A frequency domain model for AC/DC/AC conversion systems

A simple model in the frequency domain of AC/DC/AC conversion systems is presented and applied to predict DC and AC current harmonics and interharmonics. It is based on the modulation function theory, but differently from the classical approaches, it allows prediction in a fast and direct way those current interharmonics which are caused by the time variation of the actual inductance seen from the conversion system DC-link. The method utilizes a simple linearization of time varying inductances, so allowing achievement of better modeling capabilities without reducing the inherent simplicity and speed of the classical approaches. Comparative tests are performed to validate the proposed method and to demonstrate its improved performances.