Frequency-Dependent Network Equivalent (FDNE)

This component creates a multi-port, frequency-dependent network equivalent (FDNE) from given characteristics, such as impedance (Z), admittance (Y) or scattering (S) parameters. This model first approximates the parameters with rational functions, using the Vector Fitting technique. Once the parameters are expressed in rational form (pole/residue) or state-space form, an EMT-type, frequency-dependent network equivalent can be constructed, consisting of admittances and current sources.

In power systems, a Frequency-Dependent Network Equivalent (FDNE) model may typically be used to represent many system types, including wide-band, reduced-order network equivalents, high-frequency power transformers, or short transmission lines; all from frequency sweep measurements/computations. This component can be used to model high-frequency power electronic converters and filters as well.

Input Data

Input to this component is the frequency-dependent characteristics of the network to be represented by an equivalent, and is provided as a text file. The input data may be given in one of the following formats:

NOTE: In the Interface to Harmonic Impedance Solution component, the Impedance Output Type should be set to Phase Impedances.

Output Data

The component instance number and call number are used to create detailed output files (ex. fdne_<instance number>_<call number>.log) in the project temporary folder. These output files may be useful to diagnose any problems/errors that may occur. The curve-fitting detailed output files are also created for all input methods except, ABCD parameters. The output files fdne_<instance number>_<call number>_Y_MAG.out and fdne_<instance number>_<call number>_Y_ANG.out show the actual/ fitted magnitude and phase data respectively.

Power Injections

The FDNE component can be used to model a portion of a network (i.e. a sub-network) using parameters, such as impedance or admittance (these parameters only represent a passive network). However, the sub-network may consist of active elements, such as voltage sources, etc. The effect of active elements can be modeled by defining power injections at the component terminals. This will give accurate power flow and terminal voltages. When the terminal conditions (voltage, angle, active and reactive power) or current injections are defined, the model automatically calculates the current injections.

Connection Port Assignments

Input Parameters

Name	Text		Enter a unique name. Each FDNE component in a project should possess a unique name: A detailed log file is created in the project temporary folder and is useful when finding errors. This log file contains information such as curve-fitting results, etc.

Total Number of Ports	Choice		Select from 1 to 10. This is the total number of ports (or electrical connections) to the network equivalent component.

Number of Ports on One Side	INTEGER	Literal	This parameter may be used to configure port positions on the component graphic. Having the ports on both sides may help with external connections.

Reference Port	Choice		Select Ground or External Connection. When Ground is selected, the FDNE network is created with respected to the network ground. For example, assume that the FDNE represents frequency-dependent impedance (Z). If the reference port is grounded, Z is defined between the electrical connection port and the ground. If External Connection is selected, the reference will be made available for external connection on the component graphic, via a connection port. In this configuration, Z is defined between the electrical connection port and the reference port.

Detailed Log File	Choice		Select Create or Do Not Create.

Input Data File	Text		Enter a the name of the input data file.

Path to Input File	Choice		Select Relative or Absolute. Select Relative if you are giving the input data file name as relative to the current working folder. Use absolute path if you are giving the data file name as an absolute path (ex. C:\temp\harm.out).

Data Format	Choice		Select From Harmonic Impedance Component, Impedance Parameters, Scattering Parameters, Admittance Parameters, Admittance as ABCD Parameters or Scattering as ABCD Parameters. Select the type of input data to be used to calculate the network equivalent. See Input Data File Format for details.

NOTE: This category defines the curve-fitting parameters used to approximate the data from the input file only when Data Format is set to not use ABCD parameters.

Maximum Fitting Error (%)	REAL	Literal	Enter the maximum error allowed for the curve fitting process [%]. The program will incrementally increase the order of the approximation to fit the data until this error criterion is met. However, the resulting number of poles is not allowed to exceed the specified Maximum Poles per Column. Specifying a high value here will lead to a lower order approximation and thus a faster simulation.

Maximum Order of Fitting	INTEGER	Literal	Enter the maximum number of poles to be used for curve fitting.

Steady State Frequency	REAL	Literal	Enter the system steady-state frequency (F0) [Hz]. This is only important, if you want to define different weighting functions between different bands of frequencies (see below).

Weighting Factor for Minimum to Steady Sate Frequency	REAL	Literal	Provide a weighting factor for the frequency range Fmin to F0. Note: The minimum frequency Fmin is the minimum frequency defined in the data file.

Weighting Factor for Steady State Frequency	REAL	Literal	Provide a weighting factor for the steady-state frequency F0.

Weighting Factor for Steady State to Maximum Frequency	REAL	Literal	Provide a weighting factor for the frequency range F0 to Fmax. Note: The maximum frequency Fmax is the maximum frequency defined in the data file.