Flux observer for induction machine control. Part I - Sensitivity analysisas a function of sampling rate and parameters variations

In the last decades, many vector control techniques have been developed for induction machine to increase their dynamic performances. But they are bas ed on an accurate estimation of flux variables, which are not measurable in conventional induction machines. So, observer strategies are used in induc tion machine controls. Complex algorithms have been developed, but their lo ng calculation time does not allow a simple implementation in digital form. For this reason, reduced-order observers are often used when a real-time e stimation is implemented. If these structures lead to better flux estimatio ns than in the case of an open-loop model, their convergence gains have to be determined and they are sensitive to the parameters value. The authors p resent a new analytical method to elaborate a reduced-order observer. The i nfluence of the sampling rate is taken into account and the paper investiga tes the optimal gain, which minimise the sensitivity to the parameters valu e. In order to measure the observer robustness, the authors define two crit eria, which are computed in steady state: the orientation error and the mod ulus error of the rotor flux. Some examples illustrate the theory and their calculation results are presented.