Harmonic Summation and Assessment Based on Probability Distribution

At the point of common coupling, there are many cases where the phase-angle difference between harmonic vectors is unknown. In practice, for example, in calculating the steady-state rating of the ac passive harmonic filter, the arithmetic summation method is often used in determining the maximal harmonic level. This summation law is very conservative as it may result in high cost of equipment ratings. Actually, a compromise should be made in taking into account the equipment safety and the risk of overrating as well as excessive costs. Based on uniform distribution of the difference in phase angles, this letter provides an algorithm to calculate the probability upon which the magnitude of summation vector of two harmonics may exceed a given value. This may also result in a recommendation of another harmonic summation method for the standard IEC/TR 61000-3-6.