Evaluation of average models for nine-phase diode rectifiers with improved AC and DC dynamics

This paper presents an in-depth comparison and evaluation of average models for nine-phase diode rectifiers, proposing a new model featuring improved static and dynamic characteristics exceeding by far those of previously existent models. The key to the proposed model is the representation of the dc load current by means of its Taylor series expansion. The analysis revealed a 10% and 3% average error reduction of the proposed model in steady state and transient conditions respectively, as well as an accurate calculation of the converter output impedance to less than 10 degrees and 1dB phase and magnitude error. The paper shows too that average models of diode rectifiers and line-commutated converters are also subject to the sampling theorem limitations, i.e., their frequency response is limited to half of the averaging period. Finally, key steady state, transient and frequency response results are validated using a 2kW experimental prototype showing the high accuracy achieved by the proposed average model.