# Constant Current Load

Constant current load for DC or AC supply

**Library:**Simscape / Electrical / Passive

## Description

The Constant Current Load block implements a constant current load for a DC or AC supply.

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

:

The consumed current of this block is equal to the value of the

**Consumed current**parameter as long as 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

**Minimum supply voltage**, the load behaviour changes and the block models a resistive load. If the supply voltage becomes negative, the block models a small 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`

:

The root mean square consumed current of this block is equal to the value of the

**Consumed current (RMS)**parameter as long as the voltage from the AC supply is equal to or greater than the value specified for the**Minimum supply voltage (RMS)**parameter.When the voltage from the AC supply drops below the

**Minimum supply voltage (RMS)**parameter, the load behaviour changes and the block models a load with constant resistance.

### Equations

If you set the **Load type** parameter to
`AC`

, the block calculates the peak voltage,
*V _{pk}*, through harmonic
approximation of the instantaneous voltage by using a one-period-integrated Fourier
transform:

$$\begin{array}{l}\mathrm{Re}={f}_{0}{\displaystyle \int v\text{\hspace{0.17em}}sin\left(2\pi {f}_{0}t\right)}\\ \mathrm{Im}={f}_{0}{\displaystyle \int v\text{\hspace{0.17em}}sin\left(2\pi {f}_{0}t+\frac{\pi}{2}\right)}\\ {V}_{pk}=2\sqrt{{\mathrm{Re}}^{2}+I{m}^{2}}\end{array}$$

During the first period, the peak voltage is equal to `0`

`V`

. The current is defined by this equation:

$$i(t)=\frac{V(t)}{{R}_{equiv}},$$

where *R _{equiv}* is the
equivalent resistance and depends on the value of the

**Minimum supply voltage (RMS)**parameter.

If the voltage from the three-phase supply is greater than the value specified for the
**Minimum supply voltage (RMS)** parameter, the equivalent
resistance is defined by:

$${R}_{equiv}=\frac{\frac{{V}_{pk}}{\sqrt{2}}}{{I}_{RMS}{}_{consumed}},$$

where *V _{pk}* is the
voltage peak magnitude and

*I*is the value of the

_{RMSconsumed}**Consumed current (RMS)**parameter.

If the voltage from the three-phase supply is less than the value specified for the
**Minimum supply voltage (RMS)** parameter, the equivalent
resistance is defined by:

$${R}_{equiv}=\frac{{V}_{RMS}{}_{min}}{{I}_{RMS}{}_{consumed}},$$

where
*V _{RMSmin}* is
the value of the

**Minimum supply voltage (RMS)**parameter.

### Faults

The Constant Current Load block allows you to model an electrical fault as an open circuit. The block can trigger fault events either:

At a specific time

When a power limit is exceeded for longer than a specific time interval

You can also choose whether to issue an assertion when a fault occurs by using the
**Reporting when a fault occurs** parameter. The assertion can
take the form of a warning or an error. By default, the block does not issue an
assertion.

### 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

### Conserving

## Parameters

## Extended Capabilities

## See Also

**Introduced in R2021a**