Compute total harmonic distortion (THD) of signal


Control and Measurements/Measurements


The THD block computes the total harmonic distortion (THD) of a periodic distorted signal. The signal can be a measured voltage or current.

The THD is defined as the root mean square (RMS) value of the total harmonics of the signal, divided by the RMS value of its fundamental signal. For example, for currents, the THD is defined as

total harmonic distortion (THD)=IHIFIH=I22+I32++In2     In:RMS value of the harmonic nIF:RMS value of the fundamental current

The THD has a null value for a pure sinusoidal voltage or current.

Dialog Box and Parameters

Fundamental frequency of input signal (Hz)

Specify the frequency, in hertz, of the fundamental signal.

Sample time

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


Sample TimeSpecified in the Sample Time parameter
Continuous if Sample Time = 0
Scalar ExpansionYes, of the parameters


The power_RMS_THDpower_RMS_THD model uses a THD block to compute the THD of a 60 Hz signal with second harmonic and a DC bias.

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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