A new method based on periodic convolution for sensitivity analysis of multi-stage conversion systems

A new approach for sensitivity analysis of harmonics and interharmonics in multi-stage conversion systems is presented. Each component (converter, filter, transformer, etc.) is modeled by taking advantage of periodic convolution and representing the signals by means of a discrete Fourier transform. Firstly, single component frequency coupling matrices are built up starting from the component characteristics. Then, according to the specific topology of the conversion system, single-component matrices are combined to deduce a whole-system frequency coupling matrix: it provides the coupling among the harmonics and interharmonics of voltages and currents. The operative procedure to build up the frequency coupling matrix of a complex AC/DC/AC PWM adjustable speed drive is described: it is very fast and efficient. In particular, the frequency coupling matrix is utilized to perform a sensitivity analysis of the absorbed current with respect to the supplying voltage perturbations around a fixed operating point, developed with reference to a specific case-study.