MATLAB: Is it possible to include the harmonics when using the Discrete Active & Reactive Power block in SimPowerSystems 5.1 (R2009a).

Question

I am currently using the Discrete Active & Reactive Power block to compute the Power Factor in SimPowerSystems 5.1 (R2009a). However, the results seem to indicate the output from the Discrete Active & Reactive Power block filters out the harmonics in the signal and only measures P and Q at fundamental frequency. I would like to know if there is a way to include the harmonics in the measurement.

Answer 1

The ability to keep the harmonics in the measurement for the Discrete Active & Reactive Power block is not available in SimPowerSystems 5.1 (R2009a).

To work around the issue, see the attached model "variable_frequency_PQ.mdl". The example model allows calculation of PQ at variable frequency and variable harmonic content. The P and Q outputs come out as individual signals for each harmonic (defined in the mask of the PQ block) and can simply be added for total power. The test model varies frequency, voltage magnitude and also includes 3rd harmonic. The user may modify these parameters as necessary to test the measurement block. The block relies on an external signal for frequency and so this must either be known beforehand or measured somehow. If the user has a rotating mass that defines frequency, then measurement of shaft speed can be readily obtained. However, if the circuit is purely electrical and frequency is not pre-defined, the user will have to implement a customized phase-locked loop with appropriate feedback control to measure the frequency directly from the electrical waveforms.