Sequence Analyzer

Compute positive-, negative-, and zero-sequence components of three-phase signal


Control and Measurements/Measurements


The Sequence Analyzer block outputs the magnitude and phase of the positive-, negative-, and zero-sequence components of a set of three balanced or unbalanced signals. Index 1 denotes the positive sequence, index 2 denotes the negative sequence, and index 0 denotes the zero sequence. The signals can optionally contain harmonics. The three sequence components of a three-phase signal (voltages V1 V2 V0 or currents I1 I2 I0) are computed as follows:

V1=13(Va+aVb+a2Vc)V2=13(Va+a2Vb+aVc)V0=13(Va+Vb+Vc)Va,Vb,Vc=three voltage phasors at the specified frequencya=ej2π/3=1120 complex operator

A Fourier analysis over a sliding window of one cycle of the specified frequency is first applied to the three input signals. It evaluates 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.

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 using the values specified by the initial input parameters.


Fundamental frequency (Hz)

Specify the fundamental frequency, in hertz, of the three-phase input signal. Default is 60.

Harmonic n (1=fundamental)

Specify the harmonic component to evaluate the sequences. Set to 1 to compute the sequences at the fundamental frequency or to the number corresponding to the desired harmonic. Default is 1.


Specify the sequence component the block outputs. The options include Positive, Negative, Zero, and Positive Negative Zero (default). Select Positive Negative Zero to calculate all the sequences.

Initial input [ Mag, Phase (degrees) ]

Specify the initial magnitude and phase, in degrees, of the positive-sequence component of the input signal. Default is [1, 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


Connects the vectorized signal of the three [a b c] sinusoidal signals to the input.


The three-phase current signal.

|u| Magnitude

Outputs the magnitude (peak value) of the specified sequence component(s), in the same units as the abc input signals.

u Phase

Outputs the phase, in degrees, of the specified components.


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


The power_SequenceAnalyzer model shows the use of the Sequence Analyzer block to compute the three sequence components of a three-phase sinusoidal voltage. The model sample time

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.

Introduced in R2013a

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