3-Phase Sequence Analyzer (SimPowerSystems)

Measure the positive, negative, and zero sequence components of a three-phase signal

Library

Extras/Measurements

Description

The 3-Phase Sequence Analyzer block outputs the magnitude and phase of the positive (denoted by the index 1), negative (index 2), and zero sequence (index 0) components of a set of three balanced or unbalanced signals. The signals can contain harmonics or not. The three sequence components of a three-phase signal (voltages V1 V2 V0 or currents I1 I2 I0) are computed as follows:

where

A Fourier analysis over a sliding window of one cycle of the specified frequency is first applied to the three input signals. It evaluate the phasor values Va, Vb, and Vc at the specified fundamental or harmonic frequency. Then the transformation is applied to obtain the positive sequence, negative sequence, and zero sequence.

The 3-Phase Sequence Analyzer block is not sensitive to harmonics or unbalances. However, as with any filtered system, it introduces some delay. For example, its response to a step change of V1 is a one-cycle ramp.

You can modify any parameter during the simulation in order to obtain the different sequence and harmonic components of the input signals.

Dialog Box and Parameters

Fundamental frequency f1 (Hz): The fundamental frequency, in hertz, of the three-phase input signal.
Harmonic n (0=DC; 1=fundamental): Specify the harmonic component from which you want to evaluate the sequences.
Sequence: Specify which sequence component the block outputs. Select Positive to calculate the Positive sequence, select Negative to calculate the negative sequence, or select 0 to compute the zero sequence of the fundamental or specified harmonic of the three-phase input signal

Inputs and Outputs

abc

Connect to the input the vectorized signal of the three [Va Vb Vc] sinusoidal signals.

Mag

The first output give the magnitude (peak value) of the specified sequence component.

Phase

The second output gives the phase in degrees of the specified component.

Example

The psb3phsignalseq.mdl demo illustrates the use of the Sequence Analyzer blocks to observe and calculate the fundamental and harmonic components of a measured signal.

The internal voltage of the voltage source is controlled through the Discrete 3-Phase Programmable Source block. The three voltage outputs are first converted from p.u. to volts and they are connected to three Controlled Voltage Source blocks. Two 3-Phase Sequence Analyzer blocks are used to monitor the positive sequence of the three fundamental voltages Va,Vb, Vc and the negative-sequence component of the fifth harmonics.

Start the simulation and observe the positive sequence of the fundamental frequency and the negative sequence of the fifth harmonic component. The fifth harmonic internal voltage is amplified from 0.08 p.u. to 0.14 p.u. at the load terminals.

As the 3-Phase Sequence Analyzer blocks use Fourier analysis, their response time is delayed by one cycle of the fundamental frequency.

3-Phase Programmable Voltage Source Three Level Bridge