Voltage-Current Simscape Interface

Ideal coupling between Simscape Electrical Specialized Power Systems and Simscape electrical circuits

Library

Simscape / Electrical / Specialized Power Systems / Utilities

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Description

The Voltage-Current Simscape Interface block connects Simscape™ Electrical™ Specialized 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 Electrical Specialized Power Systems side, the electrical connector ports +sps and -sps act like a controlled voltage source, feeding voltage from the Simscape side to the connected Simscape Electrical Specialized Power Systems elements, while maintaining the current through the block.

• On the Simscape side, the electrical connector ports +ssc and -ssc act like a controlled current source, feeding current from the Simscape Electrical Specialized Power Systems side to the connected Simscape elements, while maintaining the voltage across the block.

The following figure gives an overview of the interface.

The block measures the voltage between the +ssc and -ssc ports and propagates it to the +sps and -sps ports, preserving the polarity. The block also measures the current flowing from the +sps to the -sps port and propagates it from the -ssc to the +ssc port.

You can specify a filter to break the algebraic loop between Simscape Electrical Specialized 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 it on the Simscape Electrical Specialized Power Systems side, to the measured voltage, or on the Simscape side, to the measured current. Depending on the measured signal where the filter is applied, 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 Sensor, Controlled Voltage Source, Current Measurement, and Controlled Current Source blocks, which might cause numerical issues.

Parameters

Direct feedthrough (no filter)

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

Filter type

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

Set this parameter to Unit delay (discrete) to implement a discrete unit delay filter between Simscape Electrical Specialized 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 Electrical Specialized 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 Electrical Specialized Power Systems side.

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

Low pass filter time constant (s)

Specify the low pass filter time constant of the filter, in seconds. Default is 1e-6. This parameter is available 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 (s)

Specify the sample time of the unit delay filter, in seconds. Default is 50e-6. This parameter is available only when the Filter type parameter is set to Unit delay (discrete).

Initial voltage (V)

Specify the initial voltage value of the measured Simscape Electrical Specialized Power Systems voltage. Default is 0.

This parameter is available only when you apply the filter on the Simscape Electrical Specialized Power Systems side.

Initial current (A)

Specify the initial current value of the measured Simscape current. Default is 0.

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

Apply filter on

Set this parameter to Specialized Power Systems side (default) to apply the filter on the measured Simscape Electrical Specialized 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 available when the Direct feedthrough (no filter) check box is selected, to First-order input filtering, or to Second-order input filtering.

Show measurement port

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

Limitations

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

Use the ode23tb solver for solving Simscape Electrical Specialized Power Systems circuits containing switches or nonlinear element. If you use other stiff solvers, Simscape Electrical Specialized 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 Electrical 
Specialized Power Systems documentation for additional information on how to 
select an appropriate integration method.
'To ignore Simscape Electrical Specialized Power Systems warnings, select
"Disable Simscape Electrical SPS warnings" in the Powergui Preferences tab.';

The Simscape Electrical Specialized 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.

Examples

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