Constant Power Load

Constant power load for DC or AC supply

Since R2020a

• 

Libraries:
Simscape / Electrical / Passive

Description

The Constant Power Load block implements a constant power load for a DC or AC supply.

If you set the Load type parameter to DC:

• The block outputs a nominal rated power as long as the voltage from the DC supply is greater than or equal to the Minimum supply voltage parameter value.

• When the voltage from the DC supply drops below the Minimum supply voltage parameter value, the load behavior changes and the block acts as a constant resistance. If the supply voltage becomes negative, the block acts as a constant reverse 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:

• The block outputs a nominal rated power at steady state as long as the voltage from the AC supply is greater than or equal to the Minimum supply voltage (RMS) parameter value. The block calculates the RMS power in harmonic approximation so that the block can calculate the power for AC voltage signals with time-dependent amplitudes. If the time scale of the amplitude change is comparable to the period of the alternating current, the instantaneous power briefly changes during the transition period.

• When the voltage from the AC supply drops below the Minimum supply voltage (RMS) parameter value, the load behavior changes and the block models a load with constant impedance.

For more information about the equations for the AC load type in a three-phase system, see the Equations section of the Constant Power Load (Three-Phase) block.

Faults

To model a fault in the Constant Power 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 Constant Power 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.

Examples

Model Constant Power Consumption with Varying AC Voltage Supply

Model constant power consumption using the Constant Power Load block in an AC circuit with varying voltage controlled by a Tap-Changing Transformer block.

• Since R2023b
• Open Live Script

Ports

Conserving

+ — Positive terminal

electrical

Electrical conserving port associated with the constant power load positive terminal.

- — Negative terminal

electrical

Electrical conserving port associated with the constant power 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.

Power consumed — Power consumed

100 W (default) | scalar

Nominal power that the block consumes.

Dependencies

To enable this parameter, set Load Type to DC.

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.

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 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.

Active power consumed — Active power consumed

500 W (default) | scalar

Active power that the block consumes.

Dependencies

To enable this parameter, set Load Type to AC.

Reactive power consumed — Reactive power consumed

0 V*A (default) | scalar

Reactive power that the block consumes.

Dependencies

To enable this parameter, set Load Type to AC.

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, the AC supply needs to give the block to act as a constant power 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 Constant Power 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 Constant Power 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 R2020a

R2024a: Improved support for inductive nodes

Prior to R2024a, to connect the Constant Power 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.