Research On The Summation Of Harmonic Sources

With the rapid growth of economics, power quality issue has increasingly captured considerable attention from both utility companies and their customers. The extensive applications for power electronic apparatus and nonlinear equipment distort the waveforms of voltages and currents. As a result, power quality is going much worse. In addition, due to the improvement of industrial automatization, such parts of an apparatus as MPU and PLC are applied to industrial process controls, which are disturbed easily by stirs from power system. Therefore modern industry needs higher power quality than old one does. Because of the random of the harmonics recourses in power system, it is exactly to use the method of statistic to describe them. Many international standards and advices use an evaluation as a limit to the level of harmonics. For example the IEC has taken on a standards to limit distortion levels define the compatibility levels of distortion 95% a day or the maximum a week.Because of the random of the harmonics recourses in power system, sometimes the effect was estimated using the method of statistic. It is impossible to fix detected devices on every node in system. It is usually used the summation of the random vectors to estimate the levels of harmonics of the node which didn't fix detected devices. So the question of summation of the random vectors was brought forward. This paper presented a new method to get the sum of random harmonic vectors (voltage or current) which phases have different probability distribution functions in the power system. Several vectors are decomposed with X-Y axis. The probability density functions (pdfs) of the sum of X-Y axis ponderances can be obtained byusing Laguerre polynomials after getting the 2kth moments of the sum of them. Basing on the pdfs of the sum of X-Y axis ponderances, the pdfs of the length of the sum of vectors are obtained.In order to assure the quality of power supply, and ensure the normal dealings between utility companies and customers in rated limits, it is indispensable to put a penalty or a premium due to the effect of a customer, which embodies the corporate responsibility for power quality. There for it is the sticking point for solving the problem about separating the duty to find methods of assessing the harmonic emission level. The effect of nonlinear loads harmonics levels on PCC was defined without other harmonics recourses. The voltage of single nonlinear loads harmonics was defined. The harmonics voltages of a given nonlinear loads is the sum of all the harmonics on the PCC. It is difficult to measure it directly because of the background harmonics. A new approach for assessing harmonic emission levels from nonlinear loads is proposed with inverse sum of probability. The model of sum of probability is based on the figure characteristics of harmonics from nonlinear load disconnected and connected. The 2k order moments are used to determine Laguerre polynomials expansion for simulating the sum probability density function (pdf): A recursive algorithm is used to calculate 2k order moments of measurements on X-Y components. The 2k order moments of sum of vectors are deduced from it.At the end of the paper the pdfs of the sum of two harmonic voltage vectors that were obtained by using true dates are compared with those obtained by using Laguerre polynomials. The method was proved validity.