Analysis of nonlinear sideband effects in small-signal input dq admittance of twelve-pulse diode rectifiers

This paper focuses on the modeling of small-signal input dq admittance of twelve-pulse diode rectifiers. It provides a comprehensive comparison of small-signal dq admittances between well-known averaged value model (AVM), switching simulation model and experimental measurements of a hardware set-up. Analytical AVM (AAVM) is used in the analysis as it has been commonly used to model diode rectifiers. In order to predict small-signal dq admittance accurately, AAVM had to be modified. The modification describes injection properties in a more natural way by considering a d-channel perturbation as magnitude modulation and by considering a q-channel perturbation as phase modulation. Analytical expressions for dq admittance of AAVM of twelve-pulse diode rectifier feeding a resistive load are derived and presented in the paper. Furthermore, it has been found that sideband admittances around multiples of switching frequency exist in the small-signal response due to the nonlinear behavior of the rectifier. The new phenomenon is analyzed theoretically, characterized in simulations with the extraction of small-signal response from the switching simulation model and captured experimentally by the hardware measurements.