This paper develops a novel multi-rate, multi-solver co-simulation framework combining dynamic phasors, transient stability, base-frequency dynamic phasors for frequency-adaptive simulation of transients, and electromagnetic transient (EMT) models. This framework subdivides a given power network into several types of subsystems based on the connected devices, required accuracy in representing dynamic details, electrical distance from perturbations, and the intended purpose of the study; as such, the paper describes methods and guidelines to simulate each subsystem using the most appropriate solver and time-step size to maximize simulation efficiency and accuracy. It also addresses the tasks of multiple interfacing and solver interactions that are essential in coupling different solvers. The proposed framework is built around an industrial-grade EMT simulator, to which other solvers are interfaced, enabling access to a variety of power system models and distinct features. The accuracy and efficiency of the framework are demonstrated through co-simulations carried out on a modified version of the 118-bus network, which includes an MMC-HVDC system.

The paper examines a number of methods for extracting dynamic phasors from samples of natural waveforms that are generated using electromagnetic transient (EMT) simulators. It delves into the theory underlying each phasor extraction method and the numerical routines used for their implementation. The paper performs an indepth analysis of the properties of the extracted phasors for general power system signals that may include electromechanical oscillations, dc and harmonic components, imbalances, and arbitrary transients. Simulation results are presented to demonstrate any limitations of these methods and to assess the resulting harmonic spectra of the phasors. An EMT-dynamic phasor co-simulation example is also included, in which various phasor extraction methods are implemented. The paper's findings are essential in selecting and implementing phasor extraction methods used in co-simulations of large power systems using EMT and dynamic phasors solvers.

This paper introduces a method to represent the dynamics of modular multilevel converters embedded in a large power system using a multi-rate co-simulation platform. The co-simulation platform comprises dynamic phasor (DP) and electromagnetic transient (EMT) solvers. It uses large simulation time-steps in the DP subsystem for accelerated computations. The specialized dynamic phasors used in the co-simulator allow retention of a large portion of the harmonic spectrum of the waveforms and as such usage of average-value Modular Multilevel Converter (MMC) models with an enriched harmonic spectrum becomes possible. The paper develops a model for the MMC including the internal dynamics of the arm currents and embeds it in the DP-side of the co-simulator. Special provisions for modeling the converters control system, which may include non-linearities, are also discussed. This approach is useful in the study of large systems with a large penetration of MMCs. The developed model allows representation of MMCs in parts of the network where average-value models suffice and where conventional EMT models are not necessary. Extensive studies of the performance of the model in terms of its accuracy and computational advantage are presented to establish its merits.

This study presents a novel multi-rate algorithm for the co-simulation of power system transients using base-frequency dynamic phasor solver for frequency adaptive simulation of transient (BFAST) and electromagnetic transient (EMT) solvers. The BFAST solver alters its solution technique from dynamic phasors to EMT based upon the frequency contents of the waveforms being simulated. A changeover algorithm between the two solvers is also presented. The BFAST solver is then integrated with an industrial-grade EMT solver to develop a BFAST–EMT multi-rate co-simulator. The interface between the two solvers is established using transmission lines at the partitioning locations. The co-simulator combines the benefits of dynamic phasors, frequency adaptive simulation of transients, parallel processing, and multi-rate simulation. The study describes the several solution modes of the proposed co-simulator. Illustrative examples are included to demonstrate the accuracy and computational benefits of the proposed co-simulator.

This paper presents a new dynamic phasor (DP) model of a modular multilevel converter (MMC) with extended frequency range for direct interfacing to an electromagnetic transient (EMT) simulator. The internal dynamics of the MMC are modeled considering dominant harmonic components of each variable. To model the external dynamics of the converter, a novel construct referred to as a base-frequency DP is employed, which allows to capture and model any number of frequency components of external variables without a significant increase in computational burden. The proposed model is validated against detailed EMT models by comparing its results for an inverter system, a back-to-back high-voltage direct current system, and a 12-bus power system built in PSCAD/EMTDC simulator. Simulation results prove that the new model is significantly more computationally efficient than existing models and is capable of maintaining a high level of accuracy. Experimental verification on a scaled-down laboratory setup is also included.

Current harmonic filter is a unit connected in parallel with the load at the load itself which injects the total harmonic current demanded by the load, and thus preventing harmonic current going into the power system. This paper describes the basic design, control modeling and simulation of a single phase current harmonic filter. Modeling and simulation is done in the MATLAB SEVIULINK environment. The filter consists of a current source inverter (CSI) with a front end fixed rectifier to obtain required dc voltage. This filter can eliminate harmonics up to about 50 th order. Analog closed loop scheme is used to control the inverter. Basic simulation of the harmonic current filter, the control system and simulation results are discussed in the paper.