TIDUF72 August 2024
For calculating the fundamental RMS voltage, a pure sine wave is generated and tightly locked to the fundamental of the incoming voltage waveform. Using the generated waveform, the fundamental voltage, fundamental active power, and fundamental reactive power are calculated by the following equations:
where
After calculating the fundamental voltage, fundamental active power, and fundamental reactive power, the fundamental current and fundamental apparent power are calculated with the following formulas:
where
Once the fundamental current and fundamental voltage are calculated, the voltage THD and current THD can also be calculated. This software supports three different methods of calculating THD that are referred to as THDIEC_F, THDIEC_R, and THDIEEE. The formulas used to calculate voltage THD (V_THD) and current THD (I_THD) with the different methods as follows:
To calculate THD correctly, it is necessary to select the proper method of THD calculation and to make sure that any reference meter used for measuring THD uses the same THD method as the method selected in software.