame of reference. We also

For systems subject to unbalanced faults, analytical model building for stability assessment is a challenging task. This letter presents a straightforward modeling approach. A generalized dynamic circuit representation is achieved by use of the Laplacian transform variable $s$ . We translate the voltage and current relationship at the fault location into the relationship of three subsystems. The final

Quantum annealing (QA) can be used to efficiently solve quadratic unconstrained binary optimization (QUBO) problems. Grid partitioning (GP), which is a classic NP-hard integer programming problem, can potentially be solved much faster using QA. However, inequality constraints in the GP optimization model are difficult to handle. In this study, a novel solution framework based on QA is proposed for

In this letter, a compressed Newton-Raphson (CNR) method is presented to achieve a high efficient and fast convergent result of power flow analysis of general DC traction network (DCTN). Due to CNR method, the higher-order Jacobian matrix of power flow equation is compressed as a 2-by-2 matrix, which can be calculated by the automatic differentiation technique. As a result, the proposed method has

This letter proposes a data-driven inertia estimator for inverter-based resources (IBRs) with grid-forming control. It is able to track both constant and time-varying inertia. By utilizing the Thevenin equivalent, the virtual frequency inside IBRs is first estimated with only its terminal voltage and current phasor measurements. The virtual frequency and the measurements are then used together to derive

We propose a comprehensive framework for the optimal day-ahead scheduling of power distribution systems (PDS), based on a mixed-integer linear programming (MILP) model. The interaction between transmission system operator (TSO) and distribution system operator (DSO) is considered, where TSO informs DSO of the day-ahead forecast concerning the expected power flow (PF) commitment at the TSO-DSO interconnection

The calculation of the unstable eigenvalues without omission is vital in small signal stability analysis of power systems. In this letter, a quasi-exponential transform is proposed to compute all unstable eigenvalues with improved efficiency and accuracy. Numerical experiments on two public source systems, namely the Xingo6u and Juba5723 systems, show the effectiveness of the proposed method.

This letter presents a technique to calculate the variance of algebraic variables of power system models represented as a set of stochastic differential-algebraic equations. The technique utilizes the solution of a Lyapunov equation and requires the calculation of the state matrix of the system. The IEEE 14-bus system serves to demonstrate the accuracy of the proposed technique over a wide range of

This letter presents a novel multi-variable analytical method to quickly calculate the energy flows in natural gas systems (NGSs). The solution, which does not require the traditional iterative method, will be applicable to the multi-scenario analysis. Case studies on several test systems verify the effectiveness of the proposed method.

This paper proposes a novel geometry-based spatial branching strategy for conic non-convex equations in integrated electricity-gas systems. The proposed strategy is embedded in a spatial branch-and-bound algorithm to solve optimal electricity-gas flow problems for their exact solutions. Numerical results on multiple test cases verify the effectiveness and superiority of the proposed method.

This letter proposes discrete changes in the power output of emerging power technologies (EPT) for controlling oscillations and frequency excursions. For the former, a new perspective is proposed that connects oscillations with the transient shift of the system equilibrium point. This is transformative as discrete control can be applied to multi-modal systems for the first time, without any model aggregation

In Tang et al. (2021) a measurement-based coordinated voltage controller for transmission systems was developed. As essential model information, the controller incorporates linear sensitivities between device set-points and voltages/power injections in the grid. This letter details how online sensitivity estimation using robust least squares can be used in place of model-based sensitivities, leading

We propose $ \mathsf{DeepOPF} $ - $ \mathsf{FT}$ as an embedded training approach to design one deep neural network (DNN) for solving multiple AC-OPF problems with flexible topology and line admittances, addressing a critical limitation of learning-based OPF schemes. The idea is to embed the discrete topology representation into the continuous admittance space and train a DNN to learn the mapping from

Increasing renewable energy penetrations bring complex feasibility and stability problems. Data-driven methods are applied in extracting and embedding these feasibility and stability rules in power system operations and planning. This paper presents a method of alternate support vector machine decision trees for rule extraction problems. The method significantly improves the classical decision-tree-based

