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Voltage source converter (VSC) is fundamental and critical in renewable energy integration and transmission and has become ubiquitous in power systems. For the design and operation of power systems with VSCs, electromagnetic transient (EMT) simulation is indispensable. However, a large number of VSCs in power systems cause a high time-consuming issue in EMT simulation. This article proposes a fast EMT simulation model for VSCs with arbitrary topology based on switch-state prediction. The accurate switch-state prediction has two steps: Preliminary switch-state prediction and simultaneous switching prediction. It avoids the iterative computation required to obtain a feasible switch-state combination in the traditional EMT simulators. Extensive tests on different types of VSCs and a dc microgrid demonstrate that the proposed fast model significantly improves the EMT simulation efficiency of power systems with VSCs. [ABSTRACT FROM AUTHOR]

In multi-infeed hybrid AC-DC (MIDC) systems, the asynchronous interconnection between regional grids, complicated system dynamics and possible emergency faults have enormous effects on the frequency stability. To address the frequency instability problems in emergency situations, this paper proposes a decentralized emergency frequency control (EFC) strategy based on coordinated droop for the MIDC system. First, a P-f droop control for LCC-HVDC systems is introduced, and the coordinated droop mechanism among LCC-HVDC systems and generators is designed. Then, to appropriately allocate the power imbalance among the LCC-HVDC systems and generators, an optimal emergency frequency control (OEFC) problem is formulated, and the optimal droop coefficients are selected in a decentralized way, which can deal with various control objectives. A Lyapunov stability analysis shows that the closed-loop equilibrium is locally asymptotically stable considering the LCC-HVDC dynamics. The effectiveness of the proposed emergency control strategy is verified through simulations. [ABSTRACT FROM AUTHOR]

As more generators and loads are integrated by power electronic converters with complicated controls, electromagnetic transients (EMTs) simulation becomes an important tool for studying dynamic characteristics of large‐scale power systems. To accelerate system‐level EMT simulations, a fine‐grained parallel algorithm on graphics processing units (GPU) is proposed. By decomposing the computational models of the EMT simulation into heterogeneous, homogeneous and network solution computations, the simulations are mapped into three unified GPU kernels. To incorporate control signals and non‐linear features of electrical components, heterogeneous computations are formulated as layered direct acyclic graphs (LDAG) of primitive operations. An LDAG kernel is designed to carry out theses primitive operations efficiently by grouped threads. Then, homogeneous computations for state updates of electrical components are modelled as sets of fused multiply‐add (FMA) operations, which are concurrently processed by an FMA kernel. Moreover, a hybrid network solution kernel is designed to solve the network equations, which can adaptively select dense or sparse solvers. Large‐scale test systems are created and simulated on an NVIDIA K20x GPU. The results show that the proposed GPU‐based EMT simulations are accurate and achieve 10x speedups over the CPU‐based ones. [ABSTRACT FROM AUTHOR]

This letter proposes a method to determine the optimal shift frequency (OSF) for shifted frequency (SF)-based simulation. The SF-based simulation algorithm is briefly introduced, and the error of SF-based simulation is quantitatively analyzed. The OSF that minimizes the error is deduced, which can improve the simulation accuracy. Furthermore, the influence of time-step size on the OSF is investigated. Numerical test results demonstrate the effectiveness of the method in determining the OSF for SF-based simulation. [ABSTRACT FROM AUTHOR]

A multi-scale transients model of a doubly fed induction generator (DFIG)-based wind energy conversion system (WECS) is developed, implemented, and validated. All ac circuit and control quantities of the electrical part are modeled by analytic signals rather than just real signals. In addition to the real parts, the analytic signals also comprise orthogonal imaginary parts. While measured Fourier spectra of real ac quantities involve positive and negative frequency components, they only involve positive frequency components when extended and represented as analytic signals. With the introduced shift frequency operator, the analytic signal can now be shifted in the frequency domain to reduce its maximum frequency contents and thus allow for a larger time-step size in accordance with the Nyquist criterion. If the shift frequency is set equal to the ac fundamental frequency, then the affiliated ac voltages and currents become dynamic phasors. At a zero shift, however, instantaneous signals can be tracked as in an electromagnetic transients program (EMTP). This is illustrated here for the voltage sourced converters (VSC) of the WECS. By appropriate selection of the shift frequency, both electromagnetic and electromechanical transients are simulated efficiently. Studies involving wind power fluctuations, three-phase-to-ground fault and single-phase-to-ground fault confirm these claims. [ABSTRACT FROM AUTHOR]

In this paper, a new synchronous machine model is developed for electromagnetic transients program type simulations. The stator circuit is expressed in the abc phase domain. The machine model is represented as a Norton equivalent with a current source in parallel with a constant Norton admittance. The machine equations are reformulated so that the computational effort required for the modeling of the machine is reduced. Test studies demonstrate the accuracy of the proposed synchronous machine model and show that the proposed model is computationally more efficient than the existing constant conductance phase domain model and voltage-behind-reactance model. [ABSTRACT FROM AUTHOR]

The twelve-phase synchronous machines are widely used for the power supply of integrated power systems on board. This paper formulates two phase-domain (PD)-type models of twelve-phase synchronous machines for the simulation of nodal analysis-based electromagnetic transients programs (i.e., EMTP-type simulation). The PD model for the twelve-phase machine is first formulated, which avoids the interface error in the qd0 model. It is well-suitable for the implementation in EMTP-type simulators. To further improve the simulation efficiency of a power system with twelve-phase machines, a constant conductance PD (CC-PD) model is proposed, avoiding the re-factorization of the network conductance matrix at every time-step. Test results demonstrate the accuracy and efficiency of the two proposed PD-type models for the EMTP-type solution. • The PD and CC-PD models for the twelve-phase machine are formulated. • It fills the gap in EMT simulation for power systems with 12-phase machines. • The CC-PD model can be adopted in real-time EMT simulations for power systems. [ABSTRACT FROM AUTHOR]

• The original shifted frequency-based EMT simulation algorithm is improved using the 3S-SDIRK for numerical integration. • The proposed shifted frequency-based EMT simulation is free from numerical oscillations. • The presented shifted frequency-based simulation is more accurate than the traditional shifted frequency-based EMT simulation. To improve the computational efficiency of electromagnetic transient (EMT) simulation, the shifted frequency (SF)-based EMT (SFEMT) simulation is proposed in the literature, and large time-step size can be adopted in the SFEMT simulation. In the existing SFEMT simulation, the trapezoidal (TR) method is used for numerical integration. Sustained oscillations will appear in the simulation due to the use of the TR method. To overcome this problem, this paper applies the three-stage singly diagonally implicit Runge–Kutta (3S-SDIRK) method to the numerical integration of SFEMT simulation. First, the SFEMT modeling is briefly reviewed, and the 3S-SDIRK method is introduced. Then, the numerical integration of SFEMT simulation using 3S-SDIRK is elaborated detailedly, and the merits of the 3S-SDIRK-based simulation are analyzed by comparing with the TR, 2S-DIRK and TR-BDF2-based simulations. Numerical results show that the SFEMT simulation using 3S-SDIRK for integration is free from numerical oscillation and is accurate and efficient. [ABSTRACT FROM AUTHOR]