## MatACDC

MATACDC is a free MATLAB based open source program for AC/DC power flow analysis. The program uses a sequential AC/DC power flow algorithm and can be used to simulate interconnected AC systems and Multi-terminal Voltage Source Converter High Voltage Direct Current (VSC HVDC) systems.

The AC/DC power flow problem is solved sequentially, meaning that the program solves the AC/DC power flow by iterating between the AC systems and the DC systems. With respect to the AC system power flow, the program completely relies on MATPOWER, a power flow and optimal power flow program in MATLAB. The package has been fully integrated with the existing AC power flow routines developed in MATPOWER, while keeping the MATPOWER original source code unaltered.

MATACDC shares the same philosophy as MATPOWER and MATDYN: “It is intended as a simulation tool for researchers and educators that is easy to use and modify.” The source code of MATACDC is available. The code is well documented, structured and easy to understand and modify.

## PowerModelsACDC

PowerModelsACDC.jl is a Julia/JuMP/PowerModels package with models for DC lines, meshed DC networks, and AC DC converters. Building upon the PowerModels architecture, the code is engineered to decouple problem specifications (e.g. Power Flow, Optimal Power Flow, …) from the power network formulations (e.g. AC, DC-approximation, SOC-relaxation, …).

## HVDC Grid Test System

The four-bus HVDC grid test system can be used as standard test system for HVDC power system studies in EMT-type software. The PSCAD simulation files contain a pre-made HVDC grid with 4 converters, connected by a meshed DC grid with five cables. The size of the HVDC grid allows to run the model also in the educational version.

A control and protection system for the HVDC grid is implemented, but can be easily modified. A full description of parameters and model components is given in this paper.

## DSAnalysis

The DSAnalysis is a easy to use Matlab toolbox supporting the analysis of dynamic systems. Given the nonlinear operations, the periodic trajectory of the system states, and the time delays presented in the converter control structure, this toolbox utilizes an enhanced harmonic state space (HSS) framework which enables the analysis of delayed linear time periodic (LTP) systems. Thus, the method accurately captures the stability properties of a future power system assets.

The current version supports:

Definition of dynamic systems by means of analytical differential equations in state-space form, their numerical parameters and inputs (control references and external sources); Calculation of periodic trajectories or equilibria; Symbolic linearisation of the analytical differential equations in state-space form; Transformation of linear time-periodic systems into linear time-invariant systems by means of frequency-lifting; Calculation of eigenvalues/characteristic roots, enabling small-signal modal analysis (including participation factors); Calculation of frequency responses, enabling frequency-domain stability assessments; Numerical integration of the differential equations, i.e. time-domain simulation.

## Z-tool

Z-tool is a Python-based implementation for the stability analysis of modern power systems. The core functionalities are frequency-domain subsystem characterization, i.e. impedance/admittance measurements, and small-signal stability assessment. The analysis relies on an existing system model in the EMT simulation software PSCAD and/or external data input.

The following features are currently implemented and validated:

• Voltage perturbation-based admittance scan at several nodes, including MMC-based systems and black-box components

• Stability assessment via Generalized Nyquist Criterion applicable to standalone-stable MIMO systems

• Oscillation mode identification via eigenvalue decomposition (EVD) and bus participation factors

• Passivity and gain assessment via Singular Value Decomposition functions