Analysis about the parameters calculation of characteristic interharmonic in the voltage source type AC/DC/AC frequency converter

The three-phase frequency conversion device has been widely used in the high voltage direct current system, AC transmissions, the distributed power generation access system and various power sources. It has been the main harmonic and interharmonic source. Taking the voltage source type AC/DC/AC frequency converter as the research object, a new approach for modeling AC/DC/AC power conversion systems is presented and discussed. The proposed method is based on the modulation theory and the switching functions. Present modulation theory only provides limited equations and it is lack of flexibility for inverters under different control modes. Thus an extended modulation theory is proposed in this paper. Considering the commutation overlap angle, the paper discussed all the states of inverters under phase control and pulse width modulation(PWM) control modes in detail. The accuracy of the results obtaing from the proposed model is demonstrated by comparing with those obtaing from using the time-domain simulation tool.