Documentation

Current-Voltage Simscape Interface (gnd)

Ideal coupling between Simscape Power Systems and Simscape electrical circuits

Library

Fundamental Blocks/Interface Elements

Description

The Current-Voltage Simscape Interface (gnd) block connects Simscape™ Power Systems™ circuits with electrical elements from the Simscape Foundation library. This block preserves current through the block and voltage across the block, conserving electrical power.

  • On the Simscape Power Systems side, the electrical connector port sps acts like a controlled current source referred to the ground, feeding current from the Simscape side to the connected Simscape Power Systems elements.

  • On the Simscape side, the electrical connector port ssc acts like a controlled voltage source referred to the ground, feeding voltage from the Simscape Power Systems side to the connected Simscape elements.

The following figure gives an overview of the interface.

The block measures the voltage between the sps port and Simscape Power Systems electrical reference and propagates it to the ssc port, preserving the polarity with respect to the Simscape electrical reference. The block also measures the current flowing from the ssc port to the Simscape electrical reference and propagates it to the sps port.

You can specify a filter to break the algebraic loop between Simscape Power Systems and Simscape ports. You can specify the filter as a first order continuous transfer function or as a discrete unit delay block. You can apply the filter on the Simscape Power Systems side, to the measured voltage, or on the Simscape side, to the measured current. Depending on the measured signal where you apply the filter, the other signal is always a direct feedthrough.

If you do not specify a filter, direct feedthrough is applied on both measured signals. However, this configuration results in an algebraic loop containing the Voltage Measurement, Controlled Voltage Source, Current Sensor, and Controlled Current Source blocks, which might cause numerical issues.

Dialog Box and Parameters

Direct feedthrough (no filter)

If selected, direct feedthrough is applied between Simscape Power Systems and Simscape ports on both sides.

Filter type

Set this parameter to Low pass filter (continuous) to implement a first order continuous transfer function filter between Simscape Power Systems and Simscape ports.

Set this parameter to Unit delay (discrete) to implement a discrete unit delay filter between Simscape Power Systems and Simscape ports.

Set this parameter to First-order input filtering to implement a first order continuous transfer function filter with first-order filtering of the Simulink-PS Converter block that provides one derivative. You can apply this filter only on the Simscape Power Systems side.

Set this parameter to Second-order input filtering to implement a first order continuous transfer function filter with second-order filtering of the Simulink-PS Converter block that provides derivatives one and two. You can apply this filter only on the Simscape Power Systems side.

The Filter type parameter is not visible when the Direct feedthrough (no filter) check box is selected.

Low pass filter constant (s)

Specify the low pass filter time constant of the filter, in seconds. This parameter is visible only when the Filter type parameter is set to Low pass filter (continuous), to First-order input filtering, or to Second-order input filtering.

Sample time of unit delay (s)

Specify the sample time of the unit delay filter, in seconds. This parameter is visible only when the Filter type parameter is set to Unit delay (discrete).

Initial voltage (V)

Specify the initial voltage value of the measured Simscape Power Systems voltage.

This parameter is visible only when you apply the filter on the Simscape Power Systems side.

Initial current (A)

Specify the initial current value of the measured Simscape current.

This parameter is visible only when you apply the filter on the Simscape side.

Apply filter on

Set this parameter to Simscape Power Systems side to apply the filter on the measured Simscape Power Systems voltage.

Set this parameter to Simscape side to apply the filter on the measured Simscape current.

The Apply filter on parameter is not visible when the Direct feedthrough (no filter) check box is selected, when the Filter type is set to First-order input filtering, or when the Filter type is set to Second-order input filtering.

Show measurement port

If selected, adds a Simulink® output to the block that returns the Simscape Power Systems current and voltage and to the Simscape current and voltages in a bus signal.

Limitations

When simulating Simscape Power Systems models along with Simscape blocks, select the Simulink solver carefully.

Use the ode23tb solver for solving Simscape Power Systems circuits containing switches or nonlinear element. If you use other stiff solvers, Simscape Power Systems software gives you the following warning:

Warning: You have required continuous-time simulation of a system containing 
switches or nonlinear elements. The ode23tb variable-step stiff solver with 
relative tolerance set to 1e-4 is recommended in order to get best accuracy 
and simulationperformance. For some highly nonlinear models it may be 
necessary to set the "Solver reset method" parameter to "Robust".
See "Improving Simulation Performance" chapter in Simscape Power Systems documentation
for additional information on how to select an appropriate integration method.
'To ignore Simscape Power Systems (Specialized Technology) warnings,
 select "Disable Simscape Power Systems ST warnings" in the Powergui Preferences tab.';

The Simscape Power Systems warning can be disabled, as described in the warning message. However, if you use the ode23tb solver for solving models containing Simscape blocks, Simscape software gives you the following warning:

Warning: The solver chosen is not recommended if the model is stiff, which is
typical for models containing Simscape components. These solvers are typically
preferred for Simscape models:ode23t, ode15s or ode14x (fixed-step). To disable
this diagnostic,change the explicit solver diagnostic setting on the Simscape
panel of the model Configuration Parameters.

The Simscape warning can also be disabled, as described in the warning message.

Example

See the power_SSCmodeling example for an example of interfacing Simscape Power Systems and Simscape models using the Current-Voltage Simscape Interface block.

Introduced in R2011b

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