Harmonics in the A-C Circuits of Grid-Controlled Rectifiers and Inverters

This paper summarizes the results of an investigation of the harmonic currents and voltages in the a-c circuits of grid-controlled rectifiers and inverters. The principal part of the paper presents the development of a theoretical method for predetermining the magnitude of the harmonics in terms of the d-c load current, the commutating reactance, the rectifier transformer secondary voltage, and the amount of grid control. Harmonic voltages in the supply circuit may then be calculated from the harmonic currents and the supply-circuit reactances at the various harmonic frequencies. General curves are given to facilitate the calculation of the harmonic currents for the range of conditions usually encountered. In addition, curves are included for the easy determination of the product of the supply-circuit current and its own telephone influence factor, the I.T product, which quantity is useful in inductive co-ordination studies. Comparisons are given between the results of tests and the results of calculations by the theoretical method presented in this paper. These and other comparisons show very satisfactory checks so that the method may be considered to be established. The case of the inverter is treated in a manner similar to that used for the grid-controlled rectifier. The general curves for the rectifier may also be applied to the inverter by appropriate choice of the defining angles. The case of a-c circuits with nonlinear frequency-reactance characteristics is briefly considered, and an empirical modification of the theoretical method is suggested.