This letter presents the discovery of a new type oscillations associated with inverter-based resources (IBRs) in weak grids. While typical weak grid oscillations become worse when the grid strength decreases and the power exporting level increases, this new type of oscillations appear when the grid becomes weaker and the power exporting level decreases. Electromagnetic transient (EMT) simulation results

At the bottom of the first page of this paper, the affiliation of all the authors currently states as follows:

At the bottom of the first page of this paper, the affiliation of all the authors currently states as follows:

The saturation of the nonlinear magnetic circuit of synchronous generators is often neglected when performing Kalman filter-based dynamic state estimation (DSE), yielding significant estimation bias. This letter addresses this problem and proposes a generalized DSE framework to handle magnetic saturation. Moreover, this letter derives a state initialization procedure that improves the Kalman filter

To accelerate the computational speed of data-driven distributionally robust optimization (DDRO), this letter presents a novel algorithmic approach to solve the inner max-min model under norm-2 type uncertainty set in DDRO. The proposed method can solve the problem in an easily implemented way instead of a time-consuming optimization process using commercial solvers. Comparisons of computational time

The cross impacts between transmission and distribution systems have drawn extensive attention, where multi-energy carriers become increasingly dominant in local market operations. Local energy hubs, integrated with multi-energy carriers, e.g., electricity, gas, heat, present great potentials to provide adequate power and reserve support for the transmission system, which could mitigate issues such

The linearized power flow (PF) model is mainly used to make the optimal power flow (OPF) problem convex. However, existing data-driven linear PF models are not applicable for OPF calculation since the Kirchhoff's law (KCL) constraints are neglected. In this letter, we propose a data-driven linear PF model incorporating the KCL constraints and can be embedded in OPF for distribution networks (DNs).

This letter proposes a general nonlinear control framework for load-sharing and voltage containment of dispatchable generators in dc networks. Our framework covers centralized, distributed, and decentralized control techniques and provides a unified perspective. First, we formulate the control objective as a steady state optimization problem and derive the Karush-Kuhn-Tucker (KKT) conditions. Second

This paper presents a methodology to estimate flexibility existing on TSO-DSO borderline, for the cases where multiple TSO-DSO connections exist (meshed grids). To do so, the work conducted exploits previous developments regarding flexibility representation through the adoption of active and reactive power flexibility maps and extends the concept for the cases where multiple TSO-DSO connection exists

This paper proposes a new decentralized transactive energy (TE) market strategy integrating wholesale and local energy markets through coordinated interactions between transmission system operator (TSO), distribution system operators (DSOs), and distributed energy resource (DER) owners. The overall market-clearing problem is formulated as an optimization problem with coupling variables between different

This letter proposes a novel coordinated current and voltage unbalance mitigation approach for networked microgrids (MGs). First, numerous dispersed PV systems in each MG are assembled as two aggregated systems with different connections. Then, a multi-MG cooperative current unbalance mitigation (CUM) method is developed for the substation transformer (ST) and the simplified linear programming (LP)-based

This paper presents a new market-based framework to exploit distributed energy resources’ (DERs) flexibility in distribution and transmission systems. This framework targets intra-hourly flexibility requirements of energy systems. In this regard, a local market is operated in distribution network to exploit DERs’ capabilities. Local market is cleared in coordination with wholesale market to optimize

To mitigate the high computational cost of adaptive robust optimization with a mixed-integer recourse objective in real-world power scheduling, a unified mixed-integer linear programming (MILP) solution framework is proposed in this paper. Numerical tests verify the superiority and practicability of the proposed solution framework over the existing decomposition-based solution algorithms.

The letter describes a novel, continuum-based approach, to capture the evolution of electromechanical dynamics in a power network following a disturbance. Such approach is based on the frequency divider formula (FDF) , which was recently proposed by the third author. A key point in obtaining the frequency divider formula (FDF) as a consequence of a continuum, is to show that the spatial rate of change

The boom of fluctuating renewable energies puts forward higher requirements on reserve capacity for maintaining the power system balance. To address this issue, this letter investigates a novel distributed event-triggered consensus control (ETCC) method of large-scale inverter air conditioners (IACs) for demand response, which can achieve the same regulation objective and response speed while significantly

