Compute positive-sequence active and reactive powers

Control and Measurements/Measurements

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:

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

V_{1} is the positive-sequence component
of input Vabc. I_{1} 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.

**Fundamental frequency (Hz)**Specify the fundamental frequency, in hertz, of the input signals.

**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.

**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.

**Sample time**Specify the sample time of the block, in seconds. Set to 0 to implement a continuous block.

`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.

Sample Time | Specified in the Sample Time parameterContinuous if Sample Time = 0 |

Scalar Expansion | No |

Dimensionalized | No |

The `power_ThreePhasePower`

`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.

Was this topic helpful?