Positive-Sequence (PLL-Driven)

Compute positive-sequence component of three-phase signal at fundamental frequency

Library

Control and Measurements/Measurements

Description

The Positive-Sequence (PLL-Driven) block computes the positive-sequence component (magnitude and phase) of the input 3 signal over a running window of one cycle of the fundamental frequency given by input 1. The reference frame required for the computation is given by the input 2. The first two inputs are normally connected to a PLL block.

The positive-sequence component of a three-phase signal (V1 or current I1) is computed as

V1=13(Va+aVb+a2Vc)Va,Vb,Vc=three voltage phasors at the fundamental frequencya=ej2π/3=1120° complex operator

A Fourier analysis over a sliding window of one cycle of the fundamental frequency (input 1) is first applied to the three input signals. The block evaluates the phasor values at the fundamental. Then the transformation is applied to obtain the positive sequence.

As the block uses a running average window to perform the Fourier analysis, one cycle of simulation must complete before the outputs give the correct magnitude and angle. For example, the block response to a step change of V1 is a one-cycle ramp. For the first cycle of simulation, the output is held constant to the values specified by the initial input parameters.

Dialog Box and Parameters

Initial frequency (Hz)

Specify the frequency of the first cycle of simulation.

Minimum frequency (Hz)

The minimum frequency value determines the buffer size of the Variable Time Delay block used inside the block to compute the phasors.

Initial input (positive component) [ Mag, Phase-relative-to-PLL (degrees) ]

Specify the initial positive-sequence magnitude and phase (relative to the PLL phase), in degrees, of the input signals.

Sample time

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

Inputs and Outputs

Freq

Fundamental frequency (Hz) required by the computation. This input is normally connected to the Freq output of a PLL block.

wt

Angle of the reference frame (rad/s) required for the computation. This input is normally connected to the wt output of a PLL block.

abc

The vectorized signal of the three [a b c] sinusoidal signals. Typical input signals are voltages or currents measured by Current Measurement or Voltage Measurement blocks.

|u|Magnitude

Outputs the magnitude of the positive-sequence component in the same unit as the input signal.

uPhase

Outputs the phase of the positive-sequence component, in degrees, relative to the reference frame wt (input 2).

Characteristics

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

Example

The power_PositiveSequencePLLDrivenpower_PositiveSequencePLLDriven model computes the positive-sequence component of a three-phase signal containing harmonics. It shows that the block outputs accurate magnitude and phase even if the fundamental frequency of the input signal varies during the simulation.

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.

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