Dynamic load for DC or AC supply

Since R2020b

Libraries:
Simscape / Electrical / Passive

Description

The Dynamic Load block implements a dynamic load for a DC or AC supply.

If you set the Load type parameter to `DC`:

• The consumed power of the block is equal to the P port as long as it is greater than the value of the Minimum consumed power parameter and the voltage from the DC supply is equal to or greater than the value specified for the Minimum supply voltage parameter.

• When the voltage from the DC supply drops below the Minimum supply voltage, the load behaviour changes and the block acts as a resistive load. If the supply voltage becomes negative, the block acts as an open circuit conductance.

To ensure smooth transitions between these behaviours, the block uses a third-order polynomial spline with continuous derivatives. You can specify the width of this transition using the Transition voltage width parameter.

If you set the Load type parameter to `AC`, this table shows how the block calculates the consumed active and reactive power based on the voltage from the supply, V.

Range of V ValuesConsumed Active and Reactive Power
$V>{V}_{\mathrm{min}}$$\begin{array}{l}{P}_{actual}={P}_{in}\\ {Q}_{actual}={Q}_{in}\end{array}$
$V<{V}_{\mathrm{min}}$The block models a load with an impedance equal to:$\begin{array}{l}R={V}_{\mathrm{min}}^{2}\frac{{P}_{in}}{{P}_{in}^{2}+{Q}_{in}^{2}}\\ X={V}_{\mathrm{min}}^{2}\frac{{Q}_{in}}{{P}_{in}^{2}+{Q}_{in}^{2}}\\ Z=\sqrt{{R}^{2}+{X}^{2}}\end{array}$

In these equations:

• Vmin is the value of the Minimum supply voltage (RMS) parameter.

• Pin is the input active power of the Dynamic Load block, determined by external input port P.

• Pactual is the consumed active power of the Dynamic Load block.

• Qin is the input reactive power of the Dynamic Load block, determined by external input port Q.

• Qactual is the consumed reactive power of the Dynamic Load block.

The Dynamic Load block consumes or generates active power depending on the polarity of input active power Pin. If Pin is greater than 0, the block consumes active power. If Pin is less than 0, the block generates active power.

Faults

To model a fault in the Dynamic Load block, in the Faults section, click the Add fault hyperlink in the parameter that corresponds to the specific fault that you want to model. When the Create Fault window opens, you use it to specify the fault properties. For more information about fault modeling, see Fault Behavior Modeling and Fault Triggering.

The Dynamic Load block allows you to model an electrical fault as an open circuit. The block can trigger fault events at a specific time.

If the block is in a network that is compatible with the frequency-time simulation mode, you can perform a load-flow analysis on the network. A load-flow analysis provides steady-state values that you can use to initialize a machine.

For more information, see Perform a Load-Flow Analysis Using Simscape Electrical and Frequency and Time Simulation Mode.

Ports

Input

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Physical signal port associated with real power, specified as a scalar.

Physical signal port associated with reactive power, specified as a scalar.

Conserving

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Electrical conserving port associated with the dynamic load positive terminal.

Electrical conserving port associated with the dynamic load negative terminal.

Parameters

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Main

Type of load. Select `DC` to use this load with a DC supply or `AC` to use this load with an AC supply.

Minimum voltage the DC supply needs to give the block to act as a constant power load.

Dependencies

To enable this parameter, set Load Type to `DC`.

Minimum amount of power consumed by the block.

Dependencies

To enable this parameter, set Load Type to `DC`.

Value of the reverse conductance when the supply voltage becomes negative.

Dependencies

To enable this parameter, set Load Type to `DC`.

Transition voltage width. This value is used to ensure smooth transitions between the block's behaviours when the supply voltage drops below the Minimum supply voltage or becomes negative.

Dependencies

To enable this parameter, set Load Type to `DC`.

Rated frequency.

Dependencies

To enable this parameter, set Load Type to `AC`.

Minimum voltage, in RMS, that the AC supply needs to give the block to act as a dynamic load.

Dependencies

To enable this parameter, set Load Type to `AC`.

Since R2024a

Time constant associated with the transients of the terminal voltage measurement.

Dependencies

To enable this parameter, set Load Type to `AC`.

Since R2024a

Terminal voltage, in RMS, at time zero.

Dependencies

To enable this parameter, set Load Type to `AC`.

Since R2024a

Angle of the terminal voltage at time zero.

Dependencies

To enable this parameter, set Load Type to `AC`.

Faults

Conductance during the open-circuit state.

Dependencies

To enable this parameter, add a fault to the Dynamic Load block by clicking the Add fault hyperlink in the Open circuit fault parameter.

After you create the fault, you can change the properties in the Fault Inspector window. When you open a block that has a fault, the Open Fault Inspector hyperlink appears instead of the Add fault hyperlink. For an example that shows how to include faults, see Analyze a DC Armature Winding Fault.

Simulation time at which the block enters the faulted state.

Dependencies

To enable this parameter, in the Fault Inspector window, set Trigger Type to `Timed`.

This parameter appears in the Trigger section of the Fault Inspector window. For more information, see Set Fault Triggers.

Version History

Introduced in R2020b

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