Complexity Reduction for Converter-Driven Stability Analysis in Transmission Systems

Purpose – Analytical determination of harmonic components of current in electric circuits containing semiconductor converters with the use of a small parameter method (SPM) in frequency domain. The paper aims to discuss these issues. Design/methodology/approach – A SPM realized in frequency domain was used in the analytical analysis of electric circuits with semiconductor converters. An automated method of formation of orthogonal harmonic components of electrical values on the basis of discrete convolution algorithm was used to provide the possibility of realization of calculation in frequency domain. A nonlinear characteristic of a semiconductor converter was presented by the method of numerical approximation. A numerical structured simulation method was applied to determination of the reference values of current in the analyzed circuit. Laws of theoretical electrical engineering were used for formation of the equations of voltage balance in the circuit with a nonlinear element. Findings – It is shown th...

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.

High Voltage Direct Current (HVDC) systems are increasingly popular in electric power grids. Control system of such devices can cause instabilities when interacting with other equipment in a power system. Depending on the control system dynamics, instability and resonance can occur in a wide range of frequencies (up to few kHz). Low and high frequency resonances have been registered in several power electronics based project. In this article, several realistic test cases where oscillations can occur between HVDC links and power system components are illustrated using electromagnetic transient (EMT) simulations. In order to analysis and identify the cause of such instabilities, this paper illustrates how to conduct a frequency domain analysis by means of EMT time domain simulation. As EMT-type models provided by the manufacturers are often inaccessible (or black-boxed), the method presented considers black-boxed HVDC link model.

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.

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

We show how frequency domain design procedures can be effectively used in nonlinear fuzzy control systems. For this purpose, theoretical justifications of the approach discussed here are provided to show that solid notions from nonlinear system and control theory can be successfully applied in the fuzzy control domain. The methodology proposed is very simple, but powerful, effective and practical. In addition, it supports systematic control system design and stability analysis in the frequency domain for systems described by mathematical, linguistic or experimental models. Several case studies are included to illustrate the usefulness of frequency response in conventional fuzzy control systems analysis and design.

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.

Most transient stability programs can solve very large systems but the representation of individual components of the system, in particular power electronic devices and control systems associated with FACTS and HVDC transmission systems cannot be represented in detail. Electromagnetic transients simulators, on the other hand, can represent system components and control systems in great detail, but are impracticable for the simulation of very large systems, and dynamic equivalents are required. It is apparent that the future of simulation lies in the development of hybrid simulators, which would allow practicable simulation of large-scale power systems with embedded modeling on power electronic devices in devices level. In this paper, an attempt has been made to incorporate an electromagnetic transient model of a static VAr compensator (SVC) into the traditional transient stability simulation program.

Chapter 7 - Overview of stability analysis methods in power electronics

The electromagnetic transient (EMT) response of a power system can be determined either by time-domain (TD) or by frequency-domain (FD) methods. This chapter deals with those aspects of frequency domain analysis and of digital signal processing that have become essential for the analysis of transients in modern power systems. It provides a brief review of basic concepts of FD methods. Continuous-time Fourier analysis is introduced as an extension of phasor analysis which is more familiar to power engineers. The chapter presents the basic differences between continuous-time and discrete-time Fourier analysis. Of special interest in the chapter are: (1) the effect of aliasing, (2) the sampling theorem and (3) the principle of conservation of information. The chapter also provides a brief overview of multirate transient analysis methods based on the discrete Fourier transform (DFT) and the numerical Laplace transform (NLT).

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.

This paper is concerned with distributed consensus control of unknown multiagent systems. As the system’s dynamics is unknown, an adaptive Fourier decomposition (AFD) based iterative learning control (ILC) dynamics adaptive matching method in frequency domain is put forward to deal with it. First, large amounts of input and output measurement data are used to estimate the frequency domain characteristics of the system by Takenaka-Malmquist functions. Second, convert the traditional time domain ILC to the frequency domain to establish a matching relationship with the estimated frequency domain features. Then, an adaptive iterative learning rate is constructed to achieve the optimal convergence at each sampling point. The feasibility of the proposed algorithm is guaranteed by the convergence of AFD in Hardy space <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$H^{2}(\mathbb {D})$ </tex-math></inline-formula> under the maximum selection principle. Compared with the reinforcement learning data-driven control scheme, the method proposed in this paper has obvious advantages in the control accuracy and convergence efficiency. In addition, this paper takes two kinds of denoising algorithms based on unwinding AFD to deal with the multi-agent systems with channel noise. Finally, the feasibility and effectiveness of the developed method are verified by a series of simulations.

Parameter estimation and identification is an important part of flight mechanic. In this study the purpose is to estimate flying parameters for resistance derivation and aircraft control. At first those parameters were estimated for lateral-directional motion with which we could reach more precise results and fewer errors in time domain. In frequency domain we could reach nearly acceptable results with a specific step in special frequency band limit. In longitude motion we also had suitable responses in time domain. But we didn't have good results in frequency domain method. So to get answers from this system we analyzed motion modes and after processing frequencies to attain effective and critical signals, analysis was done in the frequency limit and therefore better results were obtained.

The increasing penetration of renewables into modern power systems is bringing new oscillatory stability concerns. It is of significance to find all oscillatory modes concerned and evaluate components’ participation into each mode, especially the dominant one. To address this issue, a frequency-domain modal analysis method is developed in this paper. It represents the target system with a networked impedance model and works out the oscillatory modes by locating the zeros of the determinant of the loop impedance matrix or nodal admittance matrix. Loop/nodal participation factors, branch observability, and component sensitivity are derived to give insight into the oscillation, including its origin, oscillation path, and contributive components. The proposed method has been conducted on a simple passive circuit and a practical wind power system that experienced actual subsynchronous resonance incidents. Theoretical results as well as electromagnetic transient simulations have verified its effectiveness. The proposed method has the potential to analyze very large power systems with high penetration of renewables.

Future space telescopes require tight thermomechanical stability. The thermal analysis may be based on a nonlinear steady solution with a superimposed linear transient perturbation. This linearity allows frequency domain (FD) thermal solutions that retain high resolution when scaled. Linearity allows generality through superposition. Linear superelements can represent subsystems and thereby simplify interfaces. The (rare) prior spacecraft FD thermal analyses have been with N×N system matrices, converting lumped parameter (LP) time domain models to FD. This paper includes continuously distributed resistance and capacitance elements. Exact distributed element results differ greatly from LP renditions at higher frequency. Two FD methods are used together: a 2×2 matrix method with a bridge to an N×N matrix method. The 2×2 method allows the combination of elements in series/parallel configurations into overall elements. The 2×2 matrices can then be used in an N×N system matrix formulation. This paper includes FD analysis and programming methods, FD testing methods, and model to data comparisons. A thermal signal generator was developed for FD testing.