Frequency-Adaptive Power System Modeling for Multiscale Simulation of Transients

This paper presents a multi-scale model of synchronous machine in phase-domain for efficient and accurate simulation of diverse transients. It makes use of the simulation methodology frequency-adaptive simulation of transients (FAST) in which the shift frequency appears as a simulation parameter in addition to the time-step size. Through appropriate setting of both shift frequency and time-step size, the proposed synchronous machine model enables the integrative simulation of electromagnetic and electromechanical transients. Moreover, this model is established in phase coordinates leading to a direct interface with the multi-scale models of external power systems. Test studies are performed in a single-machine-infinite-bus power system. The results show that FAST simulation gives superiority over the simulation using the electromagnetic transients program (EMTP).

In this paper, a multiscale induction machine model for the simulation of diverse transients in power systems is developed in the dq0 domain. The proposed model includes main flux saturation. The equations that describe the electrical performance of the induction machine are represented through analytic signals whose Fourier spectrum can be shifted. In addition to the time-step size, the shift frequency appears as a novel simulation parameter. When the shift frequency is set to zero, then the model processes instantaneous signals for the representation of natural waveforms. When the shift frequency is set to the frequency of the stator electrical quantities in the dq reference frame, the Fourier spectra of the analytic signals are shifted to become dynamic phasors that allow for efficient envelope tracking. The setting of the shift frequency is adapted to the transients observed during simulation. Test cases verify the proposed multiscale saturable induction machine model and show that it supports accurate and efficient simulation of both electromagnetic and electromechanical transients within a simulation run.

three kinds of digital programs used in power system simulation are summarized in this paper. The electromagnetic and electromechanical transient simulation software ADPSS is introduced. Electromagnetic transient simulation, electromechanical transient simulation and electromagnetic-electromechanical transient hybrid simulation are performed respectively on Deyang-Baoji ±500KV HVDC system. The simulation result shows that the electromagnetic-electromechanical transient hybrid simulation has the advantage of electromagnetic transient simulation and electromechanical transient simulation. It can effectively analyze the process of the local electromagnetic transient in large-scale grid. The simulation speed is fast and the result is accurate and reliable.

Shifted-frequency based electromagnetic transient simulation for power system dynamics using two-stage singly diagonally implicit Runge–Kutta method

A mathematical model for the simulation of electromagnetic transients in underground high-voltage cables is presented. The solution is carried out in the time domain; therefore, this model is compatible with time-domain solution algorithms, such as the one used in the EMTP (Electromagnetic Transients Program). The frequency dependence of the cable parameters and of the modal transformation matrices is taken into account. Comparisons with analytical and measured results are included. >

When conducting system-level research, it is unacceptable to adopt a detailed MMC electromagnetic transient model to bring about the amount of calculation. Although the use of electromechanical transient simulation and electromagnetic transient hybrid simulation technology or electromagnetic transient and dynamic phasor hybrid simulation technology can retain high simulation accuracy, it is not conducive to the model mechanism analysis and the control operation. In addition, the MMC average model is also used for AC and DC transient simulation. The average modeling uses controlled power sources to describe the average response of the converter, which can also be employed to the transient simulation. Due to the modeling properties of the ABC coordinate system, the average model is only suitable for time-domain simulation. The dynamic phasor modeling method employs the d−q axis coordinate system to analyze the MMC steady-state and research the small-signal stability. The order of each component in the d−q axis coordinate system model can be selected according to the required accuracy. Thus, the MMC dynamic phasor modeling scheme has widespread application in MMC-HVDC stability research, electromechanical transient simulation and controller design, etc. This article will establish an MMC dynamic phasor model to analyze the dynamic characteristics of system circulation.

Nowadays, there is quite high demand for electromagnetic transient (EMT) analysis programs and real-time simulators for power systems. In addition to the conventional demand such as overvoltage, over-current and oscillation simulations, the new demand that includes simulations of power-electronics circuits and power quality is increasing. With this background, development groups of EMT programs and real-time simulators have made progress in terms of computational performance and user experience. In Japan, Central Research Institute of Electric Power Industry has newly developed an EMT analysis program called XTAP (eXpandable Transient Analysis Program). This article overviews these international and domestic development trends of EMT analysis programs and real-time simulators.

At present, in the simulation of large-scale AC/DC systems, electromechanical transient simulation cannot accurately describe the dynamic characteristics of the system due to the limitations of its models and parameters. And the traditional electromagnetic transient simulation lacks accuracy and real-time in the simulation analysis due to the limitation of simulation speed. Therefore, it is necessary to propose an accurate electromagnetic transient real-time simulation method. Based on the BPA dynamic equivalent data of the East China AC/DC power grid, this paper establishes a real-time simulation model of the multi-feed DC power system in HYPERSIM. First, the accurate converter valve module of the DC system is modeled to reflect the characteristics of the converter valve more accurately while ensuring the simulation speed. After that, the modeling method of the generator, load and other modules is given. Simulative results show that the steady-state and transient characteristics of the system are consistent before and after the conversion, which verifies the validity of the proposed modeling method. The research results give reference for the accurate simulation of large-scale multi-feed DC projects in the future.

