# Power

Compute active and reactive powers of voltage-current pair at fundamental frequency

## Library

Simscape / Electrical / Specialized Power Systems / Sensors and Measurements

• ## Description

The Power block computes the active power (P), in watts, and the reactive power (Q), in vars, of a voltage-current pair at fundamental frequency. To perform this computation, the block first determines the fundamental values (magnitude and phase) of the two input signals V & I. The following P and Q are then calculated:

`$\begin{array}{l}P=\frac{|V|}{\sqrt{2}}×\frac{|I|}{\sqrt{2}}×\mathrm{cos}\left(\phi \right)\\ Q=\frac{|V|}{\sqrt{2}}×\frac{|I|}{\sqrt{2}}×\mathrm{sin}\left(\phi \right)\\ \phi =\angle V-\angle I\end{array}$`

As this block uses a running average window, one cycle of simulation must complete before the outputs give the correct value. For the first cycle of simulation, the outputs are held constant using the values specified by the Voltage initial input and Current initial input parameters.

## Parameters

Fundamental frequency (Hz)

Specify the fundamental frequency, in hertz, of the input signals. Default is `60`.

Voltage initial input [ Mag, Phase (degrees) ]

Specify the voltage initial magnitude and phase to set a constant output for the first cycle of simulation. Default is ```[1, 0]```.

Current initial input [ Mag, Phase (degrees) ]

Specify the current initial magnitude and phase to set a constant output for the first cycle of simulation. Default is ```[1, 0]```.

Sample time

Specify the sample time of the block, in seconds. Set to `0` to implement a continuous block. Default is `0`.

## Inputs and Outputs

`V`

The voltage signal.

`I`

The current signal.

`P`

The active power of voltage-current pair signal, in watts.

`Q`

The reactive power of voltage-current pair signal, in vars.

## Characteristics

 Sample Time Specified in the Sample Time parameter Continuous if Sample Time = 0 Scalar Expansion Yes, of the parameters Dimensionalized Yes

## Examples

The `power_Power` model shows the accuracy of the Power block in evaluating the active and reactive powers of a voltage-current set.

The model sample time is parameterized by the Ts variable set to a default value of 50e-6 s. Set Ts to 0 in the command window to simulate the model in continuous mode.

Introduced in R2013a