PV curves are generally obtained by considering lumped models of transmission lines. This approximated model can yield an inaccurate estimation of the maximum loading condition of the system. This letter shows that accuracy can be improved by considering line models with uniformly distributed parameters. Analytical evaluations of the PV curve and of the voltage collapse point of a two-bus system are

The OPA (ORNL-PSERC-Alaska) model has been widely used in cascading failure simulations to predict likely and plausible sequences of cascading failures. This letter focuses on an algorithmic approach to enhance the OPA model whose main engine is based on quasi-steady-state models without considering the impact of collective transient dynamics of the entire system on the sequence of cascading failures

The multitudes of inverter-based distributed energy resources (DERs) can be envisioned as distributed reactive power (var) devices ( mini-SVCs ) that can offer var flexibility at the TSO-DSO interface. To facilitate this vision, a systematic methodology is proposed to derive an aggregated var capability curve of a distribution system with DERs at the substation level, analogous to a conventional bulk

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Recently, the turnover of energy services between transmission-distribution grids has continued to increase, arousing widespread attention to the efficient coordination between transmission system operator (TSO) and distribution system operator (DSO). The existing literature has characterized the feasible region of distribution networks via equivalent projection methods, which is conducive to the participation

Using machine learning to obtain solutions to AC optimal power flow has recently been a very active area of research due to the astounding speedups that result from bypassing traditional optimization techniques. However, generally ensuring feasibility of the resulting predictions while maintaining these speedups is a challenging, unsolved problem. In this letter, we train a neural network to emulate

This letter proposes a generalized stabilizer-oriented design method for grid-forming virtual synchronous generator (GFVSG) attached to weak-stiffness power networks, where a rate of change of frequency feedforward control strategy (RoCoF-FCS) is put forward to improve frequency stability, enhance damping performance, and avoid aperiodic loss of synchronization (ALoS). In addition, the feedback analytical

A linear and convex model has been recently presented for the operation of battery energy storage units that does not explicitly prevent their simultaneous charge and discharge in the problem formulation. This letter claims that the model in such a literature contribution is capable of ensuring the physical realizability of the battery dispatch only when nondiscrete decisions are considered in the

TSO-DSO coordination together with flexibility service pave the way for the grids to make the most of distributed energy resources while maintaining system secure operations. In T-D coordination, stemming from the diversity of distribution systems including sizes and renewable levels, vulnerable distribution systems may be placed in unfavorable working conditions under the same coordination with TSO

In this paper, a robust distribution system expansion planning (DSP) approach is presented to supply the load growth locally and move toward nearly zero energy local distribution areas (LDAs). In the proposed approach, a distribution system operator (DSO) is responsible for secure and optimum operation of LDAs. Therefore, investors on distribution system upgrades use this approach to maximize the profit

The hybrid AC/DC admittance of interlinking converters operating under AC voltage control mode may contain right half-plane (RHP) pole(s), and thus, the existing harmonic stability analyses on grid-tied interlinking converter systems may become inapplicable as well. Aiming at addressing this deficiency, this letter modifies the hybrid AC/DC admittance definition and re-studies the harmonic stability

Synchronization is the key of AC power system operation, but its mechanism becomes unclear with the large-scale integration of voltage-source converters (VSCs). As an important feature distinguishing VSCs from synchronous generators (SGs), the current-source characteristics of VSCs have hardly been focused from the perspective of synchronization. In this letter, a synchronization mechanism between

To limit the probability of unacceptable worst-case linearization errors that might yield risks for power system operations, this letter proposes a robust data-driven linear power flow (RD-LPF) model. It applies to both transmission and distribution systems and can achieve better robustness than the recent data-driven models. The key idea is to probabilistically constrain the worst-case errors through

Reliability evaluation has developed a trend of embedding unit commitment to replace power flow for more accurate operation strategies, while its potential reverse, embedding reliability evaluation in unit commitment, has yet to see equal exploration. This unrecognized, yet meaningful, technical attempt will encounter modeling and computational burden, largely caused by the recursive function and non-convex

This paper presents a real-word implementation of a TSO-DSO-customer coordination framework for the use of flexibility to support system operation. First, we describe the general requirements for TSO-DSO-customer coordination, including potential coordination schemes, actors and roles and the required architecture. Then, we particularise those general requirements for a real-world demonstration in