This study presents a method to interface an electromagnetic transient (EMT) simulator with a dynamic phasor (DP) simulation program. The hybrid DP–EMT simulator offers flexibility in deciding the harmonic contents to be preserved in the DP domain; additionally, it offers significant reduction in computing time of large networks compared with EMT simulation. The proposed interfacing method is based on a generic transmission line, which uses specialised numerical techniques to transfer discretised waveform samples between the two simulators. These numerical methods produce the required mapping between EMT simulation samples and their counterpart DPs. This study describes the mathematical foundations of the DP–EMT interface and demonstrates them using an illustrative example. Several large networks are then studied to assess the interface's accuracy and performance in reducing computing time.

Direct and back-flashovers across line insulators are the main cause of transmission line outages, even when shield wires are used. So, the simulation of this phenomenon can be useful to the insulation design as well as to study the effectiveness of corrective actions. The Electromagnetic Transients Program (EMTP) is one of the most important tools in the simulation of electromagnetic transients, with a large library of electric and electro mechanic component models. Also, user defined models can be integrated with the main program. In this work, the integration of user defined models with the EMTP, as well as its application in lightning studies, are shown.

Detailed switching models (DSM) of ac–dc converters are available in many offline and real-time electromagnetic transient (EMT) simulation programs. However, such discrete models typically require small simulation time steps for accurately handling the switching events without interpolation. This paper proposes a new parametric modeling approach for line-commutated and 2-level voltage-source ac–dc converters. The proposed methodology is based on parametric functions that relate ac and dc variables in the instantaneous sense, which allows the reconstruction of the waveforms of voltages and currents (with the same of details as the switching models of converters) without topological changes in the converter circuit. Thus, it can operate at larger time steps without requiring interpolation, thereby enhancing simulation efficiency. The computational advantages of the proposed models over the conventional switching models are demonstrated in offline PSCAD and real-time RTDS NovaCor simulators in terms of maximum possible time step size and accuracy. It is shown that the proposed models can accurately run with much larger time steps (up to ∼200 μs for LCRs, and up to ∼50 μs for VSCs) compared to detailed switching models, which are limited to relatively small time steps of ∼10 μs.

Electromagnetic transient (EMT) simulation is one of the routine tasks being executed in modern power systems. Typically, the most common EMT simulation method is the trapezoidal integration method, however, sustained numerical oscillations are possible to appear using this method, for instance, getting the voltage waveform across an inductance during a sudden current interruption. Two-stage diagonally implicit Runge-Kutta (2S-DIRK) method is a L-stable numerical method, which is able to avoid numerical oscillation. The 2S-DIRK method has been applied to solve simple RLC circuit simulations, in this paper, it is extended to system level EMT simulations considering the electromagnetic transient characteristics and nonlinearity for generators, transformers and loads. Case studies are performed to verify the effectiveness of the 2S-DIRK method in power system level EMT simulation, by comparing the accuracy and numerical stability with traditional methods.

Faster calculation methods are desired for electromagnetic transient (EMT) simulation programs, since circuits simulated are becoming increasingly larger and more complex. If there are time-varying and non-linear elements in the circuit to be solved, the solution process requires repeated factorization of the coefficient matrix of the circuit equations. The repeated factorization, which is often called refactorization, significantly increases the computation time. Up to now, the bottom right arranging (BRA) method has been applied for refactorization in EMT simulation programs in order to reduce the computation load. In this paper, the author proposes the use of the varying elements tracing (VET) method, which is one of the refactorization methods proposed for power flow calculations, for an offline EMT simulation program. Using some test circuits, the computation time by the BRA method and that by the VET method are examined, and the following facts are found. In most test circuits, both methods greatly improve refactorization speed, but in some test circuits, the BRA method shows degraded refactorization speed due to increased fill-ins. As for the entire EMT simulation time, the VET method improves the refactorization speed by a factor of 1.6 times at most. On the other hand, the BRA method improves the refactorization speed by a factor of 1.5 times in the best case but degrades it in some test circuits.

Since the modern power system presents a “double high” trend, the operation mechanism becomes more and more complicate, that puts forward higher requirements for power system simulation. Electro-mechanical transient(TS) simulation cannot fully reflect the fast response dynamic characteristics of power electronic equipment. Due to the speed, scale and amount limitation of calculation, current electro-magnetic transient (EMT) simulation cannot perform large-scale power grid simulation. Based on TS simulation software PSS/E and EMT simulation software RTDS, a real-time EMT-TS hybrid simulation platform was developed in the previous work, we extend it to a large scale AC/DC power system in this paper. As an important issue for hybrid simulation, an interface bus location method is proposed. Also, a power system security assessment method based on the hybrid simulation is presented. These above are tested in a real power system of China.

Parallel-in-time methods are emerging to accelerate the solution of time-consuming problems in different research fields. However, the complexity of power system component models brings challenges to realize the parallel-in-time power system electromagnetic transient (EMT) simulation, including the traveling wave transmission lines. This paper proposes a system-level parallel-in-time EMT simulation method based on traditional nodal analysis and the Parareal algorithm. A new interpretation scheme is proposed to solve the transmission line convergence problem. To integrate different kinds of traditional EMT models, a component-based EMT system solver architecture is proposed to address the increasing model complexity. An object-oriented C++ implementation is proposed to realize the parallel-in-time Parareal algorithm based on the proposed architecture. The results on the IEEE-118 test system show 2.30x speedup compared to the sequential algorithm under the same accuracy with 6 CPU threads, and a high parallel efficiency around 40%. The performance comparison of various IEEE test cases shows that the system's time-domain characteristics determine the speed-up of Parareal algorithm, and the delays in transmission lines significantly affect the performance of parallel-in-time power system EMT simulations.