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power_steadystate

Compute steady-state values of voltages and currents of model

Syntax

power_steadystate('sys')
sps = power_steadystate('sys')

Description

power_steadystate('sys') opens the Steady-State Voltages and Currents Tool dialog box that allows you to view steady-state values of the inductor currents and capacitor voltages (electrical state variables), steady-state voltages and currents of measurement blocks and sources, as well as steady-state voltages and currents of nonlinear blocks of a model. This tool can also be activated from the Powergui block dialog box by selecting Steady-State Voltages and Currents.

If the model contains power electronic switches (diodes, thyristors, IGBTs, and so on) the steady-state values are computed considering them as open-circuit. If the model contains breakers (Breaker, Three-Phase Breaker, Three-Phase Fault blocks) the steady-state values are computed considering their initial status (open-circuit or short-circuit).

sps = power_steadystate('sys') returns a structure with the fields:

FieldDescription
circuitThe name of the model
FrequenciesVector listing the source frequencies in the model
StatesThe names of the electrical states of the model
XssThe steady-state values of electrical states of the model
DependentStatesThe names of the dependent states, if any
MeasurementsThe names of the Measurement blocks of the model
Yss_MeasurementsThe steady-state values of measurement blocks of the model
SourcesThe names of the electrical source blocks of the model
Uss_SourcesThe steady-state values of the electrical sources of the model
NonlinearOutputsThe names of the outputs corresponding to the nonlinear blocks (current-source injection based models). It consist of the measured terminal voltages used by the nonlinear models to compute the corresponding current sources
Yss_NonlinearOutputsThe steady-state values of outputs used by the nonlinear blocks
NonlinearInputsThe names of the inputs corresponding to the nonlinear blocks of the model
Uss_NonlinearInputsThe steady-state values of current inputs defined by the nonlinear blocks (current-source injection based models)

    Note   When the model contains more that one source frequency, the Xss, Yss_Measurements, Uss_Sources, Yss_NonlinearOutputs, and Uss_NonlinearInputs fields return a matrix of steady-state values. For every source frequency listed in the Frequencies field, there is a corresponding column of steady-states values in the matrix.

Dialog Box

Steady state values

Display measurements of steady-state voltages and currents in the model.

Units

Set the Units parameter to Peak values to display the peak values of the selected values. Set the Units parameter to RMS to display the root-mean-square (RMS) values of the selected values.

Frequency

Allows you to choose the frequency, in hertz (Hz), that you want for display of the voltage and current phasors. The Frequency parameter lists all the different frequencies of the electrical sources of the model.

States

If selected, the window displays the steady-state phasors of the capacitor voltages and inductor currents of the circuit. The default is unselected.

Measurements

If selected, the window displays the steady-state voltage and current phasors of the measurement blocks of the circuit. The default is selected.

Sources

If selected, the window displays the steady-state voltage and current phasors of the electrical sources of the circuit. The default is unselected.

Nonlinear elements

If selected, the window displays the steady-state voltages and currents of the nonlinear blocks of the circuit. The default is unselected.

Format

In the pull-down menu, choose the format in which you want your measurements displayed. The floating point option is displayed in mantissa-exponent form with five significant figures. The best of option displays with four significant figures and uses mantissa-exponent form only for numbers larger than 9999. The final option is displayed in plain numbers with two figures to the right of the decimal point. The default is floating point.

Ordering

In the pull-down menu, choose the ordering in which you want your measurements displayed. The Value then name option displays the steady-state values in the first column followed by the names of the states variables. The Name then value option displays the name of the states variables in the first column followed by the steady-state values.

Update Steady State Values

Recompute and display the steady-state measurements.

Sign Conventions for Voltages and Currents

Unlike Simulink® signal lines and input and output ports, the Physical Modeling connection lines and terminal ports lack intrinsic directionality. The voltage and current polarities are determined, not by line direction, but instead by block orientation. To find out a block orientation, first click on the block to select it. Then enter the following command:

get_param(gcb,'Orientation')

The following table indicates the polarities of the currents and voltages for single-phase and three-phase RLC elements (branches or loads), surge arresters, and single-phase and three-phase breakers. The table also indicates the polarities of their state variables (inductor currents and capacitor voltages).

Block
Orientation

Positive Current
Direction

Measured
Voltage

right

left —> right

Vleft – Vright

left

right —> left

Vright – Vleft

down

top —> bottom

Vtop – Vbottom

up

bottom —> top

Vbottom – Vtop

The natural orientation of the blocks (that is, their orientation in the Element library) is right for horizontal blocks and down for vertical blocks.

For single-phase transformers (linear or saturable), with the winding connectors appearing on the left and right sides, the winding voltages are the voltages of the top connector with respect to the bottom connector whatever the block orientation (right or left). The winding currents are the currents entering the top connector. For three-phase transformers, the voltage polarities and positive current directions are indicated by the signal labels used in the Multimeter block.

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