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Power (Positive-Sequence)

Compute positive-sequence active and reactive powers

Library

Simscape / Electrical / Specialized Power Systems / Control & Measurements / Measurements

Simscape / Electrical / Specialized Power Systems / Fundamental Blocks / Measurements / Additional Measurements Description

The Power (Positive-Sequence) block computes the positive-sequence active power P (in watts) and reactive power Q (in vars) of a periodic set of three-phase voltages and currents. To perform this computation, the block first computes the positive sequence of the input voltages and currents with a running window over one cycle of the specified fundamental frequency. These formulas are then evaluated:

$\begin{array}{c}P=3×\frac{|{V}_{1}|}{\sqrt{2}}×\frac{|{I}_{1}|}{\sqrt{2}}×\mathrm{cos}\left(\phi \right)\\ Q=3×\frac{|{V}_{1}|}{\sqrt{2}}×\frac{|{I}_{1}|}{\sqrt{2}}×\mathrm{sin}\left(\phi \right)\\ \phi =\angle {V}_{1}-\angle {I}_{1}\end{array}$

V1 is the positive-sequence component of input Vabc. I1 is the positive-sequence component of input Iabc.

A current flowing into an RL circuit produces a positive P and a positive Q.

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 output is 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 used by the block to compute the constant output for the first cycle of simulation. Default is [0, 0].

Current initial input [ Mag, Phase (degrees) ]

Specify the current initial magnitude and phase used by the block to compute the constant output for the first cycle of simulation. Default is [0, 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

Vabc

The three-phase voltage signal.

Iabc

The three-phase current signal.

P

The positive-sequence active power, in watts.

Q

The positive-sequence reactive power, in vars.

Characteristics

 Sample Time Specified in the Sample Time parameter Continuous if Sample Time = 0 Scalar Expansion No Dimensionalized No

Examples

The power_ThreePhasePower model compares the outputs of the Power (Positive-Sequence) block with the Power (3ph, Instantaneous) and the Power (dq0, Instantaneous) block. The Power (Positive-Sequence) block gives ripple-free accurate results even with the presence of zero and negative sequences in the voltage supply.

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 and change the Simulation type parameter of the Powergui block to Continuous to simulate the model in continuous mode.