Dynamic Load

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 behavior 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 behaviors, 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 Values	Consumed Active and Reactive Power
$$V>V_{\min }$$	$$\begin{array}{l}{P}_{actual}=P_{in}\\ Q_{actual}=Q_{in}\end{array}$$
$$V<V_{\min }$$	The block models a load with an impedance equal to:$$\begin{array}{l}R=V_{\min }^2\frac{P_{in}}{P_{in}^2+Q_{in}^2}\\ X=V_{\min }^2\frac{Q_{in}}{P_{in}^2+Q_{in}^2}\\ Z=\sqrt{R^2+X^2}\end{array}$$

In these equations:

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

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

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

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

• Q_actual 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 P_in. If P_in is greater than 0, the block consumes active power. If P_in 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 next to the fault that you want to model. In the Add Fault window, 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.

Load-Flow Analysis

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

P — Real power, W

physical signal

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

Q — Reactive power, V*A

physical signal

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

Conserving

+ — Positive terminal

electrical

Electrical conserving port associated with the dynamic load positive terminal.

- — Negative terminal

electrical

Electrical conserving port associated with the dynamic load negative terminal.

Parameters

Main

Load type — Load type

DC (default) | AC

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

Minimum supply voltage — Minimum DC supply voltage

20 V (default) | scalar

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 consumed power — Minimum consumed power

1e-3 W (default) | scalar

Minimum amount of power consumed by the block.

Dependencies

To enable this parameter, set Load Type to DC.

Reverse conductance — Reverse conductance

1e-6 S (default) | scalar

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

Dependencies

To enable this parameter, set Load Type to DC.

Transition voltage width — Transition voltage width

1e-3 V (default) | scalar

Transition voltage width. This value is used to ensure smooth transitions between the block's behaviors 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 — Rated frequency

60 Hz (default) | scalar

Rated frequency.

Dependencies

To enable this parameter, set Load Type to AC.

Minimum supply voltage (RMS) — Minimum AC supply voltage

200 V (default) | scalar

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.

Voltage time constant — Time constant for voltage dynamics

0.01 s (default) | positive scalar

Since R2024a

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

Dependencies

To enable this parameter, set Load Type to AC.

Initial supply voltage (RMS) — Initial terminal voltage

300 V (default) | positive scalar

Since R2024a

Terminal voltage, in RMS, at time zero.

Dependencies

To enable this parameter, set Load Type to AC.

Initial supply voltage angle — Initial angle of terminal voltage

0 deg (default) | scalar

Since R2024a

Angle of the terminal voltage at time zero.

Dependencies

To enable this parameter, set Load Type to AC.

Faults

Open circuit fault — Option to add open circuit fault

Add fault (default)

Option to add an open-circuit fault in the Dynamic Load block.

To add a fault, click the Add fault hyperlink.

Open-circuit conductance — Open-circuit conductance

1e-4 S (default) | scalar

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.

Trigger fault at time — Time before entering faulted state

0 s (default) | nonnegative scalar

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.

Extended Capabilities

C/C++ Code Generation
Generate C and C++ code using Simulink® Coder™.

Version History

Introduced in R2020b

R2024a: Improved support for inductive nodes and bidirectional active power input

Prior to R2024a, to connect the Dynamic Load block to an inductive node, you had to provide a large parasitic resistance. From R2024a, if you set the Load type parameter to AC, you can connect this block to an inductive node by specifying the Voltage time constant, Initial supply voltage (RMS), and Initial supply voltage angle parameters. As a result of this change, the Minimum active power parameter has been removed. If your model saved in an earlier release contains this block you must set appropriate values to the new parameters.

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