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Power (Positive-Sequence)

Compute positive-sequence active and reactive powers

Library

Control and Measurements/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:

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.

Dialog Box and 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.

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 TimeSpecified in the Sample Time parameter
Continuous if Sample Time = 0
Scalar ExpansionNo
DimensionalizedNo

Example

The power_ThreePhasePowerpower_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.

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