Novel approach to selecting rotor position sensor resolution for variable frequency drives

A new and straightforward method is proposed to determine rotor position sensor resolution for variable frequency drives based on a simple specification, namely the minimum required speed loop bandwidth at the lowest working speed. The study hinges upon operating point stability analysis of the speed loop and includes the effect of quantization harmonics introduced by the position sensor. A novel metric is also introduced to evaluate the filtering action of the speed loop on the said harmonics, i.e. the quantization harmonic rejection frequency response function. The efficacy of the approach is theoretically and experimentally analyzed on a 3.6 kW permanent magnet motor drive test bench.